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This is gccint.info, produced by makeinfo version 5.2 from gccint.texi.

Copyright (C) 1988-2013 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover Texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

 (a) The FSF's Front-Cover Text is:

 A GNU Manual

 (b) The FSF's Back-Cover Text is:

 You have freedom to copy and modify this GNU Manual, like GNU software.
Copies published by the Free Software Foundation raise funds for GNU
development.
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* gccint: (gccint).            Internals of the GNU Compiler Collection.
END-INFO-DIR-ENTRY

 This file documents the internals of the GNU compilers.

 Copyright (C) 1988-2013 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover Texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

 (a) The FSF's Front-Cover Text is:

 A GNU Manual

 (b) The FSF's Back-Cover Text is:

 You have freedom to copy and modify this GNU Manual, like GNU software.
Copies published by the Free Software Foundation raise funds for GNU
development.


File: gccint.info,  Node: Top,  Next: Contributing,  Up: (DIR)

Introduction
************

This manual documents the internals of the GNU compilers, including how
to port them to new targets and some information about how to write
front ends for new languages.  It corresponds to the compilers (GCC)
version 4.8.3.  The use of the GNU compilers is documented in a separate
manual.  *Note Introduction: (gcc)Top.

 This manual is mainly a reference manual rather than a tutorial.  It
discusses how to contribute to GCC (*note Contributing::), the
characteristics of the machines supported by GCC as hosts and targets
(*note Portability::), how GCC relates to the ABIs on such systems
(*note Interface::), and the characteristics of the languages for which
GCC front ends are written (*note Languages::).  It then describes the
GCC source tree structure and build system, some of the interfaces to
GCC front ends, and how support for a target system is implemented in
GCC.

 Additional tutorial information is linked to from
<http://gcc.gnu.org/readings.html>.

* Menu:

* Contributing::    How to contribute to testing and developing GCC.
* Portability::     Goals of GCC's portability features.
* Interface::       Function-call interface of GCC output.
* Libgcc::          Low-level runtime library used by GCC.
* Languages::       Languages for which GCC front ends are written.
* Source Tree::     GCC source tree structure and build system.
* Testsuites::      GCC testsuites.
* Options::         Option specification files.
* Passes::          Order of passes, what they do, and what each file is for.
* GENERIC::         Language-independent representation generated by Front Ends
* GIMPLE::          Tuple representation used by Tree SSA optimizers
* Tree SSA::        Analysis and optimization of GIMPLE
* RTL::             Machine-dependent low-level intermediate representation.
* Control Flow::    Maintaining and manipulating the control flow graph.
* Loop Analysis and Representation:: Analysis and representation of loops
* Machine Desc::    How to write machine description instruction patterns.
* Target Macros::   How to write the machine description C macros and functions.
* Host Config::     Writing the 'xm-MACHINE.h' file.
* Fragments::       Writing the 't-TARGET' and 'x-HOST' files.
* Collect2::        How 'collect2' works; how it finds 'ld'.
* Header Dirs::     Understanding the standard header file directories.
* Type Information:: GCC's memory management; generating type information.
* Plugins::         Extending the compiler with plugins.
* LTO::             Using Link-Time Optimization.

* Funding::         How to help assure funding for free software.
* GNU Project::     The GNU Project and GNU/Linux.

* Copying::         GNU General Public License says
                    how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors::    People who have contributed to GCC.

* Option Index::    Index to command line options.
* Concept Index::   Index of concepts and symbol names.


File: gccint.info,  Node: Contributing,  Next: Portability,  Up: Top

1 Contributing to GCC Development
*********************************

If you would like to help pretest GCC releases to assure they work well,
current development sources are available by SVN (see
<http://gcc.gnu.org/svn.html>).  Source and binary snapshots are also
available for FTP; see <http://gcc.gnu.org/snapshots.html>.

 If you would like to work on improvements to GCC, please read the
advice at these URLs:

     <http://gcc.gnu.org/contribute.html>
     <http://gcc.gnu.org/contributewhy.html>

for information on how to make useful contributions and avoid
duplication of effort.  Suggested projects are listed at
<http://gcc.gnu.org/projects/>.


File: gccint.info,  Node: Portability,  Next: Interface,  Prev: Contributing,  Up: Top

2 GCC and Portability
*********************

GCC itself aims to be portable to any machine where 'int' is at least a
32-bit type.  It aims to target machines with a flat (non-segmented)
byte addressed data address space (the code address space can be
separate).  Target ABIs may have 8, 16, 32 or 64-bit 'int' type.  'char'
can be wider than 8 bits.

 GCC gets most of the information about the target machine from a
machine description which gives an algebraic formula for each of the
machine's instructions.  This is a very clean way to describe the
target.  But when the compiler needs information that is difficult to
express in this fashion, ad-hoc parameters have been defined for machine
descriptions.  The purpose of portability is to reduce the total work
needed on the compiler; it was not of interest for its own sake.

 GCC does not contain machine dependent code, but it does contain code
that depends on machine parameters such as endianness (whether the most
significant byte has the highest or lowest address of the bytes in a
word) and the availability of autoincrement addressing.  In the
RTL-generation pass, it is often necessary to have multiple strategies
for generating code for a particular kind of syntax tree, strategies
that are usable for different combinations of parameters.  Often, not
all possible cases have been addressed, but only the common ones or only
the ones that have been encountered.  As a result, a new target may
require additional strategies.  You will know if this happens because
the compiler will call 'abort'.  Fortunately, the new strategies can be
added in a machine-independent fashion, and will affect only the target
machines that need them.


File: gccint.info,  Node: Interface,  Next: Libgcc,  Prev: Portability,  Up: Top

3 Interfacing to GCC Output
***************************

GCC is normally configured to use the same function calling convention
normally in use on the target system.  This is done with the
machine-description macros described (*note Target Macros::).

 However, returning of structure and union values is done differently on
some target machines.  As a result, functions compiled with PCC
returning such types cannot be called from code compiled with GCC, and
vice versa.  This does not cause trouble often because few Unix library
routines return structures or unions.

 GCC code returns structures and unions that are 1, 2, 4 or 8 bytes long
in the same registers used for 'int' or 'double' return values.  (GCC
typically allocates variables of such types in registers also.)
Structures and unions of other sizes are returned by storing them into
an address passed by the caller (usually in a register).  The target
hook 'TARGET_STRUCT_VALUE_RTX' tells GCC where to pass this address.

 By contrast, PCC on most target machines returns structures and unions
of any size by copying the data into an area of static storage, and then
returning the address of that storage as if it were a pointer value.
The caller must copy the data from that memory area to the place where
the value is wanted.  This is slower than the method used by GCC, and
fails to be reentrant.

 On some target machines, such as RISC machines and the 80386, the
standard system convention is to pass to the subroutine the address of
where to return the value.  On these machines, GCC has been configured
to be compatible with the standard compiler, when this method is used.
It may not be compatible for structures of 1, 2, 4 or 8 bytes.

 GCC uses the system's standard convention for passing arguments.  On
some machines, the first few arguments are passed in registers; in
others, all are passed on the stack.  It would be possible to use
registers for argument passing on any machine, and this would probably
result in a significant speedup.  But the result would be complete
incompatibility with code that follows the standard convention.  So this
change is practical only if you are switching to GCC as the sole C
compiler for the system.  We may implement register argument passing on
certain machines once we have a complete GNU system so that we can
compile the libraries with GCC.

 On some machines (particularly the SPARC), certain types of arguments
are passed "by invisible reference".  This means that the value is
stored in memory, and the address of the memory location is passed to
the subroutine.

 If you use 'longjmp', beware of automatic variables.  ISO C says that
automatic variables that are not declared 'volatile' have undefined
values after a 'longjmp'.  And this is all GCC promises to do, because
it is very difficult to restore register variables correctly, and one of
GCC's features is that it can put variables in registers without your
asking it to.


File: gccint.info,  Node: Libgcc,  Next: Languages,  Prev: Interface,  Up: Top

4 The GCC low-level runtime library
***********************************

GCC provides a low-level runtime library, 'libgcc.a' or 'libgcc_s.so.1'
on some platforms.  GCC generates calls to routines in this library
automatically, whenever it needs to perform some operation that is too
complicated to emit inline code for.

 Most of the routines in 'libgcc' handle arithmetic operations that the
target processor cannot perform directly.  This includes integer
multiply and divide on some machines, and all floating-point and
fixed-point operations on other machines.  'libgcc' also includes
routines for exception handling, and a handful of miscellaneous
operations.

 Some of these routines can be defined in mostly machine-independent C.
Others must be hand-written in assembly language for each processor that
needs them.

 GCC will also generate calls to C library routines, such as 'memcpy'
and 'memset', in some cases.  The set of routines that GCC may possibly
use is documented in *note (gcc)Other Builtins::.

 These routines take arguments and return values of a specific machine
mode, not a specific C type.  *Note Machine Modes::, for an explanation
of this concept.  For illustrative purposes, in this chapter the
floating point type 'float' is assumed to correspond to 'SFmode';
'double' to 'DFmode'; and 'long double' to both 'TFmode' and 'XFmode'.
Similarly, the integer types 'int' and 'unsigned int' correspond to
'SImode'; 'long' and 'unsigned long' to 'DImode'; and 'long long' and
'unsigned long long' to 'TImode'.

* Menu:

* Integer library routines::
* Soft float library routines::
* Decimal float library routines::
* Fixed-point fractional library routines::
* Exception handling routines::
* Miscellaneous routines::


File: gccint.info,  Node: Integer library routines,  Next: Soft float library routines,  Up: Libgcc

4.1 Routines for integer arithmetic
===================================

The integer arithmetic routines are used on platforms that don't provide
hardware support for arithmetic operations on some modes.

4.1.1 Arithmetic functions
--------------------------

 -- Runtime Function: int __ashlsi3 (int A, int B)
 -- Runtime Function: long __ashldi3 (long A, int B)
 -- Runtime Function: long long __ashlti3 (long long A, int B)
     These functions return the result of shifting A left by B bits.

 -- Runtime Function: int __ashrsi3 (int A, int B)
 -- Runtime Function: long __ashrdi3 (long A, int B)
 -- Runtime Function: long long __ashrti3 (long long A, int B)
     These functions return the result of arithmetically shifting A
     right by B bits.

 -- Runtime Function: int __divsi3 (int A, int B)
 -- Runtime Function: long __divdi3 (long A, long B)
 -- Runtime Function: long long __divti3 (long long A, long long B)
     These functions return the quotient of the signed division of A and
     B.

 -- Runtime Function: int __lshrsi3 (int A, int B)
 -- Runtime Function: long __lshrdi3 (long A, int B)
 -- Runtime Function: long long __lshrti3 (long long A, int B)
     These functions return the result of logically shifting A right by
     B bits.

 -- Runtime Function: int __modsi3 (int A, int B)
 -- Runtime Function: long __moddi3 (long A, long B)
 -- Runtime Function: long long __modti3 (long long A, long long B)
     These functions return the remainder of the signed division of A
     and B.

 -- Runtime Function: int __mulsi3 (int A, int B)
 -- Runtime Function: long __muldi3 (long A, long B)
 -- Runtime Function: long long __multi3 (long long A, long long B)
     These functions return the product of A and B.

 -- Runtime Function: long __negdi2 (long A)
 -- Runtime Function: long long __negti2 (long long A)
     These functions return the negation of A.

 -- Runtime Function: unsigned int __udivsi3 (unsigned int A, unsigned
          int B)
 -- Runtime Function: unsigned long __udivdi3 (unsigned long A, unsigned
          long B)
 -- Runtime Function: unsigned long long __udivti3 (unsigned long long
          A, unsigned long long B)
     These functions return the quotient of the unsigned division of A
     and B.

 -- Runtime Function: unsigned long __udivmoddi4 (unsigned long A,
          unsigned long B, unsigned long *C)
 -- Runtime Function: unsigned long long __udivmodti4 (unsigned long
          long A, unsigned long long B, unsigned long long *C)
     These functions calculate both the quotient and remainder of the
     unsigned division of A and B.  The return value is the quotient,
     and the remainder is placed in variable pointed to by C.

 -- Runtime Function: unsigned int __umodsi3 (unsigned int A, unsigned
          int B)
 -- Runtime Function: unsigned long __umoddi3 (unsigned long A, unsigned
          long B)
 -- Runtime Function: unsigned long long __umodti3 (unsigned long long
          A, unsigned long long B)
     These functions return the remainder of the unsigned division of A
     and B.

4.1.2 Comparison functions
--------------------------

The following functions implement integral comparisons.  These functions
implement a low-level compare, upon which the higher level comparison
operators (such as less than and greater than or equal to) can be
constructed.  The returned values lie in the range zero to two, to allow
the high-level operators to be implemented by testing the returned
result using either signed or unsigned comparison.

 -- Runtime Function: int __cmpdi2 (long A, long B)
 -- Runtime Function: int __cmpti2 (long long A, long long B)
     These functions perform a signed comparison of A and B.  If A is
     less than B, they return 0; if A is greater than B, they return 2;
     and if A and B are equal they return 1.

 -- Runtime Function: int __ucmpdi2 (unsigned long A, unsigned long B)
 -- Runtime Function: int __ucmpti2 (unsigned long long A, unsigned long
          long B)
     These functions perform an unsigned comparison of A and B.  If A is
     less than B, they return 0; if A is greater than B, they return 2;
     and if A and B are equal they return 1.

4.1.3 Trapping arithmetic functions
-----------------------------------

The following functions implement trapping arithmetic.  These functions
call the libc function 'abort' upon signed arithmetic overflow.

 -- Runtime Function: int __absvsi2 (int A)
 -- Runtime Function: long __absvdi2 (long A)
     These functions return the absolute value of A.

 -- Runtime Function: int __addvsi3 (int A, int B)
 -- Runtime Function: long __addvdi3 (long A, long B)
     These functions return the sum of A and B; that is 'A + B'.

 -- Runtime Function: int __mulvsi3 (int A, int B)
 -- Runtime Function: long __mulvdi3 (long A, long B)
     The functions return the product of A and B; that is 'A * B'.

 -- Runtime Function: int __negvsi2 (int A)
 -- Runtime Function: long __negvdi2 (long A)
     These functions return the negation of A; that is '-A'.

 -- Runtime Function: int __subvsi3 (int A, int B)
 -- Runtime Function: long __subvdi3 (long A, long B)
     These functions return the difference between B and A; that is 'A -
     B'.

4.1.4 Bit operations
--------------------

 -- Runtime Function: int __clzsi2 (int A)
 -- Runtime Function: int __clzdi2 (long A)
 -- Runtime Function: int __clzti2 (long long A)
     These functions return the number of leading 0-bits in A, starting
     at the most significant bit position.  If A is zero, the result is
     undefined.

 -- Runtime Function: int __ctzsi2 (int A)
 -- Runtime Function: int __ctzdi2 (long A)
 -- Runtime Function: int __ctzti2 (long long A)
     These functions return the number of trailing 0-bits in A, starting
     at the least significant bit position.  If A is zero, the result is
     undefined.

 -- Runtime Function: int __ffsdi2 (long A)
 -- Runtime Function: int __ffsti2 (long long A)
     These functions return the index of the least significant 1-bit in
     A, or the value zero if A is zero.  The least significant bit is
     index one.

 -- Runtime Function: int __paritysi2 (int A)
 -- Runtime Function: int __paritydi2 (long A)
 -- Runtime Function: int __parityti2 (long long A)
     These functions return the value zero if the number of bits set in
     A is even, and the value one otherwise.

 -- Runtime Function: int __popcountsi2 (int A)
 -- Runtime Function: int __popcountdi2 (long A)
 -- Runtime Function: int __popcountti2 (long long A)
     These functions return the number of bits set in A.

 -- Runtime Function: int32_t __bswapsi2 (int32_t A)
 -- Runtime Function: int64_t __bswapdi2 (int64_t A)
     These functions return the A byteswapped.


File: gccint.info,  Node: Soft float library routines,  Next: Decimal float library routines,  Prev: Integer library routines,  Up: Libgcc

4.2 Routines for floating point emulation
=========================================

The software floating point library is used on machines which do not
have hardware support for floating point.  It is also used whenever
'-msoft-float' is used to disable generation of floating point
instructions.  (Not all targets support this switch.)

 For compatibility with other compilers, the floating point emulation
routines can be renamed with the 'DECLARE_LIBRARY_RENAMES' macro (*note
Library Calls::).  In this section, the default names are used.

 Presently the library does not support 'XFmode', which is used for
'long double' on some architectures.

4.2.1 Arithmetic functions
--------------------------

 -- Runtime Function: float __addsf3 (float A, float B)
 -- Runtime Function: double __adddf3 (double A, double B)
 -- Runtime Function: long double __addtf3 (long double A, long double
          B)
 -- Runtime Function: long double __addxf3 (long double A, long double
          B)
     These functions return the sum of A and B.

 -- Runtime Function: float __subsf3 (float A, float B)
 -- Runtime Function: double __subdf3 (double A, double B)
 -- Runtime Function: long double __subtf3 (long double A, long double
          B)
 -- Runtime Function: long double __subxf3 (long double A, long double
          B)
     These functions return the difference between B and A; that is,
     A - B.

 -- Runtime Function: float __mulsf3 (float A, float B)
 -- Runtime Function: double __muldf3 (double A, double B)
 -- Runtime Function: long double __multf3 (long double A, long double
          B)
 -- Runtime Function: long double __mulxf3 (long double A, long double
          B)
     These functions return the product of A and B.

 -- Runtime Function: float __divsf3 (float A, float B)
 -- Runtime Function: double __divdf3 (double A, double B)
 -- Runtime Function: long double __divtf3 (long double A, long double
          B)
 -- Runtime Function: long double __divxf3 (long double A, long double
          B)
     These functions return the quotient of A and B; that is, A / B.

 -- Runtime Function: float __negsf2 (float A)
 -- Runtime Function: double __negdf2 (double A)
 -- Runtime Function: long double __negtf2 (long double A)
 -- Runtime Function: long double __negxf2 (long double A)
     These functions return the negation of A.  They simply flip the
     sign bit, so they can produce negative zero and negative NaN.

4.2.2 Conversion functions
--------------------------

 -- Runtime Function: double __extendsfdf2 (float A)
 -- Runtime Function: long double __extendsftf2 (float A)
 -- Runtime Function: long double __extendsfxf2 (float A)
 -- Runtime Function: long double __extenddftf2 (double A)
 -- Runtime Function: long double __extenddfxf2 (double A)
     These functions extend A to the wider mode of their return type.

 -- Runtime Function: double __truncxfdf2 (long double A)
 -- Runtime Function: double __trunctfdf2 (long double A)
 -- Runtime Function: float __truncxfsf2 (long double A)
 -- Runtime Function: float __trunctfsf2 (long double A)
 -- Runtime Function: float __truncdfsf2 (double A)
     These functions truncate A to the narrower mode of their return
     type, rounding toward zero.

 -- Runtime Function: int __fixsfsi (float A)
 -- Runtime Function: int __fixdfsi (double A)
 -- Runtime Function: int __fixtfsi (long double A)
 -- Runtime Function: int __fixxfsi (long double A)
     These functions convert A to a signed integer, rounding toward
     zero.

 -- Runtime Function: long __fixsfdi (float A)
 -- Runtime Function: long __fixdfdi (double A)
 -- Runtime Function: long __fixtfdi (long double A)
 -- Runtime Function: long __fixxfdi (long double A)
     These functions convert A to a signed long, rounding toward zero.

 -- Runtime Function: long long __fixsfti (float A)
 -- Runtime Function: long long __fixdfti (double A)
 -- Runtime Function: long long __fixtfti (long double A)
 -- Runtime Function: long long __fixxfti (long double A)
     These functions convert A to a signed long long, rounding toward
     zero.

 -- Runtime Function: unsigned int __fixunssfsi (float A)
 -- Runtime Function: unsigned int __fixunsdfsi (double A)
 -- Runtime Function: unsigned int __fixunstfsi (long double A)
 -- Runtime Function: unsigned int __fixunsxfsi (long double A)
     These functions convert A to an unsigned integer, rounding toward
     zero.  Negative values all become zero.

 -- Runtime Function: unsigned long __fixunssfdi (float A)
 -- Runtime Function: unsigned long __fixunsdfdi (double A)
 -- Runtime Function: unsigned long __fixunstfdi (long double A)
 -- Runtime Function: unsigned long __fixunsxfdi (long double A)
     These functions convert A to an unsigned long, rounding toward
     zero.  Negative values all become zero.

 -- Runtime Function: unsigned long long __fixunssfti (float A)
 -- Runtime Function: unsigned long long __fixunsdfti (double A)
 -- Runtime Function: unsigned long long __fixunstfti (long double A)
 -- Runtime Function: unsigned long long __fixunsxfti (long double A)
     These functions convert A to an unsigned long long, rounding toward
     zero.  Negative values all become zero.

 -- Runtime Function: float __floatsisf (int I)
 -- Runtime Function: double __floatsidf (int I)
 -- Runtime Function: long double __floatsitf (int I)
 -- Runtime Function: long double __floatsixf (int I)
     These functions convert I, a signed integer, to floating point.

 -- Runtime Function: float __floatdisf (long I)
 -- Runtime Function: double __floatdidf (long I)
 -- Runtime Function: long double __floatditf (long I)
 -- Runtime Function: long double __floatdixf (long I)
     These functions convert I, a signed long, to floating point.

 -- Runtime Function: float __floattisf (long long I)
 -- Runtime Function: double __floattidf (long long I)
 -- Runtime Function: long double __floattitf (long long I)
 -- Runtime Function: long double __floattixf (long long I)
     These functions convert I, a signed long long, to floating point.

 -- Runtime Function: float __floatunsisf (unsigned int I)
 -- Runtime Function: double __floatunsidf (unsigned int I)
 -- Runtime Function: long double __floatunsitf (unsigned int I)
 -- Runtime Function: long double __floatunsixf (unsigned int I)
     These functions convert I, an unsigned integer, to floating point.

 -- Runtime Function: float __floatundisf (unsigned long I)
 -- Runtime Function: double __floatundidf (unsigned long I)
 -- Runtime Function: long double __floatunditf (unsigned long I)
 -- Runtime Function: long double __floatundixf (unsigned long I)
     These functions convert I, an unsigned long, to floating point.

 -- Runtime Function: float __floatuntisf (unsigned long long I)
 -- Runtime Function: double __floatuntidf (unsigned long long I)
 -- Runtime Function: long double __floatuntitf (unsigned long long I)
 -- Runtime Function: long double __floatuntixf (unsigned long long I)
     These functions convert I, an unsigned long long, to floating
     point.

4.2.3 Comparison functions
--------------------------

There are two sets of basic comparison functions.

 -- Runtime Function: int __cmpsf2 (float A, float B)
 -- Runtime Function: int __cmpdf2 (double A, double B)
 -- Runtime Function: int __cmptf2 (long double A, long double B)
     These functions calculate a <=> b.  That is, if A is less than B,
     they return -1; if A is greater than B, they return 1; and if A and
     B are equal they return 0.  If either argument is NaN they return
     1, but you should not rely on this; if NaN is a possibility, use
     one of the higher-level comparison functions.

 -- Runtime Function: int __unordsf2 (float A, float B)
 -- Runtime Function: int __unorddf2 (double A, double B)
 -- Runtime Function: int __unordtf2 (long double A, long double B)
     These functions return a nonzero value if either argument is NaN,
     otherwise 0.

 There is also a complete group of higher level functions which
correspond directly to comparison operators.  They implement the ISO C
semantics for floating-point comparisons, taking NaN into account.  Pay
careful attention to the return values defined for each set.  Under the
hood, all of these routines are implemented as

       if (__unordXf2 (a, b))
         return E;
       return __cmpXf2 (a, b);

where E is a constant chosen to give the proper behavior for NaN.  Thus,
the meaning of the return value is different for each set.  Do not rely
on this implementation; only the semantics documented below are
guaranteed.

 -- Runtime Function: int __eqsf2 (float A, float B)
 -- Runtime Function: int __eqdf2 (double A, double B)
 -- Runtime Function: int __eqtf2 (long double A, long double B)
     These functions return zero if neither argument is NaN, and A and B
     are equal.

 -- Runtime Function: int __nesf2 (float A, float B)
 -- Runtime Function: int __nedf2 (double A, double B)
 -- Runtime Function: int __netf2 (long double A, long double B)
     These functions return a nonzero value if either argument is NaN,
     or if A and B are unequal.

 -- Runtime Function: int __gesf2 (float A, float B)
 -- Runtime Function: int __gedf2 (double A, double B)
 -- Runtime Function: int __getf2 (long double A, long double B)
     These functions return a value greater than or equal to zero if
     neither argument is NaN, and A is greater than or equal to B.

 -- Runtime Function: int __ltsf2 (float A, float B)
 -- Runtime Function: int __ltdf2 (double A, double B)
 -- Runtime Function: int __lttf2 (long double A, long double B)
     These functions return a value less than zero if neither argument
     is NaN, and A is strictly less than B.

 -- Runtime Function: int __lesf2 (float A, float B)
 -- Runtime Function: int __ledf2 (double A, double B)
 -- Runtime Function: int __letf2 (long double A, long double B)
     These functions return a value less than or equal to zero if
     neither argument is NaN, and A is less than or equal to B.

 -- Runtime Function: int __gtsf2 (float A, float B)
 -- Runtime Function: int __gtdf2 (double A, double B)
 -- Runtime Function: int __gttf2 (long double A, long double B)
     These functions return a value greater than zero if neither
     argument is NaN, and A is strictly greater than B.

4.2.4 Other floating-point functions
------------------------------------

 -- Runtime Function: float __powisf2 (float A, int B)
 -- Runtime Function: double __powidf2 (double A, int B)
 -- Runtime Function: long double __powitf2 (long double A, int B)
 -- Runtime Function: long double __powixf2 (long double A, int B)
     These functions convert raise A to the power B.

 -- Runtime Function: complex float __mulsc3 (float A, float B, float C,
          float D)
 -- Runtime Function: complex double __muldc3 (double A, double B,
          double C, double D)
 -- Runtime Function: complex long double __multc3 (long double A, long
          double B, long double C, long double D)
 -- Runtime Function: complex long double __mulxc3 (long double A, long
          double B, long double C, long double D)
     These functions return the product of A + iB and C + iD, following
     the rules of C99 Annex G.

 -- Runtime Function: complex float __divsc3 (float A, float B, float C,
          float D)
 -- Runtime Function: complex double __divdc3 (double A, double B,
          double C, double D)
 -- Runtime Function: complex long double __divtc3 (long double A, long
          double B, long double C, long double D)
 -- Runtime Function: complex long double __divxc3 (long double A, long
          double B, long double C, long double D)
     These functions return the quotient of A + iB and C + iD (i.e., (A
     + iB) / (C + iD)), following the rules of C99 Annex G.


File: gccint.info,  Node: Decimal float library routines,  Next: Fixed-point fractional library routines,  Prev: Soft float library routines,  Up: Libgcc

4.3 Routines for decimal floating point emulation
=================================================

The software decimal floating point library implements IEEE 754-2008
decimal floating point arithmetic and is only activated on selected
targets.

 The software decimal floating point library supports either DPD
(Densely Packed Decimal) or BID (Binary Integer Decimal) encoding as
selected at configure time.

4.3.1 Arithmetic functions
--------------------------

 -- Runtime Function: _Decimal32 __dpd_addsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal32 __bid_addsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal64 __dpd_adddd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal64 __bid_adddd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal128 __dpd_addtd3 (_Decimal128 A,
          _Decimal128 B)
 -- Runtime Function: _Decimal128 __bid_addtd3 (_Decimal128 A,
          _Decimal128 B)
     These functions return the sum of A and B.

 -- Runtime Function: _Decimal32 __dpd_subsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal32 __bid_subsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal64 __dpd_subdd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal64 __bid_subdd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal128 __dpd_subtd3 (_Decimal128 A,
          _Decimal128 B)
 -- Runtime Function: _Decimal128 __bid_subtd3 (_Decimal128 A,
          _Decimal128 B)
     These functions return the difference between B and A; that is,
     A - B.

 -- Runtime Function: _Decimal32 __dpd_mulsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal32 __bid_mulsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal64 __dpd_muldd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal64 __bid_muldd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal128 __dpd_multd3 (_Decimal128 A,
          _Decimal128 B)
 -- Runtime Function: _Decimal128 __bid_multd3 (_Decimal128 A,
          _Decimal128 B)
     These functions return the product of A and B.

 -- Runtime Function: _Decimal32 __dpd_divsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal32 __bid_divsd3 (_Decimal32 A, _Decimal32
          B)
 -- Runtime Function: _Decimal64 __dpd_divdd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal64 __bid_divdd3 (_Decimal64 A, _Decimal64
          B)
 -- Runtime Function: _Decimal128 __dpd_divtd3 (_Decimal128 A,
          _Decimal128 B)
 -- Runtime Function: _Decimal128 __bid_divtd3 (_Decimal128 A,
          _Decimal128 B)
     These functions return the quotient of A and B; that is, A / B.

 -- Runtime Function: _Decimal32 __dpd_negsd2 (_Decimal32 A)
 -- Runtime Function: _Decimal32 __bid_negsd2 (_Decimal32 A)
 -- Runtime Function: _Decimal64 __dpd_negdd2 (_Decimal64 A)
 -- Runtime Function: _Decimal64 __bid_negdd2 (_Decimal64 A)
 -- Runtime Function: _Decimal128 __dpd_negtd2 (_Decimal128 A)
 -- Runtime Function: _Decimal128 __bid_negtd2 (_Decimal128 A)
     These functions return the negation of A.  They simply flip the
     sign bit, so they can produce negative zero and negative NaN.

4.3.2 Conversion functions
--------------------------

 -- Runtime Function: _Decimal64 __dpd_extendsddd2 (_Decimal32 A)
 -- Runtime Function: _Decimal64 __bid_extendsddd2 (_Decimal32 A)
 -- Runtime Function: _Decimal128 __dpd_extendsdtd2 (_Decimal32 A)
 -- Runtime Function: _Decimal128 __bid_extendsdtd2 (_Decimal32 A)
 -- Runtime Function: _Decimal128 __dpd_extendddtd2 (_Decimal64 A)
 -- Runtime Function: _Decimal128 __bid_extendddtd2 (_Decimal64 A)
 -- Runtime Function: _Decimal32 __dpd_truncddsd2 (_Decimal64 A)
 -- Runtime Function: _Decimal32 __bid_truncddsd2 (_Decimal64 A)
 -- Runtime Function: _Decimal32 __dpd_trunctdsd2 (_Decimal128 A)
 -- Runtime Function: _Decimal32 __bid_trunctdsd2 (_Decimal128 A)
 -- Runtime Function: _Decimal64 __dpd_trunctddd2 (_Decimal128 A)
 -- Runtime Function: _Decimal64 __bid_trunctddd2 (_Decimal128 A)
     These functions convert the value A from one decimal floating type
     to another.

 -- Runtime Function: _Decimal64 __dpd_extendsfdd (float A)
 -- Runtime Function: _Decimal64 __bid_extendsfdd (float A)
 -- Runtime Function: _Decimal128 __dpd_extendsftd (float A)
 -- Runtime Function: _Decimal128 __bid_extendsftd (float A)
 -- Runtime Function: _Decimal128 __dpd_extenddftd (double A)
 -- Runtime Function: _Decimal128 __bid_extenddftd (double A)
 -- Runtime Function: _Decimal128 __dpd_extendxftd (long double A)
 -- Runtime Function: _Decimal128 __bid_extendxftd (long double A)
 -- Runtime Function: _Decimal32 __dpd_truncdfsd (double A)
 -- Runtime Function: _Decimal32 __bid_truncdfsd (double A)
 -- Runtime Function: _Decimal32 __dpd_truncxfsd (long double A)
 -- Runtime Function: _Decimal32 __bid_truncxfsd (long double A)
 -- Runtime Function: _Decimal32 __dpd_trunctfsd (long double A)
 -- Runtime Function: _Decimal32 __bid_trunctfsd (long double A)
 -- Runtime Function: _Decimal64 __dpd_truncxfdd (long double A)
 -- Runtime Function: _Decimal64 __bid_truncxfdd (long double A)
 -- Runtime Function: _Decimal64 __dpd_trunctfdd (long double A)
 -- Runtime Function: _Decimal64 __bid_trunctfdd (long double A)
     These functions convert the value of A from a binary floating type
     to a decimal floating type of a different size.

 -- Runtime Function: float __dpd_truncddsf (_Decimal64 A)
 -- Runtime Function: float __bid_truncddsf (_Decimal64 A)
 -- Runtime Function: float __dpd_trunctdsf (_Decimal128 A)
 -- Runtime Function: float __bid_trunctdsf (_Decimal128 A)
 -- Runtime Function: double __dpd_extendsddf (_Decimal32 A)
 -- Runtime Function: double __bid_extendsddf (_Decimal32 A)
 -- Runtime Function: double __dpd_trunctddf (_Decimal128 A)
 -- Runtime Function: double __bid_trunctddf (_Decimal128 A)
 -- Runtime Function: long double __dpd_extendsdxf (_Decimal32 A)
 -- Runtime Function: long double __bid_extendsdxf (_Decimal32 A)
 -- Runtime Function: long double __dpd_extendddxf (_Decimal64 A)
 -- Runtime Function: long double __bid_extendddxf (_Decimal64 A)
 -- Runtime Function: long double __dpd_trunctdxf (_Decimal128 A)
 -- Runtime Function: long double __bid_trunctdxf (_Decimal128 A)
 -- Runtime Function: long double __dpd_extendsdtf (_Decimal32 A)
 -- Runtime Function: long double __bid_extendsdtf (_Decimal32 A)
 -- Runtime Function: long double __dpd_extendddtf (_Decimal64 A)
 -- Runtime Function: long double __bid_extendddtf (_Decimal64 A)
     These functions convert the value of A from a decimal floating type
     to a binary floating type of a different size.

 -- Runtime Function: _Decimal32 __dpd_extendsfsd (float A)
 -- Runtime Function: _Decimal32 __bid_extendsfsd (float A)
 -- Runtime Function: _Decimal64 __dpd_extenddfdd (double A)
 -- Runtime Function: _Decimal64 __bid_extenddfdd (double A)
 -- Runtime Function: _Decimal128 __dpd_extendtftd (long double A)
 -- Runtime Function: _Decimal128 __bid_extendtftd (long double A)
 -- Runtime Function: float __dpd_truncsdsf (_Decimal32 A)
 -- Runtime Function: float __bid_truncsdsf (_Decimal32 A)
 -- Runtime Function: double __dpd_truncdddf (_Decimal64 A)
 -- Runtime Function: double __bid_truncdddf (_Decimal64 A)
 -- Runtime Function: long double __dpd_trunctdtf (_Decimal128 A)
 -- Runtime Function: long double __bid_trunctdtf (_Decimal128 A)
     These functions convert the value of A between decimal and binary
     floating types of the same size.

 -- Runtime Function: int __dpd_fixsdsi (_Decimal32 A)
 -- Runtime Function: int __bid_fixsdsi (_Decimal32 A)
 -- Runtime Function: int __dpd_fixddsi (_Decimal64 A)
 -- Runtime Function: int __bid_fixddsi (_Decimal64 A)
 -- Runtime Function: int __dpd_fixtdsi (_Decimal128 A)
 -- Runtime Function: int __bid_fixtdsi (_Decimal128 A)
     These functions convert A to a signed integer.

 -- Runtime Function: long __dpd_fixsddi (_Decimal32 A)
 -- Runtime Function: long __bid_fixsddi (_Decimal32 A)
 -- Runtime Function: long __dpd_fixdddi (_Decimal64 A)
 -- Runtime Function: long __bid_fixdddi (_Decimal64 A)
 -- Runtime Function: long __dpd_fixtddi (_Decimal128 A)
 -- Runtime Function: long __bid_fixtddi (_Decimal128 A)
     These functions convert A to a signed long.

 -- Runtime Function: unsigned int __dpd_fixunssdsi (_Decimal32 A)
 -- Runtime Function: unsigned int __bid_fixunssdsi (_Decimal32 A)
 -- Runtime Function: unsigned int __dpd_fixunsddsi (_Decimal64 A)
 -- Runtime Function: unsigned int __bid_fixunsddsi (_Decimal64 A)
 -- Runtime Function: unsigned int __dpd_fixunstdsi (_Decimal128 A)
 -- Runtime Function: unsigned int __bid_fixunstdsi (_Decimal128 A)
     These functions convert A to an unsigned integer.  Negative values
     all become zero.

 -- Runtime Function: unsigned long __dpd_fixunssddi (_Decimal32 A)
 -- Runtime Function: unsigned long __bid_fixunssddi (_Decimal32 A)
 -- Runtime Function: unsigned long __dpd_fixunsdddi (_Decimal64 A)
 -- Runtime Function: unsigned long __bid_fixunsdddi (_Decimal64 A)
 -- Runtime Function: unsigned long __dpd_fixunstddi (_Decimal128 A)
 -- Runtime Function: unsigned long __bid_fixunstddi (_Decimal128 A)
     These functions convert A to an unsigned long.  Negative values all
     become zero.

 -- Runtime Function: _Decimal32 __dpd_floatsisd (int I)
 -- Runtime Function: _Decimal32 __bid_floatsisd (int I)
 -- Runtime Function: _Decimal64 __dpd_floatsidd (int I)
 -- Runtime Function: _Decimal64 __bid_floatsidd (int I)
 -- Runtime Function: _Decimal128 __dpd_floatsitd (int I)
 -- Runtime Function: _Decimal128 __bid_floatsitd (int I)
     These functions convert I, a signed integer, to decimal floating
     point.

 -- Runtime Function: _Decimal32 __dpd_floatdisd (long I)
 -- Runtime Function: _Decimal32 __bid_floatdisd (long I)
 -- Runtime Function: _Decimal64 __dpd_floatdidd (long I)
 -- Runtime Function: _Decimal64 __bid_floatdidd (long I)
 -- Runtime Function: _Decimal128 __dpd_floatditd (long I)
 -- Runtime Function: _Decimal128 __bid_floatditd (long I)
     These functions convert I, a signed long, to decimal floating
     point.

 -- Runtime Function: _Decimal32 __dpd_floatunssisd (unsigned int I)
 -- Runtime Function: _Decimal32 __bid_floatunssisd (unsigned int I)
 -- Runtime Function: _Decimal64 __dpd_floatunssidd (unsigned int I)
 -- Runtime Function: _Decimal64 __bid_floatunssidd (unsigned int I)
 -- Runtime Function: _Decimal128 __dpd_floatunssitd (unsigned int I)
 -- Runtime Function: _Decimal128 __bid_floatunssitd (unsigned int I)
     These functions convert I, an unsigned integer, to decimal floating
     point.

 -- Runtime Function: _Decimal32 __dpd_floatunsdisd (unsigned long I)
 -- Runtime Function: _Decimal32 __bid_floatunsdisd (unsigned long I)
 -- Runtime Function: _Decimal64 __dpd_floatunsdidd (unsigned long I)
 -- Runtime Function: _Decimal64 __bid_floatunsdidd (unsigned long I)
 -- Runtime Function: _Decimal128 __dpd_floatunsditd (unsigned long I)
 -- Runtime Function: _Decimal128 __bid_floatunsditd (unsigned long I)
     These functions convert I, an unsigned long, to decimal floating
     point.

4.3.3 Comparison functions
--------------------------

 -- Runtime Function: int __dpd_unordsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_unordsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_unorddd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_unorddd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_unordtd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_unordtd2 (_Decimal128 A, _Decimal128 B)
     These functions return a nonzero value if either argument is NaN,
     otherwise 0.

 There is also a complete group of higher level functions which
correspond directly to comparison operators.  They implement the ISO C
semantics for floating-point comparisons, taking NaN into account.  Pay
careful attention to the return values defined for each set.  Under the
hood, all of these routines are implemented as

       if (__bid_unordXd2 (a, b))
         return E;
       return __bid_cmpXd2 (a, b);

where E is a constant chosen to give the proper behavior for NaN.  Thus,
the meaning of the return value is different for each set.  Do not rely
on this implementation; only the semantics documented below are
guaranteed.

 -- Runtime Function: int __dpd_eqsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_eqsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_eqdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_eqdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_eqtd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_eqtd2 (_Decimal128 A, _Decimal128 B)
     These functions return zero if neither argument is NaN, and A and B
     are equal.

 -- Runtime Function: int __dpd_nesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_nesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_nedd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_nedd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_netd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_netd2 (_Decimal128 A, _Decimal128 B)
     These functions return a nonzero value if either argument is NaN,
     or if A and B are unequal.

 -- Runtime Function: int __dpd_gesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_gesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_gedd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_gedd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_getd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_getd2 (_Decimal128 A, _Decimal128 B)
     These functions return a value greater than or equal to zero if
     neither argument is NaN, and A is greater than or equal to B.

 -- Runtime Function: int __dpd_ltsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_ltsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_ltdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_ltdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_lttd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_lttd2 (_Decimal128 A, _Decimal128 B)
     These functions return a value less than zero if neither argument
     is NaN, and A is strictly less than B.

 -- Runtime Function: int __dpd_lesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_lesd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_ledd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_ledd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_letd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_letd2 (_Decimal128 A, _Decimal128 B)
     These functions return a value less than or equal to zero if
     neither argument is NaN, and A is less than or equal to B.

 -- Runtime Function: int __dpd_gtsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __bid_gtsd2 (_Decimal32 A, _Decimal32 B)
 -- Runtime Function: int __dpd_gtdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __bid_gtdd2 (_Decimal64 A, _Decimal64 B)
 -- Runtime Function: int __dpd_gttd2 (_Decimal128 A, _Decimal128 B)
 -- Runtime Function: int __bid_gttd2 (_Decimal128 A, _Decimal128 B)
     These functions return a value greater than zero if neither
     argument is NaN, and A is strictly greater than B.


File: gccint.info,  Node: Fixed-point fractional library routines,  Next: Exception handling routines,  Prev: Decimal float library routines,  Up: Libgcc

4.4 Routines for fixed-point fractional emulation
=================================================

The software fixed-point library implements fixed-point fractional
arithmetic, and is only activated on selected targets.

 For ease of comprehension 'fract' is an alias for the '_Fract' type,
'accum' an alias for '_Accum', and 'sat' an alias for '_Sat'.

 For illustrative purposes, in this section the fixed-point fractional
type 'short fract' is assumed to correspond to machine mode 'QQmode';
'unsigned short fract' to 'UQQmode'; 'fract' to 'HQmode';
'unsigned fract' to 'UHQmode'; 'long fract' to 'SQmode';
'unsigned long fract' to 'USQmode'; 'long long fract' to 'DQmode'; and
'unsigned long long fract' to 'UDQmode'.  Similarly the fixed-point
accumulator type 'short accum' corresponds to 'HAmode';
'unsigned short accum' to 'UHAmode'; 'accum' to 'SAmode';
'unsigned accum' to 'USAmode'; 'long accum' to 'DAmode';
'unsigned long accum' to 'UDAmode'; 'long long accum' to 'TAmode'; and
'unsigned long long accum' to 'UTAmode'.

4.4.1 Arithmetic functions
--------------------------

 -- Runtime Function: short fract __addqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __addhq3 (fract A, fract B)
 -- Runtime Function: long fract __addsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __adddq3 (long long fract A, long
          long fract B)
 -- Runtime Function: unsigned short fract __adduqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __adduhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __addusq3 (unsigned long fract
          A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __addudq3 (unsigned long
          long fract A, unsigned long long fract B)
 -- Runtime Function: short accum __addha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __addsa3 (accum A, accum B)
 -- Runtime Function: long accum __addda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __addta3 (long long accum A, long
          long accum B)
 -- Runtime Function: unsigned short accum __adduha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __addusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __adduda3 (unsigned long accum
          A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __adduta3 (unsigned long
          long accum A, unsigned long long accum B)
     These functions return the sum of A and B.

 -- Runtime Function: short fract __ssaddqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __ssaddhq3 (fract A, fract B)
 -- Runtime Function: long fract __ssaddsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __ssadddq3 (long long fract A,
          long long fract B)
 -- Runtime Function: short accum __ssaddha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __ssaddsa3 (accum A, accum B)
 -- Runtime Function: long accum __ssaddda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __ssaddta3 (long long accum A,
          long long accum B)
     These functions return the sum of A and B with signed saturation.

 -- Runtime Function: unsigned short fract __usadduqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __usadduhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __usaddusq3 (unsigned long
          fract A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __usaddudq3 (unsigned
          long long fract A, unsigned long long fract B)
 -- Runtime Function: unsigned short accum __usadduha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __usaddusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __usadduda3 (unsigned long
          accum A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __usadduta3 (unsigned
          long long accum A, unsigned long long accum B)
     These functions return the sum of A and B with unsigned saturation.

 -- Runtime Function: short fract __subqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __subhq3 (fract A, fract B)
 -- Runtime Function: long fract __subsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __subdq3 (long long fract A, long
          long fract B)
 -- Runtime Function: unsigned short fract __subuqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __subuhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __subusq3 (unsigned long fract
          A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __subudq3 (unsigned long
          long fract A, unsigned long long fract B)
 -- Runtime Function: short accum __subha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __subsa3 (accum A, accum B)
 -- Runtime Function: long accum __subda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __subta3 (long long accum A, long
          long accum B)
 -- Runtime Function: unsigned short accum __subuha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __subusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __subuda3 (unsigned long accum
          A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __subuta3 (unsigned long
          long accum A, unsigned long long accum B)
     These functions return the difference of A and B; that is, 'A - B'.

 -- Runtime Function: short fract __sssubqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __sssubhq3 (fract A, fract B)
 -- Runtime Function: long fract __sssubsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __sssubdq3 (long long fract A,
          long long fract B)
 -- Runtime Function: short accum __sssubha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __sssubsa3 (accum A, accum B)
 -- Runtime Function: long accum __sssubda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __sssubta3 (long long accum A,
          long long accum B)
     These functions return the difference of A and B with signed
     saturation; that is, 'A - B'.

 -- Runtime Function: unsigned short fract __ussubuqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __ussubuhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __ussubusq3 (unsigned long
          fract A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __ussubudq3 (unsigned
          long long fract A, unsigned long long fract B)
 -- Runtime Function: unsigned short accum __ussubuha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __ussubusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __ussubuda3 (unsigned long
          accum A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __ussubuta3 (unsigned
          long long accum A, unsigned long long accum B)
     These functions return the difference of A and B with unsigned
     saturation; that is, 'A - B'.

 -- Runtime Function: short fract __mulqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __mulhq3 (fract A, fract B)
 -- Runtime Function: long fract __mulsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __muldq3 (long long fract A, long
          long fract B)
 -- Runtime Function: unsigned short fract __muluqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __muluhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __mulusq3 (unsigned long fract
          A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __muludq3 (unsigned long
          long fract A, unsigned long long fract B)
 -- Runtime Function: short accum __mulha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __mulsa3 (accum A, accum B)
 -- Runtime Function: long accum __mulda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __multa3 (long long accum A, long
          long accum B)
 -- Runtime Function: unsigned short accum __muluha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __mulusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __muluda3 (unsigned long accum
          A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __muluta3 (unsigned long
          long accum A, unsigned long long accum B)
     These functions return the product of A and B.

 -- Runtime Function: short fract __ssmulqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __ssmulhq3 (fract A, fract B)
 -- Runtime Function: long fract __ssmulsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __ssmuldq3 (long long fract A,
          long long fract B)
 -- Runtime Function: short accum __ssmulha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __ssmulsa3 (accum A, accum B)
 -- Runtime Function: long accum __ssmulda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __ssmulta3 (long long accum A,
          long long accum B)
     These functions return the product of A and B with signed
     saturation.

 -- Runtime Function: unsigned short fract __usmuluqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __usmuluhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __usmulusq3 (unsigned long
          fract A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __usmuludq3 (unsigned
          long long fract A, unsigned long long fract B)
 -- Runtime Function: unsigned short accum __usmuluha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __usmulusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __usmuluda3 (unsigned long
          accum A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __usmuluta3 (unsigned
          long long accum A, unsigned long long accum B)
     These functions return the product of A and B with unsigned
     saturation.

 -- Runtime Function: short fract __divqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __divhq3 (fract A, fract B)
 -- Runtime Function: long fract __divsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __divdq3 (long long fract A, long
          long fract B)
 -- Runtime Function: short accum __divha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __divsa3 (accum A, accum B)
 -- Runtime Function: long accum __divda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __divta3 (long long accum A, long
          long accum B)
     These functions return the quotient of the signed division of A and
     B.

 -- Runtime Function: unsigned short fract __udivuqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __udivuhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __udivusq3 (unsigned long
          fract A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __udivudq3 (unsigned long
          long fract A, unsigned long long fract B)
 -- Runtime Function: unsigned short accum __udivuha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __udivusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __udivuda3 (unsigned long
          accum A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __udivuta3 (unsigned long
          long accum A, unsigned long long accum B)
     These functions return the quotient of the unsigned division of A
     and B.

 -- Runtime Function: short fract __ssdivqq3 (short fract A, short fract
          B)
 -- Runtime Function: fract __ssdivhq3 (fract A, fract B)
 -- Runtime Function: long fract __ssdivsq3 (long fract A, long fract B)
 -- Runtime Function: long long fract __ssdivdq3 (long long fract A,
          long long fract B)
 -- Runtime Function: short accum __ssdivha3 (short accum A, short accum
          B)
 -- Runtime Function: accum __ssdivsa3 (accum A, accum B)
 -- Runtime Function: long accum __ssdivda3 (long accum A, long accum B)
 -- Runtime Function: long long accum __ssdivta3 (long long accum A,
          long long accum B)
     These functions return the quotient of the signed division of A and
     B with signed saturation.

 -- Runtime Function: unsigned short fract __usdivuqq3 (unsigned short
          fract A, unsigned short fract B)
 -- Runtime Function: unsigned fract __usdivuhq3 (unsigned fract A,
          unsigned fract B)
 -- Runtime Function: unsigned long fract __usdivusq3 (unsigned long
          fract A, unsigned long fract B)
 -- Runtime Function: unsigned long long fract __usdivudq3 (unsigned
          long long fract A, unsigned long long fract B)
 -- Runtime Function: unsigned short accum __usdivuha3 (unsigned short
          accum A, unsigned short accum B)
 -- Runtime Function: unsigned accum __usdivusa3 (unsigned accum A,
          unsigned accum B)
 -- Runtime Function: unsigned long accum __usdivuda3 (unsigned long
          accum A, unsigned long accum B)
 -- Runtime Function: unsigned long long accum __usdivuta3 (unsigned
          long long accum A, unsigned long long accum B)
     These functions return the quotient of the unsigned division of A
     and B with unsigned saturation.

 -- Runtime Function: short fract __negqq2 (short fract A)
 -- Runtime Function: fract __neghq2 (fract A)
 -- Runtime Function: long fract __negsq2 (long fract A)
 -- Runtime Function: long long fract __negdq2 (long long fract A)
 -- Runtime Function: unsigned short fract __neguqq2 (unsigned short
          fract A)
 -- Runtime Function: unsigned fract __neguhq2 (unsigned fract A)
 -- Runtime Function: unsigned long fract __negusq2 (unsigned long fract
          A)
 -- Runtime Function: unsigned long long fract __negudq2 (unsigned long
          long fract A)
 -- Runtime Function: short accum __negha2 (short accum A)
 -- Runtime Function: accum __negsa2 (accum A)
 -- Runtime Function: long accum __negda2 (long accum A)
 -- Runtime Function: long long accum __negta2 (long long accum A)
 -- Runtime Function: unsigned short accum __neguha2 (unsigned short
          accum A)
 -- Runtime Function: unsigned accum __negusa2 (unsigned accum A)
 -- Runtime Function: unsigned long accum __neguda2 (unsigned long accum
          A)
 -- Runtime Function: unsigned long long accum __neguta2 (unsigned long
          long accum A)
     These functions return the negation of A.

 -- Runtime Function: short fract __ssnegqq2 (short fract A)
 -- Runtime Function: fract __ssneghq2 (fract A)
 -- Runtime Function: long fract __ssnegsq2 (long fract A)
 -- Runtime Function: long long fract __ssnegdq2 (long long fract A)
 -- Runtime Function: short accum __ssnegha2 (short accum A)
 -- Runtime Function: accum __ssnegsa2 (accum A)
 -- Runtime Function: long accum __ssnegda2 (long accum A)
 -- Runtime Function: long long accum __ssnegta2 (long long accum A)
     These functions return the negation of A with signed saturation.

 -- Runtime Function: unsigned short fract __usneguqq2 (unsigned short
          fract A)
 -- Runtime Function: unsigned fract __usneguhq2 (unsigned fract A)
 -- Runtime Function: unsigned long fract __usnegusq2 (unsigned long
          fract A)
 -- Runtime Function: unsigned long long fract __usnegudq2 (unsigned
          long long fract A)
 -- Runtime Function: unsigned short accum __usneguha2 (unsigned short
          accum A)
 -- Runtime Function: unsigned accum __usnegusa2 (unsigned accum A)
 -- Runtime Function: unsigned long accum __usneguda2 (unsigned long
          accum A)
 -- Runtime Function: unsigned long long accum __usneguta2 (unsigned
          long long accum A)
     These functions return the negation of A with unsigned saturation.

 -- Runtime Function: short fract __ashlqq3 (short fract A, int B)
 -- Runtime Function: fract __ashlhq3 (fract A, int B)
 -- Runtime Function: long fract __ashlsq3 (long fract A, int B)
 -- Runtime Function: long long fract __ashldq3 (long long fract A, int
          B)
 -- Runtime Function: unsigned short fract __ashluqq3 (unsigned short
          fract A, int B)
 -- Runtime Function: unsigned fract __ashluhq3 (unsigned fract A, int
          B)
 -- Runtime Function: unsigned long fract __ashlusq3 (unsigned long
          fract A, int B)
 -- Runtime Function: unsigned long long fract __ashludq3 (unsigned long
          long fract A, int B)
 -- Runtime Function: short accum __ashlha3 (short accum A, int B)
 -- Runtime Function: accum __ashlsa3 (accum A, int B)
 -- Runtime Function: long accum __ashlda3 (long accum A, int B)
 -- Runtime Function: long long accum __ashlta3 (long long accum A, int
          B)
 -- Runtime Function: unsigned short accum __ashluha3 (unsigned short
          accum A, int B)
 -- Runtime Function: unsigned accum __ashlusa3 (unsigned accum A, int
          B)
 -- Runtime Function: unsigned long accum __ashluda3 (unsigned long
          accum A, int B)
 -- Runtime Function: unsigned long long accum __ashluta3 (unsigned long
          long accum A, int B)
     These functions return the result of shifting A left by B bits.

 -- Runtime Function: short fract __ashrqq3 (short fract A, int B)
 -- Runtime Function: fract __ashrhq3 (fract A, int B)
 -- Runtime Function: long fract __ashrsq3 (long fract A, int B)
 -- Runtime Function: long long fract __ashrdq3 (long long fract A, int
          B)
 -- Runtime Function: short accum __ashrha3 (short accum A, int B)
 -- Runtime Function: accum __ashrsa3 (accum A, int B)
 -- Runtime Function: long accum __ashrda3 (long accum A, int B)
 -- Runtime Function: long long accum __ashrta3 (long long accum A, int
          B)
     These functions return the result of arithmetically shifting A
     right by B bits.

 -- Runtime Function: unsigned short fract __lshruqq3 (unsigned short
          fract A, int B)
 -- Runtime Function: unsigned fract __lshruhq3 (unsigned fract A, int
          B)
 -- Runtime Function: unsigned long fract __lshrusq3 (unsigned long
          fract A, int B)
 -- Runtime Function: unsigned long long fract __lshrudq3 (unsigned long
          long fract A, int B)
 -- Runtime Function: unsigned short accum __lshruha3 (unsigned short
          accum A, int B)
 -- Runtime Function: unsigned accum __lshrusa3 (unsigned accum A, int
          B)
 -- Runtime Function: unsigned long accum __lshruda3 (unsigned long
          accum A, int B)
 -- Runtime Function: unsigned long long accum __lshruta3 (unsigned long
          long accum A, int B)
     These functions return the result of logically shifting A right by
     B bits.

 -- Runtime Function: fract __ssashlhq3 (fract A, int B)
 -- Runtime Function: long fract __ssashlsq3 (long fract A, int B)
 -- Runtime Function: long long fract __ssashldq3 (long long fract A,
          int B)
 -- Runtime Function: short accum __ssashlha3 (short accum A, int B)
 -- Runtime Function: accum __ssashlsa3 (accum A, int B)
 -- Runtime Function: long accum __ssashlda3 (long accum A, int B)
 -- Runtime Function: long long accum __ssashlta3 (long long accum A,
          int B)
     These functions return the result of shifting A left by B bits with
     signed saturation.

 -- Runtime Function: unsigned short fract __usashluqq3 (unsigned short
          fract A, int B)
 -- Runtime Function: unsigned fract __usashluhq3 (unsigned fract A, int
          B)
 -- Runtime Function: unsigned long fract __usashlusq3 (unsigned long
          fract A, int B)
 -- Runtime Function: unsigned long long fract __usashludq3 (unsigned
          long long fract A, int B)
 -- Runtime Function: unsigned short accum __usashluha3 (unsigned short
          accum A, int B)
 -- Runtime Function: unsigned accum __usashlusa3 (unsigned accum A, int
          B)
 -- Runtime Function: unsigned long accum __usashluda3 (unsigned long
          accum A, int B)
 -- Runtime Function: unsigned long long accum __usashluta3 (unsigned
          long long accum A, int B)
     These functions return the result of shifting A left by B bits with
     unsigned saturation.

4.4.2 Comparison functions
--------------------------

The following functions implement fixed-point comparisons.  These
functions implement a low-level compare, upon which the higher level
comparison operators (such as less than and greater than or equal to)
can be constructed.  The returned values lie in the range zero to two,
to allow the high-level operators to be implemented by testing the
returned result using either signed or unsigned comparison.

 -- Runtime Function: int __cmpqq2 (short fract A, short fract B)
 -- Runtime Function: int __cmphq2 (fract A, fract B)
 -- Runtime Function: int __cmpsq2 (long fract A, long fract B)
 -- Runtime Function: int __cmpdq2 (long long fract A, long long fract
          B)
 -- Runtime Function: int __cmpuqq2 (unsigned short fract A, unsigned
          short fract B)
 -- Runtime Function: int __cmpuhq2 (unsigned fract A, unsigned fract B)
 -- Runtime Function: int __cmpusq2 (unsigned long fract A, unsigned
          long fract B)
 -- Runtime Function: int __cmpudq2 (unsigned long long fract A,
          unsigned long long fract B)
 -- Runtime Function: int __cmpha2 (short accum A, short accum B)
 -- Runtime Function: int __cmpsa2 (accum A, accum B)
 -- Runtime Function: int __cmpda2 (long accum A, long accum B)
 -- Runtime Function: int __cmpta2 (long long accum A, long long accum
          B)
 -- Runtime Function: int __cmpuha2 (unsigned short accum A, unsigned
          short accum B)
 -- Runtime Function: int __cmpusa2 (unsigned accum A, unsigned accum B)
 -- Runtime Function: int __cmpuda2 (unsigned long accum A, unsigned
          long accum B)
 -- Runtime Function: int __cmputa2 (unsigned long long accum A,
          unsigned long long accum B)
     These functions perform a signed or unsigned comparison of A and B
     (depending on the selected machine mode).  If A is less than B,
     they return 0; if A is greater than B, they return 2; and if A and
     B are equal they return 1.

4.4.3 Conversion functions
--------------------------

 -- Runtime Function: fract __fractqqhq2 (short fract A)
 -- Runtime Function: long fract __fractqqsq2 (short fract A)
 -- Runtime Function: long long fract __fractqqdq2 (short fract A)
 -- Runtime Function: short accum __fractqqha (short fract A)
 -- Runtime Function: accum __fractqqsa (short fract A)
 -- Runtime Function: long accum __fractqqda (short fract A)
 -- Runtime Function: long long accum __fractqqta (short fract A)
 -- Runtime Function: unsigned short fract __fractqquqq (short fract A)
 -- Runtime Function: unsigned fract __fractqquhq (short fract A)
 -- Runtime Function: unsigned long fract __fractqqusq (short fract A)
 -- Runtime Function: unsigned long long fract __fractqqudq (short fract
          A)
 -- Runtime Function: unsigned short accum __fractqquha (short fract A)
 -- Runtime Function: unsigned accum __fractqqusa (short fract A)
 -- Runtime Function: unsigned long accum __fractqquda (short fract A)
 -- Runtime Function: unsigned long long accum __fractqquta (short fract
          A)
 -- Runtime Function: signed char __fractqqqi (short fract A)
 -- Runtime Function: short __fractqqhi (short fract A)
 -- Runtime Function: int __fractqqsi (short fract A)
 -- Runtime Function: long __fractqqdi (short fract A)
 -- Runtime Function: long long __fractqqti (short fract A)
 -- Runtime Function: float __fractqqsf (short fract A)
 -- Runtime Function: double __fractqqdf (short fract A)
 -- Runtime Function: short fract __fracthqqq2 (fract A)
 -- Runtime Function: long fract __fracthqsq2 (fract A)
 -- Runtime Function: long long fract __fracthqdq2 (fract A)
 -- Runtime Function: short accum __fracthqha (fract A)
 -- Runtime Function: accum __fracthqsa (fract A)
 -- Runtime Function: long accum __fracthqda (fract A)
 -- Runtime Function: long long accum __fracthqta (fract A)
 -- Runtime Function: unsigned short fract __fracthquqq (fract A)
 -- Runtime Function: unsigned fract __fracthquhq (fract A)
 -- Runtime Function: unsigned long fract __fracthqusq (fract A)
 -- Runtime Function: unsigned long long fract __fracthqudq (fract A)
 -- Runtime Function: unsigned short accum __fracthquha (fract A)
 -- Runtime Function: unsigned accum __fracthqusa (fract A)
 -- Runtime Function: unsigned long accum __fracthquda (fract A)
 -- Runtime Function: unsigned long long accum __fracthquta (fract A)
 -- Runtime Function: signed char __fracthqqi (fract A)
 -- Runtime Function: short __fracthqhi (fract A)
 -- Runtime Function: int __fracthqsi (fract A)
 -- Runtime Function: long __fracthqdi (fract A)
 -- Runtime Function: long long __fracthqti (fract A)
 -- Runtime Function: float __fracthqsf (fract A)
 -- Runtime Function: double __fracthqdf (fract A)
 -- Runtime Function: short fract __fractsqqq2 (long fract A)
 -- Runtime Function: fract __fractsqhq2 (long fract A)
 -- Runtime Function: long long fract __fractsqdq2 (long fract A)
 -- Runtime Function: short accum __fractsqha (long fract A)
 -- Runtime Function: accum __fractsqsa (long fract A)
 -- Runtime Function: long accum __fractsqda (long fract A)
 -- Runtime Function: long long accum __fractsqta (long fract A)
 -- Runtime Function: unsigned short fract __fractsquqq (long fract A)
 -- Runtime Function: unsigned fract __fractsquhq (long fract A)
 -- Runtime Function: unsigned long fract __fractsqusq (long fract A)
 -- Runtime Function: unsigned long long fract __fractsqudq (long fract
          A)
 -- Runtime Function: unsigned short accum __fractsquha (long fract A)
 -- Runtime Function: unsigned accum __fractsqusa (long fract A)
 -- Runtime Function: unsigned long accum __fractsquda (long fract A)
 -- Runtime Function: unsigned long long accum __fractsquta (long fract
          A)
 -- Runtime Function: signed char __fractsqqi (long fract A)
 -- Runtime Function: short __fractsqhi (long fract A)
 -- Runtime Function: int __fractsqsi (long fract A)
 -- Runtime Function: long __fractsqdi (long fract A)
 -- Runtime Function: long long __fractsqti (long fract A)
 -- Runtime Function: float __fractsqsf (long fract A)
 -- Runtime Function: double __fractsqdf (long fract A)
 -- Runtime Function: short fract __fractdqqq2 (long long fract A)
 -- Runtime Function: fract __fractdqhq2 (long long fract A)
 -- Runtime Function: long fract __fractdqsq2 (long long fract A)
 -- Runtime Function: short accum __fractdqha (long long fract A)
 -- Runtime Function: accum __fractdqsa (long long fract A)
 -- Runtime Function: long accum __fractdqda (long long fract A)
 -- Runtime Function: long long accum __fractdqta (long long fract A)
 -- Runtime Function: unsigned short fract __fractdquqq (long long fract
          A)
 -- Runtime Function: unsigned fract __fractdquhq (long long fract A)
 -- Runtime Function: unsigned long fract __fractdqusq (long long fract
          A)
 -- Runtime Function: unsigned long long fract __fractdqudq (long long
          fract A)
 -- Runtime Function: unsigned short accum __fractdquha (long long fract
          A)
 -- Runtime Function: unsigned accum __fractdqusa (long long fract A)
 -- Runtime Function: unsigned long accum __fractdquda (long long fract
          A)
 -- Runtime Function: unsigned long long accum __fractdquta (long long
          fract A)
 -- Runtime Function: signed char __fractdqqi (long long fract A)
 -- Runtime Function: short __fractdqhi (long long fract A)
 -- Runtime Function: int __fractdqsi (long long fract A)
 -- Runtime Function: long __fractdqdi (long long fract A)
 -- Runtime Function: long long __fractdqti (long long fract A)
 -- Runtime Function: float __fractdqsf (long long fract A)
 -- Runtime Function: double __fractdqdf (long long fract A)
 -- Runtime Function: short fract __fracthaqq (short accum A)
 -- Runtime Function: fract __fracthahq (short accum A)
 -- Runtime Function: long fract __fracthasq (short accum A)
 -- Runtime Function: long long fract __fracthadq (short accum A)
 -- Runtime Function: accum __fracthasa2 (short accum A)
 -- Runtime Function: long accum __fracthada2 (short accum A)
 -- Runtime Function: long long accum __fracthata2 (short accum A)
 -- Runtime Function: unsigned short fract __fracthauqq (short accum A)
 -- Runtime Function: unsigned fract __fracthauhq (short accum A)
 -- Runtime Function: unsigned long fract __fracthausq (short accum A)
 -- Runtime Function: unsigned long long fract __fracthaudq (short accum
          A)
 -- Runtime Function: unsigned short accum __fracthauha (short accum A)
 -- Runtime Function: unsigned accum __fracthausa (short accum A)
 -- Runtime Function: unsigned long accum __fracthauda (short accum A)
 -- Runtime Function: unsigned long long accum __fracthauta (short accum
          A)
 -- Runtime Function: signed char __fracthaqi (short accum A)
 -- Runtime Function: short __fracthahi (short accum A)
 -- Runtime Function: int __fracthasi (short accum A)
 -- Runtime Function: long __fracthadi (short accum A)
 -- Runtime Function: long long __fracthati (short accum A)
 -- Runtime Function: float __fracthasf (short accum A)
 -- Runtime Function: double __fracthadf (short accum A)
 -- Runtime Function: short fract __fractsaqq (accum A)
 -- Runtime Function: fract __fractsahq (accum A)
 -- Runtime Function: long fract __fractsasq (accum A)
 -- Runtime Function: long long fract __fractsadq (accum A)
 -- Runtime Function: short accum __fractsaha2 (accum A)
 -- Runtime Function: long accum __fractsada2 (accum A)
 -- Runtime Function: long long accum __fractsata2 (accum A)
 -- Runtime Function: unsigned short fract __fractsauqq (accum A)
 -- Runtime Function: unsigned fract __fractsauhq (accum A)
 -- Runtime Function: unsigned long fract __fractsausq (accum A)
 -- Runtime Function: unsigned long long fract __fractsaudq (accum A)
 -- Runtime Function: unsigned short accum __fractsauha (accum A)
 -- Runtime Function: unsigned accum __fractsausa (accum A)
 -- Runtime Function: unsigned long accum __fractsauda (accum A)
 -- Runtime Function: unsigned long long accum __fractsauta (accum A)
 -- Runtime Function: signed char __fractsaqi (accum A)
 -- Runtime Function: short __fractsahi (accum A)
 -- Runtime Function: int __fractsasi (accum A)
 -- Runtime Function: long __fractsadi (accum A)
 -- Runtime Function: long long __fractsati (accum A)
 -- Runtime Function: float __fractsasf (accum A)
 -- Runtime Function: double __fractsadf (accum A)
 -- Runtime Function: short fract __fractdaqq (long accum A)
 -- Runtime Function: fract __fractdahq (long accum A)
 -- Runtime Function: long fract __fractdasq (long accum A)
 -- Runtime Function: long long fract __fractdadq (long accum A)
 -- Runtime Function: short accum __fractdaha2 (long accum A)
 -- Runtime Function: accum __fractdasa2 (long accum A)
 -- Runtime Function: long long accum __fractdata2 (long accum A)
 -- Runtime Function: unsigned short fract __fractdauqq (long accum A)
 -- Runtime Function: unsigned fract __fractdauhq (long accum A)
 -- Runtime Function: unsigned long fract __fractdausq (long accum A)
 -- Runtime Function: unsigned long long fract __fractdaudq (long accum
          A)
 -- Runtime Function: unsigned short accum __fractdauha (long accum A)
 -- Runtime Function: unsigned accum __fractdausa (long accum A)
 -- Runtime Function: unsigned long accum __fractdauda (long accum A)
 -- Runtime Function: unsigned long long accum __fractdauta (long accum
          A)
 -- Runtime Function: signed char __fractdaqi (long accum A)
 -- Runtime Function: short __fractdahi (long accum A)
 -- Runtime Function: int __fractdasi (long accum A)
 -- Runtime Function: long __fractdadi (long accum A)
 -- Runtime Function: long long __fractdati (long accum A)
 -- Runtime Function: float __fractdasf (long accum A)
 -- Runtime Function: double __fractdadf (long accum A)
 -- Runtime Function: short fract __fracttaqq (long long accum A)
 -- Runtime Function: fract __fracttahq (long long accum A)
 -- Runtime Function: long fract __fracttasq (long long accum A)
 -- Runtime Function: long long fract __fracttadq (long long accum A)
 -- Runtime Function: short accum __fracttaha2 (long long accum A)
 -- Runtime Function: accum __fracttasa2 (long long accum A)
 -- Runtime Function: long accum __fracttada2 (long long accum A)
 -- Runtime Function: unsigned short fract __fracttauqq (long long accum
          A)
 -- Runtime Function: unsigned fract __fracttauhq (long long accum A)
 -- Runtime Function: unsigned long fract __fracttausq (long long accum
          A)
 -- Runtime Function: unsigned long long fract __fracttaudq (long long
          accum A)
 -- Runtime Function: unsigned short accum __fracttauha (long long accum
          A)
 -- Runtime Function: unsigned accum __fracttausa (long long accum A)
 -- Runtime Function: unsigned long accum __fracttauda (long long accum
          A)
 -- Runtime Function: unsigned long long accum __fracttauta (long long
          accum A)
 -- Runtime Function: signed char __fracttaqi (long long accum A)
 -- Runtime Function: short __fracttahi (long long accum A)
 -- Runtime Function: int __fracttasi (long long accum A)
 -- Runtime Function: long __fracttadi (long long accum A)
 -- Runtime Function: long long __fracttati (long long accum A)
 -- Runtime Function: float __fracttasf (long long accum A)
 -- Runtime Function: double __fracttadf (long long accum A)
 -- Runtime Function: short fract __fractuqqqq (unsigned short fract A)
 -- Runtime Function: fract __fractuqqhq (unsigned short fract A)
 -- Runtime Function: long fract __fractuqqsq (unsigned short fract A)
 -- Runtime Function: long long fract __fractuqqdq (unsigned short fract
          A)
 -- Runtime Function: short accum __fractuqqha (unsigned short fract A)
 -- Runtime Function: accum __fractuqqsa (unsigned short fract A)
 -- Runtime Function: long accum __fractuqqda (unsigned short fract A)
 -- Runtime Function: long long accum __fractuqqta (unsigned short fract
          A)
 -- Runtime Function: unsigned fract __fractuqquhq2 (unsigned short
          fract A)
 -- Runtime Function: unsigned long fract __fractuqqusq2 (unsigned short
          fract A)
 -- Runtime Function: unsigned long long fract __fractuqqudq2 (unsigned
          short fract A)
 -- Runtime Function: unsigned short accum __fractuqquha (unsigned short
          fract A)
 -- Runtime Function: unsigned accum __fractuqqusa (unsigned short fract
          A)
 -- Runtime Function: unsigned long accum __fractuqquda (unsigned short
          fract A)
 -- Runtime Function: unsigned long long accum __fractuqquta (unsigned
          short fract A)
 -- Runtime Function: signed char __fractuqqqi (unsigned short fract A)
 -- Runtime Function: short __fractuqqhi (unsigned short fract A)
 -- Runtime Function: int __fractuqqsi (unsigned short fract A)
 -- Runtime Function: long __fractuqqdi (unsigned short fract A)
 -- Runtime Function: long long __fractuqqti (unsigned short fract A)
 -- Runtime Function: float __fractuqqsf (unsigned short fract A)
 -- Runtime Function: double __fractuqqdf (unsigned short fract A)
 -- Runtime Function: short fract __fractuhqqq (unsigned fract A)
 -- Runtime Function: fract __fractuhqhq (unsigned fract A)
 -- Runtime Function: long fract __fractuhqsq (unsigned fract A)
 -- Runtime Function: long long fract __fractuhqdq (unsigned fract A)
 -- Runtime Function: short accum __fractuhqha (unsigned fract A)
 -- Runtime Function: accum __fractuhqsa (unsigned fract A)
 -- Runtime Function: long accum __fractuhqda (unsigned fract A)
 -- Runtime Function: long long accum __fractuhqta (unsigned fract A)
 -- Runtime Function: unsigned short fract __fractuhquqq2 (unsigned
          fract A)
 -- Runtime Function: unsigned long fract __fractuhqusq2 (unsigned fract
          A)
 -- Runtime Function: unsigned long long fract __fractuhqudq2 (unsigned
          fract A)
 -- Runtime Function: unsigned short accum __fractuhquha (unsigned fract
          A)
 -- Runtime Function: unsigned accum __fractuhqusa (unsigned fract A)
 -- Runtime Function: unsigned long accum __fractuhquda (unsigned fract
          A)
 -- Runtime Function: unsigned long long accum __fractuhquta (unsigned
          fract A)
 -- Runtime Function: signed char __fractuhqqi (unsigned fract A)
 -- Runtime Function: short __fractuhqhi (unsigned fract A)
 -- Runtime Function: int __fractuhqsi (unsigned fract A)
 -- Runtime Function: long __fractuhqdi (unsigned fract A)
 -- Runtime Function: long long __fractuhqti (unsigned fract A)
 -- Runtime Function: float __fractuhqsf (unsigned fract A)
 -- Runtime Function: double __fractuhqdf (unsigned fract A)
 -- Runtime Function: short fract __fractusqqq (unsigned long fract A)
 -- Runtime Function: fract __fractusqhq (unsigned long fract A)
 -- Runtime Function: long fract __fractusqsq (unsigned long fract A)
 -- Runtime Function: long long fract __fractusqdq (unsigned long fract
          A)
 -- Runtime Function: short accum __fractusqha (unsigned long fract A)
 -- Runtime Function: accum __fractusqsa (unsigned long fract A)
 -- Runtime Function: long accum __fractusqda (unsigned long fract A)
 -- Runtime Function: long long accum __fractusqta (unsigned long fract
          A)
 -- Runtime Function: unsigned short fract __fractusquqq2 (unsigned long
          fract A)
 -- Runtime Function: unsigned fract __fractusquhq2 (unsigned long fract
          A)
 -- Runtime Function: unsigned long long fract __fractusqudq2 (unsigned
          long fract A)
 -- Runtime Function: unsigned short accum __fractusquha (unsigned long
          fract A)
 -- Runtime Function: unsigned accum __fractusqusa (unsigned long fract
          A)
 -- Runtime Function: unsigned long accum __fractusquda (unsigned long
          fract A)
 -- Runtime Function: unsigned long long accum __fractusquta (unsigned
          long fract A)
 -- Runtime Function: signed char __fractusqqi (unsigned long fract A)
 -- Runtime Function: short __fractusqhi (unsigned long fract A)
 -- Runtime Function: int __fractusqsi (unsigned long fract A)
 -- Runtime Function: long __fractusqdi (unsigned long fract A)
 -- Runtime Function: long long __fractusqti (unsigned long fract A)
 -- Runtime Function: float __fractusqsf (unsigned long fract A)
 -- Runtime Function: double __fractusqdf (unsigned long fract A)
 -- Runtime Function: short fract __fractudqqq (unsigned long long fract
          A)
 -- Runtime Function: fract __fractudqhq (unsigned long long fract A)
 -- Runtime Function: long fract __fractudqsq (unsigned long long fract
          A)
 -- Runtime Function: long long fract __fractudqdq (unsigned long long
          fract A)
 -- Runtime Function: short accum __fractudqha (unsigned long long fract
          A)
 -- Runtime Function: accum __fractudqsa (unsigned long long fract A)
 -- Runtime Function: long accum __fractudqda (unsigned long long fract
          A)
 -- Runtime Function: long long accum __fractudqta (unsigned long long
          fract A)
 -- Runtime Function: unsigned short fract __fractudquqq2 (unsigned long
          long fract A)
 -- Runtime Function: unsigned fract __fractudquhq2 (unsigned long long
          fract A)
 -- Runtime Function: unsigned long fract __fractudqusq2 (unsigned long
          long fract A)
 -- Runtime Function: unsigned short accum __fractudquha (unsigned long
          long fract A)
 -- Runtime Function: unsigned accum __fractudqusa (unsigned long long
          fract A)
 -- Runtime Function: unsigned long accum __fractudquda (unsigned long
          long fract A)
 -- Runtime Function: unsigned long long accum __fractudquta (unsigned
          long long fract A)
 -- Runtime Function: signed char __fractudqqi (unsigned long long fract
          A)
 -- Runtime Function: short __fractudqhi (unsigned long long fract A)
 -- Runtime Function: int __fractudqsi (unsigned long long fract A)
 -- Runtime Function: long __fractudqdi (unsigned long long fract A)
 -- Runtime Function: long long __fractudqti (unsigned long long fract
          A)
 -- Runtime Function: float __fractudqsf (unsigned long long fract A)
 -- Runtime Function: double __fractudqdf (unsigned long long fract A)
 -- Runtime Function: short fract __fractuhaqq (unsigned short accum A)
 -- Runtime Function: fract __fractuhahq (unsigned short accum A)
 -- Runtime Function: long fract __fractuhasq (unsigned short accum A)
 -- Runtime Function: long long fract __fractuhadq (unsigned short accum
          A)
 -- Runtime Function: short accum __fractuhaha (unsigned short accum A)
 -- Runtime Function: accum __fractuhasa (unsigned short accum A)
 -- Runtime Function: long accum __fractuhada (unsigned short accum A)
 -- Runtime Function: long long accum __fractuhata (unsigned short accum
          A)
 -- Runtime Function: unsigned short fract __fractuhauqq (unsigned short
          accum A)
 -- Runtime Function: unsigned fract __fractuhauhq (unsigned short accum
          A)
 -- Runtime Function: unsigned long fract __fractuhausq (unsigned short
          accum A)
 -- Runtime Function: unsigned long long fract __fractuhaudq (unsigned
          short accum A)
 -- Runtime Function: unsigned accum __fractuhausa2 (unsigned short
          accum A)
 -- Runtime Function: unsigned long accum __fractuhauda2 (unsigned short
          accum A)
 -- Runtime Function: unsigned long long accum __fractuhauta2 (unsigned
          short accum A)
 -- Runtime Function: signed char __fractuhaqi (unsigned short accum A)
 -- Runtime Function: short __fractuhahi (unsigned short accum A)
 -- Runtime Function: int __fractuhasi (unsigned short accum A)
 -- Runtime Function: long __fractuhadi (unsigned short accum A)
 -- Runtime Function: long long __fractuhati (unsigned short accum A)
 -- Runtime Function: float __fractuhasf (unsigned short accum A)
 -- Runtime Function: double __fractuhadf (unsigned short accum A)
 -- Runtime Function: short fract __fractusaqq (unsigned accum A)
 -- Runtime Function: fract __fractusahq (unsigned accum A)
 -- Runtime Function: long fract __fractusasq (unsigned accum A)
 -- Runtime Function: long long fract __fractusadq (unsigned accum A)
 -- Runtime Function: short accum __fractusaha (unsigned accum A)
 -- Runtime Function: accum __fractusasa (unsigned accum A)
 -- Runtime Function: long accum __fractusada (unsigned accum A)
 -- Runtime Function: long long accum __fractusata (unsigned accum A)
 -- Runtime Function: unsigned short fract __fractusauqq (unsigned accum
          A)
 -- Runtime Function: unsigned fract __fractusauhq (unsigned accum A)
 -- Runtime Function: unsigned long fract __fractusausq (unsigned accum
          A)
 -- Runtime Function: unsigned long long fract __fractusaudq (unsigned
          accum A)
 -- Runtime Function: unsigned short accum __fractusauha2 (unsigned
          accum A)
 -- Runtime Function: unsigned long accum __fractusauda2 (unsigned accum
          A)
 -- Runtime Function: unsigned long long accum __fractusauta2 (unsigned
          accum A)
 -- Runtime Function: signed char __fractusaqi (unsigned accum A)
 -- Runtime Function: short __fractusahi (unsigned accum A)
 -- Runtime Function: int __fractusasi (unsigned accum A)
 -- Runtime Function: long __fractusadi (unsigned accum A)
 -- Runtime Function: long long __fractusati (unsigned accum A)
 -- Runtime Function: float __fractusasf (unsigned accum A)
 -- Runtime Function: double __fractusadf (unsigned accum A)
 -- Runtime Function: short fract __fractudaqq (unsigned long accum A)
 -- Runtime Function: fract __fractudahq (unsigned long accum A)
 -- Runtime Function: long fract __fractudasq (unsigned long accum A)
 -- Runtime Function: long long fract __fractudadq (unsigned long accum
          A)
 -- Runtime Function: short accum __fractudaha (unsigned long accum A)
 -- Runtime Function: accum __fractudasa (unsigned long accum A)
 -- Runtime Function: long accum __fractudada (unsigned long accum A)
 -- Runtime Function: long long accum __fractudata (unsigned long accum
          A)
 -- Runtime Function: unsigned short fract __fractudauqq (unsigned long
          accum A)
 -- Runtime Function: unsigned fract __fractudauhq (unsigned long accum
          A)
 -- Runtime Function: unsigned long fract __fractudausq (unsigned long
          accum A)
 -- Runtime Function: unsigned long long fract __fractudaudq (unsigned
          long accum A)
 -- Runtime Function: unsigned short accum __fractudauha2 (unsigned long
          accum A)
 -- Runtime Function: unsigned accum __fractudausa2 (unsigned long accum
          A)
 -- Runtime Function: unsigned long long accum __fractudauta2 (unsigned
          long accum A)
 -- Runtime Function: signed char __fractudaqi (unsigned long accum A)
 -- Runtime Function: short __fractudahi (unsigned long accum A)
 -- Runtime Function: int __fractudasi (unsigned long accum A)
 -- Runtime Function: long __fractudadi (unsigned long accum A)
 -- Runtime Function: long long __fractudati (unsigned long accum A)
 -- Runtime Function: float __fractudasf (unsigned long accum A)
 -- Runtime Function: double __fractudadf (unsigned long accum A)
 -- Runtime Function: short fract __fractutaqq (unsigned long long accum
          A)
 -- Runtime Function: fract __fractutahq (unsigned long long accum A)
 -- Runtime Function: long fract __fractutasq (unsigned long long accum
          A)
 -- Runtime Function: long long fract __fractutadq (unsigned long long
          accum A)
 -- Runtime Function: short accum __fractutaha (unsigned long long accum
          A)
 -- Runtime Function: accum __fractutasa (unsigned long long accum A)
 -- Runtime Function: long accum __fractutada (unsigned long long accum
          A)
 -- Runtime Function: long long accum __fractutata (unsigned long long
          accum A)
 -- Runtime Function: unsigned short fract __fractutauqq (unsigned long
          long accum A)
 -- Runtime Function: unsigned fract __fractutauhq (unsigned long long
          accum A)
 -- Runtime Function: unsigned long fract __fractutausq (unsigned long
          long accum A)
 -- Runtime Function: unsigned long long fract __fractutaudq (unsigned
          long long accum A)
 -- Runtime Function: unsigned short accum __fractutauha2 (unsigned long
          long accum A)
 -- Runtime Function: unsigned accum __fractutausa2 (unsigned long long
          accum A)
 -- Runtime Function: unsigned long accum __fractutauda2 (unsigned long
          long accum A)
 -- Runtime Function: signed char __fractutaqi (unsigned long long accum
          A)
 -- Runtime Function: short __fractutahi (unsigned long long accum A)
 -- Runtime Function: int __fractutasi (unsigned long long accum A)
 -- Runtime Function: long __fractutadi (unsigned long long accum A)
 -- Runtime Function: long long __fractutati (unsigned long long accum
          A)
 -- Runtime Function: float __fractutasf (unsigned long long accum A)
 -- Runtime Function: double __fractutadf (unsigned long long accum A)
 -- Runtime Function: short fract __fractqiqq (signed char A)
 -- Runtime Function: fract __fractqihq (signed char A)
 -- Runtime Function: long fract __fractqisq (signed char A)
 -- Runtime Function: long long fract __fractqidq (signed char A)
 -- Runtime Function: short accum __fractqiha (signed char A)
 -- Runtime Function: accum __fractqisa (signed char A)
 -- Runtime Function: long accum __fractqida (signed char A)
 -- Runtime Function: long long accum __fractqita (signed char A)
 -- Runtime Function: unsigned short fract __fractqiuqq (signed char A)
 -- Runtime Function: unsigned fract __fractqiuhq (signed char A)
 -- Runtime Function: unsigned long fract __fractqiusq (signed char A)
 -- Runtime Function: unsigned long long fract __fractqiudq (signed char
          A)
 -- Runtime Function: unsigned short accum __fractqiuha (signed char A)
 -- Runtime Function: unsigned accum __fractqiusa (signed char A)
 -- Runtime Function: unsigned long accum __fractqiuda (signed char A)
 -- Runtime Function: unsigned long long accum __fractqiuta (signed char
          A)
 -- Runtime Function: short fract __fracthiqq (short A)
 -- Runtime Function: fract __fracthihq (short A)
 -- Runtime Function: long fract __fracthisq (short A)
 -- Runtime Function: long long fract __fracthidq (short A)
 -- Runtime Function: short accum __fracthiha (short A)
 -- Runtime Function: accum __fracthisa (short A)
 -- Runtime Function: long accum __fracthida (short A)
 -- Runtime Function: long long accum __fracthita (short A)
 -- Runtime Function: unsigned short fract __fracthiuqq (short A)
 -- Runtime Function: unsigned fract __fracthiuhq (short A)
 -- Runtime Function: unsigned long fract __fracthiusq (short A)
 -- Runtime Function: unsigned long long fract __fracthiudq (short A)
 -- Runtime Function: unsigned short accum __fracthiuha (short A)
 -- Runtime Function: unsigned accum __fracthiusa (short A)
 -- Runtime Function: unsigned long accum __fracthiuda (short A)
 -- Runtime Function: unsigned long long accum __fracthiuta (short A)
 -- Runtime Function: short fract __fractsiqq (int A)
 -- Runtime Function: fract __fractsihq (int A)
 -- Runtime Function: long fract __fractsisq (int A)
 -- Runtime Function: long long fract __fractsidq (int A)
 -- Runtime Function: short accum __fractsiha (int A)
 -- Runtime Function: accum __fractsisa (int A)
 -- Runtime Function: long accum __fractsida (int A)
 -- Runtime Function: long long accum __fractsita (int A)
 -- Runtime Function: unsigned short fract __fractsiuqq (int A)
 -- Runtime Function: unsigned fract __fractsiuhq (int A)
 -- Runtime Function: unsigned long fract __fractsiusq (int A)
 -- Runtime Function: unsigned long long fract __fractsiudq (int A)
 -- Runtime Function: unsigned short accum __fractsiuha (int A)
 -- Runtime Function: unsigned accum __fractsiusa (int A)
 -- Runtime Function: unsigned long accum __fractsiuda (int A)
 -- Runtime Function: unsigned long long accum __fractsiuta (int A)
 -- Runtime Function: short fract __fractdiqq (long A)
 -- Runtime Function: fract __fractdihq (long A)
 -- Runtime Function: long fract __fractdisq (long A)
 -- Runtime Function: long long fract __fractdidq (long A)
 -- Runtime Function: short accum __fractdiha (long A)
 -- Runtime Function: accum __fractdisa (long A)
 -- Runtime Function: long accum __fractdida (long A)
 -- Runtime Function: long long accum __fractdita (long A)
 -- Runtime Function: unsigned short fract __fractdiuqq (long A)
 -- Runtime Function: unsigned fract __fractdiuhq (long A)
 -- Runtime Function: unsigned long fract __fractdiusq (long A)
 -- Runtime Function: unsigned long long fract __fractdiudq (long A)
 -- Runtime Function: unsigned short accum __fractdiuha (long A)
 -- Runtime Function: unsigned accum __fractdiusa (long A)
 -- Runtime Function: unsigned long accum __fractdiuda (long A)
 -- Runtime Function: unsigned long long accum __fractdiuta (long A)
 -- Runtime Function: short fract __fracttiqq (long long A)
 -- Runtime Function: fract __fracttihq (long long A)
 -- Runtime Function: long fract __fracttisq (long long A)
 -- Runtime Function: long long fract __fracttidq (long long A)
 -- Runtime Function: short accum __fracttiha (long long A)
 -- Runtime Function: accum __fracttisa (long long A)
 -- Runtime Function: long accum __fracttida (long long A)
 -- Runtime Function: long long accum __fracttita (long long A)
 -- Runtime Function: unsigned short fract __fracttiuqq (long long A)
 -- Runtime Function: unsigned fract __fracttiuhq (long long A)
 -- Runtime Function: unsigned long fract __fracttiusq (long long A)
 -- Runtime Function: unsigned long long fract __fracttiudq (long long
          A)
 -- Runtime Function: unsigned short accum __fracttiuha (long long A)
 -- Runtime Function: unsigned accum __fracttiusa (long long A)
 -- Runtime Function: unsigned long accum __fracttiuda (long long A)
 -- Runtime Function: unsigned long long accum __fracttiuta (long long
          A)
 -- Runtime Function: short fract __fractsfqq (float A)
 -- Runtime Function: fract __fractsfhq (float A)
 -- Runtime Function: long fract __fractsfsq (float A)
 -- Runtime Function: long long fract __fractsfdq (float A)
 -- Runtime Function: short accum __fractsfha (float A)
 -- Runtime Function: accum __fractsfsa (float A)
 -- Runtime Function: long accum __fractsfda (float A)
 -- Runtime Function: long long accum __fractsfta (float A)
 -- Runtime Function: unsigned short fract __fractsfuqq (float A)
 -- Runtime Function: unsigned fract __fractsfuhq (float A)
 -- Runtime Function: unsigned long fract __fractsfusq (float A)
 -- Runtime Function: unsigned long long fract __fractsfudq (float A)
 -- Runtime Function: unsigned short accum __fractsfuha (float A)
 -- Runtime Function: unsigned accum __fractsfusa (float A)
 -- Runtime Function: unsigned long accum __fractsfuda (float A)
 -- Runtime Function: unsigned long long accum __fractsfuta (float A)
 -- Runtime Function: short fract __fractdfqq (double A)
 -- Runtime Function: fract __fractdfhq (double A)
 -- Runtime Function: long fract __fractdfsq (double A)
 -- Runtime Function: long long fract __fractdfdq (double A)
 -- Runtime Function: short accum __fractdfha (double A)
 -- Runtime Function: accum __fractdfsa (double A)
 -- Runtime Function: long accum __fractdfda (double A)
 -- Runtime Function: long long accum __fractdfta (double A)
 -- Runtime Function: unsigned short fract __fractdfuqq (double A)
 -- Runtime Function: unsigned fract __fractdfuhq (double A)
 -- Runtime Function: unsigned long fract __fractdfusq (double A)
 -- Runtime Function: unsigned long long fract __fractdfudq (double A)
 -- Runtime Function: unsigned short accum __fractdfuha (double A)
 -- Runtime Function: unsigned accum __fractdfusa (double A)
 -- Runtime Function: unsigned long accum __fractdfuda (double A)
 -- Runtime Function: unsigned long long accum __fractdfuta (double A)
     These functions convert from fractional and signed non-fractionals
     to fractionals and signed non-fractionals, without saturation.

 -- Runtime Function: fract __satfractqqhq2 (short fract A)
 -- Runtime Function: long fract __satfractqqsq2 (short fract A)
 -- Runtime Function: long long fract __satfractqqdq2 (short fract A)
 -- Runtime Function: short accum __satfractqqha (short fract A)
 -- Runtime Function: accum __satfractqqsa (short fract A)
 -- Runtime Function: long accum __satfractqqda (short fract A)
 -- Runtime Function: long long accum __satfractqqta (short fract A)
 -- Runtime Function: unsigned short fract __satfractqquqq (short fract
          A)
 -- Runtime Function: unsigned fract __satfractqquhq (short fract A)
 -- Runtime Function: unsigned long fract __satfractqqusq (short fract
          A)
 -- Runtime Function: unsigned long long fract __satfractqqudq (short
          fract A)
 -- Runtime Function: unsigned short accum __satfractqquha (short fract
          A)
 -- Runtime Function: unsigned accum __satfractqqusa (short fract A)
 -- Runtime Function: unsigned long accum __satfractqquda (short fract
          A)
 -- Runtime Function: unsigned long long accum __satfractqquta (short
          fract A)
 -- Runtime Function: short fract __satfracthqqq2 (fract A)
 -- Runtime Function: long fract __satfracthqsq2 (fract A)
 -- Runtime Function: long long fract __satfracthqdq2 (fract A)
 -- Runtime Function: short accum __satfracthqha (fract A)
 -- Runtime Function: accum __satfracthqsa (fract A)
 -- Runtime Function: long accum __satfracthqda (fract A)
 -- Runtime Function: long long accum __satfracthqta (fract A)
 -- Runtime Function: unsigned short fract __satfracthquqq (fract A)
 -- Runtime Function: unsigned fract __satfracthquhq (fract A)
 -- Runtime Function: unsigned long fract __satfracthqusq (fract A)
 -- Runtime Function: unsigned long long fract __satfracthqudq (fract A)
 -- Runtime Function: unsigned short accum __satfracthquha (fract A)
 -- Runtime Function: unsigned accum __satfracthqusa (fract A)
 -- Runtime Function: unsigned long accum __satfracthquda (fract A)
 -- Runtime Function: unsigned long long accum __satfracthquta (fract A)
 -- Runtime Function: short fract __satfractsqqq2 (long fract A)
 -- Runtime Function: fract __satfractsqhq2 (long fract A)
 -- Runtime Function: long long fract __satfractsqdq2 (long fract A)
 -- Runtime Function: short accum __satfractsqha (long fract A)
 -- Runtime Function: accum __satfractsqsa (long fract A)
 -- Runtime Function: long accum __satfractsqda (long fract A)
 -- Runtime Function: long long accum __satfractsqta (long fract A)
 -- Runtime Function: unsigned short fract __satfractsquqq (long fract
          A)
 -- Runtime Function: unsigned fract __satfractsquhq (long fract A)
 -- Runtime Function: unsigned long fract __satfractsqusq (long fract A)
 -- Runtime Function: unsigned long long fract __satfractsqudq (long
          fract A)
 -- Runtime Function: unsigned short accum __satfractsquha (long fract
          A)
 -- Runtime Function: unsigned accum __satfractsqusa (long fract A)
 -- Runtime Function: unsigned long accum __satfractsquda (long fract A)
 -- Runtime Function: unsigned long long accum __satfractsquta (long
          fract A)
 -- Runtime Function: short fract __satfractdqqq2 (long long fract A)
 -- Runtime Function: fract __satfractdqhq2 (long long fract A)
 -- Runtime Function: long fract __satfractdqsq2 (long long fract A)
 -- Runtime Function: short accum __satfractdqha (long long fract A)
 -- Runtime Function: accum __satfractdqsa (long long fract A)
 -- Runtime Function: long accum __satfractdqda (long long fract A)
 -- Runtime Function: long long accum __satfractdqta (long long fract A)
 -- Runtime Function: unsigned short fract __satfractdquqq (long long
          fract A)
 -- Runtime Function: unsigned fract __satfractdquhq (long long fract A)
 -- Runtime Function: unsigned long fract __satfractdqusq (long long
          fract A)
 -- Runtime Function: unsigned long long fract __satfractdqudq (long
          long fract A)
 -- Runtime Function: unsigned short accum __satfractdquha (long long
          fract A)
 -- Runtime Function: unsigned accum __satfractdqusa (long long fract A)
 -- Runtime Function: unsigned long accum __satfractdquda (long long
          fract A)
 -- Runtime Function: unsigned long long accum __satfractdquta (long
          long fract A)
 -- Runtime Function: short fract __satfracthaqq (short accum A)
 -- Runtime Function: fract __satfracthahq (short accum A)
 -- Runtime Function: long fract __satfracthasq (short accum A)
 -- Runtime Function: long long fract __satfracthadq (short accum A)
 -- Runtime Function: accum __satfracthasa2 (short accum A)
 -- Runtime Function: long accum __satfracthada2 (short accum A)
 -- Runtime Function: long long accum __satfracthata2 (short accum A)
 -- Runtime Function: unsigned short fract __satfracthauqq (short accum
          A)
 -- Runtime Function: unsigned fract __satfracthauhq (short accum A)
 -- Runtime Function: unsigned long fract __satfracthausq (short accum
          A)
 -- Runtime Function: unsigned long long fract __satfracthaudq (short
          accum A)
 -- Runtime Function: unsigned short accum __satfracthauha (short accum
          A)
 -- Runtime Function: unsigned accum __satfracthausa (short accum A)
 -- Runtime Function: unsigned long accum __satfracthauda (short accum
          A)
 -- Runtime Function: unsigned long long accum __satfracthauta (short
          accum A)
 -- Runtime Function: short fract __satfractsaqq (accum A)
 -- Runtime Function: fract __satfractsahq (accum A)
 -- Runtime Function: long fract __satfractsasq (accum A)
 -- Runtime Function: long long fract __satfractsadq (accum A)
 -- Runtime Function: short accum __satfractsaha2 (accum A)
 -- Runtime Function: long accum __satfractsada2 (accum A)
 -- Runtime Function: long long accum __satfractsata2 (accum A)
 -- Runtime Function: unsigned short fract __satfractsauqq (accum A)
 -- Runtime Function: unsigned fract __satfractsauhq (accum A)
 -- Runtime Function: unsigned long fract __satfractsausq (accum A)
 -- Runtime Function: unsigned long long fract __satfractsaudq (accum A)
 -- Runtime Function: unsigned short accum __satfractsauha (accum A)
 -- Runtime Function: unsigned accum __satfractsausa (accum A)
 -- Runtime Function: unsigned long accum __satfractsauda (accum A)
 -- Runtime Function: unsigned long long accum __satfractsauta (accum A)
 -- Runtime Function: short fract __satfractdaqq (long accum A)
 -- Runtime Function: fract __satfractdahq (long accum A)
 -- Runtime Function: long fract __satfractdasq (long accum A)
 -- Runtime Function: long long fract __satfractdadq (long accum A)
 -- Runtime Function: short accum __satfractdaha2 (long accum A)
 -- Runtime Function: accum __satfractdasa2 (long accum A)
 -- Runtime Function: long long accum __satfractdata2 (long accum A)
 -- Runtime Function: unsigned short fract __satfractdauqq (long accum
          A)
 -- Runtime Function: unsigned fract __satfractdauhq (long accum A)
 -- Runtime Function: unsigned long fract __satfractdausq (long accum A)
 -- Runtime Function: unsigned long long fract __satfractdaudq (long
          accum A)
 -- Runtime Function: unsigned short accum __satfractdauha (long accum
          A)
 -- Runtime Function: unsigned accum __satfractdausa (long accum A)
 -- Runtime Function: unsigned long accum __satfractdauda (long accum A)
 -- Runtime Function: unsigned long long accum __satfractdauta (long
          accum A)
 -- Runtime Function: short fract __satfracttaqq (long long accum A)
 -- Runtime Function: fract __satfracttahq (long long accum A)
 -- Runtime Function: long fract __satfracttasq (long long accum A)
 -- Runtime Function: long long fract __satfracttadq (long long accum A)
 -- Runtime Function: short accum __satfracttaha2 (long long accum A)
 -- Runtime Function: accum __satfracttasa2 (long long accum A)
 -- Runtime Function: long accum __satfracttada2 (long long accum A)
 -- Runtime Function: unsigned short fract __satfracttauqq (long long
          accum A)
 -- Runtime Function: unsigned fract __satfracttauhq (long long accum A)
 -- Runtime Function: unsigned long fract __satfracttausq (long long
          accum A)
 -- Runtime Function: unsigned long long fract __satfracttaudq (long
          long accum A)
 -- Runtime Function: unsigned short accum __satfracttauha (long long
          accum A)
 -- Runtime Function: unsigned accum __satfracttausa (long long accum A)
 -- Runtime Function: unsigned long accum __satfracttauda (long long
          accum A)
 -- Runtime Function: unsigned long long accum __satfracttauta (long
          long accum A)
 -- Runtime Function: short fract __satfractuqqqq (unsigned short fract
          A)
 -- Runtime Function: fract __satfractuqqhq (unsigned short fract A)
 -- Runtime Function: long fract __satfractuqqsq (unsigned short fract
          A)
 -- Runtime Function: long long fract __satfractuqqdq (unsigned short
          fract A)
 -- Runtime Function: short accum __satfractuqqha (unsigned short fract
          A)
 -- Runtime Function: accum __satfractuqqsa (unsigned short fract A)
 -- Runtime Function: long accum __satfractuqqda (unsigned short fract
          A)
 -- Runtime Function: long long accum __satfractuqqta (unsigned short
          fract A)
 -- Runtime Function: unsigned fract __satfractuqquhq2 (unsigned short
          fract A)
 -- Runtime Function: unsigned long fract __satfractuqqusq2 (unsigned
          short fract A)
 -- Runtime Function: unsigned long long fract __satfractuqqudq2
          (unsigned short fract A)
 -- Runtime Function: unsigned short accum __satfractuqquha (unsigned
          short fract A)
 -- Runtime Function: unsigned accum __satfractuqqusa (unsigned short
          fract A)
 -- Runtime Function: unsigned long accum __satfractuqquda (unsigned
          short fract A)
 -- Runtime Function: unsigned long long accum __satfractuqquta
          (unsigned short fract A)
 -- Runtime Function: short fract __satfractuhqqq (unsigned fract A)
 -- Runtime Function: fract __satfractuhqhq (unsigned fract A)
 -- Runtime Function: long fract __satfractuhqsq (unsigned fract A)
 -- Runtime Function: long long fract __satfractuhqdq (unsigned fract A)
 -- Runtime Function: short accum __satfractuhqha (unsigned fract A)
 -- Runtime Function: accum __satfractuhqsa (unsigned fract A)
 -- Runtime Function: long accum __satfractuhqda (unsigned fract A)
 -- Runtime Function: long long accum __satfractuhqta (unsigned fract A)
 -- Runtime Function: unsigned short fract __satfractuhquqq2 (unsigned
          fract A)
 -- Runtime Function: unsigned long fract __satfractuhqusq2 (unsigned
          fract A)
 -- Runtime Function: unsigned long long fract __satfractuhqudq2
          (unsigned fract A)
 -- Runtime Function: unsigned short accum __satfractuhquha (unsigned
          fract A)
 -- Runtime Function: unsigned accum __satfractuhqusa (unsigned fract A)
 -- Runtime Function: unsigned long accum __satfractuhquda (unsigned
          fract A)
 -- Runtime Function: unsigned long long accum __satfractuhquta
          (unsigned fract A)
 -- Runtime Function: short fract __satfractusqqq (unsigned long fract
          A)
 -- Runtime Function: fract __satfractusqhq (unsigned long fract A)
 -- Runtime Function: long fract __satfractusqsq (unsigned long fract A)
 -- Runtime Function: long long fract __satfractusqdq (unsigned long
          fract A)
 -- Runtime Function: short accum __satfractusqha (unsigned long fract
          A)
 -- Runtime Function: accum __satfractusqsa (unsigned long fract A)
 -- Runtime Function: long accum __satfractusqda (unsigned long fract A)
 -- Runtime Function: long long accum __satfractusqta (unsigned long
          fract A)
 -- Runtime Function: unsigned short fract __satfractusquqq2 (unsigned
          long fract A)
 -- Runtime Function: unsigned fract __satfractusquhq2 (unsigned long
          fract A)
 -- Runtime Function: unsigned long long fract __satfractusqudq2
          (unsigned long fract A)
 -- Runtime Function: unsigned short accum __satfractusquha (unsigned
          long fract A)
 -- Runtime Function: unsigned accum __satfractusqusa (unsigned long
          fract A)
 -- Runtime Function: unsigned long accum __satfractusquda (unsigned
          long fract A)
 -- Runtime Function: unsigned long long accum __satfractusquta
          (unsigned long fract A)
 -- Runtime Function: short fract __satfractudqqq (unsigned long long
          fract A)
 -- Runtime Function: fract __satfractudqhq (unsigned long long fract A)
 -- Runtime Function: long fract __satfractudqsq (unsigned long long
          fract A)
 -- Runtime Function: long long fract __satfractudqdq (unsigned long
          long fract A)
 -- Runtime Function: short accum __satfractudqha (unsigned long long
          fract A)
 -- Runtime Function: accum __satfractudqsa (unsigned long long fract A)
 -- Runtime Function: long accum __satfractudqda (unsigned long long
          fract A)
 -- Runtime Function: long long accum __satfractudqta (unsigned long
          long fract A)
 -- Runtime Function: unsigned short fract __satfractudquqq2 (unsigned
          long long fract A)
 -- Runtime Function: unsigned fract __satfractudquhq2 (unsigned long
          long fract A)
 -- Runtime Function: unsigned long fract __satfractudqusq2 (unsigned
          long long fract A)
 -- Runtime Function: unsigned short accum __satfractudquha (unsigned
          long long fract A)
 -- Runtime Function: unsigned accum __satfractudqusa (unsigned long
          long fract A)
 -- Runtime Function: unsigned long accum __satfractudquda (unsigned
          long long fract A)
 -- Runtime Function: unsigned long long accum __satfractudquta
          (unsigned long long fract A)
 -- Runtime Function: short fract __satfractuhaqq (unsigned short accum
          A)
 -- Runtime Function: fract __satfractuhahq (unsigned short accum A)
 -- Runtime Function: long fract __satfractuhasq (unsigned short accum
          A)
 -- Runtime Function: long long fract __satfractuhadq (unsigned short
          accum A)
 -- Runtime Function: short accum __satfractuhaha (unsigned short accum
          A)
 -- Runtime Function: accum __satfractuhasa (unsigned short accum A)
 -- Runtime Function: long accum __satfractuhada (unsigned short accum
          A)
 -- Runtime Function: long long accum __satfractuhata (unsigned short
          accum A)
 -- Runtime Function: unsigned short fract __satfractuhauqq (unsigned
          short accum A)
 -- Runtime Function: unsigned fract __satfractuhauhq (unsigned short
          accum A)
 -- Runtime Function: unsigned long fract __satfractuhausq (unsigned
          short accum A)
 -- Runtime Function: unsigned long long fract __satfractuhaudq
          (unsigned short accum A)
 -- Runtime Function: unsigned accum __satfractuhausa2 (unsigned short
          accum A)
 -- Runtime Function: unsigned long accum __satfractuhauda2 (unsigned
          short accum A)
 -- Runtime Function: unsigned long long accum __satfractuhauta2
          (unsigned short accum A)
 -- Runtime Function: short fract __satfractusaqq (unsigned accum A)
 -- Runtime Function: fract __satfractusahq (unsigned accum A)
 -- Runtime Function: long fract __satfractusasq (unsigned accum A)
 -- Runtime Function: long long fract __satfractusadq (unsigned accum A)
 -- Runtime Function: short accum __satfractusaha (unsigned accum A)
 -- Runtime Function: accum __satfractusasa (unsigned accum A)
 -- Runtime Function: long accum __satfractusada (unsigned accum A)
 -- Runtime Function: long long accum __satfractusata (unsigned accum A)
 -- Runtime Function: unsigned short fract __satfractusauqq (unsigned
          accum A)
 -- Runtime Function: unsigned fract __satfractusauhq (unsigned accum A)
 -- Runtime Function: unsigned long fract __satfractusausq (unsigned
          accum A)
 -- Runtime Function: unsigned long long fract __satfractusaudq
          (unsigned accum A)
 -- Runtime Function: unsigned short accum __satfractusauha2 (unsigned
          accum A)
 -- Runtime Function: unsigned long accum __satfractusauda2 (unsigned
          accum A)
 -- Runtime Function: unsigned long long accum __satfractusauta2
          (unsigned accum A)
 -- Runtime Function: short fract __satfractudaqq (unsigned long accum
          A)
 -- Runtime Function: fract __satfractudahq (unsigned long accum A)
 -- Runtime Function: long fract __satfractudasq (unsigned long accum A)
 -- Runtime Function: long long fract __satfractudadq (unsigned long
          accum A)
 -- Runtime Function: short accum __satfractudaha (unsigned long accum
          A)
 -- Runtime Function: accum __satfractudasa (unsigned long accum A)
 -- Runtime Function: long accum __satfractudada (unsigned long accum A)
 -- Runtime Function: long long accum __satfractudata (unsigned long
          accum A)
 -- Runtime Function: unsigned short fract __satfractudauqq (unsigned
          long accum A)
 -- Runtime Function: unsigned fract __satfractudauhq (unsigned long
          accum A)
 -- Runtime Function: unsigned long fract __satfractudausq (unsigned
          long accum A)
 -- Runtime Function: unsigned long long fract __satfractudaudq
          (unsigned long accum A)
 -- Runtime Function: unsigned short accum __satfractudauha2 (unsigned
          long accum A)
 -- Runtime Function: unsigned accum __satfractudausa2 (unsigned long
          accum A)
 -- Runtime Function: unsigned long long accum __satfractudauta2
          (unsigned long accum A)
 -- Runtime Function: short fract __satfractutaqq (unsigned long long
          accum A)
 -- Runtime Function: fract __satfractutahq (unsigned long long accum A)
 -- Runtime Function: long fract __satfractutasq (unsigned long long
          accum A)
 -- Runtime Function: long long fract __satfractutadq (unsigned long
          long accum A)
 -- Runtime Function: short accum __satfractutaha (unsigned long long
          accum A)
 -- Runtime Function: accum __satfractutasa (unsigned long long accum A)
 -- Runtime Function: long accum __satfractutada (unsigned long long
          accum A)
 -- Runtime Function: long long accum __satfractutata (unsigned long
          long accum A)
 -- Runtime Function: unsigned short fract __satfractutauqq (unsigned
          long long accum A)
 -- Runtime Function: unsigned fract __satfractutauhq (unsigned long
          long accum A)
 -- Runtime Function: unsigned long fract __satfractutausq (unsigned
          long long accum A)
 -- Runtime Function: unsigned long long fract __satfractutaudq
          (unsigned long long accum A)
 -- Runtime Function: unsigned short accum __satfractutauha2 (unsigned
          long long accum A)
 -- Runtime Function: unsigned accum __satfractutausa2 (unsigned long
          long accum A)
 -- Runtime Function: unsigned long accum __satfractutauda2 (unsigned
          long long accum A)
 -- Runtime Function: short fract __satfractqiqq (signed char A)
 -- Runtime Function: fract __satfractqihq (signed char A)
 -- Runtime Function: long fract __satfractqisq (signed char A)
 -- Runtime Function: long long fract __satfractqidq (signed char A)
 -- Runtime Function: short accum __satfractqiha (signed char A)
 -- Runtime Function: accum __satfractqisa (signed char A)
 -- Runtime Function: long accum __satfractqida (signed char A)
 -- Runtime Function: long long accum __satfractqita (signed char A)
 -- Runtime Function: unsigned short fract __satfractqiuqq (signed char
          A)
 -- Runtime Function: unsigned fract __satfractqiuhq (signed char A)
 -- Runtime Function: unsigned long fract __satfractqiusq (signed char
          A)
 -- Runtime Function: unsigned long long fract __satfractqiudq (signed
          char A)
 -- Runtime Function: unsigned short accum __satfractqiuha (signed char
          A)
 -- Runtime Function: unsigned accum __satfractqiusa (signed char A)
 -- Runtime Function: unsigned long accum __satfractqiuda (signed char
          A)
 -- Runtime Function: unsigned long long accum __satfractqiuta (signed
          char A)
 -- Runtime Function: short fract __satfracthiqq (short A)
 -- Runtime Function: fract __satfracthihq (short A)
 -- Runtime Function: long fract __satfracthisq (short A)
 -- Runtime Function: long long fract __satfracthidq (short A)
 -- Runtime Function: short accum __satfracthiha (short A)
 -- Runtime Function: accum __satfracthisa (short A)
 -- Runtime Function: long accum __satfracthida (short A)
 -- Runtime Function: long long accum __satfracthita (short A)
 -- Runtime Function: unsigned short fract __satfracthiuqq (short A)
 -- Runtime Function: unsigned fract __satfracthiuhq (short A)
 -- Runtime Function: unsigned long fract __satfracthiusq (short A)
 -- Runtime Function: unsigned long long fract __satfracthiudq (short A)
 -- Runtime Function: unsigned short accum __satfracthiuha (short A)
 -- Runtime Function: unsigned accum __satfracthiusa (short A)
 -- Runtime Function: unsigned long accum __satfracthiuda (short A)
 -- Runtime Function: unsigned long long accum __satfracthiuta (short A)
 -- Runtime Function: short fract __satfractsiqq (int A)
 -- Runtime Function: fract __satfractsihq (int A)
 -- Runtime Function: long fract __satfractsisq (int A)
 -- Runtime Function: long long fract __satfractsidq (int A)
 -- Runtime Function: short accum __satfractsiha (int A)
 -- Runtime Function: accum __satfractsisa (int A)
 -- Runtime Function: long accum __satfractsida (int A)
 -- Runtime Function: long long accum __satfractsita (int A)
 -- Runtime Function: unsigned short fract __satfractsiuqq (int A)
 -- Runtime Function: unsigned fract __satfractsiuhq (int A)
 -- Runtime Function: unsigned long fract __satfractsiusq (int A)
 -- Runtime Function: unsigned long long fract __satfractsiudq (int A)
 -- Runtime Function: unsigned short accum __satfractsiuha (int A)
 -- Runtime Function: unsigned accum __satfractsiusa (int A)
 -- Runtime Function: unsigned long accum __satfractsiuda (int A)
 -- Runtime Function: unsigned long long accum __satfractsiuta (int A)
 -- Runtime Function: short fract __satfractdiqq (long A)
 -- Runtime Function: fract __satfractdihq (long A)
 -- Runtime Function: long fract __satfractdisq (long A)
 -- Runtime Function: long long fract __satfractdidq (long A)
 -- Runtime Function: short accum __satfractdiha (long A)
 -- Runtime Function: accum __satfractdisa (long A)
 -- Runtime Function: long accum __satfractdida (long A)
 -- Runtime Function: long long accum __satfractdita (long A)
 -- Runtime Function: unsigned short fract __satfractdiuqq (long A)
 -- Runtime Function: unsigned fract __satfractdiuhq (long A)
 -- Runtime Function: unsigned long fract __satfractdiusq (long A)
 -- Runtime Function: unsigned long long fract __satfractdiudq (long A)
 -- Runtime Function: unsigned short accum __satfractdiuha (long A)
 -- Runtime Function: unsigned accum __satfractdiusa (long A)
 -- Runtime Function: unsigned long accum __satfractdiuda (long A)
 -- Runtime Function: unsigned long long accum __satfractdiuta (long A)
 -- Runtime Function: short fract __satfracttiqq (long long A)
 -- Runtime Function: fract __satfracttihq (long long A)
 -- Runtime Function: long fract __satfracttisq (long long A)
 -- Runtime Function: long long fract __satfracttidq (long long A)
 -- Runtime Function: short accum __satfracttiha (long long A)
 -- Runtime Function: accum __satfracttisa (long long A)
 -- Runtime Function: long accum __satfracttida (long long A)
 -- Runtime Function: long long accum __satfracttita (long long A)
 -- Runtime Function: unsigned short fract __satfracttiuqq (long long A)
 -- Runtime Function: unsigned fract __satfracttiuhq (long long A)
 -- Runtime Function: unsigned long fract __satfracttiusq (long long A)
 -- Runtime Function: unsigned long long fract __satfracttiudq (long
          long A)
 -- Runtime Function: unsigned short accum __satfracttiuha (long long A)
 -- Runtime Function: unsigned accum __satfracttiusa (long long A)
 -- Runtime Function: unsigned long accum __satfracttiuda (long long A)
 -- Runtime Function: unsigned long long accum __satfracttiuta (long
          long A)
 -- Runtime Function: short fract __satfractsfqq (float A)
 -- Runtime Function: fract __satfractsfhq (float A)
 -- Runtime Function: long fract __satfractsfsq (float A)
 -- Runtime Function: long long fract __satfractsfdq (float A)
 -- Runtime Function: short accum __satfractsfha (float A)
 -- Runtime Function: accum __satfractsfsa (float A)
 -- Runtime Function: long accum __satfractsfda (float A)
 -- Runtime Function: long long accum __satfractsfta (float A)
 -- Runtime Function: unsigned short fract __satfractsfuqq (float A)
 -- Runtime Function: unsigned fract __satfractsfuhq (float A)
 -- Runtime Function: unsigned long fract __satfractsfusq (float A)
 -- Runtime Function: unsigned long long fract __satfractsfudq (float A)
 -- Runtime Function: unsigned short accum __satfractsfuha (float A)
 -- Runtime Function: unsigned accum __satfractsfusa (float A)
 -- Runtime Function: unsigned long accum __satfractsfuda (float A)
 -- Runtime Function: unsigned long long accum __satfractsfuta (float A)
 -- Runtime Function: short fract __satfractdfqq (double A)
 -- Runtime Function: fract __satfractdfhq (double A)
 -- Runtime Function: long fract __satfractdfsq (double A)
 -- Runtime Function: long long fract __satfractdfdq (double A)
 -- Runtime Function: short accum __satfractdfha (double A)
 -- Runtime Function: accum __satfractdfsa (double A)
 -- Runtime Function: long accum __satfractdfda (double A)
 -- Runtime Function: long long accum __satfractdfta (double A)
 -- Runtime Function: unsigned short fract __satfractdfuqq (double A)
 -- Runtime Function: unsigned fract __satfractdfuhq (double A)
 -- Runtime Function: unsigned long fract __satfractdfusq (double A)
 -- Runtime Function: unsigned long long fract __satfractdfudq (double
          A)
 -- Runtime Function: unsigned short accum __satfractdfuha (double A)
 -- Runtime Function: unsigned accum __satfractdfusa (double A)
 -- Runtime Function: unsigned long accum __satfractdfuda (double A)
 -- Runtime Function: unsigned long long accum __satfractdfuta (double
          A)
     The functions convert from fractional and signed non-fractionals to
     fractionals, with saturation.

 -- Runtime Function: unsigned char __fractunsqqqi (short fract A)
 -- Runtime Function: unsigned short __fractunsqqhi (short fract A)
 -- Runtime Function: unsigned int __fractunsqqsi (short fract A)
 -- Runtime Function: unsigned long __fractunsqqdi (short fract A)
 -- Runtime Function: unsigned long long __fractunsqqti (short fract A)
 -- Runtime Function: unsigned char __fractunshqqi (fract A)
 -- Runtime Function: unsigned short __fractunshqhi (fract A)
 -- Runtime Function: unsigned int __fractunshqsi (fract A)
 -- Runtime Function: unsigned long __fractunshqdi (fract A)
 -- Runtime Function: unsigned long long __fractunshqti (fract A)
 -- Runtime Function: unsigned char __fractunssqqi (long fract A)
 -- Runtime Function: unsigned short __fractunssqhi (long fract A)
 -- Runtime Function: unsigned int __fractunssqsi (long fract A)
 -- Runtime Function: unsigned long __fractunssqdi (long fract A)
 -- Runtime Function: unsigned long long __fractunssqti (long fract A)
 -- Runtime Function: unsigned char __fractunsdqqi (long long fract A)
 -- Runtime Function: unsigned short __fractunsdqhi (long long fract A)
 -- Runtime Function: unsigned int __fractunsdqsi (long long fract A)
 -- Runtime Function: unsigned long __fractunsdqdi (long long fract A)
 -- Runtime Function: unsigned long long __fractunsdqti (long long fract
          A)
 -- Runtime Function: unsigned char __fractunshaqi (short accum A)
 -- Runtime Function: unsigned short __fractunshahi (short accum A)
 -- Runtime Function: unsigned int __fractunshasi (short accum A)
 -- Runtime Function: unsigned long __fractunshadi (short accum A)
 -- Runtime Function: unsigned long long __fractunshati (short accum A)
 -- Runtime Function: unsigned char __fractunssaqi (accum A)
 -- Runtime Function: unsigned short __fractunssahi (accum A)
 -- Runtime Function: unsigned int __fractunssasi (accum A)
 -- Runtime Function: unsigned long __fractunssadi (accum A)
 -- Runtime Function: unsigned long long __fractunssati (accum A)
 -- Runtime Function: unsigned char __fractunsdaqi (long accum A)
 -- Runtime Function: unsigned short __fractunsdahi (long accum A)
 -- Runtime Function: unsigned int __fractunsdasi (long accum A)
 -- Runtime Function: unsigned long __fractunsdadi (long accum A)
 -- Runtime Function: unsigned long long __fractunsdati (long accum A)
 -- Runtime Function: unsigned char __fractunstaqi (long long accum A)
 -- Runtime Function: unsigned short __fractunstahi (long long accum A)
 -- Runtime Function: unsigned int __fractunstasi (long long accum A)
 -- Runtime Function: unsigned long __fractunstadi (long long accum A)
 -- Runtime Function: unsigned long long __fractunstati (long long accum
          A)
 -- Runtime Function: unsigned char __fractunsuqqqi (unsigned short
          fract A)
 -- Runtime Function: unsigned short __fractunsuqqhi (unsigned short
          fract A)
 -- Runtime Function: unsigned int __fractunsuqqsi (unsigned short fract
          A)
 -- Runtime Function: unsigned long __fractunsuqqdi (unsigned short
          fract A)
 -- Runtime Function: unsigned long long __fractunsuqqti (unsigned short
          fract A)
 -- Runtime Function: unsigned char __fractunsuhqqi (unsigned fract A)
 -- Runtime Function: unsigned short __fractunsuhqhi (unsigned fract A)
 -- Runtime Function: unsigned int __fractunsuhqsi (unsigned fract A)
 -- Runtime Function: unsigned long __fractunsuhqdi (unsigned fract A)
 -- Runtime Function: unsigned long long __fractunsuhqti (unsigned fract
          A)
 -- Runtime Function: unsigned char __fractunsusqqi (unsigned long fract
          A)
 -- Runtime Function: unsigned short __fractunsusqhi (unsigned long
          fract A)
 -- Runtime Function: unsigned int __fractunsusqsi (unsigned long fract
          A)
 -- Runtime Function: unsigned long __fractunsusqdi (unsigned long fract
          A)
 -- Runtime Function: unsigned long long __fractunsusqti (unsigned long
          fract A)
 -- Runtime Function: unsigned char __fractunsudqqi (unsigned long long
          fract A)
 -- Runtime Function: unsigned short __fractunsudqhi (unsigned long long
          fract A)
 -- Runtime Function: unsigned int __fractunsudqsi (unsigned long long
          fract A)
 -- Runtime Function: unsigned long __fractunsudqdi (unsigned long long
          fract A)
 -- Runtime Function: unsigned long long __fractunsudqti (unsigned long
          long fract A)
 -- Runtime Function: unsigned char __fractunsuhaqi (unsigned short
          accum A)
 -- Runtime Function: unsigned short __fractunsuhahi (unsigned short
          accum A)
 -- Runtime Function: unsigned int __fractunsuhasi (unsigned short accum
          A)
 -- Runtime Function: unsigned long __fractunsuhadi (unsigned short
          accum A)
 -- Runtime Function: unsigned long long __fractunsuhati (unsigned short
          accum A)
 -- Runtime Function: unsigned char __fractunsusaqi (unsigned accum A)
 -- Runtime Function: unsigned short __fractunsusahi (unsigned accum A)
 -- Runtime Function: unsigned int __fractunsusasi (unsigned accum A)
 -- Runtime Function: unsigned long __fractunsusadi (unsigned accum A)
 -- Runtime Function: unsigned long long __fractunsusati (unsigned accum
          A)
 -- Runtime Function: unsigned char __fractunsudaqi (unsigned long accum
          A)
 -- Runtime Function: unsigned short __fractunsudahi (unsigned long
          accum A)
 -- Runtime Function: unsigned int __fractunsudasi (unsigned long accum
          A)
 -- Runtime Function: unsigned long __fractunsudadi (unsigned long accum
          A)
 -- Runtime Function: unsigned long long __fractunsudati (unsigned long
          accum A)
 -- Runtime Function: unsigned char __fractunsutaqi (unsigned long long
          accum A)
 -- Runtime Function: unsigned short __fractunsutahi (unsigned long long
          accum A)
 -- Runtime Function: unsigned int __fractunsutasi (unsigned long long
          accum A)
 -- Runtime Function: unsigned long __fractunsutadi (unsigned long long
          accum A)
 -- Runtime Function: unsigned long long __fractunsutati (unsigned long
          long accum A)
 -- Runtime Function: short fract __fractunsqiqq (unsigned char A)
 -- Runtime Function: fract __fractunsqihq (unsigned char A)
 -- Runtime Function: long fract __fractunsqisq (unsigned char A)
 -- Runtime Function: long long fract __fractunsqidq (unsigned char A)
 -- Runtime Function: short accum __fractunsqiha (unsigned char A)
 -- Runtime Function: accum __fractunsqisa (unsigned char A)
 -- Runtime Function: long accum __fractunsqida (unsigned char A)
 -- Runtime Function: long long accum __fractunsqita (unsigned char A)
 -- Runtime Function: unsigned short fract __fractunsqiuqq (unsigned
          char A)
 -- Runtime Function: unsigned fract __fractunsqiuhq (unsigned char A)
 -- Runtime Function: unsigned long fract __fractunsqiusq (unsigned char
          A)
 -- Runtime Function: unsigned long long fract __fractunsqiudq (unsigned
          char A)
 -- Runtime Function: unsigned short accum __fractunsqiuha (unsigned
          char A)
 -- Runtime Function: unsigned accum __fractunsqiusa (unsigned char A)
 -- Runtime Function: unsigned long accum __fractunsqiuda (unsigned char
          A)
 -- Runtime Function: unsigned long long accum __fractunsqiuta (unsigned
          char A)
 -- Runtime Function: short fract __fractunshiqq (unsigned short A)
 -- Runtime Function: fract __fractunshihq (unsigned short A)
 -- Runtime Function: long fract __fractunshisq (unsigned short A)
 -- Runtime Function: long long fract __fractunshidq (unsigned short A)
 -- Runtime Function: short accum __fractunshiha (unsigned short A)
 -- Runtime Function: accum __fractunshisa (unsigned short A)
 -- Runtime Function: long accum __fractunshida (unsigned short A)
 -- Runtime Function: long long accum __fractunshita (unsigned short A)
 -- Runtime Function: unsigned short fract __fractunshiuqq (unsigned
          short A)
 -- Runtime Function: unsigned fract __fractunshiuhq (unsigned short A)
 -- Runtime Function: unsigned long fract __fractunshiusq (unsigned
          short A)
 -- Runtime Function: unsigned long long fract __fractunshiudq (unsigned
          short A)
 -- Runtime Function: unsigned short accum __fractunshiuha (unsigned
          short A)
 -- Runtime Function: unsigned accum __fractunshiusa (unsigned short A)
 -- Runtime Function: unsigned long accum __fractunshiuda (unsigned
          short A)
 -- Runtime Function: unsigned long long accum __fractunshiuta (unsigned
          short A)
 -- Runtime Function: short fract __fractunssiqq (unsigned int A)
 -- Runtime Function: fract __fractunssihq (unsigned int A)
 -- Runtime Function: long fract __fractunssisq (unsigned int A)
 -- Runtime Function: long long fract __fractunssidq (unsigned int A)
 -- Runtime Function: short accum __fractunssiha (unsigned int A)
 -- Runtime Function: accum __fractunssisa (unsigned int A)
 -- Runtime Function: long accum __fractunssida (unsigned int A)
 -- Runtime Function: long long accum __fractunssita (unsigned int A)
 -- Runtime Function: unsigned short fract __fractunssiuqq (unsigned int
          A)
 -- Runtime Function: unsigned fract __fractunssiuhq (unsigned int A)
 -- Runtime Function: unsigned long fract __fractunssiusq (unsigned int
          A)
 -- Runtime Function: unsigned long long fract __fractunssiudq (unsigned
          int A)
 -- Runtime Function: unsigned short accum __fractunssiuha (unsigned int
          A)
 -- Runtime Function: unsigned accum __fractunssiusa (unsigned int A)
 -- Runtime Function: unsigned long accum __fractunssiuda (unsigned int
          A)
 -- Runtime Function: unsigned long long accum __fractunssiuta (unsigned
          int A)
 -- Runtime Function: short fract __fractunsdiqq (unsigned long A)
 -- Runtime Function: fract __fractunsdihq (unsigned long A)
 -- Runtime Function: long fract __fractunsdisq (unsigned long A)
 -- Runtime Function: long long fract __fractunsdidq (unsigned long A)
 -- Runtime Function: short accum __fractunsdiha (unsigned long A)
 -- Runtime Function: accum __fractunsdisa (unsigned long A)
 -- Runtime Function: long accum __fractunsdida (unsigned long A)
 -- Runtime Function: long long accum __fractunsdita (unsigned long A)
 -- Runtime Function: unsigned short fract __fractunsdiuqq (unsigned
          long A)
 -- Runtime Function: unsigned fract __fractunsdiuhq (unsigned long A)
 -- Runtime Function: unsigned long fract __fractunsdiusq (unsigned long
          A)
 -- Runtime Function: unsigned long long fract __fractunsdiudq (unsigned
          long A)
 -- Runtime Function: unsigned short accum __fractunsdiuha (unsigned
          long A)
 -- Runtime Function: unsigned accum __fractunsdiusa (unsigned long A)
 -- Runtime Function: unsigned long accum __fractunsdiuda (unsigned long
          A)
 -- Runtime Function: unsigned long long accum __fractunsdiuta (unsigned
          long A)
 -- Runtime Function: short fract __fractunstiqq (unsigned long long A)
 -- Runtime Function: fract __fractunstihq (unsigned long long A)
 -- Runtime Function: long fract __fractunstisq (unsigned long long A)
 -- Runtime Function: long long fract __fractunstidq (unsigned long long
          A)
 -- Runtime Function: short accum __fractunstiha (unsigned long long A)
 -- Runtime Function: accum __fractunstisa (unsigned long long A)
 -- Runtime Function: long accum __fractunstida (unsigned long long A)
 -- Runtime Function: long long accum __fractunstita (unsigned long long
          A)
 -- Runtime Function: unsigned short fract __fractunstiuqq (unsigned
          long long A)
 -- Runtime Function: unsigned fract __fractunstiuhq (unsigned long long
          A)
 -- Runtime Function: unsigned long fract __fractunstiusq (unsigned long
          long A)
 -- Runtime Function: unsigned long long fract __fractunstiudq (unsigned
          long long A)
 -- Runtime Function: unsigned short accum __fractunstiuha (unsigned
          long long A)
 -- Runtime Function: unsigned accum __fractunstiusa (unsigned long long
          A)
 -- Runtime Function: unsigned long accum __fractunstiuda (unsigned long
          long A)
 -- Runtime Function: unsigned long long accum __fractunstiuta (unsigned
          long long A)
     These functions convert from fractionals to unsigned
     non-fractionals; and from unsigned non-fractionals to fractionals,
     without saturation.

 -- Runtime Function: short fract __satfractunsqiqq (unsigned char A)
 -- Runtime Function: fract __satfractunsqihq (unsigned char A)
 -- Runtime Function: long fract __satfractunsqisq (unsigned char A)
 -- Runtime Function: long long fract __satfractunsqidq (unsigned char
          A)
 -- Runtime Function: short accum __satfractunsqiha (unsigned char A)
 -- Runtime Function: accum __satfractunsqisa (unsigned char A)
 -- Runtime Function: long accum __satfractunsqida (unsigned char A)
 -- Runtime Function: long long accum __satfractunsqita (unsigned char
          A)
 -- Runtime Function: unsigned short fract __satfractunsqiuqq (unsigned
          char A)
 -- Runtime Function: unsigned fract __satfractunsqiuhq (unsigned char
          A)
 -- Runtime Function: unsigned long fract __satfractunsqiusq (unsigned
          char A)
 -- Runtime Function: unsigned long long fract __satfractunsqiudq
          (unsigned char A)
 -- Runtime Function: unsigned short accum __satfractunsqiuha (unsigned
          char A)
 -- Runtime Function: unsigned accum __satfractunsqiusa (unsigned char
          A)
 -- Runtime Function: unsigned long accum __satfractunsqiuda (unsigned
          char A)
 -- Runtime Function: unsigned long long accum __satfractunsqiuta
          (unsigned char A)
 -- Runtime Function: short fract __satfractunshiqq (unsigned short A)
 -- Runtime Function: fract __satfractunshihq (unsigned short A)
 -- Runtime Function: long fract __satfractunshisq (unsigned short A)
 -- Runtime Function: long long fract __satfractunshidq (unsigned short
          A)
 -- Runtime Function: short accum __satfractunshiha (unsigned short A)
 -- Runtime Function: accum __satfractunshisa (unsigned short A)
 -- Runtime Function: long accum __satfractunshida (unsigned short A)
 -- Runtime Function: long long accum __satfractunshita (unsigned short
          A)
 -- Runtime Function: unsigned short fract __satfractunshiuqq (unsigned
          short A)
 -- Runtime Function: unsigned fract __satfractunshiuhq (unsigned short
          A)
 -- Runtime Function: unsigned long fract __satfractunshiusq (unsigned
          short A)
 -- Runtime Function: unsigned long long fract __satfractunshiudq
          (unsigned short A)
 -- Runtime Function: unsigned short accum __satfractunshiuha (unsigned
          short A)
 -- Runtime Function: unsigned accum __satfractunshiusa (unsigned short
          A)
 -- Runtime Function: unsigned long accum __satfractunshiuda (unsigned
          short A)
 -- Runtime Function: unsigned long long accum __satfractunshiuta
          (unsigned short A)
 -- Runtime Function: short fract __satfractunssiqq (unsigned int A)
 -- Runtime Function: fract __satfractunssihq (unsigned int A)
 -- Runtime Function: long fract __satfractunssisq (unsigned int A)
 -- Runtime Function: long long fract __satfractunssidq (unsigned int A)
 -- Runtime Function: short accum __satfractunssiha (unsigned int A)
 -- Runtime Function: accum __satfractunssisa (unsigned int A)
 -- Runtime Function: long accum __satfractunssida (unsigned int A)
 -- Runtime Function: long long accum __satfractunssita (unsigned int A)
 -- Runtime Function: unsigned short fract __satfractunssiuqq (unsigned
          int A)
 -- Runtime Function: unsigned fract __satfractunssiuhq (unsigned int A)
 -- Runtime Function: unsigned long fract __satfractunssiusq (unsigned
          int A)
 -- Runtime Function: unsigned long long fract __satfractunssiudq
          (unsigned int A)
 -- Runtime Function: unsigned short accum __satfractunssiuha (unsigned
          int A)
 -- Runtime Function: unsigned accum __satfractunssiusa (unsigned int A)
 -- Runtime Function: unsigned long accum __satfractunssiuda (unsigned
          int A)
 -- Runtime Function: unsigned long long accum __satfractunssiuta
          (unsigned int A)
 -- Runtime Function: short fract __satfractunsdiqq (unsigned long A)
 -- Runtime Function: fract __satfractunsdihq (unsigned long A)
 -- Runtime Function: long fract __satfractunsdisq (unsigned long A)
 -- Runtime Function: long long fract __satfractunsdidq (unsigned long
          A)
 -- Runtime Function: short accum __satfractunsdiha (unsigned long A)
 -- Runtime Function: accum __satfractunsdisa (unsigned long A)
 -- Runtime Function: long accum __satfractunsdida (unsigned long A)
 -- Runtime Function: long long accum __satfractunsdita (unsigned long
          A)
 -- Runtime Function: unsigned short fract __satfractunsdiuqq (unsigned
          long A)
 -- Runtime Function: unsigned fract __satfractunsdiuhq (unsigned long
          A)
 -- Runtime Function: unsigned long fract __satfractunsdiusq (unsigned
          long A)
 -- Runtime Function: unsigned long long fract __satfractunsdiudq
          (unsigned long A)
 -- Runtime Function: unsigned short accum __satfractunsdiuha (unsigned
          long A)
 -- Runtime Function: unsigned accum __satfractunsdiusa (unsigned long
          A)
 -- Runtime Function: unsigned long accum __satfractunsdiuda (unsigned
          long A)
 -- Runtime Function: unsigned long long accum __satfractunsdiuta
          (unsigned long A)
 -- Runtime Function: short fract __satfractunstiqq (unsigned long long
          A)
 -- Runtime Function: fract __satfractunstihq (unsigned long long A)
 -- Runtime Function: long fract __satfractunstisq (unsigned long long
          A)
 -- Runtime Function: long long fract __satfractunstidq (unsigned long
          long A)
 -- Runtime Function: short accum __satfractunstiha (unsigned long long
          A)
 -- Runtime Function: accum __satfractunstisa (unsigned long long A)
 -- Runtime Function: long accum __satfractunstida (unsigned long long
          A)
 -- Runtime Function: long long accum __satfractunstita (unsigned long
          long A)
 -- Runtime Function: unsigned short fract __satfractunstiuqq (unsigned
          long long A)
 -- Runtime Function: unsigned fract __satfractunstiuhq (unsigned long
          long A)
 -- Runtime Function: unsigned long fract __satfractunstiusq (unsigned
          long long A)
 -- Runtime Function: unsigned long long fract __satfractunstiudq
          (unsigned long long A)
 -- Runtime Function: unsigned short accum __satfractunstiuha (unsigned
          long long A)
 -- Runtime Function: unsigned accum __satfractunstiusa (unsigned long
          long A)
 -- Runtime Function: unsigned long accum __satfractunstiuda (unsigned
          long long A)
 -- Runtime Function: unsigned long long accum __satfractunstiuta
          (unsigned long long A)
     These functions convert from unsigned non-fractionals to
     fractionals, with saturation.


File: gccint.info,  Node: Exception handling routines,  Next: Miscellaneous routines,  Prev: Fixed-point fractional library routines,  Up: Libgcc

4.5 Language-independent routines for exception handling
========================================================

document me!

       _Unwind_DeleteException
       _Unwind_Find_FDE
       _Unwind_ForcedUnwind
       _Unwind_GetGR
       _Unwind_GetIP
       _Unwind_GetLanguageSpecificData
       _Unwind_GetRegionStart
       _Unwind_GetTextRelBase
       _Unwind_GetDataRelBase
       _Unwind_RaiseException
       _Unwind_Resume
       _Unwind_SetGR
       _Unwind_SetIP
       _Unwind_FindEnclosingFunction
       _Unwind_SjLj_Register
       _Unwind_SjLj_Unregister
       _Unwind_SjLj_RaiseException
       _Unwind_SjLj_ForcedUnwind
       _Unwind_SjLj_Resume
       __deregister_frame
       __deregister_frame_info
       __deregister_frame_info_bases
       __register_frame
       __register_frame_info
       __register_frame_info_bases
       __register_frame_info_table
       __register_frame_info_table_bases
       __register_frame_table


File: gccint.info,  Node: Miscellaneous routines,  Prev: Exception handling routines,  Up: Libgcc

4.6 Miscellaneous runtime library routines
==========================================

4.6.1 Cache control functions
-----------------------------

 -- Runtime Function: void __clear_cache (char *BEG, char *END)
     This function clears the instruction cache between BEG and END.

4.6.2 Split stack functions and variables
-----------------------------------------

 -- Runtime Function: void * __splitstack_find (void *SEGMENT_ARG, void
          *SP, size_t LEN, void **NEXT_SEGMENT, void **NEXT_SP, void
          **INITIAL_SP)
     When using '-fsplit-stack', this call may be used to iterate over
     the stack segments.  It may be called like this:
            void *next_segment = NULL;
            void *next_sp = NULL;
            void *initial_sp = NULL;
            void *stack;
            size_t stack_size;
            while ((stack = __splitstack_find (next_segment, next_sp,
                                               &stack_size, &next_segment,
                                               &next_sp, &initial_sp))
                   != NULL)
              {
                /* Stack segment starts at stack and is
                   stack_size bytes long.  */
              }

     There is no way to iterate over the stack segments of a different
     thread.  However, what is permitted is for one thread to call this
     with the SEGMENT_ARG and SP arguments NULL, to pass NEXT_SEGMENT,
     NEXT_SP, and INITIAL_SP to a different thread, and then to suspend
     one way or another.  A different thread may run the subsequent
     '__splitstack_find' iterations.  Of course, this will only work if
     the first thread is suspended while the second thread is calling
     '__splitstack_find'.  If not, the second thread could be looking at
     the stack while it is changing, and anything could happen.

 -- Variable: __morestack_segments
 -- Variable: __morestack_current_segment
 -- Variable: __morestack_initial_sp
     Internal variables used by the '-fsplit-stack' implementation.


File: gccint.info,  Node: Languages,  Next: Source Tree,  Prev: Libgcc,  Up: Top

5 Language Front Ends in GCC
****************************

The interface to front ends for languages in GCC, and in particular the
'tree' structure (*note GENERIC::), was initially designed for C, and
many aspects of it are still somewhat biased towards C and C-like
languages.  It is, however, reasonably well suited to other procedural
languages, and front ends for many such languages have been written for
GCC.

 Writing a compiler as a front end for GCC, rather than compiling
directly to assembler or generating C code which is then compiled by
GCC, has several advantages:

   * GCC front ends benefit from the support for many different target
     machines already present in GCC.
   * GCC front ends benefit from all the optimizations in GCC.  Some of
     these, such as alias analysis, may work better when GCC is
     compiling directly from source code then when it is compiling from
     generated C code.
   * Better debugging information is generated when compiling directly
     from source code than when going via intermediate generated C code.

 Because of the advantages of writing a compiler as a GCC front end, GCC
front ends have also been created for languages very different from
those for which GCC was designed, such as the declarative
logic/functional language Mercury.  For these reasons, it may also be
useful to implement compilers created for specialized purposes (for
example, as part of a research project) as GCC front ends.


File: gccint.info,  Node: Source Tree,  Next: Testsuites,  Prev: Languages,  Up: Top

6 Source Tree Structure and Build System
****************************************

This chapter describes the structure of the GCC source tree, and how GCC
is built.  The user documentation for building and installing GCC is in
a separate manual (<http://gcc.gnu.org/install/>), with which it is
presumed that you are familiar.

* Menu:

* Configure Terms:: Configuration terminology and history.
* Top Level::       The top level source directory.
* gcc Directory::   The 'gcc' subdirectory.


File: gccint.info,  Node: Configure Terms,  Next: Top Level,  Up: Source Tree

6.1 Configure Terms and History
===============================

The configure and build process has a long and colorful history, and can
be confusing to anyone who doesn't know why things are the way they are.
While there are other documents which describe the configuration process
in detail, here are a few things that everyone working on GCC should
know.

 There are three system names that the build knows about: the machine
you are building on ("build"), the machine that you are building for
("host"), and the machine that GCC will produce code for ("target").
When you configure GCC, you specify these with '--build=', '--host=',
and '--target='.

 Specifying the host without specifying the build should be avoided, as
'configure' may (and once did) assume that the host you specify is also
the build, which may not be true.

 If build, host, and target are all the same, this is called a "native".
If build and host are the same but target is different, this is called a
"cross".  If build, host, and target are all different this is called a
"canadian" (for obscure reasons dealing with Canada's political party
and the background of the person working on the build at that time).  If
host and target are the same, but build is different, you are using a
cross-compiler to build a native for a different system.  Some people
call this a "host-x-host", "crossed native", or "cross-built native".
If build and target are the same, but host is different, you are using a
cross compiler to build a cross compiler that produces code for the
machine you're building on.  This is rare, so there is no common way of
describing it.  There is a proposal to call this a "crossback".

 If build and host are the same, the GCC you are building will also be
used to build the target libraries (like 'libstdc++').  If build and
host are different, you must have already built and installed a cross
compiler that will be used to build the target libraries (if you
configured with '--target=foo-bar', this compiler will be called
'foo-bar-gcc').

 In the case of target libraries, the machine you're building for is the
machine you specified with '--target'.  So, build is the machine you're
building on (no change there), host is the machine you're building for
(the target libraries are built for the target, so host is the target
you specified), and target doesn't apply (because you're not building a
compiler, you're building libraries).  The configure/make process will
adjust these variables as needed.  It also sets '$with_cross_host' to
the original '--host' value in case you need it.

 The 'libiberty' support library is built up to three times: once for
the host, once for the target (even if they are the same), and once for
the build if build and host are different.  This allows it to be used by
all programs which are generated in the course of the build process.


File: gccint.info,  Node: Top Level,  Next: gcc Directory,  Prev: Configure Terms,  Up: Source Tree

6.2 Top Level Source Directory
==============================

The top level source directory in a GCC distribution contains several
files and directories that are shared with other software distributions
such as that of GNU Binutils.  It also contains several subdirectories
that contain parts of GCC and its runtime libraries:

'boehm-gc'
     The Boehm conservative garbage collector, used as part of the Java
     runtime library.

'config'
     Autoconf macros and Makefile fragments used throughout the tree.

'contrib'
     Contributed scripts that may be found useful in conjunction with
     GCC.  One of these, 'contrib/texi2pod.pl', is used to generate man
     pages from Texinfo manuals as part of the GCC build process.

'fixincludes'
     The support for fixing system headers to work with GCC.  See
     'fixincludes/README' for more information.  The headers fixed by
     this mechanism are installed in 'LIBSUBDIR/include-fixed'.  Along
     with those headers, 'README-fixinc' is also installed, as
     'LIBSUBDIR/include-fixed/README'.

'gcc'
     The main sources of GCC itself (except for runtime libraries),
     including optimizers, support for different target architectures,
     language front ends, and testsuites.  *Note The 'gcc' Subdirectory:
     gcc Directory, for details.

'gnattools'
     Support tools for GNAT.

'include'
     Headers for the 'libiberty' library.

'intl'
     GNU 'libintl', from GNU 'gettext', for systems which do not include
     it in 'libc'.

'libada'
     The Ada runtime library.

'libatomic'
     The runtime support library for atomic operations (e.g.  for
     '__sync' and '__atomic').

'libcpp'
     The C preprocessor library.

'libdecnumber'
     The Decimal Float support library.

'libffi'
     The 'libffi' library, used as part of the Java runtime library.

'libgcc'
     The GCC runtime library.

'libgfortran'
     The Fortran runtime library.

'libgo'
     The Go runtime library.  The bulk of this library is mirrored from
     the master Go repository (http://code.google.com/p/go/).

'libgomp'
     The GNU OpenMP runtime library.

'libiberty'
     The 'libiberty' library, used for portability and for some
     generally useful data structures and algorithms.  *Note
     Introduction: (libiberty)Top, for more information about this
     library.

'libitm'
     The runtime support library for transactional memory.

'libjava'
     The Java runtime library.

'libmudflap'
     The 'libmudflap' library, used for instrumenting pointer and array
     dereferencing operations.

'libobjc'
     The Objective-C and Objective-C++ runtime library.

'libquadmath'
     The runtime support library for quad-precision math operations.

'libssp'
     The Stack protector runtime library.

'libstdc++-v3'
     The C++ runtime library.

'lto-plugin'
     Plugin used by 'gold' if link-time optimizations are enabled.

'maintainer-scripts'
     Scripts used by the 'gccadmin' account on 'gcc.gnu.org'.

'zlib'
     The 'zlib' compression library, used by the Java front end, as part
     of the Java runtime library, and for compressing and uncompressing
     GCC's intermediate language in LTO object files.

 The build system in the top level directory, including how recursion
into subdirectories works and how building runtime libraries for
multilibs is handled, is documented in a separate manual, included with
GNU Binutils.  *Note GNU configure and build system: (configure)Top, for
details.


File: gccint.info,  Node: gcc Directory,  Prev: Top Level,  Up: Source Tree

6.3 The 'gcc' Subdirectory
==========================

The 'gcc' directory contains many files that are part of the C sources
of GCC, other files used as part of the configuration and build process,
and subdirectories including documentation and a testsuite.  The files
that are sources of GCC are documented in a separate chapter.  *Note
Passes and Files of the Compiler: Passes.

* Menu:

* Subdirectories:: Subdirectories of 'gcc'.
* Configuration::  The configuration process, and the files it uses.
* Build::          The build system in the 'gcc' directory.
* Makefile::       Targets in 'gcc/Makefile'.
* Library Files::  Library source files and headers under 'gcc/'.
* Headers::        Headers installed by GCC.
* Documentation::  Building documentation in GCC.
* Front End::      Anatomy of a language front end.
* Back End::       Anatomy of a target back end.


File: gccint.info,  Node: Subdirectories,  Next: Configuration,  Up: gcc Directory

6.3.1 Subdirectories of 'gcc'
-----------------------------

The 'gcc' directory contains the following subdirectories:

'LANGUAGE'
     Subdirectories for various languages.  Directories containing a
     file 'config-lang.in' are language subdirectories.  The contents of
     the subdirectories 'c' (for C), 'cp' (for C++), 'objc' (for
     Objective-C), 'objcp' (for Objective-C++), and 'lto' (for LTO) are
     documented in this manual (*note Passes and Files of the Compiler:
     Passes.); those for other languages are not.  *Note Anatomy of a
     Language Front End: Front End, for details of the files in these
     directories.

'common'
     Source files shared between the compiler drivers (such as 'gcc')
     and the compilers proper (such as 'cc1').  If an architecture
     defines target hooks shared between those places, it also has a
     subdirectory in 'common/config'.  *Note Target Structure::.

'config'
     Configuration files for supported architectures and operating
     systems.  *Note Anatomy of a Target Back End: Back End, for details
     of the files in this directory.

'doc'
     Texinfo documentation for GCC, together with automatically
     generated man pages and support for converting the installation
     manual to HTML.  *Note Documentation::.

'ginclude'
     System headers installed by GCC, mainly those required by the C
     standard of freestanding implementations.  *Note Headers Installed
     by GCC: Headers, for details of when these and other headers are
     installed.

'po'
     Message catalogs with translations of messages produced by GCC into
     various languages, 'LANGUAGE.po'.  This directory also contains
     'gcc.pot', the template for these message catalogues, 'exgettext',
     a wrapper around 'gettext' to extract the messages from the GCC
     sources and create 'gcc.pot', which is run by 'make gcc.pot', and
     'EXCLUDES', a list of files from which messages should not be
     extracted.

'testsuite'
     The GCC testsuites (except for those for runtime libraries).  *Note
     Testsuites::.


File: gccint.info,  Node: Configuration,  Next: Build,  Prev: Subdirectories,  Up: gcc Directory

6.3.2 Configuration in the 'gcc' Directory
------------------------------------------

The 'gcc' directory is configured with an Autoconf-generated script
'configure'.  The 'configure' script is generated from 'configure.ac'
and 'aclocal.m4'.  From the files 'configure.ac' and 'acconfig.h',
Autoheader generates the file 'config.in'.  The file 'cstamp-h.in' is
used as a timestamp.

* Menu:

* Config Fragments::     Scripts used by 'configure'.
* System Config::        The 'config.build', 'config.host', and
                         'config.gcc' files.
* Configuration Files::  Files created by running 'configure'.


File: gccint.info,  Node: Config Fragments,  Next: System Config,  Up: Configuration

6.3.2.1 Scripts Used by 'configure'
...................................

'configure' uses some other scripts to help in its work:

   * The standard GNU 'config.sub' and 'config.guess' files, kept in the
     top level directory, are used.

   * The file 'config.gcc' is used to handle configuration specific to
     the particular target machine.  The file 'config.build' is used to
     handle configuration specific to the particular build machine.  The
     file 'config.host' is used to handle configuration specific to the
     particular host machine.  (In general, these should only be used
     for features that cannot reasonably be tested in Autoconf feature
     tests.)  *Note The 'config.build'; 'config.host'; and 'config.gcc'
     Files: System Config, for details of the contents of these files.

   * Each language subdirectory has a file 'LANGUAGE/config-lang.in'
     that is used for front-end-specific configuration.  *Note The Front
     End 'config-lang.in' File: Front End Config, for details of this
     file.

   * A helper script 'configure.frag' is used as part of creating the
     output of 'configure'.


File: gccint.info,  Node: System Config,  Next: Configuration Files,  Prev: Config Fragments,  Up: Configuration

6.3.2.2 The 'config.build'; 'config.host'; and 'config.gcc' Files
.................................................................

The 'config.build' file contains specific rules for particular systems
which GCC is built on.  This should be used as rarely as possible, as
the behavior of the build system can always be detected by autoconf.

 The 'config.host' file contains specific rules for particular systems
which GCC will run on.  This is rarely needed.

 The 'config.gcc' file contains specific rules for particular systems
which GCC will generate code for.  This is usually needed.

 Each file has a list of the shell variables it sets, with descriptions,
at the top of the file.

 FIXME: document the contents of these files, and what variables should
be set to control build, host and target configuration.


File: gccint.info,  Node: Configuration Files,  Prev: System Config,  Up: Configuration

6.3.2.3 Files Created by 'configure'
....................................

Here we spell out what files will be set up by 'configure' in the 'gcc'
directory.  Some other files are created as temporary files in the
configuration process, and are not used in the subsequent build; these
are not documented.

   * 'Makefile' is constructed from 'Makefile.in', together with the
     host and target fragments (*note Makefile Fragments: Fragments.)
     't-TARGET' and 'x-HOST' from 'config', if any, and language
     Makefile fragments 'LANGUAGE/Make-lang.in'.
   * 'auto-host.h' contains information about the host machine
     determined by 'configure'.  If the host machine is different from
     the build machine, then 'auto-build.h' is also created, containing
     such information about the build machine.
   * 'config.status' is a script that may be run to recreate the current
     configuration.
   * 'configargs.h' is a header containing details of the arguments
     passed to 'configure' to configure GCC, and of the thread model
     used.
   * 'cstamp-h' is used as a timestamp.
   * If a language 'config-lang.in' file (*note The Front End
     'config-lang.in' File: Front End Config.) sets 'outputs', then the
     files listed in 'outputs' there are also generated.

 The following configuration headers are created from the Makefile,
using 'mkconfig.sh', rather than directly by 'configure'.  'config.h',
'bconfig.h' and 'tconfig.h' all contain the 'xm-MACHINE.h' header, if
any, appropriate to the host, build and target machines respectively,
the configuration headers for the target, and some definitions; for the
host and build machines, these include the autoconfigured headers
generated by 'configure'.  The other configuration headers are
determined by 'config.gcc'.  They also contain the typedefs for 'rtx',
'rtvec' and 'tree'.

   * 'config.h', for use in programs that run on the host machine.
   * 'bconfig.h', for use in programs that run on the build machine.
   * 'tconfig.h', for use in programs and libraries for the target
     machine.
   * 'tm_p.h', which includes the header 'MACHINE-protos.h' that
     contains prototypes for functions in the target 'MACHINE.c' file.
     The header 'MACHINE-protos.h' can include prototypes of functions
     that use rtl and tree data structures inside appropriate '#ifdef
     RTX_CODE' and '#ifdef TREE_CODE' conditional code segements.  The
     'MACHINE-protos.h' is included after the 'rtl.h' and/or 'tree.h'
     would have been included.  The 'tm_p.h' also includes the header
     'tm-preds.h' which is generated by 'genpreds' program during the
     build to define the declarations and inline functions for the
     predicate functions.


File: gccint.info,  Node: Build,  Next: Makefile,  Prev: Configuration,  Up: gcc Directory

6.3.3 Build System in the 'gcc' Directory
-----------------------------------------

FIXME: describe the build system, including what is built in what
stages.  Also list the various source files that are used in the build
process but aren't source files of GCC itself and so aren't documented
below (*note Passes::).


File: gccint.info,  Node: Makefile,  Next: Library Files,  Prev: Build,  Up: gcc Directory

6.3.4 Makefile Targets
----------------------

These targets are available from the 'gcc' directory:

'all'
     This is the default target.  Depending on what your
     build/host/target configuration is, it coordinates all the things
     that need to be built.

'doc'
     Produce info-formatted documentation and man pages.  Essentially it
     calls 'make man' and 'make info'.

'dvi'
     Produce DVI-formatted documentation.

'pdf'
     Produce PDF-formatted documentation.

'html'
     Produce HTML-formatted documentation.

'man'
     Generate man pages.

'info'
     Generate info-formatted pages.

'mostlyclean'
     Delete the files made while building the compiler.

'clean'
     That, and all the other files built by 'make all'.

'distclean'
     That, and all the files created by 'configure'.

'maintainer-clean'
     Distclean plus any file that can be generated from other files.
     Note that additional tools may be required beyond what is normally
     needed to build GCC.

'srcextra'
     Generates files in the source directory that are not
     version-controlled but should go into a release tarball.

'srcinfo'
'srcman'
     Copies the info-formatted and manpage documentation into the source
     directory usually for the purpose of generating a release tarball.

'install'
     Installs GCC.

'uninstall'
     Deletes installed files, though this is not supported.

'check'
     Run the testsuite.  This creates a 'testsuite' subdirectory that
     has various '.sum' and '.log' files containing the results of the
     testing.  You can run subsets with, for example, 'make check-gcc'.
     You can specify specific tests by setting 'RUNTESTFLAGS' to be the
     name of the '.exp' file, optionally followed by (for some tests) an
     equals and a file wildcard, like:

          make check-gcc RUNTESTFLAGS="execute.exp=19980413-*"

     Note that running the testsuite may require additional tools be
     installed, such as Tcl or DejaGnu.

 The toplevel tree from which you start GCC compilation is not the GCC
directory, but rather a complex Makefile that coordinates the various
steps of the build, including bootstrapping the compiler and using the
new compiler to build target libraries.

 When GCC is configured for a native configuration, the default action
for 'make' is to do a full three-stage bootstrap.  This means that GCC
is built three times--once with the native compiler, once with the
native-built compiler it just built, and once with the compiler it built
the second time.  In theory, the last two should produce the same
results, which 'make compare' can check.  Each stage is configured
separately and compiled into a separate directory, to minimize problems
due to ABI incompatibilities between the native compiler and GCC.

 If you do a change, rebuilding will also start from the first stage and
"bubble" up the change through the three stages.  Each stage is taken
from its build directory (if it had been built previously), rebuilt, and
copied to its subdirectory.  This will allow you to, for example,
continue a bootstrap after fixing a bug which causes the stage2 build to
crash.  It does not provide as good coverage of the compiler as
bootstrapping from scratch, but it ensures that the new code is
syntactically correct (e.g., that you did not use GCC extensions by
mistake), and avoids spurious bootstrap comparison failures(1).

 Other targets available from the top level include:

'bootstrap-lean'
     Like 'bootstrap', except that the various stages are removed once
     they're no longer needed.  This saves disk space.

'bootstrap2'
'bootstrap2-lean'
     Performs only the first two stages of bootstrap.  Unlike a
     three-stage bootstrap, this does not perform a comparison to test
     that the compiler is running properly.  Note that the disk space
     required by a "lean" bootstrap is approximately independent of the
     number of stages.

'stageN-bubble (N = 1...4, profile, feedback)'
     Rebuild all the stages up to N, with the appropriate flags,
     "bubbling" the changes as described above.

'all-stageN (N = 1...4, profile, feedback)'
     Assuming that stage N has already been built, rebuild it with the
     appropriate flags.  This is rarely needed.

'cleanstrap'
     Remove everything ('make clean') and rebuilds ('make bootstrap').

'compare'
     Compares the results of stages 2 and 3.  This ensures that the
     compiler is running properly, since it should produce the same
     object files regardless of how it itself was compiled.

'profiledbootstrap'
     Builds a compiler with profiling feedback information.  In this
     case, the second and third stages are named 'profile' and
     'feedback', respectively.  For more information, see *note Building
     with profile feedback: (gccinstall)Building.

'restrap'
     Restart a bootstrap, so that everything that was not built with the
     system compiler is rebuilt.

'stageN-start (N = 1...4, profile, feedback)'
     For each package that is bootstrapped, rename directories so that,
     for example, 'gcc' points to the stageN GCC, compiled with the
     stageN-1 GCC(2).

     You will invoke this target if you need to test or debug the stageN
     GCC.  If you only need to execute GCC (but you need not run 'make'
     either to rebuild it or to run test suites), you should be able to
     work directly in the 'stageN-gcc' directory.  This makes it easier
     to debug multiple stages in parallel.

'stage'
     For each package that is bootstrapped, relocate its build directory
     to indicate its stage.  For example, if the 'gcc' directory points
     to the stage2 GCC, after invoking this target it will be renamed to
     'stage2-gcc'.

 If you wish to use non-default GCC flags when compiling the stage2 and
stage3 compilers, set 'BOOT_CFLAGS' on the command line when doing
'make'.

 Usually, the first stage only builds the languages that the compiler is
written in: typically, C and maybe Ada.  If you are debugging a
miscompilation of a different stage2 front-end (for example, of the
Fortran front-end), you may want to have front-ends for other languages
in the first stage as well.  To do so, set 'STAGE1_LANGUAGES' on the
command line when doing 'make'.

 For example, in the aforementioned scenario of debugging a Fortran
front-end miscompilation caused by the stage1 compiler, you may need a
command like

     make stage2-bubble STAGE1_LANGUAGES=c,fortran

 Alternatively, you can use per-language targets to build and test
languages that are not enabled by default in stage1.  For example, 'make
f951' will build a Fortran compiler even in the stage1 build directory.

   ---------- Footnotes ----------

   (1) Except if the compiler was buggy and miscompiled some of the
files that were not modified.  In this case, it's best to use 'make
restrap'.

   (2) Customarily, the system compiler is also termed the 'stage0' GCC.


File: gccint.info,  Node: Library Files,  Next: Headers,  Prev: Makefile,  Up: gcc Directory

6.3.5 Library Source Files and Headers under the 'gcc' Directory
----------------------------------------------------------------

FIXME: list here, with explanation, all the C source files and headers
under the 'gcc' directory that aren't built into the GCC executable but
rather are part of runtime libraries and object files, such as
'crtstuff.c' and 'unwind-dw2.c'.  *Note Headers Installed by GCC:
Headers, for more information about the 'ginclude' directory.


File: gccint.info,  Node: Headers,  Next: Documentation,  Prev: Library Files,  Up: gcc Directory

6.3.6 Headers Installed by GCC
------------------------------

In general, GCC expects the system C library to provide most of the
headers to be used with it.  However, GCC will fix those headers if
necessary to make them work with GCC, and will install some headers
required of freestanding implementations.  These headers are installed
in 'LIBSUBDIR/include'.  Headers for non-C runtime libraries are also
installed by GCC; these are not documented here.  (FIXME: document them
somewhere.)

 Several of the headers GCC installs are in the 'ginclude' directory.
These headers, 'iso646.h', 'stdarg.h', 'stdbool.h', and 'stddef.h', are
installed in 'LIBSUBDIR/include', unless the target Makefile fragment
(*note Target Fragment::) overrides this by setting 'USER_H'.

 In addition to these headers and those generated by fixing system
headers to work with GCC, some other headers may also be installed in
'LIBSUBDIR/include'.  'config.gcc' may set 'extra_headers'; this
specifies additional headers under 'config' to be installed on some
systems.

 GCC installs its own version of '<float.h>', from 'ginclude/float.h'.
This is done to cope with command-line options that change the
representation of floating point numbers.

 GCC also installs its own version of '<limits.h>'; this is generated
from 'glimits.h', together with 'limitx.h' and 'limity.h' if the system
also has its own version of '<limits.h>'.  (GCC provides its own header
because it is required of ISO C freestanding implementations, but needs
to include the system header from its own header as well because other
standards such as POSIX specify additional values to be defined in
'<limits.h>'.)  The system's '<limits.h>' header is used via
'LIBSUBDIR/include/syslimits.h', which is copied from 'gsyslimits.h' if
it does not need fixing to work with GCC; if it needs fixing,
'syslimits.h' is the fixed copy.

 GCC can also install '<tgmath.h>'.  It will do this when 'config.gcc'
sets 'use_gcc_tgmath' to 'yes'.


File: gccint.info,  Node: Documentation,  Next: Front End,  Prev: Headers,  Up: gcc Directory

6.3.7 Building Documentation
----------------------------

The main GCC documentation is in the form of manuals in Texinfo format.
These are installed in Info format; DVI versions may be generated by
'make dvi', PDF versions by 'make pdf', and HTML versions by 'make
html'.  In addition, some man pages are generated from the Texinfo
manuals, there are some other text files with miscellaneous
documentation, and runtime libraries have their own documentation
outside the 'gcc' directory.  FIXME: document the documentation for
runtime libraries somewhere.

* Menu:

* Texinfo Manuals::      GCC manuals in Texinfo format.
* Man Page Generation::  Generating man pages from Texinfo manuals.
* Miscellaneous Docs::   Miscellaneous text files with documentation.


File: gccint.info,  Node: Texinfo Manuals,  Next: Man Page Generation,  Up: Documentation

6.3.7.1 Texinfo Manuals
.......................

The manuals for GCC as a whole, and the C and C++ front ends, are in
files 'doc/*.texi'.  Other front ends have their own manuals in files
'LANGUAGE/*.texi'.  Common files 'doc/include/*.texi' are provided which
may be included in multiple manuals; the following files are in
'doc/include':

'fdl.texi'
     The GNU Free Documentation License.
'funding.texi'
     The section "Funding Free Software".
'gcc-common.texi'
     Common definitions for manuals.
'gpl_v3.texi'
     The GNU General Public License.
'texinfo.tex'
     A copy of 'texinfo.tex' known to work with the GCC manuals.

 DVI-formatted manuals are generated by 'make dvi', which uses
'texi2dvi' (via the Makefile macro '$(TEXI2DVI)').  PDF-formatted
manuals are generated by 'make pdf', which uses 'texi2pdf' (via the
Makefile macro '$(TEXI2PDF)').  HTML formatted manuals are generated by
'make html'.  Info manuals are generated by 'make info' (which is run as
part of a bootstrap); this generates the manuals in the source
directory, using 'makeinfo' via the Makefile macro '$(MAKEINFO)', and
they are included in release distributions.

 Manuals are also provided on the GCC web site, in both HTML and
PostScript forms.  This is done via the script
'maintainer-scripts/update_web_docs_svn'.  Each manual to be provided
online must be listed in the definition of 'MANUALS' in that file; a
file 'NAME.texi' must only appear once in the source tree, and the
output manual must have the same name as the source file.  (However,
other Texinfo files, included in manuals but not themselves the root
files of manuals, may have names that appear more than once in the
source tree.)  The manual file 'NAME.texi' should only include other
files in its own directory or in 'doc/include'.  HTML manuals will be
generated by 'makeinfo --html', PostScript manuals by 'texi2dvi' and
'dvips', and PDF manuals by 'texi2pdf'.  All Texinfo files that are
parts of manuals must be version-controlled, even if they are generated
files, for the generation of online manuals to work.

 The installation manual, 'doc/install.texi', is also provided on the
GCC web site.  The HTML version is generated by the script
'doc/install.texi2html'.


File: gccint.info,  Node: Man Page Generation,  Next: Miscellaneous Docs,  Prev: Texinfo Manuals,  Up: Documentation

6.3.7.2 Man Page Generation
...........................

Because of user demand, in addition to full Texinfo manuals, man pages
are provided which contain extracts from those manuals.  These man pages
are generated from the Texinfo manuals using 'contrib/texi2pod.pl' and
'pod2man'.  (The man page for 'g++', 'cp/g++.1', just contains a '.so'
reference to 'gcc.1', but all the other man pages are generated from
Texinfo manuals.)

 Because many systems may not have the necessary tools installed to
generate the man pages, they are only generated if the 'configure'
script detects that recent enough tools are installed, and the Makefiles
allow generating man pages to fail without aborting the build.  Man
pages are also included in release distributions.  They are generated in
the source directory.

 Magic comments in Texinfo files starting '@c man' control what parts of
a Texinfo file go into a man page.  Only a subset of Texinfo is
supported by 'texi2pod.pl', and it may be necessary to add support for
more Texinfo features to this script when generating new man pages.  To
improve the man page output, some special Texinfo macros are provided in
'doc/include/gcc-common.texi' which 'texi2pod.pl' understands:

'@gcctabopt'
     Use in the form '@table @gcctabopt' for tables of options, where
     for printed output the effect of '@code' is better than that of
     '@option' but for man page output a different effect is wanted.
'@gccoptlist'
     Use for summary lists of options in manuals.
'@gol'
     Use at the end of each line inside '@gccoptlist'.  This is
     necessary to avoid problems with differences in how the
     '@gccoptlist' macro is handled by different Texinfo formatters.

 FIXME: describe the 'texi2pod.pl' input language and magic comments in
more detail.


File: gccint.info,  Node: Miscellaneous Docs,  Prev: Man Page Generation,  Up: Documentation

6.3.7.3 Miscellaneous Documentation
...................................

In addition to the formal documentation that is installed by GCC, there
are several other text files in the 'gcc' subdirectory with
miscellaneous documentation:

'ABOUT-GCC-NLS'
     Notes on GCC's Native Language Support.  FIXME: this should be part
     of this manual rather than a separate file.
'ABOUT-NLS'
     Notes on the Free Translation Project.
'COPYING'
'COPYING3'
     The GNU General Public License, Versions 2 and 3.
'COPYING.LIB'
'COPYING3.LIB'
     The GNU Lesser General Public License, Versions 2.1 and 3.
'*ChangeLog*'
'*/ChangeLog*'
     Change log files for various parts of GCC.
'LANGUAGES'
     Details of a few changes to the GCC front-end interface.  FIXME:
     the information in this file should be part of general
     documentation of the front-end interface in this manual.
'ONEWS'
     Information about new features in old versions of GCC.  (For recent
     versions, the information is on the GCC web site.)
'README.Portability'
     Information about portability issues when writing code in GCC.
     FIXME: why isn't this part of this manual or of the GCC Coding
     Conventions?

 FIXME: document such files in subdirectories, at least 'config', 'c',
'cp', 'objc', 'testsuite'.


File: gccint.info,  Node: Front End,  Next: Back End,  Prev: Documentation,  Up: gcc Directory

6.3.8 Anatomy of a Language Front End
-------------------------------------

A front end for a language in GCC has the following parts:

   * A directory 'LANGUAGE' under 'gcc' containing source files for that
     front end.  *Note The Front End 'LANGUAGE' Directory: Front End
     Directory, for details.
   * A mention of the language in the list of supported languages in
     'gcc/doc/install.texi'.
   * A mention of the name under which the language's runtime library is
     recognized by '--enable-shared=PACKAGE' in the documentation of
     that option in 'gcc/doc/install.texi'.
   * A mention of any special prerequisites for building the front end
     in the documentation of prerequisites in 'gcc/doc/install.texi'.
   * Details of contributors to that front end in
     'gcc/doc/contrib.texi'.  If the details are in that front end's own
     manual then there should be a link to that manual's list in
     'contrib.texi'.
   * Information about support for that language in
     'gcc/doc/frontends.texi'.
   * Information about standards for that language, and the front end's
     support for them, in 'gcc/doc/standards.texi'.  This may be a link
     to such information in the front end's own manual.
   * Details of source file suffixes for that language and '-x LANG'
     options supported, in 'gcc/doc/invoke.texi'.
   * Entries in 'default_compilers' in 'gcc.c' for source file suffixes
     for that language.
   * Preferably testsuites, which may be under 'gcc/testsuite' or
     runtime library directories.  FIXME: document somewhere how to
     write testsuite harnesses.
   * Probably a runtime library for the language, outside the 'gcc'
     directory.  FIXME: document this further.
   * Details of the directories of any runtime libraries in
     'gcc/doc/sourcebuild.texi'.
   * Check targets in 'Makefile.def' for the top-level 'Makefile' to
     check just the compiler or the compiler and runtime library for the
     language.

 If the front end is added to the official GCC source repository, the
following are also necessary:

   * At least one Bugzilla component for bugs in that front end and
     runtime libraries.  This category needs to be added to the Bugzilla
     database.
   * Normally, one or more maintainers of that front end listed in
     'MAINTAINERS'.
   * Mentions on the GCC web site in 'index.html' and 'frontends.html',
     with any relevant links on 'readings.html'.  (Front ends that are
     not an official part of GCC may also be listed on 'frontends.html',
     with relevant links.)
   * A news item on 'index.html', and possibly an announcement on the
     <gcc-announce@gcc.gnu.org> mailing list.
   * The front end's manuals should be mentioned in
     'maintainer-scripts/update_web_docs_svn' (*note Texinfo Manuals::)
     and the online manuals should be linked to from
     'onlinedocs/index.html'.
   * Any old releases or CVS repositories of the front end, before its
     inclusion in GCC, should be made available on the GCC FTP site
     <ftp://gcc.gnu.org/pub/gcc/old-releases/>.
   * The release and snapshot script 'maintainer-scripts/gcc_release'
     should be updated to generate appropriate tarballs for this front
     end.
   * If this front end includes its own version files that include the
     current date, 'maintainer-scripts/update_version' should be updated
     accordingly.

* Menu:

* Front End Directory::  The front end 'LANGUAGE' directory.
* Front End Config::     The front end 'config-lang.in' file.
* Front End Makefile::   The front end 'Make-lang.in' file.


File: gccint.info,  Node: Front End Directory,  Next: Front End Config,  Up: Front End

6.3.8.1 The Front End 'LANGUAGE' Directory
..........................................

A front end 'LANGUAGE' directory contains the source files of that front
end (but not of any runtime libraries, which should be outside the 'gcc'
directory).  This includes documentation, and possibly some subsidiary
programs built alongside the front end.  Certain files are special and
other parts of the compiler depend on their names:

'config-lang.in'
     This file is required in all language subdirectories.  *Note The
     Front End 'config-lang.in' File: Front End Config, for details of
     its contents
'Make-lang.in'
     This file is required in all language subdirectories.  *Note The
     Front End 'Make-lang.in' File: Front End Makefile, for details of
     its contents.
'lang.opt'
     This file registers the set of switches that the front end accepts
     on the command line, and their '--help' text.  *Note Options::.
'lang-specs.h'
     This file provides entries for 'default_compilers' in 'gcc.c' which
     override the default of giving an error that a compiler for that
     language is not installed.
'LANGUAGE-tree.def'
     This file, which need not exist, defines any language-specific tree
     codes.


File: gccint.info,  Node: Front End Config,  Next: Front End Makefile,  Prev: Front End Directory,  Up: Front End

6.3.8.2 The Front End 'config-lang.in' File
...........................................

Each language subdirectory contains a 'config-lang.in' file.  This file
is a shell script that may define some variables describing the
language:

'language'
     This definition must be present, and gives the name of the language
     for some purposes such as arguments to '--enable-languages'.
'lang_requires'
     If defined, this variable lists (space-separated) language front
     ends other than C that this front end requires to be enabled (with
     the names given being their 'language' settings).  For example, the
     Java front end depends on the C++ front end, so sets
     'lang_requires=c++'.
'subdir_requires'
     If defined, this variable lists (space-separated) front end
     directories other than C that this front end requires to be
     present.  For example, the Objective-C++ front end uses source
     files from the C++ and Objective-C front ends, so sets
     'subdir_requires="cp objc"'.
'target_libs'
     If defined, this variable lists (space-separated) targets in the
     top level 'Makefile' to build the runtime libraries for this
     language, such as 'target-libobjc'.
'lang_dirs'
     If defined, this variable lists (space-separated) top level
     directories (parallel to 'gcc'), apart from the runtime libraries,
     that should not be configured if this front end is not built.
'build_by_default'
     If defined to 'no', this language front end is not built unless
     enabled in a '--enable-languages' argument.  Otherwise, front ends
     are built by default, subject to any special logic in
     'configure.ac' (as is present to disable the Ada front end if the
     Ada compiler is not already installed).
'boot_language'
     If defined to 'yes', this front end is built in stage1 of the
     bootstrap.  This is only relevant to front ends written in their
     own languages.
'compilers'
     If defined, a space-separated list of compiler executables that
     will be run by the driver.  The names here will each end with
     '\$(exeext)'.
'outputs'
     If defined, a space-separated list of files that should be
     generated by 'configure' substituting values in them.  This
     mechanism can be used to create a file 'LANGUAGE/Makefile' from
     'LANGUAGE/Makefile.in', but this is deprecated, building everything
     from the single 'gcc/Makefile' is preferred.
'gtfiles'
     If defined, a space-separated list of files that should be scanned
     by 'gengtype.c' to generate the garbage collection tables and
     routines for this language.  This excludes the files that are
     common to all front ends.  *Note Type Information::.


File: gccint.info,  Node: Front End Makefile,  Prev: Front End Config,  Up: Front End

6.3.8.3 The Front End 'Make-lang.in' File
.........................................

Each language subdirectory contains a 'Make-lang.in' file.  It contains
targets 'LANG.HOOK' (where 'LANG' is the setting of 'language' in
'config-lang.in') for the following values of 'HOOK', and any other
Makefile rules required to build those targets (which may if necessary
use other Makefiles specified in 'outputs' in 'config-lang.in', although
this is deprecated).  It also adds any testsuite targets that can use
the standard rule in 'gcc/Makefile.in' to the variable 'lang_checks'.

'all.cross'
'start.encap'
'rest.encap'
     FIXME: exactly what goes in each of these targets?
'tags'
     Build an 'etags' 'TAGS' file in the language subdirectory in the
     source tree.
'info'
     Build info documentation for the front end, in the build directory.
     This target is only called by 'make bootstrap' if a suitable
     version of 'makeinfo' is available, so does not need to check for
     this, and should fail if an error occurs.
'dvi'
     Build DVI documentation for the front end, in the build directory.
     This should be done using '$(TEXI2DVI)', with appropriate '-I'
     arguments pointing to directories of included files.
'pdf'
     Build PDF documentation for the front end, in the build directory.
     This should be done using '$(TEXI2PDF)', with appropriate '-I'
     arguments pointing to directories of included files.
'html'
     Build HTML documentation for the front end, in the build directory.
'man'
     Build generated man pages for the front end from Texinfo manuals
     (*note Man Page Generation::), in the build directory.  This target
     is only called if the necessary tools are available, but should
     ignore errors so as not to stop the build if errors occur; man
     pages are optional and the tools involved may be installed in a
     broken way.
'install-common'
     Install everything that is part of the front end, apart from the
     compiler executables listed in 'compilers' in 'config-lang.in'.
'install-info'
     Install info documentation for the front end, if it is present in
     the source directory.  This target should have dependencies on info
     files that should be installed.
'install-man'
     Install man pages for the front end.  This target should ignore
     errors.
'install-plugin'
     Install headers needed for plugins.
'srcextra'
     Copies its dependencies into the source directory.  This generally
     should be used for generated files such as Bison output files which
     are not version-controlled, but should be included in any release
     tarballs.  This target will be executed during a bootstrap if
     '--enable-generated-files-in-srcdir' was specified as a 'configure'
     option.
'srcinfo'
'srcman'
     Copies its dependencies into the source directory.  These targets
     will be executed during a bootstrap if
     '--enable-generated-files-in-srcdir' was specified as a 'configure'
     option.
'uninstall'
     Uninstall files installed by installing the compiler.  This is
     currently documented not to be supported, so the hook need not do
     anything.
'mostlyclean'
'clean'
'distclean'
'maintainer-clean'
     The language parts of the standard GNU '*clean' targets.  *Note
     Standard Targets for Users: (standards)Standard Targets, for
     details of the standard targets.  For GCC, 'maintainer-clean'
     should delete all generated files in the source directory that are
     not version-controlled, but should not delete anything that is.

 'Make-lang.in' must also define a variable 'LANG_OBJS' to a list of
host object files that are used by that language.


File: gccint.info,  Node: Back End,  Prev: Front End,  Up: gcc Directory

6.3.9 Anatomy of a Target Back End
----------------------------------

A back end for a target architecture in GCC has the following parts:

   * A directory 'MACHINE' under 'gcc/config', containing a machine
     description 'MACHINE.md' file (*note Machine Descriptions: Machine
     Desc.), header files 'MACHINE.h' and 'MACHINE-protos.h' and a
     source file 'MACHINE.c' (*note Target Description Macros and
     Functions: Target Macros.), possibly a target Makefile fragment
     't-MACHINE' (*note The Target Makefile Fragment: Target Fragment.),
     and maybe some other files.  The names of these files may be
     changed from the defaults given by explicit specifications in
     'config.gcc'.
   * If necessary, a file 'MACHINE-modes.def' in the 'MACHINE'
     directory, containing additional machine modes to represent
     condition codes.  *Note Condition Code::, for further details.
   * An optional 'MACHINE.opt' file in the 'MACHINE' directory,
     containing a list of target-specific options.  You can also add
     other option files using the 'extra_options' variable in
     'config.gcc'.  *Note Options::.
   * Entries in 'config.gcc' (*note The 'config.gcc' File: System
     Config.) for the systems with this target architecture.
   * Documentation in 'gcc/doc/invoke.texi' for any command-line options
     supported by this target (*note Run-time Target Specification:
     Run-time Target.).  This means both entries in the summary table of
     options and details of the individual options.
   * Documentation in 'gcc/doc/extend.texi' for any target-specific
     attributes supported (*note Defining target-specific uses of
     '__attribute__': Target Attributes.), including where the same
     attribute is already supported on some targets, which are
     enumerated in the manual.
   * Documentation in 'gcc/doc/extend.texi' for any target-specific
     pragmas supported.
   * Documentation in 'gcc/doc/extend.texi' of any target-specific
     built-in functions supported.
   * Documentation in 'gcc/doc/extend.texi' of any target-specific
     format checking styles supported.
   * Documentation in 'gcc/doc/md.texi' of any target-specific
     constraint letters (*note Constraints for Particular Machines:
     Machine Constraints.).
   * A note in 'gcc/doc/contrib.texi' under the person or people who
     contributed the target support.
   * Entries in 'gcc/doc/install.texi' for all target triplets supported
     with this target architecture, giving details of any special notes
     about installation for this target, or saying that there are no
     special notes if there are none.
   * Possibly other support outside the 'gcc' directory for runtime
     libraries.  FIXME: reference docs for this.  The 'libstdc++'
     porting manual needs to be installed as info for this to work, or
     to be a chapter of this manual.

 If the back end is added to the official GCC source repository, the
following are also necessary:

   * An entry for the target architecture in 'readings.html' on the GCC
     web site, with any relevant links.
   * Details of the properties of the back end and target architecture
     in 'backends.html' on the GCC web site.
   * A news item about the contribution of support for that target
     architecture, in 'index.html' on the GCC web site.
   * Normally, one or more maintainers of that target listed in
     'MAINTAINERS'.  Some existing architectures may be unmaintained,
     but it would be unusual to add support for a target that does not
     have a maintainer when support is added.
   * Target triplets covering all 'config.gcc' stanzas for the target,
     in the list in 'contrib/config-list.mk'.


File: gccint.info,  Node: Testsuites,  Next: Options,  Prev: Source Tree,  Up: Top

7 Testsuites
************

GCC contains several testsuites to help maintain compiler quality.  Most
of the runtime libraries and language front ends in GCC have testsuites.
Currently only the C language testsuites are documented here; FIXME:
document the others.

* Menu:

* Test Idioms::     Idioms used in testsuite code.
* Test Directives:: Directives used within DejaGnu tests.
* Ada Tests::       The Ada language testsuites.
* C Tests::         The C language testsuites.
* libgcj Tests::    The Java library testsuites.
* LTO Testing::     Support for testing link-time optimizations.
* gcov Testing::    Support for testing gcov.
* profopt Testing:: Support for testing profile-directed optimizations.
* compat Testing::  Support for testing binary compatibility.
* Torture Tests::   Support for torture testing using multiple options.


File: gccint.info,  Node: Test Idioms,  Next: Test Directives,  Up: Testsuites

7.1 Idioms Used in Testsuite Code
=================================

In general, C testcases have a trailing '-N.c', starting with '-1.c', in
case other testcases with similar names are added later.  If the test is
a test of some well-defined feature, it should have a name referring to
that feature such as 'FEATURE-1.c'.  If it does not test a well-defined
feature but just happens to exercise a bug somewhere in the compiler,
and a bug report has been filed for this bug in the GCC bug database,
'prBUG-NUMBER-1.c' is the appropriate form of name.  Otherwise (for
miscellaneous bugs not filed in the GCC bug database), and previously
more generally, test cases are named after the date on which they were
added.  This allows people to tell at a glance whether a test failure is
because of a recently found bug that has not yet been fixed, or whether
it may be a regression, but does not give any other information about
the bug or where discussion of it may be found.  Some other language
testsuites follow similar conventions.

 In the 'gcc.dg' testsuite, it is often necessary to test that an error
is indeed a hard error and not just a warning--for example, where it is
a constraint violation in the C standard, which must become an error
with '-pedantic-errors'.  The following idiom, where the first line
shown is line LINE of the file and the line that generates the error, is
used for this:

     /* { dg-bogus "warning" "warning in place of error" } */
     /* { dg-error "REGEXP" "MESSAGE" { target *-*-* } LINE } */

 It may be necessary to check that an expression is an integer constant
expression and has a certain value.  To check that 'E' has value 'V', an
idiom similar to the following is used:

     char x[((E) == (V) ? 1 : -1)];

 In 'gcc.dg' tests, '__typeof__' is sometimes used to make assertions
about the types of expressions.  See, for example,
'gcc.dg/c99-condexpr-1.c'.  The more subtle uses depend on the exact
rules for the types of conditional expressions in the C standard; see,
for example, 'gcc.dg/c99-intconst-1.c'.

 It is useful to be able to test that optimizations are being made
properly.  This cannot be done in all cases, but it can be done where
the optimization will lead to code being optimized away (for example,
where flow analysis or alias analysis should show that certain code
cannot be called) or to functions not being called because they have
been expanded as built-in functions.  Such tests go in
'gcc.c-torture/execute'.  Where code should be optimized away, a call to
a nonexistent function such as 'link_failure ()' may be inserted; a
definition

     #ifndef __OPTIMIZE__
     void
     link_failure (void)
     {
       abort ();
     }
     #endif

will also be needed so that linking still succeeds when the test is run
without optimization.  When all calls to a built-in function should have
been optimized and no calls to the non-built-in version of the function
should remain, that function may be defined as 'static' to call 'abort
()' (although redeclaring a function as static may not work on all
targets).

 All testcases must be portable.  Target-specific testcases must have
appropriate code to avoid causing failures on unsupported systems;
unfortunately, the mechanisms for this differ by directory.

 FIXME: discuss non-C testsuites here.


File: gccint.info,  Node: Test Directives,  Next: Ada Tests,  Prev: Test Idioms,  Up: Testsuites

7.2 Directives used within DejaGnu tests
========================================

* Menu:

* Directives::  Syntax and descriptions of test directives.
* Selectors:: Selecting targets to which a test applies.
* Effective-Target Keywords:: Keywords describing target attributes.
* Add Options:: Features for 'dg-add-options'
* Require Support:: Variants of 'dg-require-SUPPORT'
* Final Actions:: Commands for use in 'dg-final'


File: gccint.info,  Node: Directives,  Next: Selectors,  Up: Test Directives

7.2.1 Syntax and Descriptions of test directives
------------------------------------------------

Test directives appear within comments in a test source file and begin
with 'dg-'.  Some of these are defined within DejaGnu and others are
local to the GCC testsuite.

 The order in which test directives appear in a test can be important:
directives local to GCC sometimes override information used by the
DejaGnu directives, which know nothing about the GCC directives, so the
DejaGnu directives must precede GCC directives.

 Several test directives include selectors (*note Selectors::) which are
usually preceded by the keyword 'target' or 'xfail'.

7.2.1.1 Specify how to build the test
.....................................

'{ dg-do DO-WHAT-KEYWORD [{ target/xfail SELECTOR }] }'
     DO-WHAT-KEYWORD specifies how the test is compiled and whether it
     is executed.  It is one of:

     'preprocess'
          Compile with '-E' to run only the preprocessor.
     'compile'
          Compile with '-S' to produce an assembly code file.
     'assemble'
          Compile with '-c' to produce a relocatable object file.
     'link'
          Compile, assemble, and link to produce an executable file.
     'run'
          Produce and run an executable file, which is expected to
          return an exit code of 0.

     The default is 'compile'.  That can be overridden for a set of
     tests by redefining 'dg-do-what-default' within the '.exp' file for
     those tests.

     If the directive includes the optional '{ target SELECTOR }' then
     the test is skipped unless the target system matches the SELECTOR.

     If DO-WHAT-KEYWORD is 'run' and the directive includes the optional
     '{ xfail SELECTOR }' and the selector is met then the test is
     expected to fail.  The 'xfail' clause is ignored for other values
     of DO-WHAT-KEYWORD; those tests can use directive 'dg-xfail-if'.

7.2.1.2 Specify additional compiler options
...........................................

'{ dg-options OPTIONS [{ target SELECTOR }] }'
     This DejaGnu directive provides a list of compiler options, to be
     used if the target system matches SELECTOR, that replace the
     default options used for this set of tests.

'{ dg-add-options FEATURE ... }'
     Add any compiler options that are needed to access certain
     features.  This directive does nothing on targets that enable the
     features by default, or that don't provide them at all.  It must
     come after all 'dg-options' directives.  For supported values of
     FEATURE see *note Add Options::.

'{ dg-additional-options OPTIONS [{ target SELECTOR }] }'
     This directive provides a list of compiler options, to be used if
     the target system matches SELECTOR, that are added to the default
     options used for this set of tests.

7.2.1.3 Modify the test timeout value
.....................................

The normal timeout limit, in seconds, is found by searching the
following in order:

   * the value defined by an earlier 'dg-timeout' directive in the test

   * variable TOOL_TIMEOUT defined by the set of tests

   * GCC,TIMEOUT set in the target board

   * 300

'{ dg-timeout N [{target SELECTOR }] }'
     Set the time limit for the compilation and for the execution of the
     test to the specified number of seconds.

'{ dg-timeout-factor X [{ target SELECTOR }] }'
     Multiply the normal time limit for compilation and execution of the
     test by the specified floating-point factor.

7.2.1.4 Skip a test for some targets
....................................

'{ dg-skip-if COMMENT { SELECTOR } [{ INCLUDE-OPTS } [{ EXCLUDE-OPTS }]] }'
     Arguments INCLUDE-OPTS and EXCLUDE-OPTS are lists in which each
     element is a string of zero or more GCC options.  Skip the test if
     all of the following conditions are met:
        * the test system is included in SELECTOR

        * for at least one of the option strings in INCLUDE-OPTS, every
          option from that string is in the set of options with which
          the test would be compiled; use '"*"' for an INCLUDE-OPTS list
          that matches any options; that is the default if INCLUDE-OPTS
          is not specified

        * for each of the option strings in EXCLUDE-OPTS, at least one
          option from that string is not in the set of options with
          which the test would be compiled; use '""' for an empty
          EXCLUDE-OPTS list; that is the default if EXCLUDE-OPTS is not
          specified

     For example, to skip a test if option '-Os' is present:

          /* { dg-skip-if "" { *-*-* }  { "-Os" } { "" } } */

     To skip a test if both options '-O2' and '-g' are present:

          /* { dg-skip-if "" { *-*-* }  { "-O2 -g" } { "" } } */

     To skip a test if either '-O2' or '-O3' is present:

          /* { dg-skip-if "" { *-*-* }  { "-O2" "-O3" } { "" } } */

     To skip a test unless option '-Os' is present:

          /* { dg-skip-if "" { *-*-* }  { "*" } { "-Os" } } */

     To skip a test if either '-O2' or '-O3' is used with '-g' but not
     if '-fpic' is also present:

          /* { dg-skip-if "" { *-*-* }  { "-O2 -g" "-O3 -g" } { "-fpic" } } */

'{ dg-require-effective-target KEYWORD [{ SELECTOR }] }'
     Skip the test if the test target, including current multilib flags,
     is not covered by the effective-target keyword.  If the directive
     includes the optional '{ SELECTOR }' then the effective-target test
     is only performed if the target system matches the SELECTOR.  This
     directive must appear after any 'dg-do' directive in the test and
     before any 'dg-additional-sources' directive.  *Note
     Effective-Target Keywords::.

'{ dg-require-SUPPORT args }'
     Skip the test if the target does not provide the required support.
     These directives must appear after any 'dg-do' directive in the
     test and before any 'dg-additional-sources' directive.  They
     require at least one argument, which can be an empty string if the
     specific procedure does not examine the argument.  *Note Require
     Support::, for a complete list of these directives.

7.2.1.5 Expect a test to fail for some targets
..............................................

'{ dg-xfail-if COMMENT { SELECTOR } [{ INCLUDE-OPTS } [{ EXCLUDE-OPTS }]] }'
     Expect the test to fail if the conditions (which are the same as
     for 'dg-skip-if') are met.  This does not affect the execute step.

'{ dg-xfail-run-if COMMENT { SELECTOR } [{ INCLUDE-OPTS } [{ EXCLUDE-OPTS }]] }'
     Expect the execute step of a test to fail if the conditions (which
     are the same as for 'dg-skip-if') are met.

7.2.1.6 Expect the test executable to fail
..........................................

'{ dg-shouldfail COMMENT [{ SELECTOR } [{ INCLUDE-OPTS } [{ EXCLUDE-OPTS }]]] }'
     Expect the test executable to return a nonzero exit status if the
     conditions (which are the same as for 'dg-skip-if') are met.

7.2.1.7 Verify compiler messages
................................

'{ dg-error REGEXP [COMMENT [{ target/xfail SELECTOR } [LINE] }]] }'
     This DejaGnu directive appears on a source line that is expected to
     get an error message, or else specifies the source line associated
     with the message.  If there is no message for that line or if the
     text of that message is not matched by REGEXP then the check fails
     and COMMENT is included in the 'FAIL' message.  The check does not
     look for the string 'error' unless it is part of REGEXP.

'{ dg-warning REGEXP [COMMENT [{ target/xfail SELECTOR } [LINE] }]] }'
     This DejaGnu directive appears on a source line that is expected to
     get a warning message, or else specifies the source line associated
     with the message.  If there is no message for that line or if the
     text of that message is not matched by REGEXP then the check fails
     and COMMENT is included in the 'FAIL' message.  The check does not
     look for the string 'warning' unless it is part of REGEXP.

'{ dg-message REGEXP [COMMENT [{ target/xfail SELECTOR } [LINE] }]] }'
     The line is expected to get a message other than an error or
     warning.  If there is no message for that line or if the text of
     that message is not matched by REGEXP then the check fails and
     COMMENT is included in the 'FAIL' message.

'{ dg-bogus REGEXP [COMMENT [{ target/xfail SELECTOR } [LINE] }]] }'
     This DejaGnu directive appears on a source line that should not get
     a message matching REGEXP, or else specifies the source line
     associated with the bogus message.  It is usually used with 'xfail'
     to indicate that the message is a known problem for a particular
     set of targets.

'{ dg-excess-errors COMMENT [{ target/xfail SELECTOR }] }'
     This DejaGnu directive indicates that the test is expected to fail
     due to compiler messages that are not handled by 'dg-error',
     'dg-warning' or 'dg-bogus'.  For this directive 'xfail' has the
     same effect as 'target'.

'{ dg-prune-output REGEXP }'
     Prune messages matching REGEXP from the test output.

7.2.1.8 Verify output of the test executable
............................................

'{ dg-output REGEXP [{ target/xfail SELECTOR }] }'
     This DejaGnu directive compares REGEXP to the combined output that
     the test executable writes to 'stdout' and 'stderr'.

7.2.1.9 Specify additional files for a test
...........................................

'{ dg-additional-files "FILELIST" }'
     Specify additional files, other than source files, that must be
     copied to the system where the compiler runs.

'{ dg-additional-sources "FILELIST" }'
     Specify additional source files to appear in the compile line
     following the main test file.

7.2.1.10 Add checks at the end of a test
........................................

'{ dg-final { LOCAL-DIRECTIVE } }'
     This DejaGnu directive is placed within a comment anywhere in the
     source file and is processed after the test has been compiled and
     run.  Multiple 'dg-final' commands are processed in the order in
     which they appear in the source file.  *Note Final Actions::, for a
     list of directives that can be used within 'dg-final'.


File: gccint.info,  Node: Selectors,  Next: Effective-Target Keywords,  Prev: Directives,  Up: Test Directives

7.2.2 Selecting targets to which a test applies
-----------------------------------------------

Several test directives include SELECTORs to limit the targets for which
a test is run or to declare that a test is expected to fail on
particular targets.

 A selector is:
   * one or more target triplets, possibly including wildcard
     characters; use '*-*-*' to match any target
   * a single effective-target keyword (*note Effective-Target
     Keywords::)
   * a logical expression

 Depending on the context, the selector specifies whether a test is
skipped and reported as unsupported or is expected to fail.  A context
that allows either 'target' or 'xfail' also allows '{ target SELECTOR1
xfail SELECTOR2 }' to skip the test for targets that don't match
SELECTOR1 and the test to fail for targets that match SELECTOR2.

 A selector expression appears within curly braces and uses a single
logical operator: one of '!', '&&', or '||'.  An operand is another
selector expression, an effective-target keyword, a single target
triplet, or a list of target triplets within quotes or curly braces.
For example:

     { target { ! "hppa*-*-* ia64*-*-*" } }
     { target { powerpc*-*-* && lp64 } }
     { xfail { lp64 || vect_no_align } }


File: gccint.info,  Node: Effective-Target Keywords,  Next: Add Options,  Prev: Selectors,  Up: Test Directives

7.2.3 Keywords describing target attributes
-------------------------------------------

Effective-target keywords identify sets of targets that support
particular functionality.  They are used to limit tests to be run only
for particular targets, or to specify that particular sets of targets
are expected to fail some tests.

 Effective-target keywords are defined in 'lib/target-supports.exp' in
the GCC testsuite, with the exception of those that are documented as
being local to a particular test directory.

 The 'effective target' takes into account all of the compiler options
with which the test will be compiled, including the multilib options.
By convention, keywords ending in '_nocache' can also include options
specified for the particular test in an earlier 'dg-options' or
'dg-add-options' directive.

7.2.3.1 Data type sizes
.......................

'ilp32'
     Target has 32-bit 'int', 'long', and pointers.

'lp64'
     Target has 32-bit 'int', 64-bit 'long' and pointers.

'llp64'
     Target has 32-bit 'int' and 'long', 64-bit 'long long' and
     pointers.

'double64'
     Target has 64-bit 'double'.

'double64plus'
     Target has 'double' that is 64 bits or longer.

'int32plus'
     Target has 'int' that is at 32 bits or longer.

'int16'
     Target has 'int' that is 16 bits or shorter.

'long_neq_int'
     Target has 'int' and 'long' with different sizes.

'large_double'
     Target supports 'double' that is longer than 'float'.

'large_long_double'
     Target supports 'long double' that is longer than 'double'.

'ptr32plus'
     Target has pointers that are 32 bits or longer.

'size32plus'
     Target supports array and structure sizes that are 32 bits or
     longer.

'4byte_wchar_t'
     Target has 'wchar_t' that is at least 4 bytes.

7.2.3.2 Fortran-specific attributes
...................................

'fortran_integer_16'
     Target supports Fortran 'integer' that is 16 bytes or longer.

'fortran_large_int'
     Target supports Fortran 'integer' kinds larger than 'integer(8)'.

'fortran_large_real'
     Target supports Fortran 'real' kinds larger than 'real(8)'.

7.2.3.3 Vector-specific attributes
..................................

'vect_condition'
     Target supports vector conditional operations.

'vect_double'
     Target supports hardware vectors of 'double'.

'vect_float'
     Target supports hardware vectors of 'float'.

'vect_int'
     Target supports hardware vectors of 'int'.

'vect_long'
     Target supports hardware vectors of 'long'.

'vect_long_long'
     Target supports hardware vectors of 'long long'.

'vect_aligned_arrays'
     Target aligns arrays to vector alignment boundary.

'vect_hw_misalign'
     Target supports a vector misalign access.

'vect_no_align'
     Target does not support a vector alignment mechanism.

'vect_no_int_max'
     Target does not support a vector max instruction on 'int'.

'vect_no_int_add'
     Target does not support a vector add instruction on 'int'.

'vect_no_bitwise'
     Target does not support vector bitwise instructions.

'vect_char_mult'
     Target supports 'vector char' multiplication.

'vect_short_mult'
     Target supports 'vector short' multiplication.

'vect_int_mult'
     Target supports 'vector int' multiplication.

'vect_extract_even_odd'
     Target supports vector even/odd element extraction.

'vect_extract_even_odd_wide'
     Target supports vector even/odd element extraction of vectors with
     elements 'SImode' or larger.

'vect_interleave'
     Target supports vector interleaving.

'vect_strided'
     Target supports vector interleaving and extract even/odd.

'vect_strided_wide'
     Target supports vector interleaving and extract even/odd for wide
     element types.

'vect_perm'
     Target supports vector permutation.

'vect_shift'
     Target supports a hardware vector shift operation.

'vect_widen_sum_hi_to_si'
     Target supports a vector widening summation of 'short' operands
     into 'int' results, or can promote (unpack) from 'short' to 'int'.

'vect_widen_sum_qi_to_hi'
     Target supports a vector widening summation of 'char' operands into
     'short' results, or can promote (unpack) from 'char' to 'short'.

'vect_widen_sum_qi_to_si'
     Target supports a vector widening summation of 'char' operands into
     'int' results.

'vect_widen_mult_qi_to_hi'
     Target supports a vector widening multiplication of 'char' operands
     into 'short' results, or can promote (unpack) from 'char' to
     'short' and perform non-widening multiplication of 'short'.

'vect_widen_mult_hi_to_si'
     Target supports a vector widening multiplication of 'short'
     operands into 'int' results, or can promote (unpack) from 'short'
     to 'int' and perform non-widening multiplication of 'int'.

'vect_sdot_qi'
     Target supports a vector dot-product of 'signed char'.

'vect_udot_qi'
     Target supports a vector dot-product of 'unsigned char'.

'vect_sdot_hi'
     Target supports a vector dot-product of 'signed short'.

'vect_udot_hi'
     Target supports a vector dot-product of 'unsigned short'.

'vect_pack_trunc'
     Target supports a vector demotion (packing) of 'short' to 'char'
     and from 'int' to 'short' using modulo arithmetic.

'vect_unpack'
     Target supports a vector promotion (unpacking) of 'char' to 'short'
     and from 'char' to 'int'.

'vect_intfloat_cvt'
     Target supports conversion from 'signed int' to 'float'.

'vect_uintfloat_cvt'
     Target supports conversion from 'unsigned int' to 'float'.

'vect_floatint_cvt'
     Target supports conversion from 'float' to 'signed int'.

'vect_floatuint_cvt'
     Target supports conversion from 'float' to 'unsigned int'.

7.2.3.4 Thread Local Storage attributes
.......................................

'tls'
     Target supports thread-local storage.

'tls_native'
     Target supports native (rather than emulated) thread-local storage.

'tls_runtime'
     Test system supports executing TLS executables.

7.2.3.5 Decimal floating point attributes
.........................................

'dfp'
     Targets supports compiling decimal floating point extension to C.

'dfp_nocache'
     Including the options used to compile this particular test, the
     target supports compiling decimal floating point extension to C.

'dfprt'
     Test system can execute decimal floating point tests.

'dfprt_nocache'
     Including the options used to compile this particular test, the
     test system can execute decimal floating point tests.

'hard_dfp'
     Target generates decimal floating point instructions with current
     options.

7.2.3.6 ARM-specific attributes
...............................

'arm32'
     ARM target generates 32-bit code.

'arm_eabi'
     ARM target adheres to the ABI for the ARM Architecture.

'arm_hf_eabi'
     ARM target adheres to the VFP and Advanced SIMD Register Arguments
     variant of the ABI for the ARM Architecture (as selected with
     '-mfloat-abi=hard').

'arm_hard_vfp_ok'
     ARM target supports '-mfpu=vfp -mfloat-abi=hard'.  Some multilibs
     may be incompatible with these options.

'arm_iwmmxt_ok'
     ARM target supports '-mcpu=iwmmxt'.  Some multilibs may be
     incompatible with this option.

'arm_neon'
     ARM target supports generating NEON instructions.

'arm_neon_hw'
     Test system supports executing NEON instructions.

'arm_neonv2_hw'
     Test system supports executing NEON v2 instructions.

'arm_neon_ok'
     ARM Target supports '-mfpu=neon -mfloat-abi=softfp' or compatible
     options.  Some multilibs may be incompatible with these options.

'arm_neonv2_ok'
     ARM Target supports '-mfpu=neon-vfpv4 -mfloat-abi=softfp' or
     compatible options.  Some multilibs may be incompatible with these
     options.

'arm_neon_fp16_ok'
     ARM Target supports '-mfpu=neon-fp16 -mfloat-abi=softfp' or
     compatible options.  Some multilibs may be incompatible with these
     options.

'arm_thumb1_ok'
     ARM target generates Thumb-1 code for '-mthumb'.

'arm_thumb2_ok'
     ARM target generates Thumb-2 code for '-mthumb'.

'arm_vfp_ok'
     ARM target supports '-mfpu=vfp -mfloat-abi=softfp'.  Some multilibs
     may be incompatible with these options.

'arm_v8_vfp_ok'
     ARM target supports '-mfpu=fp-armv8 -mfloat-abi=softfp'.  Some
     multilibs may be incompatible with these options.

'arm_v8_neon_ok'
     ARM target supports '-mfpu=neon-fp-armv8 -mfloat-abi=softfp'.  Some
     multilibs may be incompatible with these options.

'arm_prefer_ldrd_strd'
     ARM target prefers 'LDRD' and 'STRD' instructions over 'LDM' and
     'STM' instructions.

7.2.3.7 MIPS-specific attributes
................................

'mips64'
     MIPS target supports 64-bit instructions.

'nomips16'
     MIPS target does not produce MIPS16 code.

'mips16_attribute'
     MIPS target can generate MIPS16 code.

'mips_loongson'
     MIPS target is a Loongson-2E or -2F target using an ABI that
     supports the Loongson vector modes.

'mips_newabi_large_long_double'
     MIPS target supports 'long double' larger than 'double' when using
     the new ABI.

'mpaired_single'
     MIPS target supports '-mpaired-single'.

7.2.3.8 PowerPC-specific attributes
...................................

'dfp_hw'
     PowerPC target supports executing hardware DFP instructions.

'p8vector_hw'
     PowerPC target supports executing VSX instructions (ISA 2.07).

'powerpc64'
     Test system supports executing 64-bit instructions.

'powerpc_altivec'
     PowerPC target supports AltiVec.

'powerpc_altivec_ok'
     PowerPC target supports '-maltivec'.

'powerpc_eabi_ok'
     PowerPC target supports '-meabi'.

'powerpc_elfv2'
     PowerPC target supports '-mabi=elfv2'.

'powerpc_fprs'
     PowerPC target supports floating-point registers.

'powerpc_hard_double'
     PowerPC target supports hardware double-precision floating-point.

'powerpc_htm_ok'
     PowerPC target supports '-mhtm'

'powerpc_p8vector_ok'
     PowerPC target supports '-mpower8-vector'

'powerpc_ppu_ok'
     PowerPC target supports '-mcpu=cell'.

'powerpc_spe'
     PowerPC target supports PowerPC SPE.

'powerpc_spe_nocache'
     Including the options used to compile this particular test, the
     PowerPC target supports PowerPC SPE.

'powerpc_spu'
     PowerPC target supports PowerPC SPU.

'powerpc_vsx_ok'
     PowerPC target supports '-mvsx'.

'powerpc_405_nocache'
     Including the options used to compile this particular test, the
     PowerPC target supports PowerPC 405.

'ppc_recip_hw'
     PowerPC target supports executing reciprocal estimate instructions.

'spu_auto_overlay'
     SPU target has toolchain that supports automatic overlay
     generation.

'vmx_hw'
     PowerPC target supports executing AltiVec instructions.

'vsx_hw'
     PowerPC target supports executing VSX instructions (ISA 2.06).

7.2.3.9 Other hardware attributes
.................................

'avx'
     Target supports compiling 'avx' instructions.

'avx_runtime'
     Target supports the execution of 'avx' instructions.

'cell_hw'
     Test system can execute AltiVec and Cell PPU instructions.

'coldfire_fpu'
     Target uses a ColdFire FPU.

'hard_float'
     Target supports FPU instructions.

'sse'
     Target supports compiling 'sse' instructions.

'sse_runtime'
     Target supports the execution of 'sse' instructions.

'sse2'
     Target supports compiling 'sse2' instructions.

'sse2_runtime'
     Target supports the execution of 'sse2' instructions.

'sync_char_short'
     Target supports atomic operations on 'char' and 'short'.

'sync_int_long'
     Target supports atomic operations on 'int' and 'long'.

'ultrasparc_hw'
     Test environment appears to run executables on a simulator that
     accepts only 'EM_SPARC' executables and chokes on 'EM_SPARC32PLUS'
     or 'EM_SPARCV9' executables.

'vect_cmdline_needed'
     Target requires a command line argument to enable a SIMD
     instruction set.

7.2.3.10 Environment attributes
...............................

'c'
     The language for the compiler under test is C.

'c++'
     The language for the compiler under test is C++.

'c99_runtime'
     Target provides a full C99 runtime.

'correct_iso_cpp_string_wchar_protos'
     Target 'string.h' and 'wchar.h' headers provide C++ required
     overloads for 'strchr' etc.  functions.

'dummy_wcsftime'
     Target uses a dummy 'wcsftime' function that always returns zero.

'fd_truncate'
     Target can truncate a file from a file descriptor, as used by
     'libgfortran/io/unix.c:fd_truncate'; i.e.  'ftruncate' or 'chsize'.

'freestanding'
     Target is 'freestanding' as defined in section 4 of the C99
     standard.  Effectively, it is a target which supports no extra
     headers or libraries other than what is considered essential.

'init_priority'
     Target supports constructors with initialization priority
     arguments.

'inttypes_types'
     Target has the basic signed and unsigned types in 'inttypes.h'.
     This is for tests that GCC's notions of these types agree with
     those in the header, as some systems have only 'inttypes.h'.

'lax_strtofp'
     Target might have errors of a few ULP in string to floating-point
     conversion functions and overflow is not always detected correctly
     by those functions.

'mmap'
     Target supports 'mmap'.

'newlib'
     Target supports Newlib.

'pow10'
     Target provides 'pow10' function.

'pthread'
     Target can compile using 'pthread.h' with no errors or warnings.

'pthread_h'
     Target has 'pthread.h'.

'run_expensive_tests'
     Expensive testcases (usually those that consume excessive amounts
     of CPU time) should be run on this target.  This can be enabled by
     setting the 'GCC_TEST_RUN_EXPENSIVE' environment variable to a
     non-empty string.

'simulator'
     Test system runs executables on a simulator (i.e.  slowly) rather
     than hardware (i.e.  fast).

'stdint_types'
     Target has the basic signed and unsigned C types in 'stdint.h'.
     This will be obsolete when GCC ensures a working 'stdint.h' for all
     targets.

'trampolines'
     Target supports trampolines.

'uclibc'
     Target supports uClibc.

'unwrapped'
     Target does not use a status wrapper.

'vxworks_kernel'
     Target is a VxWorks kernel.

'vxworks_rtp'
     Target is a VxWorks RTP.

'wchar'
     Target supports wide characters.

7.2.3.11 Other attributes
.........................

'automatic_stack_alignment'
     Target supports automatic stack alignment.

'cxa_atexit'
     Target uses '__cxa_atexit'.

'default_packed'
     Target has packed layout of structure members by default.

'fgraphite'
     Target supports Graphite optimizations.

'fixed_point'
     Target supports fixed-point extension to C.

'fopenmp'
     Target supports OpenMP via '-fopenmp'.

'fpic'
     Target supports '-fpic' and '-fPIC'.

'freorder'
     Target supports '-freorder-blocks-and-partition'.

'fstack_protector'
     Target supports '-fstack-protector'.

'gas'
     Target uses GNU 'as'.

'gc_sections'
     Target supports '--gc-sections'.

'gld'
     Target uses GNU 'ld'.

'keeps_null_pointer_checks'
     Target keeps null pointer checks, either due to the use of
     '-fno-delete-null-pointer-checks' or hardwired into the target.

'lto'
     Compiler has been configured to support link-time optimization
     (LTO).

'naked_functions'
     Target supports the 'naked' function attribute.

'named_sections'
     Target supports named sections.

'natural_alignment_32'
     Target uses natural alignment (aligned to type size) for types of
     32 bits or less.

'target_natural_alignment_64'
     Target uses natural alignment (aligned to type size) for types of
     64 bits or less.

'nonpic'
     Target does not generate PIC by default.

'pcc_bitfield_type_matters'
     Target defines 'PCC_BITFIELD_TYPE_MATTERS'.

'pe_aligned_commons'
     Target supports '-mpe-aligned-commons'.

'pie'
     Target supports '-pie', '-fpie' and '-fPIE'.

'section_anchors'
     Target supports section anchors.

'short_enums'
     Target defaults to short enums.

'static'
     Target supports '-static'.

'static_libgfortran'
     Target supports statically linking 'libgfortran'.

'string_merging'
     Target supports merging string constants at link time.

'ucn'
     Target supports compiling and assembling UCN.

'ucn_nocache'
     Including the options used to compile this particular test, the
     target supports compiling and assembling UCN.

'unaligned_stack'
     Target does not guarantee that its 'STACK_BOUNDARY' is greater than
     or equal to the required vector alignment.

'vector_alignment_reachable'
     Vector alignment is reachable for types of 32 bits or less.

'vector_alignment_reachable_for_64bit'
     Vector alignment is reachable for types of 64 bits or less.

'wchar_t_char16_t_compatible'
     Target supports 'wchar_t' that is compatible with 'char16_t'.

'wchar_t_char32_t_compatible'
     Target supports 'wchar_t' that is compatible with 'char32_t'.

7.2.3.12 Local to tests in 'gcc.target/i386'
............................................

'3dnow'
     Target supports compiling '3dnow' instructions.

'aes'
     Target supports compiling 'aes' instructions.

'fma4'
     Target supports compiling 'fma4' instructions.

'ms_hook_prologue'
     Target supports attribute 'ms_hook_prologue'.

'pclmul'
     Target supports compiling 'pclmul' instructions.

'sse3'
     Target supports compiling 'sse3' instructions.

'sse4'
     Target supports compiling 'sse4' instructions.

'sse4a'
     Target supports compiling 'sse4a' instructions.

'ssse3'
     Target supports compiling 'ssse3' instructions.

'vaes'
     Target supports compiling 'vaes' instructions.

'vpclmul'
     Target supports compiling 'vpclmul' instructions.

'xop'
     Target supports compiling 'xop' instructions.

7.2.3.13 Local to tests in 'gcc.target/spu/ea'
..............................................

'ealib'
     Target '__ea' library functions are available.

7.2.3.14 Local to tests in 'gcc.test-framework'
...............................................

'no'
     Always returns 0.

'yes'
     Always returns 1.


File: gccint.info,  Node: Add Options,  Next: Require Support,  Prev: Effective-Target Keywords,  Up: Test Directives

7.2.4 Features for 'dg-add-options'
-----------------------------------

The supported values of FEATURE for directive 'dg-add-options' are:

'arm_neon'
     NEON support.  Only ARM targets support this feature, and only then
     in certain modes; see the *note arm_neon_ok effective target
     keyword: arm_neon_ok.

'arm_neon_fp16'
     NEON and half-precision floating point support.  Only ARM targets
     support this feature, and only then in certain modes; see the *note
     arm_neon_fp16_ok effective target keyword: arm_neon_ok.

'bind_pic_locally'
     Add the target-specific flags needed to enable functions to bind
     locally when using pic/PIC passes in the testsuite.

'c99_runtime'
     Add the target-specific flags needed to access the C99 runtime.

'ieee'
     Add the target-specific flags needed to enable full IEEE compliance
     mode.

'mips16_attribute'
     'mips16' function attributes.  Only MIPS targets support this
     feature, and only then in certain modes.

'tls'
     Add the target-specific flags needed to use thread-local storage.


File: gccint.info,  Node: Require Support,  Next: Final Actions,  Prev: Add Options,  Up: Test Directives

7.2.5 Variants of 'dg-require-SUPPORT'
--------------------------------------

A few of the 'dg-require' directives take arguments.

'dg-require-iconv CODESET'
     Skip the test if the target does not support iconv.  CODESET is the
     codeset to convert to.

'dg-require-profiling PROFOPT'
     Skip the test if the target does not support profiling with option
     PROFOPT.

'dg-require-visibility VIS'
     Skip the test if the target does not support the 'visibility'
     attribute.  If VIS is '""', support for 'visibility("hidden")' is
     checked, for 'visibility("VIS")' otherwise.

 The original 'dg-require' directives were defined before there was
support for effective-target keywords.  The directives that do not take
arguments could be replaced with effective-target keywords.

'dg-require-alias ""'
     Skip the test if the target does not support the 'alias' attribute.

'dg-require-ascii-locale ""'
     Skip the test if the host does not support an ASCII locale.

'dg-require-compat-dfp ""'
     Skip this test unless both compilers in a 'compat' testsuite
     support decimal floating point.

'dg-require-cxa-atexit ""'
     Skip the test if the target does not support '__cxa_atexit'.  This
     is equivalent to 'dg-require-effective-target cxa_atexit'.

'dg-require-dll ""'
     Skip the test if the target does not support DLL attributes.

'dg-require-fork ""'
     Skip the test if the target does not support 'fork'.

'dg-require-gc-sections ""'
     Skip the test if the target's linker does not support the
     '--gc-sections' flags.  This is equivalent to
     'dg-require-effective-target gc-sections'.

'dg-require-host-local ""'
     Skip the test if the host is remote, rather than the same as the
     build system.  Some tests are incompatible with DejaGnu's handling
     of remote hosts, which involves copying the source file to the host
     and compiling it with a relative path and "'-o a.out'".

'dg-require-mkfifo ""'
     Skip the test if the target does not support 'mkfifo'.

'dg-require-named-sections ""'
     Skip the test is the target does not support named sections.  This
     is equivalent to 'dg-require-effective-target named_sections'.

'dg-require-weak ""'
     Skip the test if the target does not support weak symbols.

'dg-require-weak-override ""'
     Skip the test if the target does not support overriding weak
     symbols.


File: gccint.info,  Node: Final Actions,  Prev: Require Support,  Up: Test Directives

7.2.6 Commands for use in 'dg-final'
------------------------------------

The GCC testsuite defines the following directives to be used within
'dg-final'.

7.2.6.1 Scan a particular file
..............................

'scan-file FILENAME REGEXP [{ target/xfail SELECTOR }]'
     Passes if REGEXP matches text in FILENAME.
'scan-file-not FILENAME REGEXP [{ target/xfail SELECTOR }]'
     Passes if REGEXP does not match text in FILENAME.
'scan-module MODULE REGEXP [{ target/xfail SELECTOR }]'
     Passes if REGEXP matches in Fortran module MODULE.

7.2.6.2 Scan the assembly output
................................

'scan-assembler REGEX [{ target/xfail SELECTOR }]'
     Passes if REGEX matches text in the test's assembler output.

'scan-assembler-not REGEX [{ target/xfail SELECTOR }]'
     Passes if REGEX does not match text in the test's assembler output.

'scan-assembler-times REGEX NUM [{ target/xfail SELECTOR }]'
     Passes if REGEX is matched exactly NUM times in the test's
     assembler output.

'scan-assembler-dem REGEX [{ target/xfail SELECTOR }]'
     Passes if REGEX matches text in the test's demangled assembler
     output.

'scan-assembler-dem-not REGEX [{ target/xfail SELECTOR }]'
     Passes if REGEX does not match text in the test's demangled
     assembler output.

'scan-hidden SYMBOL [{ target/xfail SELECTOR }]'
     Passes if SYMBOL is defined as a hidden symbol in the test's
     assembly output.

'scan-not-hidden SYMBOL [{ target/xfail SELECTOR }]'
     Passes if SYMBOL is not defined as a hidden symbol in the test's
     assembly output.

7.2.6.3 Scan optimization dump files
....................................

These commands are available for KIND of 'tree', 'rtl', and 'ipa'.

'scan-KIND-dump REGEX SUFFIX [{ target/xfail SELECTOR }]'
     Passes if REGEX matches text in the dump file with suffix SUFFIX.

'scan-KIND-dump-not REGEX SUFFIX [{ target/xfail SELECTOR }]'
     Passes if REGEX does not match text in the dump file with suffix
     SUFFIX.

'scan-KIND-dump-times REGEX NUM SUFFIX [{ target/xfail SELECTOR }]'
     Passes if REGEX is found exactly NUM times in the dump file with
     suffix SUFFIX.

'scan-KIND-dump-dem REGEX SUFFIX [{ target/xfail SELECTOR }]'
     Passes if REGEX matches demangled text in the dump file with suffix
     SUFFIX.

'scan-KIND-dump-dem-not REGEX SUFFIX [{ target/xfail SELECTOR }]'
     Passes if REGEX does not match demangled text in the dump file with
     suffix SUFFIX.

7.2.6.4 Verify that an output files exists or not
.................................................

'output-exists [{ target/xfail SELECTOR }]'
     Passes if compiler output file exists.

'output-exists-not [{ target/xfail SELECTOR }]'
     Passes if compiler output file does not exist.

7.2.6.5 Check for LTO tests
...........................

'scan-symbol REGEXP [{ target/xfail SELECTOR }]'
     Passes if the pattern is present in the final executable.

7.2.6.6 Checks for 'gcov' tests
...............................

'run-gcov SOURCEFILE'
     Check line counts in 'gcov' tests.

'run-gcov [branches] [calls] { OPTS SOURCEFILE }'
     Check branch and/or call counts, in addition to line counts, in
     'gcov' tests.

7.2.6.7 Clean up generated test files
.....................................

'cleanup-coverage-files'
     Removes coverage data files generated for this test.

'cleanup-ipa-dump SUFFIX'
     Removes IPA dump files generated for this test.

'cleanup-modules "LIST-OF-EXTRA-MODULES"'
     Removes Fortran module files generated for this test, excluding the
     module names listed in keep-modules.  Cleaning up module files is
     usually done automatically by the testsuite by looking at the
     source files and removing the modules after the test has been
     executed.
          module MoD1
          end module MoD1
          module Mod2
          end module Mod2
          module moD3
          end module moD3
          module mod4
          end module mod4
          ! { dg-final { cleanup-modules "mod1 mod2" } } ! redundant
          ! { dg-final { keep-modules "mod3 mod4" } }

'keep-modules "LIST-OF-MODULES-NOT-TO-DELETE"'
     Whitespace separated list of module names that should not be
     deleted by cleanup-modules.  If the list of modules is empty, all
     modules defined in this file are kept.
          module maybe_unneeded
          end module maybe_unneeded
          module keep1
          end module keep1
          module keep2
          end module keep2
          ! { dg-final { keep-modules "keep1 keep2" } } ! just keep these two
          ! { dg-final { keep-modules "" } } ! keep all

'cleanup-profile-file'
     Removes profiling files generated for this test.

'cleanup-repo-files'
     Removes files generated for this test for '-frepo'.

'cleanup-rtl-dump SUFFIX'
     Removes RTL dump files generated for this test.

'cleanup-saved-temps'
     Removes files for the current test which were kept for
     '-save-temps'.

'cleanup-tree-dump SUFFIX'
     Removes tree dump files matching SUFFIX which were generated for
     this test.


File: gccint.info,  Node: Ada Tests,  Next: C Tests,  Prev: Test Directives,  Up: Testsuites

7.3 Ada Language Testsuites
===========================

The Ada testsuite includes executable tests from the ACATS testsuite,
publicly available at <http://www.ada-auth.org/acats.html>.

 These tests are integrated in the GCC testsuite in the 'ada/acats'
directory, and enabled automatically when running 'make check', assuming
the Ada language has been enabled when configuring GCC.

 You can also run the Ada testsuite independently, using 'make
check-ada', or run a subset of the tests by specifying which chapter to
run, e.g.:

     $ make check-ada CHAPTERS="c3 c9"

 The tests are organized by directory, each directory corresponding to a
chapter of the Ada Reference Manual.  So for example, 'c9' corresponds
to chapter 9, which deals with tasking features of the language.

 There is also an extra chapter called 'gcc' containing a template for
creating new executable tests, although this is deprecated in favor of
the 'gnat.dg' testsuite.

 The tests are run using two 'sh' scripts: 'run_acats' and 'run_all.sh'.
To run the tests using a simulator or a cross target, see the small
customization section at the top of 'run_all.sh'.

 These tests are run using the build tree: they can be run without doing
a 'make install'.


File: gccint.info,  Node: C Tests,  Next: libgcj Tests,  Prev: Ada Tests,  Up: Testsuites

7.4 C Language Testsuites
=========================

GCC contains the following C language testsuites, in the 'gcc/testsuite'
directory:

'gcc.dg'
     This contains tests of particular features of the C compiler, using
     the more modern 'dg' harness.  Correctness tests for various
     compiler features should go here if possible.

     Magic comments determine whether the file is preprocessed,
     compiled, linked or run.  In these tests, error and warning message
     texts are compared against expected texts or regular expressions
     given in comments.  These tests are run with the options '-ansi
     -pedantic' unless other options are given in the test.  Except as
     noted below they are not run with multiple optimization options.
'gcc.dg/compat'
     This subdirectory contains tests for binary compatibility using
     'lib/compat.exp', which in turn uses the language-independent
     support (*note Support for testing binary compatibility: compat
     Testing.).
'gcc.dg/cpp'
     This subdirectory contains tests of the preprocessor.
'gcc.dg/debug'
     This subdirectory contains tests for debug formats.  Tests in this
     subdirectory are run for each debug format that the compiler
     supports.
'gcc.dg/format'
     This subdirectory contains tests of the '-Wformat' format checking.
     Tests in this directory are run with and without '-DWIDE'.
'gcc.dg/noncompile'
     This subdirectory contains tests of code that should not compile
     and does not need any special compilation options.  They are run
     with multiple optimization options, since sometimes invalid code
     crashes the compiler with optimization.
'gcc.dg/special'
     FIXME: describe this.

'gcc.c-torture'
     This contains particular code fragments which have historically
     broken easily.  These tests are run with multiple optimization
     options, so tests for features which only break at some
     optimization levels belong here.  This also contains tests to check
     that certain optimizations occur.  It might be worthwhile to
     separate the correctness tests cleanly from the code quality tests,
     but it hasn't been done yet.

'gcc.c-torture/compat'
     FIXME: describe this.

     This directory should probably not be used for new tests.
'gcc.c-torture/compile'
     This testsuite contains test cases that should compile, but do not
     need to link or run.  These test cases are compiled with several
     different combinations of optimization options.  All warnings are
     disabled for these test cases, so this directory is not suitable if
     you wish to test for the presence or absence of compiler warnings.
     While special options can be set, and tests disabled on specific
     platforms, by the use of '.x' files, mostly these test cases should
     not contain platform dependencies.  FIXME: discuss how defines such
     as 'NO_LABEL_VALUES' and 'STACK_SIZE' are used.
'gcc.c-torture/execute'
     This testsuite contains test cases that should compile, link and
     run; otherwise the same comments as for 'gcc.c-torture/compile'
     apply.
'gcc.c-torture/execute/ieee'
     This contains tests which are specific to IEEE floating point.
'gcc.c-torture/unsorted'
     FIXME: describe this.

     This directory should probably not be used for new tests.
'gcc.misc-tests'
     This directory contains C tests that require special handling.
     Some of these tests have individual expect files, and others share
     special-purpose expect files:

     'bprob*.c'
          Test '-fbranch-probabilities' using
          'gcc.misc-tests/bprob.exp', which in turn uses the generic,
          language-independent framework (*note Support for testing
          profile-directed optimizations: profopt Testing.).

     'gcov*.c'
          Test 'gcov' output using 'gcov.exp', which in turn uses the
          language-independent support (*note Support for testing gcov:
          gcov Testing.).

     'i386-pf-*.c'
          Test i386-specific support for data prefetch using
          'i386-prefetch.exp'.

'gcc.test-framework'
     'dg-*.c'
          Test the testsuite itself using
          'gcc.test-framework/test-framework.exp'.

 FIXME: merge in 'testsuite/README.gcc' and discuss the format of test
cases and magic comments more.


File: gccint.info,  Node: libgcj Tests,  Next: LTO Testing,  Prev: C Tests,  Up: Testsuites

7.5 The Java library testsuites.
================================

Runtime tests are executed via 'make check' in the
'TARGET/libjava/testsuite' directory in the build tree.  Additional
runtime tests can be checked into this testsuite.

 Regression testing of the core packages in libgcj is also covered by
the Mauve testsuite.  The Mauve Project develops tests for the Java
Class Libraries.  These tests are run as part of libgcj testing by
placing the Mauve tree within the libjava testsuite sources at
'libjava/testsuite/libjava.mauve/mauve', or by specifying the location
of that tree when invoking 'make', as in 'make MAUVEDIR=~/mauve check'.

 To detect regressions, a mechanism in 'mauve.exp' compares the failures
for a test run against the list of expected failures in
'libjava/testsuite/libjava.mauve/xfails' from the source hierarchy.
Update this file when adding new failing tests to Mauve, or when fixing
bugs in libgcj that had caused Mauve test failures.

 We encourage developers to contribute test cases to Mauve.


File: gccint.info,  Node: LTO Testing,  Next: gcov Testing,  Prev: libgcj Tests,  Up: Testsuites

7.6 Support for testing link-time optimizations
===============================================

Tests for link-time optimizations usually require multiple source files
that are compiled separately, perhaps with different sets of options.
There are several special-purpose test directives used for these tests.

'{ dg-lto-do DO-WHAT-KEYWORD }'
     DO-WHAT-KEYWORD specifies how the test is compiled and whether it
     is executed.  It is one of:

     'assemble'
          Compile with '-c' to produce a relocatable object file.
     'link'
          Compile, assemble, and link to produce an executable file.
     'run'
          Produce and run an executable file, which is expected to
          return an exit code of 0.

     The default is 'assemble'.  That can be overridden for a set of
     tests by redefining 'dg-do-what-default' within the '.exp' file for
     those tests.

     Unlike 'dg-do', 'dg-lto-do' does not support an optional 'target'
     or 'xfail' list.  Use 'dg-skip-if', 'dg-xfail-if', or
     'dg-xfail-run-if'.

'{ dg-lto-options { { OPTIONS } [{ OPTIONS }] } [{ target SELECTOR }]}'
     This directive provides a list of one or more sets of compiler
     options to override LTO_OPTIONS.  Each test will be compiled and
     run with each of these sets of options.

'{ dg-extra-ld-options OPTIONS [{ target SELECTOR }]}'
     This directive adds OPTIONS to the linker options used.

'{ dg-suppress-ld-options OPTIONS [{ target SELECTOR }]}'
     This directive removes OPTIONS from the set of linker options used.


File: gccint.info,  Node: gcov Testing,  Next: profopt Testing,  Prev: LTO Testing,  Up: Testsuites

7.7 Support for testing 'gcov'
==============================

Language-independent support for testing 'gcov', and for checking that
branch profiling produces expected values, is provided by the expect
file 'lib/gcov.exp'.  'gcov' tests also rely on procedures in
'lib/gcc-dg.exp' to compile and run the test program.  A typical 'gcov'
test contains the following DejaGnu commands within comments:

     { dg-options "-fprofile-arcs -ftest-coverage" }
     { dg-do run { target native } }
     { dg-final { run-gcov sourcefile } }

 Checks of 'gcov' output can include line counts, branch percentages,
and call return percentages.  All of these checks are requested via
commands that appear in comments in the test's source file.  Commands to
check line counts are processed by default.  Commands to check branch
percentages and call return percentages are processed if the 'run-gcov'
command has arguments 'branches' or 'calls', respectively.  For example,
the following specifies checking both, as well as passing '-b' to
'gcov':

     { dg-final { run-gcov branches calls { -b sourcefile } } }

 A line count command appears within a comment on the source line that
is expected to get the specified count and has the form 'count(CNT)'.  A
test should only check line counts for lines that will get the same
count for any architecture.

 Commands to check branch percentages ('branch') and call return
percentages ('returns') are very similar to each other.  A beginning
command appears on or before the first of a range of lines that will
report the percentage, and the ending command follows that range of
lines.  The beginning command can include a list of percentages, all of
which are expected to be found within the range.  A range is terminated
by the next command of the same kind.  A command 'branch(end)' or
'returns(end)' marks the end of a range without starting a new one.  For
example:

     if (i > 10 && j > i && j < 20)  /* branch(27 50 75) */
                                     /* branch(end) */
       foo (i, j);

 For a call return percentage, the value specified is the percentage of
calls reported to return.  For a branch percentage, the value is either
the expected percentage or 100 minus that value, since the direction of
a branch can differ depending on the target or the optimization level.

 Not all branches and calls need to be checked.  A test should not check
for branches that might be optimized away or replaced with predicated
instructions.  Don't check for calls inserted by the compiler or ones
that might be inlined or optimized away.

 A single test can check for combinations of line counts, branch
percentages, and call return percentages.  The command to check a line
count must appear on the line that will report that count, but commands
to check branch percentages and call return percentages can bracket the
lines that report them.


File: gccint.info,  Node: profopt Testing,  Next: compat Testing,  Prev: gcov Testing,  Up: Testsuites

7.8 Support for testing profile-directed optimizations
======================================================

The file 'profopt.exp' provides language-independent support for
checking correct execution of a test built with profile-directed
optimization.  This testing requires that a test program be built and
executed twice.  The first time it is compiled to generate profile data,
and the second time it is compiled to use the data that was generated
during the first execution.  The second execution is to verify that the
test produces the expected results.

 To check that the optimization actually generated better code, a test
can be built and run a third time with normal optimizations to verify
that the performance is better with the profile-directed optimizations.
'profopt.exp' has the beginnings of this kind of support.

 'profopt.exp' provides generic support for profile-directed
optimizations.  Each set of tests that uses it provides information
about a specific optimization:

'tool'
     tool being tested, e.g., 'gcc'

'profile_option'
     options used to generate profile data

'feedback_option'
     options used to optimize using that profile data

'prof_ext'
     suffix of profile data files

'PROFOPT_OPTIONS'
     list of options with which to run each test, similar to the lists
     for torture tests

'{ dg-final-generate { LOCAL-DIRECTIVE } }'
     This directive is similar to 'dg-final', but the LOCAL-DIRECTIVE is
     run after the generation of profile data.

'{ dg-final-use { LOCAL-DIRECTIVE } }'
     The LOCAL-DIRECTIVE is run after the profile data have been used.


File: gccint.info,  Node: compat Testing,  Next: Torture Tests,  Prev: profopt Testing,  Up: Testsuites

7.9 Support for testing binary compatibility
============================================

The file 'compat.exp' provides language-independent support for binary
compatibility testing.  It supports testing interoperability of two
compilers that follow the same ABI, or of multiple sets of compiler
options that should not affect binary compatibility.  It is intended to
be used for testsuites that complement ABI testsuites.

 A test supported by this framework has three parts, each in a separate
source file: a main program and two pieces that interact with each other
to split up the functionality being tested.

'TESTNAME_main.SUFFIX'
     Contains the main program, which calls a function in file
     'TESTNAME_x.SUFFIX'.

'TESTNAME_x.SUFFIX'
     Contains at least one call to a function in 'TESTNAME_y.SUFFIX'.

'TESTNAME_y.SUFFIX'
     Shares data with, or gets arguments from, 'TESTNAME_x.SUFFIX'.

 Within each test, the main program and one functional piece are
compiled by the GCC under test.  The other piece can be compiled by an
alternate compiler.  If no alternate compiler is specified, then all
three source files are all compiled by the GCC under test.  You can
specify pairs of sets of compiler options.  The first element of such a
pair specifies options used with the GCC under test, and the second
element of the pair specifies options used with the alternate compiler.
Each test is compiled with each pair of options.

 'compat.exp' defines default pairs of compiler options.  These can be
overridden by defining the environment variable 'COMPAT_OPTIONS' as:

     COMPAT_OPTIONS="[list [list {TST1} {ALT1}]
       ...[list {TSTN} {ALTN}]]"

 where TSTI and ALTI are lists of options, with TSTI used by the
compiler under test and ALTI used by the alternate compiler.  For
example, with '[list [list {-g -O0} {-O3}] [list {-fpic} {-fPIC -O2}]]',
the test is first built with '-g -O0' by the compiler under test and
with '-O3' by the alternate compiler.  The test is built a second time
using '-fpic' by the compiler under test and '-fPIC -O2' by the
alternate compiler.

 An alternate compiler is specified by defining an environment variable
to be the full pathname of an installed compiler; for C define
'ALT_CC_UNDER_TEST', and for C++ define 'ALT_CXX_UNDER_TEST'.  These
will be written to the 'site.exp' file used by DejaGnu.  The default is
to build each test with the compiler under test using the first of each
pair of compiler options from 'COMPAT_OPTIONS'.  When
'ALT_CC_UNDER_TEST' or 'ALT_CXX_UNDER_TEST' is 'same', each test is
built using the compiler under test but with combinations of the options
from 'COMPAT_OPTIONS'.

 To run only the C++ compatibility suite using the compiler under test
and another version of GCC using specific compiler options, do the
following from 'OBJDIR/gcc':

     rm site.exp
     make -k \
       ALT_CXX_UNDER_TEST=${alt_prefix}/bin/g++ \
       COMPAT_OPTIONS="LISTS AS SHOWN ABOVE" \
       check-c++ \
       RUNTESTFLAGS="compat.exp"

 A test that fails when the source files are compiled with different
compilers, but passes when the files are compiled with the same
compiler, demonstrates incompatibility of the generated code or runtime
support.  A test that fails for the alternate compiler but passes for
the compiler under test probably tests for a bug that was fixed in the
compiler under test but is present in the alternate compiler.

 The binary compatibility tests support a small number of test framework
commands that appear within comments in a test file.

'dg-require-*'
     These commands can be used in 'TESTNAME_main.SUFFIX' to skip the
     test if specific support is not available on the target.

'dg-options'
     The specified options are used for compiling this particular source
     file, appended to the options from 'COMPAT_OPTIONS'.  When this
     command appears in 'TESTNAME_main.SUFFIX' the options are also used
     to link the test program.

'dg-xfail-if'
     This command can be used in a secondary source file to specify that
     compilation is expected to fail for particular options on
     particular targets.


File: gccint.info,  Node: Torture Tests,  Prev: compat Testing,  Up: Testsuites

7.10 Support for torture testing using multiple options
=======================================================

Throughout the compiler testsuite there are several directories whose
tests are run multiple times, each with a different set of options.
These are known as torture tests.  'lib/torture-options.exp' defines
procedures to set up these lists:

'torture-init'
     Initialize use of torture lists.
'set-torture-options'
     Set lists of torture options to use for tests with and without
     loops.  Optionally combine a set of torture options with a set of
     other options, as is done with Objective-C runtime options.
'torture-finish'
     Finalize use of torture lists.

 The '.exp' file for a set of tests that use torture options must
include calls to these three procedures if:

   * It calls 'gcc-dg-runtest' and overrides DG_TORTURE_OPTIONS.

   * It calls ${TOOL}'-torture' or ${TOOL}'-torture-execute', where TOOL
     is 'c', 'fortran', or 'objc'.

   * It calls 'dg-pch'.

 It is not necessary for a '.exp' file that calls 'gcc-dg-runtest' to
call the torture procedures if the tests should use the list in
DG_TORTURE_OPTIONS defined in 'gcc-dg.exp'.

 Most uses of torture options can override the default lists by defining
TORTURE_OPTIONS or add to the default list by defining
ADDITIONAL_TORTURE_OPTIONS.  Define these in a '.dejagnurc' file or add
them to the 'site.exp' file; for example

     set ADDITIONAL_TORTURE_OPTIONS  [list \
       { -O2 -ftree-loop-linear } \
       { -O2 -fpeel-loops } ]


File: gccint.info,  Node: Options,  Next: Passes,  Prev: Testsuites,  Up: Top

8 Option specification files
****************************

Most GCC command-line options are described by special option definition
files, the names of which conventionally end in '.opt'.  This chapter
describes the format of these files.

* Menu:

* Option file format::   The general layout of the files
* Option properties::    Supported option properties


File: gccint.info,  Node: Option file format,  Next: Option properties,  Up: Options

8.1 Option file format
======================

Option files are a simple list of records in which each field occupies
its own line and in which the records themselves are separated by blank
lines.  Comments may appear on their own line anywhere within the file
and are preceded by semicolons.  Whitespace is allowed before the
semicolon.

 The files can contain the following types of record:

   * A language definition record.  These records have two fields: the
     string 'Language' and the name of the language.  Once a language
     has been declared in this way, it can be used as an option
     property.  *Note Option properties::.

   * A target specific save record to save additional information.
     These records have two fields: the string 'TargetSave', and a
     declaration type to go in the 'cl_target_option' structure.

   * A variable record to define a variable used to store option
     information.  These records have two fields: the string 'Variable',
     and a declaration of the type and name of the variable, optionally
     with an initializer (but without any trailing ';').  These records
     may be used for variables used for many options where declaring the
     initializer in a single option definition record, or duplicating it
     in many records, would be inappropriate, or for variables set in
     option handlers rather than referenced by 'Var' properties.

   * A variable record to define a variable used to store option
     information.  These records have two fields: the string
     'TargetVariable', and a declaration of the type and name of the
     variable, optionally with an initializer (but without any trailing
     ';').  'TargetVariable' is a combination of 'Variable' and
     'TargetSave' records in that the variable is defined in the
     'gcc_options' structure, but these variables are also stored in the
     'cl_target_option' structure.  The variables are saved in the
     target save code and restored in the target restore code.

   * A variable record to record any additional files that the
     'options.h' file should include.  This is useful to provide
     enumeration or structure definitions needed for target variables.
     These records have two fields: the string 'HeaderInclude' and the
     name of the include file.

   * A variable record to record any additional files that the
     'options.c' or 'options-save.c' file should include.  This is
     useful to provide inline functions needed for target variables
     and/or '#ifdef' sequences to properly set up the initialization.
     These records have two fields: the string 'SourceInclude' and the
     name of the include file.

   * An enumeration record to define a set of strings that may be used
     as arguments to an option or options.  These records have three
     fields: the string 'Enum', a space-separated list of properties and
     help text used to describe the set of strings in '--help' output.
     Properties use the same format as option properties; the following
     are valid:
     'Name(NAME)'
          This property is required; NAME must be a name (suitable for
          use in C identifiers) used to identify the set of strings in
          'Enum' option properties.

     'Type(TYPE)'
          This property is required; TYPE is the C type for variables
          set by options using this enumeration together with 'Var'.

     'UnknownError(MESSAGE)'
          The message MESSAGE will be used as an error message if the
          argument is invalid; for enumerations without 'UnknownError',
          a generic error message is used.  MESSAGE should contain a
          single '%qs' format, which will be used to format the invalid
          argument.

   * An enumeration value record to define one of the strings in a set
     given in an 'Enum' record.  These records have two fields: the
     string 'EnumValue' and a space-separated list of properties.
     Properties use the same format as option properties; the following
     are valid:
     'Enum(NAME)'
          This property is required; NAME says which 'Enum' record this
          'EnumValue' record corresponds to.

     'String(STRING)'
          This property is required; STRING is the string option
          argument being described by this record.

     'Value(VALUE)'
          This property is required; it says what value (representable
          as 'int') should be used for the given string.

     'Canonical'
          This property is optional.  If present, it says the present
          string is the canonical one among all those with the given
          value.  Other strings yielding that value will be mapped to
          this one so specs do not need to handle them.

     'DriverOnly'
          This property is optional.  If present, the present string
          will only be accepted by the driver.  This is used for cases
          such as '-march=native' that are processed by the driver so
          that 'gcc -v' shows how the options chosen depended on the
          system on which the compiler was run.

   * An option definition record.  These records have the following
     fields:
       1. the name of the option, with the leading "-" removed
       2. a space-separated list of option properties (*note Option
          properties::)
       3. the help text to use for '--help' (omitted if the second field
          contains the 'Undocumented' property).

     By default, all options beginning with "f", "W" or "m" are
     implicitly assumed to take a "no-" form.  This form should not be
     listed separately.  If an option beginning with one of these
     letters does not have a "no-" form, you can use the
     'RejectNegative' property to reject it.

     The help text is automatically line-wrapped before being displayed.
     Normally the name of the option is printed on the left-hand side of
     the output and the help text is printed on the right.  However, if
     the help text contains a tab character, the text to the left of the
     tab is used instead of the option's name and the text to the right
     of the tab forms the help text.  This allows you to elaborate on
     what type of argument the option takes.

   * A target mask record.  These records have one field of the form
     'Mask(X)'.  The options-processing script will automatically
     allocate a bit in 'target_flags' (*note Run-time Target::) for each
     mask name X and set the macro 'MASK_X' to the appropriate bitmask.
     It will also declare a 'TARGET_X' macro that has the value 1 when
     bit 'MASK_X' is set and 0 otherwise.

     They are primarily intended to declare target masks that are not
     associated with user options, either because these masks represent
     internal switches or because the options are not available on all
     configurations and yet the masks always need to be defined.


File: gccint.info,  Node: Option properties,  Prev: Option file format,  Up: Options

8.2 Option properties
=====================

The second field of an option record can specify any of the following
properties.  When an option takes an argument, it is enclosed in
parentheses following the option property name.  The parser that handles
option files is quite simplistic, and will be tricked by any nested
parentheses within the argument text itself; in this case, the entire
option argument can be wrapped in curly braces within the parentheses to
demarcate it, e.g.:

     Condition({defined (USE_CYGWIN_LIBSTDCXX_WRAPPERS)})

'Common'
     The option is available for all languages and targets.

'Target'
     The option is available for all languages but is target-specific.

'Driver'
     The option is handled by the compiler driver using code not shared
     with the compilers proper ('cc1' etc.).

'LANGUAGE'
     The option is available when compiling for the given language.

     It is possible to specify several different languages for the same
     option.  Each LANGUAGE must have been declared by an earlier
     'Language' record.  *Note Option file format::.

'RejectDriver'
     The option is only handled by the compilers proper ('cc1' etc.) and
     should not be accepted by the driver.

'RejectNegative'
     The option does not have a "no-" form.  All options beginning with
     "f", "W" or "m" are assumed to have a "no-" form unless this
     property is used.

'Negative(OTHERNAME)'
     The option will turn off another option OTHERNAME, which is the
     option name with the leading "-" removed.  This chain action will
     propagate through the 'Negative' property of the option to be
     turned off.

     As a consequence, if you have a group of mutually-exclusive
     options, their 'Negative' properties should form a circular chain.
     For example, if options '-A', '-B' and '-C' are mutually exclusive,
     their respective 'Negative' properties should be 'Negative(B)',
     'Negative(C)' and 'Negative(A)'.

'Joined'
'Separate'
     The option takes a mandatory argument.  'Joined' indicates that the
     option and argument can be included in the same 'argv' entry (as
     with '-mflush-func=NAME', for example).  'Separate' indicates that
     the option and argument can be separate 'argv' entries (as with
     '-o').  An option is allowed to have both of these properties.

'JoinedOrMissing'
     The option takes an optional argument.  If the argument is given,
     it will be part of the same 'argv' entry as the option itself.

     This property cannot be used alongside 'Joined' or 'Separate'.

'MissingArgError(MESSAGE)'
     For an option marked 'Joined' or 'Separate', the message MESSAGE
     will be used as an error message if the mandatory argument is
     missing; for options without 'MissingArgError', a generic error
     message is used.  MESSAGE should contain a single '%qs' format,
     which will be used to format the name of the option passed.

'Args(N)'
     For an option marked 'Separate', indicate that it takes N
     arguments.  The default is 1.

'UInteger'
     The option's argument is a non-negative integer.  The option parser
     will check and convert the argument before passing it to the
     relevant option handler.  'UInteger' should also be used on options
     like '-falign-loops' where both '-falign-loops' and
     '-falign-loops'=N are supported to make sure the saved options are
     given a full integer.

'ToLower'
     The option's argument should be converted to lowercase as part of
     putting it in canonical form, and before comparing with the strings
     indicated by any 'Enum' property.

'NoDriverArg'
     For an option marked 'Separate', the option only takes an argument
     in the compiler proper, not in the driver.  This is for
     compatibility with existing options that are used both directly and
     via '-Wp,'; new options should not have this property.

'Var(VAR)'
     The state of this option should be stored in variable VAR (actually
     a macro for 'global_options.x_VAR').  The way that the state is
     stored depends on the type of option:

        * If the option uses the 'Mask' or 'InverseMask' properties, VAR
          is the integer variable that contains the mask.

        * If the option is a normal on/off switch, VAR is an integer
          variable that is nonzero when the option is enabled.  The
          options parser will set the variable to 1 when the positive
          form of the option is used and 0 when the "no-" form is used.

        * If the option takes an argument and has the 'UInteger'
          property, VAR is an integer variable that stores the value of
          the argument.

        * If the option takes an argument and has the 'Enum' property,
          VAR is a variable (type given in the 'Type' property of the
          'Enum' record whose 'Name' property has the same argument as
          the 'Enum' property of this option) that stores the value of
          the argument.

        * If the option has the 'Defer' property, VAR is a pointer to a
          'VEC(cl_deferred_option,heap)' that stores the option for
          later processing.  (VAR is declared with type 'void *' and
          needs to be cast to 'VEC(cl_deferred_option,heap)' before
          use.)

        * Otherwise, if the option takes an argument, VAR is a pointer
          to the argument string.  The pointer will be null if the
          argument is optional and wasn't given.

     The option-processing script will usually zero-initialize VAR.  You
     can modify this behavior using 'Init'.

'Var(VAR, SET)'
     The option controls an integer variable VAR and is active when VAR
     equals SET.  The option parser will set VAR to SET when the
     positive form of the option is used and '!SET' when the "no-" form
     is used.

     VAR is declared in the same way as for the single-argument form
     described above.

'Init(VALUE)'
     The variable specified by the 'Var' property should be statically
     initialized to VALUE.  If more than one option using the same
     variable specifies 'Init', all must specify the same initializer.

'Mask(NAME)'
     The option is associated with a bit in the 'target_flags' variable
     (*note Run-time Target::) and is active when that bit is set.  You
     may also specify 'Var' to select a variable other than
     'target_flags'.

     The options-processing script will automatically allocate a unique
     bit for the option.  If the option is attached to 'target_flags',
     the script will set the macro 'MASK_NAME' to the appropriate
     bitmask.  It will also declare a 'TARGET_NAME' macro that has the
     value 1 when the option is active and 0 otherwise.  If you use
     'Var' to attach the option to a different variable, the bitmask
     macro with be called 'OPTION_MASK_NAME'.

'InverseMask(OTHERNAME)'
'InverseMask(OTHERNAME, THISNAME)'
     The option is the inverse of another option that has the
     'Mask(OTHERNAME)' property.  If THISNAME is given, the
     options-processing script will declare a 'TARGET_THISNAME' macro
     that is 1 when the option is active and 0 otherwise.

'Enum(NAME)'
     The option's argument is a string from the set of strings
     associated with the corresponding 'Enum' record.  The string is
     checked and converted to the integer specified in the corresponding
     'EnumValue' record before being passed to option handlers.

'Defer'
     The option should be stored in a vector, specified with 'Var', for
     later processing.

'Alias(OPT)'
'Alias(OPT, ARG)'
'Alias(OPT, POSARG, NEGARG)'
     The option is an alias for '-OPT' (or the negative form of that
     option, depending on 'NegativeAlias').  In the first form, any
     argument passed to the alias is considered to be passed to '-OPT',
     and '-OPT' is considered to be negated if the alias is used in
     negated form.  In the second form, the alias may not be negated or
     have an argument, and POSARG is considered to be passed as an
     argument to '-OPT'.  In the third form, the alias may not have an
     argument, if the alias is used in the positive form then POSARG is
     considered to be passed to '-OPT', and if the alias is used in the
     negative form then NEGARG is considered to be passed to '-OPT'.

     Aliases should not specify 'Var' or 'Mask' or 'UInteger'.  Aliases
     should normally specify the same languages as the target of the
     alias; the flags on the target will be used to determine any
     diagnostic for use of an option for the wrong language, while those
     on the alias will be used to identify what command-line text is the
     option and what text is any argument to that option.

     When an 'Alias' definition is used for an option, driver specs do
     not need to handle it and no 'OPT_' enumeration value is defined
     for it; only the canonical form of the option will be seen in those
     places.

'NegativeAlias'
     For an option marked with 'Alias(OPT)', the option is considered to
     be an alias for the positive form of '-OPT' if negated and for the
     negative form of '-OPT' if not negated.  'NegativeAlias' may not be
     used with the forms of 'Alias' taking more than one argument.

'Ignore'
     This option is ignored apart from printing any warning specified
     using 'Warn'.  The option will not be seen by specs and no 'OPT_'
     enumeration value is defined for it.

'SeparateAlias'
     For an option marked with 'Joined', 'Separate' and 'Alias', the
     option only acts as an alias when passed a separate argument; with
     a joined argument it acts as a normal option, with an 'OPT_'
     enumeration value.  This is for compatibility with the Java '-d'
     option and should not be used for new options.

'Warn(MESSAGE)'
     If this option is used, output the warning MESSAGE.  MESSAGE is a
     format string, either taking a single operand with a '%qs' format
     which is the option name, or not taking any operands, which is
     passed to the 'warning' function.  If an alias is marked 'Warn',
     the target of the alias must not also be marked 'Warn'.

'Report'
     The state of the option should be printed by '-fverbose-asm'.

'Warning'
     This is a warning option and should be shown as such in '--help'
     output.  This flag does not currently affect anything other than
     '--help'.

'Optimization'
     This is an optimization option.  It should be shown as such in
     '--help' output, and any associated variable named using 'Var'
     should be saved and restored when the optimization level is changed
     with 'optimize' attributes.

'Undocumented'
     The option is deliberately missing documentation and should not be
     included in the '--help' output.

'Condition(COND)'
     The option should only be accepted if preprocessor condition COND
     is true.  Note that any C declarations associated with the option
     will be present even if COND is false; COND simply controls whether
     the option is accepted and whether it is printed in the '--help'
     output.

'Save'
     Build the 'cl_target_option' structure to hold a copy of the
     option, add the functions 'cl_target_option_save' and
     'cl_target_option_restore' to save and restore the options.

'SetByCombined'
     The option may also be set by a combined option such as
     '-ffast-math'.  This causes the 'gcc_options' struct to have a
     field 'frontend_set_NAME', where 'NAME' is the name of the field
     holding the value of this option (without the leading 'x_').  This
     gives the front end a way to indicate that the value has been set
     explicitly and should not be changed by the combined option.  For
     example, some front ends use this to prevent '-ffast-math' and
     '-fno-fast-math' from changing the value of '-fmath-errno' for
     languages that do not use 'errno'.

'EnabledBy(OPT)'
'EnabledBy(OPT && OPT2)'
     If not explicitly set, the option is set to the value of '-OPT'.
     The second form specifies that the option is only set if both OPT
     and OPT2 are set.

'LangEnabledBy(LANGUAGE, OPT)'
'LangEnabledBy(LANGUAGE, OPT, POSARG, NEGARG)'
     When compiling for the given language, the option is set to the
     value of '-OPT', if not explicitly set.  In the second form, if OPT
     is used in the positive form then POSARG is considered to be passed
     to the option, and if OPT is used in the negative form then NEGARG
     is considered to be passed to the option.  It is possible to
     specify several different languages.  Each LANGUAGE must have been
     declared by an earlier 'Language' record.  *Note Option file
     format::.

'NoDWARFRecord'
     The option is omitted from the producer string written by
     '-grecord-gcc-switches'.


File: gccint.info,  Node: Passes,  Next: RTL,  Prev: Options,  Up: Top

9 Passes and Files of the Compiler
**********************************

This chapter is dedicated to giving an overview of the optimization and
code generation passes of the compiler.  In the process, it describes
some of the language front end interface, though this description is no
where near complete.

* Menu:

* Parsing pass::         The language front end turns text into bits.
* Gimplification pass::  The bits are turned into something we can optimize.
* Pass manager::         Sequencing the optimization passes.
* Tree SSA passes::      Optimizations on a high-level representation.
* RTL passes::           Optimizations on a low-level representation.


File: gccint.info,  Node: Parsing pass,  Next: Gimplification pass,  Up: Passes

9.1 Parsing pass
================

The language front end is invoked only once, via
'lang_hooks.parse_file', to parse the entire input.  The language front
end may use any intermediate language representation deemed appropriate.
The C front end uses GENERIC trees (*note GENERIC::), plus a double
handful of language specific tree codes defined in 'c-common.def'.  The
Fortran front end uses a completely different private representation.

 At some point the front end must translate the representation used in
the front end to a representation understood by the language-independent
portions of the compiler.  Current practice takes one of two forms.  The
C front end manually invokes the gimplifier (*note GIMPLE::) on each
function, and uses the gimplifier callbacks to convert the
language-specific tree nodes directly to GIMPLE before passing the
function off to be compiled.  The Fortran front end converts from a
private representation to GENERIC, which is later lowered to GIMPLE when
the function is compiled.  Which route to choose probably depends on how
well GENERIC (plus extensions) can be made to match up with the source
language and necessary parsing data structures.

 BUG: Gimplification must occur before nested function lowering, and
nested function lowering must be done by the front end before passing
the data off to cgraph.

 TODO: Cgraph should control nested function lowering.  It would only be
invoked when it is certain that the outer-most function is used.

 TODO: Cgraph needs a gimplify_function callback.  It should be invoked
when (1) it is certain that the function is used, (2) warning flags
specified by the user require some amount of compilation in order to
honor, (3) the language indicates that semantic analysis is not complete
until gimplification occurs.  Hum... this sounds overly complicated.
Perhaps we should just have the front end gimplify always; in most cases
it's only one function call.

 The front end needs to pass all function definitions and top level
declarations off to the middle-end so that they can be compiled and
emitted to the object file.  For a simple procedural language, it is
usually most convenient to do this as each top level declaration or
definition is seen.  There is also a distinction to be made between
generating functional code and generating complete debug information.
The only thing that is absolutely required for functional code is that
function and data _definitions_ be passed to the middle-end.  For
complete debug information, function, data and type declarations should
all be passed as well.

 In any case, the front end needs each complete top-level function or
data declaration, and each data definition should be passed to
'rest_of_decl_compilation'.  Each complete type definition should be
passed to 'rest_of_type_compilation'.  Each function definition should
be passed to 'cgraph_finalize_function'.

 TODO: I know rest_of_compilation currently has all sorts of RTL
generation semantics.  I plan to move all code generation bits (both
Tree and RTL) to compile_function.  Should we hide cgraph from the front
ends and move back to rest_of_compilation as the official interface?
Possibly we should rename all three interfaces such that the names match
in some meaningful way and that is more descriptive than "rest_of".

 The middle-end will, at its option, emit the function and data
definitions immediately or queue them for later processing.


File: gccint.info,  Node: Gimplification pass,  Next: Pass manager,  Prev: Parsing pass,  Up: Passes

9.2 Gimplification pass
=======================

"Gimplification" is a whimsical term for the process of converting the
intermediate representation of a function into the GIMPLE language
(*note GIMPLE::).  The term stuck, and so words like "gimplification",
"gimplify", "gimplifier" and the like are sprinkled throughout this
section of code.

 While a front end may certainly choose to generate GIMPLE directly if
it chooses, this can be a moderately complex process unless the
intermediate language used by the front end is already fairly simple.
Usually it is easier to generate GENERIC trees plus extensions and let
the language-independent gimplifier do most of the work.

 The main entry point to this pass is 'gimplify_function_tree' located
in 'gimplify.c'.  From here we process the entire function gimplifying
each statement in turn.  The main workhorse for this pass is
'gimplify_expr'.  Approximately everything passes through here at least
once, and it is from here that we invoke the 'lang_hooks.gimplify_expr'
callback.

 The callback should examine the expression in question and return
'GS_UNHANDLED' if the expression is not a language specific construct
that requires attention.  Otherwise it should alter the expression in
some way to such that forward progress is made toward producing valid
GIMPLE.  If the callback is certain that the transformation is complete
and the expression is valid GIMPLE, it should return 'GS_ALL_DONE'.
Otherwise it should return 'GS_OK', which will cause the expression to
be processed again.  If the callback encounters an error during the
transformation (because the front end is relying on the gimplification
process to finish semantic checks), it should return 'GS_ERROR'.


File: gccint.info,  Node: Pass manager,  Next: Tree SSA passes,  Prev: Gimplification pass,  Up: Passes

9.3 Pass manager
================

The pass manager is located in 'passes.c', 'tree-optimize.c' and
'tree-pass.h'.  Its job is to run all of the individual passes in the
correct order, and take care of standard bookkeeping that applies to
every pass.

 The theory of operation is that each pass defines a structure that
represents everything we need to know about that pass--when it should be
run, how it should be run, what intermediate language form or
on-the-side data structures it needs.  We register the pass to be run in
some particular order, and the pass manager arranges for everything to
happen in the correct order.

 The actuality doesn't completely live up to the theory at present.
Command-line switches and 'timevar_id_t' enumerations must still be
defined elsewhere.  The pass manager validates constraints but does not
attempt to (re-)generate data structures or lower intermediate language
form based on the requirements of the next pass.  Nevertheless, what is
present is useful, and a far sight better than nothing at all.

 Each pass should have a unique name.  Each pass may have its own dump
file (for GCC debugging purposes).  Passes with a name starting with a
star do not dump anything.  Sometimes passes are supposed to share a
dump file / option name.  To still give these unique names, you can use
a prefix that is delimited by a space from the part that is used for the
dump file / option name.  E.g.  When the pass name is "ud dce", the name
used for dump file/options is "dce".

 TODO: describe the global variables set up by the pass manager, and a
brief description of how a new pass should use it.  I need to look at
what info RTL passes use first...


File: gccint.info,  Node: Tree SSA passes,  Next: RTL passes,  Prev: Pass manager,  Up: Passes

9.4 Tree SSA passes
===================

The following briefly describes the Tree optimization passes that are
run after gimplification and what source files they are located in.

   * Remove useless statements

     This pass is an extremely simple sweep across the gimple code in
     which we identify obviously dead code and remove it.  Here we do
     things like simplify 'if' statements with constant conditions,
     remove exception handling constructs surrounding code that
     obviously cannot throw, remove lexical bindings that contain no
     variables, and other assorted simplistic cleanups.  The idea is to
     get rid of the obvious stuff quickly rather than wait until later
     when it's more work to get rid of it.  This pass is located in
     'tree-cfg.c' and described by 'pass_remove_useless_stmts'.

   * Mudflap declaration registration

     If mudflap (*note -fmudflap -fmudflapth -fmudflapir: (gcc)Optimize
     Options.) is enabled, we generate code to register some variable
     declarations with the mudflap runtime.  Specifically, the runtime
     tracks the lifetimes of those variable declarations that have their
     addresses taken, or whose bounds are unknown at compile time
     ('extern').  This pass generates new exception handling constructs
     ('try'/'finally'), and so must run before those are lowered.  In
     addition, the pass enqueues declarations of static variables whose
     lifetimes extend to the entire program.  The pass is located in
     'tree-mudflap.c' and is described by 'pass_mudflap_1'.

   * OpenMP lowering

     If OpenMP generation ('-fopenmp') is enabled, this pass lowers
     OpenMP constructs into GIMPLE.

     Lowering of OpenMP constructs involves creating replacement
     expressions for local variables that have been mapped using data
     sharing clauses, exposing the control flow of most synchronization
     directives and adding region markers to facilitate the creation of
     the control flow graph.  The pass is located in 'omp-low.c' and is
     described by 'pass_lower_omp'.

   * OpenMP expansion

     If OpenMP generation ('-fopenmp') is enabled, this pass expands
     parallel regions into their own functions to be invoked by the
     thread library.  The pass is located in 'omp-low.c' and is
     described by 'pass_expand_omp'.

   * Lower control flow

     This pass flattens 'if' statements ('COND_EXPR') and moves lexical
     bindings ('BIND_EXPR') out of line.  After this pass, all 'if'
     statements will have exactly two 'goto' statements in its 'then'
     and 'else' arms.  Lexical binding information for each statement
     will be found in 'TREE_BLOCK' rather than being inferred from its
     position under a 'BIND_EXPR'.  This pass is found in 'gimple-low.c'
     and is described by 'pass_lower_cf'.

   * Lower exception handling control flow

     This pass decomposes high-level exception handling constructs
     ('TRY_FINALLY_EXPR' and 'TRY_CATCH_EXPR') into a form that
     explicitly represents the control flow involved.  After this pass,
     'lookup_stmt_eh_region' will return a non-negative number for any
     statement that may have EH control flow semantics; examine
     'tree_can_throw_internal' or 'tree_can_throw_external' for exact
     semantics.  Exact control flow may be extracted from
     'foreach_reachable_handler'.  The EH region nesting tree is defined
     in 'except.h' and built in 'except.c'.  The lowering pass itself is
     in 'tree-eh.c' and is described by 'pass_lower_eh'.

   * Build the control flow graph

     This pass decomposes a function into basic blocks and creates all
     of the edges that connect them.  It is located in 'tree-cfg.c' and
     is described by 'pass_build_cfg'.

   * Find all referenced variables

     This pass walks the entire function and collects an array of all
     variables referenced in the function, 'referenced_vars'.  The index
     at which a variable is found in the array is used as a UID for the
     variable within this function.  This data is needed by the SSA
     rewriting routines.  The pass is located in 'tree-dfa.c' and is
     described by 'pass_referenced_vars'.

   * Enter static single assignment form

     This pass rewrites the function such that it is in SSA form.  After
     this pass, all 'is_gimple_reg' variables will be referenced by
     'SSA_NAME', and all occurrences of other variables will be
     annotated with 'VDEFS' and 'VUSES'; PHI nodes will have been
     inserted as necessary for each basic block.  This pass is located
     in 'tree-ssa.c' and is described by 'pass_build_ssa'.

   * Warn for uninitialized variables

     This pass scans the function for uses of 'SSA_NAME's that are fed
     by default definition.  For non-parameter variables, such uses are
     uninitialized.  The pass is run twice, before and after
     optimization (if turned on).  In the first pass we only warn for
     uses that are positively uninitialized; in the second pass we warn
     for uses that are possibly uninitialized.  The pass is located in
     'tree-ssa.c' and is defined by 'pass_early_warn_uninitialized' and
     'pass_late_warn_uninitialized'.

   * Dead code elimination

     This pass scans the function for statements without side effects
     whose result is unused.  It does not do memory life analysis, so
     any value that is stored in memory is considered used.  The pass is
     run multiple times throughout the optimization process.  It is
     located in 'tree-ssa-dce.c' and is described by 'pass_dce'.

   * Dominator optimizations

     This pass performs trivial dominator-based copy and constant
     propagation, expression simplification, and jump threading.  It is
     run multiple times throughout the optimization process.  It is
     located in 'tree-ssa-dom.c' and is described by 'pass_dominator'.

   * Forward propagation of single-use variables

     This pass attempts to remove redundant computation by substituting
     variables that are used once into the expression that uses them and
     seeing if the result can be simplified.  It is located in
     'tree-ssa-forwprop.c' and is described by 'pass_forwprop'.

   * Copy Renaming

     This pass attempts to change the name of compiler temporaries
     involved in copy operations such that SSA->normal can coalesce the
     copy away.  When compiler temporaries are copies of user variables,
     it also renames the compiler temporary to the user variable
     resulting in better use of user symbols.  It is located in
     'tree-ssa-copyrename.c' and is described by 'pass_copyrename'.

   * PHI node optimizations

     This pass recognizes forms of PHI inputs that can be represented as
     conditional expressions and rewrites them into straight line code.
     It is located in 'tree-ssa-phiopt.c' and is described by
     'pass_phiopt'.

   * May-alias optimization

     This pass performs a flow sensitive SSA-based points-to analysis.
     The resulting may-alias, must-alias, and escape analysis
     information is used to promote variables from in-memory addressable
     objects to non-aliased variables that can be renamed into SSA form.
     We also update the 'VDEF'/'VUSE' memory tags for non-renameable
     aggregates so that we get fewer false kills.  The pass is located
     in 'tree-ssa-alias.c' and is described by 'pass_may_alias'.

     Interprocedural points-to information is located in
     'tree-ssa-structalias.c' and described by 'pass_ipa_pta'.

   * Profiling

     This pass rewrites the function in order to collect runtime block
     and value profiling data.  Such data may be fed back into the
     compiler on a subsequent run so as to allow optimization based on
     expected execution frequencies.  The pass is located in 'predict.c'
     and is described by 'pass_profile'.

   * Lower complex arithmetic

     This pass rewrites complex arithmetic operations into their
     component scalar arithmetic operations.  The pass is located in
     'tree-complex.c' and is described by 'pass_lower_complex'.

   * Scalar replacement of aggregates

     This pass rewrites suitable non-aliased local aggregate variables
     into a set of scalar variables.  The resulting scalar variables are
     rewritten into SSA form, which allows subsequent optimization
     passes to do a significantly better job with them.  The pass is
     located in 'tree-sra.c' and is described by 'pass_sra'.

   * Dead store elimination

     This pass eliminates stores to memory that are subsequently
     overwritten by another store, without any intervening loads.  The
     pass is located in 'tree-ssa-dse.c' and is described by 'pass_dse'.

   * Tail recursion elimination

     This pass transforms tail recursion into a loop.  It is located in
     'tree-tailcall.c' and is described by 'pass_tail_recursion'.

   * Forward store motion

     This pass sinks stores and assignments down the flowgraph closer to
     their use point.  The pass is located in 'tree-ssa-sink.c' and is
     described by 'pass_sink_code'.

   * Partial redundancy elimination

     This pass eliminates partially redundant computations, as well as
     performing load motion.  The pass is located in 'tree-ssa-pre.c'
     and is described by 'pass_pre'.

     Just before partial redundancy elimination, if
     '-funsafe-math-optimizations' is on, GCC tries to convert divisions
     to multiplications by the reciprocal.  The pass is located in
     'tree-ssa-math-opts.c' and is described by 'pass_cse_reciprocal'.

   * Full redundancy elimination

     This is a simpler form of PRE that only eliminates redundancies
     that occur on all paths.  It is located in 'tree-ssa-pre.c' and
     described by 'pass_fre'.

   * Loop optimization

     The main driver of the pass is placed in 'tree-ssa-loop.c' and
     described by 'pass_loop'.

     The optimizations performed by this pass are:

     Loop invariant motion.  This pass moves only invariants that would
     be hard to handle on RTL level (function calls, operations that
     expand to nontrivial sequences of insns).  With '-funswitch-loops'
     it also moves operands of conditions that are invariant out of the
     loop, so that we can use just trivial invariantness analysis in
     loop unswitching.  The pass also includes store motion.  The pass
     is implemented in 'tree-ssa-loop-im.c'.

     Canonical induction variable creation.  This pass creates a simple
     counter for number of iterations of the loop and replaces the exit
     condition of the loop using it, in case when a complicated analysis
     is necessary to determine the number of iterations.  Later
     optimizations then may determine the number easily.  The pass is
     implemented in 'tree-ssa-loop-ivcanon.c'.

     Induction variable optimizations.  This pass performs standard
     induction variable optimizations, including strength reduction,
     induction variable merging and induction variable elimination.  The
     pass is implemented in 'tree-ssa-loop-ivopts.c'.

     Loop unswitching.  This pass moves the conditional jumps that are
     invariant out of the loops.  To achieve this, a duplicate of the
     loop is created for each possible outcome of conditional jump(s).
     The pass is implemented in 'tree-ssa-loop-unswitch.c'.  This pass
     should eventually replace the RTL level loop unswitching in
     'loop-unswitch.c', but currently the RTL level pass is not
     completely redundant yet due to deficiencies in tree level alias
     analysis.

     The optimizations also use various utility functions contained in
     'tree-ssa-loop-manip.c', 'cfgloop.c', 'cfgloopanal.c' and
     'cfgloopmanip.c'.

     Vectorization.  This pass transforms loops to operate on vector
     types instead of scalar types.  Data parallelism across loop
     iterations is exploited to group data elements from consecutive
     iterations into a vector and operate on them in parallel.
     Depending on available target support the loop is conceptually
     unrolled by a factor 'VF' (vectorization factor), which is the
     number of elements operated upon in parallel in each iteration, and
     the 'VF' copies of each scalar operation are fused to form a vector
     operation.  Additional loop transformations such as peeling and
     versioning may take place to align the number of iterations, and to
     align the memory accesses in the loop.  The pass is implemented in
     'tree-vectorizer.c' (the main driver), 'tree-vect-loop.c' and
     'tree-vect-loop-manip.c' (loop specific parts and general loop
     utilities), 'tree-vect-slp' (loop-aware SLP functionality),
     'tree-vect-stmts.c' and 'tree-vect-data-refs.c'.  Analysis of data
     references is in 'tree-data-ref.c'.

     SLP Vectorization.  This pass performs vectorization of
     straight-line code.  The pass is implemented in 'tree-vectorizer.c'
     (the main driver), 'tree-vect-slp.c', 'tree-vect-stmts.c' and
     'tree-vect-data-refs.c'.

     Autoparallelization.  This pass splits the loop iteration space to
     run into several threads.  The pass is implemented in
     'tree-parloops.c'.

     Graphite is a loop transformation framework based on the polyhedral
     model.  Graphite stands for Gimple Represented as Polyhedra.  The
     internals of this infrastructure are documented in
     <http://gcc.gnu.org/wiki/Graphite>.  The passes working on this
     representation are implemented in the various 'graphite-*' files.

   * Tree level if-conversion for vectorizer

     This pass applies if-conversion to simple loops to help vectorizer.
     We identify if convertible loops, if-convert statements and merge
     basic blocks in one big block.  The idea is to present loop in such
     form so that vectorizer can have one to one mapping between
     statements and available vector operations.  This pass is located
     in 'tree-if-conv.c' and is described by 'pass_if_conversion'.

   * Conditional constant propagation

     This pass relaxes a lattice of values in order to identify those
     that must be constant even in the presence of conditional branches.
     The pass is located in 'tree-ssa-ccp.c' and is described by
     'pass_ccp'.

     A related pass that works on memory loads and stores, and not just
     register values, is located in 'tree-ssa-ccp.c' and described by
     'pass_store_ccp'.

   * Conditional copy propagation

     This is similar to constant propagation but the lattice of values
     is the "copy-of" relation.  It eliminates redundant copies from the
     code.  The pass is located in 'tree-ssa-copy.c' and described by
     'pass_copy_prop'.

     A related pass that works on memory copies, and not just register
     copies, is located in 'tree-ssa-copy.c' and described by
     'pass_store_copy_prop'.

   * Value range propagation

     This transformation is similar to constant propagation but instead
     of propagating single constant values, it propagates known value
     ranges.  The implementation is based on Patterson's range
     propagation algorithm (Accurate Static Branch Prediction by Value
     Range Propagation, J. R. C. Patterson, PLDI '95).  In contrast to
     Patterson's algorithm, this implementation does not propagate
     branch probabilities nor it uses more than a single range per SSA
     name.  This means that the current implementation cannot be used
     for branch prediction (though adapting it would not be difficult).
     The pass is located in 'tree-vrp.c' and is described by 'pass_vrp'.

   * Folding built-in functions

     This pass simplifies built-in functions, as applicable, with
     constant arguments or with inferable string lengths.  It is located
     in 'tree-ssa-ccp.c' and is described by 'pass_fold_builtins'.

   * Split critical edges

     This pass identifies critical edges and inserts empty basic blocks
     such that the edge is no longer critical.  The pass is located in
     'tree-cfg.c' and is described by 'pass_split_crit_edges'.

   * Control dependence dead code elimination

     This pass is a stronger form of dead code elimination that can
     eliminate unnecessary control flow statements.  It is located in
     'tree-ssa-dce.c' and is described by 'pass_cd_dce'.

   * Tail call elimination

     This pass identifies function calls that may be rewritten into
     jumps.  No code transformation is actually applied here, but the
     data and control flow problem is solved.  The code transformation
     requires target support, and so is delayed until RTL.  In the
     meantime 'CALL_EXPR_TAILCALL' is set indicating the possibility.
     The pass is located in 'tree-tailcall.c' and is described by
     'pass_tail_calls'.  The RTL transformation is handled by
     'fixup_tail_calls' in 'calls.c'.

   * Warn for function return without value

     For non-void functions, this pass locates return statements that do
     not specify a value and issues a warning.  Such a statement may
     have been injected by falling off the end of the function.  This
     pass is run last so that we have as much time as possible to prove
     that the statement is not reachable.  It is located in 'tree-cfg.c'
     and is described by 'pass_warn_function_return'.

   * Mudflap statement annotation

     If mudflap is enabled, we rewrite some memory accesses with code to
     validate that the memory access is correct.  In particular,
     expressions involving pointer dereferences ('INDIRECT_REF',
     'ARRAY_REF', etc.)  are replaced by code that checks the selected
     address range against the mudflap runtime's database of valid
     regions.  This check includes an inline lookup into a direct-mapped
     cache, based on shift/mask operations of the pointer value, with a
     fallback function call into the runtime.  The pass is located in
     'tree-mudflap.c' and is described by 'pass_mudflap_2'.

   * Leave static single assignment form

     This pass rewrites the function such that it is in normal form.  At
     the same time, we eliminate as many single-use temporaries as
     possible, so the intermediate language is no longer GIMPLE, but
     GENERIC.  The pass is located in 'tree-outof-ssa.c' and is
     described by 'pass_del_ssa'.

   * Merge PHI nodes that feed into one another

     This is part of the CFG cleanup passes.  It attempts to join PHI
     nodes from a forwarder CFG block into another block with PHI nodes.
     The pass is located in 'tree-cfgcleanup.c' and is described by
     'pass_merge_phi'.

   * Return value optimization

     If a function always returns the same local variable, and that
     local variable is an aggregate type, then the variable is replaced
     with the return value for the function (i.e., the function's
     DECL_RESULT). This is equivalent to the C++ named return value
     optimization applied to GIMPLE.  The pass is located in
     'tree-nrv.c' and is described by 'pass_nrv'.

   * Return slot optimization

     If a function returns a memory object and is called as 'var =
     foo()', this pass tries to change the call so that the address of
     'var' is sent to the caller to avoid an extra memory copy.  This
     pass is located in 'tree-nrv.c' and is described by
     'pass_return_slot'.

   * Optimize calls to '__builtin_object_size'

     This is a propagation pass similar to CCP that tries to remove
     calls to '__builtin_object_size' when the size of the object can be
     computed at compile-time.  This pass is located in
     'tree-object-size.c' and is described by 'pass_object_sizes'.

   * Loop invariant motion

     This pass removes expensive loop-invariant computations out of
     loops.  The pass is located in 'tree-ssa-loop.c' and described by
     'pass_lim'.

   * Loop nest optimizations

     This is a family of loop transformations that works on loop nests.
     It includes loop interchange, scaling, skewing and reversal and
     they are all geared to the optimization of data locality in array
     traversals and the removal of dependencies that hamper
     optimizations such as loop parallelization and vectorization.  The
     pass is located in 'tree-loop-linear.c' and described by
     'pass_linear_transform'.

   * Removal of empty loops

     This pass removes loops with no code in them.  The pass is located
     in 'tree-ssa-loop-ivcanon.c' and described by 'pass_empty_loop'.

   * Unrolling of small loops

     This pass completely unrolls loops with few iterations.  The pass
     is located in 'tree-ssa-loop-ivcanon.c' and described by
     'pass_complete_unroll'.

   * Predictive commoning

     This pass makes the code reuse the computations from the previous
     iterations of the loops, especially loads and stores to memory.  It
     does so by storing the values of these computations to a bank of
     temporary variables that are rotated at the end of loop.  To avoid
     the need for this rotation, the loop is then unrolled and the
     copies of the loop body are rewritten to use the appropriate
     version of the temporary variable.  This pass is located in
     'tree-predcom.c' and described by 'pass_predcom'.

   * Array prefetching

     This pass issues prefetch instructions for array references inside
     loops.  The pass is located in 'tree-ssa-loop-prefetch.c' and
     described by 'pass_loop_prefetch'.

   * Reassociation

     This pass rewrites arithmetic expressions to enable optimizations
     that operate on them, like redundancy elimination and
     vectorization.  The pass is located in 'tree-ssa-reassoc.c' and
     described by 'pass_reassoc'.

   * Optimization of 'stdarg' functions

     This pass tries to avoid the saving of register arguments into the
     stack on entry to 'stdarg' functions.  If the function doesn't use
     any 'va_start' macros, no registers need to be saved.  If
     'va_start' macros are used, the 'va_list' variables don't escape
     the function, it is only necessary to save registers that will be
     used in 'va_arg' macros.  For instance, if 'va_arg' is only used
     with integral types in the function, floating point registers don't
     need to be saved.  This pass is located in 'tree-stdarg.c' and
     described by 'pass_stdarg'.


File: gccint.info,  Node: RTL passes,  Prev: Tree SSA passes,  Up: Passes

9.5 RTL passes
==============

The following briefly describes the RTL generation and optimization
passes that are run after the Tree optimization passes.

   * RTL generation

     The source files for RTL generation include 'stmt.c', 'calls.c',
     'expr.c', 'explow.c', 'expmed.c', 'function.c', 'optabs.c' and
     'emit-rtl.c'.  Also, the file 'insn-emit.c', generated from the
     machine description by the program 'genemit', is used in this pass.
     The header file 'expr.h' is used for communication within this
     pass.

     The header files 'insn-flags.h' and 'insn-codes.h', generated from
     the machine description by the programs 'genflags' and 'gencodes',
     tell this pass which standard names are available for use and which
     patterns correspond to them.

   * Generation of exception landing pads

     This pass generates the glue that handles communication between the
     exception handling library routines and the exception handlers
     within the function.  Entry points in the function that are invoked
     by the exception handling library are called "landing pads".  The
     code for this pass is located in 'except.c'.

   * Control flow graph cleanup

     This pass removes unreachable code, simplifies jumps to next, jumps
     to jump, jumps across jumps, etc.  The pass is run multiple times.
     For historical reasons, it is occasionally referred to as the "jump
     optimization pass".  The bulk of the code for this pass is in
     'cfgcleanup.c', and there are support routines in 'cfgrtl.c' and
     'jump.c'.

   * Forward propagation of single-def values

     This pass attempts to remove redundant computation by substituting
     variables that come from a single definition, and seeing if the
     result can be simplified.  It performs copy propagation and
     addressing mode selection.  The pass is run twice, with values
     being propagated into loops only on the second run.  The code is
     located in 'fwprop.c'.

   * Common subexpression elimination

     This pass removes redundant computation within basic blocks, and
     optimizes addressing modes based on cost.  The pass is run twice.
     The code for this pass is located in 'cse.c'.

   * Global common subexpression elimination

     This pass performs two different types of GCSE depending on whether
     you are optimizing for size or not (LCM based GCSE tends to
     increase code size for a gain in speed, while Morel-Renvoise based
     GCSE does not).  When optimizing for size, GCSE is done using
     Morel-Renvoise Partial Redundancy Elimination, with the exception
     that it does not try to move invariants out of loops--that is left
     to the loop optimization pass.  If MR PRE GCSE is done, code
     hoisting (aka unification) is also done, as well as load motion.
     If you are optimizing for speed, LCM (lazy code motion) based GCSE
     is done.  LCM is based on the work of Knoop, Ruthing, and Steffen.
     LCM based GCSE also does loop invariant code motion.  We also
     perform load and store motion when optimizing for speed.
     Regardless of which type of GCSE is used, the GCSE pass also
     performs global constant and copy propagation.  The source file for
     this pass is 'gcse.c', and the LCM routines are in 'lcm.c'.

   * Loop optimization

     This pass performs several loop related optimizations.  The source
     files 'cfgloopanal.c' and 'cfgloopmanip.c' contain generic loop
     analysis and manipulation code.  Initialization and finalization of
     loop structures is handled by 'loop-init.c'.  A loop invariant
     motion pass is implemented in 'loop-invariant.c'.  Basic block
     level optimizations--unrolling, peeling and unswitching loops-- are
     implemented in 'loop-unswitch.c' and 'loop-unroll.c'.  Replacing of
     the exit condition of loops by special machine-dependent
     instructions is handled by 'loop-doloop.c'.

   * Jump bypassing

     This pass is an aggressive form of GCSE that transforms the control
     flow graph of a function by propagating constants into conditional
     branch instructions.  The source file for this pass is 'gcse.c'.

   * If conversion

     This pass attempts to replace conditional branches and surrounding
     assignments with arithmetic, boolean value producing comparison
     instructions, and conditional move instructions.  In the very last
     invocation after reload/LRA, it will generate predicated
     instructions when supported by the target.  The code is located in
     'ifcvt.c'.

   * Web construction

     This pass splits independent uses of each pseudo-register.  This
     can improve effect of the other transformation, such as CSE or
     register allocation.  The code for this pass is located in 'web.c'.

   * Instruction combination

     This pass attempts to combine groups of two or three instructions
     that are related by data flow into single instructions.  It
     combines the RTL expressions for the instructions by substitution,
     simplifies the result using algebra, and then attempts to match the
     result against the machine description.  The code is located in
     'combine.c'.

   * Register movement

     This pass looks for cases where matching constraints would force an
     instruction to need a reload, and this reload would be a
     register-to-register move.  It then attempts to change the
     registers used by the instruction to avoid the move instruction.
     The code is located in 'regmove.c'.

   * Mode switching optimization

     This pass looks for instructions that require the processor to be
     in a specific "mode" and minimizes the number of mode changes
     required to satisfy all users.  What these modes are, and what they
     apply to are completely target-specific.  The code for this pass is
     located in 'mode-switching.c'.

   * Modulo scheduling

     This pass looks at innermost loops and reorders their instructions
     by overlapping different iterations.  Modulo scheduling is
     performed immediately before instruction scheduling.  The code for
     this pass is located in 'modulo-sched.c'.

   * Instruction scheduling

     This pass looks for instructions whose output will not be available
     by the time that it is used in subsequent instructions.  Memory
     loads and floating point instructions often have this behavior on
     RISC machines.  It re-orders instructions within a basic block to
     try to separate the definition and use of items that otherwise
     would cause pipeline stalls.  This pass is performed twice, before
     and after register allocation.  The code for this pass is located
     in 'haifa-sched.c', 'sched-deps.c', 'sched-ebb.c', 'sched-rgn.c'
     and 'sched-vis.c'.

   * Register allocation

     These passes make sure that all occurrences of pseudo registers are
     eliminated, either by allocating them to a hard register, replacing
     them by an equivalent expression (e.g. a constant) or by placing
     them on the stack.  This is done in several subpasses:

        * Register move optimizations.  This pass makes some simple RTL
          code transformations which improve the subsequent register
          allocation.  The source file is 'regmove.c'.

        * The integrated register allocator (IRA).  It is called
          integrated because coalescing, register live range splitting,
          and hard register preferencing are done on-the-fly during
          coloring.  It also has better integration with the reload/LRA
          pass.  Pseudo-registers spilled by the allocator or the
          reload/LRA have still a chance to get hard-registers if the
          reload/LRA evicts some pseudo-registers from hard-registers.
          The allocator helps to choose better pseudos for spilling
          based on their live ranges and to coalesce stack slots
          allocated for the spilled pseudo-registers.  IRA is a regional
          register allocator which is transformed into Chaitin-Briggs
          allocator if there is one region.  By default, IRA chooses
          regions using register pressure but the user can force it to
          use one region or regions corresponding to all loops.

          Source files of the allocator are 'ira.c', 'ira-build.c',
          'ira-costs.c', 'ira-conflicts.c', 'ira-color.c', 'ira-emit.c',
          'ira-lives', plus header files 'ira.h' and 'ira-int.h' used
          for the communication between the allocator and the rest of
          the compiler and between the IRA files.

        * Reloading.  This pass renumbers pseudo registers with the
          hardware registers numbers they were allocated.  Pseudo
          registers that did not get hard registers are replaced with
          stack slots.  Then it finds instructions that are invalid
          because a value has failed to end up in a register, or has
          ended up in a register of the wrong kind.  It fixes up these
          instructions by reloading the problematical values temporarily
          into registers.  Additional instructions are generated to do
          the copying.

          The reload pass also optionally eliminates the frame pointer
          and inserts instructions to save and restore call-clobbered
          registers around calls.

          Source files are 'reload.c' and 'reload1.c', plus the header
          'reload.h' used for communication between them.

        * This pass is a modern replacement of the reload pass.  Source
          files are 'lra.c', 'lra-assign.c', 'lra-coalesce.c',
          'lra-constraints.c', 'lra-eliminations.c', 'lra-equivs.c',
          'lra-lives.c', 'lra-saves.c', 'lra-spills.c', the header
          'lra-int.h' used for communication between them, and the
          header 'lra.h' used for communication between LRA and the rest
          of compiler.

          Unlike the reload pass, intermediate LRA decisions are
          reflected in RTL as much as possible.  This reduces the number
          of target-dependent macros and hooks, leaving instruction
          constraints as the primary source of control.

          LRA is run on targets for which TARGET_LRA_P returns true.

   * Basic block reordering

     This pass implements profile guided code positioning.  If profile
     information is not available, various types of static analysis are
     performed to make the predictions normally coming from the profile
     feedback (IE execution frequency, branch probability, etc).  It is
     implemented in the file 'bb-reorder.c', and the various prediction
     routines are in 'predict.c'.

   * Variable tracking

     This pass computes where the variables are stored at each position
     in code and generates notes describing the variable locations to
     RTL code.  The location lists are then generated according to these
     notes to debug information if the debugging information format
     supports location lists.  The code is located in 'var-tracking.c'.

   * Delayed branch scheduling

     This optional pass attempts to find instructions that can go into
     the delay slots of other instructions, usually jumps and calls.
     The code for this pass is located in 'reorg.c'.

   * Branch shortening

     On many RISC machines, branch instructions have a limited range.
     Thus, longer sequences of instructions must be used for long
     branches.  In this pass, the compiler figures out what how far each
     instruction will be from each other instruction, and therefore
     whether the usual instructions, or the longer sequences, must be
     used for each branch.  The code for this pass is located in
     'final.c'.

   * Register-to-stack conversion

     Conversion from usage of some hard registers to usage of a register
     stack may be done at this point.  Currently, this is supported only
     for the floating-point registers of the Intel 80387 coprocessor.
     The code for this pass is located in 'reg-stack.c'.

   * Final

     This pass outputs the assembler code for the function.  The source
     files are 'final.c' plus 'insn-output.c'; the latter is generated
     automatically from the machine description by the tool 'genoutput'.
     The header file 'conditions.h' is used for communication between
     these files.  If mudflap is enabled, the queue of deferred
     declarations and any addressed constants (e.g., string literals) is
     processed by 'mudflap_finish_file' into a synthetic constructor
     function containing calls into the mudflap runtime.

   * Debugging information output

     This is run after final because it must output the stack slot
     offsets for pseudo registers that did not get hard registers.
     Source files are 'dbxout.c' for DBX symbol table format, 'sdbout.c'
     for SDB symbol table format, 'dwarfout.c' for DWARF symbol table
     format, files 'dwarf2out.c' and 'dwarf2asm.c' for DWARF2 symbol
     table format, and 'vmsdbgout.c' for VMS debug symbol table format.


File: gccint.info,  Node: RTL,  Next: GENERIC,  Prev: Passes,  Up: Top

10 RTL Representation
*********************

The last part of the compiler work is done on a low-level intermediate
representation called Register Transfer Language.  In this language, the
instructions to be output are described, pretty much one by one, in an
algebraic form that describes what the instruction does.

 RTL is inspired by Lisp lists.  It has both an internal form, made up
of structures that point at other structures, and a textual form that is
used in the machine description and in printed debugging dumps.  The
textual form uses nested parentheses to indicate the pointers in the
internal form.

* Menu:

* RTL Objects::       Expressions vs vectors vs strings vs integers.
* RTL Classes::       Categories of RTL expression objects, and their structure.
* Accessors::         Macros to access expression operands or vector elts.
* Special Accessors:: Macros to access specific annotations on RTL.
* Flags::             Other flags in an RTL expression.
* Machine Modes::     Describing the size and format of a datum.
* Constants::         Expressions with constant values.
* Regs and Memory::   Expressions representing register contents or memory.
* Arithmetic::        Expressions representing arithmetic on other expressions.
* Comparisons::       Expressions representing comparison of expressions.
* Bit-Fields::        Expressions representing bit-fields in memory or reg.
* Vector Operations:: Expressions involving vector datatypes.
* Conversions::       Extending, truncating, floating or fixing.
* RTL Declarations::  Declaring volatility, constancy, etc.
* Side Effects::      Expressions for storing in registers, etc.
* Incdec::            Embedded side-effects for autoincrement addressing.
* Assembler::         Representing 'asm' with operands.
* Debug Information:: Expressions representing debugging information.
* Insns::             Expression types for entire insns.
* Calls::             RTL representation of function call insns.
* Sharing::           Some expressions are unique; others *must* be copied.
* Reading RTL::       Reading textual RTL from a file.


File: gccint.info,  Node: RTL Objects,  Next: RTL Classes,  Up: RTL

10.1 RTL Object Types
=====================

RTL uses five kinds of objects: expressions, integers, wide integers,
strings and vectors.  Expressions are the most important ones.  An RTL
expression ("RTX", for short) is a C structure, but it is usually
referred to with a pointer; a type that is given the typedef name 'rtx'.

 An integer is simply an 'int'; their written form uses decimal digits.
A wide integer is an integral object whose type is 'HOST_WIDE_INT';
their written form uses decimal digits.

 A string is a sequence of characters.  In core it is represented as a
'char *' in usual C fashion, and it is written in C syntax as well.
However, strings in RTL may never be null.  If you write an empty string
in a machine description, it is represented in core as a null pointer
rather than as a pointer to a null character.  In certain contexts,
these null pointers instead of strings are valid.  Within RTL code,
strings are most commonly found inside 'symbol_ref' expressions, but
they appear in other contexts in the RTL expressions that make up
machine descriptions.

 In a machine description, strings are normally written with double
quotes, as you would in C.  However, strings in machine descriptions may
extend over many lines, which is invalid C, and adjacent string
constants are not concatenated as they are in C.  Any string constant
may be surrounded with a single set of parentheses.  Sometimes this
makes the machine description easier to read.

 There is also a special syntax for strings, which can be useful when C
code is embedded in a machine description.  Wherever a string can
appear, it is also valid to write a C-style brace block.  The entire
brace block, including the outermost pair of braces, is considered to be
the string constant.  Double quote characters inside the braces are not
special.  Therefore, if you write string constants in the C code, you
need not escape each quote character with a backslash.

 A vector contains an arbitrary number of pointers to expressions.  The
number of elements in the vector is explicitly present in the vector.
The written form of a vector consists of square brackets ('[...]')
surrounding the elements, in sequence and with whitespace separating
them.  Vectors of length zero are not created; null pointers are used
instead.

 Expressions are classified by "expression codes" (also called RTX
codes).  The expression code is a name defined in 'rtl.def', which is
also (in uppercase) a C enumeration constant.  The possible expression
codes and their meanings are machine-independent.  The code of an RTX
can be extracted with the macro 'GET_CODE (X)' and altered with
'PUT_CODE (X, NEWCODE)'.

 The expression code determines how many operands the expression
contains, and what kinds of objects they are.  In RTL, unlike Lisp, you
cannot tell by looking at an operand what kind of object it is.
Instead, you must know from its context--from the expression code of the
containing expression.  For example, in an expression of code 'subreg',
the first operand is to be regarded as an expression and the second
operand as an integer.  In an expression of code 'plus', there are two
operands, both of which are to be regarded as expressions.  In a
'symbol_ref' expression, there is one operand, which is to be regarded
as a string.

 Expressions are written as parentheses containing the name of the
expression type, its flags and machine mode if any, and then the
operands of the expression (separated by spaces).

 Expression code names in the 'md' file are written in lowercase, but
when they appear in C code they are written in uppercase.  In this
manual, they are shown as follows: 'const_int'.

 In a few contexts a null pointer is valid where an expression is
normally wanted.  The written form of this is '(nil)'.


File: gccint.info,  Node: RTL Classes,  Next: Accessors,  Prev: RTL Objects,  Up: RTL

10.2 RTL Classes and Formats
============================

The various expression codes are divided into several "classes", which
are represented by single characters.  You can determine the class of an
RTX code with the macro 'GET_RTX_CLASS (CODE)'.  Currently, 'rtl.def'
defines these classes:

'RTX_OBJ'
     An RTX code that represents an actual object, such as a register
     ('REG') or a memory location ('MEM', 'SYMBOL_REF').  'LO_SUM') is
     also included; instead, 'SUBREG' and 'STRICT_LOW_PART' are not in
     this class, but in class 'x'.

'RTX_CONST_OBJ'
     An RTX code that represents a constant object.  'HIGH' is also
     included in this class.

'RTX_COMPARE'
     An RTX code for a non-symmetric comparison, such as 'GEU' or 'LT'.

'RTX_COMM_COMPARE'
     An RTX code for a symmetric (commutative) comparison, such as 'EQ'
     or 'ORDERED'.

'RTX_UNARY'
     An RTX code for a unary arithmetic operation, such as 'NEG', 'NOT',
     or 'ABS'.  This category also includes value extension (sign or
     zero) and conversions between integer and floating point.

'RTX_COMM_ARITH'
     An RTX code for a commutative binary operation, such as 'PLUS' or
     'AND'.  'NE' and 'EQ' are comparisons, so they have class '<'.

'RTX_BIN_ARITH'
     An RTX code for a non-commutative binary operation, such as
     'MINUS', 'DIV', or 'ASHIFTRT'.

'RTX_BITFIELD_OPS'
     An RTX code for a bit-field operation.  Currently only
     'ZERO_EXTRACT' and 'SIGN_EXTRACT'.  These have three inputs and are
     lvalues (so they can be used for insertion as well).  *Note
     Bit-Fields::.

'RTX_TERNARY'
     An RTX code for other three input operations.  Currently only
     'IF_THEN_ELSE', 'VEC_MERGE', 'SIGN_EXTRACT', 'ZERO_EXTRACT', and
     'FMA'.

'RTX_INSN'
     An RTX code for an entire instruction: 'INSN', 'JUMP_INSN', and
     'CALL_INSN'.  *Note Insns::.

'RTX_MATCH'
     An RTX code for something that matches in insns, such as
     'MATCH_DUP'.  These only occur in machine descriptions.

'RTX_AUTOINC'
     An RTX code for an auto-increment addressing mode, such as
     'POST_INC'.

'RTX_EXTRA'
     All other RTX codes.  This category includes the remaining codes
     used only in machine descriptions ('DEFINE_*', etc.).  It also
     includes all the codes describing side effects ('SET', 'USE',
     'CLOBBER', etc.)  and the non-insns that may appear on an insn
     chain, such as 'NOTE', 'BARRIER', and 'CODE_LABEL'.  'SUBREG' is
     also part of this class.

 For each expression code, 'rtl.def' specifies the number of contained
objects and their kinds using a sequence of characters called the
"format" of the expression code.  For example, the format of 'subreg' is
'ei'.

 These are the most commonly used format characters:

'e'
     An expression (actually a pointer to an expression).

'i'
     An integer.

'w'
     A wide integer.

's'
     A string.

'E'
     A vector of expressions.

 A few other format characters are used occasionally:

'u'
     'u' is equivalent to 'e' except that it is printed differently in
     debugging dumps.  It is used for pointers to insns.

'n'
     'n' is equivalent to 'i' except that it is printed differently in
     debugging dumps.  It is used for the line number or code number of
     a 'note' insn.

'S'
     'S' indicates a string which is optional.  In the RTL objects in
     core, 'S' is equivalent to 's', but when the object is read, from
     an 'md' file, the string value of this operand may be omitted.  An
     omitted string is taken to be the null string.

'V'
     'V' indicates a vector which is optional.  In the RTL objects in
     core, 'V' is equivalent to 'E', but when the object is read from an
     'md' file, the vector value of this operand may be omitted.  An
     omitted vector is effectively the same as a vector of no elements.

'B'
     'B' indicates a pointer to basic block structure.

'0'
     '0' means a slot whose contents do not fit any normal category.
     '0' slots are not printed at all in dumps, and are often used in
     special ways by small parts of the compiler.

 There are macros to get the number of operands and the format of an
expression code:

'GET_RTX_LENGTH (CODE)'
     Number of operands of an RTX of code CODE.

'GET_RTX_FORMAT (CODE)'
     The format of an RTX of code CODE, as a C string.

 Some classes of RTX codes always have the same format.  For example, it
is safe to assume that all comparison operations have format 'ee'.

'1'
     All codes of this class have format 'e'.

'<'
'c'
'2'
     All codes of these classes have format 'ee'.

'b'
'3'
     All codes of these classes have format 'eee'.

'i'
     All codes of this class have formats that begin with 'iuueiee'.
     *Note Insns::.  Note that not all RTL objects linked onto an insn
     chain are of class 'i'.

'o'
'm'
'x'
     You can make no assumptions about the format of these codes.


File: gccint.info,  Node: Accessors,  Next: Special Accessors,  Prev: RTL Classes,  Up: RTL

10.3 Access to Operands
=======================

Operands of expressions are accessed using the macros 'XEXP', 'XINT',
'XWINT' and 'XSTR'.  Each of these macros takes two arguments: an
expression-pointer (RTX) and an operand number (counting from zero).
Thus,

     XEXP (X, 2)

accesses operand 2 of expression X, as an expression.

     XINT (X, 2)

accesses the same operand as an integer.  'XSTR', used in the same
fashion, would access it as a string.

 Any operand can be accessed as an integer, as an expression or as a
string.  You must choose the correct method of access for the kind of
value actually stored in the operand.  You would do this based on the
expression code of the containing expression.  That is also how you
would know how many operands there are.

 For example, if X is a 'subreg' expression, you know that it has two
operands which can be correctly accessed as 'XEXP (X, 0)' and 'XINT (X,
1)'.  If you did 'XINT (X, 0)', you would get the address of the
expression operand but cast as an integer; that might occasionally be
useful, but it would be cleaner to write '(int) XEXP (X, 0)'.  'XEXP (X,
1)' would also compile without error, and would return the second,
integer operand cast as an expression pointer, which would probably
result in a crash when accessed.  Nothing stops you from writing 'XEXP
(X, 28)' either, but this will access memory past the end of the
expression with unpredictable results.

 Access to operands which are vectors is more complicated.  You can use
the macro 'XVEC' to get the vector-pointer itself, or the macros
'XVECEXP' and 'XVECLEN' to access the elements and length of a vector.

'XVEC (EXP, IDX)'
     Access the vector-pointer which is operand number IDX in EXP.

'XVECLEN (EXP, IDX)'
     Access the length (number of elements) in the vector which is in
     operand number IDX in EXP.  This value is an 'int'.

'XVECEXP (EXP, IDX, ELTNUM)'
     Access element number ELTNUM in the vector which is in operand
     number IDX in EXP.  This value is an RTX.

     It is up to you to make sure that ELTNUM is not negative and is
     less than 'XVECLEN (EXP, IDX)'.

 All the macros defined in this section expand into lvalues and
therefore can be used to assign the operands, lengths and vector
elements as well as to access them.


File: gccint.info,  Node: Special Accessors,  Next: Flags,  Prev: Accessors,  Up: RTL

10.4 Access to Special Operands
===============================

Some RTL nodes have special annotations associated with them.

'MEM'
     'MEM_ALIAS_SET (X)'
          If 0, X is not in any alias set, and may alias anything.
          Otherwise, X can only alias 'MEM's in a conflicting alias set.
          This value is set in a language-dependent manner in the
          front-end, and should not be altered in the back-end.  In some
          front-ends, these numbers may correspond in some way to types,
          or other language-level entities, but they need not, and the
          back-end makes no such assumptions.  These set numbers are
          tested with 'alias_sets_conflict_p'.

     'MEM_EXPR (X)'
          If this register is known to hold the value of some user-level
          declaration, this is that tree node.  It may also be a
          'COMPONENT_REF', in which case this is some field reference,
          and 'TREE_OPERAND (X, 0)' contains the declaration, or another
          'COMPONENT_REF', or null if there is no compile-time object
          associated with the reference.

     'MEM_OFFSET_KNOWN_P (X)'
          True if the offset of the memory reference from 'MEM_EXPR' is
          known.  'MEM_OFFSET (X)' provides the offset if so.

     'MEM_OFFSET (X)'
          The offset from the start of 'MEM_EXPR'.  The value is only
          valid if 'MEM_OFFSET_KNOWN_P (X)' is true.

     'MEM_SIZE_KNOWN_P (X)'
          True if the size of the memory reference is known.  'MEM_SIZE
          (X)' provides its size if so.

     'MEM_SIZE (X)'
          The size in bytes of the memory reference.  This is mostly
          relevant for 'BLKmode' references as otherwise the size is
          implied by the mode.  The value is only valid if
          'MEM_SIZE_KNOWN_P (X)' is true.

     'MEM_ALIGN (X)'
          The known alignment in bits of the memory reference.

     'MEM_ADDR_SPACE (X)'
          The address space of the memory reference.  This will commonly
          be zero for the generic address space.

'REG'
     'ORIGINAL_REGNO (X)'
          This field holds the number the register "originally" had; for
          a pseudo register turned into a hard reg this will hold the
          old pseudo register number.

     'REG_EXPR (X)'
          If this register is known to hold the value of some user-level
          declaration, this is that tree node.

     'REG_OFFSET (X)'
          If this register is known to hold the value of some user-level
          declaration, this is the offset into that logical storage.

'SYMBOL_REF'
     'SYMBOL_REF_DECL (X)'
          If the 'symbol_ref' X was created for a 'VAR_DECL' or a
          'FUNCTION_DECL', that tree is recorded here.  If this value is
          null, then X was created by back end code generation routines,
          and there is no associated front end symbol table entry.

          'SYMBOL_REF_DECL' may also point to a tree of class ''c'',
          that is, some sort of constant.  In this case, the
          'symbol_ref' is an entry in the per-file constant pool; again,
          there is no associated front end symbol table entry.

     'SYMBOL_REF_CONSTANT (X)'
          If 'CONSTANT_POOL_ADDRESS_P (X)' is true, this is the constant
          pool entry for X.  It is null otherwise.

     'SYMBOL_REF_DATA (X)'
          A field of opaque type used to store 'SYMBOL_REF_DECL' or
          'SYMBOL_REF_CONSTANT'.

     'SYMBOL_REF_FLAGS (X)'
          In a 'symbol_ref', this is used to communicate various
          predicates about the symbol.  Some of these are common enough
          to be computed by common code, some are specific to the
          target.  The common bits are:

          'SYMBOL_FLAG_FUNCTION'
               Set if the symbol refers to a function.

          'SYMBOL_FLAG_LOCAL'
               Set if the symbol is local to this "module".  See
               'TARGET_BINDS_LOCAL_P'.

          'SYMBOL_FLAG_EXTERNAL'
               Set if this symbol is not defined in this translation
               unit.  Note that this is not the inverse of
               'SYMBOL_FLAG_LOCAL'.

          'SYMBOL_FLAG_SMALL'
               Set if the symbol is located in the small data section.
               See 'TARGET_IN_SMALL_DATA_P'.

          'SYMBOL_REF_TLS_MODEL (X)'
               This is a multi-bit field accessor that returns the
               'tls_model' to be used for a thread-local storage symbol.
               It returns zero for non-thread-local symbols.

          'SYMBOL_FLAG_HAS_BLOCK_INFO'
               Set if the symbol has 'SYMBOL_REF_BLOCK' and
               'SYMBOL_REF_BLOCK_OFFSET' fields.

          'SYMBOL_FLAG_ANCHOR'
               Set if the symbol is used as a section anchor.  "Section
               anchors" are symbols that have a known position within an
               'object_block' and that can be used to access nearby
               members of that block.  They are used to implement
               '-fsection-anchors'.

               If this flag is set, then 'SYMBOL_FLAG_HAS_BLOCK_INFO'
               will be too.

          Bits beginning with 'SYMBOL_FLAG_MACH_DEP' are available for
          the target's use.

'SYMBOL_REF_BLOCK (X)'
     If 'SYMBOL_REF_HAS_BLOCK_INFO_P (X)', this is the 'object_block'
     structure to which the symbol belongs, or 'NULL' if it has not been
     assigned a block.

'SYMBOL_REF_BLOCK_OFFSET (X)'
     If 'SYMBOL_REF_HAS_BLOCK_INFO_P (X)', this is the offset of X from
     the first object in 'SYMBOL_REF_BLOCK (X)'.  The value is negative
     if X has not yet been assigned to a block, or it has not been given
     an offset within that block.


File: gccint.info,  Node: Flags,  Next: Machine Modes,  Prev: Special Accessors,  Up: RTL

10.5 Flags in an RTL Expression
===============================

RTL expressions contain several flags (one-bit bit-fields) that are used
in certain types of expression.  Most often they are accessed with the
following macros, which expand into lvalues.

'CONSTANT_POOL_ADDRESS_P (X)'
     Nonzero in a 'symbol_ref' if it refers to part of the current
     function's constant pool.  For most targets these addresses are in
     a '.rodata' section entirely separate from the function, but for
     some targets the addresses are close to the beginning of the
     function.  In either case GCC assumes these addresses can be
     addressed directly, perhaps with the help of base registers.
     Stored in the 'unchanging' field and printed as '/u'.

'RTL_CONST_CALL_P (X)'
     In a 'call_insn' indicates that the insn represents a call to a
     const function.  Stored in the 'unchanging' field and printed as
     '/u'.

'RTL_PURE_CALL_P (X)'
     In a 'call_insn' indicates that the insn represents a call to a
     pure function.  Stored in the 'return_val' field and printed as
     '/i'.

'RTL_CONST_OR_PURE_CALL_P (X)'
     In a 'call_insn', true if 'RTL_CONST_CALL_P' or 'RTL_PURE_CALL_P'
     is true.

'RTL_LOOPING_CONST_OR_PURE_CALL_P (X)'
     In a 'call_insn' indicates that the insn represents a possibly
     infinite looping call to a const or pure function.  Stored in the
     'call' field and printed as '/c'.  Only true if one of
     'RTL_CONST_CALL_P' or 'RTL_PURE_CALL_P' is true.

'INSN_ANNULLED_BRANCH_P (X)'
     In a 'jump_insn', 'call_insn', or 'insn' indicates that the branch
     is an annulling one.  See the discussion under 'sequence' below.
     Stored in the 'unchanging' field and printed as '/u'.

'INSN_DELETED_P (X)'
     In an 'insn', 'call_insn', 'jump_insn', 'code_label', 'barrier', or
     'note', nonzero if the insn has been deleted.  Stored in the
     'volatil' field and printed as '/v'.

'INSN_FROM_TARGET_P (X)'
     In an 'insn' or 'jump_insn' or 'call_insn' in a delay slot of a
     branch, indicates that the insn is from the target of the branch.
     If the branch insn has 'INSN_ANNULLED_BRANCH_P' set, this insn will
     only be executed if the branch is taken.  For annulled branches
     with 'INSN_FROM_TARGET_P' clear, the insn will be executed only if
     the branch is not taken.  When 'INSN_ANNULLED_BRANCH_P' is not set,
     this insn will always be executed.  Stored in the 'in_struct' field
     and printed as '/s'.

'LABEL_PRESERVE_P (X)'
     In a 'code_label' or 'note', indicates that the label is referenced
     by code or data not visible to the RTL of a given function.  Labels
     referenced by a non-local goto will have this bit set.  Stored in
     the 'in_struct' field and printed as '/s'.

'LABEL_REF_NONLOCAL_P (X)'
     In 'label_ref' and 'reg_label' expressions, nonzero if this is a
     reference to a non-local label.  Stored in the 'volatil' field and
     printed as '/v'.

'MEM_KEEP_ALIAS_SET_P (X)'
     In 'mem' expressions, 1 if we should keep the alias set for this
     mem unchanged when we access a component.  Set to 1, for example,
     when we are already in a non-addressable component of an aggregate.
     Stored in the 'jump' field and printed as '/j'.

'MEM_VOLATILE_P (X)'
     In 'mem', 'asm_operands', and 'asm_input' expressions, nonzero for
     volatile memory references.  Stored in the 'volatil' field and
     printed as '/v'.

'MEM_NOTRAP_P (X)'
     In 'mem', nonzero for memory references that will not trap.  Stored
     in the 'call' field and printed as '/c'.

'MEM_POINTER (X)'
     Nonzero in a 'mem' if the memory reference holds a pointer.  Stored
     in the 'frame_related' field and printed as '/f'.

'REG_FUNCTION_VALUE_P (X)'
     Nonzero in a 'reg' if it is the place in which this function's
     value is going to be returned.  (This happens only in a hard
     register.)  Stored in the 'return_val' field and printed as '/i'.

'REG_POINTER (X)'
     Nonzero in a 'reg' if the register holds a pointer.  Stored in the
     'frame_related' field and printed as '/f'.

'REG_USERVAR_P (X)'
     In a 'reg', nonzero if it corresponds to a variable present in the
     user's source code.  Zero for temporaries generated internally by
     the compiler.  Stored in the 'volatil' field and printed as '/v'.

     The same hard register may be used also for collecting the values
     of functions called by this one, but 'REG_FUNCTION_VALUE_P' is zero
     in this kind of use.

'RTX_FRAME_RELATED_P (X)'
     Nonzero in an 'insn', 'call_insn', 'jump_insn', 'barrier', or 'set'
     which is part of a function prologue and sets the stack pointer,
     sets the frame pointer, or saves a register.  This flag should also
     be set on an instruction that sets up a temporary register to use
     in place of the frame pointer.  Stored in the 'frame_related' field
     and printed as '/f'.

     In particular, on RISC targets where there are limits on the sizes
     of immediate constants, it is sometimes impossible to reach the
     register save area directly from the stack pointer.  In that case,
     a temporary register is used that is near enough to the register
     save area, and the Canonical Frame Address, i.e., DWARF2's logical
     frame pointer, register must (temporarily) be changed to be this
     temporary register.  So, the instruction that sets this temporary
     register must be marked as 'RTX_FRAME_RELATED_P'.

     If the marked instruction is overly complex (defined in terms of
     what 'dwarf2out_frame_debug_expr' can handle), you will also have
     to create a 'REG_FRAME_RELATED_EXPR' note and attach it to the
     instruction.  This note should contain a simple expression of the
     computation performed by this instruction, i.e., one that
     'dwarf2out_frame_debug_expr' can handle.

     This flag is required for exception handling support on targets
     with RTL prologues.

'MEM_READONLY_P (X)'
     Nonzero in a 'mem', if the memory is statically allocated and
     read-only.

     Read-only in this context means never modified during the lifetime
     of the program, not necessarily in ROM or in write-disabled pages.
     A common example of the later is a shared library's global offset
     table.  This table is initialized by the runtime loader, so the
     memory is technically writable, but after control is transferred
     from the runtime loader to the application, this memory will never
     be subsequently modified.

     Stored in the 'unchanging' field and printed as '/u'.

'SCHED_GROUP_P (X)'
     During instruction scheduling, in an 'insn', 'call_insn' or
     'jump_insn', indicates that the previous insn must be scheduled
     together with this insn.  This is used to ensure that certain
     groups of instructions will not be split up by the instruction
     scheduling pass, for example, 'use' insns before a 'call_insn' may
     not be separated from the 'call_insn'.  Stored in the 'in_struct'
     field and printed as '/s'.

'SET_IS_RETURN_P (X)'
     For a 'set', nonzero if it is for a return.  Stored in the 'jump'
     field and printed as '/j'.

'SIBLING_CALL_P (X)'
     For a 'call_insn', nonzero if the insn is a sibling call.  Stored
     in the 'jump' field and printed as '/j'.

'STRING_POOL_ADDRESS_P (X)'
     For a 'symbol_ref' expression, nonzero if it addresses this
     function's string constant pool.  Stored in the 'frame_related'
     field and printed as '/f'.

'SUBREG_PROMOTED_UNSIGNED_P (X)'
     Returns a value greater then zero for a 'subreg' that has
     'SUBREG_PROMOTED_VAR_P' nonzero if the object being referenced is
     kept zero-extended, zero if it is kept sign-extended, and less then
     zero if it is extended some other way via the 'ptr_extend'
     instruction.  Stored in the 'unchanging' field and 'volatil' field,
     printed as '/u' and '/v'.  This macro may only be used to get the
     value it may not be used to change the value.  Use
     'SUBREG_PROMOTED_UNSIGNED_SET' to change the value.

'SUBREG_PROMOTED_UNSIGNED_SET (X)'
     Set the 'unchanging' and 'volatil' fields in a 'subreg' to reflect
     zero, sign, or other extension.  If 'volatil' is zero, then
     'unchanging' as nonzero means zero extension and as zero means sign
     extension.  If 'volatil' is nonzero then some other type of
     extension was done via the 'ptr_extend' instruction.

'SUBREG_PROMOTED_VAR_P (X)'
     Nonzero in a 'subreg' if it was made when accessing an object that
     was promoted to a wider mode in accord with the 'PROMOTED_MODE'
     machine description macro (*note Storage Layout::).  In this case,
     the mode of the 'subreg' is the declared mode of the object and the
     mode of 'SUBREG_REG' is the mode of the register that holds the
     object.  Promoted variables are always either sign- or
     zero-extended to the wider mode on every assignment.  Stored in the
     'in_struct' field and printed as '/s'.

'SYMBOL_REF_USED (X)'
     In a 'symbol_ref', indicates that X has been used.  This is
     normally only used to ensure that X is only declared external once.
     Stored in the 'used' field.

'SYMBOL_REF_WEAK (X)'
     In a 'symbol_ref', indicates that X has been declared weak.  Stored
     in the 'return_val' field and printed as '/i'.

'SYMBOL_REF_FLAG (X)'
     In a 'symbol_ref', this is used as a flag for machine-specific
     purposes.  Stored in the 'volatil' field and printed as '/v'.

     Most uses of 'SYMBOL_REF_FLAG' are historic and may be subsumed by
     'SYMBOL_REF_FLAGS'.  Certainly use of 'SYMBOL_REF_FLAGS' is
     mandatory if the target requires more than one bit of storage.

'PREFETCH_SCHEDULE_BARRIER_P (X)'
     In a 'prefetch', indicates that the prefetch is a scheduling
     barrier.  No other INSNs will be moved over it.  Stored in the
     'volatil' field and printed as '/v'.

 These are the fields to which the above macros refer:

'call'
     In a 'mem', 1 means that the memory reference will not trap.

     In a 'call', 1 means that this pure or const call may possibly
     infinite loop.

     In an RTL dump, this flag is represented as '/c'.

'frame_related'
     In an 'insn' or 'set' expression, 1 means that it is part of a
     function prologue and sets the stack pointer, sets the frame
     pointer, saves a register, or sets up a temporary register to use
     in place of the frame pointer.

     In 'reg' expressions, 1 means that the register holds a pointer.

     In 'mem' expressions, 1 means that the memory reference holds a
     pointer.

     In 'symbol_ref' expressions, 1 means that the reference addresses
     this function's string constant pool.

     In an RTL dump, this flag is represented as '/f'.

'in_struct'
     In 'reg' expressions, it is 1 if the register has its entire life
     contained within the test expression of some loop.

     In 'subreg' expressions, 1 means that the 'subreg' is accessing an
     object that has had its mode promoted from a wider mode.

     In 'label_ref' expressions, 1 means that the referenced label is
     outside the innermost loop containing the insn in which the
     'label_ref' was found.

     In 'code_label' expressions, it is 1 if the label may never be
     deleted.  This is used for labels which are the target of non-local
     gotos.  Such a label that would have been deleted is replaced with
     a 'note' of type 'NOTE_INSN_DELETED_LABEL'.

     In an 'insn' during dead-code elimination, 1 means that the insn is
     dead code.

     In an 'insn' or 'jump_insn' during reorg for an insn in the delay
     slot of a branch, 1 means that this insn is from the target of the
     branch.

     In an 'insn' during instruction scheduling, 1 means that this insn
     must be scheduled as part of a group together with the previous
     insn.

     In an RTL dump, this flag is represented as '/s'.

'return_val'
     In 'reg' expressions, 1 means the register contains the value to be
     returned by the current function.  On machines that pass parameters
     in registers, the same register number may be used for parameters
     as well, but this flag is not set on such uses.

     In 'symbol_ref' expressions, 1 means the referenced symbol is weak.

     In 'call' expressions, 1 means the call is pure.

     In an RTL dump, this flag is represented as '/i'.

'jump'
     In a 'mem' expression, 1 means we should keep the alias set for
     this mem unchanged when we access a component.

     In a 'set', 1 means it is for a return.

     In a 'call_insn', 1 means it is a sibling call.

     In an RTL dump, this flag is represented as '/j'.

'unchanging'
     In 'reg' and 'mem' expressions, 1 means that the value of the
     expression never changes.

     In 'subreg' expressions, it is 1 if the 'subreg' references an
     unsigned object whose mode has been promoted to a wider mode.

     In an 'insn' or 'jump_insn' in the delay slot of a branch
     instruction, 1 means an annulling branch should be used.

     In a 'symbol_ref' expression, 1 means that this symbol addresses
     something in the per-function constant pool.

     In a 'call_insn' 1 means that this instruction is a call to a const
     function.

     In an RTL dump, this flag is represented as '/u'.

'used'
     This flag is used directly (without an access macro) at the end of
     RTL generation for a function, to count the number of times an
     expression appears in insns.  Expressions that appear more than
     once are copied, according to the rules for shared structure (*note
     Sharing::).

     For a 'reg', it is used directly (without an access macro) by the
     leaf register renumbering code to ensure that each register is only
     renumbered once.

     In a 'symbol_ref', it indicates that an external declaration for
     the symbol has already been written.

'volatil'
     In a 'mem', 'asm_operands', or 'asm_input' expression, it is 1 if
     the memory reference is volatile.  Volatile memory references may
     not be deleted, reordered or combined.

     In a 'symbol_ref' expression, it is used for machine-specific
     purposes.

     In a 'reg' expression, it is 1 if the value is a user-level
     variable.  0 indicates an internal compiler temporary.

     In an 'insn', 1 means the insn has been deleted.

     In 'label_ref' and 'reg_label' expressions, 1 means a reference to
     a non-local label.

     In 'prefetch' expressions, 1 means that the containing insn is a
     scheduling barrier.

     In an RTL dump, this flag is represented as '/v'.


File: gccint.info,  Node: Machine Modes,  Next: Constants,  Prev: Flags,  Up: RTL

10.6 Machine Modes
==================

A machine mode describes a size of data object and the representation
used for it.  In the C code, machine modes are represented by an
enumeration type, 'enum machine_mode', defined in 'machmode.def'.  Each
RTL expression has room for a machine mode and so do certain kinds of
tree expressions (declarations and types, to be precise).

 In debugging dumps and machine descriptions, the machine mode of an RTL
expression is written after the expression code with a colon to separate
them.  The letters 'mode' which appear at the end of each machine mode
name are omitted.  For example, '(reg:SI 38)' is a 'reg' expression with
machine mode 'SImode'.  If the mode is 'VOIDmode', it is not written at
all.

 Here is a table of machine modes.  The term "byte" below refers to an
object of 'BITS_PER_UNIT' bits (*note Storage Layout::).

'BImode'
     "Bit" mode represents a single bit, for predicate registers.

'QImode'
     "Quarter-Integer" mode represents a single byte treated as an
     integer.

'HImode'
     "Half-Integer" mode represents a two-byte integer.

'PSImode'
     "Partial Single Integer" mode represents an integer which occupies
     four bytes but which doesn't really use all four.  On some
     machines, this is the right mode to use for pointers.

'SImode'
     "Single Integer" mode represents a four-byte integer.

'PDImode'
     "Partial Double Integer" mode represents an integer which occupies
     eight bytes but which doesn't really use all eight.  On some
     machines, this is the right mode to use for certain pointers.

'DImode'
     "Double Integer" mode represents an eight-byte integer.

'TImode'
     "Tetra Integer" (?)  mode represents a sixteen-byte integer.

'OImode'
     "Octa Integer" (?)  mode represents a thirty-two-byte integer.

'QFmode'
     "Quarter-Floating" mode represents a quarter-precision (single
     byte) floating point number.

'HFmode'
     "Half-Floating" mode represents a half-precision (two byte)
     floating point number.

'TQFmode'
     "Three-Quarter-Floating" (?)  mode represents a
     three-quarter-precision (three byte) floating point number.

'SFmode'
     "Single Floating" mode represents a four byte floating point
     number.  In the common case, of a processor with IEEE arithmetic
     and 8-bit bytes, this is a single-precision IEEE floating point
     number; it can also be used for double-precision (on processors
     with 16-bit bytes) and single-precision VAX and IBM types.

'DFmode'
     "Double Floating" mode represents an eight byte floating point
     number.  In the common case, of a processor with IEEE arithmetic
     and 8-bit bytes, this is a double-precision IEEE floating point
     number.

'XFmode'
     "Extended Floating" mode represents an IEEE extended floating point
     number.  This mode only has 80 meaningful bits (ten bytes).  Some
     processors require such numbers to be padded to twelve bytes,
     others to sixteen; this mode is used for either.

'SDmode'
     "Single Decimal Floating" mode represents a four byte decimal
     floating point number (as distinct from conventional binary
     floating point).

'DDmode'
     "Double Decimal Floating" mode represents an eight byte decimal
     floating point number.

'TDmode'
     "Tetra Decimal Floating" mode represents a sixteen byte decimal
     floating point number all 128 of whose bits are meaningful.

'TFmode'
     "Tetra Floating" mode represents a sixteen byte floating point
     number all 128 of whose bits are meaningful.  One common use is the
     IEEE quad-precision format.

'QQmode'
     "Quarter-Fractional" mode represents a single byte treated as a
     signed fractional number.  The default format is "s.7".

'HQmode'
     "Half-Fractional" mode represents a two-byte signed fractional
     number.  The default format is "s.15".

'SQmode'
     "Single Fractional" mode represents a four-byte signed fractional
     number.  The default format is "s.31".

'DQmode'
     "Double Fractional" mode represents an eight-byte signed fractional
     number.  The default format is "s.63".

'TQmode'
     "Tetra Fractional" mode represents a sixteen-byte signed fractional
     number.  The default format is "s.127".

'UQQmode'
     "Unsigned Quarter-Fractional" mode represents a single byte treated
     as an unsigned fractional number.  The default format is ".8".

'UHQmode'
     "Unsigned Half-Fractional" mode represents a two-byte unsigned
     fractional number.  The default format is ".16".

'USQmode'
     "Unsigned Single Fractional" mode represents a four-byte unsigned
     fractional number.  The default format is ".32".

'UDQmode'
     "Unsigned Double Fractional" mode represents an eight-byte unsigned
     fractional number.  The default format is ".64".

'UTQmode'
     "Unsigned Tetra Fractional" mode represents a sixteen-byte unsigned
     fractional number.  The default format is ".128".

'HAmode'
     "Half-Accumulator" mode represents a two-byte signed accumulator.
     The default format is "s8.7".

'SAmode'
     "Single Accumulator" mode represents a four-byte signed
     accumulator.  The default format is "s16.15".

'DAmode'
     "Double Accumulator" mode represents an eight-byte signed
     accumulator.  The default format is "s32.31".

'TAmode'
     "Tetra Accumulator" mode represents a sixteen-byte signed
     accumulator.  The default format is "s64.63".

'UHAmode'
     "Unsigned Half-Accumulator" mode represents a two-byte unsigned
     accumulator.  The default format is "8.8".

'USAmode'
     "Unsigned Single Accumulator" mode represents a four-byte unsigned
     accumulator.  The default format is "16.16".

'UDAmode'
     "Unsigned Double Accumulator" mode represents an eight-byte
     unsigned accumulator.  The default format is "32.32".

'UTAmode'
     "Unsigned Tetra Accumulator" mode represents a sixteen-byte
     unsigned accumulator.  The default format is "64.64".

'CCmode'
     "Condition Code" mode represents the value of a condition code,
     which is a machine-specific set of bits used to represent the
     result of a comparison operation.  Other machine-specific modes may
     also be used for the condition code.  These modes are not used on
     machines that use 'cc0' (*note Condition Code::).

'BLKmode'
     "Block" mode represents values that are aggregates to which none of
     the other modes apply.  In RTL, only memory references can have
     this mode, and only if they appear in string-move or vector
     instructions.  On machines which have no such instructions,
     'BLKmode' will not appear in RTL.

'VOIDmode'
     Void mode means the absence of a mode or an unspecified mode.  For
     example, RTL expressions of code 'const_int' have mode 'VOIDmode'
     because they can be taken to have whatever mode the context
     requires.  In debugging dumps of RTL, 'VOIDmode' is expressed by
     the absence of any mode.

'QCmode, HCmode, SCmode, DCmode, XCmode, TCmode'
     These modes stand for a complex number represented as a pair of
     floating point values.  The floating point values are in 'QFmode',
     'HFmode', 'SFmode', 'DFmode', 'XFmode', and 'TFmode', respectively.

'CQImode, CHImode, CSImode, CDImode, CTImode, COImode'
     These modes stand for a complex number represented as a pair of
     integer values.  The integer values are in 'QImode', 'HImode',
     'SImode', 'DImode', 'TImode', and 'OImode', respectively.

 The machine description defines 'Pmode' as a C macro which expands into
the machine mode used for addresses.  Normally this is the mode whose
size is 'BITS_PER_WORD', 'SImode' on 32-bit machines.

 The only modes which a machine description must support are 'QImode',
and the modes corresponding to 'BITS_PER_WORD', 'FLOAT_TYPE_SIZE' and
'DOUBLE_TYPE_SIZE'.  The compiler will attempt to use 'DImode' for
8-byte structures and unions, but this can be prevented by overriding
the definition of 'MAX_FIXED_MODE_SIZE'.  Alternatively, you can have
the compiler use 'TImode' for 16-byte structures and unions.  Likewise,
you can arrange for the C type 'short int' to avoid using 'HImode'.

 Very few explicit references to machine modes remain in the compiler
and these few references will soon be removed.  Instead, the machine
modes are divided into mode classes.  These are represented by the
enumeration type 'enum mode_class' defined in 'machmode.h'.  The
possible mode classes are:

'MODE_INT'
     Integer modes.  By default these are 'BImode', 'QImode', 'HImode',
     'SImode', 'DImode', 'TImode', and 'OImode'.

'MODE_PARTIAL_INT'
     The "partial integer" modes, 'PQImode', 'PHImode', 'PSImode' and
     'PDImode'.

'MODE_FLOAT'
     Floating point modes.  By default these are 'QFmode', 'HFmode',
     'TQFmode', 'SFmode', 'DFmode', 'XFmode' and 'TFmode'.

'MODE_DECIMAL_FLOAT'
     Decimal floating point modes.  By default these are 'SDmode',
     'DDmode' and 'TDmode'.

'MODE_FRACT'
     Signed fractional modes.  By default these are 'QQmode', 'HQmode',
     'SQmode', 'DQmode' and 'TQmode'.

'MODE_UFRACT'
     Unsigned fractional modes.  By default these are 'UQQmode',
     'UHQmode', 'USQmode', 'UDQmode' and 'UTQmode'.

'MODE_ACCUM'
     Signed accumulator modes.  By default these are 'HAmode', 'SAmode',
     'DAmode' and 'TAmode'.

'MODE_UACCUM'
     Unsigned accumulator modes.  By default these are 'UHAmode',
     'USAmode', 'UDAmode' and 'UTAmode'.

'MODE_COMPLEX_INT'
     Complex integer modes.  (These are not currently implemented).

'MODE_COMPLEX_FLOAT'
     Complex floating point modes.  By default these are 'QCmode',
     'HCmode', 'SCmode', 'DCmode', 'XCmode', and 'TCmode'.

'MODE_FUNCTION'
     Algol or Pascal function variables including a static chain.
     (These are not currently implemented).

'MODE_CC'
     Modes representing condition code values.  These are 'CCmode' plus
     any 'CC_MODE' modes listed in the 'MACHINE-modes.def'.  *Note Jump
     Patterns::, also see *note Condition Code::.

'MODE_RANDOM'
     This is a catchall mode class for modes which don't fit into the
     above classes.  Currently 'VOIDmode' and 'BLKmode' are in
     'MODE_RANDOM'.

 Here are some C macros that relate to machine modes:

'GET_MODE (X)'
     Returns the machine mode of the RTX X.

'PUT_MODE (X, NEWMODE)'
     Alters the machine mode of the RTX X to be NEWMODE.

'NUM_MACHINE_MODES'
     Stands for the number of machine modes available on the target
     machine.  This is one greater than the largest numeric value of any
     machine mode.

'GET_MODE_NAME (M)'
     Returns the name of mode M as a string.

'GET_MODE_CLASS (M)'
     Returns the mode class of mode M.

'GET_MODE_WIDER_MODE (M)'
     Returns the next wider natural mode.  For example, the expression
     'GET_MODE_WIDER_MODE (QImode)' returns 'HImode'.

'GET_MODE_SIZE (M)'
     Returns the size in bytes of a datum of mode M.

'GET_MODE_BITSIZE (M)'
     Returns the size in bits of a datum of mode M.

'GET_MODE_IBIT (M)'
     Returns the number of integral bits of a datum of fixed-point mode
     M.

'GET_MODE_FBIT (M)'
     Returns the number of fractional bits of a datum of fixed-point
     mode M.

'GET_MODE_MASK (M)'
     Returns a bitmask containing 1 for all bits in a word that fit
     within mode M.  This macro can only be used for modes whose bitsize
     is less than or equal to 'HOST_BITS_PER_INT'.

'GET_MODE_ALIGNMENT (M)'
     Return the required alignment, in bits, for an object of mode M.

'GET_MODE_UNIT_SIZE (M)'
     Returns the size in bytes of the subunits of a datum of mode M.
     This is the same as 'GET_MODE_SIZE' except in the case of complex
     modes.  For them, the unit size is the size of the real or
     imaginary part.

'GET_MODE_NUNITS (M)'
     Returns the number of units contained in a mode, i.e.,
     'GET_MODE_SIZE' divided by 'GET_MODE_UNIT_SIZE'.

'GET_CLASS_NARROWEST_MODE (C)'
     Returns the narrowest mode in mode class C.

 The global variables 'byte_mode' and 'word_mode' contain modes whose
classes are 'MODE_INT' and whose bitsizes are either 'BITS_PER_UNIT' or
'BITS_PER_WORD', respectively.  On 32-bit machines, these are 'QImode'
and 'SImode', respectively.


File: gccint.info,  Node: Constants,  Next: Regs and Memory,  Prev: Machine Modes,  Up: RTL

10.7 Constant Expression Types
==============================

The simplest RTL expressions are those that represent constant values.

'(const_int I)'
     This type of expression represents the integer value I.  I is
     customarily accessed with the macro 'INTVAL' as in 'INTVAL (EXP)',
     which is equivalent to 'XWINT (EXP, 0)'.

     Constants generated for modes with fewer bits than in
     'HOST_WIDE_INT' must be sign extended to full width (e.g., with
     'gen_int_mode').  For constants for modes with more bits than in
     'HOST_WIDE_INT' the implied high order bits of that constant are
     copies of the top bit.  Note however that values are neither
     inherently signed nor inherently unsigned; where necessary,
     signedness is determined by the rtl operation instead.

     There is only one expression object for the integer value zero; it
     is the value of the variable 'const0_rtx'.  Likewise, the only
     expression for integer value one is found in 'const1_rtx', the only
     expression for integer value two is found in 'const2_rtx', and the
     only expression for integer value negative one is found in
     'constm1_rtx'.  Any attempt to create an expression of code
     'const_int' and value zero, one, two or negative one will return
     'const0_rtx', 'const1_rtx', 'const2_rtx' or 'constm1_rtx' as
     appropriate.

     Similarly, there is only one object for the integer whose value is
     'STORE_FLAG_VALUE'.  It is found in 'const_true_rtx'.  If
     'STORE_FLAG_VALUE' is one, 'const_true_rtx' and 'const1_rtx' will
     point to the same object.  If 'STORE_FLAG_VALUE' is -1,
     'const_true_rtx' and 'constm1_rtx' will point to the same object.

'(const_double:M I0 I1 ...)'
     Represents either a floating-point constant of mode M or an integer
     constant too large to fit into 'HOST_BITS_PER_WIDE_INT' bits but
     small enough to fit within twice that number of bits (GCC does not
     provide a mechanism to represent even larger constants).  In the
     latter case, M will be 'VOIDmode'.  For integral values constants
     for modes with more bits than twice the number in 'HOST_WIDE_INT'
     the implied high order bits of that constant are copies of the top
     bit of 'CONST_DOUBLE_HIGH'.  Note however that integral values are
     neither inherently signed nor inherently unsigned; where necessary,
     signedness is determined by the rtl operation instead.

     If M is 'VOIDmode', the bits of the value are stored in I0 and I1.
     I0 is customarily accessed with the macro 'CONST_DOUBLE_LOW' and I1
     with 'CONST_DOUBLE_HIGH'.

     If the constant is floating point (regardless of its precision),
     then the number of integers used to store the value depends on the
     size of 'REAL_VALUE_TYPE' (*note Floating Point::).  The integers
     represent a floating point number, but not precisely in the target
     machine's or host machine's floating point format.  To convert them
     to the precise bit pattern used by the target machine, use the
     macro 'REAL_VALUE_TO_TARGET_DOUBLE' and friends (*note Data
     Output::).

'(const_fixed:M ...)'
     Represents a fixed-point constant of mode M.  The operand is a data
     structure of type 'struct fixed_value' and is accessed with the
     macro 'CONST_FIXED_VALUE'.  The high part of data is accessed with
     'CONST_FIXED_VALUE_HIGH'; the low part is accessed with
     'CONST_FIXED_VALUE_LOW'.

'(const_vector:M [X0 X1 ...])'
     Represents a vector constant.  The square brackets stand for the
     vector containing the constant elements.  X0, X1 and so on are the
     'const_int', 'const_double' or 'const_fixed' elements.

     The number of units in a 'const_vector' is obtained with the macro
     'CONST_VECTOR_NUNITS' as in 'CONST_VECTOR_NUNITS (V)'.

     Individual elements in a vector constant are accessed with the
     macro 'CONST_VECTOR_ELT' as in 'CONST_VECTOR_ELT (V, N)' where V is
     the vector constant and N is the element desired.

'(const_string STR)'
     Represents a constant string with value STR.  Currently this is
     used only for insn attributes (*note Insn Attributes::) since
     constant strings in C are placed in memory.

'(symbol_ref:MODE SYMBOL)'
     Represents the value of an assembler label for data.  SYMBOL is a
     string that describes the name of the assembler label.  If it
     starts with a '*', the label is the rest of SYMBOL not including
     the '*'.  Otherwise, the label is SYMBOL, usually prefixed with
     '_'.

     The 'symbol_ref' contains a mode, which is usually 'Pmode'.
     Usually that is the only mode for which a symbol is directly valid.

'(label_ref:MODE LABEL)'
     Represents the value of an assembler label for code.  It contains
     one operand, an expression, which must be a 'code_label' or a
     'note' of type 'NOTE_INSN_DELETED_LABEL' that appears in the
     instruction sequence to identify the place where the label should
     go.

     The reason for using a distinct expression type for code label
     references is so that jump optimization can distinguish them.

     The 'label_ref' contains a mode, which is usually 'Pmode'.  Usually
     that is the only mode for which a label is directly valid.

'(const:M EXP)'
     Represents a constant that is the result of an assembly-time
     arithmetic computation.  The operand, EXP, is an expression that
     contains only constants ('const_int', 'symbol_ref' and 'label_ref'
     expressions) combined with 'plus' and 'minus'.  However, not all
     combinations are valid, since the assembler cannot do arbitrary
     arithmetic on relocatable symbols.

     M should be 'Pmode'.

'(high:M EXP)'
     Represents the high-order bits of EXP, usually a 'symbol_ref'.  The
     number of bits is machine-dependent and is normally the number of
     bits specified in an instruction that initializes the high order
     bits of a register.  It is used with 'lo_sum' to represent the
     typical two-instruction sequence used in RISC machines to reference
     a global memory location.

     M should be 'Pmode'.

 The macro 'CONST0_RTX (MODE)' refers to an expression with value 0 in
mode MODE.  If mode MODE is of mode class 'MODE_INT', it returns
'const0_rtx'.  If mode MODE is of mode class 'MODE_FLOAT', it returns a
'CONST_DOUBLE' expression in mode MODE.  Otherwise, it returns a
'CONST_VECTOR' expression in mode MODE.  Similarly, the macro
'CONST1_RTX (MODE)' refers to an expression with value 1 in mode MODE
and similarly for 'CONST2_RTX'.  The 'CONST1_RTX' and 'CONST2_RTX'
macros are undefined for vector modes.


File: gccint.info,  Node: Regs and Memory,  Next: Arithmetic,  Prev: Constants,  Up: RTL

10.8 Registers and Memory
=========================

Here are the RTL expression types for describing access to machine
registers and to main memory.

'(reg:M N)'
     For small values of the integer N (those that are less than
     'FIRST_PSEUDO_REGISTER'), this stands for a reference to machine
     register number N: a "hard register".  For larger values of N, it
     stands for a temporary value or "pseudo register".  The compiler's
     strategy is to generate code assuming an unlimited number of such
     pseudo registers, and later convert them into hard registers or
     into memory references.

     M is the machine mode of the reference.  It is necessary because
     machines can generally refer to each register in more than one
     mode.  For example, a register may contain a full word but there
     may be instructions to refer to it as a half word or as a single
     byte, as well as instructions to refer to it as a floating point
     number of various precisions.

     Even for a register that the machine can access in only one mode,
     the mode must always be specified.

     The symbol 'FIRST_PSEUDO_REGISTER' is defined by the machine
     description, since the number of hard registers on the machine is
     an invariant characteristic of the machine.  Note, however, that
     not all of the machine registers must be general registers.  All
     the machine registers that can be used for storage of data are
     given hard register numbers, even those that can be used only in
     certain instructions or can hold only certain types of data.

     A hard register may be accessed in various modes throughout one
     function, but each pseudo register is given a natural mode and is
     accessed only in that mode.  When it is necessary to describe an
     access to a pseudo register using a nonnatural mode, a 'subreg'
     expression is used.

     A 'reg' expression with a machine mode that specifies more than one
     word of data may actually stand for several consecutive registers.
     If in addition the register number specifies a hardware register,
     then it actually represents several consecutive hardware registers
     starting with the specified one.

     Each pseudo register number used in a function's RTL code is
     represented by a unique 'reg' expression.

     Some pseudo register numbers, those within the range of
     'FIRST_VIRTUAL_REGISTER' to 'LAST_VIRTUAL_REGISTER' only appear
     during the RTL generation phase and are eliminated before the
     optimization phases.  These represent locations in the stack frame
     that cannot be determined until RTL generation for the function has
     been completed.  The following virtual register numbers are
     defined:

     'VIRTUAL_INCOMING_ARGS_REGNUM'
          This points to the first word of the incoming arguments passed
          on the stack.  Normally these arguments are placed there by
          the caller, but the callee may have pushed some arguments that
          were previously passed in registers.

          When RTL generation is complete, this virtual register is
          replaced by the sum of the register given by
          'ARG_POINTER_REGNUM' and the value of 'FIRST_PARM_OFFSET'.

     'VIRTUAL_STACK_VARS_REGNUM'
          If 'FRAME_GROWS_DOWNWARD' is defined to a nonzero value, this
          points to immediately above the first variable on the stack.
          Otherwise, it points to the first variable on the stack.

          'VIRTUAL_STACK_VARS_REGNUM' is replaced with the sum of the
          register given by 'FRAME_POINTER_REGNUM' and the value
          'STARTING_FRAME_OFFSET'.

     'VIRTUAL_STACK_DYNAMIC_REGNUM'
          This points to the location of dynamically allocated memory on
          the stack immediately after the stack pointer has been
          adjusted by the amount of memory desired.

          This virtual register is replaced by the sum of the register
          given by 'STACK_POINTER_REGNUM' and the value
          'STACK_DYNAMIC_OFFSET'.

     'VIRTUAL_OUTGOING_ARGS_REGNUM'
          This points to the location in the stack at which outgoing
          arguments should be written when the stack is pre-pushed
          (arguments pushed using push insns should always use
          'STACK_POINTER_REGNUM').

          This virtual register is replaced by the sum of the register
          given by 'STACK_POINTER_REGNUM' and the value
          'STACK_POINTER_OFFSET'.

'(subreg:M1 REG:M2 BYTENUM)'

     'subreg' expressions are used to refer to a register in a machine
     mode other than its natural one, or to refer to one register of a
     multi-part 'reg' that actually refers to several registers.

     Each pseudo register has a natural mode.  If it is necessary to
     operate on it in a different mode, the register must be enclosed in
     a 'subreg'.

     There are currently three supported types for the first operand of
     a 'subreg':
        * pseudo registers This is the most common case.  Most 'subreg's
          have pseudo 'reg's as their first operand.

        * mem 'subreg's of 'mem' were common in earlier versions of GCC
          and are still supported.  During the reload pass these are
          replaced by plain 'mem's.  On machines that do not do
          instruction scheduling, use of 'subreg's of 'mem' are still
          used, but this is no longer recommended.  Such 'subreg's are
          considered to be 'register_operand's rather than
          'memory_operand's before and during reload.  Because of this,
          the scheduling passes cannot properly schedule instructions
          with 'subreg's of 'mem', so for machines that do scheduling,
          'subreg's of 'mem' should never be used.  To support this, the
          combine and recog passes have explicit code to inhibit the
          creation of 'subreg's of 'mem' when 'INSN_SCHEDULING' is
          defined.

          The use of 'subreg's of 'mem' after the reload pass is an area
          that is not well understood and should be avoided.  There is
          still some code in the compiler to support this, but this code
          has possibly rotted.  This use of 'subreg's is discouraged and
          will most likely not be supported in the future.

        * hard registers It is seldom necessary to wrap hard registers
          in 'subreg's; such registers would normally reduce to a single
          'reg' rtx.  This use of 'subreg's is discouraged and may not
          be supported in the future.

     'subreg's of 'subreg's are not supported.  Using
     'simplify_gen_subreg' is the recommended way to avoid this problem.

     'subreg's come in two distinct flavors, each having its own usage
     and rules:

     Paradoxical subregs
          When M1 is strictly wider than M2, the 'subreg' expression is
          called "paradoxical".  The canonical test for this class of
          'subreg' is:

               GET_MODE_SIZE (M1) > GET_MODE_SIZE (M2)

          Paradoxical 'subreg's can be used as both lvalues and rvalues.
          When used as an lvalue, the low-order bits of the source value
          are stored in REG and the high-order bits are discarded.  When
          used as an rvalue, the low-order bits of the 'subreg' are
          taken from REG while the high-order bits may or may not be
          defined.

          The high-order bits of rvalues are in the following
          circumstances:

             * 'subreg's of 'mem' When M2 is smaller than a word, the
               macro 'LOAD_EXTEND_OP', can control how the high-order
               bits are defined.

             * 'subreg' of 'reg's The upper bits are defined when
               'SUBREG_PROMOTED_VAR_P' is true.
               'SUBREG_PROMOTED_UNSIGNED_P' describes what the upper
               bits hold.  Such subregs usually represent local
               variables, register variables and parameter pseudo
               variables that have been promoted to a wider mode.

          BYTENUM is always zero for a paradoxical 'subreg', even on
          big-endian targets.

          For example, the paradoxical 'subreg':

               (set (subreg:SI (reg:HI X) 0) Y)

          stores the lower 2 bytes of Y in X and discards the upper 2
          bytes.  A subsequent:

               (set Z (subreg:SI (reg:HI X) 0))

          would set the lower two bytes of Z to Y and set the upper two
          bytes to an unknown value assuming 'SUBREG_PROMOTED_VAR_P' is
          false.

     Normal subregs
          When M1 is at least as narrow as M2 the 'subreg' expression is
          called "normal".

          Normal 'subreg's restrict consideration to certain bits of
          REG.  There are two cases.  If M1 is smaller than a word, the
          'subreg' refers to the least-significant part (or "lowpart")
          of one word of REG.  If M1 is word-sized or greater, the
          'subreg' refers to one or more complete words.

          When used as an lvalue, 'subreg' is a word-based accessor.
          Storing to a 'subreg' modifies all the words of REG that
          overlap the 'subreg', but it leaves the other words of REG
          alone.

          When storing to a normal 'subreg' that is smaller than a word,
          the other bits of the referenced word are usually left in an
          undefined state.  This laxity makes it easier to generate
          efficient code for such instructions.  To represent an
          instruction that preserves all the bits outside of those in
          the 'subreg', use 'strict_low_part' or 'zero_extract' around
          the 'subreg'.

          BYTENUM must identify the offset of the first byte of the
          'subreg' from the start of REG, assuming that REG is laid out
          in memory order.  The memory order of bytes is defined by two
          target macros, 'WORDS_BIG_ENDIAN' and 'BYTES_BIG_ENDIAN':

             * 'WORDS_BIG_ENDIAN', if set to 1, says that byte number
               zero is part of the most significant word; otherwise, it
               is part of the least significant word.

             * 'BYTES_BIG_ENDIAN', if set to 1, says that byte number
               zero is the most significant byte within a word;
               otherwise, it is the least significant byte within a
               word.

          On a few targets, 'FLOAT_WORDS_BIG_ENDIAN' disagrees with
          'WORDS_BIG_ENDIAN'.  However, most parts of the compiler treat
          floating point values as if they had the same endianness as
          integer values.  This works because they handle them solely as
          a collection of integer values, with no particular numerical
          value.  Only real.c and the runtime libraries care about
          'FLOAT_WORDS_BIG_ENDIAN'.

          Thus,

               (subreg:HI (reg:SI X) 2)

          on a 'BYTES_BIG_ENDIAN', 'UNITS_PER_WORD == 4' target is the
          same as

               (subreg:HI (reg:SI X) 0)

          on a little-endian, 'UNITS_PER_WORD == 4' target.  Both
          'subreg's access the lower two bytes of register X.

     A 'MODE_PARTIAL_INT' mode behaves as if it were as wide as the
     corresponding 'MODE_INT' mode, except that it has an unknown number
     of undefined bits.  For example:

          (subreg:PSI (reg:SI 0) 0)

     accesses the whole of '(reg:SI 0)', but the exact relationship
     between the 'PSImode' value and the 'SImode' value is not defined.
     If we assume 'UNITS_PER_WORD <= 4', then the following two
     'subreg's:

          (subreg:PSI (reg:DI 0) 0)
          (subreg:PSI (reg:DI 0) 4)

     represent independent 4-byte accesses to the two halves of '(reg:DI
     0)'.  Both 'subreg's have an unknown number of undefined bits.

     If 'UNITS_PER_WORD <= 2' then these two 'subreg's:

          (subreg:HI (reg:PSI 0) 0)
          (subreg:HI (reg:PSI 0) 2)

     represent independent 2-byte accesses that together span the whole
     of '(reg:PSI 0)'.  Storing to the first 'subreg' does not affect
     the value of the second, and vice versa.  '(reg:PSI 0)' has an
     unknown number of undefined bits, so the assignment:

          (set (subreg:HI (reg:PSI 0) 0) (reg:HI 4))

     does not guarantee that '(subreg:HI (reg:PSI 0) 0)' has the value
     '(reg:HI 4)'.

     The rules above apply to both pseudo REGs and hard REGs.  If the
     semantics are not correct for particular combinations of M1, M2 and
     hard REG, the target-specific code must ensure that those
     combinations are never used.  For example:

          CANNOT_CHANGE_MODE_CLASS (M2, M1, CLASS)

     must be true for every class CLASS that includes REG.

     The first operand of a 'subreg' expression is customarily accessed
     with the 'SUBREG_REG' macro and the second operand is customarily
     accessed with the 'SUBREG_BYTE' macro.

     It has been several years since a platform in which
     'BYTES_BIG_ENDIAN' not equal to 'WORDS_BIG_ENDIAN' has been tested.
     Anyone wishing to support such a platform in the future may be
     confronted with code rot.

'(scratch:M)'
     This represents a scratch register that will be required for the
     execution of a single instruction and not used subsequently.  It is
     converted into a 'reg' by either the local register allocator or
     the reload pass.

     'scratch' is usually present inside a 'clobber' operation (*note
     Side Effects::).

'(cc0)'
     This refers to the machine's condition code register.  It has no
     operands and may not have a machine mode.  There are two ways to
     use it:

        * To stand for a complete set of condition code flags.  This is
          best on most machines, where each comparison sets the entire
          series of flags.

          With this technique, '(cc0)' may be validly used in only two
          contexts: as the destination of an assignment (in test and
          compare instructions) and in comparison operators comparing
          against zero ('const_int' with value zero; that is to say,
          'const0_rtx').

        * To stand for a single flag that is the result of a single
          condition.  This is useful on machines that have only a single
          flag bit, and in which comparison instructions must specify
          the condition to test.

          With this technique, '(cc0)' may be validly used in only two
          contexts: as the destination of an assignment (in test and
          compare instructions) where the source is a comparison
          operator, and as the first operand of 'if_then_else' (in a
          conditional branch).

     There is only one expression object of code 'cc0'; it is the value
     of the variable 'cc0_rtx'.  Any attempt to create an expression of
     code 'cc0' will return 'cc0_rtx'.

     Instructions can set the condition code implicitly.  On many
     machines, nearly all instructions set the condition code based on
     the value that they compute or store.  It is not necessary to
     record these actions explicitly in the RTL because the machine
     description includes a prescription for recognizing the
     instructions that do so (by means of the macro 'NOTICE_UPDATE_CC').
     *Note Condition Code::.  Only instructions whose sole purpose is to
     set the condition code, and instructions that use the condition
     code, need mention '(cc0)'.

     On some machines, the condition code register is given a register
     number and a 'reg' is used instead of '(cc0)'.  This is usually the
     preferable approach if only a small subset of instructions modify
     the condition code.  Other machines store condition codes in
     general registers; in such cases a pseudo register should be used.

     Some machines, such as the SPARC and RS/6000, have two sets of
     arithmetic instructions, one that sets and one that does not set
     the condition code.  This is best handled by normally generating
     the instruction that does not set the condition code, and making a
     pattern that both performs the arithmetic and sets the condition
     code register (which would not be '(cc0)' in this case).  For
     examples, search for 'addcc' and 'andcc' in 'sparc.md'.

'(pc)'
     This represents the machine's program counter.  It has no operands
     and may not have a machine mode.  '(pc)' may be validly used only
     in certain specific contexts in jump instructions.

     There is only one expression object of code 'pc'; it is the value
     of the variable 'pc_rtx'.  Any attempt to create an expression of
     code 'pc' will return 'pc_rtx'.

     All instructions that do not jump alter the program counter
     implicitly by incrementing it, but there is no need to mention this
     in the RTL.

'(mem:M ADDR ALIAS)'
     This RTX represents a reference to main memory at an address
     represented by the expression ADDR.  M specifies how large a unit
     of memory is accessed.  ALIAS specifies an alias set for the
     reference.  In general two items are in different alias sets if
     they cannot reference the same memory address.

     The construct '(mem:BLK (scratch))' is considered to alias all
     other memories.  Thus it may be used as a memory barrier in
     epilogue stack deallocation patterns.

'(concatM RTX RTX)'
     This RTX represents the concatenation of two other RTXs.  This is
     used for complex values.  It should only appear in the RTL attached
     to declarations and during RTL generation.  It should not appear in
     the ordinary insn chain.

'(concatnM [RTX ...])'
     This RTX represents the concatenation of all the RTX to make a
     single value.  Like 'concat', this should only appear in
     declarations, and not in the insn chain.


File: gccint.info,  Node: Arithmetic,  Next: Comparisons,  Prev: Regs and Memory,  Up: RTL

10.9 RTL Expressions for Arithmetic
===================================

Unless otherwise specified, all the operands of arithmetic expressions
must be valid for mode M.  An operand is valid for mode M if it has mode
M, or if it is a 'const_int' or 'const_double' and M is a mode of class
'MODE_INT'.

 For commutative binary operations, constants should be placed in the
second operand.

'(plus:M X Y)'
'(ss_plus:M X Y)'
'(us_plus:M X Y)'

     These three expressions all represent the sum of the values
     represented by X and Y carried out in machine mode M.  They differ
     in their behavior on overflow of integer modes.  'plus' wraps round
     modulo the width of M; 'ss_plus' saturates at the maximum signed
     value representable in M; 'us_plus' saturates at the maximum
     unsigned value.

'(lo_sum:M X Y)'

     This expression represents the sum of X and the low-order bits of
     Y.  It is used with 'high' (*note Constants::) to represent the
     typical two-instruction sequence used in RISC machines to reference
     a global memory location.

     The number of low order bits is machine-dependent but is normally
     the number of bits in a 'Pmode' item minus the number of bits set
     by 'high'.

     M should be 'Pmode'.

'(minus:M X Y)'
'(ss_minus:M X Y)'
'(us_minus:M X Y)'

     These three expressions represent the result of subtracting Y from
     X, carried out in mode M.  Behavior on overflow is the same as for
     the three variants of 'plus' (see above).

'(compare:M X Y)'
     Represents the result of subtracting Y from X for purposes of
     comparison.  The result is computed without overflow, as if with
     infinite precision.

     Of course, machines can't really subtract with infinite precision.
     However, they can pretend to do so when only the sign of the result
     will be used, which is the case when the result is stored in the
     condition code.  And that is the _only_ way this kind of expression
     may validly be used: as a value to be stored in the condition
     codes, either '(cc0)' or a register.  *Note Comparisons::.

     The mode M is not related to the modes of X and Y, but instead is
     the mode of the condition code value.  If '(cc0)' is used, it is
     'VOIDmode'.  Otherwise it is some mode in class 'MODE_CC', often
     'CCmode'.  *Note Condition Code::.  If M is 'VOIDmode' or 'CCmode',
     the operation returns sufficient information (in an unspecified
     format) so that any comparison operator can be applied to the
     result of the 'COMPARE' operation.  For other modes in class
     'MODE_CC', the operation only returns a subset of this information.

     Normally, X and Y must have the same mode.  Otherwise, 'compare' is
     valid only if the mode of X is in class 'MODE_INT' and Y is a
     'const_int' or 'const_double' with mode 'VOIDmode'.  The mode of X
     determines what mode the comparison is to be done in; thus it must
     not be 'VOIDmode'.

     If one of the operands is a constant, it should be placed in the
     second operand and the comparison code adjusted as appropriate.

     A 'compare' specifying two 'VOIDmode' constants is not valid since
     there is no way to know in what mode the comparison is to be
     performed; the comparison must either be folded during the
     compilation or the first operand must be loaded into a register
     while its mode is still known.

'(neg:M X)'
'(ss_neg:M X)'
'(us_neg:M X)'
     These two expressions represent the negation (subtraction from
     zero) of the value represented by X, carried out in mode M.  They
     differ in the behavior on overflow of integer modes.  In the case
     of 'neg', the negation of the operand may be a number not
     representable in mode M, in which case it is truncated to M.
     'ss_neg' and 'us_neg' ensure that an out-of-bounds result saturates
     to the maximum or minimum signed or unsigned value.

'(mult:M X Y)'
'(ss_mult:M X Y)'
'(us_mult:M X Y)'
     Represents the signed product of the values represented by X and Y
     carried out in machine mode M.  'ss_mult' and 'us_mult' ensure that
     an out-of-bounds result saturates to the maximum or minimum signed
     or unsigned value.

     Some machines support a multiplication that generates a product
     wider than the operands.  Write the pattern for this as

          (mult:M (sign_extend:M X) (sign_extend:M Y))

     where M is wider than the modes of X and Y, which need not be the
     same.

     For unsigned widening multiplication, use the same idiom, but with
     'zero_extend' instead of 'sign_extend'.

'(fma:M X Y Z)'
     Represents the 'fma', 'fmaf', and 'fmal' builtin functions that do
     a combined multiply of X and Y and then adding toZ without doing an
     intermediate rounding step.

'(div:M X Y)'
'(ss_div:M X Y)'
     Represents the quotient in signed division of X by Y, carried out
     in machine mode M.  If M is a floating point mode, it represents
     the exact quotient; otherwise, the integerized quotient.  'ss_div'
     ensures that an out-of-bounds result saturates to the maximum or
     minimum signed value.

     Some machines have division instructions in which the operands and
     quotient widths are not all the same; you should represent such
     instructions using 'truncate' and 'sign_extend' as in,

          (truncate:M1 (div:M2 X (sign_extend:M2 Y)))

'(udiv:M X Y)'
'(us_div:M X Y)'
     Like 'div' but represents unsigned division.  'us_div' ensures that
     an out-of-bounds result saturates to the maximum or minimum
     unsigned value.

'(mod:M X Y)'
'(umod:M X Y)'
     Like 'div' and 'udiv' but represent the remainder instead of the
     quotient.

'(smin:M X Y)'
'(smax:M X Y)'
     Represents the smaller (for 'smin') or larger (for 'smax') of X and
     Y, interpreted as signed values in mode M.  When used with floating
     point, if both operands are zeros, or if either operand is 'NaN',
     then it is unspecified which of the two operands is returned as the
     result.

'(umin:M X Y)'
'(umax:M X Y)'
     Like 'smin' and 'smax', but the values are interpreted as unsigned
     integers.

'(not:M X)'
     Represents the bitwise complement of the value represented by X,
     carried out in mode M, which must be a fixed-point machine mode.

'(and:M X Y)'
     Represents the bitwise logical-and of the values represented by X
     and Y, carried out in machine mode M, which must be a fixed-point
     machine mode.

'(ior:M X Y)'
     Represents the bitwise inclusive-or of the values represented by X
     and Y, carried out in machine mode M, which must be a fixed-point
     mode.

'(xor:M X Y)'
     Represents the bitwise exclusive-or of the values represented by X
     and Y, carried out in machine mode M, which must be a fixed-point
     mode.

'(ashift:M X C)'
'(ss_ashift:M X C)'
'(us_ashift:M X C)'
     These three expressions represent the result of arithmetically
     shifting X left by C places.  They differ in their behavior on
     overflow of integer modes.  An 'ashift' operation is a plain shift
     with no special behavior in case of a change in the sign bit;
     'ss_ashift' and 'us_ashift' saturates to the minimum or maximum
     representable value if any of the bits shifted out differs from the
     final sign bit.

     X have mode M, a fixed-point machine mode.  C be a fixed-point mode
     or be a constant with mode 'VOIDmode'; which mode is determined by
     the mode called for in the machine description entry for the
     left-shift instruction.  For example, on the VAX, the mode of C is
     'QImode' regardless of M.

'(lshiftrt:M X C)'
'(ashiftrt:M X C)'
     Like 'ashift' but for right shift.  Unlike the case for left shift,
     these two operations are distinct.

'(rotate:M X C)'
'(rotatert:M X C)'
     Similar but represent left and right rotate.  If C is a constant,
     use 'rotate'.

'(abs:M X)'
'(ss_abs:M X)'
     Represents the absolute value of X, computed in mode M.  'ss_abs'
     ensures that an out-of-bounds result saturates to the maximum
     signed value.

'(sqrt:M X)'
     Represents the square root of X, computed in mode M.  Most often M
     will be a floating point mode.

'(ffs:M X)'
     Represents one plus the index of the least significant 1-bit in X,
     represented as an integer of mode M.  (The value is zero if X is
     zero.)  The mode of X must be M or 'VOIDmode'.

'(clrsb:M X)'
     Represents the number of redundant leading sign bits in X,
     represented as an integer of mode M, starting at the most
     significant bit position.  This is one less than the number of
     leading sign bits (either 0 or 1), with no special cases.  The mode
     of X must be M or 'VOIDmode'.

'(clz:M X)'
     Represents the number of leading 0-bits in X, represented as an
     integer of mode M, starting at the most significant bit position.
     If X is zero, the value is determined by
     'CLZ_DEFINED_VALUE_AT_ZERO' (*note Misc::).  Note that this is one
     of the few expressions that is not invariant under widening.  The
     mode of X must be M or 'VOIDmode'.

'(ctz:M X)'
     Represents the number of trailing 0-bits in X, represented as an
     integer of mode M, starting at the least significant bit position.
     If X is zero, the value is determined by
     'CTZ_DEFINED_VALUE_AT_ZERO' (*note Misc::).  Except for this case,
     'ctz(x)' is equivalent to 'ffs(X) - 1'.  The mode of X must be M or
     'VOIDmode'.

'(popcount:M X)'
     Represents the number of 1-bits in X, represented as an integer of
     mode M.  The mode of X must be M or 'VOIDmode'.

'(parity:M X)'
     Represents the number of 1-bits modulo 2 in X, represented as an
     integer of mode M.  The mode of X must be M or 'VOIDmode'.

'(bswap:M X)'
     Represents the value X with the order of bytes reversed, carried
     out in mode M, which must be a fixed-point machine mode.  The mode
     of X must be M or 'VOIDmode'.


File: gccint.info,  Node: Comparisons,  Next: Bit-Fields,  Prev: Arithmetic,  Up: RTL

10.10 Comparison Operations
===========================

Comparison operators test a relation on two operands and are considered
to represent a machine-dependent nonzero value described by, but not
necessarily equal to, 'STORE_FLAG_VALUE' (*note Misc::) if the relation
holds, or zero if it does not, for comparison operators whose results
have a 'MODE_INT' mode, 'FLOAT_STORE_FLAG_VALUE' (*note Misc::) if the
relation holds, or zero if it does not, for comparison operators that
return floating-point values, and a vector of either
'VECTOR_STORE_FLAG_VALUE' (*note Misc::) if the relation holds, or of
zeros if it does not, for comparison operators that return vector
results.  The mode of the comparison operation is independent of the
mode of the data being compared.  If the comparison operation is being
tested (e.g., the first operand of an 'if_then_else'), the mode must be
'VOIDmode'.

 There are two ways that comparison operations may be used.  The
comparison operators may be used to compare the condition codes '(cc0)'
against zero, as in '(eq (cc0) (const_int 0))'.  Such a construct
actually refers to the result of the preceding instruction in which the
condition codes were set.  The instruction setting the condition code
must be adjacent to the instruction using the condition code; only
'note' insns may separate them.

 Alternatively, a comparison operation may directly compare two data
objects.  The mode of the comparison is determined by the operands; they
must both be valid for a common machine mode.  A comparison with both
operands constant would be invalid as the machine mode could not be
deduced from it, but such a comparison should never exist in RTL due to
constant folding.

 In the example above, if '(cc0)' were last set to '(compare X Y)', the
comparison operation is identical to '(eq X Y)'.  Usually only one style
of comparisons is supported on a particular machine, but the combine
pass will try to merge the operations to produce the 'eq' shown in case
it exists in the context of the particular insn involved.

 Inequality comparisons come in two flavors, signed and unsigned.  Thus,
there are distinct expression codes 'gt' and 'gtu' for signed and
unsigned greater-than.  These can produce different results for the same
pair of integer values: for example, 1 is signed greater-than -1 but not
unsigned greater-than, because -1 when regarded as unsigned is actually
'0xffffffff' which is greater than 1.

 The signed comparisons are also used for floating point values.
Floating point comparisons are distinguished by the machine modes of the
operands.

'(eq:M X Y)'
     'STORE_FLAG_VALUE' if the values represented by X and Y are equal,
     otherwise 0.

'(ne:M X Y)'
     'STORE_FLAG_VALUE' if the values represented by X and Y are not
     equal, otherwise 0.

'(gt:M X Y)'
     'STORE_FLAG_VALUE' if the X is greater than Y.  If they are
     fixed-point, the comparison is done in a signed sense.

'(gtu:M X Y)'
     Like 'gt' but does unsigned comparison, on fixed-point numbers
     only.

'(lt:M X Y)'
'(ltu:M X Y)'
     Like 'gt' and 'gtu' but test for "less than".

'(ge:M X Y)'
'(geu:M X Y)'
     Like 'gt' and 'gtu' but test for "greater than or equal".

'(le:M X Y)'
'(leu:M X Y)'
     Like 'gt' and 'gtu' but test for "less than or equal".

'(if_then_else COND THEN ELSE)'
     This is not a comparison operation but is listed here because it is
     always used in conjunction with a comparison operation.  To be
     precise, COND is a comparison expression.  This expression
     represents a choice, according to COND, between the value
     represented by THEN and the one represented by ELSE.

     On most machines, 'if_then_else' expressions are valid only to
     express conditional jumps.

'(cond [TEST1 VALUE1 TEST2 VALUE2 ...] DEFAULT)'
     Similar to 'if_then_else', but more general.  Each of TEST1, TEST2,
     ... is performed in turn.  The result of this expression is the
     VALUE corresponding to the first nonzero test, or DEFAULT if none
     of the tests are nonzero expressions.

     This is currently not valid for instruction patterns and is
     supported only for insn attributes.  *Note Insn Attributes::.


File: gccint.info,  Node: Bit-Fields,  Next: Vector Operations,  Prev: Comparisons,  Up: RTL

10.11 Bit-Fields
================

Special expression codes exist to represent bit-field instructions.

'(sign_extract:M LOC SIZE POS)'
     This represents a reference to a sign-extended bit-field contained
     or starting in LOC (a memory or register reference).  The bit-field
     is SIZE bits wide and starts at bit POS.  The compilation option
     'BITS_BIG_ENDIAN' says which end of the memory unit POS counts
     from.

     If LOC is in memory, its mode must be a single-byte integer mode.
     If LOC is in a register, the mode to use is specified by the
     operand of the 'insv' or 'extv' pattern (*note Standard Names::)
     and is usually a full-word integer mode, which is the default if
     none is specified.

     The mode of POS is machine-specific and is also specified in the
     'insv' or 'extv' pattern.

     The mode M is the same as the mode that would be used for LOC if it
     were a register.

     A 'sign_extract' can not appear as an lvalue, or part thereof, in
     RTL.

'(zero_extract:M LOC SIZE POS)'
     Like 'sign_extract' but refers to an unsigned or zero-extended
     bit-field.  The same sequence of bits are extracted, but they are
     filled to an entire word with zeros instead of by sign-extension.

     Unlike 'sign_extract', this type of expressions can be lvalues in
     RTL; they may appear on the left side of an assignment, indicating
     insertion of a value into the specified bit-field.


File: gccint.info,  Node: Vector Operations,  Next: Conversions,  Prev: Bit-Fields,  Up: RTL

10.12 Vector Operations
=======================

All normal RTL expressions can be used with vector modes; they are
interpreted as operating on each part of the vector independently.
Additionally, there are a few new expressions to describe specific
vector operations.

'(vec_merge:M VEC1 VEC2 ITEMS)'
     This describes a merge operation between two vectors.  The result
     is a vector of mode M; its elements are selected from either VEC1
     or VEC2.  Which elements are selected is described by ITEMS, which
     is a bit mask represented by a 'const_int'; a zero bit indicates
     the corresponding element in the result vector is taken from VEC2
     while a set bit indicates it is taken from VEC1.

'(vec_select:M VEC1 SELECTION)'
     This describes an operation that selects parts of a vector.  VEC1
     is the source vector, and SELECTION is a 'parallel' that contains a
     'const_int' for each of the subparts of the result vector, giving
     the number of the source subpart that should be stored into it.
     The result mode M is either the submode for a single element of
     VEC1 (if only one subpart is selected), or another vector mode with
     that element submode (if multiple subparts are selected).

'(vec_concat:M X1 X2)'
     Describes a vector concat operation.  The result is a concatenation
     of the vectors or scalars X1 and X2; its length is the sum of the
     lengths of the two inputs.

'(vec_duplicate:M X)'
     This operation converts a scalar into a vector or a small vector
     into a larger one by duplicating the input values.  The output
     vector mode must have the same submodes as the input vector mode or
     the scalar modes, and the number of output parts must be an integer
     multiple of the number of input parts.


File: gccint.info,  Node: Conversions,  Next: RTL Declarations,  Prev: Vector Operations,  Up: RTL

10.13 Conversions
=================

All conversions between machine modes must be represented by explicit
conversion operations.  For example, an expression which is the sum of a
byte and a full word cannot be written as '(plus:SI (reg:QI 34) (reg:SI
80))' because the 'plus' operation requires two operands of the same
machine mode.  Therefore, the byte-sized operand is enclosed in a
conversion operation, as in

     (plus:SI (sign_extend:SI (reg:QI 34)) (reg:SI 80))

 The conversion operation is not a mere placeholder, because there may
be more than one way of converting from a given starting mode to the
desired final mode.  The conversion operation code says how to do it.

 For all conversion operations, X must not be 'VOIDmode' because the
mode in which to do the conversion would not be known.  The conversion
must either be done at compile-time or X must be placed into a register.

'(sign_extend:M X)'
     Represents the result of sign-extending the value X to machine mode
     M.  M must be a fixed-point mode and X a fixed-point value of a
     mode narrower than M.

'(zero_extend:M X)'
     Represents the result of zero-extending the value X to machine mode
     M.  M must be a fixed-point mode and X a fixed-point value of a
     mode narrower than M.

'(float_extend:M X)'
     Represents the result of extending the value X to machine mode M.
     M must be a floating point mode and X a floating point value of a
     mode narrower than M.

'(truncate:M X)'
     Represents the result of truncating the value X to machine mode M.
     M must be a fixed-point mode and X a fixed-point value of a mode
     wider than M.

'(ss_truncate:M X)'
     Represents the result of truncating the value X to machine mode M,
     using signed saturation in the case of overflow.  Both M and the
     mode of X must be fixed-point modes.

'(us_truncate:M X)'
     Represents the result of truncating the value X to machine mode M,
     using unsigned saturation in the case of overflow.  Both M and the
     mode of X must be fixed-point modes.

'(float_truncate:M X)'
     Represents the result of truncating the value X to machine mode M.
     M must be a floating point mode and X a floating point value of a
     mode wider than M.

'(float:M X)'
     Represents the result of converting fixed point value X, regarded
     as signed, to floating point mode M.

'(unsigned_float:M X)'
     Represents the result of converting fixed point value X, regarded
     as unsigned, to floating point mode M.

'(fix:M X)'
     When M is a floating-point mode, represents the result of
     converting floating point value X (valid for mode M) to an integer,
     still represented in floating point mode M, by rounding towards
     zero.

     When M is a fixed-point mode, represents the result of converting
     floating point value X to mode M, regarded as signed.  How rounding
     is done is not specified, so this operation may be used validly in
     compiling C code only for integer-valued operands.

'(unsigned_fix:M X)'
     Represents the result of converting floating point value X to fixed
     point mode M, regarded as unsigned.  How rounding is done is not
     specified.

'(fract_convert:M X)'
     Represents the result of converting fixed-point value X to
     fixed-point mode M, signed integer value X to fixed-point mode M,
     floating-point value X to fixed-point mode M, fixed-point value X
     to integer mode M regarded as signed, or fixed-point value X to
     floating-point mode M.  When overflows or underflows happen, the
     results are undefined.

'(sat_fract:M X)'
     Represents the result of converting fixed-point value X to
     fixed-point mode M, signed integer value X to fixed-point mode M,
     or floating-point value X to fixed-point mode M.  When overflows or
     underflows happen, the results are saturated to the maximum or the
     minimum.

'(unsigned_fract_convert:M X)'
     Represents the result of converting fixed-point value X to integer
     mode M regarded as unsigned, or unsigned integer value X to
     fixed-point mode M.  When overflows or underflows happen, the
     results are undefined.

'(unsigned_sat_fract:M X)'
     Represents the result of converting unsigned integer value X to
     fixed-point mode M.  When overflows or underflows happen, the
     results are saturated to the maximum or the minimum.


File: gccint.info,  Node: RTL Declarations,  Next: Side Effects,  Prev: Conversions,  Up: RTL

10.14 Declarations
==================

Declaration expression codes do not represent arithmetic operations but
rather state assertions about their operands.

'(strict_low_part (subreg:M (reg:N R) 0))'
     This expression code is used in only one context: as the
     destination operand of a 'set' expression.  In addition, the
     operand of this expression must be a non-paradoxical 'subreg'
     expression.

     The presence of 'strict_low_part' says that the part of the
     register which is meaningful in mode N, but is not part of mode M,
     is not to be altered.  Normally, an assignment to such a subreg is
     allowed to have undefined effects on the rest of the register when
     M is less than a word.


File: gccint.info,  Node: Side Effects,  Next: Incdec,  Prev: RTL Declarations,  Up: RTL

10.15 Side Effect Expressions
=============================

The expression codes described so far represent values, not actions.
But machine instructions never produce values; they are meaningful only
for their side effects on the state of the machine.  Special expression
codes are used to represent side effects.

 The body of an instruction is always one of these side effect codes;
the codes described above, which represent values, appear only as the
operands of these.

'(set LVAL X)'
     Represents the action of storing the value of X into the place
     represented by LVAL.  LVAL must be an expression representing a
     place that can be stored in: 'reg' (or 'subreg', 'strict_low_part'
     or 'zero_extract'), 'mem', 'pc', 'parallel', or 'cc0'.

     If LVAL is a 'reg', 'subreg' or 'mem', it has a machine mode; then
     X must be valid for that mode.

     If LVAL is a 'reg' whose machine mode is less than the full width
     of the register, then it means that the part of the register
     specified by the machine mode is given the specified value and the
     rest of the register receives an undefined value.  Likewise, if
     LVAL is a 'subreg' whose machine mode is narrower than the mode of
     the register, the rest of the register can be changed in an
     undefined way.

     If LVAL is a 'strict_low_part' of a subreg, then the part of the
     register specified by the machine mode of the 'subreg' is given the
     value X and the rest of the register is not changed.

     If LVAL is a 'zero_extract', then the referenced part of the
     bit-field (a memory or register reference) specified by the
     'zero_extract' is given the value X and the rest of the bit-field
     is not changed.  Note that 'sign_extract' can not appear in LVAL.

     If LVAL is '(cc0)', it has no machine mode, and X may be either a
     'compare' expression or a value that may have any mode.  The latter
     case represents a "test" instruction.  The expression '(set (cc0)
     (reg:M N))' is equivalent to '(set (cc0) (compare (reg:M N)
     (const_int 0)))'.  Use the former expression to save space during
     the compilation.

     If LVAL is a 'parallel', it is used to represent the case of a
     function returning a structure in multiple registers.  Each element
     of the 'parallel' is an 'expr_list' whose first operand is a 'reg'
     and whose second operand is a 'const_int' representing the offset
     (in bytes) into the structure at which the data in that register
     corresponds.  The first element may be null to indicate that the
     structure is also passed partly in memory.

     If LVAL is '(pc)', we have a jump instruction, and the
     possibilities for X are very limited.  It may be a 'label_ref'
     expression (unconditional jump).  It may be an 'if_then_else'
     (conditional jump), in which case either the second or the third
     operand must be '(pc)' (for the case which does not jump) and the
     other of the two must be a 'label_ref' (for the case which does
     jump).  X may also be a 'mem' or '(plus:SI (pc) Y)', where Y may be
     a 'reg' or a 'mem'; these unusual patterns are used to represent
     jumps through branch tables.

     If LVAL is neither '(cc0)' nor '(pc)', the mode of LVAL must not be
     'VOIDmode' and the mode of X must be valid for the mode of LVAL.

     LVAL is customarily accessed with the 'SET_DEST' macro and X with
     the 'SET_SRC' macro.

'(return)'
     As the sole expression in a pattern, represents a return from the
     current function, on machines where this can be done with one
     instruction, such as VAXen.  On machines where a multi-instruction
     "epilogue" must be executed in order to return from the function,
     returning is done by jumping to a label which precedes the
     epilogue, and the 'return' expression code is never used.

     Inside an 'if_then_else' expression, represents the value to be
     placed in 'pc' to return to the caller.

     Note that an insn pattern of '(return)' is logically equivalent to
     '(set (pc) (return))', but the latter form is never used.

'(simple_return)'
     Like '(return)', but truly represents only a function return, while
     '(return)' may represent an insn that also performs other functions
     of the function epilogue.  Like '(return)', this may also occur in
     conditional jumps.

'(call FUNCTION NARGS)'
     Represents a function call.  FUNCTION is a 'mem' expression whose
     address is the address of the function to be called.  NARGS is an
     expression which can be used for two purposes: on some machines it
     represents the number of bytes of stack argument; on others, it
     represents the number of argument registers.

     Each machine has a standard machine mode which FUNCTION must have.
     The machine description defines macro 'FUNCTION_MODE' to expand
     into the requisite mode name.  The purpose of this mode is to
     specify what kind of addressing is allowed, on machines where the
     allowed kinds of addressing depend on the machine mode being
     addressed.

'(clobber X)'
     Represents the storing or possible storing of an unpredictable,
     undescribed value into X, which must be a 'reg', 'scratch',
     'parallel' or 'mem' expression.

     One place this is used is in string instructions that store
     standard values into particular hard registers.  It may not be
     worth the trouble to describe the values that are stored, but it is
     essential to inform the compiler that the registers will be
     altered, lest it attempt to keep data in them across the string
     instruction.

     If X is '(mem:BLK (const_int 0))' or '(mem:BLK (scratch))', it
     means that all memory locations must be presumed clobbered.  If X
     is a 'parallel', it has the same meaning as a 'parallel' in a 'set'
     expression.

     Note that the machine description classifies certain hard registers
     as "call-clobbered".  All function call instructions are assumed by
     default to clobber these registers, so there is no need to use
     'clobber' expressions to indicate this fact.  Also, each function
     call is assumed to have the potential to alter any memory location,
     unless the function is declared 'const'.

     If the last group of expressions in a 'parallel' are each a
     'clobber' expression whose arguments are 'reg' or 'match_scratch'
     (*note RTL Template::) expressions, the combiner phase can add the
     appropriate 'clobber' expressions to an insn it has constructed
     when doing so will cause a pattern to be matched.

     This feature can be used, for example, on a machine that whose
     multiply and add instructions don't use an MQ register but which
     has an add-accumulate instruction that does clobber the MQ
     register.  Similarly, a combined instruction might require a
     temporary register while the constituent instructions might not.

     When a 'clobber' expression for a register appears inside a
     'parallel' with other side effects, the register allocator
     guarantees that the register is unoccupied both before and after
     that insn if it is a hard register clobber.  For pseudo-register
     clobber, the register allocator and the reload pass do not assign
     the same hard register to the clobber and the input operands if
     there is an insn alternative containing the '&' constraint (*note
     Modifiers::) for the clobber and the hard register is in register
     classes of the clobber in the alternative.  You can clobber either
     a specific hard register, a pseudo register, or a 'scratch'
     expression; in the latter two cases, GCC will allocate a hard
     register that is available there for use as a temporary.

     For instructions that require a temporary register, you should use
     'scratch' instead of a pseudo-register because this will allow the
     combiner phase to add the 'clobber' when required.  You do this by
     coding ('clobber' ('match_scratch' ...)).  If you do clobber a
     pseudo register, use one which appears nowhere else--generate a new
     one each time.  Otherwise, you may confuse CSE.

     There is one other known use for clobbering a pseudo register in a
     'parallel': when one of the input operands of the insn is also
     clobbered by the insn.  In this case, using the same pseudo
     register in the clobber and elsewhere in the insn produces the
     expected results.

'(use X)'
     Represents the use of the value of X.  It indicates that the value
     in X at this point in the program is needed, even though it may not
     be apparent why this is so.  Therefore, the compiler will not
     attempt to delete previous instructions whose only effect is to
     store a value in X.  X must be a 'reg' expression.

     In some situations, it may be tempting to add a 'use' of a register
     in a 'parallel' to describe a situation where the value of a
     special register will modify the behavior of the instruction.  A
     hypothetical example might be a pattern for an addition that can
     either wrap around or use saturating addition depending on the
     value of a special control register:

          (parallel [(set (reg:SI 2) (unspec:SI [(reg:SI 3)
                                                 (reg:SI 4)] 0))
                     (use (reg:SI 1))])

     This will not work, several of the optimizers only look at
     expressions locally; it is very likely that if you have multiple
     insns with identical inputs to the 'unspec', they will be optimized
     away even if register 1 changes in between.

     This means that 'use' can _only_ be used to describe that the
     register is live.  You should think twice before adding 'use'
     statements, more often you will want to use 'unspec' instead.  The
     'use' RTX is most commonly useful to describe that a fixed register
     is implicitly used in an insn.  It is also safe to use in patterns
     where the compiler knows for other reasons that the result of the
     whole pattern is variable, such as 'movmemM' or 'call' patterns.

     During the reload phase, an insn that has a 'use' as pattern can
     carry a reg_equal note.  These 'use' insns will be deleted before
     the reload phase exits.

     During the delayed branch scheduling phase, X may be an insn.  This
     indicates that X previously was located at this place in the code
     and its data dependencies need to be taken into account.  These
     'use' insns will be deleted before the delayed branch scheduling
     phase exits.

'(parallel [X0 X1 ...])'
     Represents several side effects performed in parallel.  The square
     brackets stand for a vector; the operand of 'parallel' is a vector
     of expressions.  X0, X1 and so on are individual side effect
     expressions--expressions of code 'set', 'call', 'return',
     'simple_return', 'clobber' or 'use'.

     "In parallel" means that first all the values used in the
     individual side-effects are computed, and second all the actual
     side-effects are performed.  For example,

          (parallel [(set (reg:SI 1) (mem:SI (reg:SI 1)))
                     (set (mem:SI (reg:SI 1)) (reg:SI 1))])

     says unambiguously that the values of hard register 1 and the
     memory location addressed by it are interchanged.  In both places
     where '(reg:SI 1)' appears as a memory address it refers to the
     value in register 1 _before_ the execution of the insn.

     It follows that it is _incorrect_ to use 'parallel' and expect the
     result of one 'set' to be available for the next one.  For example,
     people sometimes attempt to represent a jump-if-zero instruction
     this way:

          (parallel [(set (cc0) (reg:SI 34))
                     (set (pc) (if_then_else
                                  (eq (cc0) (const_int 0))
                                  (label_ref ...)
                                  (pc)))])

     But this is incorrect, because it says that the jump condition
     depends on the condition code value _before_ this instruction, not
     on the new value that is set by this instruction.

     Peephole optimization, which takes place together with final
     assembly code output, can produce insns whose patterns consist of a
     'parallel' whose elements are the operands needed to output the
     resulting assembler code--often 'reg', 'mem' or constant
     expressions.  This would not be well-formed RTL at any other stage
     in compilation, but it is ok then because no further optimization
     remains to be done.  However, the definition of the macro
     'NOTICE_UPDATE_CC', if any, must deal with such insns if you define
     any peephole optimizations.

'(cond_exec [COND EXPR])'
     Represents a conditionally executed expression.  The EXPR is
     executed only if the COND is nonzero.  The COND expression must not
     have side-effects, but the EXPR may very well have side-effects.

'(sequence [INSNS ...])'
     Represents a sequence of insns.  Each of the INSNS that appears in
     the vector is suitable for appearing in the chain of insns, so it
     must be an 'insn', 'jump_insn', 'call_insn', 'code_label',
     'barrier' or 'note'.

     A 'sequence' RTX is never placed in an actual insn during RTL
     generation.  It represents the sequence of insns that result from a
     'define_expand' _before_ those insns are passed to 'emit_insn' to
     insert them in the chain of insns.  When actually inserted, the
     individual sub-insns are separated out and the 'sequence' is
     forgotten.

     After delay-slot scheduling is completed, an insn and all the insns
     that reside in its delay slots are grouped together into a
     'sequence'.  The insn requiring the delay slot is the first insn in
     the vector; subsequent insns are to be placed in the delay slot.

     'INSN_ANNULLED_BRANCH_P' is set on an insn in a delay slot to
     indicate that a branch insn should be used that will conditionally
     annul the effect of the insns in the delay slots.  In such a case,
     'INSN_FROM_TARGET_P' indicates that the insn is from the target of
     the branch and should be executed only if the branch is taken;
     otherwise the insn should be executed only if the branch is not
     taken.  *Note Delay Slots::.

 These expression codes appear in place of a side effect, as the body of
an insn, though strictly speaking they do not always describe side
effects as such:

'(asm_input S)'
     Represents literal assembler code as described by the string S.

'(unspec [OPERANDS ...] INDEX)'
'(unspec_volatile [OPERANDS ...] INDEX)'
     Represents a machine-specific operation on OPERANDS.  INDEX selects
     between multiple machine-specific operations.  'unspec_volatile' is
     used for volatile operations and operations that may trap; 'unspec'
     is used for other operations.

     These codes may appear inside a 'pattern' of an insn, inside a
     'parallel', or inside an expression.

'(addr_vec:M [LR0 LR1 ...])'
     Represents a table of jump addresses.  The vector elements LR0,
     etc., are 'label_ref' expressions.  The mode M specifies how much
     space is given to each address; normally M would be 'Pmode'.

'(addr_diff_vec:M BASE [LR0 LR1 ...] MIN MAX FLAGS)'
     Represents a table of jump addresses expressed as offsets from
     BASE.  The vector elements LR0, etc., are 'label_ref' expressions
     and so is BASE.  The mode M specifies how much space is given to
     each address-difference.  MIN and MAX are set up by branch
     shortening and hold a label with a minimum and a maximum address,
     respectively.  FLAGS indicates the relative position of BASE, MIN
     and MAX to the containing insn and of MIN and MAX to BASE.  See
     rtl.def for details.

'(prefetch:M ADDR RW LOCALITY)'
     Represents prefetch of memory at address ADDR.  Operand RW is 1 if
     the prefetch is for data to be written, 0 otherwise; targets that
     do not support write prefetches should treat this as a normal
     prefetch.  Operand LOCALITY specifies the amount of temporal
     locality; 0 if there is none or 1, 2, or 3 for increasing levels of
     temporal locality; targets that do not support locality hints
     should ignore this.

     This insn is used to minimize cache-miss latency by moving data
     into a cache before it is accessed.  It should use only
     non-faulting data prefetch instructions.


File: gccint.info,  Node: Incdec,  Next: Assembler,  Prev: Side Effects,  Up: RTL

10.16 Embedded Side-Effects on Addresses
========================================

Six special side-effect expression codes appear as memory addresses.

'(pre_dec:M X)'
     Represents the side effect of decrementing X by a standard amount
     and represents also the value that X has after being decremented.
     X must be a 'reg' or 'mem', but most machines allow only a 'reg'.
     M must be the machine mode for pointers on the machine in use.  The
     amount X is decremented by is the length in bytes of the machine
     mode of the containing memory reference of which this expression
     serves as the address.  Here is an example of its use:

          (mem:DF (pre_dec:SI (reg:SI 39)))

     This says to decrement pseudo register 39 by the length of a
     'DFmode' value and use the result to address a 'DFmode' value.

'(pre_inc:M X)'
     Similar, but specifies incrementing X instead of decrementing it.

'(post_dec:M X)'
     Represents the same side effect as 'pre_dec' but a different value.
     The value represented here is the value X has before being
     decremented.

'(post_inc:M X)'
     Similar, but specifies incrementing X instead of decrementing it.

'(post_modify:M X Y)'

     Represents the side effect of setting X to Y and represents X
     before X is modified.  X must be a 'reg' or 'mem', but most
     machines allow only a 'reg'.  M must be the machine mode for
     pointers on the machine in use.

     The expression Y must be one of three forms: '(plus:M X Z)',
     '(minus:M X Z)', or '(plus:M X I)', where Z is an index register
     and I is a constant.

     Here is an example of its use:

          (mem:SF (post_modify:SI (reg:SI 42) (plus (reg:SI 42)
                                                    (reg:SI 48))))

     This says to modify pseudo register 42 by adding the contents of
     pseudo register 48 to it, after the use of what ever 42 points to.

'(pre_modify:M X EXPR)'
     Similar except side effects happen before the use.

 These embedded side effect expressions must be used with care.
Instruction patterns may not use them.  Until the 'flow' pass of the
compiler, they may occur only to represent pushes onto the stack.  The
'flow' pass finds cases where registers are incremented or decremented
in one instruction and used as an address shortly before or after; these
cases are then transformed to use pre- or post-increment or -decrement.

 If a register used as the operand of these expressions is used in
another address in an insn, the original value of the register is used.
Uses of the register outside of an address are not permitted within the
same insn as a use in an embedded side effect expression because such
insns behave differently on different machines and hence must be treated
as ambiguous and disallowed.

 An instruction that can be represented with an embedded side effect
could also be represented using 'parallel' containing an additional
'set' to describe how the address register is altered.  This is not done
because machines that allow these operations at all typically allow them
wherever a memory address is called for.  Describing them as additional
parallel stores would require doubling the number of entries in the
machine description.


File: gccint.info,  Node: Assembler,  Next: Debug Information,  Prev: Incdec,  Up: RTL

10.17 Assembler Instructions as Expressions
===========================================

The RTX code 'asm_operands' represents a value produced by a
user-specified assembler instruction.  It is used to represent an 'asm'
statement with arguments.  An 'asm' statement with a single output
operand, like this:

     asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z));

is represented using a single 'asm_operands' RTX which represents the
value that is stored in 'outputvar':

     (set RTX-FOR-OUTPUTVAR
          (asm_operands "foo %1,%2,%0" "a" 0
                        [RTX-FOR-ADDITION-RESULT RTX-FOR-*Z]
                        [(asm_input:M1 "g")
                         (asm_input:M2 "di")]))

Here the operands of the 'asm_operands' RTX are the assembler template
string, the output-operand's constraint, the index-number of the output
operand among the output operands specified, a vector of input operand
RTX's, and a vector of input-operand modes and constraints.  The mode M1
is the mode of the sum 'x+y'; M2 is that of '*z'.

 When an 'asm' statement has multiple output values, its insn has
several such 'set' RTX's inside of a 'parallel'.  Each 'set' contains an
'asm_operands'; all of these share the same assembler template and
vectors, but each contains the constraint for the respective output
operand.  They are also distinguished by the output-operand index
number, which is 0, 1, ... for successive output operands.


File: gccint.info,  Node: Debug Information,  Next: Insns,  Prev: Assembler,  Up: RTL

10.18 Variable Location Debug Information in RTL
================================================

Variable tracking relies on 'MEM_EXPR' and 'REG_EXPR' annotations to
determine what user variables memory and register references refer to.

 Variable tracking at assignments uses these notes only when they refer
to variables that live at fixed locations (e.g., addressable variables,
global non-automatic variables).  For variables whose location may vary,
it relies on the following types of notes.

'(var_location:MODE VAR EXP STAT)'
     Binds variable 'var', a tree, to value EXP, an RTL expression.  It
     appears only in 'NOTE_INSN_VAR_LOCATION' and 'DEBUG_INSN's, with
     slightly different meanings.  MODE, if present, represents the mode
     of EXP, which is useful if it is a modeless expression.  STAT is
     only meaningful in notes, indicating whether the variable is known
     to be initialized or uninitialized.

'(debug_expr:MODE DECL)'
     Stands for the value bound to the 'DEBUG_EXPR_DECL' DECL, that
     points back to it, within value expressions in 'VAR_LOCATION'
     nodes.


File: gccint.info,  Node: Insns,  Next: Calls,  Prev: Debug Information,  Up: RTL

10.19 Insns
===========

The RTL representation of the code for a function is a doubly-linked
chain of objects called "insns".  Insns are expressions with special
codes that are used for no other purpose.  Some insns are actual
instructions; others represent dispatch tables for 'switch' statements;
others represent labels to jump to or various sorts of declarative
information.

 In addition to its own specific data, each insn must have a unique
id-number that distinguishes it from all other insns in the current
function (after delayed branch scheduling, copies of an insn with the
same id-number may be present in multiple places in a function, but
these copies will always be identical and will only appear inside a
'sequence'), and chain pointers to the preceding and following insns.
These three fields occupy the same position in every insn, independent
of the expression code of the insn.  They could be accessed with 'XEXP'
and 'XINT', but instead three special macros are always used:

'INSN_UID (I)'
     Accesses the unique id of insn I.

'PREV_INSN (I)'
     Accesses the chain pointer to the insn preceding I.  If I is the
     first insn, this is a null pointer.

'NEXT_INSN (I)'
     Accesses the chain pointer to the insn following I.  If I is the
     last insn, this is a null pointer.

 The first insn in the chain is obtained by calling 'get_insns'; the
last insn is the result of calling 'get_last_insn'.  Within the chain
delimited by these insns, the 'NEXT_INSN' and 'PREV_INSN' pointers must
always correspond: if INSN is not the first insn,

     NEXT_INSN (PREV_INSN (INSN)) == INSN

is always true and if INSN is not the last insn,

     PREV_INSN (NEXT_INSN (INSN)) == INSN

is always true.

 After delay slot scheduling, some of the insns in the chain might be
'sequence' expressions, which contain a vector of insns.  The value of
'NEXT_INSN' in all but the last of these insns is the next insn in the
vector; the value of 'NEXT_INSN' of the last insn in the vector is the
same as the value of 'NEXT_INSN' for the 'sequence' in which it is
contained.  Similar rules apply for 'PREV_INSN'.

 This means that the above invariants are not necessarily true for insns
inside 'sequence' expressions.  Specifically, if INSN is the first insn
in a 'sequence', 'NEXT_INSN (PREV_INSN (INSN))' is the insn containing
the 'sequence' expression, as is the value of 'PREV_INSN (NEXT_INSN
(INSN))' if INSN is the last insn in the 'sequence' expression.  You can
use these expressions to find the containing 'sequence' expression.

 Every insn has one of the following expression codes:

'insn'
     The expression code 'insn' is used for instructions that do not
     jump and do not do function calls.  'sequence' expressions are
     always contained in insns with code 'insn' even if one of those
     insns should jump or do function calls.

     Insns with code 'insn' have four additional fields beyond the three
     mandatory ones listed above.  These four are described in a table
     below.

'jump_insn'
     The expression code 'jump_insn' is used for instructions that may
     jump (or, more generally, may contain 'label_ref' expressions to
     which 'pc' can be set in that instruction).  If there is an
     instruction to return from the current function, it is recorded as
     a 'jump_insn'.

     'jump_insn' insns have the same extra fields as 'insn' insns,
     accessed in the same way and in addition contain a field
     'JUMP_LABEL' which is defined once jump optimization has completed.

     For simple conditional and unconditional jumps, this field contains
     the 'code_label' to which this insn will (possibly conditionally)
     branch.  In a more complex jump, 'JUMP_LABEL' records one of the
     labels that the insn refers to; other jump target labels are
     recorded as 'REG_LABEL_TARGET' notes.  The exception is 'addr_vec'
     and 'addr_diff_vec', where 'JUMP_LABEL' is 'NULL_RTX' and the only
     way to find the labels is to scan the entire body of the insn.

     Return insns count as jumps, but since they do not refer to any
     labels, their 'JUMP_LABEL' is 'NULL_RTX'.

'call_insn'
     The expression code 'call_insn' is used for instructions that may
     do function calls.  It is important to distinguish these
     instructions because they imply that certain registers and memory
     locations may be altered unpredictably.

     'call_insn' insns have the same extra fields as 'insn' insns,
     accessed in the same way and in addition contain a field
     'CALL_INSN_FUNCTION_USAGE', which contains a list (chain of
     'expr_list' expressions) containing 'use', 'clobber' and sometimes
     'set' expressions that denote hard registers and 'mem's used or
     clobbered by the called function.

     A 'mem' generally points to a stack slot in which arguments passed
     to the libcall by reference (*note TARGET_PASS_BY_REFERENCE:
     Register Arguments.) are stored.  If the argument is caller-copied
     (*note TARGET_CALLEE_COPIES: Register Arguments.), the stack slot
     will be mentioned in 'clobber' and 'use' entries; if it's
     callee-copied, only a 'use' will appear, and the 'mem' may point to
     addresses that are not stack slots.

     Registers occurring inside a 'clobber' in this list augment
     registers specified in 'CALL_USED_REGISTERS' (*note Register
     Basics::).

     If the list contains a 'set' involving two registers, it indicates
     that the function returns one of its arguments.  Such a 'set' may
     look like a no-op if the same register holds the argument and the
     return value.

'code_label'
     A 'code_label' insn represents a label that a jump insn can jump
     to.  It contains two special fields of data in addition to the
     three standard ones.  'CODE_LABEL_NUMBER' is used to hold the
     "label number", a number that identifies this label uniquely among
     all the labels in the compilation (not just in the current
     function).  Ultimately, the label is represented in the assembler
     output as an assembler label, usually of the form 'LN' where N is
     the label number.

     When a 'code_label' appears in an RTL expression, it normally
     appears within a 'label_ref' which represents the address of the
     label, as a number.

     Besides as a 'code_label', a label can also be represented as a
     'note' of type 'NOTE_INSN_DELETED_LABEL'.

     The field 'LABEL_NUSES' is only defined once the jump optimization
     phase is completed.  It contains the number of times this label is
     referenced in the current function.

     The field 'LABEL_KIND' differentiates four different types of
     labels: 'LABEL_NORMAL', 'LABEL_STATIC_ENTRY', 'LABEL_GLOBAL_ENTRY',
     and 'LABEL_WEAK_ENTRY'.  The only labels that do not have type
     'LABEL_NORMAL' are "alternate entry points" to the current
     function.  These may be static (visible only in the containing
     translation unit), global (exposed to all translation units), or
     weak (global, but can be overridden by another symbol with the same
     name).

     Much of the compiler treats all four kinds of label identically.
     Some of it needs to know whether or not a label is an alternate
     entry point; for this purpose, the macro 'LABEL_ALT_ENTRY_P' is
     provided.  It is equivalent to testing whether 'LABEL_KIND (label)
     == LABEL_NORMAL'.  The only place that cares about the distinction
     between static, global, and weak alternate entry points, besides
     the front-end code that creates them, is the function
     'output_alternate_entry_point', in 'final.c'.

     To set the kind of a label, use the 'SET_LABEL_KIND' macro.

'barrier'
     Barriers are placed in the instruction stream when control cannot
     flow past them.  They are placed after unconditional jump
     instructions to indicate that the jumps are unconditional and after
     calls to 'volatile' functions, which do not return (e.g., 'exit').
     They contain no information beyond the three standard fields.

'note'
     'note' insns are used to represent additional debugging and
     declarative information.  They contain two nonstandard fields, an
     integer which is accessed with the macro 'NOTE_LINE_NUMBER' and a
     string accessed with 'NOTE_SOURCE_FILE'.

     If 'NOTE_LINE_NUMBER' is positive, the note represents the position
     of a source line and 'NOTE_SOURCE_FILE' is the source file name
     that the line came from.  These notes control generation of line
     number data in the assembler output.

     Otherwise, 'NOTE_LINE_NUMBER' is not really a line number but a
     code with one of the following values (and 'NOTE_SOURCE_FILE' must
     contain a null pointer):

     'NOTE_INSN_DELETED'
          Such a note is completely ignorable.  Some passes of the
          compiler delete insns by altering them into notes of this
          kind.

     'NOTE_INSN_DELETED_LABEL'
          This marks what used to be a 'code_label', but was not used
          for other purposes than taking its address and was transformed
          to mark that no code jumps to it.

     'NOTE_INSN_BLOCK_BEG'
     'NOTE_INSN_BLOCK_END'
          These types of notes indicate the position of the beginning
          and end of a level of scoping of variable names.  They control
          the output of debugging information.

     'NOTE_INSN_EH_REGION_BEG'
     'NOTE_INSN_EH_REGION_END'
          These types of notes indicate the position of the beginning
          and end of a level of scoping for exception handling.
          'NOTE_BLOCK_NUMBER' identifies which 'CODE_LABEL' or 'note' of
          type 'NOTE_INSN_DELETED_LABEL' is associated with the given
          region.

     'NOTE_INSN_LOOP_BEG'
     'NOTE_INSN_LOOP_END'
          These types of notes indicate the position of the beginning
          and end of a 'while' or 'for' loop.  They enable the loop
          optimizer to find loops quickly.

     'NOTE_INSN_LOOP_CONT'
          Appears at the place in a loop that 'continue' statements jump
          to.

     'NOTE_INSN_LOOP_VTOP'
          This note indicates the place in a loop where the exit test
          begins for those loops in which the exit test has been
          duplicated.  This position becomes another virtual start of
          the loop when considering loop invariants.

     'NOTE_INSN_FUNCTION_BEG'
          Appears at the start of the function body, after the function
          prologue.

     'NOTE_INSN_VAR_LOCATION'
          This note is used to generate variable location debugging
          information.  It indicates that the user variable in its
          'VAR_LOCATION' operand is at the location given in the RTL
          expression, or holds a value that can be computed by
          evaluating the RTL expression from that static point in the
          program up to the next such note for the same user variable.

     These codes are printed symbolically when they appear in debugging
     dumps.

'debug_insn'
     The expression code 'debug_insn' is used for pseudo-instructions
     that hold debugging information for variable tracking at
     assignments (see '-fvar-tracking-assignments' option).  They are
     the RTL representation of 'GIMPLE_DEBUG' statements (*note
     'GIMPLE_DEBUG'::), with a 'VAR_LOCATION' operand that binds a user
     variable tree to an RTL representation of the 'value' in the
     corresponding statement.  A 'DEBUG_EXPR' in it stands for the value
     bound to the corresponding 'DEBUG_EXPR_DECL'.

     Throughout optimization passes, binding information is kept in
     pseudo-instruction form, so that, unlike notes, it gets the same
     treatment and adjustments that regular instructions would.  It is
     the variable tracking pass that turns these pseudo-instructions
     into var location notes, analyzing control flow, value equivalences
     and changes to registers and memory referenced in value
     expressions, propagating the values of debug temporaries and
     determining expressions that can be used to compute the value of
     each user variable at as many points (ranges, actually) in the
     program as possible.

     Unlike 'NOTE_INSN_VAR_LOCATION', the value expression in an
     'INSN_VAR_LOCATION' denotes a value at that specific point in the
     program, rather than an expression that can be evaluated at any
     later point before an overriding 'VAR_LOCATION' is encountered.
     E.g., if a user variable is bound to a 'REG' and then a subsequent
     insn modifies the 'REG', the note location would keep mapping the
     user variable to the register across the insn, whereas the insn
     location would keep the variable bound to the value, so that the
     variable tracking pass would emit another location note for the
     variable at the point in which the register is modified.

 The machine mode of an insn is normally 'VOIDmode', but some phases use
the mode for various purposes.

 The common subexpression elimination pass sets the mode of an insn to
'QImode' when it is the first insn in a block that has already been
processed.

 The second Haifa scheduling pass, for targets that can multiple issue,
sets the mode of an insn to 'TImode' when it is believed that the
instruction begins an issue group.  That is, when the instruction cannot
issue simultaneously with the previous.  This may be relied on by later
passes, in particular machine-dependent reorg.

 Here is a table of the extra fields of 'insn', 'jump_insn' and
'call_insn' insns:

'PATTERN (I)'
     An expression for the side effect performed by this insn.  This
     must be one of the following codes: 'set', 'call', 'use',
     'clobber', 'return', 'simple_return', 'asm_input', 'asm_output',
     'addr_vec', 'addr_diff_vec', 'trap_if', 'unspec',
     'unspec_volatile', 'parallel', 'cond_exec', or 'sequence'.  If it
     is a 'parallel', each element of the 'parallel' must be one these
     codes, except that 'parallel' expressions cannot be nested and
     'addr_vec' and 'addr_diff_vec' are not permitted inside a
     'parallel' expression.

'INSN_CODE (I)'
     An integer that says which pattern in the machine description
     matches this insn, or -1 if the matching has not yet been
     attempted.

     Such matching is never attempted and this field remains -1 on an
     insn whose pattern consists of a single 'use', 'clobber',
     'asm_input', 'addr_vec' or 'addr_diff_vec' expression.

     Matching is also never attempted on insns that result from an 'asm'
     statement.  These contain at least one 'asm_operands' expression.
     The function 'asm_noperands' returns a non-negative value for such
     insns.

     In the debugging output, this field is printed as a number followed
     by a symbolic representation that locates the pattern in the 'md'
     file as some small positive or negative offset from a named
     pattern.

'LOG_LINKS (I)'
     A list (chain of 'insn_list' expressions) giving information about
     dependencies between instructions within a basic block.  Neither a
     jump nor a label may come between the related insns.  These are
     only used by the schedulers and by combine.  This is a deprecated
     data structure.  Def-use and use-def chains are now preferred.

'REG_NOTES (I)'
     A list (chain of 'expr_list' and 'insn_list' expressions) giving
     miscellaneous information about the insn.  It is often information
     pertaining to the registers used in this insn.

 The 'LOG_LINKS' field of an insn is a chain of 'insn_list' expressions.
Each of these has two operands: the first is an insn, and the second is
another 'insn_list' expression (the next one in the chain).  The last
'insn_list' in the chain has a null pointer as second operand.  The
significant thing about the chain is which insns appear in it (as first
operands of 'insn_list' expressions).  Their order is not significant.

 This list is originally set up by the flow analysis pass; it is a null
pointer until then.  Flow only adds links for those data dependencies
which can be used for instruction combination.  For each insn, the flow
analysis pass adds a link to insns which store into registers values
that are used for the first time in this insn.

 The 'REG_NOTES' field of an insn is a chain similar to the 'LOG_LINKS'
field but it includes 'expr_list' expressions in addition to 'insn_list'
expressions.  There are several kinds of register notes, which are
distinguished by the machine mode, which in a register note is really
understood as being an 'enum reg_note'.  The first operand OP of the
note is data whose meaning depends on the kind of note.

 The macro 'REG_NOTE_KIND (X)' returns the kind of register note.  Its
counterpart, the macro 'PUT_REG_NOTE_KIND (X, NEWKIND)' sets the
register note type of X to be NEWKIND.

 Register notes are of three classes: They may say something about an
input to an insn, they may say something about an output of an insn, or
they may create a linkage between two insns.  There are also a set of
values that are only used in 'LOG_LINKS'.

 These register notes annotate inputs to an insn:

'REG_DEAD'
     The value in OP dies in this insn; that is to say, altering the
     value immediately after this insn would not affect the future
     behavior of the program.

     It does not follow that the register OP has no useful value after
     this insn since OP is not necessarily modified by this insn.
     Rather, no subsequent instruction uses the contents of OP.

'REG_UNUSED'
     The register OP being set by this insn will not be used in a
     subsequent insn.  This differs from a 'REG_DEAD' note, which
     indicates that the value in an input will not be used subsequently.
     These two notes are independent; both may be present for the same
     register.

'REG_INC'
     The register OP is incremented (or decremented; at this level there
     is no distinction) by an embedded side effect inside this insn.
     This means it appears in a 'post_inc', 'pre_inc', 'post_dec' or
     'pre_dec' expression.

'REG_NONNEG'
     The register OP is known to have a nonnegative value when this insn
     is reached.  This is used so that decrement and branch until zero
     instructions, such as the m68k dbra, can be matched.

     The 'REG_NONNEG' note is added to insns only if the machine
     description has a 'decrement_and_branch_until_zero' pattern.

'REG_LABEL_OPERAND'
     This insn uses OP, a 'code_label' or a 'note' of type
     'NOTE_INSN_DELETED_LABEL', but is not a 'jump_insn', or it is a
     'jump_insn' that refers to the operand as an ordinary operand.  The
     label may still eventually be a jump target, but if so in an
     indirect jump in a subsequent insn.  The presence of this note
     allows jump optimization to be aware that OP is, in fact, being
     used, and flow optimization to build an accurate flow graph.

'REG_LABEL_TARGET'
     This insn is a 'jump_insn' but not an 'addr_vec' or
     'addr_diff_vec'.  It uses OP, a 'code_label' as a direct or
     indirect jump target.  Its purpose is similar to that of
     'REG_LABEL_OPERAND'.  This note is only present if the insn has
     multiple targets; the last label in the insn (in the highest
     numbered insn-field) goes into the 'JUMP_LABEL' field and does not
     have a 'REG_LABEL_TARGET' note.  *Note JUMP_LABEL: Insns.

'REG_CROSSING_JUMP'
     This insn is a branching instruction (either an unconditional jump
     or an indirect jump) which crosses between hot and cold sections,
     which could potentially be very far apart in the executable.  The
     presence of this note indicates to other optimizations that this
     branching instruction should not be "collapsed" into a simpler
     branching construct.  It is used when the optimization to partition
     basic blocks into hot and cold sections is turned on.

'REG_SETJMP'
     Appears attached to each 'CALL_INSN' to 'setjmp' or a related
     function.

 The following notes describe attributes of outputs of an insn:

'REG_EQUIV'
'REG_EQUAL'
     This note is only valid on an insn that sets only one register and
     indicates that that register will be equal to OP at run time; the
     scope of this equivalence differs between the two types of notes.
     The value which the insn explicitly copies into the register may
     look different from OP, but they will be equal at run time.  If the
     output of the single 'set' is a 'strict_low_part' expression, the
     note refers to the register that is contained in 'SUBREG_REG' of
     the 'subreg' expression.

     For 'REG_EQUIV', the register is equivalent to OP throughout the
     entire function, and could validly be replaced in all its
     occurrences by OP.  ("Validly" here refers to the data flow of the
     program; simple replacement may make some insns invalid.)  For
     example, when a constant is loaded into a register that is never
     assigned any other value, this kind of note is used.

     When a parameter is copied into a pseudo-register at entry to a
     function, a note of this kind records that the register is
     equivalent to the stack slot where the parameter was passed.
     Although in this case the register may be set by other insns, it is
     still valid to replace the register by the stack slot throughout
     the function.

     A 'REG_EQUIV' note is also used on an instruction which copies a
     register parameter into a pseudo-register at entry to a function,
     if there is a stack slot where that parameter could be stored.
     Although other insns may set the pseudo-register, it is valid for
     the compiler to replace the pseudo-register by stack slot
     throughout the function, provided the compiler ensures that the
     stack slot is properly initialized by making the replacement in the
     initial copy instruction as well.  This is used on machines for
     which the calling convention allocates stack space for register
     parameters.  See 'REG_PARM_STACK_SPACE' in *note Stack Arguments::.

     In the case of 'REG_EQUAL', the register that is set by this insn
     will be equal to OP at run time at the end of this insn but not
     necessarily elsewhere in the function.  In this case, OP is
     typically an arithmetic expression.  For example, when a sequence
     of insns such as a library call is used to perform an arithmetic
     operation, this kind of note is attached to the insn that produces
     or copies the final value.

     These two notes are used in different ways by the compiler passes.
     'REG_EQUAL' is used by passes prior to register allocation (such as
     common subexpression elimination and loop optimization) to tell
     them how to think of that value.  'REG_EQUIV' notes are used by
     register allocation to indicate that there is an available
     substitute expression (either a constant or a 'mem' expression for
     the location of a parameter on the stack) that may be used in place
     of a register if insufficient registers are available.

     Except for stack homes for parameters, which are indicated by a
     'REG_EQUIV' note and are not useful to the early optimization
     passes and pseudo registers that are equivalent to a memory
     location throughout their entire life, which is not detected until
     later in the compilation, all equivalences are initially indicated
     by an attached 'REG_EQUAL' note.  In the early stages of register
     allocation, a 'REG_EQUAL' note is changed into a 'REG_EQUIV' note
     if OP is a constant and the insn represents the only set of its
     destination register.

     Thus, compiler passes prior to register allocation need only check
     for 'REG_EQUAL' notes and passes subsequent to register allocation
     need only check for 'REG_EQUIV' notes.

 These notes describe linkages between insns.  They occur in pairs: one
insn has one of a pair of notes that points to a second insn, which has
the inverse note pointing back to the first insn.

'REG_CC_SETTER'
'REG_CC_USER'
     On machines that use 'cc0', the insns which set and use 'cc0' set
     and use 'cc0' are adjacent.  However, when branch delay slot
     filling is done, this may no longer be true.  In this case a
     'REG_CC_USER' note will be placed on the insn setting 'cc0' to
     point to the insn using 'cc0' and a 'REG_CC_SETTER' note will be
     placed on the insn using 'cc0' to point to the insn setting 'cc0'.

 These values are only used in the 'LOG_LINKS' field, and indicate the
type of dependency that each link represents.  Links which indicate a
data dependence (a read after write dependence) do not use any code,
they simply have mode 'VOIDmode', and are printed without any
descriptive text.

'REG_DEP_TRUE'
     This indicates a true dependence (a read after write dependence).

'REG_DEP_OUTPUT'
     This indicates an output dependence (a write after write
     dependence).

'REG_DEP_ANTI'
     This indicates an anti dependence (a write after read dependence).

 These notes describe information gathered from gcov profile data.  They
are stored in the 'REG_NOTES' field of an insn as an 'expr_list'.

'REG_BR_PROB'
     This is used to specify the ratio of branches to non-branches of a
     branch insn according to the profile data.  The value is stored as
     a value between 0 and REG_BR_PROB_BASE; larger values indicate a
     higher probability that the branch will be taken.

'REG_BR_PRED'
     These notes are found in JUMP insns after delayed branch scheduling
     has taken place.  They indicate both the direction and the
     likelihood of the JUMP.  The format is a bitmask of ATTR_FLAG_*
     values.

'REG_FRAME_RELATED_EXPR'
     This is used on an RTX_FRAME_RELATED_P insn wherein the attached
     expression is used in place of the actual insn pattern.  This is
     done in cases where the pattern is either complex or misleading.

 For convenience, the machine mode in an 'insn_list' or 'expr_list' is
printed using these symbolic codes in debugging dumps.

 The only difference between the expression codes 'insn_list' and
'expr_list' is that the first operand of an 'insn_list' is assumed to be
an insn and is printed in debugging dumps as the insn's unique id; the
first operand of an 'expr_list' is printed in the ordinary way as an
expression.


File: gccint.info,  Node: Calls,  Next: Sharing,  Prev: Insns,  Up: RTL

10.20 RTL Representation of Function-Call Insns
===============================================

Insns that call subroutines have the RTL expression code 'call_insn'.
These insns must satisfy special rules, and their bodies must use a
special RTL expression code, 'call'.

 A 'call' expression has two operands, as follows:

     (call (mem:FM ADDR) NBYTES)

Here NBYTES is an operand that represents the number of bytes of
argument data being passed to the subroutine, FM is a machine mode
(which must equal as the definition of the 'FUNCTION_MODE' macro in the
machine description) and ADDR represents the address of the subroutine.

 For a subroutine that returns no value, the 'call' expression as shown
above is the entire body of the insn, except that the insn might also
contain 'use' or 'clobber' expressions.

 For a subroutine that returns a value whose mode is not 'BLKmode', the
value is returned in a hard register.  If this register's number is R,
then the body of the call insn looks like this:

     (set (reg:M R)
          (call (mem:FM ADDR) NBYTES))

This RTL expression makes it clear (to the optimizer passes) that the
appropriate register receives a useful value in this insn.

 When a subroutine returns a 'BLKmode' value, it is handled by passing
to the subroutine the address of a place to store the value.  So the
call insn itself does not "return" any value, and it has the same RTL
form as a call that returns nothing.

 On some machines, the call instruction itself clobbers some register,
for example to contain the return address.  'call_insn' insns on these
machines should have a body which is a 'parallel' that contains both the
'call' expression and 'clobber' expressions that indicate which
registers are destroyed.  Similarly, if the call instruction requires
some register other than the stack pointer that is not explicitly
mentioned in its RTL, a 'use' subexpression should mention that
register.

 Functions that are called are assumed to modify all registers listed in
the configuration macro 'CALL_USED_REGISTERS' (*note Register Basics::)
and, with the exception of 'const' functions and library calls, to
modify all of memory.

 Insns containing just 'use' expressions directly precede the
'call_insn' insn to indicate which registers contain inputs to the
function.  Similarly, if registers other than those in
'CALL_USED_REGISTERS' are clobbered by the called function, insns
containing a single 'clobber' follow immediately after the call to
indicate which registers.


File: gccint.info,  Node: Sharing,  Next: Reading RTL,  Prev: Calls,  Up: RTL

10.21 Structure Sharing Assumptions
===================================

The compiler assumes that certain kinds of RTL expressions are unique;
there do not exist two distinct objects representing the same value.  In
other cases, it makes an opposite assumption: that no RTL expression
object of a certain kind appears in more than one place in the
containing structure.

 These assumptions refer to a single function; except for the RTL
objects that describe global variables and external functions, and a few
standard objects such as small integer constants, no RTL objects are
common to two functions.

   * Each pseudo-register has only a single 'reg' object to represent
     it, and therefore only a single machine mode.

   * For any symbolic label, there is only one 'symbol_ref' object
     referring to it.

   * All 'const_int' expressions with equal values are shared.

   * There is only one 'pc' expression.

   * There is only one 'cc0' expression.

   * There is only one 'const_double' expression with value 0 for each
     floating point mode.  Likewise for values 1 and 2.

   * There is only one 'const_vector' expression with value 0 for each
     vector mode, be it an integer or a double constant vector.

   * No 'label_ref' or 'scratch' appears in more than one place in the
     RTL structure; in other words, it is safe to do a tree-walk of all
     the insns in the function and assume that each time a 'label_ref'
     or 'scratch' is seen it is distinct from all others that are seen.

   * Only one 'mem' object is normally created for each static variable
     or stack slot, so these objects are frequently shared in all the
     places they appear.  However, separate but equal objects for these
     variables are occasionally made.

   * When a single 'asm' statement has multiple output operands, a
     distinct 'asm_operands' expression is made for each output operand.
     However, these all share the vector which contains the sequence of
     input operands.  This sharing is used later on to test whether two
     'asm_operands' expressions come from the same statement, so all
     optimizations must carefully preserve the sharing if they copy the
     vector at all.

   * No RTL object appears in more than one place in the RTL structure
     except as described above.  Many passes of the compiler rely on
     this by assuming that they can modify RTL objects in place without
     unwanted side-effects on other insns.

   * During initial RTL generation, shared structure is freely
     introduced.  After all the RTL for a function has been generated,
     all shared structure is copied by 'unshare_all_rtl' in
     'emit-rtl.c', after which the above rules are guaranteed to be
     followed.

   * During the combiner pass, shared structure within an insn can exist
     temporarily.  However, the shared structure is copied before the
     combiner is finished with the insn.  This is done by calling
     'copy_rtx_if_shared', which is a subroutine of 'unshare_all_rtl'.


File: gccint.info,  Node: Reading RTL,  Prev: Sharing,  Up: RTL

10.22 Reading RTL
=================

To read an RTL object from a file, call 'read_rtx'.  It takes one
argument, a stdio stream, and returns a single RTL object.  This routine
is defined in 'read-rtl.c'.  It is not available in the compiler itself,
only the various programs that generate the compiler back end from the
machine description.

 People frequently have the idea of using RTL stored as text in a file
as an interface between a language front end and the bulk of GCC.  This
idea is not feasible.

 GCC was designed to use RTL internally only.  Correct RTL for a given
program is very dependent on the particular target machine.  And the RTL
does not contain all the information about the program.

 The proper way to interface GCC to a new language front end is with the
"tree" data structure, described in the files 'tree.h' and 'tree.def'.
The documentation for this structure (*note GENERIC::) is incomplete.


File: gccint.info,  Node: GENERIC,  Next: GIMPLE,  Prev: RTL,  Up: Top

11 GENERIC
**********

The purpose of GENERIC is simply to provide a language-independent way
of representing an entire function in trees.  To this end, it was
necessary to add a few new tree codes to the back end, but most
everything was already there.  If you can express it with the codes in
'gcc/tree.def', it's GENERIC.

 Early on, there was a great deal of debate about how to think about
statements in a tree IL.  In GENERIC, a statement is defined as any
expression whose value, if any, is ignored.  A statement will always
have 'TREE_SIDE_EFFECTS' set (or it will be discarded), but a
non-statement expression may also have side effects.  A 'CALL_EXPR', for
instance.

 It would be possible for some local optimizations to work on the
GENERIC form of a function; indeed, the adapted tree inliner works fine
on GENERIC, but the current compiler performs inlining after lowering to
GIMPLE (a restricted form described in the next section).  Indeed,
currently the frontends perform this lowering before handing off to
'tree_rest_of_compilation', but this seems inelegant.

* Menu:

* Deficiencies::                Topics net yet covered in this document.
* Tree overview::               All about 'tree's.
* Types::                       Fundamental and aggregate types.
* Declarations::                Type declarations and variables.
* Attributes::                  Declaration and type attributes.
* Expressions: Expression trees.            Operating on data.
* Statements::                  Control flow and related trees.
* Functions::           	Function bodies, linkage, and other aspects.
* Language-dependent trees::    Topics and trees specific to language front ends.
* C and C++ Trees::     	Trees specific to C and C++.
* Java Trees:: 	                Trees specific to Java.


File: gccint.info,  Node: Deficiencies,  Next: Tree overview,  Up: GENERIC

11.1 Deficiencies
=================

There are many places in which this document is incomplet and incorrekt.
It is, as of yet, only _preliminary_ documentation.


File: gccint.info,  Node: Tree overview,  Next: Types,  Prev: Deficiencies,  Up: GENERIC

11.2 Overview
=============

The central data structure used by the internal representation is the
'tree'.  These nodes, while all of the C type 'tree', are of many
varieties.  A 'tree' is a pointer type, but the object to which it
points may be of a variety of types.  From this point forward, we will
refer to trees in ordinary type, rather than in 'this font', except when
talking about the actual C type 'tree'.

 You can tell what kind of node a particular tree is by using the
'TREE_CODE' macro.  Many, many macros take trees as input and return
trees as output.  However, most macros require a certain kind of tree
node as input.  In other words, there is a type-system for trees, but it
is not reflected in the C type-system.

 For safety, it is useful to configure GCC with '--enable-checking'.
Although this results in a significant performance penalty (since all
tree types are checked at run-time), and is therefore inappropriate in a
release version, it is extremely helpful during the development process.

 Many macros behave as predicates.  Many, although not all, of these
predicates end in '_P'.  Do not rely on the result type of these macros
being of any particular type.  You may, however, rely on the fact that
the type can be compared to '0', so that statements like
     if (TEST_P (t) && !TEST_P (y))
       x = 1;
and
     int i = (TEST_P (t) != 0);
are legal.  Macros that return 'int' values now may be changed to return
'tree' values, or other pointers in the future.  Even those that
continue to return 'int' may return multiple nonzero codes where
previously they returned only zero and one.  Therefore, you should not
write code like
     if (TEST_P (t) == 1)
as this code is not guaranteed to work correctly in the future.

 You should not take the address of values returned by the macros or
functions described here.  In particular, no guarantee is given that the
values are lvalues.

 In general, the names of macros are all in uppercase, while the names
of functions are entirely in lowercase.  There are rare exceptions to
this rule.  You should assume that any macro or function whose name is
made up entirely of uppercase letters may evaluate its arguments more
than once.  You may assume that a macro or function whose name is made
up entirely of lowercase letters will evaluate its arguments only once.

 The 'error_mark_node' is a special tree.  Its tree code is
'ERROR_MARK', but since there is only ever one node with that code, the
usual practice is to compare the tree against 'error_mark_node'.  (This
test is just a test for pointer equality.)  If an error has occurred
during front-end processing the flag 'errorcount' will be set.  If the
front end has encountered code it cannot handle, it will issue a message
to the user and set 'sorrycount'.  When these flags are set, any macro
or function which normally returns a tree of a particular kind may
instead return the 'error_mark_node'.  Thus, if you intend to do any
processing of erroneous code, you must be prepared to deal with the
'error_mark_node'.

 Occasionally, a particular tree slot (like an operand to an expression,
or a particular field in a declaration) will be referred to as "reserved
for the back end".  These slots are used to store RTL when the tree is
converted to RTL for use by the GCC back end.  However, if that process
is not taking place (e.g., if the front end is being hooked up to an
intelligent editor), then those slots may be used by the back end
presently in use.

 If you encounter situations that do not match this documentation, such
as tree nodes of types not mentioned here, or macros documented to
return entities of a particular kind that instead return entities of
some different kind, you have found a bug, either in the front end or in
the documentation.  Please report these bugs as you would any other bug.

* Menu:

* Macros and Functions::Macros and functions that can be used with all trees.
* Identifiers::         The names of things.
* Containers::          Lists and vectors.


File: gccint.info,  Node: Macros and Functions,  Next: Identifiers,  Up: Tree overview

11.2.1 Trees
------------

All GENERIC trees have two fields in common.  First, 'TREE_CHAIN' is a
pointer that can be used as a singly-linked list to other trees.  The
other is 'TREE_TYPE'.  Many trees store the type of an expression or
declaration in this field.

 These are some other functions for handling trees:

'tree_size'
     Return the number of bytes a tree takes.

'build0'
'build1'
'build2'
'build3'
'build4'
'build5'
'build6'

     These functions build a tree and supply values to put in each
     parameter.  The basic signature is 'code, type, [operands]'.
     'code' is the 'TREE_CODE', and 'type' is a tree representing the
     'TREE_TYPE'.  These are followed by the operands, each of which is
     also a tree.


File: gccint.info,  Node: Identifiers,  Next: Containers,  Prev: Macros and Functions,  Up: Tree overview

11.2.2 Identifiers
------------------

An 'IDENTIFIER_NODE' represents a slightly more general concept that the
standard C or C++ concept of identifier.  In particular, an
'IDENTIFIER_NODE' may contain a '$', or other extraordinary characters.

 There are never two distinct 'IDENTIFIER_NODE's representing the same
identifier.  Therefore, you may use pointer equality to compare
'IDENTIFIER_NODE's, rather than using a routine like 'strcmp'.  Use
'get_identifier' to obtain the unique 'IDENTIFIER_NODE' for a supplied
string.

 You can use the following macros to access identifiers:
'IDENTIFIER_POINTER'
     The string represented by the identifier, represented as a 'char*'.
     This string is always 'NUL'-terminated, and contains no embedded
     'NUL' characters.

'IDENTIFIER_LENGTH'
     The length of the string returned by 'IDENTIFIER_POINTER', not
     including the trailing 'NUL'.  This value of 'IDENTIFIER_LENGTH
     (x)' is always the same as 'strlen (IDENTIFIER_POINTER (x))'.

'IDENTIFIER_OPNAME_P'
     This predicate holds if the identifier represents the name of an
     overloaded operator.  In this case, you should not depend on the
     contents of either the 'IDENTIFIER_POINTER' or the
     'IDENTIFIER_LENGTH'.

'IDENTIFIER_TYPENAME_P'
     This predicate holds if the identifier represents the name of a
     user-defined conversion operator.  In this case, the 'TREE_TYPE' of
     the 'IDENTIFIER_NODE' holds the type to which the conversion
     operator converts.


File: gccint.info,  Node: Containers,  Prev: Identifiers,  Up: Tree overview

11.2.3 Containers
-----------------

Two common container data structures can be represented directly with
tree nodes.  A 'TREE_LIST' is a singly linked list containing two trees
per node.  These are the 'TREE_PURPOSE' and 'TREE_VALUE' of each node.
(Often, the 'TREE_PURPOSE' contains some kind of tag, or additional
information, while the 'TREE_VALUE' contains the majority of the
payload.  In other cases, the 'TREE_PURPOSE' is simply 'NULL_TREE',
while in still others both the 'TREE_PURPOSE' and 'TREE_VALUE' are of
equal stature.)  Given one 'TREE_LIST' node, the next node is found by
following the 'TREE_CHAIN'.  If the 'TREE_CHAIN' is 'NULL_TREE', then
you have reached the end of the list.

 A 'TREE_VEC' is a simple vector.  The 'TREE_VEC_LENGTH' is an integer
(not a tree) giving the number of nodes in the vector.  The nodes
themselves are accessed using the 'TREE_VEC_ELT' macro, which takes two
arguments.  The first is the 'TREE_VEC' in question; the second is an
integer indicating which element in the vector is desired.  The elements
are indexed from zero.


File: gccint.info,  Node: Types,  Next: Declarations,  Prev: Tree overview,  Up: GENERIC

11.3 Types
==========

All types have corresponding tree nodes.  However, you should not assume
that there is exactly one tree node corresponding to each type.  There
are often multiple nodes corresponding to the same type.

 For the most part, different kinds of types have different tree codes.
(For example, pointer types use a 'POINTER_TYPE' code while arrays use
an 'ARRAY_TYPE' code.)  However, pointers to member functions use the
'RECORD_TYPE' code.  Therefore, when writing a 'switch' statement that
depends on the code associated with a particular type, you should take
care to handle pointers to member functions under the 'RECORD_TYPE' case
label.

 The following functions and macros deal with cv-qualification of types:
'TYPE_MAIN_VARIANT'
     This macro returns the unqualified version of a type.  It may be
     applied to an unqualified type, but it is not always the identity
     function in that case.

 A few other macros and functions are usable with all types:
'TYPE_SIZE'
     The number of bits required to represent the type, represented as
     an 'INTEGER_CST'.  For an incomplete type, 'TYPE_SIZE' will be
     'NULL_TREE'.

'TYPE_ALIGN'
     The alignment of the type, in bits, represented as an 'int'.

'TYPE_NAME'
     This macro returns a declaration (in the form of a 'TYPE_DECL') for
     the type.  (Note this macro does _not_ return an 'IDENTIFIER_NODE',
     as you might expect, given its name!)  You can look at the
     'DECL_NAME' of the 'TYPE_DECL' to obtain the actual name of the
     type.  The 'TYPE_NAME' will be 'NULL_TREE' for a type that is not a
     built-in type, the result of a typedef, or a named class type.

'TYPE_CANONICAL'
     This macro returns the "canonical" type for the given type node.
     Canonical types are used to improve performance in the C++ and
     Objective-C++ front ends by allowing efficient comparison between
     two type nodes in 'same_type_p': if the 'TYPE_CANONICAL' values of
     the types are equal, the types are equivalent; otherwise, the types
     are not equivalent.  The notion of equivalence for canonical types
     is the same as the notion of type equivalence in the language
     itself.  For instance,

     When 'TYPE_CANONICAL' is 'NULL_TREE', there is no canonical type
     for the given type node.  In this case, comparison between this
     type and any other type requires the compiler to perform a deep,
     "structural" comparison to see if the two type nodes have the same
     form and properties.

     The canonical type for a node is always the most fundamental type
     in the equivalence class of types.  For instance, 'int' is its own
     canonical type.  A typedef 'I' of 'int' will have 'int' as its
     canonical type.  Similarly, 'I*' and a typedef 'IP' (defined to
     'I*') will has 'int*' as their canonical type.  When building a new
     type node, be sure to set 'TYPE_CANONICAL' to the appropriate
     canonical type.  If the new type is a compound type (built from
     other types), and any of those other types require structural
     equality, use 'SET_TYPE_STRUCTURAL_EQUALITY' to ensure that the new
     type also requires structural equality.  Finally, if for some
     reason you cannot guarantee that 'TYPE_CANONICAL' will point to the
     canonical type, use 'SET_TYPE_STRUCTURAL_EQUALITY' to make sure
     that the new type-and any type constructed based on it-requires
     structural equality.  If you suspect that the canonical type system
     is miscomparing types, pass '--param verify-canonical-types=1' to
     the compiler or configure with '--enable-checking' to force the
     compiler to verify its canonical-type comparisons against the
     structural comparisons; the compiler will then print any warnings
     if the canonical types miscompare.

'TYPE_STRUCTURAL_EQUALITY_P'
     This predicate holds when the node requires structural equality
     checks, e.g., when 'TYPE_CANONICAL' is 'NULL_TREE'.

'SET_TYPE_STRUCTURAL_EQUALITY'
     This macro states that the type node it is given requires
     structural equality checks, e.g., it sets 'TYPE_CANONICAL' to
     'NULL_TREE'.

'same_type_p'
     This predicate takes two types as input, and holds if they are the
     same type.  For example, if one type is a 'typedef' for the other,
     or both are 'typedef's for the same type.  This predicate also
     holds if the two trees given as input are simply copies of one
     another; i.e., there is no difference between them at the source
     level, but, for whatever reason, a duplicate has been made in the
     representation.  You should never use '==' (pointer equality) to
     compare types; always use 'same_type_p' instead.

 Detailed below are the various kinds of types, and the macros that can
be used to access them.  Although other kinds of types are used
elsewhere in G++, the types described here are the only ones that you
will encounter while examining the intermediate representation.

'VOID_TYPE'
     Used to represent the 'void' type.

'INTEGER_TYPE'
     Used to represent the various integral types, including 'char',
     'short', 'int', 'long', and 'long long'.  This code is not used for
     enumeration types, nor for the 'bool' type.  The 'TYPE_PRECISION'
     is the number of bits used in the representation, represented as an
     'unsigned int'.  (Note that in the general case this is not the
     same value as 'TYPE_SIZE'; suppose that there were a 24-bit integer
     type, but that alignment requirements for the ABI required 32-bit
     alignment.  Then, 'TYPE_SIZE' would be an 'INTEGER_CST' for 32,
     while 'TYPE_PRECISION' would be 24.)  The integer type is unsigned
     if 'TYPE_UNSIGNED' holds; otherwise, it is signed.

     The 'TYPE_MIN_VALUE' is an 'INTEGER_CST' for the smallest integer
     that may be represented by this type.  Similarly, the
     'TYPE_MAX_VALUE' is an 'INTEGER_CST' for the largest integer that
     may be represented by this type.

'REAL_TYPE'
     Used to represent the 'float', 'double', and 'long double' types.
     The number of bits in the floating-point representation is given by
     'TYPE_PRECISION', as in the 'INTEGER_TYPE' case.

'FIXED_POINT_TYPE'
     Used to represent the 'short _Fract', '_Fract', 'long _Fract',
     'long long _Fract', 'short _Accum', '_Accum', 'long _Accum', and
     'long long _Accum' types.  The number of bits in the fixed-point
     representation is given by 'TYPE_PRECISION', as in the
     'INTEGER_TYPE' case.  There may be padding bits, fractional bits
     and integral bits.  The number of fractional bits is given by
     'TYPE_FBIT', and the number of integral bits is given by
     'TYPE_IBIT'.  The fixed-point type is unsigned if 'TYPE_UNSIGNED'
     holds; otherwise, it is signed.  The fixed-point type is saturating
     if 'TYPE_SATURATING' holds; otherwise, it is not saturating.

'COMPLEX_TYPE'
     Used to represent GCC built-in '__complex__' data types.  The
     'TREE_TYPE' is the type of the real and imaginary parts.

'ENUMERAL_TYPE'
     Used to represent an enumeration type.  The 'TYPE_PRECISION' gives
     (as an 'int'), the number of bits used to represent the type.  If
     there are no negative enumeration constants, 'TYPE_UNSIGNED' will
     hold.  The minimum and maximum enumeration constants may be
     obtained with 'TYPE_MIN_VALUE' and 'TYPE_MAX_VALUE', respectively;
     each of these macros returns an 'INTEGER_CST'.

     The actual enumeration constants themselves may be obtained by
     looking at the 'TYPE_VALUES'.  This macro will return a
     'TREE_LIST', containing the constants.  The 'TREE_PURPOSE' of each
     node will be an 'IDENTIFIER_NODE' giving the name of the constant;
     the 'TREE_VALUE' will be an 'INTEGER_CST' giving the value assigned
     to that constant.  These constants will appear in the order in
     which they were declared.  The 'TREE_TYPE' of each of these
     constants will be the type of enumeration type itself.

'BOOLEAN_TYPE'
     Used to represent the 'bool' type.

'POINTER_TYPE'
     Used to represent pointer types, and pointer to data member types.
     The 'TREE_TYPE' gives the type to which this type points.

'REFERENCE_TYPE'
     Used to represent reference types.  The 'TREE_TYPE' gives the type
     to which this type refers.

'FUNCTION_TYPE'
     Used to represent the type of non-member functions and of static
     member functions.  The 'TREE_TYPE' gives the return type of the
     function.  The 'TYPE_ARG_TYPES' are a 'TREE_LIST' of the argument
     types.  The 'TREE_VALUE' of each node in this list is the type of
     the corresponding argument; the 'TREE_PURPOSE' is an expression for
     the default argument value, if any.  If the last node in the list
     is 'void_list_node' (a 'TREE_LIST' node whose 'TREE_VALUE' is the
     'void_type_node'), then functions of this type do not take variable
     arguments.  Otherwise, they do take a variable number of arguments.

     Note that in C (but not in C++) a function declared like 'void f()'
     is an unprototyped function taking a variable number of arguments;
     the 'TYPE_ARG_TYPES' of such a function will be 'NULL'.

'METHOD_TYPE'
     Used to represent the type of a non-static member function.  Like a
     'FUNCTION_TYPE', the return type is given by the 'TREE_TYPE'.  The
     type of '*this', i.e., the class of which functions of this type
     are a member, is given by the 'TYPE_METHOD_BASETYPE'.  The
     'TYPE_ARG_TYPES' is the parameter list, as for a 'FUNCTION_TYPE',
     and includes the 'this' argument.

'ARRAY_TYPE'
     Used to represent array types.  The 'TREE_TYPE' gives the type of
     the elements in the array.  If the array-bound is present in the
     type, the 'TYPE_DOMAIN' is an 'INTEGER_TYPE' whose 'TYPE_MIN_VALUE'
     and 'TYPE_MAX_VALUE' will be the lower and upper bounds of the
     array, respectively.  The 'TYPE_MIN_VALUE' will always be an
     'INTEGER_CST' for zero, while the 'TYPE_MAX_VALUE' will be one less
     than the number of elements in the array, i.e., the highest value
     which may be used to index an element in the array.

'RECORD_TYPE'
     Used to represent 'struct' and 'class' types, as well as pointers
     to member functions and similar constructs in other languages.
     'TYPE_FIELDS' contains the items contained in this type, each of
     which can be a 'FIELD_DECL', 'VAR_DECL', 'CONST_DECL', or
     'TYPE_DECL'.  You may not make any assumptions about the ordering
     of the fields in the type or whether one or more of them overlap.

'UNION_TYPE'
     Used to represent 'union' types.  Similar to 'RECORD_TYPE' except
     that all 'FIELD_DECL' nodes in 'TYPE_FIELD' start at bit position
     zero.

'QUAL_UNION_TYPE'
     Used to represent part of a variant record in Ada.  Similar to
     'UNION_TYPE' except that each 'FIELD_DECL' has a 'DECL_QUALIFIER'
     field, which contains a boolean expression that indicates whether
     the field is present in the object.  The type will only have one
     field, so each field's 'DECL_QUALIFIER' is only evaluated if none
     of the expressions in the previous fields in 'TYPE_FIELDS' are
     nonzero.  Normally these expressions will reference a field in the
     outer object using a 'PLACEHOLDER_EXPR'.

'LANG_TYPE'
     This node is used to represent a language-specific type.  The front
     end must handle it.

'OFFSET_TYPE'
     This node is used to represent a pointer-to-data member.  For a
     data member 'X::m' the 'TYPE_OFFSET_BASETYPE' is 'X' and the
     'TREE_TYPE' is the type of 'm'.

 There are variables whose values represent some of the basic types.
These include:
'void_type_node'
     A node for 'void'.

'integer_type_node'
     A node for 'int'.

'unsigned_type_node.'
     A node for 'unsigned int'.

'char_type_node.'
     A node for 'char'.
It may sometimes be useful to compare one of these variables with a type
in hand, using 'same_type_p'.


File: gccint.info,  Node: Declarations,  Next: Attributes,  Prev: Types,  Up: GENERIC

11.4 Declarations
=================

This section covers the various kinds of declarations that appear in the
internal representation, except for declarations of functions
(represented by 'FUNCTION_DECL' nodes), which are described in *note
Functions::.

* Menu:

* Working with declarations::  Macros and functions that work on
declarations.
* Internal structure:: How declaration nodes are represented.


File: gccint.info,  Node: Working with declarations,  Next: Internal structure,  Up: Declarations

11.4.1 Working with declarations
--------------------------------

Some macros can be used with any kind of declaration.  These include:
'DECL_NAME'
     This macro returns an 'IDENTIFIER_NODE' giving the name of the
     entity.

'TREE_TYPE'
     This macro returns the type of the entity declared.

'EXPR_FILENAME'
     This macro returns the name of the file in which the entity was
     declared, as a 'char*'.  For an entity declared implicitly by the
     compiler (like '__builtin_memcpy'), this will be the string
     '"<internal>"'.

'EXPR_LINENO'
     This macro returns the line number at which the entity was
     declared, as an 'int'.

'DECL_ARTIFICIAL'
     This predicate holds if the declaration was implicitly generated by
     the compiler.  For example, this predicate will hold of an
     implicitly declared member function, or of the 'TYPE_DECL'
     implicitly generated for a class type.  Recall that in C++ code
     like:
          struct S {};
     is roughly equivalent to C code like:
          struct S {};
          typedef struct S S;
     The implicitly generated 'typedef' declaration is represented by a
     'TYPE_DECL' for which 'DECL_ARTIFICIAL' holds.

 The various kinds of declarations include:
'LABEL_DECL'
     These nodes are used to represent labels in function bodies.  For
     more information, see *note Functions::.  These nodes only appear
     in block scopes.

'CONST_DECL'
     These nodes are used to represent enumeration constants.  The value
     of the constant is given by 'DECL_INITIAL' which will be an
     'INTEGER_CST' with the same type as the 'TREE_TYPE' of the
     'CONST_DECL', i.e., an 'ENUMERAL_TYPE'.

'RESULT_DECL'
     These nodes represent the value returned by a function.  When a
     value is assigned to a 'RESULT_DECL', that indicates that the value
     should be returned, via bitwise copy, by the function.  You can use
     'DECL_SIZE' and 'DECL_ALIGN' on a 'RESULT_DECL', just as with a
     'VAR_DECL'.

'TYPE_DECL'
     These nodes represent 'typedef' declarations.  The 'TREE_TYPE' is
     the type declared to have the name given by 'DECL_NAME'.  In some
     cases, there is no associated name.

'VAR_DECL'
     These nodes represent variables with namespace or block scope, as
     well as static data members.  The 'DECL_SIZE' and 'DECL_ALIGN' are
     analogous to 'TYPE_SIZE' and 'TYPE_ALIGN'.  For a declaration, you
     should always use the 'DECL_SIZE' and 'DECL_ALIGN' rather than the
     'TYPE_SIZE' and 'TYPE_ALIGN' given by the 'TREE_TYPE', since
     special attributes may have been applied to the variable to give it
     a particular size and alignment.  You may use the predicates
     'DECL_THIS_STATIC' or 'DECL_THIS_EXTERN' to test whether the
     storage class specifiers 'static' or 'extern' were used to declare
     a variable.

     If this variable is initialized (but does not require a
     constructor), the 'DECL_INITIAL' will be an expression for the
     initializer.  The initializer should be evaluated, and a bitwise
     copy into the variable performed.  If the 'DECL_INITIAL' is the
     'error_mark_node', there is an initializer, but it is given by an
     explicit statement later in the code; no bitwise copy is required.

     GCC provides an extension that allows either automatic variables,
     or global variables, to be placed in particular registers.  This
     extension is being used for a particular 'VAR_DECL' if
     'DECL_REGISTER' holds for the 'VAR_DECL', and if
     'DECL_ASSEMBLER_NAME' is not equal to 'DECL_NAME'.  In that case,
     'DECL_ASSEMBLER_NAME' is the name of the register into which the
     variable will be placed.

'PARM_DECL'
     Used to represent a parameter to a function.  Treat these nodes
     similarly to 'VAR_DECL' nodes.  These nodes only appear in the
     'DECL_ARGUMENTS' for a 'FUNCTION_DECL'.

     The 'DECL_ARG_TYPE' for a 'PARM_DECL' is the type that will
     actually be used when a value is passed to this function.  It may
     be a wider type than the 'TREE_TYPE' of the parameter; for example,
     the ordinary type might be 'short' while the 'DECL_ARG_TYPE' is
     'int'.

'DEBUG_EXPR_DECL'
     Used to represent an anonymous debug-information temporary created
     to hold an expression as it is optimized away, so that its value
     can be referenced in debug bind statements.

'FIELD_DECL'
     These nodes represent non-static data members.  The 'DECL_SIZE' and
     'DECL_ALIGN' behave as for 'VAR_DECL' nodes.  The position of the
     field within the parent record is specified by a combination of
     three attributes.  'DECL_FIELD_OFFSET' is the position, counting in
     bytes, of the 'DECL_OFFSET_ALIGN'-bit sized word containing the bit
     of the field closest to the beginning of the structure.
     'DECL_FIELD_BIT_OFFSET' is the bit offset of the first bit of the
     field within this word; this may be nonzero even for fields that
     are not bit-fields, since 'DECL_OFFSET_ALIGN' may be greater than
     the natural alignment of the field's type.

     If 'DECL_C_BIT_FIELD' holds, this field is a bit-field.  In a
     bit-field, 'DECL_BIT_FIELD_TYPE' also contains the type that was
     originally specified for it, while DECL_TYPE may be a modified type
     with lesser precision, according to the size of the bit field.

'NAMESPACE_DECL'
     Namespaces provide a name hierarchy for other declarations.  They
     appear in the 'DECL_CONTEXT' of other '_DECL' nodes.


File: gccint.info,  Node: Internal structure,  Prev: Working with declarations,  Up: Declarations

11.4.2 Internal structure
-------------------------

'DECL' nodes are represented internally as a hierarchy of structures.

* Menu:

* Current structure hierarchy::  The current DECL node structure
hierarchy.
* Adding new DECL node types:: How to add a new DECL node to a
frontend.


File: gccint.info,  Node: Current structure hierarchy,  Next: Adding new DECL node types,  Up: Internal structure

11.4.2.1 Current structure hierarchy
....................................

'struct tree_decl_minimal'
     This is the minimal structure to inherit from in order for common
     'DECL' macros to work.  The fields it contains are a unique ID,
     source location, context, and name.

'struct tree_decl_common'
     This structure inherits from 'struct tree_decl_minimal'.  It
     contains fields that most 'DECL' nodes need, such as a field to
     store alignment, machine mode, size, and attributes.

'struct tree_field_decl'
     This structure inherits from 'struct tree_decl_common'.  It is used
     to represent 'FIELD_DECL'.

'struct tree_label_decl'
     This structure inherits from 'struct tree_decl_common'.  It is used
     to represent 'LABEL_DECL'.

'struct tree_translation_unit_decl'
     This structure inherits from 'struct tree_decl_common'.  It is used
     to represent 'TRANSLATION_UNIT_DECL'.

'struct tree_decl_with_rtl'
     This structure inherits from 'struct tree_decl_common'.  It
     contains a field to store the low-level RTL associated with a
     'DECL' node.

'struct tree_result_decl'
     This structure inherits from 'struct tree_decl_with_rtl'.  It is
     used to represent 'RESULT_DECL'.

'struct tree_const_decl'
     This structure inherits from 'struct tree_decl_with_rtl'.  It is
     used to represent 'CONST_DECL'.

'struct tree_parm_decl'
     This structure inherits from 'struct tree_decl_with_rtl'.  It is
     used to represent 'PARM_DECL'.

'struct tree_decl_with_vis'
     This structure inherits from 'struct tree_decl_with_rtl'.  It
     contains fields necessary to store visibility information, as well
     as a section name and assembler name.

'struct tree_var_decl'
     This structure inherits from 'struct tree_decl_with_vis'.  It is
     used to represent 'VAR_DECL'.

'struct tree_function_decl'
     This structure inherits from 'struct tree_decl_with_vis'.  It is
     used to represent 'FUNCTION_DECL'.


File: gccint.info,  Node: Adding new DECL node types,  Prev: Current structure hierarchy,  Up: Internal structure

11.4.2.2 Adding new DECL node types
...................................

Adding a new 'DECL' tree consists of the following steps

Add a new tree code for the 'DECL' node
     For language specific 'DECL' nodes, there is a '.def' file in each
     frontend directory where the tree code should be added.  For 'DECL'
     nodes that are part of the middle-end, the code should be added to
     'tree.def'.

Create a new structure type for the 'DECL' node
     These structures should inherit from one of the existing structures
     in the language hierarchy by using that structure as the first
     member.

          struct tree_foo_decl
          {
             struct tree_decl_with_vis common;
          }

     Would create a structure name 'tree_foo_decl' that inherits from
     'struct tree_decl_with_vis'.

     For language specific 'DECL' nodes, this new structure type should
     go in the appropriate '.h' file.  For 'DECL' nodes that are part of
     the middle-end, the structure type should go in 'tree.h'.

Add a member to the tree structure enumerator for the node
     For garbage collection and dynamic checking purposes, each 'DECL'
     node structure type is required to have a unique enumerator value
     specified with it.  For language specific 'DECL' nodes, this new
     enumerator value should go in the appropriate '.def' file.  For
     'DECL' nodes that are part of the middle-end, the enumerator values
     are specified in 'treestruct.def'.

Update 'union tree_node'
     In order to make your new structure type usable, it must be added
     to 'union tree_node'.  For language specific 'DECL' nodes, a new
     entry should be added to the appropriate '.h' file of the form
            struct tree_foo_decl GTY ((tag ("TS_VAR_DECL"))) foo_decl;
     For 'DECL' nodes that are part of the middle-end, the additional
     member goes directly into 'union tree_node' in 'tree.h'.

Update dynamic checking info
     In order to be able to check whether accessing a named portion of
     'union tree_node' is legal, and whether a certain 'DECL' node
     contains one of the enumerated 'DECL' node structures in the
     hierarchy, a simple lookup table is used.  This lookup table needs
     to be kept up to date with the tree structure hierarchy, or else
     checking and containment macros will fail inappropriately.

     For language specific 'DECL' nodes, their is an 'init_ts' function
     in an appropriate '.c' file, which initializes the lookup table.
     Code setting up the table for new 'DECL' nodes should be added
     there.  For each 'DECL' tree code and enumerator value representing
     a member of the inheritance hierarchy, the table should contain 1
     if that tree code inherits (directly or indirectly) from that
     member.  Thus, a 'FOO_DECL' node derived from 'struct
     decl_with_rtl', and enumerator value 'TS_FOO_DECL', would be set up
     as follows
          tree_contains_struct[FOO_DECL][TS_FOO_DECL] = 1;
          tree_contains_struct[FOO_DECL][TS_DECL_WRTL] = 1;
          tree_contains_struct[FOO_DECL][TS_DECL_COMMON] = 1;
          tree_contains_struct[FOO_DECL][TS_DECL_MINIMAL] = 1;

     For 'DECL' nodes that are part of the middle-end, the setup code
     goes into 'tree.c'.

Add macros to access any new fields and flags

     Each added field or flag should have a macro that is used to access
     it, that performs appropriate checking to ensure only the right
     type of 'DECL' nodes access the field.

     These macros generally take the following form
          #define FOO_DECL_FIELDNAME(NODE) FOO_DECL_CHECK(NODE)->foo_decl.fieldname
     However, if the structure is simply a base class for further
     structures, something like the following should be used
          #define BASE_STRUCT_CHECK(T) CONTAINS_STRUCT_CHECK(T, TS_BASE_STRUCT)
          #define BASE_STRUCT_FIELDNAME(NODE) \
             (BASE_STRUCT_CHECK(NODE)->base_struct.fieldname


File: gccint.info,  Node: Attributes,  Next: Expression trees,  Prev: Declarations,  Up: GENERIC

11.5 Attributes in trees
========================

Attributes, as specified using the '__attribute__' keyword, are
represented internally as a 'TREE_LIST'.  The 'TREE_PURPOSE' is the name
of the attribute, as an 'IDENTIFIER_NODE'.  The 'TREE_VALUE' is a
'TREE_LIST' of the arguments of the attribute, if any, or 'NULL_TREE' if
there are no arguments; the arguments are stored as the 'TREE_VALUE' of
successive entries in the list, and may be identifiers or expressions.
The 'TREE_CHAIN' of the attribute is the next attribute in a list of
attributes applying to the same declaration or type, or 'NULL_TREE' if
there are no further attributes in the list.

 Attributes may be attached to declarations and to types; these
attributes may be accessed with the following macros.  All attributes
are stored in this way, and many also cause other changes to the
declaration or type or to other internal compiler data structures.

 -- Tree Macro: tree DECL_ATTRIBUTES (tree DECL)
     This macro returns the attributes on the declaration DECL.

 -- Tree Macro: tree TYPE_ATTRIBUTES (tree TYPE)
     This macro returns the attributes on the type TYPE.


File: gccint.info,  Node: Expression trees,  Next: Statements,  Prev: Attributes,  Up: GENERIC

11.6 Expressions
================

The internal representation for expressions is for the most part quite
straightforward.  However, there are a few facts that one must bear in
mind.  In particular, the expression "tree" is actually a directed
acyclic graph.  (For example there may be many references to the integer
constant zero throughout the source program; many of these will be
represented by the same expression node.)  You should not rely on
certain kinds of node being shared, nor should you rely on certain kinds
of nodes being unshared.

 The following macros can be used with all expression nodes:

'TREE_TYPE'
     Returns the type of the expression.  This value may not be
     precisely the same type that would be given the expression in the
     original program.

 In what follows, some nodes that one might expect to always have type
'bool' are documented to have either integral or boolean type.  At some
point in the future, the C front end may also make use of this same
intermediate representation, and at this point these nodes will
certainly have integral type.  The previous sentence is not meant to
imply that the C++ front end does not or will not give these nodes
integral type.

 Below, we list the various kinds of expression nodes.  Except where
noted otherwise, the operands to an expression are accessed using the
'TREE_OPERAND' macro.  For example, to access the first operand to a
binary plus expression 'expr', use:

     TREE_OPERAND (expr, 0)

 As this example indicates, the operands are zero-indexed.

* Menu:

* Constants: Constant expressions.
* Storage References::
* Unary and Binary Expressions::
* Vectors::


File: gccint.info,  Node: Constant expressions,  Next: Storage References,  Up: Expression trees

11.6.1 Constant expressions
---------------------------

The table below begins with constants, moves on to unary expressions,
then proceeds to binary expressions, and concludes with various other
kinds of expressions:

'INTEGER_CST'
     These nodes represent integer constants.  Note that the type of
     these constants is obtained with 'TREE_TYPE'; they are not always
     of type 'int'.  In particular, 'char' constants are represented
     with 'INTEGER_CST' nodes.  The value of the integer constant 'e' is
     given by
          ((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT)
          + TREE_INST_CST_LOW (e))
     HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms.
     Both 'TREE_INT_CST_HIGH' and 'TREE_INT_CST_LOW' return a
     'HOST_WIDE_INT'.  The value of an 'INTEGER_CST' is interpreted as a
     signed or unsigned quantity depending on the type of the constant.
     In general, the expression given above will overflow, so it should
     not be used to calculate the value of the constant.

     The variable 'integer_zero_node' is an integer constant with value
     zero.  Similarly, 'integer_one_node' is an integer constant with
     value one.  The 'size_zero_node' and 'size_one_node' variables are
     analogous, but have type 'size_t' rather than 'int'.

     The function 'tree_int_cst_lt' is a predicate which holds if its
     first argument is less than its second.  Both constants are assumed
     to have the same signedness (i.e., either both should be signed or
     both should be unsigned.)  The full width of the constant is used
     when doing the comparison; the usual rules about promotions and
     conversions are ignored.  Similarly, 'tree_int_cst_equal' holds if
     the two constants are equal.  The 'tree_int_cst_sgn' function
     returns the sign of a constant.  The value is '1', '0', or '-1'
     according on whether the constant is greater than, equal to, or
     less than zero.  Again, the signedness of the constant's type is
     taken into account; an unsigned constant is never less than zero,
     no matter what its bit-pattern.

'REAL_CST'

     FIXME: Talk about how to obtain representations of this constant,
     do comparisons, and so forth.

'FIXED_CST'

     These nodes represent fixed-point constants.  The type of these
     constants is obtained with 'TREE_TYPE'.  'TREE_FIXED_CST_PTR'
     points to a 'struct fixed_value'; 'TREE_FIXED_CST' returns the
     structure itself.  'struct fixed_value' contains 'data' with the
     size of two 'HOST_BITS_PER_WIDE_INT' and 'mode' as the associated
     fixed-point machine mode for 'data'.

'COMPLEX_CST'
     These nodes are used to represent complex number constants, that is
     a '__complex__' whose parts are constant nodes.  The
     'TREE_REALPART' and 'TREE_IMAGPART' return the real and the
     imaginary parts respectively.

'VECTOR_CST'
     These nodes are used to represent vector constants, whose parts are
     constant nodes.  Each individual constant node is either an integer
     or a double constant node.  The first operand is a 'TREE_LIST' of
     the constant nodes and is accessed through 'TREE_VECTOR_CST_ELTS'.

'STRING_CST'
     These nodes represent string-constants.  The 'TREE_STRING_LENGTH'
     returns the length of the string, as an 'int'.  The
     'TREE_STRING_POINTER' is a 'char*' containing the string itself.
     The string may not be 'NUL'-terminated, and it may contain embedded
     'NUL' characters.  Therefore, the 'TREE_STRING_LENGTH' includes the
     trailing 'NUL' if it is present.

     For wide string constants, the 'TREE_STRING_LENGTH' is the number
     of bytes in the string, and the 'TREE_STRING_POINTER' points to an
     array of the bytes of the string, as represented on the target
     system (that is, as integers in the target endianness).  Wide and
     non-wide string constants are distinguished only by the 'TREE_TYPE'
     of the 'STRING_CST'.

     FIXME: The formats of string constants are not well-defined when
     the target system bytes are not the same width as host system
     bytes.


File: gccint.info,  Node: Storage References,  Next: Unary and Binary Expressions,  Prev: Constant expressions,  Up: Expression trees

11.6.2 References to storage
----------------------------

'ARRAY_REF'
     These nodes represent array accesses.  The first operand is the
     array; the second is the index.  To calculate the address of the
     memory accessed, you must scale the index by the size of the type
     of the array elements.  The type of these expressions must be the
     type of a component of the array.  The third and fourth operands
     are used after gimplification to represent the lower bound and
     component size but should not be used directly; call
     'array_ref_low_bound' and 'array_ref_element_size' instead.

'ARRAY_RANGE_REF'
     These nodes represent access to a range (or "slice") of an array.
     The operands are the same as that for 'ARRAY_REF' and have the same
     meanings.  The type of these expressions must be an array whose
     component type is the same as that of the first operand.  The range
     of that array type determines the amount of data these expressions
     access.

'TARGET_MEM_REF'
     These nodes represent memory accesses whose address directly map to
     an addressing mode of the target architecture.  The first argument
     is 'TMR_SYMBOL' and must be a 'VAR_DECL' of an object with a fixed
     address.  The second argument is 'TMR_BASE' and the third one is
     'TMR_INDEX'.  The fourth argument is 'TMR_STEP' and must be an
     'INTEGER_CST'.  The fifth argument is 'TMR_OFFSET' and must be an
     'INTEGER_CST'.  Any of the arguments may be NULL if the appropriate
     component does not appear in the address.  Address of the
     'TARGET_MEM_REF' is determined in the following way.

          &TMR_SYMBOL + TMR_BASE + TMR_INDEX * TMR_STEP + TMR_OFFSET

     The sixth argument is the reference to the original memory access,
     which is preserved for the purposes of the RTL alias analysis.  The
     seventh argument is a tag representing the results of tree level
     alias analysis.

'ADDR_EXPR'
     These nodes are used to represent the address of an object.  (These
     expressions will always have pointer or reference type.)  The
     operand may be another expression, or it may be a declaration.

     As an extension, GCC allows users to take the address of a label.
     In this case, the operand of the 'ADDR_EXPR' will be a
     'LABEL_DECL'.  The type of such an expression is 'void*'.

     If the object addressed is not an lvalue, a temporary is created,
     and the address of the temporary is used.

'INDIRECT_REF'
     These nodes are used to represent the object pointed to by a
     pointer.  The operand is the pointer being dereferenced; it will
     always have pointer or reference type.

'MEM_REF'
     These nodes are used to represent the object pointed to by a
     pointer offset by a constant.  The first operand is the pointer
     being dereferenced; it will always have pointer or reference type.
     The second operand is a pointer constant.  Its type is specifying
     the type to be used for type-based alias analysis.

'COMPONENT_REF'
     These nodes represent non-static data member accesses.  The first
     operand is the object (rather than a pointer to it); the second
     operand is the 'FIELD_DECL' for the data member.  The third operand
     represents the byte offset of the field, but should not be used
     directly; call 'component_ref_field_offset' instead.


File: gccint.info,  Node: Unary and Binary Expressions,  Next: Vectors,  Prev: Storage References,  Up: Expression trees

11.6.3 Unary and Binary Expressions
-----------------------------------

'NEGATE_EXPR'
     These nodes represent unary negation of the single operand, for
     both integer and floating-point types.  The type of negation can be
     determined by looking at the type of the expression.

     The behavior of this operation on signed arithmetic overflow is
     controlled by the 'flag_wrapv' and 'flag_trapv' variables.

'ABS_EXPR'
     These nodes represent the absolute value of the single operand, for
     both integer and floating-point types.  This is typically used to
     implement the 'abs', 'labs' and 'llabs' builtins for integer types,
     and the 'fabs', 'fabsf' and 'fabsl' builtins for floating point
     types.  The type of abs operation can be determined by looking at
     the type of the expression.

     This node is not used for complex types.  To represent the modulus
     or complex abs of a complex value, use the 'BUILT_IN_CABS',
     'BUILT_IN_CABSF' or 'BUILT_IN_CABSL' builtins, as used to implement
     the C99 'cabs', 'cabsf' and 'cabsl' built-in functions.

'BIT_NOT_EXPR'
     These nodes represent bitwise complement, and will always have
     integral type.  The only operand is the value to be complemented.

'TRUTH_NOT_EXPR'
     These nodes represent logical negation, and will always have
     integral (or boolean) type.  The operand is the value being
     negated.  The type of the operand and that of the result are always
     of 'BOOLEAN_TYPE' or 'INTEGER_TYPE'.

'PREDECREMENT_EXPR'
'PREINCREMENT_EXPR'
'POSTDECREMENT_EXPR'
'POSTINCREMENT_EXPR'
     These nodes represent increment and decrement expressions.  The
     value of the single operand is computed, and the operand
     incremented or decremented.  In the case of 'PREDECREMENT_EXPR' and
     'PREINCREMENT_EXPR', the value of the expression is the value
     resulting after the increment or decrement; in the case of
     'POSTDECREMENT_EXPR' and 'POSTINCREMENT_EXPR' is the value before
     the increment or decrement occurs.  The type of the operand, like
     that of the result, will be either integral, boolean, or
     floating-point.

'FIX_TRUNC_EXPR'
     These nodes represent conversion of a floating-point value to an
     integer.  The single operand will have a floating-point type, while
     the complete expression will have an integral (or boolean) type.
     The operand is rounded towards zero.

'FLOAT_EXPR'
     These nodes represent conversion of an integral (or boolean) value
     to a floating-point value.  The single operand will have integral
     type, while the complete expression will have a floating-point
     type.

     FIXME: How is the operand supposed to be rounded?  Is this
     dependent on '-mieee'?

'COMPLEX_EXPR'
     These nodes are used to represent complex numbers constructed from
     two expressions of the same (integer or real) type.  The first
     operand is the real part and the second operand is the imaginary
     part.

'CONJ_EXPR'
     These nodes represent the conjugate of their operand.

'REALPART_EXPR'
'IMAGPART_EXPR'
     These nodes represent respectively the real and the imaginary parts
     of complex numbers (their sole argument).

'NON_LVALUE_EXPR'
     These nodes indicate that their one and only operand is not an
     lvalue.  A back end can treat these identically to the single
     operand.

'NOP_EXPR'
     These nodes are used to represent conversions that do not require
     any code-generation.  For example, conversion of a 'char*' to an
     'int*' does not require any code be generated; such a conversion is
     represented by a 'NOP_EXPR'.  The single operand is the expression
     to be converted.  The conversion from a pointer to a reference is
     also represented with a 'NOP_EXPR'.

'CONVERT_EXPR'
     These nodes are similar to 'NOP_EXPR's, but are used in those
     situations where code may need to be generated.  For example, if an
     'int*' is converted to an 'int' code may need to be generated on
     some platforms.  These nodes are never used for C++-specific
     conversions, like conversions between pointers to different classes
     in an inheritance hierarchy.  Any adjustments that need to be made
     in such cases are always indicated explicitly.  Similarly, a
     user-defined conversion is never represented by a 'CONVERT_EXPR';
     instead, the function calls are made explicit.

'FIXED_CONVERT_EXPR'
     These nodes are used to represent conversions that involve
     fixed-point values.  For example, from a fixed-point value to
     another fixed-point value, from an integer to a fixed-point value,
     from a fixed-point value to an integer, from a floating-point value
     to a fixed-point value, or from a fixed-point value to a
     floating-point value.

'LSHIFT_EXPR'
'RSHIFT_EXPR'
     These nodes represent left and right shifts, respectively.  The
     first operand is the value to shift; it will always be of integral
     type.  The second operand is an expression for the number of bits
     by which to shift.  Right shift should be treated as arithmetic,
     i.e., the high-order bits should be zero-filled when the expression
     has unsigned type and filled with the sign bit when the expression
     has signed type.  Note that the result is undefined if the second
     operand is larger than or equal to the first operand's type size.
     Unlike most nodes, these can have a vector as first operand and a
     scalar as second operand.

'BIT_IOR_EXPR'
'BIT_XOR_EXPR'
'BIT_AND_EXPR'
     These nodes represent bitwise inclusive or, bitwise exclusive or,
     and bitwise and, respectively.  Both operands will always have
     integral type.

'TRUTH_ANDIF_EXPR'
'TRUTH_ORIF_EXPR'
     These nodes represent logical "and" and logical "or", respectively.
     These operators are not strict; i.e., the second operand is
     evaluated only if the value of the expression is not determined by
     evaluation of the first operand.  The type of the operands and that
     of the result are always of 'BOOLEAN_TYPE' or 'INTEGER_TYPE'.

'TRUTH_AND_EXPR'
'TRUTH_OR_EXPR'
'TRUTH_XOR_EXPR'
     These nodes represent logical and, logical or, and logical
     exclusive or.  They are strict; both arguments are always
     evaluated.  There are no corresponding operators in C or C++, but
     the front end will sometimes generate these expressions anyhow, if
     it can tell that strictness does not matter.  The type of the
     operands and that of the result are always of 'BOOLEAN_TYPE' or
     'INTEGER_TYPE'.

'POINTER_PLUS_EXPR'
     This node represents pointer arithmetic.  The first operand is
     always a pointer/reference type.  The second operand is always an
     unsigned integer type compatible with sizetype.  This is the only
     binary arithmetic operand that can operate on pointer types.

'PLUS_EXPR'
'MINUS_EXPR'
'MULT_EXPR'
     These nodes represent various binary arithmetic operations.
     Respectively, these operations are addition, subtraction (of the
     second operand from the first) and multiplication.  Their operands
     may have either integral or floating type, but there will never be
     case in which one operand is of floating type and the other is of
     integral type.

     The behavior of these operations on signed arithmetic overflow is
     controlled by the 'flag_wrapv' and 'flag_trapv' variables.

'MULT_HIGHPART_EXPR'
     This node represents the "high-part" of a widening multiplication.
     For an integral type with B bits of precision, the result is the
     most significant B bits of the full 2B product.

'RDIV_EXPR'
     This node represents a floating point division operation.

'TRUNC_DIV_EXPR'
'FLOOR_DIV_EXPR'
'CEIL_DIV_EXPR'
'ROUND_DIV_EXPR'
     These nodes represent integer division operations that return an
     integer result.  'TRUNC_DIV_EXPR' rounds towards zero,
     'FLOOR_DIV_EXPR' rounds towards negative infinity, 'CEIL_DIV_EXPR'
     rounds towards positive infinity and 'ROUND_DIV_EXPR' rounds to the
     closest integer.  Integer division in C and C++ is truncating, i.e.
     'TRUNC_DIV_EXPR'.

     The behavior of these operations on signed arithmetic overflow,
     when dividing the minimum signed integer by minus one, is
     controlled by the 'flag_wrapv' and 'flag_trapv' variables.

'TRUNC_MOD_EXPR'
'FLOOR_MOD_EXPR'
'CEIL_MOD_EXPR'
'ROUND_MOD_EXPR'
     These nodes represent the integer remainder or modulus operation.
     The integer modulus of two operands 'a' and 'b' is defined as 'a -
     (a/b)*b' where the division calculated using the corresponding
     division operator.  Hence for 'TRUNC_MOD_EXPR' this definition
     assumes division using truncation towards zero, i.e.
     'TRUNC_DIV_EXPR'.  Integer remainder in C and C++ uses truncating
     division, i.e. 'TRUNC_MOD_EXPR'.

'EXACT_DIV_EXPR'
     The 'EXACT_DIV_EXPR' code is used to represent integer divisions
     where the numerator is known to be an exact multiple of the
     denominator.  This allows the backend to choose between the faster
     of 'TRUNC_DIV_EXPR', 'CEIL_DIV_EXPR' and 'FLOOR_DIV_EXPR' for the
     current target.

'LT_EXPR'
'LE_EXPR'
'GT_EXPR'
'GE_EXPR'
'EQ_EXPR'
'NE_EXPR'
     These nodes represent the less than, less than or equal to, greater
     than, greater than or equal to, equal, and not equal comparison
     operators.  The first and second operands will either be both of
     integral type, both of floating type or both of vector type.  The
     result type of these expressions will always be of integral,
     boolean or signed integral vector type.  These operations return
     the result type's zero value for false, the result type's one value
     for true, and a vector whose elements are zero (false) or minus one
     (true) for vectors.

     For floating point comparisons, if we honor IEEE NaNs and either
     operand is NaN, then 'NE_EXPR' always returns true and the
     remaining operators always return false.  On some targets,
     comparisons against an IEEE NaN, other than equality and
     inequality, may generate a floating point exception.

'ORDERED_EXPR'
'UNORDERED_EXPR'
     These nodes represent non-trapping ordered and unordered comparison
     operators.  These operations take two floating point operands and
     determine whether they are ordered or unordered relative to each
     other.  If either operand is an IEEE NaN, their comparison is
     defined to be unordered, otherwise the comparison is defined to be
     ordered.  The result type of these expressions will always be of
     integral or boolean type.  These operations return the result
     type's zero value for false, and the result type's one value for
     true.

'UNLT_EXPR'
'UNLE_EXPR'
'UNGT_EXPR'
'UNGE_EXPR'
'UNEQ_EXPR'
'LTGT_EXPR'
     These nodes represent the unordered comparison operators.  These
     operations take two floating point operands and determine whether
     the operands are unordered or are less than, less than or equal to,
     greater than, greater than or equal to, or equal respectively.  For
     example, 'UNLT_EXPR' returns true if either operand is an IEEE NaN
     or the first operand is less than the second.  With the possible
     exception of 'LTGT_EXPR', all of these operations are guaranteed
     not to generate a floating point exception.  The result type of
     these expressions will always be of integral or boolean type.
     These operations return the result type's zero value for false, and
     the result type's one value for true.

'MODIFY_EXPR'
     These nodes represent assignment.  The left-hand side is the first
     operand; the right-hand side is the second operand.  The left-hand
     side will be a 'VAR_DECL', 'INDIRECT_REF', 'COMPONENT_REF', or
     other lvalue.

     These nodes are used to represent not only assignment with '=' but
     also compound assignments (like '+='), by reduction to '='
     assignment.  In other words, the representation for 'i += 3' looks
     just like that for 'i = i + 3'.

'INIT_EXPR'
     These nodes are just like 'MODIFY_EXPR', but are used only when a
     variable is initialized, rather than assigned to subsequently.
     This means that we can assume that the target of the initialization
     is not used in computing its own value; any reference to the lhs in
     computing the rhs is undefined.

'COMPOUND_EXPR'
     These nodes represent comma-expressions.  The first operand is an
     expression whose value is computed and thrown away prior to the
     evaluation of the second operand.  The value of the entire
     expression is the value of the second operand.

'COND_EXPR'
     These nodes represent '?:' expressions.  The first operand is of
     boolean or integral type.  If it evaluates to a nonzero value, the
     second operand should be evaluated, and returned as the value of
     the expression.  Otherwise, the third operand is evaluated, and
     returned as the value of the expression.

     The second operand must have the same type as the entire
     expression, unless it unconditionally throws an exception or calls
     a noreturn function, in which case it should have void type.  The
     same constraints apply to the third operand.  This allows array
     bounds checks to be represented conveniently as '(i >= 0 && i < 10)
     ? i : abort()'.

     As a GNU extension, the C language front-ends allow the second
     operand of the '?:' operator may be omitted in the source.  For
     example, 'x ? : 3' is equivalent to 'x ? x : 3', assuming that 'x'
     is an expression without side-effects.  In the tree representation,
     however, the second operand is always present, possibly protected
     by 'SAVE_EXPR' if the first argument does cause side-effects.

'CALL_EXPR'
     These nodes are used to represent calls to functions, including
     non-static member functions.  'CALL_EXPR's are implemented as
     expression nodes with a variable number of operands.  Rather than
     using 'TREE_OPERAND' to extract them, it is preferable to use the
     specialized accessor macros and functions that operate specifically
     on 'CALL_EXPR' nodes.

     'CALL_EXPR_FN' returns a pointer to the function to call; it is
     always an expression whose type is a 'POINTER_TYPE'.

     The number of arguments to the call is returned by
     'call_expr_nargs', while the arguments themselves can be accessed
     with the 'CALL_EXPR_ARG' macro.  The arguments are zero-indexed and
     numbered left-to-right.  You can iterate over the arguments using
     'FOR_EACH_CALL_EXPR_ARG', as in:

          tree call, arg;
          call_expr_arg_iterator iter;
          FOR_EACH_CALL_EXPR_ARG (arg, iter, call)
            /* arg is bound to successive arguments of call.  */
            ...;

     For non-static member functions, there will be an operand
     corresponding to the 'this' pointer.  There will always be
     expressions corresponding to all of the arguments, even if the
     function is declared with default arguments and some arguments are
     not explicitly provided at the call sites.

     'CALL_EXPR's also have a 'CALL_EXPR_STATIC_CHAIN' operand that is
     used to implement nested functions.  This operand is otherwise
     null.

'CLEANUP_POINT_EXPR'
     These nodes represent full-expressions.  The single operand is an
     expression to evaluate.  Any destructor calls engendered by the
     creation of temporaries during the evaluation of that expression
     should be performed immediately after the expression is evaluated.

'CONSTRUCTOR'
     These nodes represent the brace-enclosed initializers for a
     structure or array.  The first operand is reserved for use by the
     back end.  The second operand is a 'TREE_LIST'.  If the 'TREE_TYPE'
     of the 'CONSTRUCTOR' is a 'RECORD_TYPE' or 'UNION_TYPE', then the
     'TREE_PURPOSE' of each node in the 'TREE_LIST' will be a
     'FIELD_DECL' and the 'TREE_VALUE' of each node will be the
     expression used to initialize that field.

     If the 'TREE_TYPE' of the 'CONSTRUCTOR' is an 'ARRAY_TYPE', then
     the 'TREE_PURPOSE' of each element in the 'TREE_LIST' will be an
     'INTEGER_CST' or a 'RANGE_EXPR' of two 'INTEGER_CST's.  A single
     'INTEGER_CST' indicates which element of the array (indexed from
     zero) is being assigned to.  A 'RANGE_EXPR' indicates an inclusive
     range of elements to initialize.  In both cases the 'TREE_VALUE' is
     the corresponding initializer.  It is re-evaluated for each element
     of a 'RANGE_EXPR'.  If the 'TREE_PURPOSE' is 'NULL_TREE', then the
     initializer is for the next available array element.

     In the front end, you should not depend on the fields appearing in
     any particular order.  However, in the middle end, fields must
     appear in declaration order.  You should not assume that all fields
     will be represented.  Unrepresented fields will be set to zero.

'COMPOUND_LITERAL_EXPR'
     These nodes represent ISO C99 compound literals.  The
     'COMPOUND_LITERAL_EXPR_DECL_EXPR' is a 'DECL_EXPR' containing an
     anonymous 'VAR_DECL' for the unnamed object represented by the
     compound literal; the 'DECL_INITIAL' of that 'VAR_DECL' is a
     'CONSTRUCTOR' representing the brace-enclosed list of initializers
     in the compound literal.  That anonymous 'VAR_DECL' can also be
     accessed directly by the 'COMPOUND_LITERAL_EXPR_DECL' macro.

'SAVE_EXPR'

     A 'SAVE_EXPR' represents an expression (possibly involving
     side-effects) that is used more than once.  The side-effects should
     occur only the first time the expression is evaluated.  Subsequent
     uses should just reuse the computed value.  The first operand to
     the 'SAVE_EXPR' is the expression to evaluate.  The side-effects
     should be executed where the 'SAVE_EXPR' is first encountered in a
     depth-first preorder traversal of the expression tree.

'TARGET_EXPR'
     A 'TARGET_EXPR' represents a temporary object.  The first operand
     is a 'VAR_DECL' for the temporary variable.  The second operand is
     the initializer for the temporary.  The initializer is evaluated
     and, if non-void, copied (bitwise) into the temporary.  If the
     initializer is void, that means that it will perform the
     initialization itself.

     Often, a 'TARGET_EXPR' occurs on the right-hand side of an
     assignment, or as the second operand to a comma-expression which is
     itself the right-hand side of an assignment, etc.  In this case, we
     say that the 'TARGET_EXPR' is "normal"; otherwise, we say it is
     "orphaned".  For a normal 'TARGET_EXPR' the temporary variable
     should be treated as an alias for the left-hand side of the
     assignment, rather than as a new temporary variable.

     The third operand to the 'TARGET_EXPR', if present, is a
     cleanup-expression (i.e., destructor call) for the temporary.  If
     this expression is orphaned, then this expression must be executed
     when the statement containing this expression is complete.  These
     cleanups must always be executed in the order opposite to that in
     which they were encountered.  Note that if a temporary is created
     on one branch of a conditional operator (i.e., in the second or
     third operand to a 'COND_EXPR'), the cleanup must be run only if
     that branch is actually executed.

'VA_ARG_EXPR'
     This node is used to implement support for the C/C++ variable
     argument-list mechanism.  It represents expressions like 'va_arg
     (ap, type)'.  Its 'TREE_TYPE' yields the tree representation for
     'type' and its sole argument yields the representation for 'ap'.


File: gccint.info,  Node: Vectors,  Prev: Unary and Binary Expressions,  Up: Expression trees

11.6.4 Vectors
--------------

'VEC_LSHIFT_EXPR'
'VEC_RSHIFT_EXPR'
     These nodes represent whole vector left and right shifts,
     respectively.  The first operand is the vector to shift; it will
     always be of vector type.  The second operand is an expression for
     the number of bits by which to shift.  Note that the result is
     undefined if the second operand is larger than or equal to the
     first operand's type size.

'VEC_WIDEN_MULT_HI_EXPR'
'VEC_WIDEN_MULT_LO_EXPR'
     These nodes represent widening vector multiplication of the high
     and low parts of the two input vectors, respectively.  Their
     operands are vectors that contain the same number of elements ('N')
     of the same integral type.  The result is a vector that contains
     half as many elements, of an integral type whose size is twice as
     wide.  In the case of 'VEC_WIDEN_MULT_HI_EXPR' the high 'N/2'
     elements of the two vector are multiplied to produce the vector of
     'N/2' products.  In the case of 'VEC_WIDEN_MULT_LO_EXPR' the low
     'N/2' elements of the two vector are multiplied to produce the
     vector of 'N/2' products.

'VEC_UNPACK_HI_EXPR'
'VEC_UNPACK_LO_EXPR'
     These nodes represent unpacking of the high and low parts of the
     input vector, respectively.  The single operand is a vector that
     contains 'N' elements of the same integral or floating point type.
     The result is a vector that contains half as many elements, of an
     integral or floating point type whose size is twice as wide.  In
     the case of 'VEC_UNPACK_HI_EXPR' the high 'N/2' elements of the
     vector are extracted and widened (promoted).  In the case of
     'VEC_UNPACK_LO_EXPR' the low 'N/2' elements of the vector are
     extracted and widened (promoted).

'VEC_UNPACK_FLOAT_HI_EXPR'
'VEC_UNPACK_FLOAT_LO_EXPR'
     These nodes represent unpacking of the high and low parts of the
     input vector, where the values are converted from fixed point to
     floating point.  The single operand is a vector that contains 'N'
     elements of the same integral type.  The result is a vector that
     contains half as many elements of a floating point type whose size
     is twice as wide.  In the case of 'VEC_UNPACK_HI_EXPR' the high
     'N/2' elements of the vector are extracted, converted and widened.
     In the case of 'VEC_UNPACK_LO_EXPR' the low 'N/2' elements of the
     vector are extracted, converted and widened.

'VEC_PACK_TRUNC_EXPR'
     This node represents packing of truncated elements of the two input
     vectors into the output vector.  Input operands are vectors that
     contain the same number of elements of the same integral or
     floating point type.  The result is a vector that contains twice as
     many elements of an integral or floating point type whose size is
     half as wide.  The elements of the two vectors are demoted and
     merged (concatenated) to form the output vector.

'VEC_PACK_SAT_EXPR'
     This node represents packing of elements of the two input vectors
     into the output vector using saturation.  Input operands are
     vectors that contain the same number of elements of the same
     integral type.  The result is a vector that contains twice as many
     elements of an integral type whose size is half as wide.  The
     elements of the two vectors are demoted and merged (concatenated)
     to form the output vector.

'VEC_PACK_FIX_TRUNC_EXPR'
     This node represents packing of elements of the two input vectors
     into the output vector, where the values are converted from
     floating point to fixed point.  Input operands are vectors that
     contain the same number of elements of a floating point type.  The
     result is a vector that contains twice as many elements of an
     integral type whose size is half as wide.  The elements of the two
     vectors are merged (concatenated) to form the output vector.

'VEC_COND_EXPR'
     These nodes represent '?:' expressions.  The three operands must be
     vectors of the same size and number of elements.  The second and
     third operands must have the same type as the entire expression.
     The first operand is of signed integral vector type.  If an element
     of the first operand evaluates to a zero value, the corresponding
     element of the result is taken from the third operand.  If it
     evaluates to a minus one value, it is taken from the second
     operand.  It should never evaluate to any other value currently,
     but optimizations should not rely on that property.  In contrast
     with a 'COND_EXPR', all operands are always evaluated.


File: gccint.info,  Node: Statements,  Next: Functions,  Prev: Expression trees,  Up: GENERIC

11.7 Statements
===============

Most statements in GIMPLE are assignment statements, represented by
'GIMPLE_ASSIGN'.  No other C expressions can appear at statement level;
a reference to a volatile object is converted into a 'GIMPLE_ASSIGN'.

 There are also several varieties of complex statements.

* Menu:

* Basic Statements::
* Blocks::
* Statement Sequences::
* Empty Statements::
* Jumps::
* Cleanups::
* OpenMP::


File: gccint.info,  Node: Basic Statements,  Next: Blocks,  Up: Statements

11.7.1 Basic Statements
-----------------------

'ASM_EXPR'

     Used to represent an inline assembly statement.  For an inline
     assembly statement like:
          asm ("mov x, y");
     The 'ASM_STRING' macro will return a 'STRING_CST' node for '"mov x,
     y"'.  If the original statement made use of the extended-assembly
     syntax, then 'ASM_OUTPUTS', 'ASM_INPUTS', and 'ASM_CLOBBERS' will
     be the outputs, inputs, and clobbers for the statement, represented
     as 'STRING_CST' nodes.  The extended-assembly syntax looks like:
          asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
     The first string is the 'ASM_STRING', containing the instruction
     template.  The next two strings are the output and inputs,
     respectively; this statement has no clobbers.  As this example
     indicates, "plain" assembly statements are merely a special case of
     extended assembly statements; they have no cv-qualifiers, outputs,
     inputs, or clobbers.  All of the strings will be 'NUL'-terminated,
     and will contain no embedded 'NUL'-characters.

     If the assembly statement is declared 'volatile', or if the
     statement was not an extended assembly statement, and is therefore
     implicitly volatile, then the predicate 'ASM_VOLATILE_P' will hold
     of the 'ASM_EXPR'.

'DECL_EXPR'

     Used to represent a local declaration.  The 'DECL_EXPR_DECL' macro
     can be used to obtain the entity declared.  This declaration may be
     a 'LABEL_DECL', indicating that the label declared is a local
     label.  (As an extension, GCC allows the declaration of labels with
     scope.)  In C, this declaration may be a 'FUNCTION_DECL',
     indicating the use of the GCC nested function extension.  For more
     information, *note Functions::.

'LABEL_EXPR'

     Used to represent a label.  The 'LABEL_DECL' declared by this
     statement can be obtained with the 'LABEL_EXPR_LABEL' macro.  The
     'IDENTIFIER_NODE' giving the name of the label can be obtained from
     the 'LABEL_DECL' with 'DECL_NAME'.

'GOTO_EXPR'

     Used to represent a 'goto' statement.  The 'GOTO_DESTINATION' will
     usually be a 'LABEL_DECL'.  However, if the "computed goto"
     extension has been used, the 'GOTO_DESTINATION' will be an
     arbitrary expression indicating the destination.  This expression
     will always have pointer type.

'RETURN_EXPR'

     Used to represent a 'return' statement.  Operand 0 represents the
     value to return.  It should either be the 'RESULT_DECL' for the
     containing function, or a 'MODIFY_EXPR' or 'INIT_EXPR' setting the
     function's 'RESULT_DECL'.  It will be 'NULL_TREE' if the statement
     was just
          return;

'LOOP_EXPR'
     These nodes represent "infinite" loops.  The 'LOOP_EXPR_BODY'
     represents the body of the loop.  It should be executed forever,
     unless an 'EXIT_EXPR' is encountered.

'EXIT_EXPR'
     These nodes represent conditional exits from the nearest enclosing
     'LOOP_EXPR'.  The single operand is the condition; if it is
     nonzero, then the loop should be exited.  An 'EXIT_EXPR' will only
     appear within a 'LOOP_EXPR'.

'SWITCH_STMT'

     Used to represent a 'switch' statement.  The 'SWITCH_STMT_COND' is
     the expression on which the switch is occurring.  See the
     documentation for an 'IF_STMT' for more information on the
     representation used for the condition.  The 'SWITCH_STMT_BODY' is
     the body of the switch statement.  The 'SWITCH_STMT_TYPE' is the
     original type of switch expression as given in the source, before
     any compiler conversions.

'CASE_LABEL_EXPR'

     Use to represent a 'case' label, range of 'case' labels, or a
     'default' label.  If 'CASE_LOW' is 'NULL_TREE', then this is a
     'default' label.  Otherwise, if 'CASE_HIGH' is 'NULL_TREE', then
     this is an ordinary 'case' label.  In this case, 'CASE_LOW' is an
     expression giving the value of the label.  Both 'CASE_LOW' and
     'CASE_HIGH' are 'INTEGER_CST' nodes.  These values will have the
     same type as the condition expression in the switch statement.

     Otherwise, if both 'CASE_LOW' and 'CASE_HIGH' are defined, the
     statement is a range of case labels.  Such statements originate
     with the extension that allows users to write things of the form:
          case 2 ... 5:
     The first value will be 'CASE_LOW', while the second will be
     'CASE_HIGH'.


File: gccint.info,  Node: Blocks,  Next: Statement Sequences,  Prev: Basic Statements,  Up: Statements

11.7.2 Blocks
-------------

Block scopes and the variables they declare in GENERIC are expressed
using the 'BIND_EXPR' code, which in previous versions of GCC was
primarily used for the C statement-expression extension.

 Variables in a block are collected into 'BIND_EXPR_VARS' in declaration
order through their 'TREE_CHAIN' field.  Any runtime initialization is
moved out of 'DECL_INITIAL' and into a statement in the controlled
block.  When gimplifying from C or C++, this initialization replaces the
'DECL_STMT'.  These variables will never require cleanups.  The scope of
these variables is just the body

 Variable-length arrays (VLAs) complicate this process, as their size
often refers to variables initialized earlier in the block.  To handle
this, we currently split the block at that point, and move the VLA into
a new, inner 'BIND_EXPR'.  This strategy may change in the future.

 A C++ program will usually contain more 'BIND_EXPR's than there are
syntactic blocks in the source code, since several C++ constructs have
implicit scopes associated with them.  On the other hand, although the
C++ front end uses pseudo-scopes to handle cleanups for objects with
destructors, these don't translate into the GIMPLE form; multiple
declarations at the same level use the same 'BIND_EXPR'.


File: gccint.info,  Node: Statement Sequences,  Next: Empty Statements,  Prev: Blocks,  Up: Statements

11.7.3 Statement Sequences
--------------------------

Multiple statements at the same nesting level are collected into a
'STATEMENT_LIST'.  Statement lists are modified and traversed using the
interface in 'tree-iterator.h'.


File: gccint.info,  Node: Empty Statements,  Next: Jumps,  Prev: Statement Sequences,  Up: Statements

11.7.4 Empty Statements
-----------------------

Whenever possible, statements with no effect are discarded.  But if they
are nested within another construct which cannot be discarded for some
reason, they are instead replaced with an empty statement, generated by
'build_empty_stmt'.  Initially, all empty statements were shared, after
the pattern of the Java front end, but this caused a lot of trouble in
practice.

 An empty statement is represented as '(void)0'.


File: gccint.info,  Node: Jumps,  Next: Cleanups,  Prev: Empty Statements,  Up: Statements

11.7.5 Jumps
------------

Other jumps are expressed by either 'GOTO_EXPR' or 'RETURN_EXPR'.

 The operand of a 'GOTO_EXPR' must be either a label or a variable
containing the address to jump to.

 The operand of a 'RETURN_EXPR' is either 'NULL_TREE', 'RESULT_DECL', or
a 'MODIFY_EXPR' which sets the return value.  It would be nice to move
the 'MODIFY_EXPR' into a separate statement, but the special return
semantics in 'expand_return' make that difficult.  It may still happen
in the future, perhaps by moving most of that logic into
'expand_assignment'.


File: gccint.info,  Node: Cleanups,  Next: OpenMP,  Prev: Jumps,  Up: Statements

11.7.6 Cleanups
---------------

Destructors for local C++ objects and similar dynamic cleanups are
represented in GIMPLE by a 'TRY_FINALLY_EXPR'.  'TRY_FINALLY_EXPR' has
two operands, both of which are a sequence of statements to execute.
The first sequence is executed.  When it completes the second sequence
is executed.

 The first sequence may complete in the following ways:

  1. Execute the last statement in the sequence and fall off the end.

  2. Execute a goto statement ('GOTO_EXPR') to an ordinary label outside
     the sequence.

  3. Execute a return statement ('RETURN_EXPR').

  4. Throw an exception.  This is currently not explicitly represented
     in GIMPLE.

 The second sequence is not executed if the first sequence completes by
calling 'setjmp' or 'exit' or any other function that does not return.
The second sequence is also not executed if the first sequence completes
via a non-local goto or a computed goto (in general the compiler does
not know whether such a goto statement exits the first sequence or not,
so we assume that it doesn't).

 After the second sequence is executed, if it completes normally by
falling off the end, execution continues wherever the first sequence
would have continued, by falling off the end, or doing a goto, etc.

 'TRY_FINALLY_EXPR' complicates the flow graph, since the cleanup needs
to appear on every edge out of the controlled block; this reduces the
freedom to move code across these edges.  Therefore, the EH lowering
pass which runs before most of the optimization passes eliminates these
expressions by explicitly adding the cleanup to each edge.  Rethrowing
the exception is represented using 'RESX_EXPR'.


File: gccint.info,  Node: OpenMP,  Prev: Cleanups,  Up: Statements

11.7.7 OpenMP
-------------

All the statements starting with 'OMP_' represent directives and clauses
used by the OpenMP API <http://www.openmp.org/>.

'OMP_PARALLEL'

     Represents '#pragma omp parallel [clause1 ... clauseN]'.  It has
     four operands:

     Operand 'OMP_PARALLEL_BODY' is valid while in GENERIC and High
     GIMPLE forms.  It contains the body of code to be executed by all
     the threads.  During GIMPLE lowering, this operand becomes 'NULL'
     and the body is emitted linearly after 'OMP_PARALLEL'.

     Operand 'OMP_PARALLEL_CLAUSES' is the list of clauses associated
     with the directive.

     Operand 'OMP_PARALLEL_FN' is created by 'pass_lower_omp', it
     contains the 'FUNCTION_DECL' for the function that will contain the
     body of the parallel region.

     Operand 'OMP_PARALLEL_DATA_ARG' is also created by
     'pass_lower_omp'.  If there are shared variables to be communicated
     to the children threads, this operand will contain the 'VAR_DECL'
     that contains all the shared values and variables.

'OMP_FOR'

     Represents '#pragma omp for [clause1 ... clauseN]'.  It has 5
     operands:

     Operand 'OMP_FOR_BODY' contains the loop body.

     Operand 'OMP_FOR_CLAUSES' is the list of clauses associated with
     the directive.

     Operand 'OMP_FOR_INIT' is the loop initialization code of the form
     'VAR = N1'.

     Operand 'OMP_FOR_COND' is the loop conditional expression of the
     form 'VAR {<,>,<=,>=} N2'.

     Operand 'OMP_FOR_INCR' is the loop index increment of the form 'VAR
     {+=,-=} INCR'.

     Operand 'OMP_FOR_PRE_BODY' contains side-effect code from operands
     'OMP_FOR_INIT', 'OMP_FOR_COND' and 'OMP_FOR_INC'.  These
     side-effects are part of the 'OMP_FOR' block but must be evaluated
     before the start of loop body.

     The loop index variable 'VAR' must be a signed integer variable,
     which is implicitly private to each thread.  Bounds 'N1' and 'N2'
     and the increment expression 'INCR' are required to be loop
     invariant integer expressions that are evaluated without any
     synchronization.  The evaluation order, frequency of evaluation and
     side-effects are unspecified by the standard.

'OMP_SECTIONS'

     Represents '#pragma omp sections [clause1 ... clauseN]'.

     Operand 'OMP_SECTIONS_BODY' contains the sections body, which in
     turn contains a set of 'OMP_SECTION' nodes for each of the
     concurrent sections delimited by '#pragma omp section'.

     Operand 'OMP_SECTIONS_CLAUSES' is the list of clauses associated
     with the directive.

'OMP_SECTION'

     Section delimiter for 'OMP_SECTIONS'.

'OMP_SINGLE'

     Represents '#pragma omp single'.

     Operand 'OMP_SINGLE_BODY' contains the body of code to be executed
     by a single thread.

     Operand 'OMP_SINGLE_CLAUSES' is the list of clauses associated with
     the directive.

'OMP_MASTER'

     Represents '#pragma omp master'.

     Operand 'OMP_MASTER_BODY' contains the body of code to be executed
     by the master thread.

'OMP_ORDERED'

     Represents '#pragma omp ordered'.

     Operand 'OMP_ORDERED_BODY' contains the body of code to be executed
     in the sequential order dictated by the loop index variable.

'OMP_CRITICAL'

     Represents '#pragma omp critical [name]'.

     Operand 'OMP_CRITICAL_BODY' is the critical section.

     Operand 'OMP_CRITICAL_NAME' is an optional identifier to label the
     critical section.

'OMP_RETURN'

     This does not represent any OpenMP directive, it is an artificial
     marker to indicate the end of the body of an OpenMP.  It is used by
     the flow graph ('tree-cfg.c') and OpenMP region building code
     ('omp-low.c').

'OMP_CONTINUE'

     Similarly, this instruction does not represent an OpenMP directive,
     it is used by 'OMP_FOR' and 'OMP_SECTIONS' to mark the place where
     the code needs to loop to the next iteration (in the case of
     'OMP_FOR') or the next section (in the case of 'OMP_SECTIONS').

     In some cases, 'OMP_CONTINUE' is placed right before 'OMP_RETURN'.
     But if there are cleanups that need to occur right after the
     looping body, it will be emitted between 'OMP_CONTINUE' and
     'OMP_RETURN'.

'OMP_ATOMIC'

     Represents '#pragma omp atomic'.

     Operand 0 is the address at which the atomic operation is to be
     performed.

     Operand 1 is the expression to evaluate.  The gimplifier tries
     three alternative code generation strategies.  Whenever possible,
     an atomic update built-in is used.  If that fails, a
     compare-and-swap loop is attempted.  If that also fails, a regular
     critical section around the expression is used.

'OMP_CLAUSE'

     Represents clauses associated with one of the 'OMP_' directives.
     Clauses are represented by separate sub-codes defined in 'tree.h'.
     Clauses codes can be one of: 'OMP_CLAUSE_PRIVATE',
     'OMP_CLAUSE_SHARED', 'OMP_CLAUSE_FIRSTPRIVATE',
     'OMP_CLAUSE_LASTPRIVATE', 'OMP_CLAUSE_COPYIN',
     'OMP_CLAUSE_COPYPRIVATE', 'OMP_CLAUSE_IF',
     'OMP_CLAUSE_NUM_THREADS', 'OMP_CLAUSE_SCHEDULE',
     'OMP_CLAUSE_NOWAIT', 'OMP_CLAUSE_ORDERED', 'OMP_CLAUSE_DEFAULT',
     'OMP_CLAUSE_REDUCTION', 'OMP_CLAUSE_COLLAPSE', 'OMP_CLAUSE_UNTIED',
     'OMP_CLAUSE_FINAL', and 'OMP_CLAUSE_MERGEABLE'.  Each code
     represents the corresponding OpenMP clause.

     Clauses associated with the same directive are chained together via
     'OMP_CLAUSE_CHAIN'.  Those clauses that accept a list of variables
     are restricted to exactly one, accessed with 'OMP_CLAUSE_VAR'.
     Therefore, multiple variables under the same clause 'C' need to be
     represented as multiple 'C' clauses chained together.  This
     facilitates adding new clauses during compilation.


File: gccint.info,  Node: Functions,  Next: Language-dependent trees,  Prev: Statements,  Up: GENERIC

11.8 Functions
==============

A function is represented by a 'FUNCTION_DECL' node.  It stores the
basic pieces of the function such as body, parameters, and return type
as well as information on the surrounding context, visibility, and
linkage.

* Menu:

* Function Basics::     Function names, body, and parameters.
* Function Properties:: Context, linkage, etc.


File: gccint.info,  Node: Function Basics,  Next: Function Properties,  Up: Functions

11.8.1 Function Basics
----------------------

A function has four core parts: the name, the parameters, the result,
and the body.  The following macros and functions access these parts of
a 'FUNCTION_DECL' as well as other basic features:
'DECL_NAME'
     This macro returns the unqualified name of the function, as an
     'IDENTIFIER_NODE'.  For an instantiation of a function template,
     the 'DECL_NAME' is the unqualified name of the template, not
     something like 'f<int>'.  The value of 'DECL_NAME' is undefined
     when used on a constructor, destructor, overloaded operator, or
     type-conversion operator, or any function that is implicitly
     generated by the compiler.  See below for macros that can be used
     to distinguish these cases.

'DECL_ASSEMBLER_NAME'
     This macro returns the mangled name of the function, also an
     'IDENTIFIER_NODE'.  This name does not contain leading underscores
     on systems that prefix all identifiers with underscores.  The
     mangled name is computed in the same way on all platforms; if
     special processing is required to deal with the object file format
     used on a particular platform, it is the responsibility of the back
     end to perform those modifications.  (Of course, the back end
     should not modify 'DECL_ASSEMBLER_NAME' itself.)

     Using 'DECL_ASSEMBLER_NAME' will cause additional memory to be
     allocated (for the mangled name of the entity) so it should be used
     only when emitting assembly code.  It should not be used within the
     optimizers to determine whether or not two declarations are the
     same, even though some of the existing optimizers do use it in that
     way.  These uses will be removed over time.

'DECL_ARGUMENTS'
     This macro returns the 'PARM_DECL' for the first argument to the
     function.  Subsequent 'PARM_DECL' nodes can be obtained by
     following the 'TREE_CHAIN' links.

'DECL_RESULT'
     This macro returns the 'RESULT_DECL' for the function.

'DECL_SAVED_TREE'
     This macro returns the complete body of the function.

'TREE_TYPE'
     This macro returns the 'FUNCTION_TYPE' or 'METHOD_TYPE' for the
     function.

'DECL_INITIAL'
     A function that has a definition in the current translation unit
     will have a non-'NULL' 'DECL_INITIAL'.  However, back ends should
     not make use of the particular value given by 'DECL_INITIAL'.

     It should contain a tree of 'BLOCK' nodes that mirrors the scopes
     that variables are bound in the function.  Each block contains a
     list of decls declared in a basic block, a pointer to a chain of
     blocks at the next lower scope level, then a pointer to the next
     block at the same level and a backpointer to the parent 'BLOCK' or
     'FUNCTION_DECL'.  So given a function as follows:

          void foo()
          {
            int a;
            {
              int b;
            }
            int c;
          }

     you would get the following:

          tree foo = FUNCTION_DECL;
          tree decl_a = VAR_DECL;
          tree decl_b = VAR_DECL;
          tree decl_c = VAR_DECL;
          tree block_a = BLOCK;
          tree block_b = BLOCK;
          tree block_c = BLOCK;
          BLOCK_VARS(block_a) = decl_a;
          BLOCK_SUBBLOCKS(block_a) = block_b;
          BLOCK_CHAIN(block_a) = block_c;
          BLOCK_SUPERCONTEXT(block_a) = foo;
          BLOCK_VARS(block_b) = decl_b;
          BLOCK_SUPERCONTEXT(block_b) = block_a;
          BLOCK_VARS(block_c) = decl_c;
          BLOCK_SUPERCONTEXT(block_c) = foo;
          DECL_INITIAL(foo) = block_a;


File: gccint.info,  Node: Function Properties,  Prev: Function Basics,  Up: Functions

11.8.2 Function Properties
--------------------------

To determine the scope of a function, you can use the 'DECL_CONTEXT'
macro.  This macro will return the class (either a 'RECORD_TYPE' or a
'UNION_TYPE') or namespace (a 'NAMESPACE_DECL') of which the function is
a member.  For a virtual function, this macro returns the class in which
the function was actually defined, not the base class in which the
virtual declaration occurred.

 In C, the 'DECL_CONTEXT' for a function maybe another function.  This
representation indicates that the GNU nested function extension is in
use.  For details on the semantics of nested functions, see the GCC
Manual.  The nested function can refer to local variables in its
containing function.  Such references are not explicitly marked in the
tree structure; back ends must look at the 'DECL_CONTEXT' for the
referenced 'VAR_DECL'.  If the 'DECL_CONTEXT' for the referenced
'VAR_DECL' is not the same as the function currently being processed,
and neither 'DECL_EXTERNAL' nor 'TREE_STATIC' hold, then the reference
is to a local variable in a containing function, and the back end must
take appropriate action.

'DECL_EXTERNAL'
     This predicate holds if the function is undefined.

'TREE_PUBLIC'
     This predicate holds if the function has external linkage.

'TREE_STATIC'
     This predicate holds if the function has been defined.

'TREE_THIS_VOLATILE'
     This predicate holds if the function does not return normally.

'TREE_READONLY'
     This predicate holds if the function can only read its arguments.

'DECL_PURE_P'
     This predicate holds if the function can only read its arguments,
     but may also read global memory.

'DECL_VIRTUAL_P'
     This predicate holds if the function is virtual.

'DECL_ARTIFICIAL'
     This macro holds if the function was implicitly generated by the
     compiler, rather than explicitly declared.  In addition to
     implicitly generated class member functions, this macro holds for
     the special functions created to implement static initialization
     and destruction, to compute run-time type information, and so
     forth.

'DECL_FUNCTION_SPECIFIC_TARGET'
     This macro returns a tree node that holds the target options that
     are to be used to compile this particular function or 'NULL_TREE'
     if the function is to be compiled with the target options specified
     on the command line.

'DECL_FUNCTION_SPECIFIC_OPTIMIZATION'
     This macro returns a tree node that holds the optimization options
     that are to be used to compile this particular function or
     'NULL_TREE' if the function is to be compiled with the optimization
     options specified on the command line.


File: gccint.info,  Node: Language-dependent trees,  Next: C and C++ Trees,  Prev: Functions,  Up: GENERIC

11.9 Language-dependent trees
=============================

Front ends may wish to keep some state associated with various GENERIC
trees while parsing.  To support this, trees provide a set of flags that
may be used by the front end.  They are accessed using
'TREE_LANG_FLAG_n' where 'n' is currently 0 through 6.

 If necessary, a front end can use some language-dependent tree codes in
its GENERIC representation, so long as it provides a hook for converting
them to GIMPLE and doesn't expect them to work with any (hypothetical)
optimizers that run before the conversion to GIMPLE.  The intermediate
representation used while parsing C and C++ looks very little like
GENERIC, but the C and C++ gimplifier hooks are perfectly happy to take
it as input and spit out GIMPLE.


File: gccint.info,  Node: C and C++ Trees,  Next: Java Trees,  Prev: Language-dependent trees,  Up: GENERIC

11.10 C and C++ Trees
=====================

This section documents the internal representation used by GCC to
represent C and C++ source programs.  When presented with a C or C++
source program, GCC parses the program, performs semantic analysis
(including the generation of error messages), and then produces the
internal representation described here.  This representation contains a
complete representation for the entire translation unit provided as
input to the front end.  This representation is then typically processed
by a code-generator in order to produce machine code, but could also be
used in the creation of source browsers, intelligent editors, automatic
documentation generators, interpreters, and any other programs needing
the ability to process C or C++ code.

 This section explains the internal representation.  In particular, it
documents the internal representation for C and C++ source constructs,
and the macros, functions, and variables that can be used to access
these constructs.  The C++ representation is largely a superset of the
representation used in the C front end.  There is only one construct
used in C that does not appear in the C++ front end and that is the GNU
"nested function" extension.  Many of the macros documented here do not
apply in C because the corresponding language constructs do not appear
in C.

 The C and C++ front ends generate a mix of GENERIC trees and ones
specific to C and C++.  These language-specific trees are higher-level
constructs than the ones in GENERIC to make the parser's job easier.
This section describes those trees that aren't part of GENERIC as well
as aspects of GENERIC trees that are treated in a language-specific
manner.

 If you are developing a "back end", be it is a code-generator or some
other tool, that uses this representation, you may occasionally find
that you need to ask questions not easily answered by the functions and
macros available here.  If that situation occurs, it is quite likely
that GCC already supports the functionality you desire, but that the
interface is simply not documented here.  In that case, you should ask
the GCC maintainers (via mail to <gcc@gcc.gnu.org>) about documenting
the functionality you require.  Similarly, if you find yourself writing
functions that do not deal directly with your back end, but instead
might be useful to other people using the GCC front end, you should
submit your patches for inclusion in GCC.

* Menu:

* Types for C++::               Fundamental and aggregate types.
* Namespaces::                  Namespaces.
* Classes::                     Classes.
* Functions for C++::           Overloading and accessors for C++.
* Statements for C++::          Statements specific to C and C++.
* C++ Expressions::    From 'typeid' to 'throw'.


File: gccint.info,  Node: Types for C++,  Next: Namespaces,  Up: C and C++ Trees

11.10.1 Types for C++
---------------------

In C++, an array type is not qualified; rather the type of the array
elements is qualified.  This situation is reflected in the intermediate
representation.  The macros described here will always examine the
qualification of the underlying element type when applied to an array
type.  (If the element type is itself an array, then the recursion
continues until a non-array type is found, and the qualification of this
type is examined.)  So, for example, 'CP_TYPE_CONST_P' will hold of the
type 'const int ()[7]', denoting an array of seven 'int's.

 The following functions and macros deal with cv-qualification of types:
'cp_type_quals'
     This function returns the set of type qualifiers applied to this
     type.  This value is 'TYPE_UNQUALIFIED' if no qualifiers have been
     applied.  The 'TYPE_QUAL_CONST' bit is set if the type is
     'const'-qualified.  The 'TYPE_QUAL_VOLATILE' bit is set if the type
     is 'volatile'-qualified.  The 'TYPE_QUAL_RESTRICT' bit is set if
     the type is 'restrict'-qualified.

'CP_TYPE_CONST_P'
     This macro holds if the type is 'const'-qualified.

'CP_TYPE_VOLATILE_P'
     This macro holds if the type is 'volatile'-qualified.

'CP_TYPE_RESTRICT_P'
     This macro holds if the type is 'restrict'-qualified.

'CP_TYPE_CONST_NON_VOLATILE_P'
     This predicate holds for a type that is 'const'-qualified, but
     _not_ 'volatile'-qualified; other cv-qualifiers are ignored as
     well: only the 'const'-ness is tested.

 A few other macros and functions are usable with all types:
'TYPE_SIZE'
     The number of bits required to represent the type, represented as
     an 'INTEGER_CST'.  For an incomplete type, 'TYPE_SIZE' will be
     'NULL_TREE'.

'TYPE_ALIGN'
     The alignment of the type, in bits, represented as an 'int'.

'TYPE_NAME'
     This macro returns a declaration (in the form of a 'TYPE_DECL') for
     the type.  (Note this macro does _not_ return an 'IDENTIFIER_NODE',
     as you might expect, given its name!)  You can look at the
     'DECL_NAME' of the 'TYPE_DECL' to obtain the actual name of the
     type.  The 'TYPE_NAME' will be 'NULL_TREE' for a type that is not a
     built-in type, the result of a typedef, or a named class type.

'CP_INTEGRAL_TYPE'
     This predicate holds if the type is an integral type.  Notice that
     in C++, enumerations are _not_ integral types.

'ARITHMETIC_TYPE_P'
     This predicate holds if the type is an integral type (in the C++
     sense) or a floating point type.

'CLASS_TYPE_P'
     This predicate holds for a class-type.

'TYPE_BUILT_IN'
     This predicate holds for a built-in type.

'TYPE_PTRDATAMEM_P'
     This predicate holds if the type is a pointer to data member.

'TYPE_PTR_P'
     This predicate holds if the type is a pointer type, and the pointee
     is not a data member.

'TYPE_PTRFN_P'
     This predicate holds for a pointer to function type.

'TYPE_PTROB_P'
     This predicate holds for a pointer to object type.  Note however
     that it does not hold for the generic pointer to object type 'void
     *'.  You may use 'TYPE_PTROBV_P' to test for a pointer to object
     type as well as 'void *'.

 The table below describes types specific to C and C++ as well as
language-dependent info about GENERIC types.

'POINTER_TYPE'
     Used to represent pointer types, and pointer to data member types.
     If 'TREE_TYPE' is a pointer to data member type, then
     'TYPE_PTRDATAMEM_P' will hold.  For a pointer to data member type
     of the form 'T X::*', 'TYPE_PTRMEM_CLASS_TYPE' will be the type
     'X', while 'TYPE_PTRMEM_POINTED_TO_TYPE' will be the type 'T'.

'RECORD_TYPE'
     Used to represent 'struct' and 'class' types in C and C++.  If
     'TYPE_PTRMEMFUNC_P' holds, then this type is a pointer-to-member
     type.  In that case, the 'TYPE_PTRMEMFUNC_FN_TYPE' is a
     'POINTER_TYPE' pointing to a 'METHOD_TYPE'.  The 'METHOD_TYPE' is
     the type of a function pointed to by the pointer-to-member
     function.  If 'TYPE_PTRMEMFUNC_P' does not hold, this type is a
     class type.  For more information, *note Classes::.

'UNKNOWN_TYPE'
     This node is used to represent a type the knowledge of which is
     insufficient for a sound processing.

'TYPENAME_TYPE'
     Used to represent a construct of the form 'typename T::A'.  The
     'TYPE_CONTEXT' is 'T'; the 'TYPE_NAME' is an 'IDENTIFIER_NODE' for
     'A'.  If the type is specified via a template-id, then
     'TYPENAME_TYPE_FULLNAME' yields a 'TEMPLATE_ID_EXPR'.  The
     'TREE_TYPE' is non-'NULL' if the node is implicitly generated in
     support for the implicit typename extension; in which case the
     'TREE_TYPE' is a type node for the base-class.

'TYPEOF_TYPE'
     Used to represent the '__typeof__' extension.  The 'TYPE_FIELDS' is
     the expression the type of which is being represented.


File: gccint.info,  Node: Namespaces,  Next: Classes,  Prev: Types for C++,  Up: C and C++ Trees

11.10.2 Namespaces
------------------

The root of the entire intermediate representation is the variable
'global_namespace'.  This is the namespace specified with '::' in C++
source code.  All other namespaces, types, variables, functions, and so
forth can be found starting with this namespace.

 However, except for the fact that it is distinguished as the root of
the representation, the global namespace is no different from any other
namespace.  Thus, in what follows, we describe namespaces generally,
rather than the global namespace in particular.

 A namespace is represented by a 'NAMESPACE_DECL' node.

 The following macros and functions can be used on a 'NAMESPACE_DECL':

'DECL_NAME'
     This macro is used to obtain the 'IDENTIFIER_NODE' corresponding to
     the unqualified name of the name of the namespace (*note
     Identifiers::).  The name of the global namespace is '::', even
     though in C++ the global namespace is unnamed.  However, you should
     use comparison with 'global_namespace', rather than 'DECL_NAME' to
     determine whether or not a namespace is the global one.  An unnamed
     namespace will have a 'DECL_NAME' equal to
     'anonymous_namespace_name'.  Within a single translation unit, all
     unnamed namespaces will have the same name.

'DECL_CONTEXT'
     This macro returns the enclosing namespace.  The 'DECL_CONTEXT' for
     the 'global_namespace' is 'NULL_TREE'.

'DECL_NAMESPACE_ALIAS'
     If this declaration is for a namespace alias, then
     'DECL_NAMESPACE_ALIAS' is the namespace for which this one is an
     alias.

     Do not attempt to use 'cp_namespace_decls' for a namespace which is
     an alias.  Instead, follow 'DECL_NAMESPACE_ALIAS' links until you
     reach an ordinary, non-alias, namespace, and call
     'cp_namespace_decls' there.

'DECL_NAMESPACE_STD_P'
     This predicate holds if the namespace is the special '::std'
     namespace.

'cp_namespace_decls'
     This function will return the declarations contained in the
     namespace, including types, overloaded functions, other namespaces,
     and so forth.  If there are no declarations, this function will
     return 'NULL_TREE'.  The declarations are connected through their
     'TREE_CHAIN' fields.

     Although most entries on this list will be declarations,
     'TREE_LIST' nodes may also appear.  In this case, the 'TREE_VALUE'
     will be an 'OVERLOAD'.  The value of the 'TREE_PURPOSE' is
     unspecified; back ends should ignore this value.  As with the other
     kinds of declarations returned by 'cp_namespace_decls', the
     'TREE_CHAIN' will point to the next declaration in this list.

     For more information on the kinds of declarations that can occur on
     this list, *Note Declarations::.  Some declarations will not appear
     on this list.  In particular, no 'FIELD_DECL', 'LABEL_DECL', or
     'PARM_DECL' nodes will appear here.

     This function cannot be used with namespaces that have
     'DECL_NAMESPACE_ALIAS' set.


File: gccint.info,  Node: Classes,  Next: Functions for C++,  Prev: Namespaces,  Up: C and C++ Trees

11.10.3 Classes
---------------

Besides namespaces, the other high-level scoping construct in C++ is the
class.  (Throughout this manual the term "class" is used to mean the
types referred to in the ANSI/ISO C++ Standard as classes; these include
types defined with the 'class', 'struct', and 'union' keywords.)

 A class type is represented by either a 'RECORD_TYPE' or a
'UNION_TYPE'.  A class declared with the 'union' tag is represented by a
'UNION_TYPE', while classes declared with either the 'struct' or the
'class' tag are represented by 'RECORD_TYPE's.  You can use the
'CLASSTYPE_DECLARED_CLASS' macro to discern whether or not a particular
type is a 'class' as opposed to a 'struct'.  This macro will be true
only for classes declared with the 'class' tag.

 Almost all non-function members are available on the 'TYPE_FIELDS'
list.  Given one member, the next can be found by following the
'TREE_CHAIN'.  You should not depend in any way on the order in which
fields appear on this list.  All nodes on this list will be 'DECL'
nodes.  A 'FIELD_DECL' is used to represent a non-static data member, a
'VAR_DECL' is used to represent a static data member, and a 'TYPE_DECL'
is used to represent a type.  Note that the 'CONST_DECL' for an
enumeration constant will appear on this list, if the enumeration type
was declared in the class.  (Of course, the 'TYPE_DECL' for the
enumeration type will appear here as well.)  There are no entries for
base classes on this list.  In particular, there is no 'FIELD_DECL' for
the "base-class portion" of an object.

 The 'TYPE_VFIELD' is a compiler-generated field used to point to
virtual function tables.  It may or may not appear on the 'TYPE_FIELDS'
list.  However, back ends should handle the 'TYPE_VFIELD' just like all
the entries on the 'TYPE_FIELDS' list.

 The function members are available on the 'TYPE_METHODS' list.  Again,
subsequent members are found by following the 'TREE_CHAIN' field.  If a
function is overloaded, each of the overloaded functions appears; no
'OVERLOAD' nodes appear on the 'TYPE_METHODS' list.  Implicitly declared
functions (including default constructors, copy constructors, assignment
operators, and destructors) will appear on this list as well.

 Every class has an associated "binfo", which can be obtained with
'TYPE_BINFO'.  Binfos are used to represent base-classes.  The binfo
given by 'TYPE_BINFO' is the degenerate case, whereby every class is
considered to be its own base-class.  The base binfos for a particular
binfo are held in a vector, whose length is obtained with
'BINFO_N_BASE_BINFOS'.  The base binfos themselves are obtained with
'BINFO_BASE_BINFO' and 'BINFO_BASE_ITERATE'.  To add a new binfo, use
'BINFO_BASE_APPEND'.  The vector of base binfos can be obtained with
'BINFO_BASE_BINFOS', but normally you do not need to use that.  The
class type associated with a binfo is given by 'BINFO_TYPE'.  It is not
always the case that 'BINFO_TYPE (TYPE_BINFO (x))', because of typedefs
and qualified types.  Neither is it the case that 'TYPE_BINFO
(BINFO_TYPE (y))' is the same binfo as 'y'.  The reason is that if 'y'
is a binfo representing a base-class 'B' of a derived class 'D', then
'BINFO_TYPE (y)' will be 'B', and 'TYPE_BINFO (BINFO_TYPE (y))' will be
'B' as its own base-class, rather than as a base-class of 'D'.

 The access to a base type can be found with 'BINFO_BASE_ACCESS'.  This
will produce 'access_public_node', 'access_private_node' or
'access_protected_node'.  If bases are always public,
'BINFO_BASE_ACCESSES' may be 'NULL'.

 'BINFO_VIRTUAL_P' is used to specify whether the binfo is inherited
virtually or not.  The other flags, 'BINFO_MARKED_P' and 'BINFO_FLAG_1'
to 'BINFO_FLAG_6' can be used for language specific use.

 The following macros can be used on a tree node representing a
class-type.

'LOCAL_CLASS_P'
     This predicate holds if the class is local class _i.e._ declared
     inside a function body.

'TYPE_POLYMORPHIC_P'
     This predicate holds if the class has at least one virtual function
     (declared or inherited).

'TYPE_HAS_DEFAULT_CONSTRUCTOR'
     This predicate holds whenever its argument represents a class-type
     with default constructor.

'CLASSTYPE_HAS_MUTABLE'
'TYPE_HAS_MUTABLE_P'
     These predicates hold for a class-type having a mutable data
     member.

'CLASSTYPE_NON_POD_P'
     This predicate holds only for class-types that are not PODs.

'TYPE_HAS_NEW_OPERATOR'
     This predicate holds for a class-type that defines 'operator new'.

'TYPE_HAS_ARRAY_NEW_OPERATOR'
     This predicate holds for a class-type for which 'operator new[]' is
     defined.

'TYPE_OVERLOADS_CALL_EXPR'
     This predicate holds for class-type for which the function call
     'operator()' is overloaded.

'TYPE_OVERLOADS_ARRAY_REF'
     This predicate holds for a class-type that overloads 'operator[]'

'TYPE_OVERLOADS_ARROW'
     This predicate holds for a class-type for which 'operator->' is
     overloaded.


File: gccint.info,  Node: Functions for C++,  Next: Statements for C++,  Prev: Classes,  Up: C and C++ Trees

11.10.4 Functions for C++
-------------------------

A function is represented by a 'FUNCTION_DECL' node.  A set of
overloaded functions is sometimes represented by an 'OVERLOAD' node.

 An 'OVERLOAD' node is not a declaration, so none of the 'DECL_' macros
should be used on an 'OVERLOAD'.  An 'OVERLOAD' node is similar to a
'TREE_LIST'.  Use 'OVL_CURRENT' to get the function associated with an
'OVERLOAD' node; use 'OVL_NEXT' to get the next 'OVERLOAD' node in the
list of overloaded functions.  The macros 'OVL_CURRENT' and 'OVL_NEXT'
are actually polymorphic; you can use them to work with 'FUNCTION_DECL'
nodes as well as with overloads.  In the case of a 'FUNCTION_DECL',
'OVL_CURRENT' will always return the function itself, and 'OVL_NEXT'
will always be 'NULL_TREE'.

 To determine the scope of a function, you can use the 'DECL_CONTEXT'
macro.  This macro will return the class (either a 'RECORD_TYPE' or a
'UNION_TYPE') or namespace (a 'NAMESPACE_DECL') of which the function is
a member.  For a virtual function, this macro returns the class in which
the function was actually defined, not the base class in which the
virtual declaration occurred.

 If a friend function is defined in a class scope, the
'DECL_FRIEND_CONTEXT' macro can be used to determine the class in which
it was defined.  For example, in
     class C { friend void f() {} };
the 'DECL_CONTEXT' for 'f' will be the 'global_namespace', but the
'DECL_FRIEND_CONTEXT' will be the 'RECORD_TYPE' for 'C'.

 The following macros and functions can be used on a 'FUNCTION_DECL':
'DECL_MAIN_P'
     This predicate holds for a function that is the program entry point
     '::code'.

'DECL_LOCAL_FUNCTION_P'
     This predicate holds if the function was declared at block scope,
     even though it has a global scope.

'DECL_ANTICIPATED'
     This predicate holds if the function is a built-in function but its
     prototype is not yet explicitly declared.

'DECL_EXTERN_C_FUNCTION_P'
     This predicate holds if the function is declared as an ''extern
     "C"'' function.

'DECL_LINKONCE_P'
     This macro holds if multiple copies of this function may be emitted
     in various translation units.  It is the responsibility of the
     linker to merge the various copies.  Template instantiations are
     the most common example of functions for which 'DECL_LINKONCE_P'
     holds; G++ instantiates needed templates in all translation units
     which require them, and then relies on the linker to remove
     duplicate instantiations.

     FIXME: This macro is not yet implemented.

'DECL_FUNCTION_MEMBER_P'
     This macro holds if the function is a member of a class, rather
     than a member of a namespace.

'DECL_STATIC_FUNCTION_P'
     This predicate holds if the function a static member function.

'DECL_NONSTATIC_MEMBER_FUNCTION_P'
     This macro holds for a non-static member function.

'DECL_CONST_MEMFUNC_P'
     This predicate holds for a 'const'-member function.

'DECL_VOLATILE_MEMFUNC_P'
     This predicate holds for a 'volatile'-member function.

'DECL_CONSTRUCTOR_P'
     This macro holds if the function is a constructor.

'DECL_NONCONVERTING_P'
     This predicate holds if the constructor is a non-converting
     constructor.

'DECL_COMPLETE_CONSTRUCTOR_P'
     This predicate holds for a function which is a constructor for an
     object of a complete type.

'DECL_BASE_CONSTRUCTOR_P'
     This predicate holds for a function which is a constructor for a
     base class sub-object.

'DECL_COPY_CONSTRUCTOR_P'
     This predicate holds for a function which is a copy-constructor.

'DECL_DESTRUCTOR_P'
     This macro holds if the function is a destructor.

'DECL_COMPLETE_DESTRUCTOR_P'
     This predicate holds if the function is the destructor for an
     object a complete type.

'DECL_OVERLOADED_OPERATOR_P'
     This macro holds if the function is an overloaded operator.

'DECL_CONV_FN_P'
     This macro holds if the function is a type-conversion operator.

'DECL_GLOBAL_CTOR_P'
     This predicate holds if the function is a file-scope initialization
     function.

'DECL_GLOBAL_DTOR_P'
     This predicate holds if the function is a file-scope finalization
     function.

'DECL_THUNK_P'
     This predicate holds if the function is a thunk.

     These functions represent stub code that adjusts the 'this' pointer
     and then jumps to another function.  When the jumped-to function
     returns, control is transferred directly to the caller, without
     returning to the thunk.  The first parameter to the thunk is always
     the 'this' pointer; the thunk should add 'THUNK_DELTA' to this
     value.  (The 'THUNK_DELTA' is an 'int', not an 'INTEGER_CST'.)

     Then, if 'THUNK_VCALL_OFFSET' (an 'INTEGER_CST') is nonzero the
     adjusted 'this' pointer must be adjusted again.  The complete
     calculation is given by the following pseudo-code:

          this += THUNK_DELTA
          if (THUNK_VCALL_OFFSET)
            this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]

     Finally, the thunk should jump to the location given by
     'DECL_INITIAL'; this will always be an expression for the address
     of a function.

'DECL_NON_THUNK_FUNCTION_P'
     This predicate holds if the function is _not_ a thunk function.

'GLOBAL_INIT_PRIORITY'
     If either 'DECL_GLOBAL_CTOR_P' or 'DECL_GLOBAL_DTOR_P' holds, then
     this gives the initialization priority for the function.  The
     linker will arrange that all functions for which
     'DECL_GLOBAL_CTOR_P' holds are run in increasing order of priority
     before 'main' is called.  When the program exits, all functions for
     which 'DECL_GLOBAL_DTOR_P' holds are run in the reverse order.

'TYPE_RAISES_EXCEPTIONS'
     This macro returns the list of exceptions that a (member-)function
     can raise.  The returned list, if non 'NULL', is comprised of nodes
     whose 'TREE_VALUE' represents a type.

'TYPE_NOTHROW_P'
     This predicate holds when the exception-specification of its
     arguments is of the form ''()''.

'DECL_ARRAY_DELETE_OPERATOR_P'
     This predicate holds if the function an overloaded 'operator
     delete[]'.


File: gccint.info,  Node: Statements for C++,  Next: C++ Expressions,  Prev: Functions for C++,  Up: C and C++ Trees

11.10.5 Statements for C++
--------------------------

A function that has a definition in the current translation unit will
have a non-'NULL' 'DECL_INITIAL'.  However, back ends should not make
use of the particular value given by 'DECL_INITIAL'.

 The 'DECL_SAVED_TREE' macro will give the complete body of the
function.

11.10.5.1 Statements
....................

There are tree nodes corresponding to all of the source-level statement
constructs, used within the C and C++ frontends.  These are enumerated
here, together with a list of the various macros that can be used to
obtain information about them.  There are a few macros that can be used
with all statements:

'STMT_IS_FULL_EXPR_P'
     In C++, statements normally constitute "full expressions";
     temporaries created during a statement are destroyed when the
     statement is complete.  However, G++ sometimes represents
     expressions by statements; these statements will not have
     'STMT_IS_FULL_EXPR_P' set.  Temporaries created during such
     statements should be destroyed when the innermost enclosing
     statement with 'STMT_IS_FULL_EXPR_P' set is exited.

 Here is the list of the various statement nodes, and the macros used to
access them.  This documentation describes the use of these nodes in
non-template functions (including instantiations of template functions).
In template functions, the same nodes are used, but sometimes in
slightly different ways.

 Many of the statements have substatements.  For example, a 'while' loop
will have a body, which is itself a statement.  If the substatement is
'NULL_TREE', it is considered equivalent to a statement consisting of a
single ';', i.e., an expression statement in which the expression has
been omitted.  A substatement may in fact be a list of statements,
connected via their 'TREE_CHAIN's.  So, you should always process the
statement tree by looping over substatements, like this:
     void process_stmt (stmt)
          tree stmt;
     {
       while (stmt)
         {
           switch (TREE_CODE (stmt))
             {
             case IF_STMT:
               process_stmt (THEN_CLAUSE (stmt));
               /* More processing here.  */
               break;

             ...
             }

           stmt = TREE_CHAIN (stmt);
         }
     }
 In other words, while the 'then' clause of an 'if' statement in C++ can
be only one statement (although that one statement may be a compound
statement), the intermediate representation will sometimes use several
statements chained together.

'BREAK_STMT'

     Used to represent a 'break' statement.  There are no additional
     fields.

'CLEANUP_STMT'

     Used to represent an action that should take place upon exit from
     the enclosing scope.  Typically, these actions are calls to
     destructors for local objects, but back ends cannot rely on this
     fact.  If these nodes are in fact representing such destructors,
     'CLEANUP_DECL' will be the 'VAR_DECL' destroyed.  Otherwise,
     'CLEANUP_DECL' will be 'NULL_TREE'.  In any case, the
     'CLEANUP_EXPR' is the expression to execute.  The cleanups executed
     on exit from a scope should be run in the reverse order of the
     order in which the associated 'CLEANUP_STMT's were encountered.

'CONTINUE_STMT'

     Used to represent a 'continue' statement.  There are no additional
     fields.

'CTOR_STMT'

     Used to mark the beginning (if 'CTOR_BEGIN_P' holds) or end (if
     'CTOR_END_P' holds of the main body of a constructor.  See also
     'SUBOBJECT' for more information on how to use these nodes.

'DO_STMT'

     Used to represent a 'do' loop.  The body of the loop is given by
     'DO_BODY' while the termination condition for the loop is given by
     'DO_COND'.  The condition for a 'do'-statement is always an
     expression.

'EMPTY_CLASS_EXPR'

     Used to represent a temporary object of a class with no data whose
     address is never taken.  (All such objects are interchangeable.)
     The 'TREE_TYPE' represents the type of the object.

'EXPR_STMT'

     Used to represent an expression statement.  Use 'EXPR_STMT_EXPR' to
     obtain the expression.

'FOR_STMT'

     Used to represent a 'for' statement.  The 'FOR_INIT_STMT' is the
     initialization statement for the loop.  The 'FOR_COND' is the
     termination condition.  The 'FOR_EXPR' is the expression executed
     right before the 'FOR_COND' on each loop iteration; often, this
     expression increments a counter.  The body of the loop is given by
     'FOR_BODY'.  Note that 'FOR_INIT_STMT' and 'FOR_BODY' return
     statements, while 'FOR_COND' and 'FOR_EXPR' return expressions.

'HANDLER'

     Used to represent a C++ 'catch' block.  The 'HANDLER_TYPE' is the
     type of exception that will be caught by this handler; it is equal
     (by pointer equality) to 'NULL' if this handler is for all types.
     'HANDLER_PARMS' is the 'DECL_STMT' for the catch parameter, and
     'HANDLER_BODY' is the code for the block itself.

'IF_STMT'

     Used to represent an 'if' statement.  The 'IF_COND' is the
     expression.

     If the condition is a 'TREE_LIST', then the 'TREE_PURPOSE' is a
     statement (usually a 'DECL_STMT').  Each time the condition is
     evaluated, the statement should be executed.  Then, the
     'TREE_VALUE' should be used as the conditional expression itself.
     This representation is used to handle C++ code like this:

     C++ distinguishes between this and 'COND_EXPR' for handling
     templates.

          if (int i = 7) ...

     where there is a new local variable (or variables) declared within
     the condition.

     The 'THEN_CLAUSE' represents the statement given by the 'then'
     condition, while the 'ELSE_CLAUSE' represents the statement given
     by the 'else' condition.

'SUBOBJECT'

     In a constructor, these nodes are used to mark the point at which a
     subobject of 'this' is fully constructed.  If, after this point, an
     exception is thrown before a 'CTOR_STMT' with 'CTOR_END_P' set is
     encountered, the 'SUBOBJECT_CLEANUP' must be executed.  The
     cleanups must be executed in the reverse order in which they
     appear.

'SWITCH_STMT'

     Used to represent a 'switch' statement.  The 'SWITCH_STMT_COND' is
     the expression on which the switch is occurring.  See the
     documentation for an 'IF_STMT' for more information on the
     representation used for the condition.  The 'SWITCH_STMT_BODY' is
     the body of the switch statement.  The 'SWITCH_STMT_TYPE' is the
     original type of switch expression as given in the source, before
     any compiler conversions.

'TRY_BLOCK'
     Used to represent a 'try' block.  The body of the try block is
     given by 'TRY_STMTS'.  Each of the catch blocks is a 'HANDLER'
     node.  The first handler is given by 'TRY_HANDLERS'.  Subsequent
     handlers are obtained by following the 'TREE_CHAIN' link from one
     handler to the next.  The body of the handler is given by
     'HANDLER_BODY'.

     If 'CLEANUP_P' holds of the 'TRY_BLOCK', then the 'TRY_HANDLERS'
     will not be a 'HANDLER' node.  Instead, it will be an expression
     that should be executed if an exception is thrown in the try block.
     It must rethrow the exception after executing that code.  And, if
     an exception is thrown while the expression is executing,
     'terminate' must be called.

'USING_STMT'
     Used to represent a 'using' directive.  The namespace is given by
     'USING_STMT_NAMESPACE', which will be a NAMESPACE_DECL.  This node
     is needed inside template functions, to implement using directives
     during instantiation.

'WHILE_STMT'

     Used to represent a 'while' loop.  The 'WHILE_COND' is the
     termination condition for the loop.  See the documentation for an
     'IF_STMT' for more information on the representation used for the
     condition.

     The 'WHILE_BODY' is the body of the loop.


File: gccint.info,  Node: C++ Expressions,  Prev: Statements for C++,  Up: C and C++ Trees

11.10.6 C++ Expressions
-----------------------

This section describes expressions specific to the C and C++ front ends.

'TYPEID_EXPR'

     Used to represent a 'typeid' expression.

'NEW_EXPR'
'VEC_NEW_EXPR'

     Used to represent a call to 'new' and 'new[]' respectively.

'DELETE_EXPR'
'VEC_DELETE_EXPR'

     Used to represent a call to 'delete' and 'delete[]' respectively.

'MEMBER_REF'

     Represents a reference to a member of a class.

'THROW_EXPR'

     Represents an instance of 'throw' in the program.  Operand 0, which
     is the expression to throw, may be 'NULL_TREE'.

'AGGR_INIT_EXPR'
     An 'AGGR_INIT_EXPR' represents the initialization as the return
     value of a function call, or as the result of a constructor.  An
     'AGGR_INIT_EXPR' will only appear as a full-expression, or as the
     second operand of a 'TARGET_EXPR'.  'AGGR_INIT_EXPR's have a
     representation similar to that of 'CALL_EXPR's.  You can use the
     'AGGR_INIT_EXPR_FN' and 'AGGR_INIT_EXPR_ARG' macros to access the
     function to call and the arguments to pass.

     If 'AGGR_INIT_VIA_CTOR_P' holds of the 'AGGR_INIT_EXPR', then the
     initialization is via a constructor call.  The address of the
     'AGGR_INIT_EXPR_SLOT' operand, which is always a 'VAR_DECL', is
     taken, and this value replaces the first argument in the argument
     list.

     In either case, the expression is void.


File: gccint.info,  Node: Java Trees,  Prev: C and C++ Trees,  Up: GENERIC

11.11 Java Trees
================


File: gccint.info,  Node: GIMPLE,  Next: Tree SSA,  Prev: GENERIC,  Up: Top

12 GIMPLE
*********

GIMPLE is a three-address representation derived from GENERIC by
breaking down GENERIC expressions into tuples of no more than 3 operands
(with some exceptions like function calls).  GIMPLE was heavily
influenced by the SIMPLE IL used by the McCAT compiler project at McGill
University, though we have made some different choices.  For one thing,
SIMPLE doesn't support 'goto'.

 Temporaries are introduced to hold intermediate values needed to
compute complex expressions.  Additionally, all the control structures
used in GENERIC are lowered into conditional jumps, lexical scopes are
removed and exception regions are converted into an on the side
exception region tree.

 The compiler pass which converts GENERIC into GIMPLE is referred to as
the 'gimplifier'.  The gimplifier works recursively, generating GIMPLE
tuples out of the original GENERIC expressions.

 One of the early implementation strategies used for the GIMPLE
representation was to use the same internal data structures used by
front ends to represent parse trees.  This simplified implementation
because we could leverage existing functionality and interfaces.
However, GIMPLE is a much more restrictive representation than abstract
syntax trees (AST), therefore it does not require the full structural
complexity provided by the main tree data structure.

 The GENERIC representation of a function is stored in the
'DECL_SAVED_TREE' field of the associated 'FUNCTION_DECL' tree node.  It
is converted to GIMPLE by a call to 'gimplify_function_tree'.

 If a front end wants to include language-specific tree codes in the
tree representation which it provides to the back end, it must provide a
definition of 'LANG_HOOKS_GIMPLIFY_EXPR' which knows how to convert the
front end trees to GIMPLE.  Usually such a hook will involve much of the
same code for expanding front end trees to RTL.  This function can
return fully lowered GIMPLE, or it can return GENERIC trees and let the
main gimplifier lower them the rest of the way; this is often simpler.
GIMPLE that is not fully lowered is known as "High GIMPLE" and consists
of the IL before the pass 'pass_lower_cf'.  High GIMPLE contains some
container statements like lexical scopes (represented by 'GIMPLE_BIND')
and nested expressions (e.g., 'GIMPLE_TRY'), while "Low GIMPLE" exposes
all of the implicit jumps for control and exception expressions directly
in the IL and EH region trees.

 The C and C++ front ends currently convert directly from front end
trees to GIMPLE, and hand that off to the back end rather than first
converting to GENERIC.  Their gimplifier hooks know about all the
'_STMT' nodes and how to convert them to GENERIC forms.  There was some
work done on a genericization pass which would run first, but the
existence of 'STMT_EXPR' meant that in order to convert all of the C
statements into GENERIC equivalents would involve walking the entire
tree anyway, so it was simpler to lower all the way.  This might change
in the future if someone writes an optimization pass which would work
better with higher-level trees, but currently the optimizers all expect
GIMPLE.

 You can request to dump a C-like representation of the GIMPLE form with
the flag '-fdump-tree-gimple'.

* Menu:

* Tuple representation::
* GIMPLE instruction set::
* GIMPLE Exception Handling::
* Temporaries::
* Operands::
* Manipulating GIMPLE statements::
* Tuple specific accessors::
* GIMPLE sequences::
* Sequence iterators::
* Adding a new GIMPLE statement code::
* Statement and operand traversals::


File: gccint.info,  Node: Tuple representation,  Next: GIMPLE instruction set,  Up: GIMPLE

12.1 Tuple representation
=========================

GIMPLE instructions are tuples of variable size divided in two groups: a
header describing the instruction and its locations, and a variable
length body with all the operands.  Tuples are organized into a
hierarchy with 3 main classes of tuples.

12.1.1 'gimple_statement_base' (gsbase)
---------------------------------------

This is the root of the hierarchy, it holds basic information needed by
most GIMPLE statements.  There are some fields that may not be relevant
to every GIMPLE statement, but those were moved into the base structure
to take advantage of holes left by other fields (thus making the
structure more compact).  The structure takes 4 words (32 bytes) on 64
bit hosts:

Field                   Size (bits)
'code'                  8
'subcode'               16
'no_warning'            1
'visited'               1
'nontemporal_move'      1
'plf'                   2
'modified'              1
'has_volatile_ops'      1
'references_memory_p'   1
'uid'                   32
'location'              32
'num_ops'               32
'bb'                    64
'block'                 63
Total size              32 bytes

   * 'code' Main identifier for a GIMPLE instruction.

   * 'subcode' Used to distinguish different variants of the same basic
     instruction or provide flags applicable to a given code.  The
     'subcode' flags field has different uses depending on the code of
     the instruction, but mostly it distinguishes instructions of the
     same family.  The most prominent use of this field is in
     assignments, where subcode indicates the operation done on the RHS
     of the assignment.  For example, a = b + c is encoded as
     'GIMPLE_ASSIGN <PLUS_EXPR, a, b, c>'.

   * 'no_warning' Bitflag to indicate whether a warning has already been
     issued on this statement.

   * 'visited' General purpose "visited" marker.  Set and cleared by
     each pass when needed.

   * 'nontemporal_move' Bitflag used in assignments that represent
     non-temporal moves.  Although this bitflag is only used in
     assignments, it was moved into the base to take advantage of the
     bit holes left by the previous fields.

   * 'plf' Pass Local Flags.  This 2-bit mask can be used as general
     purpose markers by any pass.  Passes are responsible for clearing
     and setting these two flags accordingly.

   * 'modified' Bitflag to indicate whether the statement has been
     modified.  Used mainly by the operand scanner to determine when to
     re-scan a statement for operands.

   * 'has_volatile_ops' Bitflag to indicate whether this statement
     contains operands that have been marked volatile.

   * 'references_memory_p' Bitflag to indicate whether this statement
     contains memory references (i.e., its operands are either global
     variables, or pointer dereferences or anything that must reside in
     memory).

   * 'uid' This is an unsigned integer used by passes that want to
     assign IDs to every statement.  These IDs must be assigned and used
     by each pass.

   * 'location' This is a 'location_t' identifier to specify source code
     location for this statement.  It is inherited from the front end.

   * 'num_ops' Number of operands that this statement has.  This
     specifies the size of the operand vector embedded in the tuple.
     Only used in some tuples, but it is declared in the base tuple to
     take advantage of the 32-bit hole left by the previous fields.

   * 'bb' Basic block holding the instruction.

   * 'block' Lexical block holding this statement.  Also used for debug
     information generation.

12.1.2 'gimple_statement_with_ops'
----------------------------------

This tuple is actually split in two: 'gimple_statement_with_ops_base'
and 'gimple_statement_with_ops'.  This is needed to accommodate the way
the operand vector is allocated.  The operand vector is defined to be an
array of 1 element.  So, to allocate a dynamic number of operands, the
memory allocator ('gimple_alloc') simply allocates enough memory to hold
the structure itself plus 'N - 1' operands which run "off the end" of
the structure.  For example, to allocate space for a tuple with 3
operands, 'gimple_alloc' reserves 'sizeof (struct
gimple_statement_with_ops) + 2 * sizeof (tree)' bytes.

 On the other hand, several fields in this tuple need to be shared with
the 'gimple_statement_with_memory_ops' tuple.  So, these common fields
are placed in 'gimple_statement_with_ops_base' which is then inherited
from the other two tuples.

'gsbase'    256
'def_ops'   64
'use_ops'   64
'op'        'num_ops' * 64
Total       48 + 8 * 'num_ops' bytes
size

   * 'gsbase' Inherited from 'struct gimple_statement_base'.

   * 'def_ops' Array of pointers into the operand array indicating all
     the slots that contain a variable written-to by the statement.
     This array is also used for immediate use chaining.  Note that it
     would be possible to not rely on this array, but the changes
     required to implement this are pretty invasive.

   * 'use_ops' Similar to 'def_ops' but for variables read by the
     statement.

   * 'op' Array of trees with 'num_ops' slots.

12.1.3 'gimple_statement_with_memory_ops'
-----------------------------------------

This tuple is essentially identical to 'gimple_statement_with_ops',
except that it contains 4 additional fields to hold vectors related
memory stores and loads.  Similar to the previous case, the structure is
split in two to accommodate for the operand vector
('gimple_statement_with_memory_ops_base' and
'gimple_statement_with_memory_ops').

Field        Size (bits)
'gsbase'     256
'def_ops'    64
'use_ops'    64
'vdef_ops'   64
'vuse_ops'   64
'stores'     64
'loads'      64
'op'         'num_ops' * 64
Total size   80 + 8 * 'num_ops' bytes

   * 'vdef_ops' Similar to 'def_ops' but for 'VDEF' operators.  There is
     one entry per memory symbol written by this statement.  This is
     used to maintain the memory SSA use-def and def-def chains.

   * 'vuse_ops' Similar to 'use_ops' but for 'VUSE' operators.  There is
     one entry per memory symbol loaded by this statement.  This is used
     to maintain the memory SSA use-def chains.

   * 'stores' Bitset with all the UIDs for the symbols written-to by the
     statement.  This is different than 'vdef_ops' in that all the
     affected symbols are mentioned in this set.  If memory partitioning
     is enabled, the 'vdef_ops' vector will refer to memory partitions.
     Furthermore, no SSA information is stored in this set.

   * 'loads' Similar to 'stores', but for memory loads.  (Note that
     there is some amount of redundancy here, it should be possible to
     reduce memory utilization further by removing these sets).

 All the other tuples are defined in terms of these three basic ones.
Each tuple will add some fields.  The main gimple type is defined to be
the union of all these structures ('GTY' markers elided for clarity):

     union gimple_statement_d
     {
       struct gimple_statement_base gsbase;
       struct gimple_statement_with_ops gsops;
       struct gimple_statement_with_memory_ops gsmem;
       struct gimple_statement_omp omp;
       struct gimple_statement_bind gimple_bind;
       struct gimple_statement_catch gimple_catch;
       struct gimple_statement_eh_filter gimple_eh_filter;
       struct gimple_statement_phi gimple_phi;
       struct gimple_statement_resx gimple_resx;
       struct gimple_statement_try gimple_try;
       struct gimple_statement_wce gimple_wce;
       struct gimple_statement_asm gimple_asm;
       struct gimple_statement_omp_critical gimple_omp_critical;
       struct gimple_statement_omp_for gimple_omp_for;
       struct gimple_statement_omp_parallel gimple_omp_parallel;
       struct gimple_statement_omp_task gimple_omp_task;
       struct gimple_statement_omp_sections gimple_omp_sections;
       struct gimple_statement_omp_single gimple_omp_single;
       struct gimple_statement_omp_continue gimple_omp_continue;
       struct gimple_statement_omp_atomic_load gimple_omp_atomic_load;
       struct gimple_statement_omp_atomic_store gimple_omp_atomic_store;
     };


File: gccint.info,  Node: GIMPLE instruction set,  Next: GIMPLE Exception Handling,  Prev: Tuple representation,  Up: GIMPLE

12.2 GIMPLE instruction set
===========================

The following table briefly describes the GIMPLE instruction set.

Instruction                    High GIMPLE   Low GIMPLE
'GIMPLE_ASM'                   x             x
'GIMPLE_ASSIGN'                x             x
'GIMPLE_BIND'                  x
'GIMPLE_CALL'                  x             x
'GIMPLE_CATCH'                 x
'GIMPLE_COND'                  x             x
'GIMPLE_DEBUG'                 x             x
'GIMPLE_EH_FILTER'             x
'GIMPLE_GOTO'                  x             x
'GIMPLE_LABEL'                 x             x
'GIMPLE_NOP'                   x             x
'GIMPLE_OMP_ATOMIC_LOAD'       x             x
'GIMPLE_OMP_ATOMIC_STORE'      x             x
'GIMPLE_OMP_CONTINUE'          x             x
'GIMPLE_OMP_CRITICAL'          x             x
'GIMPLE_OMP_FOR'               x             x
'GIMPLE_OMP_MASTER'            x             x
'GIMPLE_OMP_ORDERED'           x             x
'GIMPLE_OMP_PARALLEL'          x             x
'GIMPLE_OMP_RETURN'            x             x
'GIMPLE_OMP_SECTION'           x             x
'GIMPLE_OMP_SECTIONS'          x             x
'GIMPLE_OMP_SECTIONS_SWITCH'   x             x
'GIMPLE_OMP_SINGLE'            x             x
'GIMPLE_PHI'                                 x
'GIMPLE_RESX'                                x
'GIMPLE_RETURN'                x             x
'GIMPLE_SWITCH'                x             x
'GIMPLE_TRY'                   x


File: gccint.info,  Node: GIMPLE Exception Handling,  Next: Temporaries,  Prev: GIMPLE instruction set,  Up: GIMPLE

12.3 Exception Handling
=======================

Other exception handling constructs are represented using
'GIMPLE_TRY_CATCH'.  'GIMPLE_TRY_CATCH' has two operands.  The first
operand is a sequence of statements to execute.  If executing these
statements does not throw an exception, then the second operand is
ignored.  Otherwise, if an exception is thrown, then the second operand
of the 'GIMPLE_TRY_CATCH' is checked.  The second operand may have the
following forms:

  1. A sequence of statements to execute.  When an exception occurs,
     these statements are executed, and then the exception is rethrown.

  2. A sequence of 'GIMPLE_CATCH' statements.  Each 'GIMPLE_CATCH' has a
     list of applicable exception types and handler code.  If the thrown
     exception matches one of the caught types, the associated handler
     code is executed.  If the handler code falls off the bottom,
     execution continues after the original 'GIMPLE_TRY_CATCH'.

  3. A 'GIMPLE_EH_FILTER' statement.  This has a list of permitted
     exception types, and code to handle a match failure.  If the thrown
     exception does not match one of the allowed types, the associated
     match failure code is executed.  If the thrown exception does
     match, it continues unwinding the stack looking for the next
     handler.

 Currently throwing an exception is not directly represented in GIMPLE,
since it is implemented by calling a function.  At some point in the
future we will want to add some way to express that the call will throw
an exception of a known type.

 Just before running the optimizers, the compiler lowers the high-level
EH constructs above into a set of 'goto's, magic labels, and EH regions.
Continuing to unwind at the end of a cleanup is represented with a
'GIMPLE_RESX'.


File: gccint.info,  Node: Temporaries,  Next: Operands,  Prev: GIMPLE Exception Handling,  Up: GIMPLE

12.4 Temporaries
================

When gimplification encounters a subexpression that is too complex, it
creates a new temporary variable to hold the value of the subexpression,
and adds a new statement to initialize it before the current statement.
These special temporaries are known as 'expression temporaries', and are
allocated using 'get_formal_tmp_var'.  The compiler tries to always
evaluate identical expressions into the same temporary, to simplify
elimination of redundant calculations.

 We can only use expression temporaries when we know that it will not be
reevaluated before its value is used, and that it will not be otherwise
modified(1).  Other temporaries can be allocated using
'get_initialized_tmp_var' or 'create_tmp_var'.

 Currently, an expression like 'a = b + 5' is not reduced any further.
We tried converting it to something like
     T1 = b + 5;
     a = T1;
 but this bloated the representation for minimal benefit.  However, a
variable which must live in memory cannot appear in an expression; its
value is explicitly loaded into a temporary first.  Similarly, storing
the value of an expression to a memory variable goes through a
temporary.

   ---------- Footnotes ----------

   (1) These restrictions are derived from those in Morgan 4.8.


File: gccint.info,  Node: Operands,  Next: Manipulating GIMPLE statements,  Prev: Temporaries,  Up: GIMPLE

12.5 Operands
=============

In general, expressions in GIMPLE consist of an operation and the
appropriate number of simple operands; these operands must either be a
GIMPLE rvalue ('is_gimple_val'), i.e. a constant or a register variable.
More complex operands are factored out into temporaries, so that
     a = b + c + d
 becomes
     T1 = b + c;
     a = T1 + d;

 The same rule holds for arguments to a 'GIMPLE_CALL'.

 The target of an assignment is usually a variable, but can also be a
'MEM_REF' or a compound lvalue as described below.

* Menu:

* Compound Expressions::
* Compound Lvalues::
* Conditional Expressions::
* Logical Operators::


File: gccint.info,  Node: Compound Expressions,  Next: Compound Lvalues,  Up: Operands

12.5.1 Compound Expressions
---------------------------

The left-hand side of a C comma expression is simply moved into a
separate statement.


File: gccint.info,  Node: Compound Lvalues,  Next: Conditional Expressions,  Prev: Compound Expressions,  Up: Operands

12.5.2 Compound Lvalues
-----------------------

Currently compound lvalues involving array and structure field
references are not broken down; an expression like 'a.b[2] = 42' is not
reduced any further (though complex array subscripts are).  This
restriction is a workaround for limitations in later optimizers; if we
were to convert this to

     T1 = &a.b;
     T1[2] = 42;

 alias analysis would not remember that the reference to 'T1[2]' came by
way of 'a.b', so it would think that the assignment could alias another
member of 'a'; this broke 'struct-alias-1.c'.  Future optimizer
improvements may make this limitation unnecessary.


File: gccint.info,  Node: Conditional Expressions,  Next: Logical Operators,  Prev: Compound Lvalues,  Up: Operands

12.5.3 Conditional Expressions
------------------------------

A C '?:' expression is converted into an 'if' statement with each branch
assigning to the same temporary.  So,

     a = b ? c : d;
 becomes
     if (b == 1)
       T1 = c;
     else
       T1 = d;
     a = T1;

 The GIMPLE level if-conversion pass re-introduces '?:' expression, if
appropriate.  It is used to vectorize loops with conditions using vector
conditional operations.

 Note that in GIMPLE, 'if' statements are represented using
'GIMPLE_COND', as described below.


File: gccint.info,  Node: Logical Operators,  Prev: Conditional Expressions,  Up: Operands

12.5.4 Logical Operators
------------------------

Except when they appear in the condition operand of a 'GIMPLE_COND',
logical 'and' and 'or' operators are simplified as follows: 'a = b && c'
becomes

     T1 = (bool)b;
     if (T1 == true)
       T1 = (bool)c;
     a = T1;

 Note that 'T1' in this example cannot be an expression temporary,
because it has two different assignments.

12.5.5 Manipulating operands
----------------------------

All gimple operands are of type 'tree'.  But only certain types of trees
are allowed to be used as operand tuples.  Basic validation is
controlled by the function 'get_gimple_rhs_class', which given a tree
code, returns an 'enum' with the following values of type 'enum
gimple_rhs_class'

   * 'GIMPLE_INVALID_RHS' The tree cannot be used as a GIMPLE operand.

   * 'GIMPLE_TERNARY_RHS' The tree is a valid GIMPLE ternary operation.

   * 'GIMPLE_BINARY_RHS' The tree is a valid GIMPLE binary operation.

   * 'GIMPLE_UNARY_RHS' The tree is a valid GIMPLE unary operation.

   * 'GIMPLE_SINGLE_RHS' The tree is a single object, that cannot be
     split into simpler operands (for instance, 'SSA_NAME', 'VAR_DECL',
     'COMPONENT_REF', etc).

     This operand class also acts as an escape hatch for tree nodes that
     may be flattened out into the operand vector, but would need more
     than two slots on the RHS. For instance, a 'COND_EXPR' expression
     of the form '(a op b) ? x : y' could be flattened out on the
     operand vector using 4 slots, but it would also require additional
     processing to distinguish 'c = a op b' from 'c = a op b ? x : y'.
     Something similar occurs with 'ASSERT_EXPR'.  In time, these
     special case tree expressions should be flattened into the operand
     vector.

 For tree nodes in the categories 'GIMPLE_TERNARY_RHS',
'GIMPLE_BINARY_RHS' and 'GIMPLE_UNARY_RHS', they cannot be stored inside
tuples directly.  They first need to be flattened and separated into
individual components.  For instance, given the GENERIC expression

     a = b + c

 its tree representation is:

     MODIFY_EXPR <VAR_DECL  <a>, PLUS_EXPR <VAR_DECL <b>, VAR_DECL <c>>>

 In this case, the GIMPLE form for this statement is logically identical
to its GENERIC form but in GIMPLE, the 'PLUS_EXPR' on the RHS of the
assignment is not represented as a tree, instead the two operands are
taken out of the 'PLUS_EXPR' sub-tree and flattened into the GIMPLE
tuple as follows:

     GIMPLE_ASSIGN <PLUS_EXPR, VAR_DECL <a>, VAR_DECL <b>, VAR_DECL <c>>

12.5.6 Operand vector allocation
--------------------------------

The operand vector is stored at the bottom of the three tuple structures
that accept operands.  This means, that depending on the code of a given
statement, its operand vector will be at different offsets from the base
of the structure.  To access tuple operands use the following accessors

 -- GIMPLE function: unsigned gimple_num_ops (gimple g)
     Returns the number of operands in statement G.

 -- GIMPLE function: tree gimple_op (gimple g, unsigned i)
     Returns operand 'I' from statement 'G'.

 -- GIMPLE function: tree * gimple_ops (gimple g)
     Returns a pointer into the operand vector for statement 'G'.  This
     is computed using an internal table called 'gimple_ops_offset_'[].
     This table is indexed by the gimple code of 'G'.

     When the compiler is built, this table is filled-in using the sizes
     of the structures used by each statement code defined in
     gimple.def.  Since the operand vector is at the bottom of the
     structure, for a gimple code 'C' the offset is computed as sizeof
     (struct-of 'C') - sizeof (tree).

     This mechanism adds one memory indirection to every access when
     using 'gimple_op'(), if this becomes a bottleneck, a pass can
     choose to memoize the result from 'gimple_ops'() and use that to
     access the operands.

12.5.7 Operand validation
-------------------------

When adding a new operand to a gimple statement, the operand will be
validated according to what each tuple accepts in its operand vector.
These predicates are called by the 'gimple_NAME_set_...()'.  Each tuple
will use one of the following predicates (Note, this list is not
exhaustive):

 -- GIMPLE function: bool is_gimple_val (tree t)
     Returns true if t is a "GIMPLE value", which are all the
     non-addressable stack variables (variables for which
     'is_gimple_reg' returns true) and constants (expressions for which
     'is_gimple_min_invariant' returns true).

 -- GIMPLE function: bool is_gimple_addressable (tree t)
     Returns true if t is a symbol or memory reference whose address can
     be taken.

 -- GIMPLE function: bool is_gimple_asm_val (tree t)
     Similar to 'is_gimple_val' but it also accepts hard registers.

 -- GIMPLE function: bool is_gimple_call_addr (tree t)
     Return true if t is a valid expression to use as the function
     called by a 'GIMPLE_CALL'.

 -- GIMPLE function: bool is_gimple_mem_ref_addr (tree t)
     Return true if t is a valid expression to use as first operand of a
     'MEM_REF' expression.

 -- GIMPLE function: bool is_gimple_constant (tree t)
     Return true if t is a valid gimple constant.

 -- GIMPLE function: bool is_gimple_min_invariant (tree t)
     Return true if t is a valid minimal invariant.  This is different
     from constants, in that the specific value of t may not be known at
     compile time, but it is known that it doesn't change (e.g., the
     address of a function local variable).

 -- GIMPLE function: bool is_gimple_ip_invariant (tree t)
     Return true if t is an interprocedural invariant.  This means that
     t is a valid invariant in all functions (e.g.  it can be an address
     of a global variable but not of a local one).

 -- GIMPLE function: bool is_gimple_ip_invariant_address (tree t)
     Return true if t is an 'ADDR_EXPR' that does not change once the
     program is running (and which is valid in all functions).

12.5.8 Statement validation
---------------------------

 -- GIMPLE function: bool is_gimple_assign (gimple g)
     Return true if the code of g is 'GIMPLE_ASSIGN'.

 -- GIMPLE function: bool is_gimple_call (gimple g)
     Return true if the code of g is 'GIMPLE_CALL'.

 -- GIMPLE function: bool is_gimple_debug (gimple g)
     Return true if the code of g is 'GIMPLE_DEBUG'.

 -- GIMPLE function: bool gimple_assign_cast_p (gimple g)
     Return true if g is a 'GIMPLE_ASSIGN' that performs a type cast
     operation.

 -- GIMPLE function: bool gimple_debug_bind_p (gimple g)
     Return true if g is a 'GIMPLE_DEBUG' that binds the value of an
     expression to a variable.


File: gccint.info,  Node: Manipulating GIMPLE statements,  Next: Tuple specific accessors,  Prev: Operands,  Up: GIMPLE

12.6 Manipulating GIMPLE statements
===================================

This section documents all the functions available to handle each of the
GIMPLE instructions.

12.6.1 Common accessors
-----------------------

The following are common accessors for gimple statements.

 -- GIMPLE function: enum gimple_code gimple_code (gimple g)
     Return the code for statement 'G'.

 -- GIMPLE function: basic_block gimple_bb (gimple g)
     Return the basic block to which statement 'G' belongs to.

 -- GIMPLE function: tree gimple_block (gimple g)
     Return the lexical scope block holding statement 'G'.

 -- GIMPLE function: tree gimple_expr_type (gimple stmt)
     Return the type of the main expression computed by 'STMT'.  Return
     'void_type_node' if 'STMT' computes nothing.  This will only return
     something meaningful for 'GIMPLE_ASSIGN', 'GIMPLE_COND' and
     'GIMPLE_CALL'.  For all other tuple codes, it will return
     'void_type_node'.

 -- GIMPLE function: enum tree_code gimple_expr_code (gimple stmt)
     Return the tree code for the expression computed by 'STMT'.  This
     is only meaningful for 'GIMPLE_CALL', 'GIMPLE_ASSIGN' and
     'GIMPLE_COND'.  If 'STMT' is 'GIMPLE_CALL', it will return
     'CALL_EXPR'.  For 'GIMPLE_COND', it returns the code of the
     comparison predicate.  For 'GIMPLE_ASSIGN' it returns the code of
     the operation performed by the 'RHS' of the assignment.

 -- GIMPLE function: void gimple_set_block (gimple g, tree block)
     Set the lexical scope block of 'G' to 'BLOCK'.

 -- GIMPLE function: location_t gimple_locus (gimple g)
     Return locus information for statement 'G'.

 -- GIMPLE function: void gimple_set_locus (gimple g, location_t locus)
     Set locus information for statement 'G'.

 -- GIMPLE function: bool gimple_locus_empty_p (gimple g)
     Return true if 'G' does not have locus information.

 -- GIMPLE function: bool gimple_no_warning_p (gimple stmt)
     Return true if no warnings should be emitted for statement 'STMT'.

 -- GIMPLE function: void gimple_set_visited (gimple stmt, bool
          visited_p)
     Set the visited status on statement 'STMT' to 'VISITED_P'.

 -- GIMPLE function: bool gimple_visited_p (gimple stmt)
     Return the visited status on statement 'STMT'.

 -- GIMPLE function: void gimple_set_plf (gimple stmt, enum plf_mask
          plf, bool val_p)
     Set pass local flag 'PLF' on statement 'STMT' to 'VAL_P'.

 -- GIMPLE function: unsigned int gimple_plf (gimple stmt, enum plf_mask
          plf)
     Return the value of pass local flag 'PLF' on statement 'STMT'.

 -- GIMPLE function: bool gimple_has_ops (gimple g)
     Return true if statement 'G' has register or memory operands.

 -- GIMPLE function: bool gimple_has_mem_ops (gimple g)
     Return true if statement 'G' has memory operands.

 -- GIMPLE function: unsigned gimple_num_ops (gimple g)
     Return the number of operands for statement 'G'.

 -- GIMPLE function: tree * gimple_ops (gimple g)
     Return the array of operands for statement 'G'.

 -- GIMPLE function: tree gimple_op (gimple g, unsigned i)
     Return operand 'I' for statement 'G'.

 -- GIMPLE function: tree * gimple_op_ptr (gimple g, unsigned i)
     Return a pointer to operand 'I' for statement 'G'.

 -- GIMPLE function: void gimple_set_op (gimple g, unsigned i, tree op)
     Set operand 'I' of statement 'G' to 'OP'.

 -- GIMPLE function: bitmap gimple_addresses_taken (gimple stmt)
     Return the set of symbols that have had their address taken by
     'STMT'.

 -- GIMPLE function: struct def_optype_d * gimple_def_ops (gimple g)
     Return the set of 'DEF' operands for statement 'G'.

 -- GIMPLE function: void gimple_set_def_ops (gimple g, struct
          def_optype_d *def)
     Set 'DEF' to be the set of 'DEF' operands for statement 'G'.

 -- GIMPLE function: struct use_optype_d * gimple_use_ops (gimple g)
     Return the set of 'USE' operands for statement 'G'.

 -- GIMPLE function: void gimple_set_use_ops (gimple g, struct
          use_optype_d *use)
     Set 'USE' to be the set of 'USE' operands for statement 'G'.

 -- GIMPLE function: struct voptype_d * gimple_vuse_ops (gimple g)
     Return the set of 'VUSE' operands for statement 'G'.

 -- GIMPLE function: void gimple_set_vuse_ops (gimple g, struct
          voptype_d *ops)
     Set 'OPS' to be the set of 'VUSE' operands for statement 'G'.

 -- GIMPLE function: struct voptype_d * gimple_vdef_ops (gimple g)
     Return the set of 'VDEF' operands for statement 'G'.

 -- GIMPLE function: void gimple_set_vdef_ops (gimple g, struct
          voptype_d *ops)
     Set 'OPS' to be the set of 'VDEF' operands for statement 'G'.

 -- GIMPLE function: bitmap gimple_loaded_syms (gimple g)
     Return the set of symbols loaded by statement 'G'.  Each element of
     the set is the 'DECL_UID' of the corresponding symbol.

 -- GIMPLE function: bitmap gimple_stored_syms (gimple g)
     Return the set of symbols stored by statement 'G'.  Each element of
     the set is the 'DECL_UID' of the corresponding symbol.

 -- GIMPLE function: bool gimple_modified_p (gimple g)
     Return true if statement 'G' has operands and the modified field
     has been set.

 -- GIMPLE function: bool gimple_has_volatile_ops (gimple stmt)
     Return true if statement 'STMT' contains volatile operands.

 -- GIMPLE function: void gimple_set_has_volatile_ops (gimple stmt, bool
          volatilep)
     Return true if statement 'STMT' contains volatile operands.

 -- GIMPLE function: void update_stmt (gimple s)
     Mark statement 'S' as modified, and update it.

 -- GIMPLE function: void update_stmt_if_modified (gimple s)
     Update statement 'S' if it has been marked modified.

 -- GIMPLE function: gimple gimple_copy (gimple stmt)
     Return a deep copy of statement 'STMT'.


File: gccint.info,  Node: Tuple specific accessors,  Next: GIMPLE sequences,  Prev: Manipulating GIMPLE statements,  Up: GIMPLE

12.7 Tuple specific accessors
=============================

* Menu:

* 'GIMPLE_ASM'::
* 'GIMPLE_ASSIGN'::
* 'GIMPLE_BIND'::
* 'GIMPLE_CALL'::
* 'GIMPLE_CATCH'::
* 'GIMPLE_COND'::
* 'GIMPLE_DEBUG'::
* 'GIMPLE_EH_FILTER'::
* 'GIMPLE_LABEL'::
* 'GIMPLE_NOP'::
* 'GIMPLE_OMP_ATOMIC_LOAD'::
* 'GIMPLE_OMP_ATOMIC_STORE'::
* 'GIMPLE_OMP_CONTINUE'::
* 'GIMPLE_OMP_CRITICAL'::
* 'GIMPLE_OMP_FOR'::
* 'GIMPLE_OMP_MASTER'::
* 'GIMPLE_OMP_ORDERED'::
* 'GIMPLE_OMP_PARALLEL'::
* 'GIMPLE_OMP_RETURN'::
* 'GIMPLE_OMP_SECTION'::
* 'GIMPLE_OMP_SECTIONS'::
* 'GIMPLE_OMP_SINGLE'::
* 'GIMPLE_PHI'::
* 'GIMPLE_RESX'::
* 'GIMPLE_RETURN'::
* 'GIMPLE_SWITCH'::
* 'GIMPLE_TRY'::
* 'GIMPLE_WITH_CLEANUP_EXPR'::


File: gccint.info,  Node: 'GIMPLE_ASM',  Next: 'GIMPLE_ASSIGN',  Up: Tuple specific accessors

12.7.1 'GIMPLE_ASM'
-------------------

 -- GIMPLE function: gimple gimple_build_asm (const char *string,
          ninputs, noutputs, nclobbers, ...)
     Build a 'GIMPLE_ASM' statement.  This statement is used for
     building in-line assembly constructs.  'STRING' is the assembly
     code.  'NINPUT' is the number of register inputs.  'NOUTPUT' is the
     number of register outputs.  'NCLOBBERS' is the number of clobbered
     registers.  The rest of the arguments trees for each input, output,
     and clobbered registers.

 -- GIMPLE function: gimple gimple_build_asm_vec (const char *,
          VEC(tree,gc) *, VEC(tree,gc) *, VEC(tree,gc) *)
     Identical to gimple_build_asm, but the arguments are passed in
     VECs.

 -- GIMPLE function: unsigned gimple_asm_ninputs (gimple g)
     Return the number of input operands for 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: unsigned gimple_asm_noutputs (gimple g)
     Return the number of output operands for 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: unsigned gimple_asm_nclobbers (gimple g)
     Return the number of clobber operands for 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: tree gimple_asm_input_op (gimple g, unsigned index)
     Return input operand 'INDEX' of 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: void gimple_asm_set_input_op (gimple g, unsigned
          index, tree in_op)
     Set 'IN_OP' to be input operand 'INDEX' in 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: tree gimple_asm_output_op (gimple g, unsigned
          index)
     Return output operand 'INDEX' of 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: void gimple_asm_set_output_op (gimple g, unsigned
          index, tree out_op)
     Set 'OUT_OP' to be output operand 'INDEX' in 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: tree gimple_asm_clobber_op (gimple g, unsigned
          index)
     Return clobber operand 'INDEX' of 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: void gimple_asm_set_clobber_op (gimple g, unsigned
          index, tree clobber_op)
     Set 'CLOBBER_OP' to be clobber operand 'INDEX' in 'GIMPLE_ASM' 'G'.

 -- GIMPLE function: const char * gimple_asm_string (gimple g)
     Return the string representing the assembly instruction in
     'GIMPLE_ASM' 'G'.

 -- GIMPLE function: bool gimple_asm_volatile_p (gimple g)
     Return true if 'G' is an asm statement marked volatile.

 -- GIMPLE function: void gimple_asm_set_volatile (gimple g)
     Mark asm statement 'G' as volatile.

 -- GIMPLE function: void gimple_asm_clear_volatile (gimple g)
     Remove volatile marker from asm statement 'G'.


File: gccint.info,  Node: 'GIMPLE_ASSIGN',  Next: 'GIMPLE_BIND',  Prev: 'GIMPLE_ASM',  Up: Tuple specific accessors

12.7.2 'GIMPLE_ASSIGN'
----------------------

 -- GIMPLE function: gimple gimple_build_assign (tree lhs, tree rhs)
     Build a 'GIMPLE_ASSIGN' statement.  The left-hand side is an lvalue
     passed in lhs.  The right-hand side can be either a unary or binary
     tree expression.  The expression tree rhs will be flattened and its
     operands assigned to the corresponding operand slots in the new
     statement.  This function is useful when you already have a tree
     expression that you want to convert into a tuple.  However, try to
     avoid building expression trees for the sole purpose of calling
     this function.  If you already have the operands in separate trees,
     it is better to use 'gimple_build_assign_with_ops'.

 -- GIMPLE function: gimple gimplify_assign (tree dst, tree src,
          gimple_seq *seq_p)
     Build a new 'GIMPLE_ASSIGN' tuple and append it to the end of
     '*SEQ_P'.

 'DST'/'SRC' are the destination and source respectively.  You can pass
ungimplified trees in 'DST' or 'SRC', in which case they will be
converted to a gimple operand if necessary.

 This function returns the newly created 'GIMPLE_ASSIGN' tuple.

 -- GIMPLE function: gimple gimple_build_assign_with_ops (enum tree_code
          subcode, tree lhs, tree op1, tree op2)
     This function is similar to 'gimple_build_assign', but is used to
     build a 'GIMPLE_ASSIGN' statement when the operands of the
     right-hand side of the assignment are already split into different
     operands.

     The left-hand side is an lvalue passed in lhs.  Subcode is the
     'tree_code' for the right-hand side of the assignment.  Op1 and op2
     are the operands.  If op2 is null, subcode must be a 'tree_code'
     for a unary expression.

 -- GIMPLE function: enum tree_code gimple_assign_rhs_code (gimple g)
     Return the code of the expression computed on the 'RHS' of
     assignment statement 'G'.

 -- GIMPLE function: enum gimple_rhs_class gimple_assign_rhs_class
          (gimple g)
     Return the gimple rhs class of the code for the expression computed
     on the rhs of assignment statement 'G'.  This will never return
     'GIMPLE_INVALID_RHS'.

 -- GIMPLE function: tree gimple_assign_lhs (gimple g)
     Return the 'LHS' of assignment statement 'G'.

 -- GIMPLE function: tree * gimple_assign_lhs_ptr (gimple g)
     Return a pointer to the 'LHS' of assignment statement 'G'.

 -- GIMPLE function: tree gimple_assign_rhs1 (gimple g)
     Return the first operand on the 'RHS' of assignment statement 'G'.

 -- GIMPLE function: tree * gimple_assign_rhs1_ptr (gimple g)
     Return the address of the first operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: tree gimple_assign_rhs2 (gimple g)
     Return the second operand on the 'RHS' of assignment statement 'G'.

 -- GIMPLE function: tree * gimple_assign_rhs2_ptr (gimple g)
     Return the address of the second operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: tree gimple_assign_rhs3 (gimple g)
     Return the third operand on the 'RHS' of assignment statement 'G'.

 -- GIMPLE function: tree * gimple_assign_rhs3_ptr (gimple g)
     Return the address of the third operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: void gimple_assign_set_lhs (gimple g, tree lhs)
     Set 'LHS' to be the 'LHS' operand of assignment statement 'G'.

 -- GIMPLE function: void gimple_assign_set_rhs1 (gimple g, tree rhs)
     Set 'RHS' to be the first operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: void gimple_assign_set_rhs2 (gimple g, tree rhs)
     Set 'RHS' to be the second operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: void gimple_assign_set_rhs3 (gimple g, tree rhs)
     Set 'RHS' to be the third operand on the 'RHS' of assignment
     statement 'G'.

 -- GIMPLE function: bool gimple_assign_cast_p (gimple s)
     Return true if 'S' is a type-cast assignment.


File: gccint.info,  Node: 'GIMPLE_BIND',  Next: 'GIMPLE_CALL',  Prev: 'GIMPLE_ASSIGN',  Up: Tuple specific accessors

12.7.3 'GIMPLE_BIND'
--------------------

 -- GIMPLE function: gimple gimple_build_bind (tree vars, gimple_seq
          body)
     Build a 'GIMPLE_BIND' statement with a list of variables in 'VARS'
     and a body of statements in sequence 'BODY'.

 -- GIMPLE function: tree gimple_bind_vars (gimple g)
     Return the variables declared in the 'GIMPLE_BIND' statement 'G'.

 -- GIMPLE function: void gimple_bind_set_vars (gimple g, tree vars)
     Set 'VARS' to be the set of variables declared in the 'GIMPLE_BIND'
     statement 'G'.

 -- GIMPLE function: void gimple_bind_append_vars (gimple g, tree vars)
     Append 'VARS' to the set of variables declared in the 'GIMPLE_BIND'
     statement 'G'.

 -- GIMPLE function: gimple_seq gimple_bind_body (gimple g)
     Return the GIMPLE sequence contained in the 'GIMPLE_BIND' statement
     'G'.

 -- GIMPLE function: void gimple_bind_set_body (gimple g, gimple_seq
          seq)
     Set 'SEQ' to be sequence contained in the 'GIMPLE_BIND' statement
     'G'.

 -- GIMPLE function: void gimple_bind_add_stmt (gimple gs, gimple stmt)
     Append a statement to the end of a 'GIMPLE_BIND''s body.

 -- GIMPLE function: void gimple_bind_add_seq (gimple gs, gimple_seq
          seq)
     Append a sequence of statements to the end of a 'GIMPLE_BIND''s
     body.

 -- GIMPLE function: tree gimple_bind_block (gimple g)
     Return the 'TREE_BLOCK' node associated with 'GIMPLE_BIND'
     statement 'G'.  This is analogous to the 'BIND_EXPR_BLOCK' field in
     trees.

 -- GIMPLE function: void gimple_bind_set_block (gimple g, tree block)
     Set 'BLOCK' to be the 'TREE_BLOCK' node associated with
     'GIMPLE_BIND' statement 'G'.


File: gccint.info,  Node: 'GIMPLE_CALL',  Next: 'GIMPLE_CATCH',  Prev: 'GIMPLE_BIND',  Up: Tuple specific accessors

12.7.4 'GIMPLE_CALL'
--------------------

 -- GIMPLE function: gimple gimple_build_call (tree fn, unsigned nargs,
          ...)
     Build a 'GIMPLE_CALL' statement to function 'FN'.  The argument
     'FN' must be either a 'FUNCTION_DECL' or a gimple call address as
     determined by 'is_gimple_call_addr'.  'NARGS' are the number of
     arguments.  The rest of the arguments follow the argument 'NARGS',
     and must be trees that are valid as rvalues in gimple (i.e., each
     operand is validated with 'is_gimple_operand').

 -- GIMPLE function: gimple gimple_build_call_from_tree (tree call_expr)
     Build a 'GIMPLE_CALL' from a 'CALL_EXPR' node.  The arguments and
     the function are taken from the expression directly.  This routine
     assumes that 'call_expr' is already in GIMPLE form.  That is, its
     operands are GIMPLE values and the function call needs no further
     simplification.  All the call flags in 'call_expr' are copied over
     to the new 'GIMPLE_CALL'.

 -- GIMPLE function: gimple gimple_build_call_vec (tree fn, 'VEC'(tree,
          heap) *args)
     Identical to 'gimple_build_call' but the arguments are stored in a
     'VEC'().

 -- GIMPLE function: tree gimple_call_lhs (gimple g)
     Return the 'LHS' of call statement 'G'.

 -- GIMPLE function: tree * gimple_call_lhs_ptr (gimple g)
     Return a pointer to the 'LHS' of call statement 'G'.

 -- GIMPLE function: void gimple_call_set_lhs (gimple g, tree lhs)
     Set 'LHS' to be the 'LHS' operand of call statement 'G'.

 -- GIMPLE function: tree gimple_call_fn (gimple g)
     Return the tree node representing the function called by call
     statement 'G'.

 -- GIMPLE function: void gimple_call_set_fn (gimple g, tree fn)
     Set 'FN' to be the function called by call statement 'G'.  This has
     to be a gimple value specifying the address of the called function.

 -- GIMPLE function: tree gimple_call_fndecl (gimple g)
     If a given 'GIMPLE_CALL''s callee is a 'FUNCTION_DECL', return it.
     Otherwise return 'NULL'.  This function is analogous to
     'get_callee_fndecl' in 'GENERIC'.

 -- GIMPLE function: tree gimple_call_set_fndecl (gimple g, tree fndecl)
     Set the called function to 'FNDECL'.

 -- GIMPLE function: tree gimple_call_return_type (gimple g)
     Return the type returned by call statement 'G'.

 -- GIMPLE function: tree gimple_call_chain (gimple g)
     Return the static chain for call statement 'G'.

 -- GIMPLE function: void gimple_call_set_chain (gimple g, tree chain)
     Set 'CHAIN' to be the static chain for call statement 'G'.

 -- GIMPLE function: unsigned gimple_call_num_args (gimple g)
     Return the number of arguments used by call statement 'G'.

 -- GIMPLE function: tree gimple_call_arg (gimple g, unsigned index)
     Return the argument at position 'INDEX' for call statement 'G'.
     The first argument is 0.

 -- GIMPLE function: tree * gimple_call_arg_ptr (gimple g, unsigned
          index)
     Return a pointer to the argument at position 'INDEX' for call
     statement 'G'.

 -- GIMPLE function: void gimple_call_set_arg (gimple g, unsigned index,
          tree arg)
     Set 'ARG' to be the argument at position 'INDEX' for call statement
     'G'.

 -- GIMPLE function: void gimple_call_set_tail (gimple s)
     Mark call statement 'S' as being a tail call (i.e., a call just
     before the exit of a function).  These calls are candidate for tail
     call optimization.

 -- GIMPLE function: bool gimple_call_tail_p (gimple s)
     Return true if 'GIMPLE_CALL' 'S' is marked as a tail call.

 -- GIMPLE function: void gimple_call_mark_uninlinable (gimple s)
     Mark 'GIMPLE_CALL' 'S' as being uninlinable.

 -- GIMPLE function: bool gimple_call_cannot_inline_p (gimple s)
     Return true if 'GIMPLE_CALL' 'S' cannot be inlined.

 -- GIMPLE function: bool gimple_call_noreturn_p (gimple s)
     Return true if 'S' is a noreturn call.

 -- GIMPLE function: gimple gimple_call_copy_skip_args (gimple stmt,
          bitmap args_to_skip)
     Build a 'GIMPLE_CALL' identical to 'STMT' but skipping the
     arguments in the positions marked by the set 'ARGS_TO_SKIP'.


File: gccint.info,  Node: 'GIMPLE_CATCH',  Next: 'GIMPLE_COND',  Prev: 'GIMPLE_CALL',  Up: Tuple specific accessors

12.7.5 'GIMPLE_CATCH'
---------------------

 -- GIMPLE function: gimple gimple_build_catch (tree types, gimple_seq
          handler)
     Build a 'GIMPLE_CATCH' statement.  'TYPES' are the tree types this
     catch handles.  'HANDLER' is a sequence of statements with the code
     for the handler.

 -- GIMPLE function: tree gimple_catch_types (gimple g)
     Return the types handled by 'GIMPLE_CATCH' statement 'G'.

 -- GIMPLE function: tree * gimple_catch_types_ptr (gimple g)
     Return a pointer to the types handled by 'GIMPLE_CATCH' statement
     'G'.

 -- GIMPLE function: gimple_seq gimple_catch_handler (gimple g)
     Return the GIMPLE sequence representing the body of the handler of
     'GIMPLE_CATCH' statement 'G'.

 -- GIMPLE function: void gimple_catch_set_types (gimple g, tree t)
     Set 'T' to be the set of types handled by 'GIMPLE_CATCH' 'G'.

 -- GIMPLE function: void gimple_catch_set_handler (gimple g, gimple_seq
          handler)
     Set 'HANDLER' to be the body of 'GIMPLE_CATCH' 'G'.


File: gccint.info,  Node: 'GIMPLE_COND',  Next: 'GIMPLE_DEBUG',  Prev: 'GIMPLE_CATCH',  Up: Tuple specific accessors

12.7.6 'GIMPLE_COND'
--------------------

 -- GIMPLE function: gimple gimple_build_cond (enum tree_code pred_code,
          tree lhs, tree rhs, tree t_label, tree f_label)
     Build a 'GIMPLE_COND' statement.  'A' 'GIMPLE_COND' statement
     compares 'LHS' and 'RHS' and if the condition in 'PRED_CODE' is
     true, jump to the label in 't_label', otherwise jump to the label
     in 'f_label'.  'PRED_CODE' are relational operator tree codes like
     'EQ_EXPR', 'LT_EXPR', 'LE_EXPR', 'NE_EXPR', etc.

 -- GIMPLE function: gimple gimple_build_cond_from_tree (tree cond, tree
          t_label, tree f_label)
     Build a 'GIMPLE_COND' statement from the conditional expression
     tree 'COND'.  'T_LABEL' and 'F_LABEL' are as in
     'gimple_build_cond'.

 -- GIMPLE function: enum tree_code gimple_cond_code (gimple g)
     Return the code of the predicate computed by conditional statement
     'G'.

 -- GIMPLE function: void gimple_cond_set_code (gimple g, enum tree_code
          code)
     Set 'CODE' to be the predicate code for the conditional statement
     'G'.

 -- GIMPLE function: tree gimple_cond_lhs (gimple g)
     Return the 'LHS' of the predicate computed by conditional statement
     'G'.

 -- GIMPLE function: void gimple_cond_set_lhs (gimple g, tree lhs)
     Set 'LHS' to be the 'LHS' operand of the predicate computed by
     conditional statement 'G'.

 -- GIMPLE function: tree gimple_cond_rhs (gimple g)
     Return the 'RHS' operand of the predicate computed by conditional
     'G'.

 -- GIMPLE function: void gimple_cond_set_rhs (gimple g, tree rhs)
     Set 'RHS' to be the 'RHS' operand of the predicate computed by
     conditional statement 'G'.

 -- GIMPLE function: tree gimple_cond_true_label (gimple g)
     Return the label used by conditional statement 'G' when its
     predicate evaluates to true.

 -- GIMPLE function: void gimple_cond_set_true_label (gimple g, tree
          label)
     Set 'LABEL' to be the label used by conditional statement 'G' when
     its predicate evaluates to true.

 -- GIMPLE function: void gimple_cond_set_false_label (gimple g, tree
          label)
     Set 'LABEL' to be the label used by conditional statement 'G' when
     its predicate evaluates to false.

 -- GIMPLE function: tree gimple_cond_false_label (gimple g)
     Return the label used by conditional statement 'G' when its
     predicate evaluates to false.

 -- GIMPLE function: void gimple_cond_make_false (gimple g)
     Set the conditional 'COND_STMT' to be of the form 'if (1 == 0)'.

 -- GIMPLE function: void gimple_cond_make_true (gimple g)
     Set the conditional 'COND_STMT' to be of the form 'if (1 == 1)'.


File: gccint.info,  Node: 'GIMPLE_DEBUG',  Next: 'GIMPLE_EH_FILTER',  Prev: 'GIMPLE_COND',  Up: Tuple specific accessors

12.7.7 'GIMPLE_DEBUG'
---------------------

 -- GIMPLE function: gimple gimple_build_debug_bind (tree var, tree
          value, gimple stmt)
     Build a 'GIMPLE_DEBUG' statement with 'GIMPLE_DEBUG_BIND' of
     'subcode'.  The effect of this statement is to tell debug
     information generation machinery that the value of user variable
     'var' is given by 'value' at that point, and to remain with that
     value until 'var' runs out of scope, a dynamically-subsequent debug
     bind statement overrides the binding, or conflicting values reach a
     control flow merge point.  Even if components of the 'value'
     expression change afterwards, the variable is supposed to retain
     the same value, though not necessarily the same location.

     It is expected that 'var' be most often a tree for automatic user
     variables ('VAR_DECL' or 'PARM_DECL') that satisfy the requirements
     for gimple registers, but it may also be a tree for a scalarized
     component of a user variable ('ARRAY_REF', 'COMPONENT_REF'), or a
     debug temporary ('DEBUG_EXPR_DECL').

     As for 'value', it can be an arbitrary tree expression, but it is
     recommended that it be in a suitable form for a gimple assignment
     'RHS'.  It is not expected that user variables that could appear as
     'var' ever appear in 'value', because in the latter we'd have their
     'SSA_NAME's instead, but even if they were not in SSA form, user
     variables appearing in 'value' are to be regarded as part of the
     executable code space, whereas those in 'var' are to be regarded as
     part of the source code space.  There is no way to refer to the
     value bound to a user variable within a 'value' expression.

     If 'value' is 'GIMPLE_DEBUG_BIND_NOVALUE', debug information
     generation machinery is informed that the variable 'var' is
     unbound, i.e., that its value is indeterminate, which sometimes
     means it is really unavailable, and other times that the compiler
     could not keep track of it.

     Block and location information for the newly-created stmt are taken
     from 'stmt', if given.

 -- GIMPLE function: tree gimple_debug_bind_get_var (gimple stmt)
     Return the user variable VAR that is bound at 'stmt'.

 -- GIMPLE function: tree gimple_debug_bind_get_value (gimple stmt)
     Return the value expression that is bound to a user variable at
     'stmt'.

 -- GIMPLE function: tree * gimple_debug_bind_get_value_ptr (gimple
          stmt)
     Return a pointer to the value expression that is bound to a user
     variable at 'stmt'.

 -- GIMPLE function: void gimple_debug_bind_set_var (gimple stmt, tree
          var)
     Modify the user variable bound at 'stmt' to VAR.

 -- GIMPLE function: void gimple_debug_bind_set_value (gimple stmt, tree
          var)
     Modify the value bound to the user variable bound at 'stmt' to
     VALUE.

 -- GIMPLE function: void gimple_debug_bind_reset_value (gimple stmt)
     Modify the value bound to the user variable bound at 'stmt' so that
     the variable becomes unbound.

 -- GIMPLE function: bool gimple_debug_bind_has_value_p (gimple stmt)
     Return 'TRUE' if 'stmt' binds a user variable to a value, and
     'FALSE' if it unbinds the variable.


File: gccint.info,  Node: 'GIMPLE_EH_FILTER',  Next: 'GIMPLE_LABEL',  Prev: 'GIMPLE_DEBUG',  Up: Tuple specific accessors

12.7.8 'GIMPLE_EH_FILTER'
-------------------------

 -- GIMPLE function: gimple gimple_build_eh_filter (tree types,
          gimple_seq failure)
     Build a 'GIMPLE_EH_FILTER' statement.  'TYPES' are the filter's
     types.  'FAILURE' is a sequence with the filter's failure action.

 -- GIMPLE function: tree gimple_eh_filter_types (gimple g)
     Return the types handled by 'GIMPLE_EH_FILTER' statement 'G'.

 -- GIMPLE function: tree * gimple_eh_filter_types_ptr (gimple g)
     Return a pointer to the types handled by 'GIMPLE_EH_FILTER'
     statement 'G'.

 -- GIMPLE function: gimple_seq gimple_eh_filter_failure (gimple g)
     Return the sequence of statement to execute when 'GIMPLE_EH_FILTER'
     statement fails.

 -- GIMPLE function: void gimple_eh_filter_set_types (gimple g, tree
          types)
     Set 'TYPES' to be the set of types handled by 'GIMPLE_EH_FILTER'
     'G'.

 -- GIMPLE function: void gimple_eh_filter_set_failure (gimple g,
          gimple_seq failure)
     Set 'FAILURE' to be the sequence of statements to execute on
     failure for 'GIMPLE_EH_FILTER' 'G'.

 -- GIMPLE function: bool gimple_eh_filter_must_not_throw (gimple g)
     Return the 'EH_FILTER_MUST_NOT_THROW' flag.

 -- GIMPLE function: void gimple_eh_filter_set_must_not_throw (gimple g,
          bool mntp)
     Set the 'EH_FILTER_MUST_NOT_THROW' flag.


File: gccint.info,  Node: 'GIMPLE_LABEL',  Next: 'GIMPLE_NOP',  Prev: 'GIMPLE_EH_FILTER',  Up: Tuple specific accessors

12.7.9 'GIMPLE_LABEL'
---------------------

 -- GIMPLE function: gimple gimple_build_label (tree label)
     Build a 'GIMPLE_LABEL' statement with corresponding to the tree
     label, 'LABEL'.

 -- GIMPLE function: tree gimple_label_label (gimple g)
     Return the 'LABEL_DECL' node used by 'GIMPLE_LABEL' statement 'G'.

 -- GIMPLE function: void gimple_label_set_label (gimple g, tree label)
     Set 'LABEL' to be the 'LABEL_DECL' node used by 'GIMPLE_LABEL'
     statement 'G'.

 -- GIMPLE function: gimple gimple_build_goto (tree dest)
     Build a 'GIMPLE_GOTO' statement to label 'DEST'.

 -- GIMPLE function: tree gimple_goto_dest (gimple g)
     Return the destination of the unconditional jump 'G'.

 -- GIMPLE function: void gimple_goto_set_dest (gimple g, tree dest)
     Set 'DEST' to be the destination of the unconditional jump 'G'.


File: gccint.info,  Node: 'GIMPLE_NOP',  Next: 'GIMPLE_OMP_ATOMIC_LOAD',  Prev: 'GIMPLE_LABEL',  Up: Tuple specific accessors

12.7.10 'GIMPLE_NOP'
--------------------

 -- GIMPLE function: gimple gimple_build_nop (void)
     Build a 'GIMPLE_NOP' statement.

 -- GIMPLE function: bool gimple_nop_p (gimple g)
     Returns 'TRUE' if statement 'G' is a 'GIMPLE_NOP'.


File: gccint.info,  Node: 'GIMPLE_OMP_ATOMIC_LOAD',  Next: 'GIMPLE_OMP_ATOMIC_STORE',  Prev: 'GIMPLE_NOP',  Up: Tuple specific accessors

12.7.11 'GIMPLE_OMP_ATOMIC_LOAD'
--------------------------------

 -- GIMPLE function: gimple gimple_build_omp_atomic_load (tree lhs, tree
          rhs)
     Build a 'GIMPLE_OMP_ATOMIC_LOAD' statement.  'LHS' is the left-hand
     side of the assignment.  'RHS' is the right-hand side of the
     assignment.

 -- GIMPLE function: void gimple_omp_atomic_load_set_lhs (gimple g, tree
          lhs)
     Set the 'LHS' of an atomic load.

 -- GIMPLE function: tree gimple_omp_atomic_load_lhs (gimple g)
     Get the 'LHS' of an atomic load.

 -- GIMPLE function: void gimple_omp_atomic_load_set_rhs (gimple g, tree
          rhs)
     Set the 'RHS' of an atomic set.

 -- GIMPLE function: tree gimple_omp_atomic_load_rhs (gimple g)
     Get the 'RHS' of an atomic set.


File: gccint.info,  Node: 'GIMPLE_OMP_ATOMIC_STORE',  Next: 'GIMPLE_OMP_CONTINUE',  Prev: 'GIMPLE_OMP_ATOMIC_LOAD',  Up: Tuple specific accessors

12.7.12 'GIMPLE_OMP_ATOMIC_STORE'
---------------------------------

 -- GIMPLE function: gimple gimple_build_omp_atomic_store (tree val)
     Build a 'GIMPLE_OMP_ATOMIC_STORE' statement.  'VAL' is the value to
     be stored.

 -- GIMPLE function: void gimple_omp_atomic_store_set_val (gimple g,
          tree val)
     Set the value being stored in an atomic store.

 -- GIMPLE function: tree gimple_omp_atomic_store_val (gimple g)
     Return the value being stored in an atomic store.


File: gccint.info,  Node: 'GIMPLE_OMP_CONTINUE',  Next: 'GIMPLE_OMP_CRITICAL',  Prev: 'GIMPLE_OMP_ATOMIC_STORE',  Up: Tuple specific accessors

12.7.13 'GIMPLE_OMP_CONTINUE'
-----------------------------

 -- GIMPLE function: gimple gimple_build_omp_continue (tree control_def,
          tree control_use)
     Build a 'GIMPLE_OMP_CONTINUE' statement.  'CONTROL_DEF' is the
     definition of the control variable.  'CONTROL_USE' is the use of
     the control variable.

 -- GIMPLE function: tree gimple_omp_continue_control_def (gimple s)
     Return the definition of the control variable on a
     'GIMPLE_OMP_CONTINUE' in 'S'.

 -- GIMPLE function: tree gimple_omp_continue_control_def_ptr (gimple s)
     Same as above, but return the pointer.

 -- GIMPLE function: tree gimple_omp_continue_set_control_def (gimple s)
     Set the control variable definition for a 'GIMPLE_OMP_CONTINUE'
     statement in 'S'.

 -- GIMPLE function: tree gimple_omp_continue_control_use (gimple s)
     Return the use of the control variable on a 'GIMPLE_OMP_CONTINUE'
     in 'S'.

 -- GIMPLE function: tree gimple_omp_continue_control_use_ptr (gimple s)
     Same as above, but return the pointer.

 -- GIMPLE function: tree gimple_omp_continue_set_control_use (gimple s)
     Set the control variable use for a 'GIMPLE_OMP_CONTINUE' statement
     in 'S'.


File: gccint.info,  Node: 'GIMPLE_OMP_CRITICAL',  Next: 'GIMPLE_OMP_FOR',  Prev: 'GIMPLE_OMP_CONTINUE',  Up: Tuple specific accessors

12.7.14 'GIMPLE_OMP_CRITICAL'
-----------------------------

 -- GIMPLE function: gimple gimple_build_omp_critical (gimple_seq body,
          tree name)
     Build a 'GIMPLE_OMP_CRITICAL' statement.  'BODY' is the sequence of
     statements for which only one thread can execute.  'NAME' is an
     optional identifier for this critical block.

 -- GIMPLE function: tree gimple_omp_critical_name (gimple g)
     Return the name associated with 'OMP_CRITICAL' statement 'G'.

 -- GIMPLE function: tree * gimple_omp_critical_name_ptr (gimple g)
     Return a pointer to the name associated with 'OMP' critical
     statement 'G'.

 -- GIMPLE function: void gimple_omp_critical_set_name (gimple g, tree
          name)
     Set 'NAME' to be the name associated with 'OMP' critical statement
     'G'.


File: gccint.info,  Node: 'GIMPLE_OMP_FOR',  Next: 'GIMPLE_OMP_MASTER',  Prev: 'GIMPLE_OMP_CRITICAL',  Up: Tuple specific accessors

12.7.15 'GIMPLE_OMP_FOR'
------------------------

 -- GIMPLE function: gimple gimple_build_omp_for (gimple_seq body, tree
          clauses, tree index, tree initial, tree final, tree incr,
          gimple_seq pre_body, enum tree_code omp_for_cond)
     Build a 'GIMPLE_OMP_FOR' statement.  'BODY' is sequence of
     statements inside the for loop.  'CLAUSES', are any of the 'OMP'
     loop construct's clauses: private, firstprivate, lastprivate,
     reductions, ordered, schedule, and nowait.  'PRE_BODY' is the
     sequence of statements that are loop invariant.  'INDEX' is the
     index variable.  'INITIAL' is the initial value of 'INDEX'.
     'FINAL' is final value of 'INDEX'.  OMP_FOR_COND is the predicate
     used to compare 'INDEX' and 'FINAL'.  'INCR' is the increment
     expression.

 -- GIMPLE function: tree gimple_omp_for_clauses (gimple g)
     Return the clauses associated with 'OMP_FOR' 'G'.

 -- GIMPLE function: tree * gimple_omp_for_clauses_ptr (gimple g)
     Return a pointer to the 'OMP_FOR' 'G'.

 -- GIMPLE function: void gimple_omp_for_set_clauses (gimple g, tree
          clauses)
     Set 'CLAUSES' to be the list of clauses associated with 'OMP_FOR'
     'G'.

 -- GIMPLE function: tree gimple_omp_for_index (gimple g)
     Return the index variable for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree * gimple_omp_for_index_ptr (gimple g)
     Return a pointer to the index variable for 'OMP_FOR' 'G'.

 -- GIMPLE function: void gimple_omp_for_set_index (gimple g, tree
          index)
     Set 'INDEX' to be the index variable for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree gimple_omp_for_initial (gimple g)
     Return the initial value for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree * gimple_omp_for_initial_ptr (gimple g)
     Return a pointer to the initial value for 'OMP_FOR' 'G'.

 -- GIMPLE function: void gimple_omp_for_set_initial (gimple g, tree
          initial)
     Set 'INITIAL' to be the initial value for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree gimple_omp_for_final (gimple g)
     Return the final value for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree * gimple_omp_for_final_ptr (gimple g)
     turn a pointer to the final value for 'OMP_FOR' 'G'.

 -- GIMPLE function: void gimple_omp_for_set_final (gimple g, tree
          final)
     Set 'FINAL' to be the final value for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree gimple_omp_for_incr (gimple g)
     Return the increment value for 'OMP_FOR' 'G'.

 -- GIMPLE function: tree * gimple_omp_for_incr_ptr (gimple g)
     Return a pointer to the increment value for 'OMP_FOR' 'G'.

 -- GIMPLE function: void gimple_omp_for_set_incr (gimple g, tree incr)
     Set 'INCR' to be the increment value for 'OMP_FOR' 'G'.

 -- GIMPLE function: gimple_seq gimple_omp_for_pre_body (gimple g)
     Return the sequence of statements to execute before the 'OMP_FOR'
     statement 'G' starts.

 -- GIMPLE function: void gimple_omp_for_set_pre_body (gimple g,
          gimple_seq pre_body)
     Set 'PRE_BODY' to be the sequence of statements to execute before
     the 'OMP_FOR' statement 'G' starts.

 -- GIMPLE function: void gimple_omp_for_set_cond (gimple g, enum
          tree_code cond)
     Set 'COND' to be the condition code for 'OMP_FOR' 'G'.

 -- GIMPLE function: enum tree_code gimple_omp_for_cond (gimple g)
     Return the condition code associated with 'OMP_FOR' 'G'.


File: gccint.info,  Node: 'GIMPLE_OMP_MASTER',  Next: 'GIMPLE_OMP_ORDERED',  Prev: 'GIMPLE_OMP_FOR',  Up: Tuple specific accessors

12.7.16 'GIMPLE_OMP_MASTER'
---------------------------

 -- GIMPLE function: gimple gimple_build_omp_master (gimple_seq body)
     Build a 'GIMPLE_OMP_MASTER' statement.  'BODY' is the sequence of
     statements to be executed by just the master.


File: gccint.info,  Node: 'GIMPLE_OMP_ORDERED',  Next: 'GIMPLE_OMP_PARALLEL',  Prev: 'GIMPLE_OMP_MASTER',  Up: Tuple specific accessors

12.7.17 'GIMPLE_OMP_ORDERED'
----------------------------

 -- GIMPLE function: gimple gimple_build_omp_ordered (gimple_seq body)
     Build a 'GIMPLE_OMP_ORDERED' statement.

 'BODY' is the sequence of statements inside a loop that will executed
in sequence.


File: gccint.info,  Node: 'GIMPLE_OMP_PARALLEL',  Next: 'GIMPLE_OMP_RETURN',  Prev: 'GIMPLE_OMP_ORDERED',  Up: Tuple specific accessors

12.7.18 'GIMPLE_OMP_PARALLEL'
-----------------------------

 -- GIMPLE function: gimple gimple_build_omp_parallel (gimple_seq body,
          tree clauses, tree child_fn, tree data_arg)
     Build a 'GIMPLE_OMP_PARALLEL' statement.

 'BODY' is sequence of statements which are executed in parallel.
'CLAUSES', are the 'OMP' parallel construct's clauses.  'CHILD_FN' is
the function created for the parallel threads to execute.  'DATA_ARG'
are the shared data argument(s).

 -- GIMPLE function: bool gimple_omp_parallel_combined_p (gimple g)
     Return true if 'OMP' parallel statement 'G' has the
     'GF_OMP_PARALLEL_COMBINED' flag set.

 -- GIMPLE function: void gimple_omp_parallel_set_combined_p (gimple g)
     Set the 'GF_OMP_PARALLEL_COMBINED' field in 'OMP' parallel
     statement 'G'.

 -- GIMPLE function: gimple_seq gimple_omp_body (gimple g)
     Return the body for the 'OMP' statement 'G'.

 -- GIMPLE function: void gimple_omp_set_body (gimple g, gimple_seq
          body)
     Set 'BODY' to be the body for the 'OMP' statement 'G'.

 -- GIMPLE function: tree gimple_omp_parallel_clauses (gimple g)
     Return the clauses associated with 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: tree * gimple_omp_parallel_clauses_ptr (gimple g)
     Return a pointer to the clauses associated with 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: void gimple_omp_parallel_set_clauses (gimple g,
          tree clauses)
     Set 'CLAUSES' to be the list of clauses associated with
     'OMP_PARALLEL' 'G'.

 -- GIMPLE function: tree gimple_omp_parallel_child_fn (gimple g)
     Return the child function used to hold the body of 'OMP_PARALLEL'
     'G'.

 -- GIMPLE function: tree * gimple_omp_parallel_child_fn_ptr (gimple g)
     Return a pointer to the child function used to hold the body of
     'OMP_PARALLEL' 'G'.

 -- GIMPLE function: void gimple_omp_parallel_set_child_fn (gimple g,
          tree child_fn)
     Set 'CHILD_FN' to be the child function for 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: tree gimple_omp_parallel_data_arg (gimple g)
     Return the artificial argument used to send variables and values
     from the parent to the children threads in 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: tree * gimple_omp_parallel_data_arg_ptr (gimple g)
     Return a pointer to the data argument for 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: void gimple_omp_parallel_set_data_arg (gimple g,
          tree data_arg)
     Set 'DATA_ARG' to be the data argument for 'OMP_PARALLEL' 'G'.

 -- GIMPLE function: bool is_gimple_omp (gimple stmt)
     Returns true when the gimple statement 'STMT' is any of the OpenMP
     types.


File: gccint.info,  Node: 'GIMPLE_OMP_RETURN',  Next: 'GIMPLE_OMP_SECTION',  Prev: 'GIMPLE_OMP_PARALLEL',  Up: Tuple specific accessors

12.7.19 'GIMPLE_OMP_RETURN'
---------------------------

 -- GIMPLE function: gimple gimple_build_omp_return (bool wait_p)
     Build a 'GIMPLE_OMP_RETURN' statement.  'WAIT_P' is true if this is
     a non-waiting return.

 -- GIMPLE function: void gimple_omp_return_set_nowait (gimple s)
     Set the nowait flag on 'GIMPLE_OMP_RETURN' statement 'S'.

 -- GIMPLE function: bool gimple_omp_return_nowait_p (gimple g)
     Return true if 'OMP' return statement 'G' has the
     'GF_OMP_RETURN_NOWAIT' flag set.


File: gccint.info,  Node: 'GIMPLE_OMP_SECTION',  Next: 'GIMPLE_OMP_SECTIONS',  Prev: 'GIMPLE_OMP_RETURN',  Up: Tuple specific accessors

12.7.20 'GIMPLE_OMP_SECTION'
----------------------------

 -- GIMPLE function: gimple gimple_build_omp_section (gimple_seq body)
     Build a 'GIMPLE_OMP_SECTION' statement for a sections statement.

 'BODY' is the sequence of statements in the section.

 -- GIMPLE function: bool gimple_omp_section_last_p (gimple g)
     Return true if 'OMP' section statement 'G' has the
     'GF_OMP_SECTION_LAST' flag set.

 -- GIMPLE function: void gimple_omp_section_set_last (gimple g)
     Set the 'GF_OMP_SECTION_LAST' flag on 'G'.


File: gccint.info,  Node: 'GIMPLE_OMP_SECTIONS',  Next: 'GIMPLE_OMP_SINGLE',  Prev: 'GIMPLE_OMP_SECTION',  Up: Tuple specific accessors

12.7.21 'GIMPLE_OMP_SECTIONS'
-----------------------------

 -- GIMPLE function: gimple gimple_build_omp_sections (gimple_seq body,
          tree clauses)
     Build a 'GIMPLE_OMP_SECTIONS' statement.  'BODY' is a sequence of
     section statements.  'CLAUSES' are any of the 'OMP' sections
     construct's clauses: private, firstprivate, lastprivate, reduction,
     and nowait.

 -- GIMPLE function: gimple gimple_build_omp_sections_switch (void)
     Build a 'GIMPLE_OMP_SECTIONS_SWITCH' statement.

 -- GIMPLE function: tree gimple_omp_sections_control (gimple g)
     Return the control variable associated with the
     'GIMPLE_OMP_SECTIONS' in 'G'.

 -- GIMPLE function: tree * gimple_omp_sections_control_ptr (gimple g)
     Return a pointer to the clauses associated with the
     'GIMPLE_OMP_SECTIONS' in 'G'.

 -- GIMPLE function: void gimple_omp_sections_set_control (gimple g,
          tree control)
     Set 'CONTROL' to be the set of clauses associated with the
     'GIMPLE_OMP_SECTIONS' in 'G'.

 -- GIMPLE function: tree gimple_omp_sections_clauses (gimple g)
     Return the clauses associated with 'OMP_SECTIONS' 'G'.

 -- GIMPLE function: tree * gimple_omp_sections_clauses_ptr (gimple g)
     Return a pointer to the clauses associated with 'OMP_SECTIONS' 'G'.

 -- GIMPLE function: void gimple_omp_sections_set_clauses (gimple g,
          tree clauses)
     Set 'CLAUSES' to be the set of clauses associated with
     'OMP_SECTIONS' 'G'.


File: gccint.info,  Node: 'GIMPLE_OMP_SINGLE',  Next: 'GIMPLE_PHI',  Prev: 'GIMPLE_OMP_SECTIONS',  Up: Tuple specific accessors

12.7.22 'GIMPLE_OMP_SINGLE'
---------------------------

 -- GIMPLE function: gimple gimple_build_omp_single (gimple_seq body,
          tree clauses)
     Build a 'GIMPLE_OMP_SINGLE' statement.  'BODY' is the sequence of
     statements that will be executed once.  'CLAUSES' are any of the
     'OMP' single construct's clauses: private, firstprivate,
     copyprivate, nowait.

 -- GIMPLE function: tree gimple_omp_single_clauses (gimple g)
     Return the clauses associated with 'OMP_SINGLE' 'G'.

 -- GIMPLE function: tree * gimple_omp_single_clauses_ptr (gimple g)
     Return a pointer to the clauses associated with 'OMP_SINGLE' 'G'.

 -- GIMPLE function: void gimple_omp_single_set_clauses (gimple g, tree
          clauses)
     Set 'CLAUSES' to be the clauses associated with 'OMP_SINGLE' 'G'.


File: gccint.info,  Node: 'GIMPLE_PHI',  Next: 'GIMPLE_RESX',  Prev: 'GIMPLE_OMP_SINGLE',  Up: Tuple specific accessors

12.7.23 'GIMPLE_PHI'
--------------------

 -- GIMPLE function: unsigned gimple_phi_capacity (gimple g)
     Return the maximum number of arguments supported by 'GIMPLE_PHI'
     'G'.

 -- GIMPLE function: unsigned gimple_phi_num_args (gimple g)
     Return the number of arguments in 'GIMPLE_PHI' 'G'.  This must
     always be exactly the number of incoming edges for the basic block
     holding 'G'.

 -- GIMPLE function: tree gimple_phi_result (gimple g)
     Return the 'SSA' name created by 'GIMPLE_PHI' 'G'.

 -- GIMPLE function: tree * gimple_phi_result_ptr (gimple g)
     Return a pointer to the 'SSA' name created by 'GIMPLE_PHI' 'G'.

 -- GIMPLE function: void gimple_phi_set_result (gimple g, tree result)
     Set 'RESULT' to be the 'SSA' name created by 'GIMPLE_PHI' 'G'.

 -- GIMPLE function: struct phi_arg_d * gimple_phi_arg (gimple g, index)
     Return the 'PHI' argument corresponding to incoming edge 'INDEX'
     for 'GIMPLE_PHI' 'G'.

 -- GIMPLE function: void gimple_phi_set_arg (gimple g, index, struct
          phi_arg_d * phiarg)
     Set 'PHIARG' to be the argument corresponding to incoming edge
     'INDEX' for 'GIMPLE_PHI' 'G'.


File: gccint.info,  Node: 'GIMPLE_RESX',  Next: 'GIMPLE_RETURN',  Prev: 'GIMPLE_PHI',  Up: Tuple specific accessors

12.7.24 'GIMPLE_RESX'
---------------------

 -- GIMPLE function: gimple gimple_build_resx (int region)
     Build a 'GIMPLE_RESX' statement which is a statement.  This
     statement is a placeholder for _Unwind_Resume before we know if a
     function call or a branch is needed.  'REGION' is the exception
     region from which control is flowing.

 -- GIMPLE function: int gimple_resx_region (gimple g)
     Return the region number for 'GIMPLE_RESX' 'G'.

 -- GIMPLE function: void gimple_resx_set_region (gimple g, int region)
     Set 'REGION' to be the region number for 'GIMPLE_RESX' 'G'.


File: gccint.info,  Node: 'GIMPLE_RETURN',  Next: 'GIMPLE_SWITCH',  Prev: 'GIMPLE_RESX',  Up: Tuple specific accessors

12.7.25 'GIMPLE_RETURN'
-----------------------

 -- GIMPLE function: gimple gimple_build_return (tree retval)
     Build a 'GIMPLE_RETURN' statement whose return value is retval.

 -- GIMPLE function: tree gimple_return_retval (gimple g)
     Return the return value for 'GIMPLE_RETURN' 'G'.

 -- GIMPLE function: void gimple_return_set_retval (gimple g, tree
          retval)
     Set 'RETVAL' to be the return value for 'GIMPLE_RETURN' 'G'.


File: gccint.info,  Node: 'GIMPLE_SWITCH',  Next: 'GIMPLE_TRY',  Prev: 'GIMPLE_RETURN',  Up: Tuple specific accessors

12.7.26 'GIMPLE_SWITCH'
-----------------------

 -- GIMPLE function: gimple gimple_build_switch (tree index, tree
          default_label, 'VEC'(tree,heap) *args)
     Build a 'GIMPLE_SWITCH' statement.  'INDEX' is the index variable
     to switch on, and 'DEFAULT_LABEL' represents the default label.
     'ARGS' is a vector of 'CASE_LABEL_EXPR' trees that contain the
     non-default case labels.  Each label is a tree of code
     'CASE_LABEL_EXPR'.

 -- GIMPLE function: unsigned gimple_switch_num_labels (gimple g)
     Return the number of labels associated with the switch statement
     'G'.

 -- GIMPLE function: void gimple_switch_set_num_labels (gimple g,
          unsigned nlabels)
     Set 'NLABELS' to be the number of labels for the switch statement
     'G'.

 -- GIMPLE function: tree gimple_switch_index (gimple g)
     Return the index variable used by the switch statement 'G'.

 -- GIMPLE function: void gimple_switch_set_index (gimple g, tree index)
     Set 'INDEX' to be the index variable for switch statement 'G'.

 -- GIMPLE function: tree gimple_switch_label (gimple g, unsigned index)
     Return the label numbered 'INDEX'.  The default label is 0,
     followed by any labels in a switch statement.

 -- GIMPLE function: void gimple_switch_set_label (gimple g, unsigned
          index, tree label)
     Set the label number 'INDEX' to 'LABEL'.  0 is always the default
     label.

 -- GIMPLE function: tree gimple_switch_default_label (gimple g)
     Return the default label for a switch statement.

 -- GIMPLE function: void gimple_switch_set_default_label (gimple g,
          tree label)
     Set the default label for a switch statement.


File: gccint.info,  Node: 'GIMPLE_TRY',  Next: 'GIMPLE_WITH_CLEANUP_EXPR',  Prev: 'GIMPLE_SWITCH',  Up: Tuple specific accessors

12.7.27 'GIMPLE_TRY'
--------------------

 -- GIMPLE function: gimple gimple_build_try (gimple_seq eval,
          gimple_seq cleanup, unsigned int kind)
     Build a 'GIMPLE_TRY' statement.  'EVAL' is a sequence with the
     expression to evaluate.  'CLEANUP' is a sequence of statements to
     run at clean-up time.  'KIND' is the enumeration value
     'GIMPLE_TRY_CATCH' if this statement denotes a try/catch construct
     or 'GIMPLE_TRY_FINALLY' if this statement denotes a try/finally
     construct.

 -- GIMPLE function: enum gimple_try_flags gimple_try_kind (gimple g)
     Return the kind of try block represented by 'GIMPLE_TRY' 'G'.  This
     is either 'GIMPLE_TRY_CATCH' or 'GIMPLE_TRY_FINALLY'.

 -- GIMPLE function: bool gimple_try_catch_is_cleanup (gimple g)
     Return the 'GIMPLE_TRY_CATCH_IS_CLEANUP' flag.

 -- GIMPLE function: gimple_seq gimple_try_eval (gimple g)
     Return the sequence of statements used as the body for 'GIMPLE_TRY'
     'G'.

 -- GIMPLE function: gimple_seq gimple_try_cleanup (gimple g)
     Return the sequence of statements used as the cleanup body for
     'GIMPLE_TRY' 'G'.

 -- GIMPLE function: void gimple_try_set_catch_is_cleanup (gimple g,
          bool catch_is_cleanup)
     Set the 'GIMPLE_TRY_CATCH_IS_CLEANUP' flag.

 -- GIMPLE function: void gimple_try_set_eval (gimple g, gimple_seq
          eval)
     Set 'EVAL' to be the sequence of statements to use as the body for
     'GIMPLE_TRY' 'G'.

 -- GIMPLE function: void gimple_try_set_cleanup (gimple g, gimple_seq
          cleanup)
     Set 'CLEANUP' to be the sequence of statements to use as the
     cleanup body for 'GIMPLE_TRY' 'G'.


File: gccint.info,  Node: 'GIMPLE_WITH_CLEANUP_EXPR',  Prev: 'GIMPLE_TRY',  Up: Tuple specific accessors

12.7.28 'GIMPLE_WITH_CLEANUP_EXPR'
----------------------------------

 -- GIMPLE function: gimple gimple_build_wce (gimple_seq cleanup)
     Build a 'GIMPLE_WITH_CLEANUP_EXPR' statement.  'CLEANUP' is the
     clean-up expression.

 -- GIMPLE function: gimple_seq gimple_wce_cleanup (gimple g)
     Return the cleanup sequence for cleanup statement 'G'.

 -- GIMPLE function: void gimple_wce_set_cleanup (gimple g, gimple_seq
          cleanup)
     Set 'CLEANUP' to be the cleanup sequence for 'G'.

 -- GIMPLE function: bool gimple_wce_cleanup_eh_only (gimple g)
     Return the 'CLEANUP_EH_ONLY' flag for a 'WCE' tuple.

 -- GIMPLE function: void gimple_wce_set_cleanup_eh_only (gimple g, bool
          eh_only_p)
     Set the 'CLEANUP_EH_ONLY' flag for a 'WCE' tuple.


File: gccint.info,  Node: GIMPLE sequences,  Next: Sequence iterators,  Prev: Tuple specific accessors,  Up: GIMPLE

12.8 GIMPLE sequences
=====================

GIMPLE sequences are the tuple equivalent of 'STATEMENT_LIST''s used in
'GENERIC'.  They are used to chain statements together, and when used in
conjunction with sequence iterators, provide a framework for iterating
through statements.

 GIMPLE sequences are of type struct 'gimple_sequence', but are more
commonly passed by reference to functions dealing with sequences.  The
type for a sequence pointer is 'gimple_seq' which is the same as struct
'gimple_sequence' *.  When declaring a local sequence, you can define a
local variable of type struct 'gimple_sequence'.  When declaring a
sequence allocated on the garbage collected heap, use the function
'gimple_seq_alloc' documented below.

 There are convenience functions for iterating through sequences in the
section entitled Sequence Iterators.

 Below is a list of functions to manipulate and query sequences.

 -- GIMPLE function: void gimple_seq_add_stmt (gimple_seq *seq, gimple
          g)
     Link a gimple statement to the end of the sequence *'SEQ' if 'G' is
     not 'NULL'.  If *'SEQ' is 'NULL', allocate a sequence before
     linking.

 -- GIMPLE function: void gimple_seq_add_seq (gimple_seq *dest,
          gimple_seq src)
     Append sequence 'SRC' to the end of sequence *'DEST' if 'SRC' is
     not 'NULL'.  If *'DEST' is 'NULL', allocate a new sequence before
     appending.

 -- GIMPLE function: gimple_seq gimple_seq_deep_copy (gimple_seq src)
     Perform a deep copy of sequence 'SRC' and return the result.

 -- GIMPLE function: gimple_seq gimple_seq_reverse (gimple_seq seq)
     Reverse the order of the statements in the sequence 'SEQ'.  Return
     'SEQ'.

 -- GIMPLE function: gimple gimple_seq_first (gimple_seq s)
     Return the first statement in sequence 'S'.

 -- GIMPLE function: gimple gimple_seq_last (gimple_seq s)
     Return the last statement in sequence 'S'.

 -- GIMPLE function: void gimple_seq_set_last (gimple_seq s, gimple
          last)
     Set the last statement in sequence 'S' to the statement in 'LAST'.

 -- GIMPLE function: void gimple_seq_set_first (gimple_seq s, gimple
          first)
     Set the first statement in sequence 'S' to the statement in
     'FIRST'.

 -- GIMPLE function: void gimple_seq_init (gimple_seq s)
     Initialize sequence 'S' to an empty sequence.

 -- GIMPLE function: gimple_seq gimple_seq_alloc (void)
     Allocate a new sequence in the garbage collected store and return
     it.

 -- GIMPLE function: void gimple_seq_copy (gimple_seq dest, gimple_seq
          src)
     Copy the sequence 'SRC' into the sequence 'DEST'.

 -- GIMPLE function: bool gimple_seq_empty_p (gimple_seq s)
     Return true if the sequence 'S' is empty.

 -- GIMPLE function: gimple_seq bb_seq (basic_block bb)
     Returns the sequence of statements in 'BB'.

 -- GIMPLE function: void set_bb_seq (basic_block bb, gimple_seq seq)
     Sets the sequence of statements in 'BB' to 'SEQ'.

 -- GIMPLE function: bool gimple_seq_singleton_p (gimple_seq seq)
     Determine whether 'SEQ' contains exactly one statement.


File: gccint.info,  Node: Sequence iterators,  Next: Adding a new GIMPLE statement code,  Prev: GIMPLE sequences,  Up: GIMPLE

12.9 Sequence iterators
=======================

Sequence iterators are convenience constructs for iterating through
statements in a sequence.  Given a sequence 'SEQ', here is a typical use
of gimple sequence iterators:

     gimple_stmt_iterator gsi;

     for (gsi = gsi_start (seq); !gsi_end_p (gsi); gsi_next (&gsi))
       {
         gimple g = gsi_stmt (gsi);
         /* Do something with gimple statement G.  */
       }

 Backward iterations are possible:

             for (gsi = gsi_last (seq); !gsi_end_p (gsi); gsi_prev (&gsi))

 Forward and backward iterations on basic blocks are possible with
'gsi_start_bb' and 'gsi_last_bb'.

 In the documentation below we sometimes refer to enum
'gsi_iterator_update'.  The valid options for this enumeration are:

   * 'GSI_NEW_STMT' Only valid when a single statement is added.  Move
     the iterator to it.

   * 'GSI_SAME_STMT' Leave the iterator at the same statement.

   * 'GSI_CONTINUE_LINKING' Move iterator to whatever position is
     suitable for linking other statements in the same direction.

 Below is a list of the functions used to manipulate and use statement
iterators.

 -- GIMPLE function: gimple_stmt_iterator gsi_start (gimple_seq seq)
     Return a new iterator pointing to the sequence 'SEQ''s first
     statement.  If 'SEQ' is empty, the iterator's basic block is
     'NULL'.  Use 'gsi_start_bb' instead when the iterator needs to
     always have the correct basic block set.

 -- GIMPLE function: gimple_stmt_iterator gsi_start_bb (basic_block bb)
     Return a new iterator pointing to the first statement in basic
     block 'BB'.

 -- GIMPLE function: gimple_stmt_iterator gsi_last (gimple_seq seq)
     Return a new iterator initially pointing to the last statement of
     sequence 'SEQ'.  If 'SEQ' is empty, the iterator's basic block is
     'NULL'.  Use 'gsi_last_bb' instead when the iterator needs to
     always have the correct basic block set.

 -- GIMPLE function: gimple_stmt_iterator gsi_last_bb (basic_block bb)
     Return a new iterator pointing to the last statement in basic block
     'BB'.

 -- GIMPLE function: bool gsi_end_p (gimple_stmt_iterator i)
     Return 'TRUE' if at the end of 'I'.

 -- GIMPLE function: bool gsi_one_before_end_p (gimple_stmt_iterator i)
     Return 'TRUE' if we're one statement before the end of 'I'.

 -- GIMPLE function: void gsi_next (gimple_stmt_iterator *i)
     Advance the iterator to the next gimple statement.

 -- GIMPLE function: void gsi_prev (gimple_stmt_iterator *i)
     Advance the iterator to the previous gimple statement.

 -- GIMPLE function: gimple gsi_stmt (gimple_stmt_iterator i)
     Return the current stmt.

 -- GIMPLE function: gimple_stmt_iterator gsi_after_labels (basic_block
          bb)
     Return a block statement iterator that points to the first
     non-label statement in block 'BB'.

 -- GIMPLE function: gimple * gsi_stmt_ptr (gimple_stmt_iterator *i)
     Return a pointer to the current stmt.

 -- GIMPLE function: basic_block gsi_bb (gimple_stmt_iterator i)
     Return the basic block associated with this iterator.

 -- GIMPLE function: gimple_seq gsi_seq (gimple_stmt_iterator i)
     Return the sequence associated with this iterator.

 -- GIMPLE function: void gsi_remove (gimple_stmt_iterator *i, bool
          remove_eh_info)
     Remove the current stmt from the sequence.  The iterator is updated
     to point to the next statement.  When 'REMOVE_EH_INFO' is true we
     remove the statement pointed to by iterator 'I' from the 'EH'
     tables.  Otherwise we do not modify the 'EH' tables.  Generally,
     'REMOVE_EH_INFO' should be true when the statement is going to be
     removed from the 'IL' and not reinserted elsewhere.

 -- GIMPLE function: void gsi_link_seq_before (gimple_stmt_iterator *i,
          gimple_seq seq, enum gsi_iterator_update mode)
     Links the sequence of statements 'SEQ' before the statement pointed
     by iterator 'I'.  'MODE' indicates what to do with the iterator
     after insertion (see 'enum gsi_iterator_update' above).

 -- GIMPLE function: void gsi_link_before (gimple_stmt_iterator *i,
          gimple g, enum gsi_iterator_update mode)
     Links statement 'G' before the statement pointed-to by iterator
     'I'.  Updates iterator 'I' according to 'MODE'.

 -- GIMPLE function: void gsi_link_seq_after (gimple_stmt_iterator *i,
          gimple_seq seq, enum gsi_iterator_update mode)
     Links sequence 'SEQ' after the statement pointed-to by iterator
     'I'.  'MODE' is as in 'gsi_insert_after'.

 -- GIMPLE function: void gsi_link_after (gimple_stmt_iterator *i,
          gimple g, enum gsi_iterator_update mode)
     Links statement 'G' after the statement pointed-to by iterator 'I'.
     'MODE' is as in 'gsi_insert_after'.

 -- GIMPLE function: gimple_seq gsi_split_seq_after
          (gimple_stmt_iterator i)
     Move all statements in the sequence after 'I' to a new sequence.
     Return this new sequence.

 -- GIMPLE function: gimple_seq gsi_split_seq_before
          (gimple_stmt_iterator *i)
     Move all statements in the sequence before 'I' to a new sequence.
     Return this new sequence.

 -- GIMPLE function: void gsi_replace (gimple_stmt_iterator *i, gimple
          stmt, bool update_eh_info)
     Replace the statement pointed-to by 'I' to 'STMT'.  If
     'UPDATE_EH_INFO' is true, the exception handling information of the
     original statement is moved to the new statement.

 -- GIMPLE function: void gsi_insert_before (gimple_stmt_iterator *i,
          gimple stmt, enum gsi_iterator_update mode)
     Insert statement 'STMT' before the statement pointed-to by iterator
     'I', update 'STMT''s basic block and scan it for new operands.
     'MODE' specifies how to update iterator 'I' after insertion (see
     enum 'gsi_iterator_update').

 -- GIMPLE function: void gsi_insert_seq_before (gimple_stmt_iterator
          *i, gimple_seq seq, enum gsi_iterator_update mode)
     Like 'gsi_insert_before', but for all the statements in 'SEQ'.

 -- GIMPLE function: void gsi_insert_after (gimple_stmt_iterator *i,
          gimple stmt, enum gsi_iterator_update mode)
     Insert statement 'STMT' after the statement pointed-to by iterator
     'I', update 'STMT''s basic block and scan it for new operands.
     'MODE' specifies how to update iterator 'I' after insertion (see
     enum 'gsi_iterator_update').

 -- GIMPLE function: void gsi_insert_seq_after (gimple_stmt_iterator *i,
          gimple_seq seq, enum gsi_iterator_update mode)
     Like 'gsi_insert_after', but for all the statements in 'SEQ'.

 -- GIMPLE function: gimple_stmt_iterator gsi_for_stmt (gimple stmt)
     Finds iterator for 'STMT'.

 -- GIMPLE function: void gsi_move_after (gimple_stmt_iterator *from,
          gimple_stmt_iterator *to)
     Move the statement at 'FROM' so it comes right after the statement
     at 'TO'.

 -- GIMPLE function: void gsi_move_before (gimple_stmt_iterator *from,
          gimple_stmt_iterator *to)
     Move the statement at 'FROM' so it comes right before the statement
     at 'TO'.

 -- GIMPLE function: void gsi_move_to_bb_end (gimple_stmt_iterator
          *from, basic_block bb)
     Move the statement at 'FROM' to the end of basic block 'BB'.

 -- GIMPLE function: void gsi_insert_on_edge (edge e, gimple stmt)
     Add 'STMT' to the pending list of edge 'E'.  No actual insertion is
     made until a call to 'gsi_commit_edge_inserts'() is made.

 -- GIMPLE function: void gsi_insert_seq_on_edge (edge e, gimple_seq
          seq)
     Add the sequence of statements in 'SEQ' to the pending list of edge
     'E'.  No actual insertion is made until a call to
     'gsi_commit_edge_inserts'() is made.

 -- GIMPLE function: basic_block gsi_insert_on_edge_immediate (edge e,
          gimple stmt)
     Similar to 'gsi_insert_on_edge'+'gsi_commit_edge_inserts'.  If a
     new block has to be created, it is returned.

 -- GIMPLE function: void gsi_commit_one_edge_insert (edge e,
          basic_block *new_bb)
     Commit insertions pending at edge 'E'.  If a new block is created,
     set 'NEW_BB' to this block, otherwise set it to 'NULL'.

 -- GIMPLE function: void gsi_commit_edge_inserts (void)
     This routine will commit all pending edge insertions, creating any
     new basic blocks which are necessary.


File: gccint.info,  Node: Adding a new GIMPLE statement code,  Next: Statement and operand traversals,  Prev: Sequence iterators,  Up: GIMPLE

12.10 Adding a new GIMPLE statement code
========================================

The first step in adding a new GIMPLE statement code, is modifying the
file 'gimple.def', which contains all the GIMPLE codes.  Then you must
add a corresponding structure, and an entry in 'union
gimple_statement_d', both of which are located in 'gimple.h'.  This in
turn, will require you to add a corresponding 'GTY' tag in
'gsstruct.def', and code to handle this tag in 'gss_for_code' which is
located in 'gimple.c'.

 In order for the garbage collector to know the size of the structure
you created in 'gimple.h', you need to add a case to handle your new
GIMPLE statement in 'gimple_size' which is located in 'gimple.c'.

 You will probably want to create a function to build the new gimple
statement in 'gimple.c'.  The function should be called
'gimple_build_NEW-TUPLE-NAME', and should return the new tuple of type
gimple.

 If your new statement requires accessors for any members or operands it
may have, put simple inline accessors in 'gimple.h' and any non-trivial
accessors in 'gimple.c' with a corresponding prototype in 'gimple.h'.


File: gccint.info,  Node: Statement and operand traversals,  Prev: Adding a new GIMPLE statement code,  Up: GIMPLE

12.11 Statement and operand traversals
======================================

There are two functions available for walking statements and sequences:
'walk_gimple_stmt' and 'walk_gimple_seq', accordingly, and a third
function for walking the operands in a statement: 'walk_gimple_op'.

 -- GIMPLE function: tree walk_gimple_stmt (gimple_stmt_iterator *gsi,
          walk_stmt_fn callback_stmt, walk_tree_fn callback_op, struct
          walk_stmt_info *wi)
     This function is used to walk the current statement in 'GSI',
     optionally using traversal state stored in 'WI'.  If 'WI' is
     'NULL', no state is kept during the traversal.

     The callback 'CALLBACK_STMT' is called.  If 'CALLBACK_STMT' returns
     true, it means that the callback function has handled all the
     operands of the statement and it is not necessary to walk its
     operands.

     If 'CALLBACK_STMT' is 'NULL' or it returns false, 'CALLBACK_OP' is
     called on each operand of the statement via 'walk_gimple_op'.  If
     'walk_gimple_op' returns non-'NULL' for any operand, the remaining
     operands are not scanned.

     The return value is that returned by the last call to
     'walk_gimple_op', or 'NULL_TREE' if no 'CALLBACK_OP' is specified.

 -- GIMPLE function: tree walk_gimple_op (gimple stmt, walk_tree_fn
          callback_op, struct walk_stmt_info *wi)
     Use this function to walk the operands of statement 'STMT'.  Every
     operand is walked via 'walk_tree' with optional state information
     in 'WI'.

     'CALLBACK_OP' is called on each operand of 'STMT' via 'walk_tree'.
     Additional parameters to 'walk_tree' must be stored in 'WI'.  For
     each operand 'OP', 'walk_tree' is called as:

          walk_tree (&OP, CALLBACK_OP, WI, PSET)

     If 'CALLBACK_OP' returns non-'NULL' for an operand, the remaining
     operands are not scanned.  The return value is that returned by the
     last call to 'walk_tree', or 'NULL_TREE' if no 'CALLBACK_OP' is
     specified.

 -- GIMPLE function: tree walk_gimple_seq (gimple_seq seq, walk_stmt_fn
          callback_stmt, walk_tree_fn callback_op, struct walk_stmt_info
          *wi)
     This function walks all the statements in the sequence 'SEQ'
     calling 'walk_gimple_stmt' on each one.  'WI' is as in
     'walk_gimple_stmt'.  If 'walk_gimple_stmt' returns non-'NULL', the
     walk is stopped and the value returned.  Otherwise, all the
     statements are walked and 'NULL_TREE' returned.


File: gccint.info,  Node: Tree SSA,  Next: Loop Analysis and Representation,  Prev: GIMPLE,  Up: Top

13 Analysis and Optimization of GIMPLE tuples
*********************************************

GCC uses three main intermediate languages to represent the program
during compilation: GENERIC, GIMPLE and RTL.  GENERIC is a
language-independent representation generated by each front end.  It is
used to serve as an interface between the parser and optimizer.  GENERIC
is a common representation that is able to represent programs written in
all the languages supported by GCC.

 GIMPLE and RTL are used to optimize the program.  GIMPLE is used for
target and language independent optimizations (e.g., inlining, constant
propagation, tail call elimination, redundancy elimination, etc).  Much
like GENERIC, GIMPLE is a language independent, tree based
representation.  However, it differs from GENERIC in that the GIMPLE
grammar is more restrictive: expressions contain no more than 3 operands
(except function calls), it has no control flow structures and
expressions with side-effects are only allowed on the right hand side of
assignments.  See the chapter describing GENERIC and GIMPLE for more
details.

 This chapter describes the data structures and functions used in the
GIMPLE optimizers (also known as "tree optimizers" or "middle end").  In
particular, it focuses on all the macros, data structures, functions and
programming constructs needed to implement optimization passes for
GIMPLE.

* Menu:

* Annotations::         Attributes for variables.
* SSA Operands::        SSA names referenced by GIMPLE statements.
* SSA::                 Static Single Assignment representation.
* Alias analysis::      Representing aliased loads and stores.
* Memory model::        Memory model used by the middle-end.


File: gccint.info,  Node: Annotations,  Next: SSA Operands,  Up: Tree SSA

13.1 Annotations
================

The optimizers need to associate attributes with variables during the
optimization process.  For instance, we need to know whether a variable
has aliases.  All these attributes are stored in data structures called
annotations which are then linked to the field 'ann' in 'struct
tree_common'.

 Presently, we define annotations for variables ('var_ann_t').
Annotations are defined and documented in 'tree-flow.h'.


File: gccint.info,  Node: SSA Operands,  Next: SSA,  Prev: Annotations,  Up: Tree SSA

13.2 SSA Operands
=================

Almost every GIMPLE statement will contain a reference to a variable or
memory location.  Since statements come in different shapes and sizes,
their operands are going to be located at various spots inside the
statement's tree.  To facilitate access to the statement's operands,
they are organized into lists associated inside each statement's
annotation.  Each element in an operand list is a pointer to a
'VAR_DECL', 'PARM_DECL' or 'SSA_NAME' tree node.  This provides a very
convenient way of examining and replacing operands.

 Data flow analysis and optimization is done on all tree nodes
representing variables.  Any node for which 'SSA_VAR_P' returns nonzero
is considered when scanning statement operands.  However, not all
'SSA_VAR_P' variables are processed in the same way.  For the purposes
of optimization, we need to distinguish between references to local
scalar variables and references to globals, statics, structures, arrays,
aliased variables, etc.  The reason is simple, the compiler can gather
complete data flow information for a local scalar.  On the other hand, a
global variable may be modified by a function call, it may not be
possible to keep track of all the elements of an array or the fields of
a structure, etc.

 The operand scanner gathers two kinds of operands: "real" and
"virtual".  An operand for which 'is_gimple_reg' returns true is
considered real, otherwise it is a virtual operand.  We also distinguish
between uses and definitions.  An operand is used if its value is loaded
by the statement (e.g., the operand at the RHS of an assignment).  If
the statement assigns a new value to the operand, the operand is
considered a definition (e.g., the operand at the LHS of an assignment).

 Virtual and real operands also have very different data flow
properties.  Real operands are unambiguous references to the full object
that they represent.  For instance, given

     {
       int a, b;
       a = b
     }

 Since 'a' and 'b' are non-aliased locals, the statement 'a = b' will
have one real definition and one real use because variable 'a' is
completely modified with the contents of variable 'b'.  Real definition
are also known as "killing definitions".  Similarly, the use of 'b'
reads all its bits.

 In contrast, virtual operands are used with variables that can have a
partial or ambiguous reference.  This includes structures, arrays,
globals, and aliased variables.  In these cases, we have two types of
definitions.  For globals, structures, and arrays, we can determine from
a statement whether a variable of these types has a killing definition.
If the variable does, then the statement is marked as having a "must
definition" of that variable.  However, if a statement is only defining
a part of the variable (i.e. a field in a structure), or if we know that
a statement might define the variable but we cannot say for sure, then
we mark that statement as having a "may definition".  For instance,
given

     {
       int a, b, *p;

       if (...)
         p = &a;
       else
         p = &b;
       *p = 5;
       return *p;
     }

 The assignment '*p = 5' may be a definition of 'a' or 'b'.  If we
cannot determine statically where 'p' is pointing to at the time of the
store operation, we create virtual definitions to mark that statement as
a potential definition site for 'a' and 'b'.  Memory loads are similarly
marked with virtual use operands.  Virtual operands are shown in tree
dumps right before the statement that contains them.  To request a tree
dump with virtual operands, use the '-vops' option to '-fdump-tree':

     {
       int a, b, *p;

       if (...)
         p = &a;
       else
         p = &b;
       # a = VDEF <a>
       # b = VDEF <b>
       *p = 5;

       # VUSE <a>
       # VUSE <b>
       return *p;
     }

 Notice that 'VDEF' operands have two copies of the referenced variable.
This indicates that this is not a killing definition of that variable.
In this case we refer to it as a "may definition" or "aliased store".
The presence of the second copy of the variable in the 'VDEF' operand
will become important when the function is converted into SSA form.
This will be used to link all the non-killing definitions to prevent
optimizations from making incorrect assumptions about them.

 Operands are updated as soon as the statement is finished via a call to
'update_stmt'.  If statement elements are changed via 'SET_USE' or
'SET_DEF', then no further action is required (i.e., those macros take
care of updating the statement).  If changes are made by manipulating
the statement's tree directly, then a call must be made to 'update_stmt'
when complete.  Calling one of the 'bsi_insert' routines or
'bsi_replace' performs an implicit call to 'update_stmt'.

13.2.1 Operand Iterators And Access Routines
--------------------------------------------

Operands are collected by 'tree-ssa-operands.c'.  They are stored inside
each statement's annotation and can be accessed through either the
operand iterators or an access routine.

 The following access routines are available for examining operands:

  1. 'SINGLE_SSA_{USE,DEF,TREE}_OPERAND': These accessors will return
     NULL unless there is exactly one operand matching the specified
     flags.  If there is exactly one operand, the operand is returned as
     either a 'tree', 'def_operand_p', or 'use_operand_p'.

          tree t = SINGLE_SSA_TREE_OPERAND (stmt, flags);
          use_operand_p u = SINGLE_SSA_USE_OPERAND (stmt, SSA_ALL_VIRTUAL_USES);
          def_operand_p d = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_ALL_DEFS);

  2. 'ZERO_SSA_OPERANDS': This macro returns true if there are no
     operands matching the specified flags.

          if (ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
            return;

  3. 'NUM_SSA_OPERANDS': This macro Returns the number of operands
     matching 'flags'.  This actually executes a loop to perform the
     count, so only use this if it is really needed.

          int count = NUM_SSA_OPERANDS (stmt, flags)

 If you wish to iterate over some or all operands, use the
'FOR_EACH_SSA_{USE,DEF,TREE}_OPERAND' iterator.  For example, to print
all the operands for a statement:

     void
     print_ops (tree stmt)
     {
       ssa_op_iter;
       tree var;

       FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_ALL_OPERANDS)
         print_generic_expr (stderr, var, TDF_SLIM);
     }

 How to choose the appropriate iterator:

  1. Determine whether you are need to see the operand pointers, or just
     the trees, and choose the appropriate macro:

          Need            Macro:
          ----            -------
          use_operand_p   FOR_EACH_SSA_USE_OPERAND
          def_operand_p   FOR_EACH_SSA_DEF_OPERAND
          tree            FOR_EACH_SSA_TREE_OPERAND

  2. You need to declare a variable of the type you are interested in,
     and an ssa_op_iter structure which serves as the loop controlling
     variable.

  3. Determine which operands you wish to use, and specify the flags of
     those you are interested in.  They are documented in
     'tree-ssa-operands.h':

          #define SSA_OP_USE              0x01    /* Real USE operands.  */
          #define SSA_OP_DEF              0x02    /* Real DEF operands.  */
          #define SSA_OP_VUSE             0x04    /* VUSE operands.  */
          #define SSA_OP_VMAYUSE          0x08    /* USE portion of VDEFS.  */
          #define SSA_OP_VDEF             0x10    /* DEF portion of VDEFS.  */

          /* These are commonly grouped operand flags.  */
          #define SSA_OP_VIRTUAL_USES     (SSA_OP_VUSE | SSA_OP_VMAYUSE)
          #define SSA_OP_VIRTUAL_DEFS     (SSA_OP_VDEF)
          #define SSA_OP_ALL_USES         (SSA_OP_VIRTUAL_USES | SSA_OP_USE)
          #define SSA_OP_ALL_DEFS         (SSA_OP_VIRTUAL_DEFS | SSA_OP_DEF)
          #define SSA_OP_ALL_OPERANDS     (SSA_OP_ALL_USES | SSA_OP_ALL_DEFS)

 So if you want to look at the use pointers for all the 'USE' and 'VUSE'
operands, you would do something like:

       use_operand_p use_p;
       ssa_op_iter iter;

       FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, (SSA_OP_USE | SSA_OP_VUSE))
         {
           process_use_ptr (use_p);
         }

 The 'TREE' macro is basically the same as the 'USE' and 'DEF' macros,
only with the use or def dereferenced via 'USE_FROM_PTR (use_p)' and
'DEF_FROM_PTR (def_p)'.  Since we aren't using operand pointers, use and
defs flags can be mixed.

       tree var;
       ssa_op_iter iter;

       FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_VUSE)
         {
            print_generic_expr (stderr, var, TDF_SLIM);
         }

 'VDEF's are broken into two flags, one for the 'DEF' portion
('SSA_OP_VDEF') and one for the USE portion ('SSA_OP_VMAYUSE').  If all
you want to look at are the 'VDEF's together, there is a fourth iterator
macro for this, which returns both a def_operand_p and a use_operand_p
for each 'VDEF' in the statement.  Note that you don't need any flags
for this one.

       use_operand_p use_p;
       def_operand_p def_p;
       ssa_op_iter iter;

       FOR_EACH_SSA_MAYDEF_OPERAND (def_p, use_p, stmt, iter)
         {
           my_code;
         }

 There are many examples in the code as well, as well as the
documentation in 'tree-ssa-operands.h'.

 There are also a couple of variants on the stmt iterators regarding PHI
nodes.

 'FOR_EACH_PHI_ARG' Works exactly like 'FOR_EACH_SSA_USE_OPERAND',
except it works over 'PHI' arguments instead of statement operands.

     /* Look at every virtual PHI use.  */
     FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_VIRTUAL_USES)
     {
        my_code;
     }

     /* Look at every real PHI use.  */
     FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_USES)
       my_code;

     /* Look at every PHI use.  */
     FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_ALL_USES)
       my_code;

 'FOR_EACH_PHI_OR_STMT_{USE,DEF}' works exactly like
'FOR_EACH_SSA_{USE,DEF}_OPERAND', except it will function on either a
statement or a 'PHI' node.  These should be used when it is appropriate
but they are not quite as efficient as the individual 'FOR_EACH_PHI' and
'FOR_EACH_SSA' routines.

     FOR_EACH_PHI_OR_STMT_USE (use_operand_p, stmt, iter, flags)
       {
          my_code;
       }

     FOR_EACH_PHI_OR_STMT_DEF (def_operand_p, phi, iter, flags)
       {
          my_code;
       }

13.2.2 Immediate Uses
---------------------

Immediate use information is now always available.  Using the immediate
use iterators, you may examine every use of any 'SSA_NAME'.  For
instance, to change each use of 'ssa_var' to 'ssa_var2' and call
fold_stmt on each stmt after that is done:

       use_operand_p imm_use_p;
       imm_use_iterator iterator;
       tree ssa_var, stmt;


       FOR_EACH_IMM_USE_STMT (stmt, iterator, ssa_var)
         {
           FOR_EACH_IMM_USE_ON_STMT (imm_use_p, iterator)
             SET_USE (imm_use_p, ssa_var_2);
           fold_stmt (stmt);
         }

 There are 2 iterators which can be used.  'FOR_EACH_IMM_USE_FAST' is
used when the immediate uses are not changed, i.e., you are looking at
the uses, but not setting them.

 If they do get changed, then care must be taken that things are not
changed under the iterators, so use the 'FOR_EACH_IMM_USE_STMT' and
'FOR_EACH_IMM_USE_ON_STMT' iterators.  They attempt to preserve the
sanity of the use list by moving all the uses for a statement into a
controlled position, and then iterating over those uses.  Then the
optimization can manipulate the stmt when all the uses have been
processed.  This is a little slower than the FAST version since it adds
a placeholder element and must sort through the list a bit for each
statement.  This placeholder element must be also be removed if the loop
is terminated early.  The macro 'BREAK_FROM_IMM_USE_SAFE' is provided to
do this :

       FOR_EACH_IMM_USE_STMT (stmt, iterator, ssa_var)
         {
           if (stmt == last_stmt)
             BREAK_FROM_SAFE_IMM_USE (iter);

           FOR_EACH_IMM_USE_ON_STMT (imm_use_p, iterator)
             SET_USE (imm_use_p, ssa_var_2);
           fold_stmt (stmt);
         }

 There are checks in 'verify_ssa' which verify that the immediate use
list is up to date, as well as checking that an optimization didn't
break from the loop without using this macro.  It is safe to simply
'break'; from a 'FOR_EACH_IMM_USE_FAST' traverse.

 Some useful functions and macros:
  1. 'has_zero_uses (ssa_var)' : Returns true if there are no uses of
     'ssa_var'.
  2. 'has_single_use (ssa_var)' : Returns true if there is only a single
     use of 'ssa_var'.
  3. 'single_imm_use (ssa_var, use_operand_p *ptr, tree *stmt)' :
     Returns true if there is only a single use of 'ssa_var', and also
     returns the use pointer and statement it occurs in, in the second
     and third parameters.
  4. 'num_imm_uses (ssa_var)' : Returns the number of immediate uses of
     'ssa_var'.  It is better not to use this if possible since it
     simply utilizes a loop to count the uses.
  5. 'PHI_ARG_INDEX_FROM_USE (use_p)' : Given a use within a 'PHI' node,
     return the index number for the use.  An assert is triggered if the
     use isn't located in a 'PHI' node.
  6. 'USE_STMT (use_p)' : Return the statement a use occurs in.

 Note that uses are not put into an immediate use list until their
statement is actually inserted into the instruction stream via a 'bsi_*'
routine.

 It is also still possible to utilize lazy updating of statements, but
this should be used only when absolutely required.  Both alias analysis
and the dominator optimizations currently do this.

 When lazy updating is being used, the immediate use information is out
of date and cannot be used reliably.  Lazy updating is achieved by
simply marking statements modified via calls to 'mark_stmt_modified'
instead of 'update_stmt'.  When lazy updating is no longer required, all
the modified statements must have 'update_stmt' called in order to bring
them up to date.  This must be done before the optimization is finished,
or 'verify_ssa' will trigger an abort.

 This is done with a simple loop over the instruction stream:
       block_stmt_iterator bsi;
       basic_block bb;
       FOR_EACH_BB (bb)
         {
           for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
             update_stmt_if_modified (bsi_stmt (bsi));
         }


File: gccint.info,  Node: SSA,  Next: Alias analysis,  Prev: SSA Operands,  Up: Tree SSA

13.3 Static Single Assignment
=============================

Most of the tree optimizers rely on the data flow information provided
by the Static Single Assignment (SSA) form.  We implement the SSA form
as described in 'R. Cytron, J. Ferrante, B. Rosen, M. Wegman, and K.
Zadeck. Efficiently Computing Static Single Assignment Form and the
Control Dependence Graph. ACM Transactions on Programming Languages and
Systems, 13(4):451-490, October 1991'.

 The SSA form is based on the premise that program variables are
assigned in exactly one location in the program.  Multiple assignments
to the same variable create new versions of that variable.  Naturally,
actual programs are seldom in SSA form initially because variables tend
to be assigned multiple times.  The compiler modifies the program
representation so that every time a variable is assigned in the code, a
new version of the variable is created.  Different versions of the same
variable are distinguished by subscripting the variable name with its
version number.  Variables used in the right-hand side of expressions
are renamed so that their version number matches that of the most recent
assignment.

 We represent variable versions using 'SSA_NAME' nodes.  The renaming
process in 'tree-ssa.c' wraps every real and virtual operand with an
'SSA_NAME' node which contains the version number and the statement that
created the 'SSA_NAME'.  Only definitions and virtual definitions may
create new 'SSA_NAME' nodes.

 Sometimes, flow of control makes it impossible to determine the most
recent version of a variable.  In these cases, the compiler inserts an
artificial definition for that variable called "PHI function" or "PHI
node".  This new definition merges all the incoming versions of the
variable to create a new name for it.  For instance,

     if (...)
       a_1 = 5;
     else if (...)
       a_2 = 2;
     else
       a_3 = 13;

     # a_4 = PHI <a_1, a_2, a_3>
     return a_4;

 Since it is not possible to determine which of the three branches will
be taken at runtime, we don't know which of 'a_1', 'a_2' or 'a_3' to use
at the return statement.  So, the SSA renamer creates a new version
'a_4' which is assigned the result of "merging" 'a_1', 'a_2' and 'a_3'.
Hence, PHI nodes mean "one of these operands.  I don't know which".

 The following macros can be used to examine PHI nodes

 -- Macro: PHI_RESULT (PHI)
     Returns the 'SSA_NAME' created by PHI node PHI (i.e., PHI's LHS).

 -- Macro: PHI_NUM_ARGS (PHI)
     Returns the number of arguments in PHI.  This number is exactly the
     number of incoming edges to the basic block holding PHI.

 -- Macro: PHI_ARG_ELT (PHI, I)
     Returns a tuple representing the Ith argument of PHI.  Each element
     of this tuple contains an 'SSA_NAME' VAR and the incoming edge
     through which VAR flows.

 -- Macro: PHI_ARG_EDGE (PHI, I)
     Returns the incoming edge for the Ith argument of PHI.

 -- Macro: PHI_ARG_DEF (PHI, I)
     Returns the 'SSA_NAME' for the Ith argument of PHI.

13.3.1 Preserving the SSA form
------------------------------

Some optimization passes make changes to the function that invalidate
the SSA property.  This can happen when a pass has added new symbols or
changed the program so that variables that were previously aliased
aren't anymore.  Whenever something like this happens, the affected
symbols must be renamed into SSA form again.  Transformations that emit
new code or replicate existing statements will also need to update the
SSA form.

 Since GCC implements two different SSA forms for register and virtual
variables, keeping the SSA form up to date depends on whether you are
updating register or virtual names.  In both cases, the general idea
behind incremental SSA updates is similar: when new SSA names are
created, they typically are meant to replace other existing names in the
program.

 For instance, given the following code:

          1  L0:
          2  x_1 = PHI (0, x_5)
          3  if (x_1 < 10)
          4    if (x_1 > 7)
          5      y_2 = 0
          6    else
          7      y_3 = x_1 + x_7
          8    endif
          9    x_5 = x_1 + 1
          10   goto L0;
          11 endif

 Suppose that we insert new names 'x_10' and 'x_11' (lines '4' and '8').

          1  L0:
          2  x_1 = PHI (0, x_5)
          3  if (x_1 < 10)
          4    x_10 = ...
          5    if (x_1 > 7)
          6      y_2 = 0
          7    else
          8      x_11 = ...
          9      y_3 = x_1 + x_7
          10   endif
          11   x_5 = x_1 + 1
          12   goto L0;
          13 endif

 We want to replace all the uses of 'x_1' with the new definitions of
'x_10' and 'x_11'.  Note that the only uses that should be replaced are
those at lines '5', '9' and '11'.  Also, the use of 'x_7' at line '9'
should _not_ be replaced (this is why we cannot just mark symbol 'x' for
renaming).

 Additionally, we may need to insert a PHI node at line '11' because
that is a merge point for 'x_10' and 'x_11'.  So the use of 'x_1' at
line '11' will be replaced with the new PHI node.  The insertion of PHI
nodes is optional.  They are not strictly necessary to preserve the SSA
form, and depending on what the caller inserted, they may not even be
useful for the optimizers.

 Updating the SSA form is a two step process.  First, the pass has to
identify which names need to be updated and/or which symbols need to be
renamed into SSA form for the first time.  When new names are introduced
to replace existing names in the program, the mapping between the old
and the new names are registered by calling 'register_new_name_mapping'
(note that if your pass creates new code by duplicating basic blocks,
the call to 'tree_duplicate_bb' will set up the necessary mappings
automatically).

 After the replacement mappings have been registered and new symbols
marked for renaming, a call to 'update_ssa' makes the registered
changes.  This can be done with an explicit call or by creating 'TODO'
flags in the 'tree_opt_pass' structure for your pass.  There are several
'TODO' flags that control the behavior of 'update_ssa':

   * 'TODO_update_ssa'.  Update the SSA form inserting PHI nodes for
     newly exposed symbols and virtual names marked for updating.  When
     updating real names, only insert PHI nodes for a real name 'O_j' in
     blocks reached by all the new and old definitions for 'O_j'.  If
     the iterated dominance frontier for 'O_j' is not pruned, we may end
     up inserting PHI nodes in blocks that have one or more edges with
     no incoming definition for 'O_j'.  This would lead to uninitialized
     warnings for 'O_j''s symbol.

   * 'TODO_update_ssa_no_phi'.  Update the SSA form without inserting
     any new PHI nodes at all.  This is used by passes that have either
     inserted all the PHI nodes themselves or passes that need only to
     patch use-def and def-def chains for virtuals (e.g., DCE).

   * 'TODO_update_ssa_full_phi'.  Insert PHI nodes everywhere they are
     needed.  No pruning of the IDF is done.  This is used by passes
     that need the PHI nodes for 'O_j' even if it means that some
     arguments will come from the default definition of 'O_j''s symbol
     (e.g., 'pass_linear_transform').

     WARNING: If you need to use this flag, chances are that your pass
     may be doing something wrong.  Inserting PHI nodes for an old name
     where not all edges carry a new replacement may lead to silent
     codegen errors or spurious uninitialized warnings.

   * 'TODO_update_ssa_only_virtuals'.  Passes that update the SSA form
     on their own may want to delegate the updating of virtual names to
     the generic updater.  Since FUD chains are easier to maintain, this
     simplifies the work they need to do.  NOTE: If this flag is used,
     any OLD->NEW mappings for real names are explicitly destroyed and
     only the symbols marked for renaming are processed.

13.3.2 Preserving the virtual SSA form
--------------------------------------

The virtual SSA form is harder to preserve than the non-virtual SSA form
mainly because the set of virtual operands for a statement may change at
what some would consider unexpected times.  In general, statement
modifications should be bracketed between calls to 'push_stmt_changes'
and 'pop_stmt_changes'.  For example,

         munge_stmt (tree stmt)
         {
            push_stmt_changes (&stmt);
            ... rewrite STMT ...
            pop_stmt_changes (&stmt);
         }

 The call to 'push_stmt_changes' saves the current state of the
statement operands and the call to 'pop_stmt_changes' compares the saved
state with the current one and does the appropriate symbol marking for
the SSA renamer.

 It is possible to modify several statements at a time, provided that
'push_stmt_changes' and 'pop_stmt_changes' are called in LIFO order, as
when processing a stack of statements.

 Additionally, if the pass discovers that it did not need to make
changes to the statement after calling 'push_stmt_changes', it can
simply discard the topmost change buffer by calling
'discard_stmt_changes'.  This will avoid the expensive operand re-scan
operation and the buffer comparison that determines if symbols need to
be marked for renaming.

13.3.3 Examining 'SSA_NAME' nodes
---------------------------------

The following macros can be used to examine 'SSA_NAME' nodes

 -- Macro: SSA_NAME_DEF_STMT (VAR)
     Returns the statement S that creates the 'SSA_NAME' VAR.  If S is
     an empty statement (i.e., 'IS_EMPTY_STMT (S)' returns 'true'), it
     means that the first reference to this variable is a USE or a VUSE.

 -- Macro: SSA_NAME_VERSION (VAR)
     Returns the version number of the 'SSA_NAME' object VAR.

13.3.4 Walking use-def chains
-----------------------------

 -- Tree SSA function: void walk_use_def_chains (VAR, FN, DATA)

     Walks use-def chains starting at the 'SSA_NAME' node VAR.  Calls
     function FN at each reaching definition found.  Function FN takes
     three arguments: VAR, its defining statement (DEF_STMT) and a
     generic pointer to whatever state information that FN may want to
     maintain (DATA).  Function FN is able to stop the walk by returning
     'true', otherwise in order to continue the walk, FN should return
     'false'.

     Note, that if DEF_STMT is a 'PHI' node, the semantics are slightly
     different.  For each argument ARG of the PHI node, this function
     will:

       1. Walk the use-def chains for ARG.
       2. Call 'FN (ARG, PHI, DATA)'.

     Note how the first argument to FN is no longer the original
     variable VAR, but the PHI argument currently being examined.  If FN
     wants to get at VAR, it should call 'PHI_RESULT' (PHI).

13.3.5 Walking the dominator tree
---------------------------------

 -- Tree SSA function: void walk_dominator_tree (WALK_DATA, BB)

     This function walks the dominator tree for the current CFG calling
     a set of callback functions defined in STRUCT DOM_WALK_DATA in
     'domwalk.h'.  The call back functions you need to define give you
     hooks to execute custom code at various points during traversal:

       1. Once to initialize any local data needed while processing BB
          and its children.  This local data is pushed into an internal
          stack which is automatically pushed and popped as the walker
          traverses the dominator tree.

       2. Once before traversing all the statements in the BB.

       3. Once for every statement inside BB.

       4. Once after traversing all the statements and before recursing
          into BB's dominator children.

       5. It then recurses into all the dominator children of BB.

       6. After recursing into all the dominator children of BB it can,
          optionally, traverse every statement in BB again (i.e.,
          repeating steps 2 and 3).

       7. Once after walking the statements in BB and BB's dominator
          children.  At this stage, the block local data stack is
          popped.


File: gccint.info,  Node: Alias analysis,  Next: Memory model,  Prev: SSA,  Up: Tree SSA

13.4 Alias analysis
===================

Alias analysis in GIMPLE SSA form consists of two pieces.  First the
virtual SSA web ties conflicting memory accesses and provides a SSA
use-def chain and SSA immediate-use chains for walking possibly
dependent memory accesses.  Second an alias-oracle can be queried to
disambiguate explicit and implicit memory references.

  1. Memory SSA form.

     All statements that may use memory have exactly one accompanied use
     of a virtual SSA name that represents the state of memory at the
     given point in the IL.

     All statements that may define memory have exactly one accompanied
     definition of a virtual SSA name using the previous state of memory
     and defining the new state of memory after the given point in the
     IL.

          int i;
          int foo (void)
          {
            # .MEM_3 = VDEF <.MEM_2(D)>
            i = 1;
            # VUSE <.MEM_3>
            return i;
          }

     The virtual SSA names in this case are '.MEM_2(D)' and '.MEM_3'.
     The store to the global variable 'i' defines '.MEM_3' invalidating
     '.MEM_2(D)'.  The load from 'i' uses that new state '.MEM_3'.

     The virtual SSA web serves as constraints to SSA optimizers
     preventing illegitimate code-motion and optimization.  It also
     provides a way to walk related memory statements.

  2. Points-to and escape analysis.

     Points-to analysis builds a set of constraints from the GIMPLE SSA
     IL representing all pointer operations and facts we do or do not
     know about pointers.  Solving this set of constraints yields a
     conservatively correct solution for each pointer variable in the
     program (though we are only interested in SSA name pointers) as to
     what it may possibly point to.

     This points-to solution for a given SSA name pointer is stored in
     the 'pt_solution' sub-structure of the 'SSA_NAME_PTR_INFO' record.
     The following accessor functions are available:

        * 'pt_solution_includes'
        * 'pt_solutions_intersect'

     Points-to analysis also computes the solution for two special set
     of pointers, 'ESCAPED' and 'CALLUSED'.  Those represent all memory
     that has escaped the scope of analysis or that is used by pure or
     nested const calls.

  3. Type-based alias analysis

     Type-based alias analysis is frontend dependent though generic
     support is provided by the middle-end in 'alias.c'.  TBAA code is
     used by both tree optimizers and RTL optimizers.

     Every language that wishes to perform language-specific alias
     analysis should define a function that computes, given a 'tree'
     node, an alias set for the node.  Nodes in different alias sets are
     not allowed to alias.  For an example, see the C front-end function
     'c_get_alias_set'.

  4. Tree alias-oracle

     The tree alias-oracle provides means to disambiguate two memory
     references and memory references against statements.  The following
     queries are available:

        * 'refs_may_alias_p'
        * 'ref_maybe_used_by_stmt_p'
        * 'stmt_may_clobber_ref_p'

     In addition to those two kind of statement walkers are available
     walking statements related to a reference ref.
     'walk_non_aliased_vuses' walks over dominating memory defining
     statements and calls back if the statement does not clobber ref
     providing the non-aliased VUSE. The walk stops at the first
     clobbering statement or if asked to.  'walk_aliased_vdefs' walks
     over dominating memory defining statements and calls back on each
     statement clobbering ref providing its aliasing VDEF. The walk
     stops if asked to.


File: gccint.info,  Node: Memory model,  Prev: Alias analysis,  Up: Tree SSA

13.5 Memory model
=================

The memory model used by the middle-end models that of the C/C++
languages.  The middle-end has the notion of an effective type of a
memory region which is used for type-based alias analysis.

 The following is a refinement of ISO C99 6.5/6, clarifying the block
copy case to follow common sense and extending the concept of a dynamic
effective type to objects with a declared type as required for C++.

     The effective type of an object for an access to its stored value is
     the declared type of the object or the effective type determined by
     a previous store to it.  If a value is stored into an object through
     an lvalue having a type that is not a character type, then the
     type of the lvalue becomes the effective type of the object for that
     access and for subsequent accesses that do not modify the stored value.
     If a value is copied into an object using memcpy or memmove,
     or is copied as an array of character type, then the effective type
     of the modified object for that access and for subsequent accesses that
     do not modify the value is undetermined.  For all other accesses to an
     object, the effective type of the object is simply the type of the
     lvalue used for the access.


File: gccint.info,  Node: Loop Analysis and Representation,  Next: Control Flow,  Prev: Tree SSA,  Up: Top

14 Analysis and Representation of Loops
***************************************

GCC provides extensive infrastructure for work with natural loops, i.e.,
strongly connected components of CFG with only one entry block.  This
chapter describes representation of loops in GCC, both on GIMPLE and in
RTL, as well as the interfaces to loop-related analyses (induction
variable analysis and number of iterations analysis).

* Menu:

* Loop representation::         Representation and analysis of loops.
* Loop querying::               Getting information about loops.
* Loop manipulation::           Loop manipulation functions.
* LCSSA::                       Loop-closed SSA form.
* Scalar evolutions::           Induction variables on GIMPLE.
* loop-iv::                     Induction variables on RTL.
* Number of iterations::        Number of iterations analysis.
* Dependency analysis::         Data dependency analysis.
* Lambda::                      Linear loop transformations framework.
* Omega::                       A solver for linear programming problems.


File: gccint.info,  Node: Loop representation,  Next: Loop querying,  Up: Loop Analysis and Representation

14.1 Loop representation
========================

This chapter describes the representation of loops in GCC, and functions
that can be used to build, modify and analyze this representation.  Most
of the interfaces and data structures are declared in 'cfgloop.h'.  At
the moment, loop structures are analyzed and this information is updated
only by the optimization passes that deal with loops, but some efforts
are being made to make it available throughout most of the optimization
passes.

 In general, a natural loop has one entry block (header) and possibly
several back edges (latches) leading to the header from the inside of
the loop.  Loops with several latches may appear if several loops share
a single header, or if there is a branching in the middle of the loop.
The representation of loops in GCC however allows only loops with a
single latch.  During loop analysis, headers of such loops are split and
forwarder blocks are created in order to disambiguate their structures.
Heuristic based on profile information and structure of the induction
variables in the loops is used to determine whether the latches
correspond to sub-loops or to control flow in a single loop.  This means
that the analysis sometimes changes the CFG, and if you run it in the
middle of an optimization pass, you must be able to deal with the new
blocks.  You may avoid CFG changes by passing
'LOOPS_MAY_HAVE_MULTIPLE_LATCHES' flag to the loop discovery, note
however that most other loop manipulation functions will not work
correctly for loops with multiple latch edges (the functions that only
query membership of blocks to loops and subloop relationships, or
enumerate and test loop exits, can be expected to work).

 Body of the loop is the set of blocks that are dominated by its header,
and reachable from its latch against the direction of edges in CFG.  The
loops are organized in a containment hierarchy (tree) such that all the
loops immediately contained inside loop L are the children of L in the
tree.  This tree is represented by the 'struct loops' structure.  The
root of this tree is a fake loop that contains all blocks in the
function.  Each of the loops is represented in a 'struct loop'
structure.  Each loop is assigned an index ('num' field of the 'struct
loop' structure), and the pointer to the loop is stored in the
corresponding field of the 'larray' vector in the loops structure.  The
indices do not have to be continuous, there may be empty ('NULL')
entries in the 'larray' created by deleting loops.  Also, there is no
guarantee on the relative order of a loop and its subloops in the
numbering.  The index of a loop never changes.

 The entries of the 'larray' field should not be accessed directly.  The
function 'get_loop' returns the loop description for a loop with the
given index.  'number_of_loops' function returns number of loops in the
function.  To traverse all loops, use 'FOR_EACH_LOOP' macro.  The
'flags' argument of the macro is used to determine the direction of
traversal and the set of loops visited.  Each loop is guaranteed to be
visited exactly once, regardless of the changes to the loop tree, and
the loops may be removed during the traversal.  The newly created loops
are never traversed, if they need to be visited, this must be done
separately after their creation.  The 'FOR_EACH_LOOP' macro allocates
temporary variables.  If the 'FOR_EACH_LOOP' loop were ended using break
or goto, they would not be released; 'FOR_EACH_LOOP_BREAK' macro must be
used instead.

 Each basic block contains the reference to the innermost loop it
belongs to ('loop_father').  For this reason, it is only possible to
have one 'struct loops' structure initialized at the same time for each
CFG.  The global variable 'current_loops' contains the 'struct loops'
structure.  Many of the loop manipulation functions assume that
dominance information is up-to-date.

 The loops are analyzed through 'loop_optimizer_init' function.  The
argument of this function is a set of flags represented in an integer
bitmask.  These flags specify what other properties of the loop
structures should be calculated/enforced and preserved later:

   * 'LOOPS_MAY_HAVE_MULTIPLE_LATCHES': If this flag is set, no changes
     to CFG will be performed in the loop analysis, in particular, loops
     with multiple latch edges will not be disambiguated.  If a loop has
     multiple latches, its latch block is set to NULL.  Most of the loop
     manipulation functions will not work for loops in this shape.  No
     other flags that require CFG changes can be passed to
     loop_optimizer_init.
   * 'LOOPS_HAVE_PREHEADERS': Forwarder blocks are created in such a way
     that each loop has only one entry edge, and additionally, the
     source block of this entry edge has only one successor.  This
     creates a natural place where the code can be moved out of the
     loop, and ensures that the entry edge of the loop leads from its
     immediate super-loop.
   * 'LOOPS_HAVE_SIMPLE_LATCHES': Forwarder blocks are created to force
     the latch block of each loop to have only one successor.  This
     ensures that the latch of the loop does not belong to any of its
     sub-loops, and makes manipulation with the loops significantly
     easier.  Most of the loop manipulation functions assume that the
     loops are in this shape.  Note that with this flag, the "normal"
     loop without any control flow inside and with one exit consists of
     two basic blocks.
   * 'LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS': Basic blocks and edges in
     the strongly connected components that are not natural loops (have
     more than one entry block) are marked with 'BB_IRREDUCIBLE_LOOP'
     and 'EDGE_IRREDUCIBLE_LOOP' flags.  The flag is not set for blocks
     and edges that belong to natural loops that are in such an
     irreducible region (but it is set for the entry and exit edges of
     such a loop, if they lead to/from this region).
   * 'LOOPS_HAVE_RECORDED_EXITS': The lists of exits are recorded and
     updated for each loop.  This makes some functions (e.g.,
     'get_loop_exit_edges') more efficient.  Some functions (e.g.,
     'single_exit') can be used only if the lists of exits are recorded.

 These properties may also be computed/enforced later, using functions
'create_preheaders', 'force_single_succ_latches',
'mark_irreducible_loops' and 'record_loop_exits'.

 The memory occupied by the loops structures should be freed with
'loop_optimizer_finalize' function.

 The CFG manipulation functions in general do not update loop
structures.  Specialized versions that additionally do so are provided
for the most common tasks.  On GIMPLE, 'cleanup_tree_cfg_loop' function
can be used to cleanup CFG while updating the loops structures if
'current_loops' is set.


File: gccint.info,  Node: Loop querying,  Next: Loop manipulation,  Prev: Loop representation,  Up: Loop Analysis and Representation

14.2 Loop querying
==================

The functions to query the information about loops are declared in
'cfgloop.h'.  Some of the information can be taken directly from the
structures.  'loop_father' field of each basic block contains the
innermost loop to that the block belongs.  The most useful fields of
loop structure (that are kept up-to-date at all times) are:

   * 'header', 'latch': Header and latch basic blocks of the loop.
   * 'num_nodes': Number of basic blocks in the loop (including the
     basic blocks of the sub-loops).
   * 'depth': The depth of the loop in the loops tree, i.e., the number
     of super-loops of the loop.
   * 'outer', 'inner', 'next': The super-loop, the first sub-loop, and
     the sibling of the loop in the loops tree.

 There are other fields in the loop structures, many of them used only
by some of the passes, or not updated during CFG changes; in general,
they should not be accessed directly.

 The most important functions to query loop structures are:

   * 'flow_loops_dump': Dumps the information about loops to a file.
   * 'verify_loop_structure': Checks consistency of the loop structures.
   * 'loop_latch_edge': Returns the latch edge of a loop.
   * 'loop_preheader_edge': If loops have preheaders, returns the
     preheader edge of a loop.
   * 'flow_loop_nested_p': Tests whether loop is a sub-loop of another
     loop.
   * 'flow_bb_inside_loop_p': Tests whether a basic block belongs to a
     loop (including its sub-loops).
   * 'find_common_loop': Finds the common super-loop of two loops.
   * 'superloop_at_depth': Returns the super-loop of a loop with the
     given depth.
   * 'tree_num_loop_insns', 'num_loop_insns': Estimates the number of
     insns in the loop, on GIMPLE and on RTL.
   * 'loop_exit_edge_p': Tests whether edge is an exit from a loop.
   * 'mark_loop_exit_edges': Marks all exit edges of all loops with
     'EDGE_LOOP_EXIT' flag.
   * 'get_loop_body', 'get_loop_body_in_dom_order',
     'get_loop_body_in_bfs_order': Enumerates the basic blocks in the
     loop in depth-first search order in reversed CFG, ordered by
     dominance relation, and breath-first search order, respectively.
   * 'single_exit': Returns the single exit edge of the loop, or 'NULL'
     if the loop has more than one exit.  You can only use this function
     if LOOPS_HAVE_MARKED_SINGLE_EXITS property is used.
   * 'get_loop_exit_edges': Enumerates the exit edges of a loop.
   * 'just_once_each_iteration_p': Returns true if the basic block is
     executed exactly once during each iteration of a loop (that is, it
     does not belong to a sub-loop, and it dominates the latch of the
     loop).


File: gccint.info,  Node: Loop manipulation,  Next: LCSSA,  Prev: Loop querying,  Up: Loop Analysis and Representation

14.3 Loop manipulation
======================

The loops tree can be manipulated using the following functions:

   * 'flow_loop_tree_node_add': Adds a node to the tree.
   * 'flow_loop_tree_node_remove': Removes a node from the tree.
   * 'add_bb_to_loop': Adds a basic block to a loop.
   * 'remove_bb_from_loops': Removes a basic block from loops.

 Most low-level CFG functions update loops automatically.  The following
functions handle some more complicated cases of CFG manipulations:

   * 'remove_path': Removes an edge and all blocks it dominates.
   * 'split_loop_exit_edge': Splits exit edge of the loop, ensuring that
     PHI node arguments remain in the loop (this ensures that
     loop-closed SSA form is preserved).  Only useful on GIMPLE.

 Finally, there are some higher-level loop transformations implemented.
While some of them are written so that they should work on non-innermost
loops, they are mostly untested in that case, and at the moment, they
are only reliable for the innermost loops:

   * 'create_iv': Creates a new induction variable.  Only works on
     GIMPLE.  'standard_iv_increment_position' can be used to find a
     suitable place for the iv increment.
   * 'duplicate_loop_to_header_edge',
     'tree_duplicate_loop_to_header_edge': These functions (on RTL and
     on GIMPLE) duplicate the body of the loop prescribed number of
     times on one of the edges entering loop header, thus performing
     either loop unrolling or loop peeling.  'can_duplicate_loop_p'
     ('can_unroll_loop_p' on GIMPLE) must be true for the duplicated
     loop.
   * 'loop_version', 'tree_ssa_loop_version': These function create a
     copy of a loop, and a branch before them that selects one of them
     depending on the prescribed condition.  This is useful for
     optimizations that need to verify some assumptions in runtime (one
     of the copies of the loop is usually left unchanged, while the
     other one is transformed in some way).
   * 'tree_unroll_loop': Unrolls the loop, including peeling the extra
     iterations to make the number of iterations divisible by unroll
     factor, updating the exit condition, and removing the exits that
     now cannot be taken.  Works only on GIMPLE.


File: gccint.info,  Node: LCSSA,  Next: Scalar evolutions,  Prev: Loop manipulation,  Up: Loop Analysis and Representation

14.4 Loop-closed SSA form
=========================

Throughout the loop optimizations on tree level, one extra condition is
enforced on the SSA form: No SSA name is used outside of the loop in
that it is defined.  The SSA form satisfying this condition is called
"loop-closed SSA form" - LCSSA.  To enforce LCSSA, PHI nodes must be
created at the exits of the loops for the SSA names that are used
outside of them.  Only the real operands (not virtual SSA names) are
held in LCSSA, in order to save memory.

 There are various benefits of LCSSA:

   * Many optimizations (value range analysis, final value replacement)
     are interested in the values that are defined in the loop and used
     outside of it, i.e., exactly those for that we create new PHI
     nodes.
   * In induction variable analysis, it is not necessary to specify the
     loop in that the analysis should be performed - the scalar
     evolution analysis always returns the results with respect to the
     loop in that the SSA name is defined.
   * It makes updating of SSA form during loop transformations simpler.
     Without LCSSA, operations like loop unrolling may force creation of
     PHI nodes arbitrarily far from the loop, while in LCSSA, the SSA
     form can be updated locally.  However, since we only keep real
     operands in LCSSA, we cannot use this advantage (we could have
     local updating of real operands, but it is not much more efficient
     than to use generic SSA form updating for it as well; the amount of
     changes to SSA is the same).

 However, it also means LCSSA must be updated.  This is usually
straightforward, unless you create a new value in loop and use it
outside, or unless you manipulate loop exit edges (functions are
provided to make these manipulations simple).
'rewrite_into_loop_closed_ssa' is used to rewrite SSA form to LCSSA, and
'verify_loop_closed_ssa' to check that the invariant of LCSSA is
preserved.


File: gccint.info,  Node: Scalar evolutions,  Next: loop-iv,  Prev: LCSSA,  Up: Loop Analysis and Representation

14.5 Scalar evolutions
======================

Scalar evolutions (SCEV) are used to represent results of induction
variable analysis on GIMPLE.  They enable us to represent variables with
complicated behavior in a simple and consistent way (we only use it to
express values of polynomial induction variables, but it is possible to
extend it).  The interfaces to SCEV analysis are declared in
'tree-scalar-evolution.h'.  To use scalar evolutions analysis,
'scev_initialize' must be used.  To stop using SCEV, 'scev_finalize'
should be used.  SCEV analysis caches results in order to save time and
memory.  This cache however is made invalid by most of the loop
transformations, including removal of code.  If such a transformation is
performed, 'scev_reset' must be called to clean the caches.

 Given an SSA name, its behavior in loops can be analyzed using the
'analyze_scalar_evolution' function.  The returned SCEV however does not
have to be fully analyzed and it may contain references to other SSA
names defined in the loop.  To resolve these (potentially recursive)
references, 'instantiate_parameters' or 'resolve_mixers' functions must
be used.  'instantiate_parameters' is useful when you use the results of
SCEV only for some analysis, and when you work with whole nest of loops
at once.  It will try replacing all SSA names by their SCEV in all
loops, including the super-loops of the current loop, thus providing a
complete information about the behavior of the variable in the loop
nest.  'resolve_mixers' is useful if you work with only one loop at a
time, and if you possibly need to create code based on the value of the
induction variable.  It will only resolve the SSA names defined in the
current loop, leaving the SSA names defined outside unchanged, even if
their evolution in the outer loops is known.

 The SCEV is a normal tree expression, except for the fact that it may
contain several special tree nodes.  One of them is 'SCEV_NOT_KNOWN',
used for SSA names whose value cannot be expressed.  The other one is
'POLYNOMIAL_CHREC'.  Polynomial chrec has three arguments - base, step
and loop (both base and step may contain further polynomial chrecs).
Type of the expression and of base and step must be the same.  A
variable has evolution 'POLYNOMIAL_CHREC(base, step, loop)' if it is (in
the specified loop) equivalent to 'x_1' in the following example

     while (...)
       {
         x_1 = phi (base, x_2);
         x_2 = x_1 + step;
       }

 Note that this includes the language restrictions on the operations.
For example, if we compile C code and 'x' has signed type, then the
overflow in addition would cause undefined behavior, and we may assume
that this does not happen.  Hence, the value with this SCEV cannot
overflow (which restricts the number of iterations of such a loop).

 In many cases, one wants to restrict the attention just to affine
induction variables.  In this case, the extra expressive power of SCEV
is not useful, and may complicate the optimizations.  In this case,
'simple_iv' function may be used to analyze a value - the result is a
loop-invariant base and step.


File: gccint.info,  Node: loop-iv,  Next: Number of iterations,  Prev: Scalar evolutions,  Up: Loop Analysis and Representation

14.6 IV analysis on RTL
=======================

The induction variable on RTL is simple and only allows analysis of
affine induction variables, and only in one loop at once.  The interface
is declared in 'cfgloop.h'.  Before analyzing induction variables in a
loop L, 'iv_analysis_loop_init' function must be called on L. After the
analysis (possibly calling 'iv_analysis_loop_init' for several loops) is
finished, 'iv_analysis_done' should be called.  The following functions
can be used to access the results of the analysis:

   * 'iv_analyze': Analyzes a single register used in the given insn.
     If no use of the register in this insn is found, the following
     insns are scanned, so that this function can be called on the insn
     returned by get_condition.
   * 'iv_analyze_result': Analyzes result of the assignment in the given
     insn.
   * 'iv_analyze_expr': Analyzes a more complicated expression.  All its
     operands are analyzed by 'iv_analyze', and hence they must be used
     in the specified insn or one of the following insns.

 The description of the induction variable is provided in 'struct
rtx_iv'.  In order to handle subregs, the representation is a bit
complicated; if the value of the 'extend' field is not 'UNKNOWN', the
value of the induction variable in the i-th iteration is

     delta + mult * extend_{extend_mode} (subreg_{mode} (base + i * step)),

 with the following exception: if 'first_special' is true, then the
value in the first iteration (when 'i' is zero) is 'delta + mult *
base'.  However, if 'extend' is equal to 'UNKNOWN', then 'first_special'
must be false, 'delta' 0, 'mult' 1 and the value in the i-th iteration
is

     subreg_{mode} (base + i * step)

 The function 'get_iv_value' can be used to perform these calculations.


File: gccint.info,  Node: Number of iterations,  Next: Dependency analysis,  Prev: loop-iv,  Up: Loop Analysis and Representation

14.7 Number of iterations analysis
==================================

Both on GIMPLE and on RTL, there are functions available to determine
the number of iterations of a loop, with a similar interface.  The
number of iterations of a loop in GCC is defined as the number of
executions of the loop latch.  In many cases, it is not possible to
determine the number of iterations unconditionally - the determined
number is correct only if some assumptions are satisfied.  The analysis
tries to verify these conditions using the information contained in the
program; if it fails, the conditions are returned together with the
result.  The following information and conditions are provided by the
analysis:

   * 'assumptions': If this condition is false, the rest of the
     information is invalid.
   * 'noloop_assumptions' on RTL, 'may_be_zero' on GIMPLE: If this
     condition is true, the loop exits in the first iteration.
   * 'infinite': If this condition is true, the loop is infinite.  This
     condition is only available on RTL.  On GIMPLE, conditions for
     finiteness of the loop are included in 'assumptions'.
   * 'niter_expr' on RTL, 'niter' on GIMPLE: The expression that gives
     number of iterations.  The number of iterations is defined as the
     number of executions of the loop latch.

 Both on GIMPLE and on RTL, it necessary for the induction variable
analysis framework to be initialized (SCEV on GIMPLE, loop-iv on RTL).
On GIMPLE, the results are stored to 'struct tree_niter_desc' structure.
Number of iterations before the loop is exited through a given exit can
be determined using 'number_of_iterations_exit' function.  On RTL, the
results are returned in 'struct niter_desc' structure.  The
corresponding function is named 'check_simple_exit'.  There are also
functions that pass through all the exits of a loop and try to find one
with easy to determine number of iterations - 'find_loop_niter' on
GIMPLE and 'find_simple_exit' on RTL.  Finally, there are functions that
provide the same information, but additionally cache it, so that
repeated calls to number of iterations are not so costly -
'number_of_latch_executions' on GIMPLE and 'get_simple_loop_desc' on
RTL.

 Note that some of these functions may behave slightly differently than
others - some of them return only the expression for the number of
iterations, and fail if there are some assumptions.  The function
'number_of_latch_executions' works only for single-exit loops.  The
function 'number_of_cond_exit_executions' can be used to determine
number of executions of the exit condition of a single-exit loop (i.e.,
the 'number_of_latch_executions' increased by one).


File: gccint.info,  Node: Dependency analysis,  Next: Lambda,  Prev: Number of iterations,  Up: Loop Analysis and Representation

14.8 Data Dependency Analysis
=============================

The code for the data dependence analysis can be found in
'tree-data-ref.c' and its interface and data structures are described in
'tree-data-ref.h'.  The function that computes the data dependences for
all the array and pointer references for a given loop is
'compute_data_dependences_for_loop'.  This function is currently used by
the linear loop transform and the vectorization passes.  Before calling
this function, one has to allocate two vectors: a first vector will
contain the set of data references that are contained in the analyzed
loop body, and the second vector will contain the dependence relations
between the data references.  Thus if the vector of data references is
of size 'n', the vector containing the dependence relations will contain
'n*n' elements.  However if the analyzed loop contains side effects,
such as calls that potentially can interfere with the data references in
the current analyzed loop, the analysis stops while scanning the loop
body for data references, and inserts a single 'chrec_dont_know' in the
dependence relation array.

 The data references are discovered in a particular order during the
scanning of the loop body: the loop body is analyzed in execution order,
and the data references of each statement are pushed at the end of the
data reference array.  Two data references syntactically occur in the
program in the same order as in the array of data references.  This
syntactic order is important in some classical data dependence tests,
and mapping this order to the elements of this array avoids costly
queries to the loop body representation.

 Three types of data references are currently handled: ARRAY_REF,
INDIRECT_REF and COMPONENT_REF.  The data structure for the data
reference is 'data_reference', where 'data_reference_p' is a name of a
pointer to the data reference structure.  The structure contains the
following elements:

   * 'base_object_info': Provides information about the base object of
     the data reference and its access functions.  These access
     functions represent the evolution of the data reference in the loop
     relative to its base, in keeping with the classical meaning of the
     data reference access function for the support of arrays.  For
     example, for a reference 'a.b[i][j]', the base object is 'a.b' and
     the access functions, one for each array subscript, are: '{i_init,
     + i_step}_1, {j_init, +, j_step}_2'.

   * 'first_location_in_loop': Provides information about the first
     location accessed by the data reference in the loop and about the
     access function used to represent evolution relative to this
     location.  This data is used to support pointers, and is not used
     for arrays (for which we have base objects).  Pointer accesses are
     represented as a one-dimensional access that starts from the first
     location accessed in the loop.  For example:

                for1 i
                   for2 j
                    *((int *)p + i + j) = a[i][j];

     The access function of the pointer access is '{0, + 4B}_for2'
     relative to 'p + i'.  The access functions of the array are
     '{i_init, + i_step}_for1' and '{j_init, +, j_step}_for2' relative
     to 'a'.

     Usually, the object the pointer refers to is either unknown, or we
     can't prove that the access is confined to the boundaries of a
     certain object.

     Two data references can be compared only if at least one of these
     two representations has all its fields filled for both data
     references.

     The current strategy for data dependence tests is as follows: If
     both 'a' and 'b' are represented as arrays, compare 'a.base_object'
     and 'b.base_object'; if they are equal, apply dependence tests (use
     access functions based on base_objects).  Else if both 'a' and 'b'
     are represented as pointers, compare 'a.first_location' and
     'b.first_location'; if they are equal, apply dependence tests (use
     access functions based on first location).  However, if 'a' and 'b'
     are represented differently, only try to prove that the bases are
     definitely different.

   * Aliasing information.
   * Alignment information.

 The structure describing the relation between two data references is
'data_dependence_relation' and the shorter name for a pointer to such a
structure is 'ddr_p'.  This structure contains:

   * a pointer to each data reference,
   * a tree node 'are_dependent' that is set to 'chrec_known' if the
     analysis has proved that there is no dependence between these two
     data references, 'chrec_dont_know' if the analysis was not able to
     determine any useful result and potentially there could exist a
     dependence between these data references, and 'are_dependent' is
     set to 'NULL_TREE' if there exist a dependence relation between the
     data references, and the description of this dependence relation is
     given in the 'subscripts', 'dir_vects', and 'dist_vects' arrays,
   * a boolean that determines whether the dependence relation can be
     represented by a classical distance vector,
   * an array 'subscripts' that contains a description of each subscript
     of the data references.  Given two array accesses a subscript is
     the tuple composed of the access functions for a given dimension.
     For example, given 'A[f1][f2][f3]' and 'B[g1][g2][g3]', there are
     three subscripts: '(f1, g1), (f2, g2), (f3, g3)'.
   * two arrays 'dir_vects' and 'dist_vects' that contain classical
     representations of the data dependences under the form of direction
     and distance dependence vectors,
   * an array of loops 'loop_nest' that contains the loops to which the
     distance and direction vectors refer to.

 Several functions for pretty printing the information extracted by the
data dependence analysis are available: 'dump_ddrs' prints with a
maximum verbosity the details of a data dependence relations array,
'dump_dist_dir_vectors' prints only the classical distance and direction
vectors for a data dependence relations array, and
'dump_data_references' prints the details of the data references
contained in a data reference array.


File: gccint.info,  Node: Lambda,  Next: Omega,  Prev: Dependency analysis,  Up: Loop Analysis and Representation

14.9 Linear loop transformations framework
==========================================

Lambda is a framework that allows transformations of loops using
non-singular matrix based transformations of the iteration space and
loop bounds.  This allows compositions of skewing, scaling, interchange,
and reversal transformations.  These transformations are often used to
improve cache behavior or remove inner loop dependencies to allow
parallelization and vectorization to take place.

 To perform these transformations, Lambda requires that the loopnest be
converted into an internal form that can be matrix transformed easily.
To do this conversion, the function 'gcc_loopnest_to_lambda_loopnest' is
provided.  If the loop cannot be transformed using lambda, this function
will return NULL.

 Once a 'lambda_loopnest' is obtained from the conversion function, it
can be transformed by using 'lambda_loopnest_transform', which takes a
transformation matrix to apply.  Note that it is up to the caller to
verify that the transformation matrix is legal to apply to the loop
(dependence respecting, etc).  Lambda simply applies whatever matrix it
is told to provide.  It can be extended to make legal matrices out of
any non-singular matrix, but this is not currently implemented.
Legality of a matrix for a given loopnest can be verified using
'lambda_transform_legal_p'.

 Given a transformed loopnest, conversion back into gcc IR is done by
'lambda_loopnest_to_gcc_loopnest'.  This function will modify the loops
so that they match the transformed loopnest.


File: gccint.info,  Node: Omega,  Prev: Lambda,  Up: Loop Analysis and Representation

14.10 Omega a solver for linear programming problems
====================================================

The data dependence analysis contains several solvers triggered
sequentially from the less complex ones to the more sophisticated.  For
ensuring the consistency of the results of these solvers, a data
dependence check pass has been implemented based on two different
solvers.  The second method that has been integrated to GCC is based on
the Omega dependence solver, written in the 1990's by William Pugh and
David Wonnacott.  Data dependence tests can be formulated using a subset
of the Presburger arithmetics that can be translated to linear
constraint systems.  These linear constraint systems can then be solved
using the Omega solver.

 The Omega solver is using Fourier-Motzkin's algorithm for variable
elimination: a linear constraint system containing 'n' variables is
reduced to a linear constraint system with 'n-1' variables.  The Omega
solver can also be used for solving other problems that can be expressed
under the form of a system of linear equalities and inequalities.  The
Omega solver is known to have an exponential worst case, also known
under the name of "omega nightmare" in the literature, but in practice,
the omega test is known to be efficient for the common data dependence
tests.

 The interface used by the Omega solver for describing the linear
programming problems is described in 'omega.h', and the solver is
'omega_solve_problem'.


File: gccint.info,  Node: Control Flow,  Next: Machine Desc,  Prev: Loop Analysis and Representation,  Up: Top

15 Control Flow Graph
*********************

A control flow graph (CFG) is a data structure built on top of the
intermediate code representation (the RTL or 'GIMPLE' instruction
stream) abstracting the control flow behavior of a function that is
being compiled.  The CFG is a directed graph where the vertices
represent basic blocks and edges represent possible transfer of control
flow from one basic block to another.  The data structures used to
represent the control flow graph are defined in 'basic-block.h'.

 In GCC, the representation of control flow is maintained throughout the
compilation process, from constructing the CFG early in 'pass_build_cfg'
to 'pass_free_cfg' (see 'passes.c').  The CFG takes various different
modes and may undergo extensive manipulations, but the graph is always
valid between its construction and its release.  This way, transfer of
information such as data flow, a measured profile, or the loop tree, can
be propagated through the passes pipeline, and even from 'GIMPLE' to
'RTL'.

 Often the CFG may be better viewed as integral part of instruction
chain, than structure built on the top of it.  Updating the compiler's
intermediate representation for instructions can not be easily done
without proper maintenance of the CFG simultaneously.

* Menu:

* Basic Blocks::           The definition and representation of basic blocks.
* Edges::                  Types of edges and their representation.
* Profile information::    Representation of frequencies and probabilities.
* Maintaining the CFG::    Keeping the control flow graph and up to date.
* Liveness information::   Using and maintaining liveness information.


File: gccint.info,  Node: Basic Blocks,  Next: Edges,  Up: Control Flow

15.1 Basic Blocks
=================

A basic block is a straight-line sequence of code with only one entry
point and only one exit.  In GCC, basic blocks are represented using the
'basic_block' data type.

 Special basic blocks represent possible entry and exit points of a
function.  These blocks are called 'ENTRY_BLOCK_PTR' and
'EXIT_BLOCK_PTR'.  These blocks do not contain any code.

 The 'BASIC_BLOCK' array contains all basic blocks in an unspecified
order.  Each 'basic_block' structure has a field that holds a unique
integer identifier 'index' that is the index of the block in the
'BASIC_BLOCK' array.  The total number of basic blocks in the function
is 'n_basic_blocks'.  Both the basic block indices and the total number
of basic blocks may vary during the compilation process, as passes
reorder, create, duplicate, and destroy basic blocks.  The index for any
block should never be greater than 'last_basic_block'.  The indices 0
and 1 are special codes reserved for 'ENTRY_BLOCK' and 'EXIT_BLOCK', the
indices of 'ENTRY_BLOCK_PTR' and 'EXIT_BLOCK_PTR'.

 Two pointer members of the 'basic_block' structure are the pointers
'next_bb' and 'prev_bb'.  These are used to keep doubly linked chain of
basic blocks in the same order as the underlying instruction stream.
The chain of basic blocks is updated transparently by the provided API
for manipulating the CFG.  The macro 'FOR_EACH_BB' can be used to visit
all the basic blocks in lexicographical order, except 'ENTRY_BLOCK' and
'EXIT_BLOCK'.  The macro 'FOR_ALL_BB' also visits all basic blocks in
lexicographical order, including 'ENTRY_BLOCK' and 'EXIT_BLOCK'.

 The functions 'post_order_compute' and 'inverted_post_order_compute'
can be used to compute topological orders of the CFG. The orders are
stored as vectors of basic block indices.  The 'BASIC_BLOCK' array can
be used to iterate each basic block by index.  Dominator traversals are
also possible using 'walk_dominator_tree'.  Given two basic blocks A and
B, block A dominates block B if A is _always_ executed before B.

 Each 'basic_block' also contains pointers to the first instruction (the
"head") and the last instruction (the "tail") or "end" of the
instruction stream contained in a basic block.  In fact, since the
'basic_block' data type is used to represent blocks in both major
intermediate representations of GCC ('GIMPLE' and RTL), there are
pointers to the head and end of a basic block for both representations,
stored in intermediate representation specific data in the 'il' field of
'struct basic_block_def'.

 For RTL, these pointers are 'BB_HEAD' and 'BB_END'.

 In the RTL representation of a function, the instruction stream
contains not only the "real" instructions, but also "notes" or "insn
notes" (to distinguish them from "reg notes").  Any function that moves
or duplicates the basic blocks needs to take care of updating of these
notes.  Many of these notes expect that the instruction stream consists
of linear regions, so updating can sometimes be tedious.  All types of
insn notes are defined in 'insn-notes.def'.

 In the RTL function representation, the instructions contained in a
basic block always follow a 'NOTE_INSN_BASIC_BLOCK', but zero or more
'CODE_LABEL' nodes can precede the block note.  A basic block ends with
a control flow instruction or with the last instruction before the next
'CODE_LABEL' or 'NOTE_INSN_BASIC_BLOCK'.  By definition, a 'CODE_LABEL'
cannot appear in the middle of the instruction stream of a basic block.

 In addition to notes, the jump table vectors are also represented as
"pseudo-instructions" inside the insn stream.  These vectors never
appear in the basic block and should always be placed just after the
table jump instructions referencing them.  After removing the table-jump
it is often difficult to eliminate the code computing the address and
referencing the vector, so cleaning up these vectors is postponed until
after liveness analysis.  Thus the jump table vectors may appear in the
insn stream unreferenced and without any purpose.  Before any edge is
made "fall-thru", the existence of such construct in the way needs to be
checked by calling 'can_fallthru' function.

 For the 'GIMPLE' representation, the PHI nodes and statements contained
in a basic block are in a 'gimple_seq' pointed to by the basic block
intermediate language specific pointers.  Abstract containers and
iterators are used to access the PHI nodes and statements in a basic
blocks.  These iterators are called "GIMPLE statement iterators" (GSIs).
Grep for '^gsi' in the various 'gimple-*' and 'tree-*' files.  The
following snippet will pretty-print all PHI nodes the statements of the
current function in the GIMPLE representation.

     basic_block bb;

     FOR_EACH_BB (bb)
       {
        gimple_stmt_iterator si;

        for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
          {
            gimple phi = gsi_stmt (si);
            print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
          }
        for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))
          {
            gimple stmt = gsi_stmt (si);
            print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
          }
       }


File: gccint.info,  Node: Edges,  Next: Profile information,  Prev: Basic Blocks,  Up: Control Flow

15.2 Edges
==========

Edges represent possible control flow transfers from the end of some
basic block A to the head of another basic block B.  We say that A is a
predecessor of B, and B is a successor of A.  Edges are represented in
GCC with the 'edge' data type.  Each 'edge' acts as a link between two
basic blocks: The 'src' member of an edge points to the predecessor
basic block of the 'dest' basic block.  The members 'preds' and 'succs'
of the 'basic_block' data type point to type-safe vectors of edges to
the predecessors and successors of the block.

 When walking the edges in an edge vector, "edge iterators" should be
used.  Edge iterators are constructed using the 'edge_iterator' data
structure and several methods are available to operate on them:

'ei_start'
     This function initializes an 'edge_iterator' that points to the
     first edge in a vector of edges.

'ei_last'
     This function initializes an 'edge_iterator' that points to the
     last edge in a vector of edges.

'ei_end_p'
     This predicate is 'true' if an 'edge_iterator' represents the last
     edge in an edge vector.

'ei_one_before_end_p'
     This predicate is 'true' if an 'edge_iterator' represents the
     second last edge in an edge vector.

'ei_next'
     This function takes a pointer to an 'edge_iterator' and makes it
     point to the next edge in the sequence.

'ei_prev'
     This function takes a pointer to an 'edge_iterator' and makes it
     point to the previous edge in the sequence.

'ei_edge'
     This function returns the 'edge' currently pointed to by an
     'edge_iterator'.

'ei_safe_safe'
     This function returns the 'edge' currently pointed to by an
     'edge_iterator', but returns 'NULL' if the iterator is pointing at
     the end of the sequence.  This function has been provided for
     existing code makes the assumption that a 'NULL' edge indicates the
     end of the sequence.

 The convenience macro 'FOR_EACH_EDGE' can be used to visit all of the
edges in a sequence of predecessor or successor edges.  It must not be
used when an element might be removed during the traversal, otherwise
elements will be missed.  Here is an example of how to use the macro:

     edge e;
     edge_iterator ei;

     FOR_EACH_EDGE (e, ei, bb->succs)
       {
          if (e->flags & EDGE_FALLTHRU)
            break;
       }

 There are various reasons why control flow may transfer from one block
to another.  One possibility is that some instruction, for example a
'CODE_LABEL', in a linearized instruction stream just always starts a
new basic block.  In this case a "fall-thru" edge links the basic block
to the first following basic block.  But there are several other reasons
why edges may be created.  The 'flags' field of the 'edge' data type is
used to store information about the type of edge we are dealing with.
Each edge is of one of the following types:

_jump_
     No type flags are set for edges corresponding to jump instructions.
     These edges are used for unconditional or conditional jumps and in
     RTL also for table jumps.  They are the easiest to manipulate as
     they may be freely redirected when the flow graph is not in SSA
     form.

_fall-thru_
     Fall-thru edges are present in case where the basic block may
     continue execution to the following one without branching.  These
     edges have the 'EDGE_FALLTHRU' flag set.  Unlike other types of
     edges, these edges must come into the basic block immediately
     following in the instruction stream.  The function
     'force_nonfallthru' is available to insert an unconditional jump in
     the case that redirection is needed.  Note that this may require
     creation of a new basic block.

_exception handling_
     Exception handling edges represent possible control transfers from
     a trapping instruction to an exception handler.  The definition of
     "trapping" varies.  In C++, only function calls can throw, but for
     Java and Ada, exceptions like division by zero or segmentation
     fault are defined and thus each instruction possibly throwing this
     kind of exception needs to be handled as control flow instruction.
     Exception edges have the 'EDGE_ABNORMAL' and 'EDGE_EH' flags set.

     When updating the instruction stream it is easy to change possibly
     trapping instruction to non-trapping, by simply removing the
     exception edge.  The opposite conversion is difficult, but should
     not happen anyway.  The edges can be eliminated via
     'purge_dead_edges' call.

     In the RTL representation, the destination of an exception edge is
     specified by 'REG_EH_REGION' note attached to the insn.  In case of
     a trapping call the 'EDGE_ABNORMAL_CALL' flag is set too.  In the
     'GIMPLE' representation, this extra flag is not set.

     In the RTL representation, the predicate 'may_trap_p' may be used
     to check whether instruction still may trap or not.  For the tree
     representation, the 'tree_could_trap_p' predicate is available, but
     this predicate only checks for possible memory traps, as in
     dereferencing an invalid pointer location.

_sibling calls_
     Sibling calls or tail calls terminate the function in a
     non-standard way and thus an edge to the exit must be present.
     'EDGE_SIBCALL' and 'EDGE_ABNORMAL' are set in such case.  These
     edges only exist in the RTL representation.

_computed jumps_
     Computed jumps contain edges to all labels in the function
     referenced from the code.  All those edges have 'EDGE_ABNORMAL'
     flag set.  The edges used to represent computed jumps often cause
     compile time performance problems, since functions consisting of
     many taken labels and many computed jumps may have _very_ dense
     flow graphs, so these edges need to be handled with special care.
     During the earlier stages of the compilation process, GCC tries to
     avoid such dense flow graphs by factoring computed jumps.  For
     example, given the following series of jumps,

            goto *x;
            [ ... ]

            goto *x;
            [ ... ]

            goto *x;
            [ ... ]

     factoring the computed jumps results in the following code sequence
     which has a much simpler flow graph:

            goto y;
            [ ... ]

            goto y;
            [ ... ]

            goto y;
            [ ... ]

          y:
            goto *x;

     However, the classic problem with this transformation is that it
     has a runtime cost in there resulting code: An extra jump.
     Therefore, the computed jumps are un-factored in the later passes
     of the compiler (in the pass called
     'pass_duplicate_computed_gotos').  Be aware of that when you work
     on passes in that area.  There have been numerous examples already
     where the compile time for code with unfactored computed jumps
     caused some serious headaches.

_nonlocal goto handlers_
     GCC allows nested functions to return into caller using a 'goto' to
     a label passed to as an argument to the callee.  The labels passed
     to nested functions contain special code to cleanup after function
     call.  Such sections of code are referred to as "nonlocal goto
     receivers".  If a function contains such nonlocal goto receivers,
     an edge from the call to the label is created with the
     'EDGE_ABNORMAL' and 'EDGE_ABNORMAL_CALL' flags set.

_function entry points_
     By definition, execution of function starts at basic block 0, so
     there is always an edge from the 'ENTRY_BLOCK_PTR' to basic block
     0.  There is no 'GIMPLE' representation for alternate entry points
     at this moment.  In RTL, alternate entry points are specified by
     'CODE_LABEL' with 'LABEL_ALTERNATE_NAME' defined.  This feature is
     currently used for multiple entry point prologues and is limited to
     post-reload passes only.  This can be used by back-ends to emit
     alternate prologues for functions called from different contexts.
     In future full support for multiple entry functions defined by
     Fortran 90 needs to be implemented.

_function exits_
     In the pre-reload representation a function terminates after the
     last instruction in the insn chain and no explicit return
     instructions are used.  This corresponds to the fall-thru edge into
     exit block.  After reload, optimal RTL epilogues are used that use
     explicit (conditional) return instructions that are represented by
     edges with no flags set.


File: gccint.info,  Node: Profile information,  Next: Maintaining the CFG,  Prev: Edges,  Up: Control Flow

15.3 Profile information
========================

In many cases a compiler must make a choice whether to trade speed in
one part of code for speed in another, or to trade code size for code
speed.  In such cases it is useful to know information about how often
some given block will be executed.  That is the purpose for maintaining
profile within the flow graph.  GCC can handle profile information
obtained through "profile feedback", but it can also estimate branch
probabilities based on statics and heuristics.

 The feedback based profile is produced by compiling the program with
instrumentation, executing it on a train run and reading the numbers of
executions of basic blocks and edges back to the compiler while
re-compiling the program to produce the final executable.  This method
provides very accurate information about where a program spends most of
its time on the train run.  Whether it matches the average run of course
depends on the choice of train data set, but several studies have shown
that the behavior of a program usually changes just marginally over
different data sets.

 When profile feedback is not available, the compiler may be asked to
attempt to predict the behavior of each branch in the program using a
set of heuristics (see 'predict.def' for details) and compute estimated
frequencies of each basic block by propagating the probabilities over
the graph.

 Each 'basic_block' contains two integer fields to represent profile
information: 'frequency' and 'count'.  The 'frequency' is an estimation
how often is basic block executed within a function.  It is represented
as an integer scaled in the range from 0 to 'BB_FREQ_BASE'.  The most
frequently executed basic block in function is initially set to
'BB_FREQ_BASE' and the rest of frequencies are scaled accordingly.
During optimization, the frequency of the most frequent basic block can
both decrease (for instance by loop unrolling) or grow (for instance by
cross-jumping optimization), so scaling sometimes has to be performed
multiple times.

 The 'count' contains hard-counted numbers of execution measured during
training runs and is nonzero only when profile feedback is available.
This value is represented as the host's widest integer (typically a 64
bit integer) of the special type 'gcov_type'.

 Most optimization passes can use only the frequency information of a
basic block, but a few passes may want to know hard execution counts.
The frequencies should always match the counts after scaling, however
during updating of the profile information numerical error may
accumulate into quite large errors.

 Each edge also contains a branch probability field: an integer in the
range from 0 to 'REG_BR_PROB_BASE'.  It represents probability of
passing control from the end of the 'src' basic block to the 'dest'
basic block, i.e. the probability that control will flow along this
edge.  The 'EDGE_FREQUENCY' macro is available to compute how frequently
a given edge is taken.  There is a 'count' field for each edge as well,
representing same information as for a basic block.

 The basic block frequencies are not represented in the instruction
stream, but in the RTL representation the edge frequencies are
represented for conditional jumps (via the 'REG_BR_PROB' macro) since
they are used when instructions are output to the assembly file and the
flow graph is no longer maintained.

 The probability that control flow arrives via a given edge to its
destination basic block is called "reverse probability" and is not
directly represented, but it may be easily computed from frequencies of
basic blocks.

 Updating profile information is a delicate task that can unfortunately
not be easily integrated with the CFG manipulation API.  Many of the
functions and hooks to modify the CFG, such as
'redirect_edge_and_branch', do not have enough information to easily
update the profile, so updating it is in the majority of cases left up
to the caller.  It is difficult to uncover bugs in the profile updating
code, because they manifest themselves only by producing worse code, and
checking profile consistency is not possible because of numeric error
accumulation.  Hence special attention needs to be given to this issue
in each pass that modifies the CFG.

 It is important to point out that 'REG_BR_PROB_BASE' and 'BB_FREQ_BASE'
are both set low enough to be possible to compute second power of any
frequency or probability in the flow graph, it is not possible to even
square the 'count' field, as modern CPUs are fast enough to execute
$2^32$ operations quickly.


File: gccint.info,  Node: Maintaining the CFG,  Next: Liveness information,  Prev: Profile information,  Up: Control Flow

15.4 Maintaining the CFG
========================

An important task of each compiler pass is to keep both the control flow
graph and all profile information up-to-date.  Reconstruction of the
control flow graph after each pass is not an option, since it may be
very expensive and lost profile information cannot be reconstructed at
all.

 GCC has two major intermediate representations, and both use the
'basic_block' and 'edge' data types to represent control flow.  Both
representations share as much of the CFG maintenance code as possible.
For each representation, a set of "hooks" is defined so that each
representation can provide its own implementation of CFG manipulation
routines when necessary.  These hooks are defined in 'cfghooks.h'.
There are hooks for almost all common CFG manipulations, including block
splitting and merging, edge redirection and creating and deleting basic
blocks.  These hooks should provide everything you need to maintain and
manipulate the CFG in both the RTL and 'GIMPLE' representation.

 At the moment, the basic block boundaries are maintained transparently
when modifying instructions, so there rarely is a need to move them
manually (such as in case someone wants to output instruction outside
basic block explicitly).

 In the RTL representation, each instruction has a 'BLOCK_FOR_INSN'
value that represents pointer to the basic block that contains the
instruction.  In the 'GIMPLE' representation, the function 'gimple_bb'
returns a pointer to the basic block containing the queried statement.

 When changes need to be applied to a function in its 'GIMPLE'
representation, "GIMPLE statement iterators" should be used.  These
iterators provide an integrated abstraction of the flow graph and the
instruction stream.  Block statement iterators are constructed using the
'gimple_stmt_iterator' data structure and several modifier are
available, including the following:

'gsi_start'
     This function initializes a 'gimple_stmt_iterator' that points to
     the first non-empty statement in a basic block.

'gsi_last'
     This function initializes a 'gimple_stmt_iterator' that points to
     the last statement in a basic block.

'gsi_end_p'
     This predicate is 'true' if a 'gimple_stmt_iterator' represents the
     end of a basic block.

'gsi_next'
     This function takes a 'gimple_stmt_iterator' and makes it point to
     its successor.

'gsi_prev'
     This function takes a 'gimple_stmt_iterator' and makes it point to
     its predecessor.

'gsi_insert_after'
     This function inserts a statement after the 'gimple_stmt_iterator'
     passed in.  The final parameter determines whether the statement
     iterator is updated to point to the newly inserted statement, or
     left pointing to the original statement.

'gsi_insert_before'
     This function inserts a statement before the 'gimple_stmt_iterator'
     passed in.  The final parameter determines whether the statement
     iterator is updated to point to the newly inserted statement, or
     left pointing to the original statement.

'gsi_remove'
     This function removes the 'gimple_stmt_iterator' passed in and
     rechains the remaining statements in a basic block, if any.

 In the RTL representation, the macros 'BB_HEAD' and 'BB_END' may be
used to get the head and end 'rtx' of a basic block.  No abstract
iterators are defined for traversing the insn chain, but you can just
use 'NEXT_INSN' and 'PREV_INSN' instead.  *Note Insns::.

 Usually a code manipulating pass simplifies the instruction stream and
the flow of control, possibly eliminating some edges.  This may for
example happen when a conditional jump is replaced with an unconditional
jump, but also when simplifying possibly trapping instruction to
non-trapping while compiling Java.  Updating of edges is not transparent
and each optimization pass is required to do so manually.  However only
few cases occur in practice.  The pass may call 'purge_dead_edges' on a
given basic block to remove superfluous edges, if any.

 Another common scenario is redirection of branch instructions, but this
is best modeled as redirection of edges in the control flow graph and
thus use of 'redirect_edge_and_branch' is preferred over more low level
functions, such as 'redirect_jump' that operate on RTL chain only.  The
CFG hooks defined in 'cfghooks.h' should provide the complete API
required for manipulating and maintaining the CFG.

 It is also possible that a pass has to insert control flow instruction
into the middle of a basic block, thus creating an entry point in the
middle of the basic block, which is impossible by definition: The block
must be split to make sure it only has one entry point, i.e. the head of
the basic block.  The CFG hook 'split_block' may be used when an
instruction in the middle of a basic block has to become the target of a
jump or branch instruction.

 For a global optimizer, a common operation is to split edges in the
flow graph and insert instructions on them.  In the RTL representation,
this can be easily done using the 'insert_insn_on_edge' function that
emits an instruction "on the edge", caching it for a later
'commit_edge_insertions' call that will take care of moving the inserted
instructions off the edge into the instruction stream contained in a
basic block.  This includes the creation of new basic blocks where
needed.  In the 'GIMPLE' representation, the equivalent functions are
'gsi_insert_on_edge' which inserts a block statement iterator on an
edge, and 'gsi_commit_edge_inserts' which flushes the instruction to
actual instruction stream.

 While debugging the optimization pass, the 'verify_flow_info' function
may be useful to find bugs in the control flow graph updating code.


File: gccint.info,  Node: Liveness information,  Prev: Maintaining the CFG,  Up: Control Flow

15.5 Liveness information
=========================

Liveness information is useful to determine whether some register is
"live" at given point of program, i.e. that it contains a value that may
be used at a later point in the program.  This information is used, for
instance, during register allocation, as the pseudo registers only need
to be assigned to a unique hard register or to a stack slot if they are
live.  The hard registers and stack slots may be freely reused for other
values when a register is dead.

 Liveness information is available in the back end starting with
'pass_df_initialize' and ending with 'pass_df_finish'.  Three flavors of
live analysis are available: With 'LR', it is possible to determine at
any point 'P' in the function if the register may be used on some path
from 'P' to the end of the function.  With 'UR', it is possible to
determine if there is a path from the beginning of the function to 'P'
that defines the variable.  'LIVE' is the intersection of the 'LR' and
'UR' and a variable is live at 'P' if there is both an assignment that
reaches it from the beginning of the function and a use that can be
reached on some path from 'P' to the end of the function.

 In general 'LIVE' is the most useful of the three.  The macros
'DF_[LR,UR,LIVE]_[IN,OUT]' can be used to access this information.  The
macros take a basic block number and return a bitmap that is indexed by
the register number.  This information is only guaranteed to be up to
date after calls are made to 'df_analyze'.  See the file 'df-core.c' for
details on using the dataflow.

 The liveness information is stored partly in the RTL instruction stream
and partly in the flow graph.  Local information is stored in the
instruction stream: Each instruction may contain 'REG_DEAD' notes
representing that the value of a given register is no longer needed, or
'REG_UNUSED' notes representing that the value computed by the
instruction is never used.  The second is useful for instructions
computing multiple values at once.


File: gccint.info,  Node: Machine Desc,  Next: Target Macros,  Prev: Control Flow,  Up: Top

16 Machine Descriptions
***********************

A machine description has two parts: a file of instruction patterns
('.md' file) and a C header file of macro definitions.

 The '.md' file for a target machine contains a pattern for each
instruction that the target machine supports (or at least each
instruction that is worth telling the compiler about).  It may also
contain comments.  A semicolon causes the rest of the line to be a
comment, unless the semicolon is inside a quoted string.

 See the next chapter for information on the C header file.

* Menu:

* Overview::            How the machine description is used.
* Patterns::            How to write instruction patterns.
* Example::             An explained example of a 'define_insn' pattern.
* RTL Template::        The RTL template defines what insns match a pattern.
* Output Template::     The output template says how to make assembler code
                        from such an insn.
* Output Statement::    For more generality, write C code to output
                        the assembler code.
* Predicates::          Controlling what kinds of operands can be used
                        for an insn.
* Constraints::         Fine-tuning operand selection.
* Standard Names::      Names mark patterns to use for code generation.
* Pattern Ordering::    When the order of patterns makes a difference.
* Dependent Patterns::  Having one pattern may make you need another.
* Jump Patterns::       Special considerations for patterns for jump insns.
* Looping Patterns::    How to define patterns for special looping insns.
* Insn Canonicalizations::Canonicalization of Instructions
* Expander Definitions::Generating a sequence of several RTL insns
                        for a standard operation.
* Insn Splitting::      Splitting Instructions into Multiple Instructions.
* Including Patterns::  Including Patterns in Machine Descriptions.
* Peephole Definitions::Defining machine-specific peephole optimizations.
* Insn Attributes::     Specifying the value of attributes for generated insns.
* Conditional Execution::Generating 'define_insn' patterns for
                         predication.
* Define Subst::	Generating 'define_insn' and 'define_expand'
			patterns from other patterns.
* Constant Definitions::Defining symbolic constants that can be used in the
                        md file.
* Iterators::           Using iterators to generate patterns from a template.


File: gccint.info,  Node: Overview,  Next: Patterns,  Up: Machine Desc

16.1 Overview of How the Machine Description is Used
====================================================

There are three main conversions that happen in the compiler:

  1. The front end reads the source code and builds a parse tree.

  2. The parse tree is used to generate an RTL insn list based on named
     instruction patterns.

  3. The insn list is matched against the RTL templates to produce
     assembler code.

 For the generate pass, only the names of the insns matter, from either
a named 'define_insn' or a 'define_expand'.  The compiler will choose
the pattern with the right name and apply the operands according to the
documentation later in this chapter, without regard for the RTL template
or operand constraints.  Note that the names the compiler looks for are
hard-coded in the compiler--it will ignore unnamed patterns and patterns
with names it doesn't know about, but if you don't provide a named
pattern it needs, it will abort.

 If a 'define_insn' is used, the template given is inserted into the
insn list.  If a 'define_expand' is used, one of three things happens,
based on the condition logic.  The condition logic may manually create
new insns for the insn list, say via 'emit_insn()', and invoke 'DONE'.
For certain named patterns, it may invoke 'FAIL' to tell the compiler to
use an alternate way of performing that task.  If it invokes neither
'DONE' nor 'FAIL', the template given in the pattern is inserted, as if
the 'define_expand' were a 'define_insn'.

 Once the insn list is generated, various optimization passes convert,
replace, and rearrange the insns in the insn list.  This is where the
'define_split' and 'define_peephole' patterns get used, for example.

 Finally, the insn list's RTL is matched up with the RTL templates in
the 'define_insn' patterns, and those patterns are used to emit the
final assembly code.  For this purpose, each named 'define_insn' acts
like it's unnamed, since the names are ignored.


File: gccint.info,  Node: Patterns,  Next: Example,  Prev: Overview,  Up: Machine Desc

16.2 Everything about Instruction Patterns
==========================================

Each instruction pattern contains an incomplete RTL expression, with
pieces to be filled in later, operand constraints that restrict how the
pieces can be filled in, and an output pattern or C code to generate the
assembler output, all wrapped up in a 'define_insn' expression.

 A 'define_insn' is an RTL expression containing four or five operands:

  1. An optional name.  The presence of a name indicate that this
     instruction pattern can perform a certain standard job for the
     RTL-generation pass of the compiler.  This pass knows certain names
     and will use the instruction patterns with those names, if the
     names are defined in the machine description.

     The absence of a name is indicated by writing an empty string where
     the name should go.  Nameless instruction patterns are never used
     for generating RTL code, but they may permit several simpler insns
     to be combined later on.

     Names that are not thus known and used in RTL-generation have no
     effect; they are equivalent to no name at all.

     For the purpose of debugging the compiler, you may also specify a
     name beginning with the '*' character.  Such a name is used only
     for identifying the instruction in RTL dumps; it is entirely
     equivalent to having a nameless pattern for all other purposes.

  2. The "RTL template" (*note RTL Template::) is a vector of incomplete
     RTL expressions which show what the instruction should look like.
     It is incomplete because it may contain 'match_operand',
     'match_operator', and 'match_dup' expressions that stand for
     operands of the instruction.

     If the vector has only one element, that element is the template
     for the instruction pattern.  If the vector has multiple elements,
     then the instruction pattern is a 'parallel' expression containing
     the elements described.

  3. A condition.  This is a string which contains a C expression that
     is the final test to decide whether an insn body matches this
     pattern.

     For a named pattern, the condition (if present) may not depend on
     the data in the insn being matched, but only the
     target-machine-type flags.  The compiler needs to test these
     conditions during initialization in order to learn exactly which
     named instructions are available in a particular run.

     For nameless patterns, the condition is applied only when matching
     an individual insn, and only after the insn has matched the
     pattern's recognition template.  The insn's operands may be found
     in the vector 'operands'.  For an insn where the condition has once
     matched, it can't be used to control register allocation, for
     example by excluding certain hard registers or hard register
     combinations.

  4. The "output template": a string that says how to output matching
     insns as assembler code.  '%' in this string specifies where to
     substitute the value of an operand.  *Note Output Template::.

     When simple substitution isn't general enough, you can specify a
     piece of C code to compute the output.  *Note Output Statement::.

  5. Optionally, a vector containing the values of attributes for insns
     matching this pattern.  *Note Insn Attributes::.


File: gccint.info,  Node: Example,  Next: RTL Template,  Prev: Patterns,  Up: Machine Desc

16.3 Example of 'define_insn'
=============================

Here is an actual example of an instruction pattern, for the
68000/68020.

     (define_insn "tstsi"
       [(set (cc0)
             (match_operand:SI 0 "general_operand" "rm"))]
       ""
       "*
     {
       if (TARGET_68020 || ! ADDRESS_REG_P (operands[0]))
         return \"tstl %0\";
       return \"cmpl #0,%0\";
     }")

This can also be written using braced strings:

     (define_insn "tstsi"
       [(set (cc0)
             (match_operand:SI 0 "general_operand" "rm"))]
       ""
     {
       if (TARGET_68020 || ! ADDRESS_REG_P (operands[0]))
         return "tstl %0";
       return "cmpl #0,%0";
     })

 This is an instruction that sets the condition codes based on the value
of a general operand.  It has no condition, so any insn whose RTL
description has the form shown may be handled according to this pattern.
The name 'tstsi' means "test a 'SImode' value" and tells the RTL
generation pass that, when it is necessary to test such a value, an insn
to do so can be constructed using this pattern.

 The output control string is a piece of C code which chooses which
output template to return based on the kind of operand and the specific
type of CPU for which code is being generated.

 '"rm"' is an operand constraint.  Its meaning is explained below.


File: gccint.info,  Node: RTL Template,  Next: Output Template,  Prev: Example,  Up: Machine Desc

16.4 RTL Template
=================

The RTL template is used to define which insns match the particular
pattern and how to find their operands.  For named patterns, the RTL
template also says how to construct an insn from specified operands.

 Construction involves substituting specified operands into a copy of
the template.  Matching involves determining the values that serve as
the operands in the insn being matched.  Both of these activities are
controlled by special expression types that direct matching and
substitution of the operands.

'(match_operand:M N PREDICATE CONSTRAINT)'
     This expression is a placeholder for operand number N of the insn.
     When constructing an insn, operand number N will be substituted at
     this point.  When matching an insn, whatever appears at this
     position in the insn will be taken as operand number N; but it must
     satisfy PREDICATE or this instruction pattern will not match at
     all.

     Operand numbers must be chosen consecutively counting from zero in
     each instruction pattern.  There may be only one 'match_operand'
     expression in the pattern for each operand number.  Usually
     operands are numbered in the order of appearance in 'match_operand'
     expressions.  In the case of a 'define_expand', any operand numbers
     used only in 'match_dup' expressions have higher values than all
     other operand numbers.

     PREDICATE is a string that is the name of a function that accepts
     two arguments, an expression and a machine mode.  *Note
     Predicates::.  During matching, the function will be called with
     the putative operand as the expression and M as the mode argument
     (if M is not specified, 'VOIDmode' will be used, which normally
     causes PREDICATE to accept any mode).  If it returns zero, this
     instruction pattern fails to match.  PREDICATE may be an empty
     string; then it means no test is to be done on the operand, so
     anything which occurs in this position is valid.

     Most of the time, PREDICATE will reject modes other than M--but not
     always.  For example, the predicate 'address_operand' uses M as the
     mode of memory ref that the address should be valid for.  Many
     predicates accept 'const_int' nodes even though their mode is
     'VOIDmode'.

     CONSTRAINT controls reloading and the choice of the best register
     class to use for a value, as explained later (*note Constraints::).
     If the constraint would be an empty string, it can be omitted.

     People are often unclear on the difference between the constraint
     and the predicate.  The predicate helps decide whether a given insn
     matches the pattern.  The constraint plays no role in this
     decision; instead, it controls various decisions in the case of an
     insn which does match.

'(match_scratch:M N CONSTRAINT)'
     This expression is also a placeholder for operand number N and
     indicates that operand must be a 'scratch' or 'reg' expression.

     When matching patterns, this is equivalent to

          (match_operand:M N "scratch_operand" PRED)

     but, when generating RTL, it produces a ('scratch':M) expression.

     If the last few expressions in a 'parallel' are 'clobber'
     expressions whose operands are either a hard register or
     'match_scratch', the combiner can add or delete them when
     necessary.  *Note Side Effects::.

'(match_dup N)'
     This expression is also a placeholder for operand number N.  It is
     used when the operand needs to appear more than once in the insn.

     In construction, 'match_dup' acts just like 'match_operand': the
     operand is substituted into the insn being constructed.  But in
     matching, 'match_dup' behaves differently.  It assumes that operand
     number N has already been determined by a 'match_operand' appearing
     earlier in the recognition template, and it matches only an
     identical-looking expression.

     Note that 'match_dup' should not be used to tell the compiler that
     a particular register is being used for two operands (example:
     'add' that adds one register to another; the second register is
     both an input operand and the output operand).  Use a matching
     constraint (*note Simple Constraints::) for those.  'match_dup' is
     for the cases where one operand is used in two places in the
     template, such as an instruction that computes both a quotient and
     a remainder, where the opcode takes two input operands but the RTL
     template has to refer to each of those twice; once for the quotient
     pattern and once for the remainder pattern.

'(match_operator:M N PREDICATE [OPERANDS...])'
     This pattern is a kind of placeholder for a variable RTL expression
     code.

     When constructing an insn, it stands for an RTL expression whose
     expression code is taken from that of operand N, and whose operands
     are constructed from the patterns OPERANDS.

     When matching an expression, it matches an expression if the
     function PREDICATE returns nonzero on that expression _and_ the
     patterns OPERANDS match the operands of the expression.

     Suppose that the function 'commutative_operator' is defined as
     follows, to match any expression whose operator is one of the
     commutative arithmetic operators of RTL and whose mode is MODE:

          int
          commutative_integer_operator (x, mode)
               rtx x;
               enum machine_mode mode;
          {
            enum rtx_code code = GET_CODE (x);
            if (GET_MODE (x) != mode)
              return 0;
            return (GET_RTX_CLASS (code) == RTX_COMM_ARITH
                    || code == EQ || code == NE);
          }

     Then the following pattern will match any RTL expression consisting
     of a commutative operator applied to two general operands:

          (match_operator:SI 3 "commutative_operator"
            [(match_operand:SI 1 "general_operand" "g")
             (match_operand:SI 2 "general_operand" "g")])

     Here the vector '[OPERANDS...]' contains two patterns because the
     expressions to be matched all contain two operands.

     When this pattern does match, the two operands of the commutative
     operator are recorded as operands 1 and 2 of the insn.  (This is
     done by the two instances of 'match_operand'.)  Operand 3 of the
     insn will be the entire commutative expression: use 'GET_CODE
     (operands[3])' to see which commutative operator was used.

     The machine mode M of 'match_operator' works like that of
     'match_operand': it is passed as the second argument to the
     predicate function, and that function is solely responsible for
     deciding whether the expression to be matched "has" that mode.

     When constructing an insn, argument 3 of the gen-function will
     specify the operation (i.e. the expression code) for the expression
     to be made.  It should be an RTL expression, whose expression code
     is copied into a new expression whose operands are arguments 1 and
     2 of the gen-function.  The subexpressions of argument 3 are not
     used; only its expression code matters.

     When 'match_operator' is used in a pattern for matching an insn, it
     usually best if the operand number of the 'match_operator' is
     higher than that of the actual operands of the insn.  This improves
     register allocation because the register allocator often looks at
     operands 1 and 2 of insns to see if it can do register tying.

     There is no way to specify constraints in 'match_operator'.  The
     operand of the insn which corresponds to the 'match_operator' never
     has any constraints because it is never reloaded as a whole.
     However, if parts of its OPERANDS are matched by 'match_operand'
     patterns, those parts may have constraints of their own.

'(match_op_dup:M N[OPERANDS...])'
     Like 'match_dup', except that it applies to operators instead of
     operands.  When constructing an insn, operand number N will be
     substituted at this point.  But in matching, 'match_op_dup' behaves
     differently.  It assumes that operand number N has already been
     determined by a 'match_operator' appearing earlier in the
     recognition template, and it matches only an identical-looking
     expression.

'(match_parallel N PREDICATE [SUBPAT...])'
     This pattern is a placeholder for an insn that consists of a
     'parallel' expression with a variable number of elements.  This
     expression should only appear at the top level of an insn pattern.

     When constructing an insn, operand number N will be substituted at
     this point.  When matching an insn, it matches if the body of the
     insn is a 'parallel' expression with at least as many elements as
     the vector of SUBPAT expressions in the 'match_parallel', if each
     SUBPAT matches the corresponding element of the 'parallel', _and_
     the function PREDICATE returns nonzero on the 'parallel' that is
     the body of the insn.  It is the responsibility of the predicate to
     validate elements of the 'parallel' beyond those listed in the
     'match_parallel'.

     A typical use of 'match_parallel' is to match load and store
     multiple expressions, which can contain a variable number of
     elements in a 'parallel'.  For example,

          (define_insn ""
            [(match_parallel 0 "load_multiple_operation"
               [(set (match_operand:SI 1 "gpc_reg_operand" "=r")
                     (match_operand:SI 2 "memory_operand" "m"))
                (use (reg:SI 179))
                (clobber (reg:SI 179))])]
            ""
            "loadm 0,0,%1,%2")

     This example comes from 'a29k.md'.  The function
     'load_multiple_operation' is defined in 'a29k.c' and checks that
     subsequent elements in the 'parallel' are the same as the 'set' in
     the pattern, except that they are referencing subsequent registers
     and memory locations.

     An insn that matches this pattern might look like:

          (parallel
           [(set (reg:SI 20) (mem:SI (reg:SI 100)))
            (use (reg:SI 179))
            (clobber (reg:SI 179))
            (set (reg:SI 21)
                 (mem:SI (plus:SI (reg:SI 100)
                                  (const_int 4))))
            (set (reg:SI 22)
                 (mem:SI (plus:SI (reg:SI 100)
                                  (const_int 8))))])

'(match_par_dup N [SUBPAT...])'
     Like 'match_op_dup', but for 'match_parallel' instead of
     'match_operator'.


File: gccint.info,  Node: Output Template,  Next: Output Statement,  Prev: RTL Template,  Up: Machine Desc

16.5 Output Templates and Operand Substitution
==============================================

The "output template" is a string which specifies how to output the
assembler code for an instruction pattern.  Most of the template is a
fixed string which is output literally.  The character '%' is used to
specify where to substitute an operand; it can also be used to identify
places where different variants of the assembler require different
syntax.

 In the simplest case, a '%' followed by a digit N says to output
operand N at that point in the string.

 '%' followed by a letter and a digit says to output an operand in an
alternate fashion.  Four letters have standard, built-in meanings
described below.  The machine description macro 'PRINT_OPERAND' can
define additional letters with nonstandard meanings.

 '%cDIGIT' can be used to substitute an operand that is a constant value
without the syntax that normally indicates an immediate operand.

 '%nDIGIT' is like '%cDIGIT' except that the value of the constant is
negated before printing.

 '%aDIGIT' can be used to substitute an operand as if it were a memory
reference, with the actual operand treated as the address.  This may be
useful when outputting a "load address" instruction, because often the
assembler syntax for such an instruction requires you to write the
operand as if it were a memory reference.

 '%lDIGIT' is used to substitute a 'label_ref' into a jump instruction.

 '%=' outputs a number which is unique to each instruction in the entire
compilation.  This is useful for making local labels to be referred to
more than once in a single template that generates multiple assembler
instructions.

 '%' followed by a punctuation character specifies a substitution that
does not use an operand.  Only one case is standard: '%%' outputs a '%'
into the assembler code.  Other nonstandard cases can be defined in the
'PRINT_OPERAND' macro.  You must also define which punctuation
characters are valid with the 'PRINT_OPERAND_PUNCT_VALID_P' macro.

 The template may generate multiple assembler instructions.  Write the
text for the instructions, with '\;' between them.

 When the RTL contains two operands which are required by constraint to
match each other, the output template must refer only to the
lower-numbered operand.  Matching operands are not always identical, and
the rest of the compiler arranges to put the proper RTL expression for
printing into the lower-numbered operand.

 One use of nonstandard letters or punctuation following '%' is to
distinguish between different assembler languages for the same machine;
for example, Motorola syntax versus MIT syntax for the 68000.  Motorola
syntax requires periods in most opcode names, while MIT syntax does not.
For example, the opcode 'movel' in MIT syntax is 'move.l' in Motorola
syntax.  The same file of patterns is used for both kinds of output
syntax, but the character sequence '%.' is used in each place where
Motorola syntax wants a period.  The 'PRINT_OPERAND' macro for Motorola
syntax defines the sequence to output a period; the macro for MIT syntax
defines it to do nothing.

 As a special case, a template consisting of the single character '#'
instructs the compiler to first split the insn, and then output the
resulting instructions separately.  This helps eliminate redundancy in
the output templates.  If you have a 'define_insn' that needs to emit
multiple assembler instructions, and there is a matching 'define_split'
already defined, then you can simply use '#' as the output template
instead of writing an output template that emits the multiple assembler
instructions.

 If the macro 'ASSEMBLER_DIALECT' is defined, you can use construct of
the form '{option0|option1|option2}' in the templates.  These describe
multiple variants of assembler language syntax.  *Note Instruction
Output::.


File: gccint.info,  Node: Output Statement,  Next: Predicates,  Prev: Output Template,  Up: Machine Desc

16.6 C Statements for Assembler Output
======================================

Often a single fixed template string cannot produce correct and
efficient assembler code for all the cases that are recognized by a
single instruction pattern.  For example, the opcodes may depend on the
kinds of operands; or some unfortunate combinations of operands may
require extra machine instructions.

 If the output control string starts with a '@', then it is actually a
series of templates, each on a separate line.  (Blank lines and leading
spaces and tabs are ignored.)  The templates correspond to the pattern's
constraint alternatives (*note Multi-Alternative::).  For example, if a
target machine has a two-address add instruction 'addr' to add into a
register and another 'addm' to add a register to memory, you might write
this pattern:

     (define_insn "addsi3"
       [(set (match_operand:SI 0 "general_operand" "=r,m")
             (plus:SI (match_operand:SI 1 "general_operand" "0,0")
                      (match_operand:SI 2 "general_operand" "g,r")))]
       ""
       "@
        addr %2,%0
        addm %2,%0")

 If the output control string starts with a '*', then it is not an
output template but rather a piece of C program that should compute a
template.  It should execute a 'return' statement to return the
template-string you want.  Most such templates use C string literals,
which require doublequote characters to delimit them.  To include these
doublequote characters in the string, prefix each one with '\'.

 If the output control string is written as a brace block instead of a
double-quoted string, it is automatically assumed to be C code.  In that
case, it is not necessary to put in a leading asterisk, or to escape the
doublequotes surrounding C string literals.

 The operands may be found in the array 'operands', whose C data type is
'rtx []'.

 It is very common to select different ways of generating assembler code
based on whether an immediate operand is within a certain range.  Be
careful when doing this, because the result of 'INTVAL' is an integer on
the host machine.  If the host machine has more bits in an 'int' than
the target machine has in the mode in which the constant will be used,
then some of the bits you get from 'INTVAL' will be superfluous.  For
proper results, you must carefully disregard the values of those bits.

 It is possible to output an assembler instruction and then go on to
output or compute more of them, using the subroutine 'output_asm_insn'.
This receives two arguments: a template-string and a vector of operands.
The vector may be 'operands', or it may be another array of 'rtx' that
you declare locally and initialize yourself.

 When an insn pattern has multiple alternatives in its constraints,
often the appearance of the assembler code is determined mostly by which
alternative was matched.  When this is so, the C code can test the
variable 'which_alternative', which is the ordinal number of the
alternative that was actually satisfied (0 for the first, 1 for the
second alternative, etc.).

 For example, suppose there are two opcodes for storing zero, 'clrreg'
for registers and 'clrmem' for memory locations.  Here is how a pattern
could use 'which_alternative' to choose between them:

     (define_insn ""
       [(set (match_operand:SI 0 "general_operand" "=r,m")
             (const_int 0))]
       ""
       {
       return (which_alternative == 0
               ? "clrreg %0" : "clrmem %0");
       })

 The example above, where the assembler code to generate was _solely_
determined by the alternative, could also have been specified as
follows, having the output control string start with a '@':

     (define_insn ""
       [(set (match_operand:SI 0 "general_operand" "=r,m")
             (const_int 0))]
       ""
       "@
        clrreg %0
        clrmem %0")

 If you just need a little bit of C code in one (or a few) alternatives,
you can use '*' inside of a '@' multi-alternative template:

     (define_insn ""
       [(set (match_operand:SI 0 "general_operand" "=r,<,m")
             (const_int 0))]
       ""
       "@
        clrreg %0
        * return stack_mem_p (operands[0]) ? \"push 0\" : \"clrmem %0\";
        clrmem %0")


File: gccint.info,  Node: Predicates,  Next: Constraints,  Prev: Output Statement,  Up: Machine Desc

16.7 Predicates
===============

A predicate determines whether a 'match_operand' or 'match_operator'
expression matches, and therefore whether the surrounding instruction
pattern will be used for that combination of operands.  GCC has a number
of machine-independent predicates, and you can define machine-specific
predicates as needed.  By convention, predicates used with
'match_operand' have names that end in '_operand', and those used with
'match_operator' have names that end in '_operator'.

 All predicates are Boolean functions (in the mathematical sense) of two
arguments: the RTL expression that is being considered at that position
in the instruction pattern, and the machine mode that the
'match_operand' or 'match_operator' specifies.  In this section, the
first argument is called OP and the second argument MODE.  Predicates
can be called from C as ordinary two-argument functions; this can be
useful in output templates or other machine-specific code.

 Operand predicates can allow operands that are not actually acceptable
to the hardware, as long as the constraints give reload the ability to
fix them up (*note Constraints::).  However, GCC will usually generate
better code if the predicates specify the requirements of the machine
instructions as closely as possible.  Reload cannot fix up operands that
must be constants ("immediate operands"); you must use a predicate that
allows only constants, or else enforce the requirement in the extra
condition.

 Most predicates handle their MODE argument in a uniform manner.  If
MODE is 'VOIDmode' (unspecified), then OP can have any mode.  If MODE is
anything else, then OP must have the same mode, unless OP is a
'CONST_INT' or integer 'CONST_DOUBLE'.  These RTL expressions always
have 'VOIDmode', so it would be counterproductive to check that their
mode matches.  Instead, predicates that accept 'CONST_INT' and/or
integer 'CONST_DOUBLE' check that the value stored in the constant will
fit in the requested mode.

 Predicates with this behavior are called "normal".  'genrecog' can
optimize the instruction recognizer based on knowledge of how normal
predicates treat modes.  It can also diagnose certain kinds of common
errors in the use of normal predicates; for instance, it is almost
always an error to use a normal predicate without specifying a mode.

 Predicates that do something different with their MODE argument are
called "special".  The generic predicates 'address_operand' and
'pmode_register_operand' are special predicates.  'genrecog' does not do
any optimizations or diagnosis when special predicates are used.

* Menu:

* Machine-Independent Predicates::  Predicates available to all back ends.
* Defining Predicates::             How to write machine-specific predicate
                                    functions.


File: gccint.info,  Node: Machine-Independent Predicates,  Next: Defining Predicates,  Up: Predicates

16.7.1 Machine-Independent Predicates
-------------------------------------

These are the generic predicates available to all back ends.  They are
defined in 'recog.c'.  The first category of predicates allow only
constant, or "immediate", operands.

 -- Function: immediate_operand
     This predicate allows any sort of constant that fits in MODE.  It
     is an appropriate choice for instructions that take operands that
     must be constant.

 -- Function: const_int_operand
     This predicate allows any 'CONST_INT' expression that fits in MODE.
     It is an appropriate choice for an immediate operand that does not
     allow a symbol or label.

 -- Function: const_double_operand
     This predicate accepts any 'CONST_DOUBLE' expression that has
     exactly MODE.  If MODE is 'VOIDmode', it will also accept
     'CONST_INT'.  It is intended for immediate floating point
     constants.

The second category of predicates allow only some kind of machine
register.

 -- Function: register_operand
     This predicate allows any 'REG' or 'SUBREG' expression that is
     valid for MODE.  It is often suitable for arithmetic instruction
     operands on a RISC machine.

 -- Function: pmode_register_operand
     This is a slight variant on 'register_operand' which works around a
     limitation in the machine-description reader.

          (match_operand N "pmode_register_operand" CONSTRAINT)

     means exactly what

          (match_operand:P N "register_operand" CONSTRAINT)

     would mean, if the machine-description reader accepted ':P' mode
     suffixes.  Unfortunately, it cannot, because 'Pmode' is an alias
     for some other mode, and might vary with machine-specific options.
     *Note Misc::.

 -- Function: scratch_operand
     This predicate allows hard registers and 'SCRATCH' expressions, but
     not pseudo-registers.  It is used internally by 'match_scratch'; it
     should not be used directly.

The third category of predicates allow only some kind of memory
reference.

 -- Function: memory_operand
     This predicate allows any valid reference to a quantity of mode
     MODE in memory, as determined by the weak form of
     'GO_IF_LEGITIMATE_ADDRESS' (*note Addressing Modes::).

 -- Function: address_operand
     This predicate is a little unusual; it allows any operand that is a
     valid expression for the _address_ of a quantity of mode MODE,
     again determined by the weak form of 'GO_IF_LEGITIMATE_ADDRESS'.
     To first order, if '(mem:MODE (EXP))' is acceptable to
     'memory_operand', then EXP is acceptable to 'address_operand'.
     Note that EXP does not necessarily have the mode MODE.

 -- Function: indirect_operand
     This is a stricter form of 'memory_operand' which allows only
     memory references with a 'general_operand' as the address
     expression.  New uses of this predicate are discouraged, because
     'general_operand' is very permissive, so it's hard to tell what an
     'indirect_operand' does or does not allow.  If a target has
     different requirements for memory operands for different
     instructions, it is better to define target-specific predicates
     which enforce the hardware's requirements explicitly.

 -- Function: push_operand
     This predicate allows a memory reference suitable for pushing a
     value onto the stack.  This will be a 'MEM' which refers to
     'stack_pointer_rtx', with a side-effect in its address expression
     (*note Incdec::); which one is determined by the 'STACK_PUSH_CODE'
     macro (*note Frame Layout::).

 -- Function: pop_operand
     This predicate allows a memory reference suitable for popping a
     value off the stack.  Again, this will be a 'MEM' referring to
     'stack_pointer_rtx', with a side-effect in its address expression.
     However, this time 'STACK_POP_CODE' is expected.

The fourth category of predicates allow some combination of the above
operands.

 -- Function: nonmemory_operand
     This predicate allows any immediate or register operand valid for
     MODE.

 -- Function: nonimmediate_operand
     This predicate allows any register or memory operand valid for
     MODE.

 -- Function: general_operand
     This predicate allows any immediate, register, or memory operand
     valid for MODE.

Finally, there are two generic operator predicates.

 -- Function: comparison_operator
     This predicate matches any expression which performs an arithmetic
     comparison in MODE; that is, 'COMPARISON_P' is true for the
     expression code.

 -- Function: ordered_comparison_operator
     This predicate matches any expression which performs an arithmetic
     comparison in MODE and whose expression code is valid for integer
     modes; that is, the expression code will be one of 'eq', 'ne',
     'lt', 'ltu', 'le', 'leu', 'gt', 'gtu', 'ge', 'geu'.


File: gccint.info,  Node: Defining Predicates,  Prev: Machine-Independent Predicates,  Up: Predicates

16.7.2 Defining Machine-Specific Predicates
-------------------------------------------

Many machines have requirements for their operands that cannot be
expressed precisely using the generic predicates.  You can define
additional predicates using 'define_predicate' and
'define_special_predicate' expressions.  These expressions have three
operands:

   * The name of the predicate, as it will be referred to in
     'match_operand' or 'match_operator' expressions.

   * An RTL expression which evaluates to true if the predicate allows
     the operand OP, false if it does not.  This expression can only use
     the following RTL codes:

     'MATCH_OPERAND'
          When written inside a predicate expression, a 'MATCH_OPERAND'
          expression evaluates to true if the predicate it names would
          allow OP.  The operand number and constraint are ignored.  Due
          to limitations in 'genrecog', you can only refer to generic
          predicates and predicates that have already been defined.

     'MATCH_CODE'
          This expression evaluates to true if OP or a specified
          subexpression of OP has one of a given list of RTX codes.

          The first operand of this expression is a string constant
          containing a comma-separated list of RTX code names (in lower
          case).  These are the codes for which the 'MATCH_CODE' will be
          true.

          The second operand is a string constant which indicates what
          subexpression of OP to examine.  If it is absent or the empty
          string, OP itself is examined.  Otherwise, the string constant
          must be a sequence of digits and/or lowercase letters.  Each
          character indicates a subexpression to extract from the
          current expression; for the first character this is OP, for
          the second and subsequent characters it is the result of the
          previous character.  A digit N extracts 'XEXP (E, N)'; a
          letter L extracts 'XVECEXP (E, 0, N)' where N is the
          alphabetic ordinal of L (0 for 'a', 1 for 'b', and so on).
          The 'MATCH_CODE' then examines the RTX code of the
          subexpression extracted by the complete string.  It is not
          possible to extract components of an 'rtvec' that is not at
          position 0 within its RTX object.

     'MATCH_TEST'
          This expression has one operand, a string constant containing
          a C expression.  The predicate's arguments, OP and MODE, are
          available with those names in the C expression.  The
          'MATCH_TEST' evaluates to true if the C expression evaluates
          to a nonzero value.  'MATCH_TEST' expressions must not have
          side effects.

     'AND'
     'IOR'
     'NOT'
     'IF_THEN_ELSE'
          The basic 'MATCH_' expressions can be combined using these
          logical operators, which have the semantics of the C operators
          '&&', '||', '!', and '? :' respectively.  As in Common Lisp,
          you may give an 'AND' or 'IOR' expression an arbitrary number
          of arguments; this has exactly the same effect as writing a
          chain of two-argument 'AND' or 'IOR' expressions.

   * An optional block of C code, which should execute 'return true' if
     the predicate is found to match and 'return false' if it does not.
     It must not have any side effects.  The predicate arguments, OP and
     MODE, are available with those names.

     If a code block is present in a predicate definition, then the RTL
     expression must evaluate to true _and_ the code block must execute
     'return true' for the predicate to allow the operand.  The RTL
     expression is evaluated first; do not re-check anything in the code
     block that was checked in the RTL expression.

 The program 'genrecog' scans 'define_predicate' and
'define_special_predicate' expressions to determine which RTX codes are
possibly allowed.  You should always make this explicit in the RTL
predicate expression, using 'MATCH_OPERAND' and 'MATCH_CODE'.

 Here is an example of a simple predicate definition, from the IA64
machine description:

     ;; True if OP is a 'SYMBOL_REF' which refers to the sdata section.
     (define_predicate "small_addr_symbolic_operand"
       (and (match_code "symbol_ref")
            (match_test "SYMBOL_REF_SMALL_ADDR_P (op)")))

And here is another, showing the use of the C block.

     ;; True if OP is a register operand that is (or could be) a GR reg.
     (define_predicate "gr_register_operand"
       (match_operand 0 "register_operand")
     {
       unsigned int regno;
       if (GET_CODE (op) == SUBREG)
         op = SUBREG_REG (op);

       regno = REGNO (op);
       return (regno >= FIRST_PSEUDO_REGISTER || GENERAL_REGNO_P (regno));
     })

 Predicates written with 'define_predicate' automatically include a test
that MODE is 'VOIDmode', or OP has the same mode as MODE, or OP is a
'CONST_INT' or 'CONST_DOUBLE'.  They do _not_ check specifically for
integer 'CONST_DOUBLE', nor do they test that the value of either kind
of constant fits in the requested mode.  This is because target-specific
predicates that take constants usually have to do more stringent value
checks anyway.  If you need the exact same treatment of 'CONST_INT' or
'CONST_DOUBLE' that the generic predicates provide, use a
'MATCH_OPERAND' subexpression to call 'const_int_operand',
'const_double_operand', or 'immediate_operand'.

 Predicates written with 'define_special_predicate' do not get any
automatic mode checks, and are treated as having special mode handling
by 'genrecog'.

 The program 'genpreds' is responsible for generating code to test
predicates.  It also writes a header file containing function
declarations for all machine-specific predicates.  It is not necessary
to declare these predicates in 'CPU-protos.h'.


File: gccint.info,  Node: Constraints,  Next: Standard Names,  Prev: Predicates,  Up: Machine Desc

16.8 Operand Constraints
========================

Each 'match_operand' in an instruction pattern can specify constraints
for the operands allowed.  The constraints allow you to fine-tune
matching within the set of operands allowed by the predicate.

 Constraints can say whether an operand may be in a register, and which
kinds of register; whether the operand can be a memory reference, and
which kinds of address; whether the operand may be an immediate
constant, and which possible values it may have.  Constraints can also
require two operands to match.  Side-effects aren't allowed in operands
of inline 'asm', unless '<' or '>' constraints are used, because there
is no guarantee that the side-effects will happen exactly once in an
instruction that can update the addressing register.

* Menu:

* Simple Constraints::  Basic use of constraints.
* Multi-Alternative::   When an insn has two alternative constraint-patterns.
* Class Preferences::   Constraints guide which hard register to put things in.
* Modifiers::           More precise control over effects of constraints.
* Machine Constraints:: Existing constraints for some particular machines.
* Disable Insn Alternatives:: Disable insn alternatives using the 'enabled' attribute.
* Define Constraints::  How to define machine-specific constraints.
* C Constraint Interface:: How to test constraints from C code.


File: gccint.info,  Node: Simple Constraints,  Next: Multi-Alternative,  Up: Constraints

16.8.1 Simple Constraints
-------------------------

The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted.  Here are the
letters that are allowed:

whitespace
     Whitespace characters are ignored and can be inserted at any
     position except the first.  This enables each alternative for
     different operands to be visually aligned in the machine
     description even if they have different number of constraints and
     modifiers.

'm'
     A memory operand is allowed, with any kind of address that the
     machine supports in general.  Note that the letter used for the
     general memory constraint can be re-defined by a back end using the
     'TARGET_MEM_CONSTRAINT' macro.

'o'
     A memory operand is allowed, but only if the address is
     "offsettable".  This means that adding a small integer (actually,
     the width in bytes of the operand, as determined by its machine
     mode) may be added to the address and the result is also a valid
     memory address.

     For example, an address which is constant is offsettable; so is an
     address that is the sum of a register and a constant (as long as a
     slightly larger constant is also within the range of
     address-offsets supported by the machine); but an autoincrement or
     autodecrement address is not offsettable.  More complicated
     indirect/indexed addresses may or may not be offsettable depending
     on the other addressing modes that the machine supports.

     Note that in an output operand which can be matched by another
     operand, the constraint letter 'o' is valid only when accompanied
     by both '<' (if the target machine has predecrement addressing) and
     '>' (if the target machine has preincrement addressing).

'V'
     A memory operand that is not offsettable.  In other words, anything
     that would fit the 'm' constraint but not the 'o' constraint.

'<'
     A memory operand with autodecrement addressing (either predecrement
     or postdecrement) is allowed.  In inline 'asm' this constraint is
     only allowed if the operand is used exactly once in an instruction
     that can handle the side-effects.  Not using an operand with '<' in
     constraint string in the inline 'asm' pattern at all or using it in
     multiple instructions isn't valid, because the side-effects
     wouldn't be performed or would be performed more than once.
     Furthermore, on some targets the operand with '<' in constraint
     string must be accompanied by special instruction suffixes like
     '%U0' instruction suffix on PowerPC or '%P0' on IA-64.

'>'
     A memory operand with autoincrement addressing (either preincrement
     or postincrement) is allowed.  In inline 'asm' the same
     restrictions as for '<' apply.

'r'
     A register operand is allowed provided that it is in a general
     register.

'i'
     An immediate integer operand (one with constant value) is allowed.
     This includes symbolic constants whose values will be known only at
     assembly time or later.

'n'
     An immediate integer operand with a known numeric value is allowed.
     Many systems cannot support assembly-time constants for operands
     less than a word wide.  Constraints for these operands should use
     'n' rather than 'i'.

'I', 'J', 'K', ... 'P'
     Other letters in the range 'I' through 'P' may be defined in a
     machine-dependent fashion to permit immediate integer operands with
     explicit integer values in specified ranges.  For example, on the
     68000, 'I' is defined to stand for the range of values 1 to 8.
     This is the range permitted as a shift count in the shift
     instructions.

'E'
     An immediate floating operand (expression code 'const_double') is
     allowed, but only if the target floating point format is the same
     as that of the host machine (on which the compiler is running).

'F'
     An immediate floating operand (expression code 'const_double' or
     'const_vector') is allowed.

'G', 'H'
     'G' and 'H' may be defined in a machine-dependent fashion to permit
     immediate floating operands in particular ranges of values.

's'
     An immediate integer operand whose value is not an explicit integer
     is allowed.

     This might appear strange; if an insn allows a constant operand
     with a value not known at compile time, it certainly must allow any
     known value.  So why use 's' instead of 'i'?  Sometimes it allows
     better code to be generated.

     For example, on the 68000 in a fullword instruction it is possible
     to use an immediate operand; but if the immediate value is between
     -128 and 127, better code results from loading the value into a
     register and using the register.  This is because the load into the
     register can be done with a 'moveq' instruction.  We arrange for
     this to happen by defining the letter 'K' to mean "any integer
     outside the range -128 to 127", and then specifying 'Ks' in the
     operand constraints.

'g'
     Any register, memory or immediate integer operand is allowed,
     except for registers that are not general registers.

'X'
     Any operand whatsoever is allowed, even if it does not satisfy
     'general_operand'.  This is normally used in the constraint of a
     'match_scratch' when certain alternatives will not actually require
     a scratch register.

'0', '1', '2', ... '9'
     An operand that matches the specified operand number is allowed.
     If a digit is used together with letters within the same
     alternative, the digit should come last.

     This number is allowed to be more than a single digit.  If multiple
     digits are encountered consecutively, they are interpreted as a
     single decimal integer.  There is scant chance for ambiguity, since
     to-date it has never been desirable that '10' be interpreted as
     matching either operand 1 _or_ operand 0.  Should this be desired,
     one can use multiple alternatives instead.

     This is called a "matching constraint" and what it really means is
     that the assembler has only a single operand that fills two roles
     considered separate in the RTL insn.  For example, an add insn has
     two input operands and one output operand in the RTL, but on most
     CISC machines an add instruction really has only two operands, one
     of them an input-output operand:

          addl #35,r12

     Matching constraints are used in these circumstances.  More
     precisely, the two operands that match must include one input-only
     operand and one output-only operand.  Moreover, the digit must be a
     smaller number than the number of the operand that uses it in the
     constraint.

     For operands to match in a particular case usually means that they
     are identical-looking RTL expressions.  But in a few special cases
     specific kinds of dissimilarity are allowed.  For example, '*x' as
     an input operand will match '*x++' as an output operand.  For
     proper results in such cases, the output template should always use
     the output-operand's number when printing the operand.

'p'
     An operand that is a valid memory address is allowed.  This is for
     "load address" and "push address" instructions.

     'p' in the constraint must be accompanied by 'address_operand' as
     the predicate in the 'match_operand'.  This predicate interprets
     the mode specified in the 'match_operand' as the mode of the memory
     reference for which the address would be valid.

OTHER-LETTERS
     Other letters can be defined in machine-dependent fashion to stand
     for particular classes of registers or other arbitrary operand
     types.  'd', 'a' and 'f' are defined on the 68000/68020 to stand
     for data, address and floating point registers.

 In order to have valid assembler code, each operand must satisfy its
constraint.  But a failure to do so does not prevent the pattern from
applying to an insn.  Instead, it directs the compiler to modify the
code so that the constraint will be satisfied.  Usually this is done by
copying an operand into a register.

 Contrast, therefore, the two instruction patterns that follow:

     (define_insn ""
       [(set (match_operand:SI 0 "general_operand" "=r")
             (plus:SI (match_dup 0)
                      (match_operand:SI 1 "general_operand" "r")))]
       ""
       "...")

which has two operands, one of which must appear in two places, and

     (define_insn ""
       [(set (match_operand:SI 0 "general_operand" "=r")
             (plus:SI (match_operand:SI 1 "general_operand" "0")
                      (match_operand:SI 2 "general_operand" "r")))]
       ""
       "...")

which has three operands, two of which are required by a constraint to
be identical.  If we are considering an insn of the form

     (insn N PREV NEXT
       (set (reg:SI 3)
            (plus:SI (reg:SI 6) (reg:SI 109)))
       ...)

the first pattern would not apply at all, because this insn does not
contain two identical subexpressions in the right place.  The pattern
would say, "That does not look like an add instruction; try other
patterns".  The second pattern would say, "Yes, that's an add
instruction, but there is something wrong with it".  It would direct the
reload pass of the compiler to generate additional insns to make the
constraint true.  The results might look like this:

     (insn N2 PREV N
       (set (reg:SI 3) (reg:SI 6))
       ...)

     (insn N N2 NEXT
       (set (reg:SI 3)
            (plus:SI (reg:SI 3) (reg:SI 109)))
       ...)

 It is up to you to make sure that each operand, in each pattern, has
constraints that can handle any RTL expression that could be present for
that operand.  (When multiple alternatives are in use, each pattern
must, for each possible combination of operand expressions, have at
least one alternative which can handle that combination of operands.)
The constraints don't need to _allow_ any possible operand--when this is
the case, they do not constrain--but they must at least point the way to
reloading any possible operand so that it will fit.

   * If the constraint accepts whatever operands the predicate permits,
     there is no problem: reloading is never necessary for this operand.

     For example, an operand whose constraints permit everything except
     registers is safe provided its predicate rejects registers.

     An operand whose predicate accepts only constant values is safe
     provided its constraints include the letter 'i'.  If any possible
     constant value is accepted, then nothing less than 'i' will do; if
     the predicate is more selective, then the constraints may also be
     more selective.

   * Any operand expression can be reloaded by copying it into a
     register.  So if an operand's constraints allow some kind of
     register, it is certain to be safe.  It need not permit all classes
     of registers; the compiler knows how to copy a register into
     another register of the proper class in order to make an
     instruction valid.

   * A nonoffsettable memory reference can be reloaded by copying the
     address into a register.  So if the constraint uses the letter 'o',
     all memory references are taken care of.

   * A constant operand can be reloaded by allocating space in memory to
     hold it as preinitialized data.  Then the memory reference can be
     used in place of the constant.  So if the constraint uses the
     letters 'o' or 'm', constant operands are not a problem.

   * If the constraint permits a constant and a pseudo register used in
     an insn was not allocated to a hard register and is equivalent to a
     constant, the register will be replaced with the constant.  If the
     predicate does not permit a constant and the insn is re-recognized
     for some reason, the compiler will crash.  Thus the predicate must
     always recognize any objects allowed by the constraint.

 If the operand's predicate can recognize registers, but the constraint
does not permit them, it can make the compiler crash.  When this operand
happens to be a register, the reload pass will be stymied, because it
does not know how to copy a register temporarily into memory.

 If the predicate accepts a unary operator, the constraint applies to
the operand.  For example, the MIPS processor at ISA level 3 supports an
instruction which adds two registers in 'SImode' to produce a 'DImode'
result, but only if the registers are correctly sign extended.  This
predicate for the input operands accepts a 'sign_extend' of an 'SImode'
register.  Write the constraint to indicate the type of register that is
required for the operand of the 'sign_extend'.


File: gccint.info,  Node: Multi-Alternative,  Next: Class Preferences,  Prev: Simple Constraints,  Up: Constraints

16.8.2 Multiple Alternative Constraints
---------------------------------------

Sometimes a single instruction has multiple alternative sets of possible
operands.  For example, on the 68000, a logical-or instruction can
combine register or an immediate value into memory, or it can combine
any kind of operand into a register; but it cannot combine one memory
location into another.

 These constraints are represented as multiple alternatives.  An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.  Here is how it is done for fullword logical-or on the
68000:

     (define_insn "iorsi3"
       [(set (match_operand:SI 0 "general_operand" "=m,d")
             (ior:SI (match_operand:SI 1 "general_operand" "%0,0")
                     (match_operand:SI 2 "general_operand" "dKs,dmKs")))]
       ...)

 The first alternative has 'm' (memory) for operand 0, '0' for operand 1
(meaning it must match operand 0), and 'dKs' for operand 2.  The second
alternative has 'd' (data register) for operand 0, '0' for operand 1,
and 'dmKs' for operand 2.  The '=' and '%' in the constraints apply to
all the alternatives; their meaning is explained in the next section
(*note Class Preferences::).

 If all the operands fit any one alternative, the instruction is valid.
Otherwise, for each alternative, the compiler counts how many
instructions must be added to copy the operands so that that alternative
applies.  The alternative requiring the least copying is chosen.  If two
alternatives need the same amount of copying, the one that comes first
is chosen.  These choices can be altered with the '?' and '!'
characters:

'?'
     Disparage slightly the alternative that the '?' appears in, as a
     choice when no alternative applies exactly.  The compiler regards
     this alternative as one unit more costly for each '?' that appears
     in it.

'!'
     Disparage severely the alternative that the '!' appears in.  This
     alternative can still be used if it fits without reloading, but if
     reloading is needed, some other alternative will be used.

 When an insn pattern has multiple alternatives in its constraints,
often the appearance of the assembler code is determined mostly by which
alternative was matched.  When this is so, the C code for writing the
assembler code can use the variable 'which_alternative', which is the
ordinal number of the alternative that was actually satisfied (0 for the
first, 1 for the second alternative, etc.).  *Note Output Statement::.


File: gccint.info,  Node: Class Preferences,  Next: Modifiers,  Prev: Multi-Alternative,  Up: Constraints

16.8.3 Register Class Preferences
---------------------------------

The operand constraints have another function: they enable the compiler
to decide which kind of hardware register a pseudo register is best
allocated to.  The compiler examines the constraints that apply to the
insns that use the pseudo register, looking for the machine-dependent
letters such as 'd' and 'a' that specify classes of registers.  The
pseudo register is put in whichever class gets the most "votes".  The
constraint letters 'g' and 'r' also vote: they vote in favor of a
general register.  The machine description says which registers are
considered general.

 Of course, on some machines all registers are equivalent, and no
register classes are defined.  Then none of this complexity is relevant.


File: gccint.info,  Node: Modifiers,  Next: Machine Constraints,  Prev: Class Preferences,  Up: Constraints

16.8.4 Constraint Modifier Characters
-------------------------------------

Here are constraint modifier characters.

'='
     Means that this operand is write-only for this instruction: the
     previous value is discarded and replaced by output data.

'+'
     Means that this operand is both read and written by the
     instruction.

     When the compiler fixes up the operands to satisfy the constraints,
     it needs to know which operands are inputs to the instruction and
     which are outputs from it.  '=' identifies an output; '+'
     identifies an operand that is both input and output; all other
     operands are assumed to be input only.

     If you specify '=' or '+' in a constraint, you put it in the first
     character of the constraint string.

'&'
     Means (in a particular alternative) that this operand is an
     "earlyclobber" operand, which is modified before the instruction is
     finished using the input operands.  Therefore, this operand may not
     lie in a register that is used as an input operand or as part of
     any memory address.

     '&' applies only to the alternative in which it is written.  In
     constraints with multiple alternatives, sometimes one alternative
     requires '&' while others do not.  See, for example, the 'movdf'
     insn of the 68000.

     An input operand can be tied to an earlyclobber operand if its only
     use as an input occurs before the early result is written.  Adding
     alternatives of this form often allows GCC to produce better code
     when only some of the inputs can be affected by the earlyclobber.
     See, for example, the 'mulsi3' insn of the ARM.

     '&' does not obviate the need to write '='.

'%'
     Declares the instruction to be commutative for this operand and the
     following operand.  This means that the compiler may interchange
     the two operands if that is the cheapest way to make all operands
     fit the constraints.  This is often used in patterns for addition
     instructions that really have only two operands: the result must go
     in one of the arguments.  Here for example, is how the 68000
     halfword-add instruction is defined:

          (define_insn "addhi3"
            [(set (match_operand:HI 0 "general_operand" "=m,r")
               (plus:HI (match_operand:HI 1 "general_operand" "%0,0")
                        (match_operand:HI 2 "general_operand" "di,g")))]
            ...)
     GCC can only handle one commutative pair in an asm; if you use
     more, the compiler may fail.  Note that you need not use the
     modifier if the two alternatives are strictly identical; this would
     only waste time in the reload pass.  The modifier is not
     operational after register allocation, so the result of
     'define_peephole2' and 'define_split's performed after reload
     cannot rely on '%' to make the intended insn match.

'#'
     Says that all following characters, up to the next comma, are to be
     ignored as a constraint.  They are significant only for choosing
     register preferences.

'*'
     Says that the following character should be ignored when choosing
     register preferences.  '*' has no effect on the meaning of the
     constraint as a constraint, and no effect on reloading.  For LRA
     '*' additionally disparages slightly the alternative if the
     following character matches the operand.

     Here is an example: the 68000 has an instruction to sign-extend a
     halfword in a data register, and can also sign-extend a value by
     copying it into an address register.  While either kind of register
     is acceptable, the constraints on an address-register destination
     are less strict, so it is best if register allocation makes an
     address register its goal.  Therefore, '*' is used so that the 'd'
     constraint letter (for data register) is ignored when computing
     register preferences.

          (define_insn "extendhisi2"
            [(set (match_operand:SI 0 "general_operand" "=*d,a")
                  (sign_extend:SI
                   (match_operand:HI 1 "general_operand" "0,g")))]
            ...)


File: gccint.info,  Node: Machine Constraints,  Next: Disable Insn Alternatives,  Prev: Modifiers,  Up: Constraints

16.8.5 Constraints for Particular Machines
------------------------------------------

Whenever possible, you should use the general-purpose constraint letters
in 'asm' arguments, since they will convey meaning more readily to
people reading your code.  Failing that, use the constraint letters that
usually have very similar meanings across architectures.  The most
commonly used constraints are 'm' and 'r' (for memory and
general-purpose registers respectively; *note Simple Constraints::), and
'I', usually the letter indicating the most common immediate-constant
format.

 Each architecture defines additional constraints.  These constraints
are used by the compiler itself for instruction generation, as well as
for 'asm' statements; therefore, some of the constraints are not
particularly useful for 'asm'.  Here is a summary of some of the
machine-dependent constraints available on some particular machines; it
includes both constraints that are useful for 'asm' and constraints that
aren't.  The compiler source file mentioned in the table heading for
each architecture is the definitive reference for the meanings of that
architecture's constraints.

_AArch64 family--'config/aarch64/constraints.md'_
     'k'
          The stack pointer register ('SP')

     'w'
          Floating point or SIMD vector register

     'I'
          Integer constant that is valid as an immediate operand in an
          'ADD' instruction

     'J'
          Integer constant that is valid as an immediate operand in a
          'SUB' instruction (once negated)

     'K'
          Integer constant that can be used with a 32-bit logical
          instruction

     'L'
          Integer constant that can be used with a 64-bit logical
          instruction

     'M'
          Integer constant that is valid as an immediate operand in a
          32-bit 'MOV' pseudo instruction.  The 'MOV' may be assembled
          to one of several different machine instructions depending on
          the value

     'N'
          Integer constant that is valid as an immediate operand in a
          64-bit 'MOV' pseudo instruction

     'S'
          An absolute symbolic address or a label reference

     'Y'
          Floating point constant zero

     'Z'
          Integer constant zero

     'Usa'
          An absolute symbolic address

     'Ush'
          The high part (bits 12 and upwards) of the pc-relative address
          of a symbol within 4GB of the instruction

     'Q'
          A memory address which uses a single base register with no
          offset

     'Ump'
          A memory address suitable for a load/store pair instruction in
          SI, DI, SF and DF modes

_ARM family--'config/arm/constraints.md'_
     'w'
          VFP floating-point register

     'G'
          The floating-point constant 0.0

     'I'
          Integer that is valid as an immediate operand in a data
          processing instruction.  That is, an integer in the range 0 to
          255 rotated by a multiple of 2

     'J'
          Integer in the range -4095 to 4095

     'K'
          Integer that satisfies constraint 'I' when inverted (ones
          complement)

     'L'
          Integer that satisfies constraint 'I' when negated (twos
          complement)

     'M'
          Integer in the range 0 to 32

     'Q'
          A memory reference where the exact address is in a single
          register (''m'' is preferable for 'asm' statements)

     'R'
          An item in the constant pool

     'S'
          A symbol in the text segment of the current file

     'Uv'
          A memory reference suitable for VFP load/store insns
          (reg+constant offset)

     'Uy'
          A memory reference suitable for iWMMXt load/store
          instructions.

     'Uq'
          A memory reference suitable for the ARMv4 ldrsb instruction.

_AVR family--'config/avr/constraints.md'_
     'l'
          Registers from r0 to r15

     'a'
          Registers from r16 to r23

     'd'
          Registers from r16 to r31

     'w'
          Registers from r24 to r31.  These registers can be used in
          'adiw' command

     'e'
          Pointer register (r26-r31)

     'b'
          Base pointer register (r28-r31)

     'q'
          Stack pointer register (SPH:SPL)

     't'
          Temporary register r0

     'x'
          Register pair X (r27:r26)

     'y'
          Register pair Y (r29:r28)

     'z'
          Register pair Z (r31:r30)

     'I'
          Constant greater than -1, less than 64

     'J'
          Constant greater than -64, less than 1

     'K'
          Constant integer 2

     'L'
          Constant integer 0

     'M'
          Constant that fits in 8 bits

     'N'
          Constant integer -1

     'O'
          Constant integer 8, 16, or 24

     'P'
          Constant integer 1

     'G'
          A floating point constant 0.0

     'Q'
          A memory address based on Y or Z pointer with displacement.

_Epiphany--'config/epiphany/constraints.md'_
     'U16'
          An unsigned 16-bit constant.

     'K'
          An unsigned 5-bit constant.

     'L'
          A signed 11-bit constant.

     'Cm1'
          A signed 11-bit constant added to -1.  Can only match when the
          '-m1reg-REG' option is active.

     'Cl1'
          Left-shift of -1, i.e., a bit mask with a block of leading
          ones, the rest being a block of trailing zeroes.  Can only
          match when the '-m1reg-REG' option is active.

     'Cr1'
          Right-shift of -1, i.e., a bit mask with a trailing block of
          ones, the rest being zeroes.  Or to put it another way, one
          less than a power of two.  Can only match when the
          '-m1reg-REG' option is active.

     'Cal'
          Constant for arithmetic/logical operations.  This is like 'i',
          except that for position independent code, no symbols /
          expressions needing relocations are allowed.

     'Csy'
          Symbolic constant for call/jump instruction.

     'Rcs'
          The register class usable in short insns.  This is a register
          class constraint, and can thus drive register allocation.
          This constraint won't match unless '-mprefer-short-insn-regs'
          is in effect.

     'Rsc'
          The the register class of registers that can be used to hold a
          sibcall call address.  I.e., a caller-saved register.

     'Rct'
          Core control register class.

     'Rgs'
          The register group usable in short insns.  This constraint
          does not use a register class, so that it only passively
          matches suitable registers, and doesn't drive register
          allocation.

     'Car'
          Constant suitable for the addsi3_r pattern.  This is a valid
          offset For byte, halfword, or word addressing.

     'Rra'
          Matches the return address if it can be replaced with the link
          register.

     'Rcc'
          Matches the integer condition code register.

     'Sra'
          Matches the return address if it is in a stack slot.

     'Cfm'
          Matches control register values to switch fp mode, which are
          encapsulated in 'UNSPEC_FP_MODE'.

_CR16 Architecture--'config/cr16/cr16.h'_

     'b'
          Registers from r0 to r14 (registers without stack pointer)

     't'
          Register from r0 to r11 (all 16-bit registers)

     'p'
          Register from r12 to r15 (all 32-bit registers)

     'I'
          Signed constant that fits in 4 bits

     'J'
          Signed constant that fits in 5 bits

     'K'
          Signed constant that fits in 6 bits

     'L'
          Unsigned constant that fits in 4 bits

     'M'
          Signed constant that fits in 32 bits

     'N'
          Check for 64 bits wide constants for add/sub instructions

     'G'
          Floating point constant that is legal for store immediate

_Hewlett-Packard PA-RISC--'config/pa/pa.h'_
     'a'
          General register 1

     'f'
          Floating point register

     'q'
          Shift amount register

     'x'
          Floating point register (deprecated)

     'y'
          Upper floating point register (32-bit), floating point
          register (64-bit)

     'Z'
          Any register

     'I'
          Signed 11-bit integer constant

     'J'
          Signed 14-bit integer constant

     'K'
          Integer constant that can be deposited with a 'zdepi'
          instruction

     'L'
          Signed 5-bit integer constant

     'M'
          Integer constant 0

     'N'
          Integer constant that can be loaded with a 'ldil' instruction

     'O'
          Integer constant whose value plus one is a power of 2

     'P'
          Integer constant that can be used for 'and' operations in
          'depi' and 'extru' instructions

     'S'
          Integer constant 31

     'U'
          Integer constant 63

     'G'
          Floating-point constant 0.0

     'A'
          A 'lo_sum' data-linkage-table memory operand

     'Q'
          A memory operand that can be used as the destination operand
          of an integer store instruction

     'R'
          A scaled or unscaled indexed memory operand

     'T'
          A memory operand for floating-point loads and stores

     'W'
          A register indirect memory operand

_picoChip family--'picochip.h'_
     'k'
          Stack register.

     'f'
          Pointer register.  A register which can be used to access
          memory without supplying an offset.  Any other register can be
          used to access memory, but will need a constant offset.  In
          the case of the offset being zero, it is more efficient to use
          a pointer register, since this reduces code size.

     't'
          A twin register.  A register which may be paired with an
          adjacent register to create a 32-bit register.

     'a'
          Any absolute memory address (e.g., symbolic constant, symbolic
          constant + offset).

     'I'
          4-bit signed integer.

     'J'
          4-bit unsigned integer.

     'K'
          8-bit signed integer.

     'M'
          Any constant whose absolute value is no greater than 4-bits.

     'N'
          10-bit signed integer

     'O'
          16-bit signed integer.

_PowerPC and IBM RS6000--'config/rs6000/constraints.md'_
     'b'
          Address base register

     'd'
          Floating point register (containing 64-bit value)

     'f'
          Floating point register (containing 32-bit value)

     'v'
          Altivec vector register

     'wa'
          Any VSX register if the -mvsx option was used or NO_REGS.

     'wd'
          VSX vector register to hold vector double data or NO_REGS.

     'wf'
          VSX vector register to hold vector float data or NO_REGS.

     'wg'
          If '-mmfpgpr' was used, a floating point register or NO_REGS.

     'wl'
          Floating point register if the LFIWAX instruction is enabled
          or NO_REGS.

     'wm'
          VSX register if direct move instructions are enabled, or
          NO_REGS.

     'wn'
          No register (NO_REGS).

     'wr'
          General purpose register if 64-bit instructions are enabled or
          NO_REGS.

     'ws'
          VSX vector register to hold scalar double values or NO_REGS.

     'wt'
          VSX vector register to hold 128 bit integer or NO_REGS.

     'wu'
          Altivec register to use for float/32-bit int loads/stores or
          NO_REGS.

     'wv'
          Altivec register to use for double loads/stores or NO_REGS.

     'ww'
          FP or VSX register to perform float operations under '-mvsx'
          or NO_REGS.

     'wx'
          Floating point register if the STFIWX instruction is enabled
          or NO_REGS.

     'wy'
          VSX vector register to hold scalar float values or NO_REGS.

     'wz'
          Floating point register if the LFIWZX instruction is enabled
          or NO_REGS.

     'wQ'
          A memory address that will work with the 'lq' and 'stq'
          instructions.

     'h'
          'MQ', 'CTR', or 'LINK' register

     'q'
          'MQ' register

     'c'
          'CTR' register

     'l'
          'LINK' register

     'x'
          'CR' register (condition register) number 0

     'y'
          'CR' register (condition register)

     'z'
          'XER[CA]' carry bit (part of the XER register)

     'I'
          Signed 16-bit constant

     'J'
          Unsigned 16-bit constant shifted left 16 bits (use 'L' instead
          for 'SImode' constants)

     'K'
          Unsigned 16-bit constant

     'L'
          Signed 16-bit constant shifted left 16 bits

     'M'
          Constant larger than 31

     'N'
          Exact power of 2

     'O'
          Zero

     'P'
          Constant whose negation is a signed 16-bit constant

     'G'
          Floating point constant that can be loaded into a register
          with one instruction per word

     'H'
          Integer/Floating point constant that can be loaded into a
          register using three instructions

     'm'
          Memory operand.  Normally, 'm' does not allow addresses that
          update the base register.  If '<' or '>' constraint is also
          used, they are allowed and therefore on PowerPC targets in
          that case it is only safe to use 'm<>' in an 'asm' statement
          if that 'asm' statement accesses the operand exactly once.
          The 'asm' statement must also use '%U<OPNO>' as a placeholder
          for the "update" flag in the corresponding load or store
          instruction.  For example:

               asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val));

          is correct but:

               asm ("st %1,%0" : "=m<>" (mem) : "r" (val));

          is not.

     'es'
          A "stable" memory operand; that is, one which does not include
          any automodification of the base register.  This used to be
          useful when 'm' allowed automodification of the base register,
          but as those are now only allowed when '<' or '>' is used,
          'es' is basically the same as 'm' without '<' and '>'.

     'Q'
          Memory operand that is an offset from a register (it is
          usually better to use 'm' or 'es' in 'asm' statements)

     'Z'
          Memory operand that is an indexed or indirect from a register
          (it is usually better to use 'm' or 'es' in 'asm' statements)

     'R'
          AIX TOC entry

     'a'
          Address operand that is an indexed or indirect from a register
          ('p' is preferable for 'asm' statements)

     'S'
          Constant suitable as a 64-bit mask operand

     'T'
          Constant suitable as a 32-bit mask operand

     'U'
          System V Release 4 small data area reference

     't'
          AND masks that can be performed by two rldic{l, r}
          instructions

     'W'
          Vector constant that does not require memory

     'j'
          Vector constant that is all zeros.

_Intel 386--'config/i386/constraints.md'_
     'R'
          Legacy register--the eight integer registers available on all
          i386 processors ('a', 'b', 'c', 'd', 'si', 'di', 'bp', 'sp').

     'q'
          Any register accessible as 'Rl'.  In 32-bit mode, 'a', 'b',
          'c', and 'd'; in 64-bit mode, any integer register.

     'Q'
          Any register accessible as 'Rh': 'a', 'b', 'c', and 'd'.

     'l'
          Any register that can be used as the index in a base+index
          memory access: that is, any general register except the stack
          pointer.

     'a'
          The 'a' register.

     'b'
          The 'b' register.

     'c'
          The 'c' register.

     'd'
          The 'd' register.

     'S'
          The 'si' register.

     'D'
          The 'di' register.

     'A'
          The 'a' and 'd' registers.  This class is used for
          instructions that return double word results in the 'ax:dx'
          register pair.  Single word values will be allocated either in
          'ax' or 'dx'.  For example on i386 the following implements
          'rdtsc':

               unsigned long long rdtsc (void)
               {
                 unsigned long long tick;
                 __asm__ __volatile__("rdtsc":"=A"(tick));
                 return tick;
               }

          This is not correct on x86_64 as it would allocate tick in
          either 'ax' or 'dx'.  You have to use the following variant
          instead:

               unsigned long long rdtsc (void)
               {
                 unsigned int tickl, tickh;
                 __asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
                 return ((unsigned long long)tickh << 32)|tickl;
               }

     'f'
          Any 80387 floating-point (stack) register.

     't'
          Top of 80387 floating-point stack ('%st(0)').

     'u'
          Second from top of 80387 floating-point stack ('%st(1)').

     'y'
          Any MMX register.

     'x'
          Any SSE register.

     'Yz'
          First SSE register ('%xmm0').

     'Y2'
          Any SSE register, when SSE2 is enabled.

     'Yi'
          Any SSE register, when SSE2 and inter-unit moves are enabled.

     'Ym'
          Any MMX register, when inter-unit moves are enabled.

     'I'
          Integer constant in the range 0 ... 31, for 32-bit shifts.

     'J'
          Integer constant in the range 0 ... 63, for 64-bit shifts.

     'K'
          Signed 8-bit integer constant.

     'L'
          '0xFF' or '0xFFFF', for andsi as a zero-extending move.

     'M'
          0, 1, 2, or 3 (shifts for the 'lea' instruction).

     'N'
          Unsigned 8-bit integer constant (for 'in' and 'out'
          instructions).

     'O'
          Integer constant in the range 0 ... 127, for 128-bit shifts.

     'G'
          Standard 80387 floating point constant.

     'C'
          Standard SSE floating point constant.

     'e'
          32-bit signed integer constant, or a symbolic reference known
          to fit that range (for immediate operands in sign-extending
          x86-64 instructions).

     'Z'
          32-bit unsigned integer constant, or a symbolic reference
          known to fit that range (for immediate operands in
          zero-extending x86-64 instructions).

_Intel IA-64--'config/ia64/ia64.h'_
     'a'
          General register 'r0' to 'r3' for 'addl' instruction

     'b'
          Branch register

     'c'
          Predicate register ('c' as in "conditional")

     'd'
          Application register residing in M-unit

     'e'
          Application register residing in I-unit

     'f'
          Floating-point register

     'm'
          Memory operand.  If used together with '<' or '>', the operand
          can have postincrement and postdecrement which require
          printing with '%Pn' on IA-64.

     'G'
          Floating-point constant 0.0 or 1.0

     'I'
          14-bit signed integer constant

     'J'
          22-bit signed integer constant

     'K'
          8-bit signed integer constant for logical instructions

     'L'
          8-bit adjusted signed integer constant for compare pseudo-ops

     'M'
          6-bit unsigned integer constant for shift counts

     'N'
          9-bit signed integer constant for load and store
          postincrements

     'O'
          The constant zero

     'P'
          0 or -1 for 'dep' instruction

     'Q'
          Non-volatile memory for floating-point loads and stores

     'R'
          Integer constant in the range 1 to 4 for 'shladd' instruction

     'S'
          Memory operand except postincrement and postdecrement.  This
          is now roughly the same as 'm' when not used together with '<'
          or '>'.

_FRV--'config/frv/frv.h'_
     'a'
          Register in the class 'ACC_REGS' ('acc0' to 'acc7').

     'b'
          Register in the class 'EVEN_ACC_REGS' ('acc0' to 'acc7').

     'c'
          Register in the class 'CC_REGS' ('fcc0' to 'fcc3' and 'icc0'
          to 'icc3').

     'd'
          Register in the class 'GPR_REGS' ('gr0' to 'gr63').

     'e'
          Register in the class 'EVEN_REGS' ('gr0' to 'gr63').  Odd
          registers are excluded not in the class but through the use of
          a machine mode larger than 4 bytes.

     'f'
          Register in the class 'FPR_REGS' ('fr0' to 'fr63').

     'h'
          Register in the class 'FEVEN_REGS' ('fr0' to 'fr63').  Odd
          registers are excluded not in the class but through the use of
          a machine mode larger than 4 bytes.

     'l'
          Register in the class 'LR_REG' (the 'lr' register).

     'q'
          Register in the class 'QUAD_REGS' ('gr2' to 'gr63').  Register
          numbers not divisible by 4 are excluded not in the class but
          through the use of a machine mode larger than 8 bytes.

     't'
          Register in the class 'ICC_REGS' ('icc0' to 'icc3').

     'u'
          Register in the class 'FCC_REGS' ('fcc0' to 'fcc3').

     'v'
          Register in the class 'ICR_REGS' ('cc4' to 'cc7').

     'w'
          Register in the class 'FCR_REGS' ('cc0' to 'cc3').

     'x'
          Register in the class 'QUAD_FPR_REGS' ('fr0' to 'fr63').
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

     'z'
          Register in the class 'SPR_REGS' ('lcr' and 'lr').

     'A'
          Register in the class 'QUAD_ACC_REGS' ('acc0' to 'acc7').

     'B'
          Register in the class 'ACCG_REGS' ('accg0' to 'accg7').

     'C'
          Register in the class 'CR_REGS' ('cc0' to 'cc7').

     'G'
          Floating point constant zero

     'I'
          6-bit signed integer constant

     'J'
          10-bit signed integer constant

     'L'
          16-bit signed integer constant

     'M'
          16-bit unsigned integer constant

     'N'
          12-bit signed integer constant that is negative--i.e. in the
          range of -2048 to -1

     'O'
          Constant zero

     'P'
          12-bit signed integer constant that is greater than zero--i.e.
          in the range of 1 to 2047.

_Blackfin family--'config/bfin/constraints.md'_
     'a'
          P register

     'd'
          D register

     'z'
          A call clobbered P register.

     'qN'
          A single register.  If N is in the range 0 to 7, the
          corresponding D register.  If it is 'A', then the register P0.

     'D'
          Even-numbered D register

     'W'
          Odd-numbered D register

     'e'
          Accumulator register.

     'A'
          Even-numbered accumulator register.

     'B'
          Odd-numbered accumulator register.

     'b'
          I register

     'v'
          B register

     'f'
          M register

     'c'
          Registers used for circular buffering, i.e.  I, B, or L
          registers.

     'C'
          The CC register.

     't'
          LT0 or LT1.

     'k'
          LC0 or LC1.

     'u'
          LB0 or LB1.

     'x'
          Any D, P, B, M, I or L register.

     'y'
          Additional registers typically used only in prologues and
          epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and
          USP.

     'w'
          Any register except accumulators or CC.

     'Ksh'
          Signed 16 bit integer (in the range -32768 to 32767)

     'Kuh'
          Unsigned 16 bit integer (in the range 0 to 65535)

     'Ks7'
          Signed 7 bit integer (in the range -64 to 63)

     'Ku7'
          Unsigned 7 bit integer (in the range 0 to 127)

     'Ku5'
          Unsigned 5 bit integer (in the range 0 to 31)

     'Ks4'
          Signed 4 bit integer (in the range -8 to 7)

     'Ks3'
          Signed 3 bit integer (in the range -3 to 4)

     'Ku3'
          Unsigned 3 bit integer (in the range 0 to 7)

     'PN'
          Constant N, where N is a single-digit constant in the range 0
          to 4.

     'PA'
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use with either accumulator.

     'PB'
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use only with accumulator A1.

     'M1'
          Constant 255.

     'M2'
          Constant 65535.

     'J'
          An integer constant with exactly a single bit set.

     'L'
          An integer constant with all bits set except exactly one.

     'H'

     'Q'
          Any SYMBOL_REF.

_M32C--'config/m32c/m32c.c'_
     'Rsp'
     'Rfb'
     'Rsb'
          '$sp', '$fb', '$sb'.

     'Rcr'
          Any control register, when they're 16 bits wide (nothing if
          control registers are 24 bits wide)

     'Rcl'
          Any control register, when they're 24 bits wide.

     'R0w'
     'R1w'
     'R2w'
     'R3w'
          $r0, $r1, $r2, $r3.

     'R02'
          $r0 or $r2, or $r2r0 for 32 bit values.

     'R13'
          $r1 or $r3, or $r3r1 for 32 bit values.

     'Rdi'
          A register that can hold a 64 bit value.

     'Rhl'
          $r0 or $r1 (registers with addressable high/low bytes)

     'R23'
          $r2 or $r3

     'Raa'
          Address registers

     'Raw'
          Address registers when they're 16 bits wide.

     'Ral'
          Address registers when they're 24 bits wide.

     'Rqi'
          Registers that can hold QI values.

     'Rad'
          Registers that can be used with displacements ($a0, $a1, $sb).

     'Rsi'
          Registers that can hold 32 bit values.

     'Rhi'
          Registers that can hold 16 bit values.

     'Rhc'
          Registers chat can hold 16 bit values, including all control
          registers.

     'Rra'
          $r0 through R1, plus $a0 and $a1.

     'Rfl'
          The flags register.

     'Rmm'
          The memory-based pseudo-registers $mem0 through $mem15.

     'Rpi'
          Registers that can hold pointers (16 bit registers for r8c,
          m16c; 24 bit registers for m32cm, m32c).

     'Rpa'
          Matches multiple registers in a PARALLEL to form a larger
          register.  Used to match function return values.

     'Is3'
          -8 ... 7

     'IS1'
          -128 ... 127

     'IS2'
          -32768 ... 32767

     'IU2'
          0 ... 65535

     'In4'
          -8 ... -1 or 1 ... 8

     'In5'
          -16 ... -1 or 1 ... 16

     'In6'
          -32 ... -1 or 1 ... 32

     'IM2'
          -65536 ... -1

     'Ilb'
          An 8 bit value with exactly one bit set.

     'Ilw'
          A 16 bit value with exactly one bit set.

     'Sd'
          The common src/dest memory addressing modes.

     'Sa'
          Memory addressed using $a0 or $a1.

     'Si'
          Memory addressed with immediate addresses.

     'Ss'
          Memory addressed using the stack pointer ($sp).

     'Sf'
          Memory addressed using the frame base register ($fb).

     'Ss'
          Memory addressed using the small base register ($sb).

     'S1'
          $r1h

_MeP--'config/mep/constraints.md'_

     'a'
          The $sp register.

     'b'
          The $tp register.

     'c'
          Any control register.

     'd'
          Either the $hi or the $lo register.

     'em'
          Coprocessor registers that can be directly loaded ($c0-$c15).

     'ex'
          Coprocessor registers that can be moved to each other.

     'er'
          Coprocessor registers that can be moved to core registers.

     'h'
          The $hi register.

     'j'
          The $rpc register.

     'l'
          The $lo register.

     't'
          Registers which can be used in $tp-relative addressing.

     'v'
          The $gp register.

     'x'
          The coprocessor registers.

     'y'
          The coprocessor control registers.

     'z'
          The $0 register.

     'A'
          User-defined register set A.

     'B'
          User-defined register set B.

     'C'
          User-defined register set C.

     'D'
          User-defined register set D.

     'I'
          Offsets for $gp-rel addressing.

     'J'
          Constants that can be used directly with boolean insns.

     'K'
          Constants that can be moved directly to registers.

     'L'
          Small constants that can be added to registers.

     'M'
          Long shift counts.

     'N'
          Small constants that can be compared to registers.

     'O'
          Constants that can be loaded into the top half of registers.

     'S'
          Signed 8-bit immediates.

     'T'
          Symbols encoded for $tp-rel or $gp-rel addressing.

     'U'
          Non-constant addresses for loading/saving coprocessor
          registers.

     'W'
          The top half of a symbol's value.

     'Y'