[v3] Use noexcept in array swap

Index: include/bits/move.h
===================================================================
--- include/bits/move.h	(revision 175263)
+++ include/bits/move.h	(working copy)
@@ -152,12 +152,22 @@ 
       __b = _GLIBCXX_MOVE(__tmp);
     }
 
+#ifdef __GXX_EXPERIMENTAL_CXX0X__
+  // To work around c++/49045.
+  template<typename _Tp>
+    struct __is_nothrow_swappable
+    { static const bool value = noexcept(swap(std::declval<_Tp&>(),
+					      std::declval<_Tp&>())); };
+#endif
+
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // DR 809. std::swap should be overloaded for array types.
   template<typename _Tp, size_t _Nm>
     inline void
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
-    // noexcept waits for c++/49045
+#ifdef __GXX_EXPERIMENTAL_CXX0X__
+    noexcept(__is_nothrow_swappable<_Tp>::value)
+#endif
     {
       for (size_t __n = 0; __n < _Nm; ++__n)
 	swap(__a[__n], __b[__n]);
Index: include/bits/algorithmfwd.h
===================================================================
--- include/bits/algorithmfwd.h	(revision 175263)
+++ include/bits/algorithmfwd.h	(working copy)
@@ -558,7 +558,11 @@ 
 
   template<typename _Tp, size_t _Nm>
     void
-    swap(_Tp (&)[_Nm], _Tp (&)[_Nm]);
+    swap(_Tp (&)[_Nm], _Tp (&)[_Nm])
+#ifdef __GXX_EXPERIMENTAL_CXX0X__
+    noexcept(__is_nothrow_swappable<_Tp>::value)
+#endif
+    ;
 
   template<typename _FIter1, typename _FIter2>
     _FIter2 
Index: testsuite/25_algorithms/swap/noexcept.cc
===================================================================
--- testsuite/25_algorithms/swap/noexcept.cc	(revision 0)
+++ testsuite/25_algorithms/swap/noexcept.cc	(revision 0)
@@ -0,0 +1,26 @@ 
+// { dg-do compile }
+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2011 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/>.
+
+#include <utility>
+
+static_assert(noexcept(std::swap(std::declval<int&>(),
+				 std::declval<int&>())), "Error");
+static_assert(noexcept(std::swap(std::declval<int(&)[5]>(),
+				 std::declval<int(&)[5]>())), "Error");