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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106868] [12/13 Regression] Bogus
 -Wdangling-pointer warning with -O1
Date: Wed, 07 Sep 2022 09:05:39 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: diagnostic
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106868

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Keywords|                            |diagnostic
            Summary|Bogus -Wdangling-pointer    |[12/13 Regression] Bogus
                   |warning with -O1            |-Wdangling-pointer warning
                   |                            |with -O1
          Component|c                           |tree-optimization
   Last reconfirmed|                            |2022-09-07
             Status|UNCONFIRMED                 |NEW
           Priority|P3                          |P2
                 CC|                            |msebor at gcc dot gnu.org
   Target Milestone|---                         |12.3

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

<bb 2> [local count: 1073741824]:
alloc (&q);
q.0_1 =3D q;
*p_4(D) =3D q.0_1;
q =3D{v} {CLOBBER(eol)};
a_8 =3D __builtin_memcpy (q.0_1, "", 1);
*a_8 =3D 0;
return;

(gdb) p debug_gimple_stmt (use_stmt)
# .MEM_9 =3D VDEF <.MEM_7>
*a_8 =3D 0;
(gdb) p debug_gimple_stmt (stmt)
# .MEM_6 =3D VDEF <.MEM_5>
q =3D{v} {CLOBBER(eol)};

we somehow confuse q.0_1 =3D q; as assigning the address of the object 'q'.
Some addr vs deref mismatch somewhere in the code.

A regression with -Wall.=