[all-commits] [llvm/llvm-project] c22f56: [LICM] Drop poison-generating flags when reassocia...

[Justin Lebar via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c22f5665a9d631742a58e87b80b15359f65b3a66
      https://github.com/llvm/llvm-project/commit/c22f5665a9d631742a58e87b80b15359f65b3a66
  Author: Justin Lebar <justin.lebar at gmail.com>
  Date:   2026-05-30 (Sat, 30 May 2026)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LICM.cpp
    M llvm/test/Transforms/LICM/hoist-add-sub.ll

  Log Message:
  -----------
  [LICM] Drop poison-generating flags when reassociating an icmp (#200344)

`hoistAdd`/`hoistSub` turn `LV + C1 <pred> C2` into `LV <pred> C2 - C1`,
changing the icmp's LHS. A `samesign` flag asserted about the old
operands need not hold for the new LHS, so keeping it can turn a defined
comparison into poison (e.g. for `%iv = -3`, `samesign slt(2, 100)` is
true but the reassociated `samesign slt(-3, 95)` has
opposite-sign operands → poison). Drop the icmp's poison-generating
flags after the rewrite, as `hoistMulAddAssociation` already does.

This bug was found by a large run of Opus 4.7 looking for bugs in LLVM.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply at anthropic.com>



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