Yes, that's what undefined behaviour is for. Eg requiring that implementations handle integer overflow needlessly degrades efficiency of the overwhelming majority of tasks where integers do not if fact overflow.

> The problem is that there's no way for programs to specify which corner cases they do or don't need.

Wait, are you just asking (the situationally appropriate equivalent of) `(int32_t)((uint32_t)x+(uint32_t)y)` and/or `#pragma unsafe assert(p!=NULL)`? Because while it's a shame the standard doesn't provide standardized ways to specify these things (as I admitted upthread) programs are prefectly capable of using the former, and implementations are perfectly capable of supporting the latter; I'm just arguing that the defaults should be sensible.