[all-commits] [llvm/llvm-project] 92a038: [x86] add special-case lowering for usubsat for pr...

[RotateRight via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 92a0389b0425a9535a99a0ce13ba0eeda2bce7ad
      https://github.com/llvm/llvm-project/commit/92a0389b0425a9535a99a0ce13ba0eeda2bce7ad
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-10-19 (Tue, 19 Oct 2021)

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

  Log Message:
  -----------
  [x86] add special-case lowering for usubsat for pre-SSE4

usubsat X, SMIN --> (X ^ SMIN) & (X s>> BW-1)

This would be a regression with D112085 where we combine to
usubsat more aggressively, so avoid that by matching the
special-case where we are subtracting SMIN (signmask):
https://alive2.llvm.org/ce/z/4_3gBD

Differential Revision: https://reviews.llvm.org/D112095