[PATCH] D124867: [SLP][NFC] Pre-commit test showing horizontal reduction preventing FMA

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


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Comment at: llvm/test/Transforms/SLPVectorizer/X86/slp-reduc-fma-loss.ll:40
+  %x.616 = fadd fast double %x.615, %x.597
+  br i1 undef, label %exit, label %loop
+
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wjschmidt wrote:
> vporpo wrote:
> > The test should still work without the loop
> Sadly, it does not.  If I remove the loop branches and the phi and replace the phi uses with undef, the vectorizer no longer finds the horizontal reduction profitable.
Please avoid using undef. In most cases, it prevents automatic verification or at least makes it more difficult. 


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https://reviews.llvm.org/D124867