[PATCH] D100865: [COST] Improve shuffle kind detection if shuffle mask is provided.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


================
Comment at: llvm/include/llvm/CodeGen/BasicTTIImpl.h:748
+        return TargetTransformInfo::SK_Reverse;
+      if (ShuffleVectorInst::isZeroEltSplatMask(Mask))
+        return TargetTransformInfo::SK_Broadcast;
----------------
CarolineConcatto wrote:
> 
> Why are you changing this to broadcast I don't see that happening in SLPVectorizer.cpp.
> Before your implementation
> 
> ```
> Kind == TTI::SK_PermuteSingleSrc
> ``` 
> would call:
> 
> 
> ```
> return getPermuteShuffleOverhead(cast<FixedVectorType>(Tp));
> ```
> 
> 
> But now it calls:
> 
> 
> ```
> return getBroadcastShuffleOverhead(cast<FixedVectorType>(Tp));
> ```
> 
> Is that correct?
> 
> In my view, some tests would fail because now it has another cost model being called.
> 
> Oddly, there is not test failure, despite, in my view and with my knowledge, it would make some tests fail because you are changing the code path for the cost model.
> 
> Do you mind adding some tests for that as well?
Yes, there was no such thing in SLP vectorizer, I just extended functionality. Will try to add the tests for it.


Repository:
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  https://reviews.llvm.org/D100865/new/

https://reviews.llvm.org/D100865