Unsigned integer overflow is defined.

I agree that the carry flag shouldn't be exposed directly, but the ability to express "add and check for overflow" would be useful and allow for these optimisations where the architecture supports it.

Edit: But if you want to exploit the processor to its fullest, go with assembly. The compiler is good, but proving optimisations is a hard problem, and complex, single-instruction-specific optimisations aren't going to take off any time soon.