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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/110237] gcc.dg/torture/pr58955-2.c is
 miscompiled by RTL scheduling after reload
Date: Tue, 27 Jun 2023 09:50:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110237

--- Comment #21 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #19)
> But the size argument doesn't have anything to do with TBAA (and
> may_alias is about TBAA).  I don't think we have any way to circumvent
> C object access rules.  That is, for example, with -fno-strict-aliasing
> the following isn't going to work.
>=20
> int a;
> int b;
>=20
> int main()
> {
>   a =3D 1;
>   b =3D 2;
>   if (&a + 1 =3D=3D &b) // equality compare of unrelated pointers OK
>     {
>       long x =3D *(long *)&a; // access outside of 'a' not OK
>       if (x !=3D 0x0000000100000002)
>         abort ();
>     }
> }
>=20
> there's no command-line flag or attribute to form a pointer
> to an object composing 'a' and 'b' besides changing how the
> storage is declared.

But store-merging and SLP can introduce a wide long-sized access where on
source level you had two adjacent loads or even memcpy's, so we really seem=
 to
have a problem here and might need to be able to annotate types or individu=
al
accesses as "may-alias-with-oob-ok" in the IR: PR 110431.=