The code analyzer doesn't follow returns, issued within the loops:

warnloop.d:
> int main()
> {
>   for (;;)
>     return 0;
> }    

warning - warnloop.d(1): function warnloop.main no return at end of function

The workaround at the moment is to insert an assertion:

> int main()
> {
>   for (;;)
>     return 0;
>   assert(0);
> }    

When assertions are skipped over (later on), this becomes:

> int main()
> {
>   for (;;)
>     return 0;
>   assert(0);
>   return 0;
> }    

However, at the moment this gives another warning:
warning - warnloop.d(6): statement is not reachable

--anders