[Bug target/51954] __int128_t (and long long on x86) negation can be optimized

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51954

--- Comment #5 from Hongtao.liu <crazylht at gmail dot com> ---
> 
> Yes, neg rdx = (0 - rdx) = (0 - (rdx + CF)(last def)) = (sbb 0, rdx)

And we need an extra register for it.