https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61584
--- Comment #2 from David Krauss <potswa at mac dot com> --- C "compatible type" determines integer conversion rank (C11 §6.3.1.1). C++ fixes the rank by a heuristic which the implementation cannot decide (C++11 §4.5/3). Currently, enum promotions are incompatible between C and C++ modes. Furthermore, when C++ requires promotion to signed int but the underlying type is unsigned int, integer overflow may occur. I think this adds up to a bug and the C++ behavior should get its own bullet at the end of that manual page.
