[PATCH] D150142: [InstCombine] Add simplifications for div/rem with `i1` operands; PR62607

[Zhu Siyuan via Phabricator via llvm-commits]

floatshadow added a comment.

In D150142#4327941 <https://reviews.llvm.org/D150142#4327941>, @goldstein.w.n wrote:

> Edit:
> Hers a minimal reproduction:
>
>   define i1 @foo(i1 %c, i1 %x, i1 %y) {
>     br i1 %c, label %true, label %false
>   true:
>     %y_true = and i1 %y, 0
>     br label %done
>   false:
>     %y_false = and i1 %y, 0
>     br label %done
>   done:
>     %yy = phi i1 [ %y_false, %false ], [ %y_true, %true ]
>     %r = sdiv i1 %x, %yy
>     ret i1 %r
>   }
>
> There needs to be some non-trivial zero pattern so it doesn't get constant folded.
> Either returning `poison` or `op0` is fine:
> https://alive2.llvm.org/ce/z/9RuT_m
> poison probably makes more sense though.

I guess this reproduction need some refinement.  `KnownBits` actually neglects zero cases, but the `threadBinOpOverPHI` would do recursive check which later got folded in a pattern match `if (match(Op1, m_Zero()))` in `simplifyDivRem`


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https://reviews.llvm.org/D150142