[all-commits] [llvm/llvm-project] d0c1ea: [InstCombine] Pull unary shuffles through fneg/fab...

[Luke Lau via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d0c1ea928c5c4a99689ff3dcbf1ca578d56b80a3
      https://github.com/llvm/llvm-project/commit/d0c1ea928c5c4a99689ff3dcbf1ca578d56b80a3
  Author: Luke Lau <luke at igalia.com>
  Date:   2025-06-30 (Mon, 30 Jun 2025)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    M llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
    M llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
    M llvm/test/Transforms/InstCombine/matrix-multiplication-negation.ll
    M llvm/test/Transforms/InstCombine/vec_shuffle-inseltpoison.ll
    M llvm/test/Transforms/InstCombine/vec_shuffle.ll
    M llvm/test/Transforms/SLPVectorizer/X86/alternate-cast-inseltpoison.ll
    M llvm/test/Transforms/SLPVectorizer/X86/alternate-cast.ll

  Log Message:
  -----------
  [InstCombine] Pull unary shuffles through fneg/fabs (#144933)

This canonicalizes fneg/fabs (shuffle X, poison, mask) -> shuffle
(fneg/fabs X), posion, mask

This undoes part of b331a7ebc1e02f9939d1a4a1509e7eb6cdda3d38 and
a8f13dbdeb31be37ee15b5febb7cc2137bbece67, but keeps the binary shuffle
case i.e. shuffle fneg, fneg, mask.

By pulling out the shuffle we bring it inline with the same
canonicalisation we perform on binary ops and intrinsics, which the
original commit acknowledges it goes in the opposite direction.

However nowadays VectorCombine is more powerful and can do more
optimisations when the shuffle is pulled out, so I think we should
revisit this. In particular we get more shuffles folded and can perform
scalarization.



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