[PATCH] D126680: [VPlan] Replace BranchOnCount with BranchOnCond if TC <= UF * VF.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
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Try to simplify BranchOnCount to `BranchOnCond true` if TC <= UF * VF.

This is an alternative to D121899 <https://reviews.llvm.org/D121899> which simplifies the VPlan directly
instead of doing so late in code-gen.

The potential benefit of doing this in VPlan is that this may help
cost-modeling in the future. The reason this is done in prepareToExecute
at the moment is that a single plan may be used for multiple VFs/UFs.

There are further simplifications that can be applied as follow ups:

1. Replace inductions with constants
2. Replace vector region with regular block.

Fixes #55354.

Depends on D126679 <https://reviews.llvm.org/D126679>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126680

Files:
  llvm/lib/Transforms/Vectorize/VPlan.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/sve-low-trip-count.ll
  llvm/test/Transforms/LoopVectorize/X86/constant-fold.ll
  llvm/test/Transforms/LoopVectorize/X86/outer_loop_test1_no_explicit_vect_width.ll
  llvm/test/Transforms/LoopVectorize/X86/pr34438.ll
  llvm/test/Transforms/LoopVectorize/X86/pr42674.ll

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