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

[glisse at gcc dot gnu.org]

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

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
(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...