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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/98465] Bogus warning stringop-overread wuth
 -std=gnu++20 -O2 and std::string::insert
Date: Wed, 06 Jan 2021 22:59:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98465

--- Comment #6 from Martin Sebor <msebor at gcc dot gnu.org> ---
Different -std=3D settings also affect the warning, again as a result of in=
lining
and the explicit instantiation declarations.  The basic_string.tcc file has=
 the
following block toward the end which explains when implicit instantiation is
suppressed:

  // Inhibit implicit instantiations for required instantiations,
  // which are defined via explicit instantiations elsewhere.
#if _GLIBCXX_EXTERN_TEMPLATE
  // The explicit instantiation definitions in src/c++11/string-inst.cc and
  // src/c++17/string-inst.cc only instantiate the members required for C++=
17
  // and earlier standards (so not C++20's starts_with and ends_with).
  // Suppress the explicit instantiation declarations for C++20, so C++20
  // code will implicitly instantiate std::string and std::wstring as neede=
d.
# if __cplusplus <=3D 201703L && _GLIBCXX_EXTERN_TEMPLATE > 0
  extern template class basic_string<char>;
# elif ! _GLIBCXX_USE_CXX11_ABI
  // Still need to prevent implicit instantiation of the COW empty rep,
  // to ensure the definition in libstdc++.so is unique (PR 86138).
  extern template basic_string<char>::size_type
    basic_string<char>::_Rep::_S_empty_rep_storage[];
# endif=