PR libstdc++/87822 fix layout change for nested std::pair

The introduction of the empty __pair_base base class for PR 86751
changed the layout of std::pair<std::pair<...>, ...>. The outer pair and
its first member both have a base class of the same type, which cannot
exist at the same address. This causes the first member to be at a
non-zero offset.

The solution is to make the base class depend on the template
parameters, so that each pair type has a different base class type,
which allows the base classes of the outer pair and its first member to
have the same address.

	PR libstdc++/87822
	* include/bits/stl_pair.h (__pair_base): Change to class template.
	(pair): Make base class type depend on template parameters.
	* testsuite/20_util/pair/87822.cc: New test.

From-SVN: r265678

3 files changed, 56 insertions, 2 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index d9d4f0e..ac4df1a 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2018-10-31  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/87822
+	* include/bits/stl_pair.h (__pair_base): Change to class template.
+	(pair): Make base class type depend on template parameters.
+	* testsuite/20_util/pair/87822.cc: New test.
+
 2018-10-30  Marek Polacek  <polacek@redhat.com>
 
 	Implement P0892R2, explicit(bool).
diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h
index ea8bd98..48af2b0 100644
--- a/libstdc++-v3/include/bits/stl_pair.h
+++ b/libstdc++-v3/include/bits/stl_pair.h
@@ -187,7 +187,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   };
 #endif // C++11
 
-  class __pair_base
+  template<typename _U1, typename _U2> class __pair_base
   {
 #if __cplusplus >= 201103L
     template<typename _T1, typename _T2> friend struct pair;
@@ -206,7 +206,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    */
   template<typename _T1, typename _T2>
     struct pair
-    : private __pair_base
+    : private __pair_base<_T1, _T2>
     {
       typedef _T1 first_type;    /// @c first_type is the first bound type
       typedef _T2 second_type;   /// @c second_type is the second bound type
diff --git a/libstdc++-v3/testsuite/20_util/pair/87822.cc b/libstdc++-v3/testsuite/20_util/pair/87822.cc
new file mode 100644
index 0000000..cd099d6
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/pair/87822.cc
@@ -0,0 +1,47 @@
+// Copyright (C) 2018 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>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::pair<std::pair<int, int>, int> p;
+#if __cplusplus >= 201103L
+  static_assert(sizeof(p) == (3 * sizeof(int)), "PR libstdc++/87822");
+#endif
+  VERIFY( (void*)&p == (void*)&p.first );
+}
+
+struct empty { };
+
+void
+test02()
+{
+  std::pair<std::pair<empty, empty>, empty> p;
+#if __cplusplus >= 201103L
+  static_assert(sizeof(p) == (3 * sizeof(empty)), "PR libstdc++/87822");
+#endif
+  VERIFY( (void*)&p == (void*)&p.first );
+}
+
+int main()
+{
+  test01();
+  test02();
+}