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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/110754] assume create spurious load for volatile
 variable
Date: Thu, 20 Jul 2023 22:45:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110754

--- Comment #4 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> (In reply to Xi Ruoyao from comment #1)
> > Is this a bug?  The standard defines accessing volatile objects as
> > side-effects so it's not allowed to merge volatile loads, AFAIU.
>=20
> Yes because assume attribute is defined not to have any side effects.
>=20
> Confirmed.
>=20
> gimplifier produces:
>=20
>   [[assume (D.2786)]]
>     {
>       {
>         int n.0;
>=20
>         n.0 =3D n;
>         D.2786 =3D n.0 =3D=3D 1;
>       }
>     }
>=20
> And then lowering produces:
>   _2 =3D n;
>   .ASSUME (_Z3bari._assume.0, _2);
>=20
> But really it should have passed the address of n rather than the value
> since n is volatile here .

Alright, I mistakenly believed [[assume(x)]]; is same as if (!x)
unreachable();.=