fix libstdc++/55908

diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index 0b5d475..714b3ed 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -648,7 +648,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
 
       template<typename _Tp, typename... _Args>
 	using _RequireValidArgs2
-	  = _Require<_NotSame<_Class, _Tp>, _NotSame<_Class*, _Tp>,
+	  = _Require<_NotSame<_Class, _Tp>, _NotSame<const _Class*, _Tp>,
 		     _AllConvertible<_Pack<_Args...>, _Pack<_ArgTypes...>>>;
 
       template<typename _Tp, typename... _Args>
@@ -727,7 +727,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
 
       template<typename _Tp, typename... _Args>
 	using _RequireValidArgs2
-	  = _Require<_NotSame<_Class, _Tp>, _NotSame<_Class*, _Tp>,
+	  = _Require<_NotSame<_Class, _Tp>, _NotSame<volatile _Class*, _Tp>,
 		     _AllConvertible<_Pack<_Args...>, _Pack<_ArgTypes...>>>;
 
       template<typename _Tp, typename... _Args>
@@ -807,7 +807,8 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
 
       template<typename _Tp, typename... _Args>
 	using _RequireValidArgs2
-	  = _Require<_NotSame<_Class, _Tp>, _NotSame<_Class*, _Tp>,
+	  = _Require<_NotSame<_Class, _Tp>,
+		     _NotSame<const volatile _Class*, _Tp>,
 		     _AllConvertible<_Pack<_Args...>, _Pack<_ArgTypes...>>>;
 
       template<typename _Tp, typename... _Args>
diff --git a/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc b/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
index 9854176..f65baa0 100644
--- a/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
@@ -30,10 +30,10 @@  void test01()
 {
   const int dummy = 0;
   std::bind(&inc, _1)(0);               // { dg-error  "no match" }
-  // { dg-error "rvalue|const" "" { target *-*-* } 1346 }
-  // { dg-error "rvalue|const" "" { target *-*-* } 1360 }
-  // { dg-error "rvalue|const" "" { target *-*-* } 1374 }
-  // { dg-error "rvalue|const" "" { target *-*-* } 1388 }
+  // { dg-error "rvalue|const" "" { target *-*-* } 1347 }
+  // { dg-error "rvalue|const" "" { target *-*-* } 1361 }
+  // { dg-error "rvalue|const" "" { target *-*-* } 1375 }
+  // { dg-error "rvalue|const" "" { target *-*-* } 1389 }
   std::bind(&inc, std::ref(dummy))();	// { dg-error  "no match" }
 }
 
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/mem_fn/55908.cc b/libstdc++-v3/testsuite/20_util/function_objects/mem_fn/55908.cc
new file mode 100644
index 0000000..7bbdb34
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/function_objects/mem_fn/55908.cc
@@ -0,0 +1,34 @@ 
+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2013 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/>.
+
+// PR libstdc++/55908 calling const member function via const pointer
+
+#include <functional>
+
+struct foo
+{
+  void f(int) const { }
+
+  void g() const
+  {
+    auto mf = std::mem_fn(&foo::f);
+    mf(this, 1);
+  }
+};