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

[guojiufu at gcc dot gnu.org via Gcc-bugs]

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

--- Comment #5 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
(In reply to bin cheng from comment #4)
> (In reply to Jiu Fu Guo from comment #3)
> > Yes, while the code in adjust_cond_for_loop_until_wrap seems somehow tricky:
> > 
> >   /* Only support simple cases for the moment.  */
> >   if (TREE_CODE (iv0->base) != INTEGER_CST
> >       || TREE_CODE (iv1->base) != INTEGER_CST)
> >     return false;
> > 
> > This code requires both sides are constant.
> Actually it requires an IV with constant base.

I also feel that the intention of this function may only require one side
constant for IV0 CODE IV1.
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 below code, adjust_cond_for_loop_until_wrap returns true:
  i = UINT_MAX - 200;
  while (++i > 100)
    *a++ = *b++ + 1;