There is one solution that would keep the crazy semantics of C, but would still allow for 2's complement arithmetic to be well-defined when one wants to. C99 d

There is one solution that would keep the crazy semantics of C, but would still allow for 2's complement arithmetic to be well-defined when one wants to. C99 defines int8_t, if it exists, to be a 2's complement signed integer of exactly 8 bits. Same for 16, 32, etc. The standard could very well define behavior on overflow for these (that is, turn them into actual types instead of typedefs), and leave int, long, etc alone. I think this would be a viable, realistic, solution. Integer conversions would probably still be a pain, though.