[PATCH] D150425: [ValueTracking] deduce `X * Y != 0` if `LowestKnownBit(X) * LowestKnownBit(Y) != 0`
Noah Goldstein via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sat May 13 12:17:03 PDT 2023
goldstein.w.n added a comment.
In D150425#4340180 <https://reviews.llvm.org/D150425#4340180>, @nikic wrote:
> I find the formulation here kind of confusing. Wouldn't something like this be more obvious? https://alive2.llvm.org/ce/z/p5wWid
That works for the second proof, but not the first. We can't actually compute the LSB. Only the Lowest KnownBit.
Truthfully the first formula is enough for everything (as the arbitrary `x_subset` and `y_subset` include the set
of an known lowest bit).
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