[all-commits] [llvm/llvm-project] c592eb: [VPlan] Use RPOT in CSE, fixing potential crash (#...

[Ramkumar Ramachandra via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c592eba498a2a62101d503b1b32505fb292e6b51
      https://github.com/llvm/llvm-project/commit/c592eba498a2a62101d503b1b32505fb292e6b51
  Author: Ramkumar Ramachandra <artagnon at tenstorrent.com>
  Date:   2026-03-31 (Tue, 31 Mar 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

  Log Message:
  -----------
  [VPlan] Use RPOT in CSE, fixing potential crash (#187548)

A CSE crash is observed arising from outdated hash values unless we
forbid replacements in successor phis in blocks that are not dominated
by the def: the crash is observed when there is a block with CSE'able
phis with CSE'able incoming values, with incoming values coming from a
non-dominating block, under the condition that the block with the phis
is visited before the non-dominating block. It is unfortunately
impossible to write a test case showing a crash at present, but crashes
do occur when attempting to CSE DerivedIV recipes. The root cause of the
crash is visiting a non-dominated use before a def, and hence would be
fixed by a reverse post-order traversal.

Fixes #187499.

Co-authored-by: Luke Lau <luke at igalia.com>



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