[PATCH] D99719: [SLP] Better estimate cost of no-op extracts on target vectors.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


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Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:3495-3498
+        unsigned MaxVecRegSize = getMaxVecRegSize();
+        unsigned EltSize = getVectorElementSize(VL[0]);
+        unsigned EltsPerVector = MaxVecRegSize / EltSize;
+        unsigned Idx = 0;
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fhahn wrote:
> ABataev wrote:
> > I think it is better to use `TLI->getTypeLegalizationCost(DL, cast<ExtractElementInst>(V)->getVectorOperandType());` to get the real machine vector type and the number of splits.
> I think using `TargetLoweringInfo` would indeed be better, but unfortunately I don't think we can access it here, as it is defined in CodeGen? I tried to see if there are any other such uses in `llvm/lib/Transforms` but couldn't. Perhaps there's a way to use it I am missing?
You can use `TTI->getNumberOfParts()` to get the number of registers and then calculate EltsPerVector.
Also, what if there are extracts from 2 different vectors with the different numbers of elements?


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  https://reviews.llvm.org/D99719/new/

https://reviews.llvm.org/D99719