re PR libstdc++/70437 (Instantiation loop with pair and is_constructible)

 	PR libstdc++/70437
 	* include/bits/stl_pair.h (_ConstructiblePair,
	_ImplicitlyConvertiblePair, _MoveConstructiblePair,
	_ImplicitlyMoveConvertiblePair): Add shortcut conditions
	for same-type cases.
	* testsuite/20_util/pair/70437.cc: New.

From-SVN: r234743

libstdc++-v3/ChangeLog

+2016-04-05  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+	PR libstdc++/70437
+	* include/bits/stl_pair.h (_ConstructiblePair,
+	_ImplicitlyConvertiblePair, _MoveConstructiblePair,
+	_ImplicitlyMoveConvertiblePair): Add shortcut conditions
+	for same-type cases.
+	* testsuite/20_util/pair/70437.cc: New.
+
 2016-03-24  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/69945

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

@@ -87,32 +87,51 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Concept utility functions, reused in conditionally-explicit
   // constructors.
+  // See PR 70437, don't look at is_constructible or
+  // is_convertible if the decayed types are the same to
+  // avoid querying those properties for incomplete types.
   template <typename _T1, typename _T2, typename _U1, typename _U2>
   constexpr bool _ConstructiblePair()
   {
-    return __and_<is_constructible<_T1, const _U1&>,
-		  is_constructible<_T2, const _U2&>>::value;
+    return __and_<__or_<is_same<typename decay<_T1>::type,
+				typename decay<_U1>::type>,
+			is_constructible<_T1, const _U1&>>,
+		  __or_<is_same<typename decay<_T2>::type,
+				typename decay<_U2>::type>,
+			is_constructible<_T2, const _U2&>>>::value;
   }
 
   template <typename _T1, typename _T2, typename _U1, typename _U2>
   constexpr bool _ImplicitlyConvertiblePair()
   {
-    return __and_<is_convertible<const _U1&, _T1>,
-		  is_convertible<const _U2&, _T2>>::value;
+    return __and_<__or_<is_same<typename decay<_T1>::type,
+				typename decay<_U1>::type>,
+			is_convertible<const _U1&, _T1>>,
+		  __or_<is_same<typename decay<_T2>::type,
+				typename decay<_U2>::type>,
+		       is_convertible<const _U2&, _T2>>>::value;
   }
 
   template <typename _T1, typename _T2, typename _U1, typename _U2>
   constexpr bool _MoveConstructiblePair()
   {
-    return __and_<is_constructible<_T1, _U1&&>,
-		  is_constructible<_T2, _U2&&>>::value;
+    return __and_<__or_<is_same<typename decay<_T1>::type,
+				typename decay<_U1>::type>,
+			is_constructible<_T1, _U1&&>>,
+		  __or_<is_same<typename decay<_T2>::type,
+				typename decay<_U2>::type>,
+			is_constructible<_T2, _U2&&>>>::value;
   }
 
   template <typename _T1, typename _T2, typename _U1, typename _U2>
   constexpr bool _ImplicitlyMoveConvertiblePair()
   {
-    return __and_<is_convertible<_U1&&, _T1>,
-		  is_convertible<_U2&&, _T2>>::value;
+    return __and_<__or_<is_same<typename decay<_T1>::type,
+				typename decay<_U1>::type>,
+			is_convertible<_U1&&, _T1>>,
+		  __or_<is_same<typename decay<_T2>::type,
+				typename decay<_U2>::type>,
+		       is_convertible<_U2&&, _T2>>>::value;
   }
 
 

libstdc++-v3/testsuite/20_util/pair/70437.cc

+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2016 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>
+
+template <class T> struct B;
+
+template <class T> struct A
+{
+  A(A&&) = default;
+  A(const B<T> &);
+};
+
+template <class T> struct B
+{
+  std::pair<A<T>,int> a;
+  B(B&&) = default;
+};
+
+bool b = std::is_move_constructible<A<int> >::value;