unsigned / double propagation weirdness?

[Robert Dewar]

Joe Buck wrote:

> So the warning would only be generated if an unsigned negation is
> widened (or potentially widened, in the case of conversions to long,
> to alert the programmer to portability issues).
> 
> This should eliminate Robert's concerns about intentional use of -
> for two's complement: in such cases, the result would not be widened.

Yes, that sounds right, although I wonder how common this case is ...