[PATCH] D142271: [ValueTracking] Add KnownBits patterns `xor(x, x - 1)` and `and(x, -x)` for knowing upper bits to be zero

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

In D142271#4077955 <https://reviews.llvm.org/D142271#4077955>, @goldstein.w.n wrote:

> I see, yeah that makes sense although I would design it as a static API b.c we can technically get more information from `-x` or `x - 1` than `x` itself if it happens to match some assume.

Is that really going to happen in practice? To me it seems so unlikely as to be not worth worrying about, for the sake a a nice simple API.


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https://reviews.llvm.org/D142271