[PATCH] D148599: ValueTrackng: Handle sign bit for fptrunc
Matt Arsenault via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 18 03:42:45 PDT 2023
arsenm added a comment.
In D148599#4277139 <https://reviews.llvm.org/D148599#4277139>, @foad wrote:
> I feel like there are undocumented assumptions here.
>
> Does fptrunc +/- 0.0 preserve sign?
Yes
> Is Known.SignBit supposed to be accurate even for Nans? That seems unfortunate, since for a lot of operations you won't be able to propagate it unless you can prove something isn't Nan.
That’s the only reason you need it. Otherwise you can infer from the mask. I only expect it to be useful for the few signbit operations
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https://reviews.llvm.org/D148599/new/
https://reviews.llvm.org/D148599
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