[PATCH] D140974: [LICM][WIP] Transform and hoist select instructions if possible

[Nikita Popov via Phabricator via llvm-commits]

nikic added a subscriber: spatel.
nikic added a comment.

In D140974#4026009 <https://reviews.llvm.org/D140974#4026009>, @StephenFan wrote:

> In D140974#4025888 <https://reviews.llvm.org/D140974#4025888>, @nikic wrote:
>
>> Shouldn't this be handled by adding this fold to InstCombine? https://alive2.llvm.org/ce/z/EXY5JH
>
> Thanks for your advice! I will try to handle this in InstCombine. But it seems it is not a beneficial transformation if we transform
>
>   define i8 @src(i1 %c, i8 %x) {
>     %add = add i8 %x, 10
>     %select = select i1 %c, i8 %x, i8 %add
>     ret i8 %select
>   }
>
> to
>
>   define i8 @tgt(i1 %c, i8 %x) {
>     %select = select i1 %c, i8 0, i8 10
>     %add = add i8 %select, %x
>     ret i8 %add
>   }
>
> https://godbolt.org/z/zxeojTxqb

This looks beneficial from a middle-end perspective, so we probably need to undo in the backend? @spatel Any thoughts?


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https://reviews.llvm.org/D140974