[PATCH] D60426: [InstCombine] prevent possible miscompile with negate+sdiv of vector op

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri accepted this revision.
lebedev.ri added a comment.

This LG, thank you!

In D60426#1459186 <https://reviews.llvm.org/D60426#1459186>, @shchenz wrote:

> LGTM for this patch.
>
> But should we also consider about the following pattern in file `test/Transforms/InstCombine/div.ll`
>
>   define <2 x i64> @test34(<2 x i64> %x) {
>   ; CHECK-LABEL: @test34(
>   ; CHECK-NEXT:    [[DIV:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
>   ; CHECK-NEXT:    ret <2 x i64> [[DIV]]
>   ;
>     %neg = sub nsw <2 x i64> zeroinitializer, %x
>     %div = sdiv exact <2 x i64> %neg, <i64 3, i64 4>
>     ret <2 x i64> %div
>   }
>
>
> This one is `sdiv (neg(%x), constant)`, it should have same issue, right? But I think this should be another issue about `sdiv` combination?


Yes, that seems to have the same general problem.
https://godbolt.org/z/vPVHmh



================
Comment at: llvm/test/Transforms/InstCombine/div.ll:820
 ;
   %div = sdiv <2 x i8> %x, <i8 -1, i8 1>
   %neg = sub <2 x i8> zeroinitializer, %div
----------------
Could also add a test for SINT_MIN (yes, i have seen the next test here)


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