[all-commits] [llvm/llvm-project] 7b03fd: [X86] Add basic computeKnownBits support for X86IS...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7b03fdbd560ca10bc7873a4887eda3cc6738d186
      https://github.com/llvm/llvm-project/commit/7b03fdbd560ca10bc7873a4887eda3cc6738d186
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-08-09 (Fri, 09 Aug 2024)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/combine-sub.ll
    M llvm/test/CodeGen/X86/ctlo.ll
    M llvm/test/CodeGen/X86/ctlz.ll
    M llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
    M llvm/test/CodeGen/X86/div-rem-pair-recomposition-unsigned.ll
    M llvm/test/CodeGen/X86/lzcnt-cmp.ll
    M llvm/test/CodeGen/X86/pr38539.ll
    M llvm/test/CodeGen/X86/pr40090.ll
    M llvm/test/CodeGen/X86/scheduler-backtracking.ll

  Log Message:
  -----------
  [X86] Add basic computeKnownBits support for X86ISD::BSR (#102474)

Resurrect https://reviews.llvm.org/D89214 (by @topperc)

The behaviour is undefined for an input of 0, otherwise the result is the position of the most significant set bit which must be in the range [0, bitwidth-1]. So any bits above log2 of bitwidth must be 0.

Fixes #74101



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