[PATCH] D36922: [LibCallSimplifier] try harder to fold memcmp with constant arguments

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added a subscriber: mcrosier.

Try to fold:
memcmp(X, C, ConstantLength) != 0  --> load X == *C

Without this change, we're unnecessarily checking the alignment of the constant data, so we miss the transform in the first 2 tests in the patch.

I noted this shortcoming of LibCallSimpifier in one of the recent CGP memcmp expansion patches. This doesn't help the example in:
https://bugs.llvm.org/show_bug.cgi?id=34032#c13
...directly, but I think it's worth short-circuiting more of these simple cases since we're already trying to do that.


https://reviews.llvm.org/D36922

Files:
  lib/Transforms/Utils/SimplifyLibCalls.cpp
  test/Transforms/InstCombine/memcmp-constant-fold.ll

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