Signed integer overflow undefined behavior or not?

[Kagamin via Digitalmars-d]

On Friday, 13 November 2015 at 09:37:41 UTC, deadalnix wrote:
> It is not that it is complicated, but that signed wraparound is 
> almost always a bug. In C/C++, that result in very questionable 
> optimizations. But defining the thing as wraparound is also 
> preventing it to become an error.

What about unsigned integers? Most of the time they are used as 
positive numbers, positive number overflow is the same bug.