[PATCH] D140811: [DAGCombiner][X86] `visitVECTOR_SHUFFLE()`: splats with a single non-undef element are not splats

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: llvm/test/CodeGen/X86/haddsub-undef.ll:471
+; SSE-SLOW-NEXT:    movapd %xmm0, %xmm1
+; SSE-SLOW-NEXT:    unpckhpd {{.*#+}} xmm1 = xmm1[1],xmm0[1]
+; SSE-SLOW-NEXT:    addpd %xmm1, %xmm0
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lebedev.ri wrote:
> lebedev.ri wrote:
> > @RKSimon these no longer match because previously we had shuffle-fadd-shuffle,
> > so `isHorizontalBinOp()` called `shouldUseHorizontalOp()` with `IsSingleSource=false`,
> > and now we have shuffle-fadd, and `shouldUseHorizontalOp()` is called with `IsSingleSource=false`.
> > So this really doesn't look like a regression to me.
> and now we have shuffle-fadd, and `shouldUseHorizontalOp()` is called with `IsSingleSource=true`, of course that is
yes - for slow hops, 2shuffles+alu is the threshold for using hop (unless building for size)


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https://reviews.llvm.org/D140811