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

Tue Jan 24 12:51:27 PST 2023

goldstein.w.n added a comment.

In D142271#4077990 <https://reviews.llvm.org/D142271#4077990>, @foad wrote:

> 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.

Personally in favor of completeness.

Repository:
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  https://reviews.llvm.org/D142271/new/

https://reviews.llvm.org/D142271