basic_string.h (operator+(basic_string<>&&, basic_string<>&&)): Optimize better.

2010-12-19  Paolo Carlini  <paolo.carlini@oracle.com>

	* include/bits/basic_string.h (operator+(basic_string<>&&,
	basic_string<>&&)): Optimize better.
	* include/ext/vstring.h (operator+(__versa_string<>&&,
	__versa_string<>&)): Likewise.

From-SVN: r168061

libstdc++-v3/ChangeLog

 2010-12-19  Paolo Carlini  <paolo.carlini@oracle.com>
 
+	* include/bits/basic_string.h (operator+(basic_string<>&&,
+	basic_string<>&&)): Optimize better.
+	* include/ext/vstring.h (operator+(__versa_string<>&&,
+	__versa_string<>&)): Likewise.
+
+2010-12-19  Paolo Carlini  <paolo.carlini@oracle.com>
+
 	* testsuite/21_strings/basic_string/operators/char/4.cc: New.
 	* testsuite/21_strings/basic_string/operators/wchar_t/4.cc: Likewise.
 	* testsuite/ext/vstring/operators/2.cc: Likewise.

libstdc++-v3/include/bits/basic_string.h

@@ -2380,7 +2380,13 @@ _GLIBCXX_BEGIN_NAMESPACE(std)
     inline basic_string<_CharT, _Traits, _Alloc>
     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
 	      basic_string<_CharT, _Traits, _Alloc>&& __rhs)
-    { return std::move(__lhs.append(__rhs)); }
+    {
+      const auto __size = __lhs.size() + __rhs.size();
+      const bool __cond = (__size > __lhs.capacity()
+			   && __size <= __rhs.capacity());
+      return __cond ? std::move(__rhs.insert(0, __lhs))
+	            : std::move(__lhs.append(__rhs));
+    }
 
   template<typename _CharT, typename _Traits, typename _Alloc>
     inline basic_string<_CharT, _Traits, _Alloc>
@@ -2390,8 +2396,8 @@ _GLIBCXX_BEGIN_NAMESPACE(std)
 
   template<typename _CharT, typename _Traits, typename _Alloc>
     inline basic_string<_CharT, _Traits, _Alloc>
-    operator+(_CharT __lhs, basic_string<_CharT,
-	      _Traits, _Alloc>&& __rhs)
+    operator+(_CharT __lhs,
+	      basic_string<_CharT, _Traits, _Alloc>&& __rhs)
     { return std::move(__rhs.insert(0, 1, __lhs)); }
 
   template<typename _CharT, typename _Traits, typename _Alloc>

libstdc++-v3/include/ext/vstring.h

@@ -2118,7 +2118,13 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
     inline __versa_string<_CharT, _Traits, _Alloc, _Base>
     operator+(__versa_string<_CharT, _Traits, _Alloc, _Base>&& __lhs,
 	      __versa_string<_CharT, _Traits, _Alloc, _Base>&& __rhs)
-    { return std::move(__lhs.append(__rhs)); }
+    {
+      const auto __size = __lhs.size() + __rhs.size();
+      const bool __cond = (__size > __lhs.capacity()
+			   && __size <= __rhs.capacity());
+      return __cond ? std::move(__rhs.insert(0, __lhs))
+	            : std::move(__lhs.append(__rhs));
+    }
 
   template<typename _CharT, typename _Traits, typename _Alloc,
 	   template <typename, typename, typename> class _Base>