https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113119
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Without the second redundant __builtin_add_overflow, we get a.0_1 = a; _7 = .ADD_OVERFLOW (a.0_1, 0); _2 = REALPART_EXPR <_7>; _3 = IMAGPART_EXPR <_7>; _4 = (_Bool) _3; c = _4; _5 = (_BitInt(8)) _2; b = _5; before bitint lowering and lower it well, but the redundant call results in a.0_1 = a; _7 = .ADD_OVERFLOW (a.0_1, 0); _2 = IMAGPART_EXPR <_7>; _3 = (_Bool) _2; c = _3; _4 = REALPART_EXPR <_7>; _5 = (_BitInt(8)) _4; b = _5; and optimizable_arith_overflow doesn't flag that as non-optimizable, so the bitint lowering of .ADD_OVERFLOW happens in that case on the REALPART_EXPR stmt. optimizable_arith_overflow checks if both REALPART_EXPR and IMAGPART_EXPR appear in the same bb (and that there are no other uses), but doesn't check that REALPART_EXPR is first. Either it should check that or perhaps allow it first but require that it is not used in statements before the REALPART_EXPR.
