hhoffstaette
commented
2 years ago I was just poking around in thirdparty/picojson and can re-recreate the warning by adding -O2 to the Makefile:
In file included from test.cc:28:
In copy constructor 'picojson::value::value(const picojson::value&)',
inlined from 'void std::__new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = picojson::value; _Args = {picojson::value}; _Tp = picojson::value]' at /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/g++-v12/bits/new_allocator.h:175:4,
inlined from 'static void std::allocator_traits<std::allocator<_CharT> >::construct(allocator_type&, _Up*, _Args&& ...) [with _Up = picojson::value; _Args = {picojson::value}; _Tp = picojson::value]' at /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/g++-v12/bits/alloc_traits.h:516:17,
inlined from 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {picojson::value}; _Tp = picojson::value; _Alloc = std::allocator<picojson::value>]' at /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/g++-v12/bits/vector.tcc:117:30,
inlined from 'void std::vector<_Tp, _Alloc>::push_back(value_type&&) [with _Tp = picojson::value; _Alloc = std::allocator<picojson::value>]' at /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/g++-v12/bits/stl_vector.h:1294:21,
inlined from 'bool picojson::default_parse_context::parse_array_item(picojson::input<Iter>&, size_t) [with Iter = std::istreambuf_iterator<char, std::char_traits<char> >]' at picojson.h:853:18,
inlined from 'bool picojson::_parse_array(Context&, input<Iter>&) [with Context = default_parse_context; Iter = std::istreambuf_iterator<char, std::char_traits<char> >]' at picojson.h:695:33,
inlined from 'bool picojson::_parse(Context&, input<Iter>&) [with Context = default_parse_context; Iter = std::istreambuf_iterator<char, std::char_traits<char> >]' at picojson.h:762:26:
picojson.h:249:10: warning: '<unnamed>.picojson::value::u_' may be used uninitialized [-Wmaybe-uninitialized]
249 | u_ = x.u_;
| ~~~^~~~~~
picojson.h: In function 'bool picojson::_parse(Context&, input<Iter>&) [with Context = default_parse_context; Iter = std::istreambuf_iterator<char, std::char_traits<char> >]':
picojson.h:853:19: note: '<anonymous>' declared here
853 | a.push_back(value());
| ^~~~~~~Probably due to inlining/move optimizations kicking in. picojson's build uses no optimizations by default, which is probably why this has not surfaced earlier.
This also explains why I haven't been able to reproduce this when building valijson from git: by default it also doesn't add any optimization flags. Simply running cmake with -DCMAKE_CXX_FLAGS="-O2" does the trick.
tristanpenman
After packaging valijson-0.7 for Gentoo without any problems using gcc-11.3 & clang-14 - including running the test suite - I was recently alerted to a new test compilation failure with gcc-12:
This is an interesting problem for several reasons:
The obvious solution is to build everything with clang ;-) but I would still like to understand what is wrong here, but so far I have not been able to understand what valijson does to/with picojson (other than using it), and what gcc complains about. I looked at picojson.h:249 aka value::value(..) and it does some funky conditional definition that seems to trip gcc's lifetime analyser.
I realize you can't help with the Gentoo build details, but maybe you have an idea why picojson has this problem (or what it is doing here to begin with, because I don't get it) and why gcc-12 complains about it.