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))) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
