[Bug target/70734] __builtin_add_overflow emits poor code on x86-64

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70734

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #2)
> (In reply to Marc Glisse from comment #1)
> > 	movl	%edi, (%rdx)
> 
> Looks like we fail to notice that the result of the addition is unused and
> keep this dead store...

It's not unused, it's stored to memory.