[PATCH] D71312: [InstCombine] Fold X / abs(X) to X < 0 ? -1 : 1

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D71312#1778585 <https://reviews.llvm.org/D71312#1778585>, @xbolva00 wrote:

> Isn't abs(INT_MIN) undefined?
>
> expensive div is removed:
>
>   _Z4fooai: # @_Z4fooai
>     mov eax, edi
>     mov ecx, edi
>     neg ecx
>     cmovl ecx, edi
>     cdq
>     idiv ecx
>     ret
>   _Z5fooari: # @_Z5fooari
>     mov eax, edi
>     sar eax, 31
>     or eax, 1
>     ret
>
>
> GCC knows this trick too.


abs(INT_MIN) is only undefined if the sub 0, %x operation that SPF_ABS matched has the nsw flag set on it.


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