[all-commits] [llvm/llvm-project] 4257da: [LV] Always try to use fixed VF for low TC loops i...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4257da8ee2e84b3e62d2a2a5010e81823b799805
      https://github.com/llvm/llvm-project/commit/4257da8ee2e84b3e62d2a2a5010e81823b799805
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2026-09-26 (Sat, 26 Sep 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    A llvm/test/Transforms/LoopVectorize/AArch64/low-trip-count-fixed-vf-no-epilogue.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/short-trip-count.ll

  Log Message:
  -----------
  [LV] Always try to use fixed VF for low TC loops if no epilogue allowed. (#226318)

Remove the MaxPowerOf2RuntimeVF gate for falling back to using fixed
width VFs when no epilogue is allowed and the trip count is below the
minimum for tail folding.

MaxPowerOf2RuntimeVF being not set means we cannot compute the maximum
runtime VF, due to missing max vscale. In that case we are not able to
determine if a epilogue loop remains for scalable VFs, but we can still
pick a fixed VF, if no epilogue remains for it.

Also updates processLoop to ignore CM_EpilogueNotNeededFoldTail, if the
trip count is below the tail-folding threshold.

PR: https://github.com/llvm/llvm-project/pull/226318



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