[all-commits] [llvm/llvm-project] 1b0400: [X86] combineSubABS - handle NEG(ABD()) expanded p...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1b0400eed8613108d9f293b9ddd3380e3241ac60
      https://github.com/llvm/llvm-project/commit/1b0400eed8613108d9f293b9ddd3380e3241ac60
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-09-11 (Wed, 11 Sep 2024)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/abds-neg.ll
    M llvm/test/CodeGen/X86/abdu-neg.ll

  Log Message:
  -----------
  [X86] combineSubABS - handle NEG(ABD()) expanded patterns

combineSubABS already handles the "(sub Y, cmovns X, -X) -> (add Y, cmovns -X, X)" fold by flipping the cmov operands.

We can do something similar for the negation of ABDS/U patterns which have been expanded to a CMOVL/CMOVB with a pair of commuted subtractions: "NEG(ABD(X,Y)) -> NEG(CMOV(SUB(X,Y),SUB(Y,X))) -> CMOV(SUB(Y,X),SUB(X,Y))"



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