[all-commits] [llvm/llvm-project] bf5748: [x86] fold vector (X > -1) & Y to shift+andn

[RotateRight via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bf5748a1af0d2f6f9396d9dc6ac89d15de41eee7
      https://github.com/llvm/llvm-project/commit/bf5748a1af0d2f6f9396d9dc6ac89d15de41eee7
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-11-12 (Fri, 12 Nov 2021)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/vector-pcmp.ll
    M llvm/test/CodeGen/X86/vselect-zero.ll

  Log Message:
  -----------
  [x86] fold vector (X > -1) & Y to shift+andn

and (pcmpgt X, -1), Y --> pandn (vsrai X, BitWidth-1), Y

This avoids the -1 constant vector in favor of an arithmetic shift
instruction if it exists (the ISA is still not complete after all
these years...).

We catch this pattern late in combining by matching PCMPGT, so it
should not interfere with more general folds.

Differential Revision: https://reviews.llvm.org/D113603