[PATCH] D128364: [InstCombine] Look through more casts when folding memchr and memcmp

[Martin Sebor via Phabricator via llvm-commits]

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The `memchr` and `memcmp` folders fail for the results of pointer addition involving fractional offsets into constants of types other than `i8`, such as in

  const int a[] = { 0x01010101, 0x02020202 };
  
  void* f (void)
  {
    return memchr((const char*)a + 1, 1, 7);
  }

and similar examples involving structs and unions.  This is due to what seems like an overly restrictive check in the `getConstantDataArrayInfo` that keeps the function from "looking through [all] bitcast instructions and geps" despite the comment documenting this intent.

In conjunction with the recent enhancement to let all libcall folders work with subobjects of constants of arbitrary types (D125114 <https://reviews.llvm.org/D125114>), this change removes the limitation above, bringing the `memchr` and `memcmp` folders up to par with GCC.  Tested on by running `make check-all` on x86_64-linux.

(The code in `getConstantDataArrayInfo` could stand to be simplified by letting the function take a `DataLayout` argument.  I stopped short of making that change in this patch to minimize the extent of the changes.)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D128364

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/memchr-9.ll
  llvm/test/Transforms/InstCombine/memcmp-7.ll

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