[PATCH] D125114: [SimplifyLibCalls] handle subobjects of constant aggregates

[Martin Sebor via Phabricator via llvm-commits]

msebor created this revision.
msebor added reviewers: spatel, MatzeB, nikic, xbolva00.
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This change removes the known limitation of the library function call folders to only work with top-level arrays of characters (as per the TODO comment in the code)  and allows them to also fold calls involving subobjects of constant aggregates such as member arrays.  It does that by

1. adding a new function, `ReadByteArrayFromGlobal` that returns the byte representation of the initializer of a global constant, as a `ConstantArray`, and
2. removing the restriction from `getConstantDataArrayInfo` to only consider simple strings and having it use `ReadByteArrayFromGlobal` to convert other aggregates to arrays of bytes.

This initial change only handles constant offsets into these aggregates.

I have tested the change by building LLVM on x86_64 and running `check-all`.  In full disclosure, the patch seems to cause a few surprising regressions in the test suite that I'm yet to investigate:

  LLVM :: CodeGen/AArch64/arm64-2012-05-07-MemcpyAlignBug.ll
  LLVM :: CodeGen/ARM/constantpool-promote-ldrh.ll
  LLVM :: CodeGen/BPF/remove_truncate_5.ll
  LLVM :: CodeGen/BPF/rodata_2.ll
  LLVM :: CodeGen/PowerPC/aix-vec-arg-spills-mir.ll
  LLVM :: CodeGen/PowerPC/aix-vec-arg-spills.ll
  LLVM :: DebugInfo/COFF/types-array.ll


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D125114

Files:
  llvm/include/llvm/Analysis/ConstantFolding.h
  llvm/lib/Analysis/ConstantFolding.cpp
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/memchr-5.ll
  llvm/test/Transforms/InstCombine/memcmp-3.ll
  llvm/test/Transforms/InstCombine/memrchr-5.ll
  llvm/test/Transforms/InstCombine/sprintf-2.ll
  llvm/test/Transforms/InstCombine/str-int-3.ll
  llvm/test/Transforms/InstCombine/strcmp-3.ll
  llvm/test/Transforms/InstCombine/strlen-5.ll
  llvm/test/Transforms/InstCombine/strlen-6.ll
  llvm/test/Transforms/InstCombine/strlen-7.ll
  llvm/test/Transforms/InstCombine/strlen-8.ll
  llvm/test/Transforms/InstCombine/strncmp-4.ll

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