[PATCH] D153697: [LV] Freeze start value for select-reductions.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
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When creating select-reductions, we are introducing multiple new uses of
the reduction start value. If the start value may be undef or poison,
then differnet uses (e.g in the final select or vector compares) can
evaluate to different values, leading to incorrect results.

To avoid this, freeze the start value in the preheader by introducing a
new Freeze VPInstruction.

Depends on D153696 <https://reviews.llvm.org/D153696>.

Fixes #62565.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153697

Files:
  llvm/include/llvm/Transforms/Utils/LoopUtils.h
  llvm/lib/Transforms/Utils/LoopUtils.cpp
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/sve-select-cmp.ll
  llvm/test/Transforms/LoopVectorize/select-cmp.ll
  llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll

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