[all-commits] [llvm/llvm-project] 0c91e9: [VectorCombine] Refine cost model and decision log...

[Igor Kirillov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0c91e977c0509d39aca2baa0742a959b3e8a6ffe
      https://github.com/llvm/llvm-project/commit/0c91e977c0509d39aca2baa0742a959b3e8a6ffe
  Author: Igor Kirillov <igor.kirillov at arm.com>
  Date:   2025-07-25 (Fri, 25 Jul 2025)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VectorCombine.cpp
    M llvm/test/Transforms/PhaseOrdering/AArch64/slpordering.ll

  Log Message:
  -----------
  [VectorCombine] Refine cost model and decision logic in foldSelectShuffle (#146694)

After PR #136329, shuffle indices may differ, which can cause the
existing cost-based logic to miss optimisation opportunities for
binop/shuffle sequences.

This patch improves the cost model in foldSelectShuffle to more
accurately assess costs, recognising when certain duplicate shuffles do
not require actual instructions.

Additionally, in break-even cases, this change introduces a check for
whether the pattern ultimately feeds into a vector reduction, allowing
the transform to proceed when it is likely to be profitable overall.



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