[PATCH] D124293: [SLP][NFC] Pre-commit test showing deficiency in current roots selection algorithm

Mon Apr 25 09:51:14 PDT 2022

vdmitrie added inline comments.

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Comment at: llvm/test/Transforms/SLPVectorizer/X86/vectorize-pair-path.ll:48
+  %i03 = fmul fast double undef, %i02
+  %i04 = fsub fast double %i03, undef
+  %i05 = fmul fast double %i04, 4.0
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vdmitrie wrote:
> ABataev wrote:
> > RKSimon wrote:
> > > Why are there undef float-ops? Is this the only way to expose the issue? If you run this through opt -O3 all you get is a posion result.
> > It is ok for SLP to have some undefs unless you do not use instcombine. You can treat undef here as a specific op kind, different from others. Just to reduce the size of the test.
> Yeah, this shouldn't go through instcombine. There were even more undefs after bugpoint reduced the original case so I had to step beck a bit and replaced some with FP constants to make tracing SLP vectorizer behavior easier. 
> 
typo: back (not "beck")

Repository:
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  https://reviews.llvm.org/D124293/new/

https://reviews.llvm.org/D124293