https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109561
Bug ID: 109561
Summary: -Wmaybe-uninitialized false positive false positive
false positive false positive false positive
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: f.heckenb...@fh-soft.de
Target Milestone: ---
(code and error below)
I don't know how to put this nicely, this is a terrible message:
- Most of it consists of standard library internals.
- The actual message ("may be used uninitialized") is buried well within it and
also refers to internal fields.
- It is reported no less than 5 times!?
- Most of all, AFAICS, it's bogus. The default constructor of std::optional
should construct an object that does not contain a value and such objects can
be copied just fine.
- Like many such bogus warnings apparently, it's rather volatile. Unrelated
changes, e.g. to i or removing the defaulted constructor declaration, can make
it disappear. Producing this minimal example was a lot of guesswork what can be
removed in which order without disturbing the message.
- It's a regression from 10.2.1 and 11.3.
% cat test.cpp
#include <optional>
#include <vector>
#include <string>
struct O
{
std::optional <int> i;
std::optional <std::string> s;
O () = default;
};
std::vector <O> a;
void f ()
{
for (auto &i: a)
i = { };
}
% g++ --std=c++20 -O2 -Wall -c test.cpp
In file included from /usr/include/c++/12/string:53,
from test.cpp:3:
In member function ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::pointer std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_data()
const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’,
inlined from ‘constexpr bool std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_is_local() const [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/usr/include/c++/12/bits/basic_string.h:274:23,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with
_CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:859:23,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:194:19,
inlined from ‘constexpr std::_Optional_payload<_Tp, true, false, false>&
std::_Optional_payload<_Tp, true, false,
false>::operator=(std::_Optional_payload<_Tp, true, false, false>&&) [with _Tp
= std::__cxx11::basic_string<char>]’ at /usr/include/c++/12/optional:420:22,
inlined from ‘constexpr std::_Optional_payload<_Tp, false, _Copy, _Move>&
std::_Optional_payload<_Tp, false, _Copy,
_Move>::operator=(std::_Optional_payload<_Tp, false, _Copy, _Move>&&) [with _Tp
= std::__cxx11::basic_string<char>; bool _Copy = false; bool _Move = false]’ at
/usr/include/c++/12/optional:436:26,
inlined from ‘constexpr std::_Optional_base<_Tp, <anonymous>, <anonymous>
>& std::_Optional_base<_Tp, <anonymous>, <anonymous>
>::operator=(std::_Optional_base<_Tp, <anonymous>, <anonymous> >&&) [with _Tp =
std::__cxx11::basic_string<char>; bool <anonymous> = false; bool <anonymous> =
false]’ at /usr/include/c++/12/optional:550:23,
inlined from ‘constexpr std::optional<std::__cxx11::basic_string<char> >&
std::optional<std::__cxx11::basic_string<char>
>::operator=(std::optional<std::__cxx11::basic_string<char> >&&)’ at
/usr/include/c++/12/optional:705:11,
inlined from ‘constexpr O& O::operator=(O&&)’ at test.cpp:5:8,
inlined from ‘void f()’ at test.cpp:17:11:
/usr/include/c++/12/bits/basic_string.h:234:28: warning: ‘*(const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*)((char*)&<unnamed> + offsetof(O,
O::s.std::optional<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::<unnamed>.std::_Optional_base<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >, false,
false>::<unnamed>)).std::__cxx11::basic_string<char>::_M_dataplus.std::__cxx11::basic_string<char>::_Alloc_hider::_M_p’
may be used uninitialized [-Wmaybe-uninitialized]
234 | { return _M_dataplus._M_p; }
| ^~~~
test.cpp: In function ‘void f()’:
test.cpp:17:11: note: ‘<anonymous>’ declared here
17 | i = { };
| ^
In member function ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size()
const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with
_CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:866:17,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:194:19,
inlined from ‘constexpr std::_Optional_payload<_Tp, true, false, false>&
std::_Optional_payload<_Tp, true, false,
false>::operator=(std::_Optional_payload<_Tp, true, false, false>&&) [with _Tp
= std::__cxx11::basic_string<char>]’ at /usr/include/c++/12/optional:420:22,
inlined from ‘constexpr std::_Optional_payload<_Tp, false, _Copy, _Move>&
std::_Optional_payload<_Tp, false, _Copy,
_Move>::operator=(std::_Optional_payload<_Tp, false, _Copy, _Move>&&) [with _Tp
= std::__cxx11::basic_string<char>; bool _Copy = false; bool _Move = false]’ at
/usr/include/c++/12/optional:436:26,
inlined from ‘constexpr std::_Optional_base<_Tp, <anonymous>, <anonymous>
>& std::_Optional_base<_Tp, <anonymous>, <anonymous>
>::operator=(std::_Optional_base<_Tp, <anonymous>, <anonymous> >&&) [with _Tp =
std::__cxx11::basic_string<char>; bool <anonymous> = false; bool <anonymous> =
false]’ at /usr/include/c++/12/optional:550:23,
inlined from ‘constexpr std::optional<std::__cxx11::basic_string<char> >&
std::optional<std::__cxx11::basic_string<char>
>::operator=(std::optional<std::__cxx11::basic_string<char> >&&)’ at
/usr/include/c++/12/optional:705:11,
inlined from ‘constexpr O& O::operator=(O&&)’ at test.cpp:5:8,
inlined from ‘void f()’ at test.cpp:17:11:
/usr/include/c++/12/bits/basic_string.h:1064:16: warning: ‘*(const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*)((char*)&<unnamed> + offsetof(O,
O::s.std::optional<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::<unnamed>.std::_Optional_base<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >, false,
false>::<unnamed>)).std::__cxx11::basic_string<char>::_M_string_length’ may be
used uninitialized [-Wmaybe-uninitialized]
1064 | { return _M_string_length; }
| ^~~~~~~~~~~~~~~~
test.cpp: In function ‘void f()’:
test.cpp:17:11: note: ‘<anonymous>’ declared here
17 | i = { };
| ^
In member function ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size()
const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with
_CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:866:17,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:194:19,
inlined from ‘constexpr std::_Optional_payload<_Tp, true, false, false>&
std::_Optional_payload<_Tp, true, false,
false>::operator=(std::_Optional_payload<_Tp, true, false, false>&&) [with _Tp
= std::__cxx11::basic_string<char>]’ at /usr/include/c++/12/optional:420:22,
inlined from ‘constexpr std::_Optional_payload<_Tp, false, _Copy, _Move>&
std::_Optional_payload<_Tp, false, _Copy,
_Move>::operator=(std::_Optional_payload<_Tp, false, _Copy, _Move>&&) [with _Tp
= std::__cxx11::basic_string<char>; bool _Copy = false; bool _Move = false]’ at
/usr/include/c++/12/optional:436:26,
inlined from ‘constexpr std::_Optional_base<_Tp, <anonymous>, <anonymous>
>& std::_Optional_base<_Tp, <anonymous>, <anonymous>
>::operator=(std::_Optional_base<_Tp, <anonymous>, <anonymous> >&&) [with _Tp =
std::__cxx11::basic_string<char>; bool <anonymous> = false; bool <anonymous> =
false]’ at /usr/include/c++/12/optional:550:23,
inlined from ‘constexpr std::optional<std::__cxx11::basic_string<char> >&
std::optional<std::__cxx11::basic_string<char>
>::operator=(std::optional<std::__cxx11::basic_string<char> >&&)’ at
/usr/include/c++/12/optional:705:11,
inlined from ‘constexpr O& O::operator=(O&&)’ at test.cpp:5:8,
inlined from ‘void f()’ at test.cpp:17:11:
/usr/include/c++/12/bits/basic_string.h:1064:16: warning: ‘*(const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*)((char*)&<unnamed> + offsetof(O,
O::s.std::optional<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::<unnamed>.std::_Optional_base<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >, false,
false>::<unnamed>)).std::__cxx11::basic_string<char>::_M_string_length’ may be
used uninitialized [-Wmaybe-uninitialized]
1064 | { return _M_string_length; }
| ^~~~~~~~~~~~~~~~
test.cpp: In function ‘void f()’:
test.cpp:17:11: note: ‘<anonymous>’ declared here
17 | i = { };
| ^
In member function ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::length() const [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]’,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:676:22,
inlined from ‘constexpr void std::_Construct(_Tp*, _Args&& ...) [with _Tp =
__cxx11::basic_string<char>; _Args = {__cxx11::basic_string<char,
char_traits<char>, allocator<char> >}]’ at
/usr/include/c++/12/bits/stl_construct.h:119:7,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_construct(_Args&& ...) [with _Args =
{std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>}; _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:278:19,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:198:26,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:189:7,
inlined from ‘constexpr std::_Optional_payload<_Tp, true, false, false>&
std::_Optional_payload<_Tp, true, false,
false>::operator=(std::_Optional_payload<_Tp, true, false, false>&&) [with _Tp
= std::__cxx11::basic_string<char>]’ at /usr/include/c++/12/optional:420:22,
inlined from ‘constexpr std::_Optional_payload<_Tp, false, _Copy, _Move>&
std::_Optional_payload<_Tp, false, _Copy,
_Move>::operator=(std::_Optional_payload<_Tp, false, _Copy, _Move>&&) [with _Tp
= std::__cxx11::basic_string<char>; bool _Copy = false; bool _Move = false]’ at
/usr/include/c++/12/optional:436:26,
inlined from ‘constexpr std::_Optional_base<_Tp, <anonymous>, <anonymous>
>& std::_Optional_base<_Tp, <anonymous>, <anonymous>
>::operator=(std::_Optional_base<_Tp, <anonymous>, <anonymous> >&&) [with _Tp =
std::__cxx11::basic_string<char>; bool <anonymous> = false; bool <anonymous> =
false]’ at /usr/include/c++/12/optional:550:23,
inlined from ‘constexpr std::optional<std::__cxx11::basic_string<char> >&
std::optional<std::__cxx11::basic_string<char>
>::operator=(std::optional<std::__cxx11::basic_string<char> >&&)’ at
/usr/include/c++/12/optional:705:11,
inlined from ‘constexpr O& O::operator=(O&&)’ at test.cpp:5:8,
inlined from ‘void f()’ at test.cpp:17:11:
/usr/include/c++/12/bits/basic_string.h:1071:16: warning: ‘*(const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*)((char*)&<unnamed> + offsetof(O,
O::s.std::optional<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::<unnamed>.std::_Optional_base<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >, false,
false>::<unnamed>)).std::__cxx11::basic_string<char>::_M_string_length’ may be
used uninitialized [-Wmaybe-uninitialized]
1071 | { return _M_string_length; }
| ^~~~~~~~~~~~~~~~
test.cpp: In function ‘void f()’:
test.cpp:17:11: note: ‘<anonymous>’ declared here
17 | i = { };
| ^
In member function ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::length() const [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]’,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:676:22,
inlined from ‘constexpr void std::_Construct(_Tp*, _Args&& ...) [with _Tp =
__cxx11::basic_string<char>; _Args = {__cxx11::basic_string<char,
char_traits<char>, allocator<char> >}]’ at
/usr/include/c++/12/bits/stl_construct.h:119:7,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_construct(_Args&& ...) [with _Args =
{std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>}; _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:278:19,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:198:26,
inlined from ‘constexpr void
std::_Optional_payload_base<_Tp>::_M_move_assign(std::_Optional_payload_base<_Tp>&&)
[with _Tp = std::__cxx11::basic_string<char>]’ at
/usr/include/c++/12/optional:189:7,
inlined from ‘constexpr std::_Optional_payload<_Tp, true, false, false>&
std::_Optional_payload<_Tp, true, false,
false>::operator=(std::_Optional_payload<_Tp, true, false, false>&&) [with _Tp
= std::__cxx11::basic_string<char>]’ at /usr/include/c++/12/optional:420:22,
inlined from ‘constexpr std::_Optional_payload<_Tp, false, _Copy, _Move>&
std::_Optional_payload<_Tp, false, _Copy,
_Move>::operator=(std::_Optional_payload<_Tp, false, _Copy, _Move>&&) [with _Tp
= std::__cxx11::basic_string<char>; bool _Copy = false; bool _Move = false]’ at
/usr/include/c++/12/optional:436:26,
inlined from ‘constexpr std::_Optional_base<_Tp, <anonymous>, <anonymous>
>& std::_Optional_base<_Tp, <anonymous>, <anonymous>
>::operator=(std::_Optional_base<_Tp, <anonymous>, <anonymous> >&&) [with _Tp =
std::__cxx11::basic_string<char>; bool <anonymous> = false; bool <anonymous> =
false]’ at /usr/include/c++/12/optional:550:23,
inlined from ‘constexpr std::optional<std::__cxx11::basic_string<char> >&
std::optional<std::__cxx11::basic_string<char>
>::operator=(std::optional<std::__cxx11::basic_string<char> >&&)’ at
/usr/include/c++/12/optional:705:11,
inlined from ‘constexpr O& O::operator=(O&&)’ at test.cpp:5:8,
inlined from ‘void f()’ at test.cpp:17:11:
/usr/include/c++/12/bits/basic_string.h:1071:16: warning: ‘*(const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*)((char*)&<unnamed> + offsetof(O,
O::s.std::optional<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::<unnamed>.std::_Optional_base<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >, false,
false>::<unnamed>)).std::__cxx11::basic_string<char>::_M_string_length’ may be
used uninitialized [-Wmaybe-uninitialized]
1071 | { return _M_string_length; }
| ^~~~~~~~~~~~~~~~
test.cpp: In function ‘void f()’:
test.cpp:17:11: note: ‘<anonymous>’ declared here
17 | i = { };
| ^
