[PATCH] D144958: [SLP]Initial support for reshuffling of non-starting buildvector/gather nodes.

Tue Mar 7 09:37:18 PST 2023

RKSimon added inline comments.

================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:6998
       bool NeedShuffle =
-          VL.front() != *It || !all_of(VL.drop_front(), UndefValue::classof);
+          count(VL, *It) > 1 &&
+          (VL.front() != *It || !all_of(VL.drop_front(), UndefValue::classof));
----------------
vdmitrie wrote:
> ABataev wrote:
> > vdmitrie wrote:
> > > What is a case when count(VL, *It) == 1?
> > It's when you have something like `<poison, poison, v, poison>`.
> Thanks. I see now. I did not realize that isSplat returns true for even single non-undef value in a vector.
Yes - its a problem in both IR and DAG :( 

Repository:
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  https://reviews.llvm.org/D144958/new/

https://reviews.llvm.org/D144958