tree 7606a16507eaf930eeb113a1b7e621b17ab87ea9
parent 9a9114552358239004beb0ba7eaf5199f160c68d
author David Gross <dgross@google.com> 1494973672 -0700
committer David Gross <dgross@google.com> 1496957179 -0700

Refactor attribute stripping for libbcc and llvm-rs-as.

There is an existing StripUnknownAttributes pass we use to remove
attributes unknown to old versions of LLVM before writing out bitcode.
This is needed to avoid errors when writing or reading the bitcode.

This change does three things:
- Refactors code so that we can strip unknown attributes without
  depending on the pass infrastructure, and so that we have a library
  to strip unknown attributes.  This is needed so that we can use this
  functionality in places where we're not using the pass manager and
  so that we can use it outside of slang (specifically, in libbcc).
- Strips unknown attributes in llvm-rs-as, in order to satisfy
  frameworks/compile/libbcc/tests/run-lit-tests.sh
  (test_reduce_general_metadata.ll).  See details below.
- Updates some stale comments.

Why do we need to strip unknown attributes in llvm-rs-as, even if the
input .ll does not contain those attributes?  Because the LLVM parser
calls llvm::UpgradeCallsToIntrinsic() to canonicalize the attributes
of intrinsic functions.  For example, test_reduce_general_metadata.ll
contains a call to @llvm.memcpy.p0i8.p0i8.i64, which gets
canonicalized to have the argmemonly attribute.

Remember that we're writing an old fixed version of bitcode, older
than the "native" LLVM IR we're using, so there may be attributes in
that IR that are not representible in that old fixed version of
bitcode.  Furthermore, argmemonly is one of a set of attributes that
seem to be designed as "transient" -- they can appear in the IR
(possibly only on intrinsics, or as the result of some analysis?) but
can never appear in bitcode.

Bug: 37720701

Test: aosp_x86_64-eng FORCE_BUILD_LLVM_DISABLE_NDEBUG=true
      1) slang/tests
      2) slang/lit-tests
      3) RsTest (32-bit, 64-bit) -- but did not run math_fp16 (http://b/62452374)
      4) RsTest_11 -- but then got runtime error (http://b/62452065)
      5) cts -m RenderscriptTest

Change-Id: I481f9a9d9ea5a0bd164ac4eeb68dd479eba5a187
(cherry picked from commit 88cd94d5165bf8a266d3f3095946fc25bc4809af)