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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
This commit is contained in:
Jonathan Wakely 2018-10-31 12:29:02 +00:00 committed by Jonathan Wakely
parent ef976be1a2
commit 0db78d0a5e
3 changed files with 56 additions and 2 deletions
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7
libstdc++-v3/ChangeLog
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@ -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).

4
libstdc++-v3/include/bits/stl_pair.h
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@ -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

47
libstdc++-v3/testsuite/20_util/pair/87822.cc Normal file
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@ -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();
}