https://gcc.gnu.org/bugzilla/show_bug.cgi?id=12395
--- Comment #18 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is what is produced (at least for 7.3.0):
movl a(%rip), %edx
movl $0, %eax
leal 2(%rdx), %ecx
cmpl $-1, %edx
cmovne %ecx, %eax
movl %eax, a(%rip)
ret
