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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/108374] [12/13 Regression] unexpected
 -Wstringop-overflow when using std::atomic and std::shared_ptr
Date: Thu, 12 Jan 2023 09:43:57 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
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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=3D108374

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
           Priority|P3                          |P2
   Target Milestone|---                         |12.3
   Last reconfirmed|                            |2023-01-12
     Ever confirmed|0                           |1
            Version|unknown                     |12.2.0

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We now say

cc1plus: note: destination object is likely at address zero

<bb 2> [local count: 1073741824]:
_9 =3D MEM[(const struct __shared_ptr &)pointer_2(D)]._M_ptr;
_10 =3D MEM[(const struct __shared_count &)pointer_2(D) + 8]._M_pi;
if (_10 !=3D 0B)
  goto <bb 4>; [53.47%]
else
  goto <bb 3>; [46.53%]

<bb 3> [local count: 499612072]:
__atomic_load_8 (16B, 5); [tail call]
D.37576 =3D{v} {CLOBBER};
D.37576 =3D{v} {CLOBBER(eol)};
goto <bb 19>; [100.00%] (leads straight to return)

so we have __shared_count of pointer _M_pi =3D=3D 0 here, whatever that mea=
ns
and not sure why we atomically load here.

Confirmed.=