[PATCH] D79100: [LV][TTI] Emit new IR intrinsic llvm.get.active.mask

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer updated this revision to Diff 264579.
SjoerdMeijer retitled this revision from "[LV][TTI] Emit new IR intrinsic llvm.set.loop.elements" to "[LV][TTI] Emit new IR intrinsic llvm.get.active.mask".
SjoerdMeijer edited the summary of this revision.
SjoerdMeijer added a reviewer: efriedma.
SjoerdMeijer added a subscriber: efriedma.
SjoerdMeijer added a comment.
Herald added a subscriber: vkmr.

This was discussed on the list and implements the approach as suggested by @efriedma :

http://lists.llvm.org/pipermail/llvm-dev/2020-May/141360.html

I.e., we now emit a llvm.get.active.mask intrinsic into the vector body, which is used by the masked load/stores, and its operands allows to reconstruct to the required information in backend passes. For example, a relevant snippet of a vector body with the tail-folded looks like this:

  %induction = add <4 x i64> %broadcast.splat, <i64 0, i64 1, i64 2, i64 3>
  %[[PRED:.*]] = icmp ule <4 x i64> %induction, <i64 429, i64 429, i64 429, i64 429>
  %[[MASK:.*]] = call <4 x i1> @llvm.get.active.mask.v4i1.v4i1(<4 x i1> %[[PRED]])
  %[[WML1:.*]] = call <4 x i32> @llvm.masked.load.v4i32.p0v4i32({{.*}}<4 x i1> %[[MASK]]
  %[[WML2:.*]] = call <4 x i32> @llvm.masked.load.v4i32.p0v4i32({{.*}}<4 x i1> %[[MASK]]

The induction and cmp feed the active.mask intrinsic, which is used by the masked loads/stores. This new intrinsic can now be easily picked up in backend passes, and the 429 in this example represents the backedge taken iteration count of the scalar loop, which we need to set up the tail-predication.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79100/new/

https://reviews.llvm.org/D79100

Files:
  llvm/include/llvm/Analysis/TargetTransformInfo.h
  llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
  llvm/include/llvm/CodeGen/BasicTTIImpl.h
  llvm/include/llvm/IR/Intrinsics.td
  llvm/lib/Analysis/TargetTransformInfo.cpp
  llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
  llvm/lib/Target/ARM/ARMTargetTransformInfo.h
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/lib/Transforms/Vectorize/VPlan.cpp
  llvm/lib/Transforms/Vectorize/VPlan.h
  llvm/test/Transforms/LoopVectorize/ARM/tail-loop-folding.ll

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