https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92679
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Without optimisation it prints your expected output for me (with any version of
GCC). It only fails with optimisation.
ASan seems to show a problem in your code:
==428329==ERROR: AddressSanitizer: stack-use-after-scope on address
0x7ffcfe3b22f0 at pc 0x0000004060c0 bp 0x7ffcfe3b1be0 sp 0x7ffcfe3b1bd8
READ of size 8 at 0x7ffcfe3b22f0 thread T0
#0 0x4060bf in std::_Function_base::_M_empty() const
/home/jwakely/gcc/8/include/c++/8.3.1/bits/std_function.h:260
#1 0x4060bf in std::function<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > (int&)>::operator()(int&) const
/home/jwakely/gcc/8/include/c++/8.3.1/bits/std_function.h:685
#2 0x4060bf in any_visitor<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >
>::accept<int>(std::function<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >
(int&)>)::{lambda(std::any&)#1}::operator()(std::any&) const /tmp/92679.cc:18
#3 0x4060bf in std::_Function_handler<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > (std::any&),
any_visitor<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >
>::accept<int>(std::function<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >
(int&)>)::{lambda(std::any&)#1}>::_M_invoke(std::_Any_data const&, std::any&)
/home/jwakely/gcc/8/include/c++/8.3.1/bits/std_function.h:283
#4 0x407187 in std::function<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >
(std::any&)>::operator()(std::any&) const
/home/jwakely/gcc/8/include/c++/8.3.1/bits/std_function.h:687
#5 0x407187 in any_visitor<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > >::operator()(std::any&)
/tmp/92679.cc:26
#6 0x4032d0 in main /tmp/92679.cc:45
#7 0x7fe45c0001a2 in __libc_start_main ../csu/libc-start.c:308
#8 0x4023cd in _start (/tmp/a.out+0x4023cd)
