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

["romain.geissler at amadeus dot com" <gcc-bugzilla@gcc.gnu.org>]

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

            Bug ID: 108374
           Summary: [12/13 Regression] unexpected -Wstringop-overflow when
                    using std::atomic and std::shared_ptr
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: romain.geissler at amadeus dot com
  Target Milestone: ---

Hi,

The following snippet produces an unexpected -Wstringop-overflow with gcc 12
and current trunk:

#include <atomic>
#include <memory>

struct A: public std::enable_shared_from_this<A>
{
    std::atomic<size_t> _attr;
};

void f(std::shared_ptr<A> pointer)
{
    std::weak_ptr<A> weakPointer(pointer);

    [[maybe_unused]] const unsigned int aAttr = weakPointer.lock()->_attr;
}


Compiler Explorer output:
In file included from
/opt/compiler-explorer/gcc-trunk-20230111/include/c++/13.0.0/atomic:41,
                 from <source>:1:
In member function 'std::__atomic_base<_IntTp>::__int_type
std::__atomic_base<_IntTp>::load(std::memory_order) const [with _ITp = long
unsigned int]',
    inlined from 'std::__atomic_base<_IntTp>::operator __int_type() const [with
_ITp = long unsigned int]' at
/opt/compiler-explorer/gcc-trunk-20230111/include/c++/13.0.0/bits/atomic_base.h:365:20,
    inlined from 'void f(std::shared_ptr<A>)' at <source>:13:69:
/opt/compiler-explorer/gcc-trunk-20230111/include/c++/13.0.0/bits/atomic_base.h:505:31:
error: 'long unsigned int __atomic_load_8(const volatile void*, int)' writing 8
bytes into a region of size 0 overflows the destination
[-Werror=stringop-overflow=]
  505 |         return __atomic_load_n(&_M_i, int(__m));
      |                ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
In function 'void f(std::shared_ptr<A>)':
cc1plus: note: destination object is likely at address zero
cc1plus: some warnings being treated as errors
Compiler returned: 1


I have found bug #104475 which seems to also deal with atomics and
-Wstringop-overflow however I can't judge if it looks like a duplicate or a
different issue.

Cheers,
Romain