[PATCH] D115261: [LV] Disable runtime unrolling for vectorized loops.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: Ayal, gilr, reames, dmgreen, lebedev.ri.
Herald added a subscriber: hiraditya.
fhahn requested review of this revision.
Herald added a project: LLVM.

This patch adds metadata to disable runtime unrolling to the vectorized
loop. If runtime unrolling/interleaving is considered profitable, LV
will interleave the loop directly. There should be no need to perform
runtime unrolling at a later stage.

Note that we already add metadata to disable runtime unrolling to the
scalar loop after vectorization.

The additional unrolling unnecessarily increases code size and compile
time. In addition to that we have several bug reports of unncessary
runtime unrolling for vectorized loops, e.g. PR40961

Compile-time improvements:

  NewPM-O3: -2.08%
  NewPM-ReleaseThinLTO: -1.09%
  NewPM-ReleaseLTO-g: -1.59%

http://llvm-compile-time-tracker.com/compare.php?from=398dffd4ffc7cbc320e15207c8c04ca682d821c4&to=86c8f5499f5c9ef34d018491f8eb4364579dca16&stat=instructions


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115261

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/sve-vector-reverse.ll
  llvm/test/Transforms/LoopVectorize/ARM/mve-qabs.ll
  llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll
  llvm/test/Transforms/LoopVectorize/ARM/tail-folding-scalar-epilogue-fallback.ll
  llvm/test/Transforms/LoopVectorize/X86/already-vectorized.ll
  llvm/test/Transforms/LoopVectorize/X86/float-induction-x86.ll
  llvm/test/Transforms/LoopVectorize/X86/gather_scatter.ll
  llvm/test/Transforms/LoopVectorize/X86/invariant-store-vectorization.ll
  llvm/test/Transforms/LoopVectorize/X86/masked_load_store.ll
  llvm/test/Transforms/LoopVectorize/X86/tail_loop_folding.ll
  llvm/test/Transforms/LoopVectorize/invariant-store-vectorization-2.ll
  llvm/test/Transforms/LoopVectorize/memdep-fold-tail.ll
  llvm/test/Transforms/LoopVectorize/pr45679-fold-tail-by-masking.ll
  llvm/test/Transforms/LoopVectorize/runtime-check-small-clamped-bounds.ll
  llvm/test/Transforms/LoopVectorize/tail-folding-vectorization-factor-1.ll
  llvm/test/Transforms/LoopVectorize/use-scalar-epilogue-if-tp-fails.ll
  llvm/test/Transforms/LoopVectorize/vectorize-once.ll

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