2018-06-22  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/86138
	* include/bits/basic_string.tcc:
	[__cplusplus > 201402 && !_GLIBCXX_USE_CXX11_ABI]
	(basic_string<char>::_Rep::_S_empty_rep_storage)
	(basic_string<wchar_t>::_Rep::_S_empty_rep_storage): Add explicit
	instantiation declarations.
	[__cplusplus > 201402] (operator>>, operator<<, getline): Re-enable
	explicit instantiation declarations.
	* testsuite/21_strings/basic_string/cons/char/86138.cc: New.
	* testsuite/21_strings/basic_string/cons/wchar_t/86138.cc: New.

--- libstdc++-v3/include/bits/basic_string.tcc
+++ libstdc++-v3/include/bits/basic_string.tcc
@@ -1597,8 +1597,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Inhibit implicit instantiations for required instantiations,
   // which are defined via explicit instantiations elsewhere.
-#if _GLIBCXX_EXTERN_TEMPLATE > 0 && __cplusplus <= 201402L
+#if _GLIBCXX_EXTERN_TEMPLATE > 0
+  // The explicit instantiations definitions in src/c++11/string-inst.cc
+  // are compiled as C++14, so the new C++17 members aren't instantiated.
+  // Until those definitions are compiled as C++17 suppress the declaration,
+  // so C++17 code will implicitly instantiate std::string and std::wstring
+  // as needed.
+# if __cplusplus <= 201402L
   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
+
   extern template
     basic_istream<char>&
     operator>>(basic_istream<char>&, string&);
@@ -1613,7 +1626,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     getline(basic_istream<char>&, string&);
 
 #ifdef _GLIBCXX_USE_WCHAR_T
+# if __cplusplus <= 201402L
   extern template class basic_string<wchar_t>;
+# elif ! _GLIBCXX_USE_CXX11_ABI
+  extern template basic_string<wchar_t>::size_type
+    basic_string<wchar_t>::_Rep::_S_empty_rep_storage[];
+# endif
+
   extern template
     basic_istream<wchar_t>&
     operator>>(basic_istream<wchar_t>&, wstring&);
@@ -1626,8 +1645,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   extern template
     basic_istream<wchar_t>&
     getline(basic_istream<wchar_t>&, wstring&);
-#endif
-#endif
+#endif // _GLIBCXX_USE_WCHAR_T
+#endif // _GLIBCXX_EXTERN_TEMPLATE > 0
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
--- /dev/null
+++ libstdc++-v3/testsuite/21_strings/basic_string/cons/char/86138.cc
@@ -0,0 +1,30 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++1z } }
+// { dg-final { scan-assembler-not "_ZNSs4_Rep20_S_empty_rep_storageE:" } }
+
+#undef _GLIBCXX_USE_CXX11_ABI
+#define _GLIBCXX_USE_CXX11_ABI 0
+#include <string>
+
+void
+test01(std::string* s)
+{
+  s->~basic_string();
+}
--- /dev/null
+++ libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/86138.cc
@@ -0,0 +1,30 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++1z } }
+// { dg-final { scan-assembler-not "_ZNSbIwSt11char_traitsIwESaIwEE4_Rep20_S_empty_rep_storageE:" } }
+
+#undef _GLIBCXX_USE_CXX11_ABI
+#define _GLIBCXX_USE_CXX11_ABI 0
+#include <string>
+
+void
+test01(std::wstring* s)
+{
+  s->~basic_string();
+}