http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50168
--- Comment #4 from Gunther Piez <gpiez at web dot de> 2011-08-23 22:00:31 UTC --- On 23.08.2011 19:58, jakub at gcc dot gnu.org wrote: > While __builtin_c[lt]z* documentation > says that the result is undefined in that case, I wonder if it would be fine > even if long l = (int) __builtin_c[lt]z* (x); gave a value that wasn't > actually > sign-extended to 64 bits. So that software operating on the assumption that the value return by __builtin_c[lt]z* is always int, even in the undefined case, would break as soon at it sees a value outside the int range. Which could very well be the case, AFAIK in the zero case the value of the target register is just unchanged. IMHO this is ok, I doubt that such code exists and even if, it is very broken by design :-) Just my 2 cent.
