[PATCH] D157713: [VPlan] Perform tail folding as VPlan transform. (WIP)

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: Ayal, gilr, rengolin, dmgreen.
Herald added subscribers: StephenFan, tschuett, psnobl, rogfer01, bollu, hiraditya.
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fhahn requested review of this revision.
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This patch splits off the tail-folding logic from general mask handling
to it's own transform, which

- introduces the required mask to the VPlan
- updates existing masks to be the AND of the existing mask and the mask for the header block,
- adds masks to recipes that require masks with tail-folding.

This moves tail folding to be part of the gradual lowering & refinement
of a VPlan. Moving tail-folding to a VPlan2VPlan transform makes it
independent of the underlying IR and allows it to be applied to generic
VPlans.

NOTE: there are a few remaining test failures due to slightly different
ordering of instructions computing the mask. I will fix them once we
converge on the review. I wanted to share this early.

Depends on D157037 <https://reviews.llvm.org/D157037>.
Depends on D157443 <https://reviews.llvm.org/D157443>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157713

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/lib/Transforms/Vectorize/VPRecipeBuilder.h
  llvm/lib/Transforms/Vectorize/VPlan.h
  llvm/test/Transforms/LoopVectorize/tail-folding-vectorization-factor-1.ll

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