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From: "alvaro.begue at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/108667] New: Spurious "maybe used uninitialized
 [-Wmaybe-uninitialized]" warning
Date: Fri, 03 Feb 2023 22:02:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108667

            Bug ID: 108667
           Summary: Spurious "maybe used uninitialized
                    [-Wmaybe-uninitialized]" warning
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alvaro.begue at gmail dot com
  Target Milestone: ---

I am using g++-12.1.0 on x86-64, but g++-12.2.0 in godbolt.org shows the sa=
me
problem

The options are -O3 -Wmaybe-uninitialized .

The code:

#include <functional>

struct S {
    S(std::function<void()> f) : f(f) {}

    std::function<void()> g;
    std::function<void()> f;
};

int main() {
    S s([](){});
    s.f();
}

Compiler output (from godbolt.org):
In file included from
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/functional:59,
                 from <source>:1:
In copy constructor 'std::function<_Res(_ArgTypes ...)>::function(const
std::function<_Res(_ArgTypes ...)>&) [with _Res =3D void; _ArgTypes =3D {}]=
',
    inlined from 'S::S(std::function<void()>)' at <source>:4:34,
    inlined from 'int main()' at <source>:11:15:
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/bits/std_function.h:39=
1:17:
warning: '<anonymous>' may be used uninitialized [-Wmaybe-uninitialized]
  391 |             __x._M_manager(_M_functor, __x._M_functor,
__clone_functor);
      |             ~~~~^~~~~~~~~~
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/bits/std_function.h: In
function 'int main()':
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/bits/std_function.h:26=
7:7:
note: by argument 2 of type 'const std::_Any_data&' to 'static bool
std::_Function_handler<_Res(_ArgTypes ...),
_Functor>::_M_manager(std::_Any_data&, const std::_Any_data&,
std::_Manager_operation) [with _Res =3D void; _Functor =3D main()::<lambda(=
)>;
_ArgTypes =3D {}]' declared here
  267 |       _M_manager(_Any_data& __dest, const _Any_data& __source,
      |       ^~~~~~~~~~
<source>:11:15: note: '<anonymous>' declared here
   11 |     S s([](){});
      |               ^
Compiler returned: 0=