[all-commits] [llvm/llvm-project] 05a2b1: [LV] Optimize FindLast recurrences to FindIV (NFCI...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 05a2b146fbc2944507fd3570254d0e456dc2a795
      https://github.com/llvm/llvm-project/commit/05a2b146fbc2944507fd3570254d0e456dc2a795
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2026-02-05 (Thu, 05 Feb 2026)

  Changed paths:
    M llvm/include/llvm/Analysis/IVDescriptors.h
    M llvm/lib/Analysis/IVDescriptors.cpp
    M llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
    M llvm/lib/Transforms/Vectorize/VPlan.h
    M llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.h
    M llvm/test/Transforms/LoopVectorize/vplan-print-after-all.ll

  Log Message:
  -----------
  [LV] Optimize FindLast recurrences to FindIV (NFCI). (#177870)

This patch restructures Find(First|Last)IV handling. Instead of
differentiating between FindLast, FindFirstIV and FindLastIV up front,
this patch simplifies the logic in IVDescriptor to just identify the
FindLast pattern up-front.

It then adds a new VPlan transformation to optimize FindLast reductions
to FindIV reductions if there is a suitable sentinel value.
Find(Last|First)IV recurrence kinds to a single FindIV kind.

This is simpler and more accurate, given selecting the first/last
induction of the final IV reduction is directly controlled by the
corresponding recurrence kind of the ComputeReductionResult.

The new structure also allows further optimizations, like vectorizing
FindLastIV with another boolean reduction that tracks if the condition
in the loop was ever true, if there is no suitable sentinel value.

PR: https://github.com/llvm/llvm-project/pull/177870



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