[PATCH] D119661: [LV] Support chained phis as incoming values for first-order recurs.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 453103.
fhahn marked 3 inline comments as done.
fhahn added a comment.

Addressed latest comments, thanks!

In D119661#3726864 <https://reviews.llvm.org/D119661#3726864>, @Ayal wrote:

> In D119661#3723058 <https://reviews.llvm.org/D119661#3723058>, @fhahn wrote:
>
>> In D119661#3722786 <https://reviews.llvm.org/D119661#3722786>, @Ayal wrote:
>>
>>> Nice reuse of chained FOR's!
>
> Yeah, it seems `First` is no longer accurate for both LVLegality and IVDescriptors (but is for the recipes). Is there any benefit in caching the non-header-phi `Previous` in the IVDescriptor, given the iteration-by-iteration implementation?

Updated the naming. I've not added the filed for the non-header previous yet, because its uses currently are minimal.

>>> Wonder if some instCombine pattern may subsequently fold the multiple shuffles (and the multiple incoming vectors each holding a single element) to optimize higher-order recurrence where some phi's feed only other phi's w/o other users.
>>
>> Unfortunately it doesn't look like instcombine will be able to fold those shuffles, e.g.: https://llvm.godbolt.org/z/a8YoM6ev9
>
> Worth leaving a TODO somewhere?

I added a TODO at the point where we construct VPFirstOrderRecurrencePHIRecipe.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119661/new/

https://reviews.llvm.org/D119661

Files:
  llvm/include/llvm/Analysis/IVDescriptors.h
  llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h
  llvm/lib/Analysis/IVDescriptors.cpp
  llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
  llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains-vplan.ll
  llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains.ll
  llvm/test/Transforms/LoopVectorize/first-order-recurrence.ll

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