http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59615
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Marc Glisse from comment #6) > (In reply to Jakub Jelinek from comment #4) > > Anyway, you definitely don't want > > to use inline asm in this case, if there is some code GCC doesn't optimize > > as good as you'd like to, just report that. > > One common similar case where people are tempted to use asm goto with an > output operand is, on x86: compute a*b and check if it overflowed. x86 has > flags for that but AFAIR they are not modeled in the .md files. (I was also > interested in output operands for asm goto in PR52381, but there is no good > example there) They are modelled in the .md files now, we just don't have general purpose builtins for this yet in GCC 4.9, it is only used for -fsanitize=undefined right now.
