[Bug tree-optimization/108374] [12/13 Regression] unexpected -Wstringop-overflow when using std::atomic and std::shared_ptr

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108374

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 = MEM[(const struct __shared_ptr &)pointer_2(D)]._M_ptr;
_10 = MEM[(const struct __shared_count &)pointer_2(D) + 8]._M_pi;
if (_10 != 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 ={v} {CLOBBER};
D.37576 ={v} {CLOBBER(eol)};
goto <bb 19>; [100.00%] (leads straight to return)

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

Confirmed.