[all-commits] [llvm/llvm-project] 6c2a4f: [TTI][LV] preferPredicateOverEpilogue

[sjoerdmeijer via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 6c2a4f5ff93e16c3b86c18543e02a193ced2d956
      https://github.com/llvm/llvm-project/commit/6c2a4f5ff93e16c3b86c18543e02a193ced2d956
  Author: Sjoerd Meijer <sjoerd.meijer at arm.com>
  Date:   2019-11-06 (Wed, 06 Nov 2019)

  Changed paths:
    M llvm/include/llvm/Analysis/TargetTransformInfo.h
    M llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
    M llvm/include/llvm/CodeGen/BasicTTIImpl.h
    M llvm/lib/Analysis/TargetTransformInfo.cpp
    M llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
    M llvm/lib/Target/ARM/ARMTargetTransformInfo.h
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    A llvm/test/Transforms/LoopVectorize/ARM/prefer-tail-loop-folding.ll
    M llvm/test/Transforms/LoopVectorize/ARM/tail-loop-folding.ll

  Log Message:
  -----------
  [TTI][LV] preferPredicateOverEpilogue

We have two ways to steer creating a predicated vector body over creating a
scalar epilogue. To force this, we have 1) a command line option and 2) a
pragma available. This adds a third: a target hook to TargetTransformInfo that
can be queried whether predication is preferred or not, which allows the
vectoriser to make the decision without forcing it.

While this change behaves as a non-functional change for now, it shows the
required TTI plumbing, usage of this new hook in the vectoriser, and the
beginning of an ARM MVE implementation. I will follow up on this with:
- a complete MVE implementation, see D69845.
- a patch to disable this, i.e. we should respect "vector_predicate(disable)"
  and its corresponding loophint.

Differential Revision: https://reviews.llvm.org/D69040