https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81291
--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> --- To answer your last question (from comment 1) first: at expand time we have: d.3_10 = d; _11 = (long long unsigned int) d.3_10; c.4_12 = c; e.5_14 = e; _15 = (long long unsigned int) e.5_14; _20 = _11 + _15; _19 = c.4_12 + _20; return _19; so it is adding a bunch of u64's. We could add them as 32-bit words (it cannot overflow) and only then convert to 64-bit, but the gimple optimisers do not figure that out. combine is left to pick up the pieces, but it does something wrong it seems.
