[Bug tree-optimization/101145] niter analysis fails for until-wrap condition

["guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101145

--- Comment #6 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
> As tests, for below loop, adjust_cond_for_loop_until_wrap return false:
> 
> foo (int *__restrict__ a, int *__restrict__ b, unsigned i)
> {
>   while (++i > 100)
>     *a++ = *b++ + 1;
> }
For the above code, niter still may be zero: e.g. "i < 100" at the start.
For the below code, niter can be determined as constant at compiling time.
> 
> For below code, adjust_cond_for_loop_until_wrap returns true:
>   i = UINT_MAX - 200;
>   while (++i > 100)
>     *a++ = *b++ + 1;

For below code, niter is also may be zero: e.g. "UINT_MAX - 100 < n" .
   i = UINT_MAX - 200
   while (++i > n)
     *a++ = *b++ + 1;