[PATCH] D96596: [AArch64] Convert CMP/SELECT sign patterns to OR & ASR.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: SjoerdMeijer, dmgreen, aemerson, t.p.northover.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls.
fhahn requested review of this revision.
Herald added a project: LLVM.

ICMP & SELECT patterns extracting the sign of a value can be simplified
to OR & ASR (see  https://alive2.llvm.org/ce/z/Xx4iZ0).

This does not save any instructions in IR, but it is profitable on
AArch64, because we need at least 2 extra instructions to materialize 1
and -1 for the SELECT.

The improvements result in ~5% speedups on loops of the form

  static int sign_of(int x) {
    if (x < 0) return -1;
    return 1;
  }
  
  void foo(const int *x, int *res, int cnt) {
    for (int i=0;i<cnt;i++)
      res[i] = sign_of(x[i]);
  }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96596

Files:
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/test/CodeGen/AArch64/cmp-select-sign.ll

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