[all-commits] [llvm/llvm-project] a4cccd: [VPlan] Remove constant branches early. (#183397)

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a4cccdc393ec8930c03d633ecf932e47d914466b
      https://github.com/llvm/llvm-project/commit/a4cccdc393ec8930c03d633ecf932e47d914466b
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2026-04-17 (Fri, 17 Apr 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/lib/Transforms/Vectorize/VPlan.cpp
    M llvm/lib/Transforms/Vectorize/VPlan.h
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/predicated-costs.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/gather-scatter-cost.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/masked_gather_scatter.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/runtime-check-dependent-on-stride.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll
    M llvm/test/Transforms/LoopVectorize/VPlan/RISCV/vplan-riscv-vector-reverse.ll
    M llvm/test/Transforms/LoopVectorize/VPlan/conditional-scalar-assignment-vplan.ll
    M llvm/test/Transforms/LoopVectorize/VPlan/first-order-recurrence-sink-replicate-region.ll
    M llvm/test/Transforms/LoopVectorize/VPlan/icmp-uniforms.ll
    M llvm/test/Transforms/LoopVectorize/VPlan/vplan-sink-scalars-and-merge.ll

  Log Message:
  -----------
  [VPlan] Remove constant branches early. (#183397)

Simplify constant branches early, after introducing the check in the
middle block.

This removes any trivial branches in the input CFG (e.g. over-reduced
test cases) early and also folds branches on true/false created by
addMiddleChecks. This allows to check if there's a scalar tail instead
to check if the tail has been folded, as mentioned in
https://github.com/llvm/llvm-project/pull/182507

This requires to remove recipes in the new unreachable blocks, as
otherwise we would fail during verification, due to uses in unreachable
blocks. Alternatively, we may be able to skip verification for uses in
unreachable blocks.

Depends on https://github.com/llvm/llvm-project/pull/181252.

PR: https://github.com/llvm/llvm-project/pull/183397



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