[PATCH] D132506: [SLP][NFC] Add test case exposing deficiency in finding reductions that feed buildvector sequence.

[Valeriy Dmitriev via Phabricator via llvm-commits]

vdmitrie added a comment.

Just a small note. When the problem was originally discovered it only reproduced with 4 reductions. The behavior was the following: the first time we tried to match a reduction it only matched one of four (because we do not traverse insertelement operands) and then 2 buildvector operands were vectorized with VF=2 and eventually the remaining one was matched in another iteration and we thus end up with two vectorized reductions and a chain of 2-way vectorization.
With just two reductions we would vectorize both merely with different SLP iterations so the problem would remain hidden. It only started to show up with just two reductions after https://reviews.llvm.org/D131965.


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  https://reviews.llvm.org/D132506/new/

https://reviews.llvm.org/D132506