[Bug c++/86465] [8/9/10/11 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[Bug c++/86465] [8/9/10/11 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 49449
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49449&action=edit
preprocessed source, unreduced, gzipped

Here's another example that produces this kind of warning, this time from the
libstdc++ sources (when built with -Wsystem-headers -Werror)

It seems to be complaining about the std::allocator<char> object, which is an
empty class so (1) who cares if it's uninitialized and (2) it's not
uninitialized.

$ ~/gcc/11/bin/g++ -O2 -Wall cow-fs_path.ii -c      
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
In static member function ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:589:7,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&) [with
_InIterator = const char*; _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:5151:30,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _CharT*, std::basic_string<_CharT, _Traits,
_Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3620:9,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::basic_string<_CharT, _Traits, _Alloc>::__sv_wrapper,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3541:65,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _Tp&, const _Alloc&) [with _Tp =
std::basic_string_view<char>; <template-parameter-2-2> = void; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3731:58,
    inlined from ‘std::filesystem::path::path(const _Source&,
std::filesystem::path::format) [with _Source = std::basic_string_view<char>;
_Require = std::filesystem::path]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9,
    inlined from ‘void
std::filesystem::path::_M_concat(std::basic_string_view<char>)’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:340:24:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:604:36:
warning: ‘<anonymous>’ may be used uninitialized [-Wmaybe-uninitialized]
  604 |         _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
      |                     ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:
In member function ‘void
std::filesystem::path::_M_concat(std::basic_string_view<char>)’:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:980:5:
note: by argument 3 of type ‘const std::allocator<char>&’ to ‘static
std::basic_string<_CharT, _Traits, _Alloc>::_Rep* std::basic_string<_CharT,
_Traits, _Alloc>::_Rep::_S_create(std::basic_string<_CharT, _Traits,
_Alloc>::size_type, std::basic_string<_CharT, _Traits, _Alloc>::size_type,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ declared here
  980 |     basic_string<_CharT, _Traits, _Alloc>::_Rep::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:44,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9:
note: ‘<anonymous>’ declared here
  304 |       : _M_pathname(_S_convert(__detail::__effective_range(__source)))
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
In static member function ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:589:7,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&) [with
_InIterator = const char*; _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:5151:30,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _CharT*, std::basic_string<_CharT, _Traits,
_Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3620:9,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::basic_string<_CharT, _Traits, _Alloc>::__sv_wrapper,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3541:65,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _Tp&, const _Alloc&) [with _Tp =
std::basic_string_view<char>; <template-parameter-2-2> = void; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3731:58,
    inlined from ‘std::filesystem::path::path(const _Source&,
std::filesystem::path::format) [with _Source = char [2]; _Require =
std::filesystem::path]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9,
    inlined from ‘std::filesystem::__detail::_Path<_Source>&
std::filesystem::path::operator=(const _Source&) [with _Source = char [2]]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:340:24:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:604:36:
warning: ‘<anonymous>’ may be used uninitialized [-Wmaybe-uninitialized]
  604 |         _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
      |                     ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:
In function ‘std::filesystem::__detail::_Path<_Source>&
std::filesystem::path::operator=(const _Source&) [with _Source = char [2]]’:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:980:5:
note: by argument 3 of type ‘const std::allocator<char>&’ to ‘static
std::basic_string<_CharT, _Traits, _Alloc>::_Rep* std::basic_string<_CharT,
_Traits, _Alloc>::_Rep::_S_create(std::basic_string<_CharT, _Traits,
_Alloc>::size_type, std::basic_string<_CharT, _Traits, _Alloc>::size_type,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ declared here
  980 |     basic_string<_CharT, _Traits, _Alloc>::_Rep::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:44,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9:
note: ‘<anonymous>’ declared here
  304 |       : _M_pathname(_S_convert(__detail::__effective_range(__source)))
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
In static member function ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&,
std::forward_iterator_tag) [with _FwdIterator = const char*; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:589:7,
    inlined from ‘static _CharT* std::basic_string<_CharT, _Traits,
_Alloc>::_S_construct(_InIterator, _InIterator, const _Alloc&) [with
_InIterator = const char*; _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:5151:30,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _CharT*, std::basic_string<_CharT, _Traits,
_Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3620:9,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::basic_string<_CharT, _Traits, _Alloc>::__sv_wrapper,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3541:65,
    inlined from ‘std::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _Tp&, const _Alloc&) [with _Tp =
std::basic_string_view<char>; <template-parameter-2-2> = void; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.h:3731:58,
    inlined from ‘std::filesystem::path::path(const _Source&,
std::filesystem::path::format) [with _Source = std::basic_string_view<char>;
_Require = std::filesystem::path]’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9,
    inlined from ‘void
std::filesystem::path::_M_append(std::basic_string_view<char>)’ at
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:340:24:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:604:36:
warning: ‘<anonymous>’ may be used uninitialized [-Wmaybe-uninitialized]
  604 |         _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
      |                     ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/string:55,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/stdexcept:38,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/system_error:40,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_fwd.h:35,
                 from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:43,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:
In member function ‘void
std::filesystem::path::_M_append(std::basic_string_view<char>)’:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:980:5:
note: by argument 3 of type ‘const std::allocator<char>&’ to ‘static
std::basic_string<_CharT, _Traits, _Alloc>::_Rep* std::basic_string<_CharT,
_Traits, _Alloc>::_Rep::_S_create(std::basic_string<_CharT, _Traits,
_Alloc>::size_type, std::basic_string<_CharT, _Traits, _Alloc>::size_type,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ declared here
  980 |     basic_string<_CharT, _Traits, _Alloc>::_Rep::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/filesystem:44,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/fs_path.cc:34,
                 from
/home/jwakely/src/gcc/libstdc++-v3/src/c++17/cow-fs_path.cc:26:
/home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/bits/fs_path.h:304:9:
note: ‘<anonymous>’ declared here
  304 |       : _M_pathname(_S_convert(__detail::__effective_range(__source)))
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Bug c++/86465] [8/9/10/11 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #10)
> Created attachment 49449 [details]
> preprocessed source, unreduced, gzipped
> 
> Here's another example that produces this kind of warning, this time from
> the libstdc++ sources (when built with -Wsystem-headers -Werror)
> 
> It seems to be complaining about the std::allocator<char> object, which is
> an empty class so (1) who cares if it's uninitialized and (2) it's not
> uninitialized.

That one seems to be the same as PR 97840

[Bug tree-optimization/86465] [8/9/10/11 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
          Component|c++                         |tree-optimization

--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> ---
Changing component.

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[geoff3jones at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

--- Comment #15 from Geoff <geoff3jones at googlemail dot com> ---
This appears to still be an issue in gcc 11.2 minimal reproduced example using
std::optional https://godbolt.org/z/ebbMe3Wva


std::optional<bool> empty_optional(int x){
    return {};
}

std::optional<bool> empty_optional_or_true(int x){
    if(x > 0){
        return std::make_optional(true);
    }
    return {}; // <- second here
}

int main(){
empty_optional_or_true
}

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[geoff3jones at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

--- Comment #16 from Geoff <geoff3jones at googlemail dot com> ---
This appears to still be an issue in gcc 11.2 minimal reproduced example using
std::optional https://godbolt.org/z/ebbMe3Wva.

-std=c++17 -O3 -fsanitize=address -Wall -Werror -Wno-unused

std::optional<bool> empty_optional_or_true(int x){
    if(x > 0){
        return std::make_optional(true);
    }
    return {};
    //      ^ error here
}

int main(){
    empty_optional_or_true(0)
}

------------

In function 'std::optional<bool> empty_optional_or_true(int)',
    inlined from 'std::optional<bool> empty_optional_or_true(int)' at
<source>:28:21:
<source>:7:13: error: '*(unsigned char*)((char*)&<unnamed> +
offsetof(std::optional<bool>,std::optional<bool>::<unnamed>.std::_Optional_base<bool,
true, true>::<unnamed>))' may be used uninitialized
[-Werror=maybe-uninitialized]
    7 |     return {};
      |             ^
<source>: In function 'std::optional<bool> empty_optional_or_true(int)':
<source>:7:13: note: '<anonymous>' declared here
    7 |     return {}; // <- second here
      |    

In the linked example it can be see that making the global function static or
wrapping it in an anonymous namespace will cause the error to disappear.

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[marc@nieper-wisskirchen.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

--- Comment #17 from Marc Nieper-Wißkirchen <marc@nieper-wisskirchen.de> ---
Does a viable workaround exist that doesn't amount to disabling the warning
option altogether?

In my case, the actual warning is triggered inside the standard library, which
is used by my code that uses std::optional.

Thanks.

[Bug tree-optimization/86465] [9/10/11/12 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[marc@nieper-wisskirchen.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

Marc Nieper-Wißkirchen <marc@nieper-wisskirchen.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marc@nieper-wisskirchen.de

--- Comment #18 from Marc Nieper-Wißkirchen <marc@nieper-wisskirchen.de> ---
Does a viable workaround exist that doesn't amount to disabling the warning
option altogether?

In my case, the actual warning is triggered inside the standard library, which
is used by my code that uses std::optional.

Thanks.

[Bug tree-optimization/86465] [10/11/12/13 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #19 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug tree-optimization/86465] [10/11/12/13 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #20 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug tree-optimization/86465] [10/11/12/13 Regression] C++17 <optional> triggers: ‘<anonymous>’ may be used uninitialized in this function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86465

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
The original, the heavy simplified and Jonathans example no longer reproduce
diagnostics for me on any active branch.  The latest reported issue still is
diagnosed with -fsanitize=address but that's a different issue.

So let's close this.