[PATCH] D115526: [InstCombine] don't automatically drop poison-generating flags in SimplifyVectorDemandedElts

Mon Dec 13 18:18:16 PST 2021

aqjune added a comment.

In D115526#3185703 <https://reviews.llvm.org/D115526#3185703>, @spatel wrote:

> In D115526#3185635 <https://reviews.llvm.org/D115526#3185635>, @nikic wrote:
>
>> It looks like the shufflevector poison change hasn't landed yet? D93818 <https://reviews.llvm.org/D93818> / D103874 <https://reviews.llvm.org/D103874>
>
> Thanks for the reminder! ( cc @aqjune @hyeongyukim @regehr  )

Hi, sorry for my late reply.
The patch is blocked at the moment because the `mm*_undefined*` intrinsics must be correctly lowered first. (see: https://reviews.llvm.org/D103874#3022980)
Simply fixing them to return a zero vector would be the simplest solution, but not sure whether it will have no performance regression, and no one (including me) has no time to explore...

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