[PATCH] D82953: [ARM][MVE] Don't tail-fold float reductions

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer created this revision.
SjoerdMeijer added reviewers: samparker, dmgreen.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls.
Herald added a project: LLVM.

If a vector body has live-out values, it is probably a reduction, which needs a final reduction step after the loop. MVE has a VADDV instruction to reduce integer vectors, but doesn't have an equivalent one for float vectors. A live-out value that is not recognised as reduction later in the optimisation pipeline will result in the tail-predicated loop to be reverted to a non-predicated loop and this is very expensive, i.e. it has a significant performance impact, which is what we hope to avoid with fine tuning the ARM TTI hook preferPredicateOverEpilogue implementation.


https://reviews.llvm.org/D82953

Files:
  llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
  llvm/test/Transforms/LoopVectorize/ARM/tail-loop-folding.ll

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