https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79173
--- Comment #32 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- (In reply to Jakub Jelinek from comment #31) > (In reply to Vincent Lefèvre from comment #30) > > (In reply to Jakub Jelinek from comment #29) > > > I mean that if the compiler can't see it is in [0, 1], it will need > > > to use 2 additions and or the 2 carry bits together. But, because > > > the ored carry bits are in [0, 1] range, all the higher limbs could > > > be done using addc. > > > > If the compiler can't see that carryin is in [0, 1], then it must not "or" > > the carry bits; it needs to add them, as carryout may be 2. > > That is not how the clang builtin works, which is why I've implemented the | > and documented it that way, as it is a compatibility builtin. I'm confused. In Comment 14, you said that *carry_out = c1 + c2; was used. This is an addition, not an OR.
