hotspot/src/share/vm/code/dependencies.hpp - platform/libcore - Git at Google

 /*
  * Copyright 2005-2006 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */

 //** Dependencies represent assertions (approximate invariants) within
 // the class hierarchy.  An example is an assertion that a given
 // method is not overridden; another example is that a type has only
 // one concrete subtype.  Compiled code which relies on such
 // assertions must be discarded if they are overturned by changes in
 // the class hierarchy.  We can think of these assertions as
 // approximate invariants, because we expect them to be overturned
 // very infrequently.  We are willing to perform expensive recovery
 // operations when they are overturned.  The benefit, of course, is
 // performing optimistic optimizations (!) on the object code.
 //
 // Changes in the class hierarchy due to dynamic linking or
 // class evolution can violate dependencies.  There is enough
 // indexing between classes and nmethods to make dependency
 // checking reasonably efficient.

 class ciEnv;
 class nmethod;
 class OopRecorder;
 class xmlStream;
 class CompileLog;
 class DepChange;
 class No_Safepoint_Verifier;

 class Dependencies: public ResourceObj {
  public:
   // Note: In the comments on dependency types, most uses of the terms
   // subtype and supertype are used in a "non-strict" or "inclusive"
   // sense, and are starred to remind the reader of this fact.
   // Strict uses of the terms use the word "proper".
   //
   // Specifically, every class is its own subtype* and supertype*.
   // (This trick is easier than continually saying things like "Y is a
   // subtype of X or X itself".)
   //
   // Sometimes we write X > Y to mean X is a proper supertype of Y.
   // The notation X > {Y, Z} means X has proper subtypes Y, Z.
   // The notation X.m > Y means that Y inherits m from X, while
   // X.m > Y.m means Y overrides X.m.  A star denotes abstractness,
   // as *I > A, meaning (abstract) interface I is a super type of A,
   // or A.*m > B.m, meaning B.m implements abstract method A.m.
   //
   // In this module, the terms "subtype" and "supertype" refer to
   // Java-level reference type conversions, as detected by
   // "instanceof" and performed by "checkcast" operations.  The method
   // Klass::is_subtype_of tests these relations.  Note that "subtype"
   // is richer than "subclass" (as tested by Klass::is_subclass_of),
   // since it takes account of relations involving interface and array
   // types.
   //
   // To avoid needless complexity, dependencies involving array types
   // are not accepted.  If you need to make an assertion about an
   // array type, make the assertion about its corresponding element
   // types.  Any assertion that might change about an array type can
   // be converted to an assertion about its element type.
   //
   // Most dependencies are evaluated over a "context type" CX, which
   // stands for the set Subtypes(CX) of every Java type that is a subtype*
   // of CX.  When the system loads a new class or interface N, it is
   // responsible for re-evaluating changed dependencies whose context
   // type now includes N, that is, all super types of N.
   //
   enum DepType {
     end_marker = 0,

     // An 'evol' dependency simply notes that the contents of the
     // method were used.  If it evolves (is replaced), the nmethod
     // must be recompiled.  No other dependencies are implied.
     evol_method,
     FIRST_TYPE = evol_method,

     // A context type CX is a leaf it if has no proper subtype.
     leaf_type,

     // An abstract class CX has exactly one concrete subtype CC.
     abstract_with_unique_concrete_subtype,

     // The type CX is purely abstract, with no concrete subtype* at all.
     abstract_with_no_concrete_subtype,

     // The concrete CX is free of concrete proper subtypes.
     concrete_with_no_concrete_subtype,

     // Given a method M1 and a context class CX, the set MM(CX, M1) of
     // "concrete matching methods" in CX of M1 is the set of every
     // concrete M2 for which it is possible to create an invokevirtual
     // or invokeinterface call site that can reach either M1 or M2.
     // That is, M1 and M2 share a name, signature, and vtable index.
     // We wish to notice when the set MM(CX, M1) is just {M1}, or
     // perhaps a set of two {M1,M2}, and issue dependencies on this.

     // The set MM(CX, M1) can be computed by starting with any matching
     // concrete M2 that is inherited into CX, and then walking the
     // subtypes* of CX looking for concrete definitions.

     // The parameters to this dependency are the method M1 and the
     // context class CX.  M1 must be either inherited in CX or defined
     // in a subtype* of CX.  It asserts that MM(CX, M1) is no greater
     // than {M1}.
     unique_concrete_method,       // one unique concrete method under CX

     // An "exclusive" assertion concerns two methods or subtypes, and
     // declares that there are at most two (or perhaps later N>2)
     // specific items that jointly satisfy the restriction.
     // We list all items explicitly rather than just giving their
     // count, for robustness in the face of complex schema changes.

     // A context class CX (which may be either abstract or concrete)
     // has two exclusive concrete subtypes* C1, C2 if every concrete
     // subtype* of CX is either C1 or C2.  Note that if neither C1 or C2
     // are equal to CX, then CX itself must be abstract.  But it is
     // also possible (for example) that C1 is CX (a concrete class)
     // and C2 is a proper subtype of C1.
     abstract_with_exclusive_concrete_subtypes_2,

     // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
     exclusive_concrete_methods_2,

     // This dependency asserts that no instances of class or it's
     // subclasses require finalization registration.
     no_finalizable_subclasses,

     TYPE_LIMIT
   };
   enum {
     LG2_TYPE_LIMIT = 4,  // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))

     // handy categorizations of dependency types:
     all_types      = ((1<<TYPE_LIMIT)-1) & ((-1)<<FIRST_TYPE),
     non_ctxk_types = (1<<evol_method),
     ctxk_types     = all_types & ~non_ctxk_types,

     max_arg_count = 3,   // current maximum number of arguments (incl. ctxk)

     // A "context type" is a class or interface that
     // provides context for evaluating a dependency.
     // When present, it is one of the arguments (dep_context_arg).
     //
     // If a dependency does not have a context type, there is a
     // default context, depending on the type of the dependency.
     // This bit signals that a default context has been compressed away.
     default_context_type_bit = (1<<LG2_TYPE_LIMIT)
   };

   static const char* dep_name(DepType dept);
   static int         dep_args(DepType dept);
   static int  dep_context_arg(DepType dept) {
     return dept_in_mask(dept, ctxk_types)? 0: -1;
   }

  private:
   // State for writing a new set of dependencies:
   GrowableArray<int>*       _dep_seen;  // (seen[h->ident] & (1<<dept))
   GrowableArray<ciObject*>* _deps[TYPE_LIMIT];

   static const char* _dep_name[TYPE_LIMIT];
   static int         _dep_args[TYPE_LIMIT];

   static bool dept_in_mask(DepType dept, int mask) {
     return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
   }

   bool note_dep_seen(int dept, ciObject* x) {
     assert(dept < BitsPerInt, "oob");
     int x_id = x->ident();
     assert(_dep_seen != NULL, "deps must be writable");
     int seen = _dep_seen->at_grow(x_id, 0);
     _dep_seen->at_put(x_id, seen | (1<<dept));
     // return true if we've already seen dept/x
     return (seen & (1<<dept)) != 0;
   }

   bool maybe_merge_ctxk(GrowableArray<ciObject*>* deps,
                         int ctxk_i, ciKlass* ctxk);

   void sort_all_deps();
   size_t estimate_size_in_bytes();

   // Initialize _deps, etc.
   void initialize(ciEnv* env);

   // State for making a new set of dependencies:
   OopRecorder* _oop_recorder;

   // Logging support
   CompileLog* _log;

   address  _content_bytes;  // everything but the oop references, encoded
   size_t   _size_in_bytes;

  public:
   // Make a new empty dependencies set.
   Dependencies(ciEnv* env) {
     initialize(env);
   }

  private:
   // Check for a valid context type.
   // Enforce the restriction against array types.
   static void check_ctxk(ciKlass* ctxk) {
     assert(ctxk->is_instance_klass(), "java types only");
   }
   static void check_ctxk_concrete(ciKlass* ctxk) {
     assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
   }
   static void check_ctxk_abstract(ciKlass* ctxk) {
     check_ctxk(ctxk);
     assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
   }

   void assert_common_1(DepType dept, ciObject* x);
   void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);
   void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* x2);

  public:
   // Adding assertions to a new dependency set at compile time:
   void assert_evol_method(ciMethod* m);
   void assert_leaf_type(ciKlass* ctxk);
   void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
   void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
   void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
   void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
   void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
   void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
   void assert_has_no_finalizable_subclasses(ciKlass* ctxk);

   // Define whether a given method or type is concrete.
   // These methods define the term "concrete" as used in this module.
   // For this module, an "abstract" class is one which is non-concrete.
   //
   // Future optimizations may allow some classes to remain
   // non-concrete until their first instantiation, and allow some
   // methods to remain non-concrete until their first invocation.
   // In that case, there would be a middle ground between concrete
   // and abstract (as defined by the Java language and VM).
   static bool is_concrete_klass(klassOop k);    // k is instantiable
   static bool is_concrete_method(methodOop m);  // m is invocable
   static Klass* find_finalizable_subclass(Klass* k);

   // These versions of the concreteness queries work through the CI.
   // The CI versions are allowed to skew sometimes from the VM
   // (oop-based) versions.  The cost of such a difference is a
   // (safely) aborted compilation, or a deoptimization, or a missed
   // optimization opportunity.
   //
   // In order to prevent spurious assertions, query results must
   // remain stable within any single ciEnv instance.  (I.e., they must
   // not go back into the VM to get their value; they must cache the
   // bit in the CI, either eagerly or lazily.)
   static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
   static bool is_concrete_method(ciMethod* m);       // m appears invocable
   static bool has_finalizable_subclass(ciInstanceKlass* k);

   // As a general rule, it is OK to compile under the assumption that
   // a given type or method is concrete, even if it at some future
   // point becomes abstract.  So dependency checking is one-sided, in
   // that it permits supposedly concrete classes or methods to turn up
   // as really abstract.  (This shouldn't happen, except during class
   // evolution, but that's the logic of the checking.)  However, if a
   // supposedly abstract class or method suddenly becomes concrete, a
   // dependency on it must fail.

   // Checking old assertions at run-time (in the VM only):
   static klassOop check_evol_method(methodOop m);
   static klassOop check_leaf_type(klassOop ctxk);
   static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,
                                                               DepChange* changes = NULL);
   static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,
                                                           DepChange* changes = NULL);
   static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,
                                                           DepChange* changes = NULL);
   static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,
                                                DepChange* changes = NULL);
   static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
                                                                   DepChange* changes = NULL);
   static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,
                                                    DepChange* changes = NULL);
   static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,
                                                       DepChange* changes = NULL);
   // A returned klassOop is NULL if the dependency assertion is still
   // valid.  A non-NULL klassOop is a 'witness' to the assertion
   // failure, a point in the class hierarchy where the assertion has
   // been proven false.  For example, if check_leaf_type returns
   // non-NULL, the value is a subtype of the supposed leaf type.  This
   // witness value may be useful for logging the dependency failure.
   // Note that, when a dependency fails, there may be several possible
   // witnesses to the failure.  The value returned from the check_foo
   // method is chosen arbitrarily.

   // The 'changes' value, if non-null, requests a limited spot-check
   // near the indicated recent changes in the class hierarchy.
   // It is used by DepStream::spot_check_dependency_at.

   // Detecting possible new assertions:
   static klassOop  find_unique_concrete_subtype(klassOop ctxk);
   static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);
   static int       find_exclusive_concrete_subtypes(klassOop ctxk, int klen, klassOop k[]);
   static int       find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);

   // Create the encoding which will be stored in an nmethod.
   void encode_content_bytes();

   address content_bytes() {
     assert(_content_bytes != NULL, "encode it first");
     return _content_bytes;
   }
   size_t size_in_bytes() {
     assert(_content_bytes != NULL, "encode it first");
     return _size_in_bytes;
   }

   OopRecorder* oop_recorder() { return _oop_recorder; }
   CompileLog*  log()          { return _log; }

   void copy_to(nmethod* nm);

   void log_all_dependencies();
   void log_dependency(DepType dept, int nargs, ciObject* args[]) {
     write_dependency_to(log(), dept, nargs, args);
   }
   void log_dependency(DepType dept,
                       ciObject* x0,
                       ciObject* x1 = NULL,
                       ciObject* x2 = NULL) {
     if (log() == NULL)  return;
     ciObject* args[max_arg_count];
     args[0] = x0;
     args[1] = x1;
     args[2] = x2;
     assert(2 < max_arg_count, "");
     log_dependency(dept, dep_args(dept), args);
   }

   static void write_dependency_to(CompileLog* log,
                                   DepType dept,
                                   int nargs, ciObject* args[],
                                   klassOop witness = NULL);
   static void write_dependency_to(CompileLog* log,
                                   DepType dept,
                                   int nargs, oop args[],
                                   klassOop witness = NULL);
   static void write_dependency_to(xmlStream* xtty,
                                   DepType dept,
                                   int nargs, oop args[],
                                   klassOop witness = NULL);
   static void print_dependency(DepType dept,
                                int nargs, oop args[],
                                klassOop witness = NULL);

  private:
   // helper for encoding common context types as zero:
   static ciKlass* ctxk_encoded_as_null(DepType dept, ciObject* x);

   static klassOop ctxk_encoded_as_null(DepType dept, oop x);

  public:
   // Use this to iterate over an nmethod's dependency set.
   // Works on new and old dependency sets.
   // Usage:
   //
   // ;
   // Dependencies::DepType dept;
   // for (Dependencies::DepStream deps(nm); deps.next(); ) {
   //   ...
   // }
   //
   // The caller must be in the VM, since oops are not wrapped in handles.
   class DepStream {
   private:
     nmethod*              _code;   // null if in a compiler thread
     Dependencies*         _deps;   // null if not in a compiler thread
     CompressedReadStream  _bytes;
 #ifdef ASSERT
     size_t                _byte_limit;
 #endif

     // iteration variables:
     DepType               _type;
     int                   _xi[max_arg_count+1];

     void initial_asserts(size_t byte_limit) NOT_DEBUG({});

     inline oop recorded_oop_at(int i);
         // => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)

     klassOop check_dependency_impl(DepChange* changes);

   public:
     DepStream(Dependencies* deps)
       : _deps(deps),
         _code(NULL),
         _bytes(deps->content_bytes())
     {
       initial_asserts(deps->size_in_bytes());
     }
     DepStream(nmethod* code)
       : _deps(NULL),
         _code(code),
         _bytes(code->dependencies_begin())
     {
       initial_asserts(code->dependencies_size());
     }

     bool next();

     DepType type()               { return _type; }
     int argument_count()         { return dep_args(type()); }
     int argument_index(int i)    { assert(0 <= i && i < argument_count(), "oob");
                                    return _xi[i]; }
     oop argument(int i);         // => recorded_oop_at(argument_index(i))
     klassOop context_type();

     methodOop method_argument(int i) {
       oop x = argument(i);
       assert(x->is_method(), "type");
       return (methodOop) x;
     }
     klassOop type_argument(int i) {
       oop x = argument(i);
       assert(x->is_klass(), "type");
       return (klassOop) x;
     }

     // The point of the whole exercise:  Is this dep is still OK?
     klassOop check_dependency() {
       return check_dependency_impl(NULL);
     }
     // A lighter version:  Checks only around recent changes in a class
     // hierarchy.  (See Universe::flush_dependents_on.)
     klassOop spot_check_dependency_at(DepChange& changes);

     // Log the current dependency to xtty or compilation log.
     void log_dependency(klassOop witness = NULL);

     // Print the current dependency to tty.
     void print_dependency(klassOop witness = NULL, bool verbose = false);
   };
   friend class Dependencies::DepStream;

   static void print_statistics() PRODUCT_RETURN;
 };

 // A class hierarchy change coming through the VM (under the Compile_lock).
 // The change is structured as a single new type with any number of supers
 // and implemented interface types.  Other than the new type, any of the
 // super types can be context types for a relevant dependency, which the
 // new type could invalidate.
 class DepChange : public StackObj {
  private:
   enum ChangeType {
     NO_CHANGE = 0,              // an uninvolved klass
     Change_new_type,            // a newly loaded type
     Change_new_sub,             // a super with a new subtype
     Change_new_impl,            // an interface with a new implementation
     CHANGE_LIMIT,
     Start_Klass = CHANGE_LIMIT  // internal indicator for ContextStream
   };

   // each change set is rooted in exactly one new type (at present):
   KlassHandle _new_type;

   void initialize();

  public:
   // notes the new type, marks it and all its super-types
   DepChange(KlassHandle new_type)
     : _new_type(new_type)
   {
     initialize();
   }

   // cleans up the marks
   ~DepChange();

   klassOop new_type()                   { return _new_type(); }

   // involves_context(k) is true if k is new_type or any of the super types
   bool involves_context(klassOop k);

   // Usage:
   // for (DepChange::ContextStream str(changes); str.next(); ) {
   //   klassOop k = str.klass();
   //   switch (str.change_type()) {
   //     ...
   //   }
   // }
   class ContextStream : public StackObj {
    private:
     DepChange&       _changes;
     friend class DepChange;

     // iteration variables:
     ChangeType            _change_type;
     klassOop              _klass;
     objArrayOop           _ti_base;    // i.e., transitive_interfaces
     int                   _ti_index;
     int                   _ti_limit;

     // start at the beginning:
     void start() {
       klassOop new_type = _changes.new_type();
       _change_type = (new_type == NULL ? NO_CHANGE: Start_Klass);
       _klass = new_type;
       _ti_base = NULL;
       _ti_index = 0;
       _ti_limit = 0;
     }

     ContextStream(DepChange& changes)
       : _changes(changes)
     { start(); }

    public:
     ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)
       : _changes(changes)
       // the nsv argument makes it safe to hold oops like _klass
     { start(); }

     bool next();

     klassOop   klass()           { return _klass; }
   };
   friend class DepChange::ContextStream;

   void print();
 };
	/*
	* Copyright 2005-2006 Sun Microsystems, Inc. All Rights Reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
	* CA 95054 USA or visit www.sun.com if you need additional information or
	* have any questions.
	*
	*/

	//** Dependencies represent assertions (approximate invariants) within
	// the class hierarchy. An example is an assertion that a given
	// method is not overridden; another example is that a type has only
	// one concrete subtype. Compiled code which relies on such
	// assertions must be discarded if they are overturned by changes in
	// the class hierarchy. We can think of these assertions as
	// approximate invariants, because we expect them to be overturned
	// very infrequently. We are willing to perform expensive recovery
	// operations when they are overturned. The benefit, of course, is
	// performing optimistic optimizations (!) on the object code.
	//
	// Changes in the class hierarchy due to dynamic linking or
	// class evolution can violate dependencies. There is enough
	// indexing between classes and nmethods to make dependency
	// checking reasonably efficient.

	class ciEnv;
	class nmethod;
	class OopRecorder;
	class xmlStream;
	class CompileLog;
	class DepChange;
	class No_Safepoint_Verifier;

	class Dependencies: public ResourceObj {
	public:
	// Note: In the comments on dependency types, most uses of the terms
	// subtype and supertype are used in a "non-strict" or "inclusive"
	// sense, and are starred to remind the reader of this fact.
	// Strict uses of the terms use the word "proper".
	//
	// Specifically, every class is its own subtype* and supertype*.
	// (This trick is easier than continually saying things like "Y is a
	// subtype of X or X itself".)
	//
	// Sometimes we write X > Y to mean X is a proper supertype of Y.
	// The notation X > {Y, Z} means X has proper subtypes Y, Z.
	// The notation X.m > Y means that Y inherits m from X, while
	// X.m > Y.m means Y overrides X.m. A star denotes abstractness,
	// as *I > A, meaning (abstract) interface I is a super type of A,
	// or A.*m > B.m, meaning B.m implements abstract method A.m.
	//
	// In this module, the terms "subtype" and "supertype" refer to
	// Java-level reference type conversions, as detected by
	// "instanceof" and performed by "checkcast" operations. The method
	// Klass::is_subtype_of tests these relations. Note that "subtype"
	// is richer than "subclass" (as tested by Klass::is_subclass_of),
	// since it takes account of relations involving interface and array
	// types.
	//
	// To avoid needless complexity, dependencies involving array types
	// are not accepted. If you need to make an assertion about an
	// array type, make the assertion about its corresponding element
	// types. Any assertion that might change about an array type can
	// be converted to an assertion about its element type.
	//
	// Most dependencies are evaluated over a "context type" CX, which
	// stands for the set Subtypes(CX) of every Java type that is a subtype*
	// of CX. When the system loads a new class or interface N, it is
	// responsible for re-evaluating changed dependencies whose context
	// type now includes N, that is, all super types of N.
	//
	enum DepType {
	end_marker = 0,

	// An 'evol' dependency simply notes that the contents of the
	// method were used. If it evolves (is replaced), the nmethod
	// must be recompiled. No other dependencies are implied.
	evol_method,
	FIRST_TYPE = evol_method,

	// A context type CX is a leaf it if has no proper subtype.
	leaf_type,

	// An abstract class CX has exactly one concrete subtype CC.
	abstract_with_unique_concrete_subtype,

	// The type CX is purely abstract, with no concrete subtype* at all.
	abstract_with_no_concrete_subtype,

	// The concrete CX is free of concrete proper subtypes.
	concrete_with_no_concrete_subtype,

	// Given a method M1 and a context class CX, the set MM(CX, M1) of
	// "concrete matching methods" in CX of M1 is the set of every
	// concrete M2 for which it is possible to create an invokevirtual
	// or invokeinterface call site that can reach either M1 or M2.
	// That is, M1 and M2 share a name, signature, and vtable index.
	// We wish to notice when the set MM(CX, M1) is just {M1}, or
	// perhaps a set of two {M1,M2}, and issue dependencies on this.

	// The set MM(CX, M1) can be computed by starting with any matching
	// concrete M2 that is inherited into CX, and then walking the
	// subtypes* of CX looking for concrete definitions.

	// The parameters to this dependency are the method M1 and the
	// context class CX. M1 must be either inherited in CX or defined
	// in a subtype* of CX. It asserts that MM(CX, M1) is no greater
	// than {M1}.
	unique_concrete_method, // one unique concrete method under CX

	// An "exclusive" assertion concerns two methods or subtypes, and
	// declares that there are at most two (or perhaps later N>2)
	// specific items that jointly satisfy the restriction.
	// We list all items explicitly rather than just giving their
	// count, for robustness in the face of complex schema changes.

	// A context class CX (which may be either abstract or concrete)
	// has two exclusive concrete subtypes* C1, C2 if every concrete
	// subtype* of CX is either C1 or C2. Note that if neither C1 or C2
	// are equal to CX, then CX itself must be abstract. But it is
	// also possible (for example) that C1 is CX (a concrete class)
	// and C2 is a proper subtype of C1.
	abstract_with_exclusive_concrete_subtypes_2,

	// This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
	exclusive_concrete_methods_2,

	// This dependency asserts that no instances of class or it's
	// subclasses require finalization registration.
	no_finalizable_subclasses,

	TYPE_LIMIT
	};
	enum {
	LG2_TYPE_LIMIT = 4, // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))

	// handy categorizations of dependency types:
	all_types = ((1<<TYPE_LIMIT)-1) & ((-1)<<FIRST_TYPE),
	non_ctxk_types = (1<<evol_method),
	ctxk_types = all_types & ~non_ctxk_types,

	max_arg_count = 3, // current maximum number of arguments (incl. ctxk)

	// A "context type" is a class or interface that
	// provides context for evaluating a dependency.
	// When present, it is one of the arguments (dep_context_arg).
	//
	// If a dependency does not have a context type, there is a
	// default context, depending on the type of the dependency.
	// This bit signals that a default context has been compressed away.
	default_context_type_bit = (1<<LG2_TYPE_LIMIT)
	};

	static const char* dep_name(DepType dept);
	static int dep_args(DepType dept);
	static int dep_context_arg(DepType dept) {
	return dept_in_mask(dept, ctxk_types)? 0: -1;
	}

	private:
	// State for writing a new set of dependencies:
	GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
	GrowableArray<ciObject> _deps[TYPE_LIMIT];

	static const char* _dep_name[TYPE_LIMIT];
	static int _dep_args[TYPE_LIMIT];

	static bool dept_in_mask(DepType dept, int mask) {
	return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
	}

	bool note_dep_seen(int dept, ciObject* x) {
	assert(dept < BitsPerInt, "oob");
	int x_id = x->ident();
	assert(_dep_seen != NULL, "deps must be writable");
	int seen = _dep_seen->at_grow(x_id, 0);
	_dep_seen->at_put(x_id, seen \| (1<<dept));
	// return true if we've already seen dept/x
	return (seen & (1<<dept)) != 0;
	}

	bool maybe_merge_ctxk(GrowableArray<ciObject> deps,
	int ctxk_i, ciKlass* ctxk);

	void sort_all_deps();
	size_t estimate_size_in_bytes();

	// Initialize _deps, etc.
	void initialize(ciEnv* env);

	// State for making a new set of dependencies:
	OopRecorder* _oop_recorder;

	// Logging support
	CompileLog* _log;

	address _content_bytes; // everything but the oop references, encoded
	size_t _size_in_bytes;

	public:
	// Make a new empty dependencies set.
	Dependencies(ciEnv* env) {
	initialize(env);
	}

	private:
	// Check for a valid context type.
	// Enforce the restriction against array types.
	static void check_ctxk(ciKlass* ctxk) {
	assert(ctxk->is_instance_klass(), "java types only");
	}
	static void check_ctxk_concrete(ciKlass* ctxk) {
	assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
	}
	static void check_ctxk_abstract(ciKlass* ctxk) {
	check_ctxk(ctxk);
	assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
	}

	void assert_common_1(DepType dept, ciObject* x);
	void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);
	void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* x2);

	public:
	// Adding assertions to a new dependency set at compile time:
	void assert_evol_method(ciMethod* m);
	void assert_leaf_type(ciKlass* ctxk);
	void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
	void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
	void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
	void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
	void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
	void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
	void assert_has_no_finalizable_subclasses(ciKlass* ctxk);

	// Define whether a given method or type is concrete.
	// These methods define the term "concrete" as used in this module.
	// For this module, an "abstract" class is one which is non-concrete.
	//
	// Future optimizations may allow some classes to remain
	// non-concrete until their first instantiation, and allow some
	// methods to remain non-concrete until their first invocation.
	// In that case, there would be a middle ground between concrete
	// and abstract (as defined by the Java language and VM).
	static bool is_concrete_klass(klassOop k); // k is instantiable
	static bool is_concrete_method(methodOop m); // m is invocable
	static Klass* find_finalizable_subclass(Klass* k);

	// These versions of the concreteness queries work through the CI.
	// The CI versions are allowed to skew sometimes from the VM
	// (oop-based) versions. The cost of such a difference is a
	// (safely) aborted compilation, or a deoptimization, or a missed
	// optimization opportunity.
	//
	// In order to prevent spurious assertions, query results must
	// remain stable within any single ciEnv instance. (I.e., they must
	// not go back into the VM to get their value; they must cache the
	// bit in the CI, either eagerly or lazily.)
	static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
	static bool is_concrete_method(ciMethod* m); // m appears invocable
	static bool has_finalizable_subclass(ciInstanceKlass* k);

	// As a general rule, it is OK to compile under the assumption that
	// a given type or method is concrete, even if it at some future
	// point becomes abstract. So dependency checking is one-sided, in
	// that it permits supposedly concrete classes or methods to turn up
	// as really abstract. (This shouldn't happen, except during class
	// evolution, but that's the logic of the checking.) However, if a
	// supposedly abstract class or method suddenly becomes concrete, a
	// dependency on it must fail.

	// Checking old assertions at run-time (in the VM only):
	static klassOop check_evol_method(methodOop m);
	static klassOop check_leaf_type(klassOop ctxk);
	static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,
	DepChange* changes = NULL);
	static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,
	DepChange* changes = NULL);
	static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,
	DepChange* changes = NULL);
	static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,
	DepChange* changes = NULL);
	static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
	DepChange* changes = NULL);
	static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,
	DepChange* changes = NULL);
	static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,
	DepChange* changes = NULL);
	// A returned klassOop is NULL if the dependency assertion is still
	// valid. A non-NULL klassOop is a 'witness' to the assertion
	// failure, a point in the class hierarchy where the assertion has
	// been proven false. For example, if check_leaf_type returns
	// non-NULL, the value is a subtype of the supposed leaf type. This
	// witness value may be useful for logging the dependency failure.
	// Note that, when a dependency fails, there may be several possible
	// witnesses to the failure. The value returned from the check_foo
	// method is chosen arbitrarily.

	// The 'changes' value, if non-null, requests a limited spot-check
	// near the indicated recent changes in the class hierarchy.
	// It is used by DepStream::spot_check_dependency_at.

	// Detecting possible new assertions:
	static klassOop find_unique_concrete_subtype(klassOop ctxk);
	static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);
	static int find_exclusive_concrete_subtypes(klassOop ctxk, int klen, klassOop k[]);
	static int find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);

	// Create the encoding which will be stored in an nmethod.
	void encode_content_bytes();

	address content_bytes() {
	assert(_content_bytes != NULL, "encode it first");
	return _content_bytes;
	}
	size_t size_in_bytes() {
	assert(_content_bytes != NULL, "encode it first");
	return _size_in_bytes;
	}

	OopRecorder* oop_recorder() { return _oop_recorder; }
	CompileLog* log() { return _log; }

	void copy_to(nmethod* nm);

	void log_all_dependencies();
	void log_dependency(DepType dept, int nargs, ciObject* args[]) {
	write_dependency_to(log(), dept, nargs, args);
	}
	void log_dependency(DepType dept,
	ciObject* x0,
	ciObject* x1 = NULL,
	ciObject* x2 = NULL) {
	if (log() == NULL) return;
	ciObject* args[max_arg_count];
	args[0] = x0;
	args[1] = x1;
	args[2] = x2;
	assert(2 < max_arg_count, "");
	log_dependency(dept, dep_args(dept), args);
	}

	static void write_dependency_to(CompileLog* log,
	DepType dept,
	int nargs, ciObject* args[],
	klassOop witness = NULL);
	static void write_dependency_to(CompileLog* log,
	DepType dept,
	int nargs, oop args[],
	klassOop witness = NULL);
	static void write_dependency_to(xmlStream* xtty,
	DepType dept,
	int nargs, oop args[],
	klassOop witness = NULL);
	static void print_dependency(DepType dept,
	int nargs, oop args[],
	klassOop witness = NULL);

	private:
	// helper for encoding common context types as zero:
	static ciKlass* ctxk_encoded_as_null(DepType dept, ciObject* x);

	static klassOop ctxk_encoded_as_null(DepType dept, oop x);

	public:
	// Use this to iterate over an nmethod's dependency set.
	// Works on new and old dependency sets.
	// Usage:
	//
	// ;
	// Dependencies::DepType dept;
	// for (Dependencies::DepStream deps(nm); deps.next(); ) {
	// ...
	// }
	//
	// The caller must be in the VM, since oops are not wrapped in handles.
	class DepStream {
	private:
	nmethod* _code; // null if in a compiler thread
	Dependencies* _deps; // null if not in a compiler thread
	CompressedReadStream _bytes;
	#ifdef ASSERT
	size_t _byte_limit;
	#endif

	// iteration variables:
	DepType _type;
	int _xi[max_arg_count+1];

	void initial_asserts(size_t byte_limit) NOT_DEBUG({});

	inline oop recorded_oop_at(int i);
	// => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)

	klassOop check_dependency_impl(DepChange* changes);

	public:
	DepStream(Dependencies* deps)
	: _deps(deps),
	_code(NULL),
	_bytes(deps->content_bytes())
	{
	initial_asserts(deps->size_in_bytes());
	}
	DepStream(nmethod* code)
	: _deps(NULL),
	_code(code),
	_bytes(code->dependencies_begin())
	{
	initial_asserts(code->dependencies_size());
	}

	bool next();

	DepType type() { return _type; }
	int argument_count() { return dep_args(type()); }
	int argument_index(int i) { assert(0 <= i && i < argument_count(), "oob");
	return _xi[i]; }
	oop argument(int i); // => recorded_oop_at(argument_index(i))
	klassOop context_type();

	methodOop method_argument(int i) {
	oop x = argument(i);
	assert(x->is_method(), "type");
	return (methodOop) x;
	}
	klassOop type_argument(int i) {
	oop x = argument(i);
	assert(x->is_klass(), "type");
	return (klassOop) x;
	}

	// The point of the whole exercise: Is this dep is still OK?
	klassOop check_dependency() {
	return check_dependency_impl(NULL);
	}
	// A lighter version: Checks only around recent changes in a class
	// hierarchy. (See Universe::flush_dependents_on.)
	klassOop spot_check_dependency_at(DepChange& changes);

	// Log the current dependency to xtty or compilation log.
	void log_dependency(klassOop witness = NULL);

	// Print the current dependency to tty.
	void print_dependency(klassOop witness = NULL, bool verbose = false);
	};
	friend class Dependencies::DepStream;

	static void print_statistics() PRODUCT_RETURN;
	};

	// A class hierarchy change coming through the VM (under the Compile_lock).
	// The change is structured as a single new type with any number of supers
	// and implemented interface types. Other than the new type, any of the
	// super types can be context types for a relevant dependency, which the
	// new type could invalidate.
	class DepChange : public StackObj {
	private:
	enum ChangeType {
	NO_CHANGE = 0, // an uninvolved klass
	Change_new_type, // a newly loaded type
	Change_new_sub, // a super with a new subtype
	Change_new_impl, // an interface with a new implementation
	CHANGE_LIMIT,
	Start_Klass = CHANGE_LIMIT // internal indicator for ContextStream
	};

	// each change set is rooted in exactly one new type (at present):
	KlassHandle _new_type;

	void initialize();

	public:
	// notes the new type, marks it and all its super-types
	DepChange(KlassHandle new_type)
	: _new_type(new_type)
	{
	initialize();
	}

	// cleans up the marks
	~DepChange();

	klassOop new_type() { return _new_type(); }

	// involves_context(k) is true if k is new_type or any of the super types
	bool involves_context(klassOop k);

	// Usage:
	// for (DepChange::ContextStream str(changes); str.next(); ) {
	// klassOop k = str.klass();
	// switch (str.change_type()) {
	// ...
	// }
	// }
	class ContextStream : public StackObj {
	private:
	DepChange& _changes;
	friend class DepChange;

	// iteration variables:
	ChangeType _change_type;
	klassOop _klass;
	objArrayOop _ti_base; // i.e., transitive_interfaces
	int _ti_index;
	int _ti_limit;

	// start at the beginning:
	void start() {
	klassOop new_type = _changes.new_type();
	_change_type = (new_type == NULL ? NO_CHANGE: Start_Klass);
	_klass = new_type;
	_ti_base = NULL;
	_ti_index = 0;
	_ti_limit = 0;
	}

	ContextStream(DepChange& changes)
	: _changes(changes)
	{ start(); }

	public:
	ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)
	: _changes(changes)
	// the nsv argument makes it safe to hold oops like _klass
	{ start(); }

	bool next();

	klassOop klass() { return _klass; }
	};
	friend class DepChange::ContextStream;

	void print();
	};