[PATCH] D151163: ValueTracking: Ignore -0 for nsz sqrt with UseInstrInfo in computeKnownFPClass

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D151163#4363921 <https://reviews.llvm.org/D151163#4363921>, @arsenm wrote:

> In D151163#4363911 <https://reviews.llvm.org/D151163#4363911>, @foad wrote:
>
>> Looks OK but shouldn't the nsz flag be applied more generally to the result of every computeKnownFPClass call?
>
>
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> In D151163#4363911 <https://reviews.llvm.org/D151163#4363911>, @foad wrote:
>
>> Looks OK but shouldn't the nsz flag be applied more generally to the result of every computeKnownFPClass call?
>
> No because of nsz’s bizarre definition. It doesn’t mean no -0 appears, it means you don’t care about the sign of zero.

This might be too strong as it is since it implies poison for -0, but I’m guessing that’s what the UseInstrInfo is for. Otherwise we would need another flag for stronger nsz interpretation


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