[all-commits] [llvm/llvm-project] 2a27c0: [X86] Use BSR passthrough behaviour to fold (CMOV ...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2a27c059eccd96b6e46464dbdf69fd2f6237a56c
      https://github.com/llvm/llvm-project/commit/2a27c059eccd96b6e46464dbdf69fd2f6237a56c
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2025-06-12 (Thu, 12 Jun 2025)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/bsr.ll
    M llvm/test/CodeGen/X86/pr40090.ll

  Log Message:
  -----------
  [X86] Use BSR passthrough behaviour to fold (CMOV (BSR ?, X), Y, (X == 0)) -> (BSR Y, X) (#143662)

Make use of targets that support BSR "pass through behaviour" on a zero input to remove a CMOV thats performing the same function

BSF will be a trickier patch as we need to make sure it works with the "REP BSF" hack in X86MCInstLower



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