[all-commits] [llvm/llvm-project] 211147: [AArch64] Convert CMP/SELECT sign patterns to OR &...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 211147c5ba49a17c8624186f50519885d89ca33d
      https://github.com/llvm/llvm-project/commit/211147c5ba49a17c8624186f50519885d89ca33d
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2021-02-16 (Tue, 16 Feb 2021)

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

  Log Message:
  -----------
  [AArch64] Convert CMP/SELECT sign patterns to OR & ASR.

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]);
    }

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D96596