diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index ae6530fcdc9..842e5f012f1 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -542,6 +542,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       basic_string(basic_string&& __str) noexcept
       : _M_dataplus(_M_local_data(), std::move(__str._M_get_allocator()))
       {
+	// Must use _M_length() here not _M_set_length() because
+	// basic_stringbuf relies on writing into unallocated capacity so
+	// we mess up the contents if we put a '\0' in the string.
+	_M_length(__str.length());
+
 	if (__str._M_is_local())
 	  {
 	    traits_type::copy(_M_local_buf, __str._M_local_buf,
@@ -551,14 +556,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	  {
 	    _M_data(__str._M_data());
 	    _M_capacity(__str._M_allocated_capacity);
+	    __str._M_data(__str._M_local_data());
+	    __str._M_set_length(0);
 	  }
-
-	// Must use _M_length() here not _M_set_length() because
-	// basic_stringbuf relies on writing into unallocated capacity so
-	// we mess up the contents if we put a '\0' in the string.
-	_M_length(__str.length());
-	__str._M_data(__str._M_local_data());
-	__str._M_set_length(0);
       }
 
       /**
@@ -746,7 +746,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
 	if (__str._M_is_local())
 	  {
-	    // We've always got room for a short string, just copy it.
+	    // We've always got room for a small string, just copy it.
 	    if (__str.size())
 	      this->_S_copy(_M_data(), __str._M_data(), __str.size());
 	    _M_set_length(__str.size());
@@ -756,34 +756,38 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	    || _M_get_allocator() == __str._M_get_allocator())
 	  {
 	    // Just move the allocated pointer, our allocator can free it.
-	    pointer __data = nullptr;
-	    size_type __capacity;
-	    if (!_M_is_local())
+	    if (_M_is_local())
 	      {
-		if (_Alloc_traits::_S_always_equal())
-		  {
-		    // __str can reuse our existing storage.
-		    __data = _M_data();
-		    __capacity = _M_allocated_capacity;
-		  }
-		else // __str can't use it, so free it.
-		  _M_destroy(_M_allocated_capacity);
+		_M_data(__str._M_data());
+		_M_length(__str.length());
+		_M_capacity(__str._M_allocated_capacity);
+		__str._M_data(__str._M_local_buf);
 	      }
-
-	    _M_data(__str._M_data());
-	    _M_length(__str.length());
-	    _M_capacity(__str._M_allocated_capacity);
-	    if (__data)
+	    else if (_Alloc_traits::_S_always_equal()
+		|| _M_get_allocator() == __str._M_get_allocator())
 	      {
+		// __str can reuse our existing storage.
+		pointer __data = _M_data();
+		size_type __capacity = _M_allocated_capacity;
+		_M_data(__str._M_data());
+		_M_length(__str.length());
+		_M_capacity(__str._M_allocated_capacity);
 		__str._M_data(__data);
 		__str._M_capacity(__capacity);
 	      }
 	    else
-	      __str._M_data(__str._M_local_buf);
+	      {
+		// __str can't use it, so free it.
+		_M_destroy(_M_allocated_capacity);
+		_M_data(__str._M_data());
+		_M_length(__str.length());
+		_M_capacity(__str._M_allocated_capacity);
+		__str._M_data(__str._M_local_buf);
+	      }
+	    __str.clear();
 	  }
 	else // Need to do a deep copy
 	  assign(__str);
-	__str.clear();
 	return *this;
       }
 
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable.cc
index 21932cf7736..e19cd85925b 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable.cc
@@ -1,5 +1,4 @@
 // { dg-do run { target c++11 } }
-// { dg-require-string-conversions "" }
 
 // Copyright (C) 2010-2018 Free Software Foundation, Inc.
 //
@@ -18,10 +17,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -31,11 +26,30 @@ void test01()
   std::string a, b;
   a.push_back('1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#else
+  a.clear();
+#endif
+
+  a.reserve(200);  // defeat small string optimization
+  a.push_back('1');
+  b = std::move(a);
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  VERIFY( a.size() == 0 );  // size is unspecified, but true for our string
 
   std::string c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == '1' );
+  VERIFY( b.size() == 0 );  // size is unspecified, but true for our string
+
+  b.push_back('1'); // for SSO string this uses local buffer
+  std::string d(std::move(b));
+  VERIFY( d.size() == 1 && d[0] == '1' );
+#if ! _GLIBCXX_USE_CXX11_ABI
   VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2.cc
index 8488b9698ff..cb4c7f2e39e 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2.cc
@@ -19,10 +19,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -40,11 +36,18 @@ void test01()
   tstring a, b;
   a.push_back('1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   tstring c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == '1' );
+  // b.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
   VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2_c++17.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2_c++17.cc
index a6e2ebcade0..706605c5c20 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2_c++17.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/moveable2_c++17.cc
@@ -18,10 +18,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -39,11 +35,18 @@ void test01()
   tstring a, b;
   a.push_back('1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   tstring c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == '1' );
+  // b.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
   VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable.cc
index aa6a52749dc..b7ba4865b16 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable.cc
@@ -1,5 +1,4 @@
 // { dg-do run { target c++11 } }
-// { dg-require-string-conversions "" }
 
 // Copyright (C) 2010-2018 Free Software Foundation, Inc.
 //
@@ -18,10 +17,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -31,11 +26,30 @@ void test01()
   std::wstring a, b;
   a.push_back(L'1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == L'1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == L'1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#else
+  a.clear();
+#endif
+
+  a.reserve(200);  // defeat small string optimization
+  a.push_back(L'1');
+  b = std::move(a);
+  VERIFY( b.size() == 1 && b[0] == L'1' );
+  VERIFY( a.size() == 0 );  // size is unspecified, but true for our string
 
   std::wstring c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == L'1' );
   VERIFY( b.size() == 0 );
+
+  b.push_back(L'1'); // for SSO string this uses local buffer
+  std::wstring d(std::move(b));
+  VERIFY( d.size() == 1 && d[0] == L'1' );
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2.cc
index 389adc5205d..61d26d85081 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2.cc
@@ -1,6 +1,5 @@
 // { dg-options "-fno-inline" }
 // { dg-do run { target c++11 } }
-// { dg-require-string-conversions "" }
 
 // Copyright (C) 2011-2018 Free Software Foundation, Inc.
 //
@@ -19,10 +18,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -40,11 +35,18 @@ void test01()
   twstring a, b;
   a.push_back(L'1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == L'1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   twstring c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == L'1' );
+  // b.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
   VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2_c++17.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2_c++17.cc
index 3c05a48dd7d..cda7e0f6b96 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2_c++17.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/moveable2_c++17.cc
@@ -18,10 +18,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changed
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -39,11 +35,18 @@ void test01()
   tstring a, b;
   a.push_back(L'1');
   b = std::move(a);
-  VERIFY( b.size() == 1 && b[0] == L'1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == L'1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   tstring c(std::move(b));
   VERIFY( c.size() == 1 && c[0] == L'1' );
+  // b.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
   VERIFY( b.size() == 0 );
+#endif
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc
index 7089fea04c2..4fbf6bab1cb 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc
@@ -1,5 +1,4 @@
 // { dg-do run { target c++11 } }
-// { dg-require-string-conversions "" }
 
 // Copyright (C) 2010-2018 Free Software Foundation, Inc.
 //
@@ -18,10 +17,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changes
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -31,7 +26,11 @@ void test01()
   std::string a, b;
   a.push_back('1');
   b.assign(std::move(a));
-  VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == '1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   // True for std::allocator because is_always_equal, but not true in general:
   static_assert(noexcept(a.assign(std::move(b))), "lwg 2063");
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc
index 8d394602a9f..e0550c4f283 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc
@@ -1,5 +1,4 @@
 // { dg-do run { target c++11 } }
-// { dg-require-string-conversions "" }
 
 // Copyright (C) 2010-2018 Free Software Foundation, Inc.
 //
@@ -18,10 +17,6 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// NOTE: This makes use of the fact that we know how moveable
-// is implemented on string (via swap). If the implementation changes
-// this test may begin to fail.
-
 #include <string>
 #include <utility>
 #include <testsuite_hooks.h>
@@ -31,7 +26,11 @@ void test01()
   std::wstring a, b;
   a.push_back(L'1');
   b.assign(std::move(a));
-  VERIFY( b.size() == 1 && b[0] == '1' && a.size() == 0 );
+  VERIFY( b.size() == 1 && b[0] == L'1' );
+  // a.size() is unspecified after a move
+#if ! _GLIBCXX_USE_CXX11_ABI
+  VERIFY( a.size() == 0 );
+#endif
 
   // True for std::allocator because is_always_equal, but not true in general:
   static_assert(noexcept(a.assign(std::move(b))), "lwg 2063");
