> It also means that the behavior needs to be stable across time I don't think IB has to be stable over time? For instance, whether and which extended integer

> It also means that the behavior needs to be stable across time I don't think IB has to be stable over time? For instance, whether and which extended integer types exist is IB and that has definitely changed over time. > and that tools cannot report this behavior as a bug. It's absolutely possible to report IB as a bug (or even fully-specified behavior, as demonstrated by -fsanitize=unsigned-integer-overflow or -fsanitize=implicit-integer-conversion).