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From: "guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108757] We do not simplify (a - (N*M)) / N +
 M -> a / N
Date: Fri, 12 May 2023 01:52:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108757

--- Comment #22 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #21)
> (In reply to Jiu Fu Guo from comment #20)
> > Interesting thing:
> > the VR is always VR_VARYING, even for the below simple case:
> >=20
> > typedef unsigned long INT;
> > INT __attribute__ ((noinline)) foo (INT x)
> > {
> >   if (x < 4)
> >     return 0;
> >   INT a =3D x + 18446744073709551612ULL;
> >   INT b =3D a >> 2;
> >   return b + 1;
> > }
>=20
> Yes that is because x does not have a "global" range.

I also tried "get_range_query (cfun)->range_of_expr (vr0, @0)",=20
>=20
> You could try the following testcase:
> ```
> typedef unsigned long INT;
> INT __attribute__ ((noinline)) foo (INT x)
> {
>   if (x < 4)
>     __builtin_unreachable();
>   INT a =3D x + 18446744073709551612ULL;
>   INT b =3D a >> 2;
>   return b + 1;
> }
> ```
>=20
> Which gets a (global) range for x_1(D) during forwprop3:
>   # RANGE [irange] INT [4, +INF]
>   INTD.2750 x_1(D) =3D xD.2751;

(In reply to Andrew Pinski from comment #21)
> (In reply to Jiu Fu Guo from comment #20)
> > Interesting thing:
> > the VR is always VR_VARYING, even for the below simple case:
> >=20
> > typedef unsigned long INT;
> > INT __attribute__ ((noinline)) foo (INT x)
> > {
> >   if (x < 4)
> >     return 0;
> >   INT a =3D x + 18446744073709551612ULL;
> >   INT b =3D a >> 2;
> >   return b + 1;
> > }
>=20
> Yes that is because x does not have a "global" range.
>=20
> You could try the following testcase:
> ```
> typedef unsigned long INT;
> INT __attribute__ ((noinline)) foo (INT x)
> {
>   if (x < 4)
>     __builtin_unreachable();
>   INT a =3D x + 18446744073709551612ULL;
>   INT b =3D a >> 2;
>   return b + 1;
> }
> ```
>=20
> Which gets a (global) range for x_1(D) during forwprop3:
>   # RANGE [irange] INT [4, +INF]
>   INTD.2750 x_1(D) =3D xD.2751;

Thanks so much!
"get_range_query (cfun)->range_of_expr (vr0, @0)" works for both the case!=