[PATCH] D105009: [LSR] Handle case 1*reg => reg. PR50918

Tue Jun 29 21:00:33 PDT 2021

mkazantsev added a comment.

In D105009#2849126 <https://reviews.llvm.org/D105009#2849126>, @huihuiz wrote:

> Another note on LSRInstance::GenerateReassociationsImpl() where 1*reg is created, eventually trigger this assertion.
>
> Looks like LSR is rewriting Formula
>
>   reg((-64 + (32 * ((112 * (((trunc i32 undef to i8) * ((trunc i32 %tmp3 to i8) + {94,+,-3}<%bb1>)) + {-94,+,3}<%bb1>)) + (-56 * (trunc i32 %tmp3 to i8)) + {-110,+,88}<%bb1>)))) + 1*reg({0,+,-128}<%bb21>)
>
> into
>
>   reg({0,+,-128}<%bb21>) + imm(256)
>
> I am not sure this rewrite is correct ?

Yes it is, because 1st register contains undef and therefore whole thing is undef.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D105009/new/

https://reviews.llvm.org/D105009