[PATCH] D116473: [VPlan] Don't consider VPWidenCanonicalIVRecipe phi-like.

[Florian Hahn via Phabricator via llvm-commits]

fhahn marked an inline comment as done.
fhahn added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:8451
     // This is used instead of IV < TC because TC may wrap, unlike BTC.
     // Start by constructing the desired canonical IV in the header block.
     VPValue *IV = nullptr;
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Ayal wrote:
> How about ironing this a bit, while we're here, e.g.:
> 
> ```
>     // Introduce the early-exit compare IV <= BTC to form header block mask.
>     // This is used instead of IV < TC because TC may wrap, unlike BTC.
>     // Start by constructing the desired canonical IV in the header block as its first non-phi instructions.
>     assert(CM.foldTailByMasking() && "must fold the tail");
>     VPBasicBlock *HeaderVPBB = Plan->getEntry()->getEntryBasicBlock();
>     auto NewInsertionPoint = HeaderVPBB->getFirstNonPhi();
> 
>     VPValue *IV = nullptr;
>     if (Legal->getPrimaryInduction())
>       IV = Plan->getOrAddVPValue(Legal->getPrimaryInduction());
>     else {
>       auto *IVRecipe = new VPWidenCanonicalIVRecipe();
>       HeaderVPBB->insert(IVRecipe, NewInsertionPoint);
>       IV = IVRecipe;
>     }
> 
>     assert(Builder.getInsertBlock() == HeaderVPBB && "..."); // if desired?
>     VPBuilder::InsertPointGuard Guard(Builder);
>     Builder.setInsertPoint(HeaderVPBB, NewInsertionPoint);
> ```
This now means that the compare recipe always gets created in the header VPBB whereas before it may be created in a different VPBB (but still reachable from the header through single branches). This causes some slight changes in the order the IR is generated, but overall seems like a nice simplification. I updated the patch.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D116473/new/

https://reviews.llvm.org/D116473