[PATCH] D136582: [InstCombine] fold sub pattern to and

Mon Oct 24 15:16:46 PDT 2022

bcl5980 added a comment.

In D136582#3880098 <https://reviews.llvm.org/D136582#3880098>, @spatel wrote:

> I don't know if it would have any effect on this patch, but we seem to be missing a constant-shrinking (DemandedBits) opportunity for sub nuw:
> https://alive2.llvm.org/ce/z/7Lb_Dy
>
> We can clear high-bits of the mask constant based on the highest bit set in the subtract constant.

Yeah, I also find the shrinking. And that part has no effect on this patch. Condition 1/3 don't care any high-bits for C2.

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