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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 12:24:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101145

--- 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:
>=20
> foo (int *__restrict__ a, int *__restrict__ b, unsigned i)
> {
>   while (++i > 100)
>     *a++ =3D *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.
>=20
> For below code, adjust_cond_for_loop_until_wrap returns true:
>   i =3D UINT_MAX - 200;
>   while (++i > 100)
>     *a++ =3D *b++ + 1;

For below code, niter is also may be zero: e.g. "UINT_MAX - 100 < n" .
   i =3D UINT_MAX - 200
   while (++i > n)
     *a++ =3D *b++ + 1;=