https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98465
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Comparing the code emitted by GCC 10 and the current trunk shows that the
former doesn't inline std::string::replace() regardless of the inlining limit.
The translation unit obtained with the former shows declarations of explicit
instantiations of basic_string:
$ g++-10 -O2 -E -Wall -g t.C | grep template | grep basic_string
template<typename, typename, typename> friend class basic_stringbuf;
extern template class basic_string<char>;
extern template class basic_string<wchar_t>;
Current trunk doesn't declare them which is what allows std::string::replace to
be inlined.
Removing the declaration of the explicit instantiation from the translation
unit lets GCC 10 inline string::replace but the warning is not issued because
the location of the call is in a system header. But enabling warning for those
via -Wsystem-headers shows the warning even with GCC 10:
$ g++-10 -E pr98465.C | sed "/extern template class basic_string/d" >
pr98465.ii && g++-10 -O2 -S -Wall -Wsystem-headers pr98465.ii
In file included from
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/string:56,
from pr98465.C:1:
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:
In function ‘void f(std::string&)’:
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/basic_string.tcc:456:20:
warning: offset ‘2’ outside bounds of constant string [-Warray-bounds]
456 | this->_S_copy(__p, __s + __len2 - __len1, __len2);
| ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr98465.C:3:12: note: ‘constantString’ declared here
3 | const char constantString[] = {42, 53};
| ^~~~~~~~~~~~~~
In file included from
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/string:40,
from pr98465.C:1:
In static member function ‘static std::char_traits<char>::char_type*
std::char_traits<char>::copy(std::char_traits<char>::char_type*, const
char_type*, std::size_t)’,
inlined from ‘void f(std::string&)’ at
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/basic_string.h:351:21:
/build/gcc-10-branch/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/char_traits.h:395:49:
warning: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’
reading 2 bytes from a region of size 0 [-Wstringop-overflow=]
395 | return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n));
| ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
