https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110304
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> --- The reason for | rather than + is clang compatibility with its misdesigned interface. It never returns 2 as carry-out, even if you add 0xffffffffU, 0xfffffffU and 0xfffffffU. But, if pattern matching can prove the carry-in is only in [0, 1] range, then all of +, | or ^ act the same and if target provides uaddc5/usubc5 patterns, it will be pattern matched.
