[all-commits] [llvm/llvm-project] c0a7bb: [VPlan] Scalarize to first-lane-only directly on V...

[Andrei Elovikov via All-commits]

  Branch: refs/heads/users/eas/vplan-based-first-lane-only-scalarize
  Home:   https://github.com/llvm/llvm-project
  Commit: c0a7bb30d696f04d019c51f0b1248f38df25ff8a
      https://github.com/llvm/llvm-project/commit/c0a7bb30d696f04d019c51f0b1248f38df25ff8a
  Author: Andrei Elovikov <andrei.elovikov at sifive.com>
  Date:   2026-03-02 (Mon, 02 Mar 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.h
    M llvm/test/Transforms/LoopVectorize/VPlan/vplan-print-after-all.ll
    M llvm/test/Transforms/LoopVectorize/X86/drop-poison-generating-flags.ll
    M llvm/test/Transforms/LoopVectorize/pr37248.ll
    M llvm/test/Transforms/LoopVectorize/runtime-check-needed-but-empty.ll

  Log Message:
  -----------
  [VPlan] Scalarize to first-lane-only directly on VPlan

This is needed to enable subsequent https://github.com/llvm/llvm-project/pull/182595.

I don't think we can fully port all scalarization logic from the legacy
path to VPlan-based right now because that would require us to introduce
interleave groups much earlier in VPlan pipeline, and without that we
can't really `assert` this new decision matches the previous CM-based
one. And without those `assert`s it's really hard to ensure we properly
port all the previous logic.

As such, I decided just to implement something much simpler that would
be enough for #182595. However, we perform this transformation before
delegating to the old CM-based decision, so it **is** effective
immediately and taking precedence even for consecutive loads/stores
right away.



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