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From: "guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/101145] niter analysis fails for until-wrap
 condition
Date: Fri, 25 Jun 2021 10:13:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101145

--- 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 tr=
icky:
> >=20
> >   /* Only support simple cases for the moment.  */
> >   if (TREE_CODE (iv0->base) !=3D INTEGER_CST
> >       || TREE_CODE (iv1->base) !=3D INTEGER_CST)
> >     return false;
> >=20
> > 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++ =3D *b++ + 1;
}

For below code, adjust_cond_for_loop_until_wrap returns true:
  i =3D UINT_MAX - 200;
  while (++i > 100)
    *a++ =3D *b++ + 1;=