[PATCH] D152541: [InstCombine] Remove swapMayExposeCSEOpportunities() fold

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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InstCombine tries to swap compare operands to match sub instructions in order to expose "CSE opportunities". However, it doesn't really make sense to perform this transform in the middle-end, as we cannot actually CSE the instructions there.

The backend already performs this fold in https://github.com/llvm/llvm-project/blob/18f5446a45da5a61dbfb1b7667d27fb441ac62db/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp#L4236 (as well as a number of more target-dependent places, e.g. optimizeCompareInstr), so I don't think we should have this in InstCombine.


https://reviews.llvm.org/D152541

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/abs-intrinsic.ll
  llvm/test/Transforms/InstCombine/icmp.ll
  llvm/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
  llvm/test/Transforms/InstCombine/strict-sub-underflow-check-to-comparison-of-sub-operands.ll
  llvm/test/Transforms/InstCombine/sub-ashr-or-to-icmp-select.ll
  llvm/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll
  llvm/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll

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