[all-commits] [llvm/llvm-project] cd61d4: [LV] Do not LoopSimplify/LCSSA after generating ma...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cd61d4bd2fcd5ba212747bfe48f32f121010e1a6
      https://github.com/llvm/llvm-project/commit/cd61d4bd2fcd5ba212747bfe48f32f121010e1a6
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2022-05-20 (Fri, 20 May 2022)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/sve-epilog-vect-inloop-reductions.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/sve-epilog-vect-reductions.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/sve-epilog-vect-strict-reductions.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/sve-epilog-vect.ll
    M llvm/test/Transforms/LoopVectorize/PowerPC/optimal-epilog-vectorization.ll
    M llvm/test/Transforms/LoopVectorize/X86/invariant-load-gather.ll
    M llvm/test/Transforms/LoopVectorize/X86/invariant-store-vectorization.ll
    M llvm/test/Transforms/LoopVectorize/X86/limit-vf-by-tripcount.ll
    M llvm/test/Transforms/LoopVectorize/X86/masked_load_store.ll
    M llvm/test/Transforms/LoopVectorize/epilog-vectorization-reductions.ll
    M llvm/test/Transforms/LoopVectorize/optimal-epilog-vectorization-liveout.ll
    M llvm/test/Transforms/LoopVectorize/optimal-epilog-vectorization.ll

  Log Message:
  -----------
  [LV] Do not LoopSimplify/LCSSA after generating main vector loop.

At the moment LV runs LoopSimplify and reconstructs LCSSA form after
generating the main vector loop and before generating the epilogue
vector loop.

In practice, this adds a new exit block for the scalar loop because the
middle block now also branches to the original exit block of the scalar
loop. It also requires adding a new LCSSA phi in the newly created exit
block.

This complicates things when modeling exit values in VPlan, because we
would need to update the VPlan for the epilogue loop to update the newly
created LCSSA phi node.

But none of that should be necessary, as all analysis requiring
loop-simplify form is already done at this point and LCSSA form of the
original loop is not broken.

Reviewed By: bmahjour

Differential Revision: https://reviews.llvm.org/D125810