Initial checkin of GCC 4.9.0 from trunk (r208799).

Change-Id: I48a3c08bb98542aa215912a75f03c0890e497dba

1 files changed, 1553 insertions, 0 deletions

diff --git a/gcc-4.9/libstdc++-v3/include/bits/shared_ptr_base.h b/gcc-4.9/libstdc++-v3/include/bits/shared_ptr_base.h
new file mode 100644
index 0000000..536df01
--- /dev/null
+++ b/gcc-4.9/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -0,0 +1,1553 @@
+// shared_ptr and weak_ptr implementation details -*- C++ -*-
+
+// Copyright (C) 2007-2014 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+// GCC Note: Based on files from version 1.32.0 of the Boost library.
+
+//  shared_count.hpp
+//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
+
+//  shared_ptr.hpp
+//  Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
+//  Copyright (C) 2001, 2002, 2003 Peter Dimov
+
+//  weak_ptr.hpp
+//  Copyright (C) 2001, 2002, 2003 Peter Dimov
+
+//  enable_shared_from_this.hpp
+//  Copyright (C) 2002 Peter Dimov
+
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+/** @file bits/shared_ptr_base.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly. @headername{memory}
+ */
+
+#ifndef _SHARED_PTR_BASE_H
+#define _SHARED_PTR_BASE_H 1
+
+#include <ext/aligned_buffer.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+#if _GLIBCXX_USE_DEPRECATED
+  template<typename> class auto_ptr;
+#endif
+
+ /**
+   *  @brief  Exception possibly thrown by @c shared_ptr.
+   *  @ingroup exceptions
+   */
+  class bad_weak_ptr : public std::exception
+  {
+  public:
+    virtual char const*
+    what() const noexcept;
+
+    virtual ~bad_weak_ptr() noexcept;    
+  };
+
+  // Substitute for bad_weak_ptr object in the case of -fno-exceptions.
+  inline void
+  __throw_bad_weak_ptr()
+  { _GLIBCXX_THROW_OR_ABORT(bad_weak_ptr()); }
+
+  using __gnu_cxx::_Lock_policy;
+  using __gnu_cxx::__default_lock_policy;
+  using __gnu_cxx::_S_single;
+  using __gnu_cxx::_S_mutex;
+  using __gnu_cxx::_S_atomic;
+
+  // Empty helper class except when the template argument is _S_mutex.
+  template<_Lock_policy _Lp>
+    class _Mutex_base
+    {
+    protected:
+      // The atomic policy uses fully-fenced builtins, single doesn't care.
+      enum { _S_need_barriers = 0 };
+    };
+
+  template<>
+    class _Mutex_base<_S_mutex>
+    : public __gnu_cxx::__mutex
+    {
+    protected:
+      // This policy is used when atomic builtins are not available.
+      // The replacement atomic operations might not have the necessary
+      // memory barriers.
+      enum { _S_need_barriers = 1 };
+    };
+
+  template<_Lock_policy _Lp = __default_lock_policy>
+    class _Sp_counted_base
+    : public _Mutex_base<_Lp>
+    {
+    public:  
+      _Sp_counted_base() noexcept
+      : _M_use_count(1), _M_weak_count(1) { }
+      
+      virtual
+      ~_Sp_counted_base() noexcept
+      { }
+  
+      // Called when _M_use_count drops to zero, to release the resources
+      // managed by *this.
+      virtual void
+      _M_dispose() noexcept = 0;
+      
+      // Called when _M_weak_count drops to zero.
+      virtual void
+      _M_destroy() noexcept
+      { delete this; }
+      
+      virtual void*
+      _M_get_deleter(const std::type_info&) noexcept = 0;
+
+      void
+      _M_add_ref_copy()
+      { __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
+  
+      void
+      _M_add_ref_lock();
+
+      bool
+      _M_add_ref_lock_nothrow();
+
+      void
+      _M_release() noexcept
+      {
+        // Be race-detector-friendly.  For more info see bits/c++config.
+        _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_use_count);
+	if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
+	  {
+            _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_use_count);
+	    _M_dispose();
+	    // There must be a memory barrier between dispose() and destroy()
+	    // to ensure that the effects of dispose() are observed in the
+	    // thread that runs destroy().
+	    // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
+	    if (_Mutex_base<_Lp>::_S_need_barriers)
+	      {
+	        _GLIBCXX_READ_MEM_BARRIER;
+	        _GLIBCXX_WRITE_MEM_BARRIER;
+	      }
+
+            // Be race-detector-friendly.  For more info see bits/c++config.
+            _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
+	    if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
+						       -1) == 1)
+              {
+                _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
+	        _M_destroy();
+              }
+	  }
+      }
+  
+      void
+      _M_weak_add_ref() noexcept
+      { __gnu_cxx::__atomic_add_dispatch(&_M_weak_count, 1); }
+
+      void
+      _M_weak_release() noexcept
+      {
+        // Be race-detector-friendly. For more info see bits/c++config.
+        _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_weak_count);
+	if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
+	  {
+            _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_weak_count);
+	    if (_Mutex_base<_Lp>::_S_need_barriers)
+	      {
+	        // See _M_release(),
+	        // destroy() must observe results of dispose()
+	        _GLIBCXX_READ_MEM_BARRIER;
+	        _GLIBCXX_WRITE_MEM_BARRIER;
+	      }
+	    _M_destroy();
+	  }
+      }
+  
+      long
+      _M_get_use_count() const noexcept
+      {
+        // No memory barrier is used here so there is no synchronization
+        // with other threads.
+        return __atomic_load_n(&_M_use_count, __ATOMIC_RELAXED);
+      }
+
+    private:  
+      _Sp_counted_base(_Sp_counted_base const&) = delete;
+      _Sp_counted_base& operator=(_Sp_counted_base const&) = delete;
+
+      _Atomic_word  _M_use_count;     // #shared
+      _Atomic_word  _M_weak_count;    // #weak + (#shared != 0)
+    };
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_single>::
+    _M_add_ref_lock()
+    {
+      if (_M_use_count == 0)
+	__throw_bad_weak_ptr();
+      ++_M_use_count;
+    }
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_mutex>::
+    _M_add_ref_lock()
+    {
+      __gnu_cxx::__scoped_lock sentry(*this);
+      if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
+	{
+	  _M_use_count = 0;
+	  __throw_bad_weak_ptr();
+	}
+    }
+
+  template<> 
+    inline void
+    _Sp_counted_base<_S_atomic>::
+    _M_add_ref_lock()
+    {
+      // Perform lock-free add-if-not-zero operation.
+      _Atomic_word __count = _M_get_use_count();
+      do
+	{
+	  if (__count == 0)
+	    __throw_bad_weak_ptr();
+	  // Replace the current counter value with the old value + 1, as
+	  // long as it's not changed meanwhile. 
+	}
+      while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
+					  true, __ATOMIC_ACQ_REL, 
+					  __ATOMIC_RELAXED));
+    }
+
+  template<>
+    inline bool
+    _Sp_counted_base<_S_single>::
+    _M_add_ref_lock_nothrow()
+    {
+      if (_M_use_count == 0)
+	return false;
+      ++_M_use_count;
+      return true;
+    }
+
+  template<>
+    inline bool
+    _Sp_counted_base<_S_mutex>::
+    _M_add_ref_lock_nothrow()
+    {
+      __gnu_cxx::__scoped_lock sentry(*this);
+      if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
+	{
+	  _M_use_count = 0;
+	  return false;
+	}
+      return true;
+    }
+
+  template<>
+    inline bool
+    _Sp_counted_base<_S_atomic>::
+    _M_add_ref_lock_nothrow()
+    {
+      // Perform lock-free add-if-not-zero operation.
+      _Atomic_word __count = _M_get_use_count();
+      do
+	{
+	  if (__count == 0)
+	    return false;
+	  // Replace the current counter value with the old value + 1, as
+	  // long as it's not changed meanwhile.
+	}
+      while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
+					  true, __ATOMIC_ACQ_REL,
+					  __ATOMIC_RELAXED));
+      return true;
+    }
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_single>::_M_add_ref_copy()
+    { ++_M_use_count; }
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_single>::_M_release() noexcept
+    {
+      if (--_M_use_count == 0)
+        {
+          _M_dispose();
+          if (--_M_weak_count == 0)
+            _M_destroy();
+        }
+    }
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_single>::_M_weak_add_ref() noexcept
+    { ++_M_weak_count; }
+
+  template<>
+    inline void
+    _Sp_counted_base<_S_single>::_M_weak_release() noexcept
+    {
+      if (--_M_weak_count == 0)
+        _M_destroy();
+    }
+
+  template<>
+    inline long
+    _Sp_counted_base<_S_single>::_M_get_use_count() const noexcept
+    { return _M_use_count; }
+
+
+  // Forward declarations.
+  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
+    class __shared_ptr;
+
+  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
+    class __weak_ptr;
+
+  template<typename _Tp, _Lock_policy _Lp = __default_lock_policy>
+    class __enable_shared_from_this;
+
+  template<typename _Tp>
+    class shared_ptr;
+
+  template<typename _Tp>
+    class weak_ptr;
+
+  template<typename _Tp>
+    struct owner_less;
+
+  template<typename _Tp>
+    class enable_shared_from_this;
+
+  template<_Lock_policy _Lp = __default_lock_policy>
+    class __weak_count;
+
+  template<_Lock_policy _Lp = __default_lock_policy>
+    class __shared_count;
+
+
+  // Counted ptr with no deleter or allocator support
+  template<typename _Ptr, _Lock_policy _Lp>
+    class _Sp_counted_ptr final : public _Sp_counted_base<_Lp>
+    {
+    public:
+      explicit
+      _Sp_counted_ptr(_Ptr __p) noexcept
+      : _M_ptr(__p) { }
+
+      virtual void
+      _M_dispose() noexcept
+      { delete _M_ptr; }
+
+      virtual void
+      _M_destroy() noexcept
+      { delete this; }
+
+      virtual void*
+      _M_get_deleter(const std::type_info&) noexcept
+      { return nullptr; }
+
+      _Sp_counted_ptr(const _Sp_counted_ptr&) = delete;
+      _Sp_counted_ptr& operator=(const _Sp_counted_ptr&) = delete;
+
+    private:
+      _Ptr             _M_ptr;
+    };
+
+  template<>
+    inline void
+    _Sp_counted_ptr<nullptr_t, _S_single>::_M_dispose() noexcept { }
+
+  template<>
+    inline void
+    _Sp_counted_ptr<nullptr_t, _S_mutex>::_M_dispose() noexcept { }
+
+  template<>
+    inline void
+    _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
+
+  template<int _Nm, typename _Tp,
+	   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
+    struct _Sp_ebo_helper;
+
+  /// Specialization using EBO.
+  template<int _Nm, typename _Tp>
+    struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
+    {
+      explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
+
+      static _Tp&
+      _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
+    };
+
+  /// Specialization not using EBO.
+  template<int _Nm, typename _Tp>
+    struct _Sp_ebo_helper<_Nm, _Tp, false>
+    {
+      explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
+
+      static _Tp&
+      _S_get(_Sp_ebo_helper& __eboh)
+      { return __eboh._M_tp; }
+
+    private:
+      _Tp _M_tp;
+    };
+
+  // Support for custom deleter and/or allocator
+  template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>
+    class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>
+    {
+      class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>
+      {
+	typedef _Sp_ebo_helper<0, _Deleter>	_Del_base;
+	typedef _Sp_ebo_helper<1, _Alloc>	_Alloc_base;
+
+      public:
+	_Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
+	: _M_ptr(__p), _Del_base(__d), _Alloc_base(__a)
+	{ }
+
+	_Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }
+	_Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }
+
+	_Ptr _M_ptr;
+      };
+
+    public:
+      // __d(__p) must not throw.
+      _Sp_counted_deleter(_Ptr __p, _Deleter __d) noexcept
+      : _M_impl(__p, __d, _Alloc()) { }
+
+      // __d(__p) must not throw.
+      _Sp_counted_deleter(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept
+      : _M_impl(__p, __d, __a) { }
+
+      ~_Sp_counted_deleter() noexcept { }
+
+      virtual void
+      _M_dispose() noexcept
+      { _M_impl._M_del()(_M_impl._M_ptr); }
+
+      virtual void
+      _M_destroy() noexcept
+      {
+	typedef typename allocator_traits<_Alloc>::template
+	  rebind_traits<_Sp_counted_deleter> _Alloc_traits;
+	typename _Alloc_traits::allocator_type __a(_M_impl._M_alloc());
+	_Alloc_traits::destroy(__a, this);
+	_Alloc_traits::deallocate(__a, this, 1);
+      }
+
+      virtual void*
+      _M_get_deleter(const std::type_info& __ti) noexcept
+      {
+#ifdef __GXX_RTTI
+        return __ti == typeid(_Deleter) ? &_M_impl._M_del() : nullptr;
+#else
+        return nullptr;
+#endif
+      }
+
+    private:
+      _Impl _M_impl;
+    };
+
+  // helpers for make_shared / allocate_shared
+
+  struct _Sp_make_shared_tag { };
+
+  template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
+    class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>
+    {
+      class _Impl : _Sp_ebo_helper<0, _Alloc>
+      {
+	typedef _Sp_ebo_helper<0, _Alloc>	_A_base;
+
+      public:
+	explicit _Impl(_Alloc __a) noexcept : _A_base(__a) { }
+
+	_Alloc& _M_alloc() noexcept { return _A_base::_S_get(*this); }
+
+	__gnu_cxx::__aligned_buffer<_Tp> _M_storage;
+      };
+
+    public:
+      template<typename... _Args>
+	_Sp_counted_ptr_inplace(_Alloc __a, _Args&&... __args)
+	: _M_impl(__a)
+	{
+	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+	  // 2070.  allocate_shared should use allocator_traits<A>::construct
+	  allocator_traits<_Alloc>::construct(__a, _M_ptr(),
+	      std::forward<_Args>(__args)...); // might throw
+	}
+
+      ~_Sp_counted_ptr_inplace() noexcept { }
+
+      virtual void
+      _M_dispose() noexcept
+      {
+	allocator_traits<_Alloc>::destroy(_M_impl._M_alloc(), _M_ptr());
+      }
+
+      // Override because the allocator needs to know the dynamic type
+      virtual void
+      _M_destroy() noexcept
+      {
+	typedef typename allocator_traits<_Alloc>::template
+	  rebind_traits<_Sp_counted_ptr_inplace> _Alloc_traits;
+	typename _Alloc_traits::allocator_type __a(_M_impl._M_alloc());
+	_Alloc_traits::destroy(__a, this);
+	_Alloc_traits::deallocate(__a, this, 1);
+      }
+
+      // Sneaky trick so __shared_ptr can get the managed pointer
+      virtual void*
+      _M_get_deleter(const std::type_info& __ti) noexcept
+      {
+#ifdef __GXX_RTTI
+	if (__ti == typeid(_Sp_make_shared_tag))
+	  return const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
+#endif
+	return nullptr;
+      }
+
+    private:
+      _Tp* _M_ptr() noexcept { return _M_impl._M_storage._M_ptr(); }
+
+      _Impl _M_impl;
+    };
+
+
+  template<_Lock_policy _Lp>
+    class __shared_count
+    {
+    public:
+      constexpr __shared_count() noexcept : _M_pi(0)
+      { }
+
+      template<typename _Ptr>
+        explicit
+	__shared_count(_Ptr __p) : _M_pi(0)
+	{
+	  __try
+	    {
+	      _M_pi = new _Sp_counted_ptr<_Ptr, _Lp>(__p);
+	    }
+	  __catch(...)
+	    {
+	      delete __p;
+	      __throw_exception_again;
+	    }
+	}
+
+      template<typename _Ptr, typename _Deleter>
+	__shared_count(_Ptr __p, _Deleter __d)
+	: __shared_count(__p, std::move(__d), allocator<void>())
+	{ }
+
+      template<typename _Ptr, typename _Deleter, typename _Alloc>
+	__shared_count(_Ptr __p, _Deleter __d, _Alloc __a) : _M_pi(0)
+	{
+	  typedef _Sp_counted_deleter<_Ptr, _Deleter, _Alloc, _Lp> _Sp_cd_type;
+	  typedef typename allocator_traits<_Alloc>::template
+	    rebind_traits<_Sp_cd_type> _Alloc_traits;
+	  typename _Alloc_traits::allocator_type __a2(__a);
+	  _Sp_cd_type* __mem = 0;
+	  __try
+	    {
+	      __mem = _Alloc_traits::allocate(__a2, 1);
+	      _Alloc_traits::construct(__a2, __mem,
+		  __p, std::move(__d), std::move(__a));
+	      _M_pi = __mem;
+	    }
+	  __catch(...)
+	    {
+	      __d(__p); // Call _Deleter on __p.
+	      if (__mem)
+	        _Alloc_traits::deallocate(__a2, __mem, 1);
+	      __throw_exception_again;
+	    }
+	}
+
+      template<typename _Tp, typename _Alloc, typename... _Args>
+	__shared_count(_Sp_make_shared_tag, _Tp*, const _Alloc& __a,
+		       _Args&&... __args)
+	: _M_pi(0)
+	{
+	  typedef _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> _Sp_cp_type;
+	  typedef typename allocator_traits<_Alloc>::template
+	    rebind_traits<_Sp_cp_type> _Alloc_traits;
+	  typename _Alloc_traits::allocator_type __a2(__a);
+	  _Sp_cp_type* __mem = _Alloc_traits::allocate(__a2, 1);
+	  __try
+	    {
+	      _Alloc_traits::construct(__a2, __mem, std::move(__a),
+		    std::forward<_Args>(__args)...);
+	      _M_pi = __mem;
+	    }
+	  __catch(...)
+	    {
+	      _Alloc_traits::deallocate(__a2, __mem, 1);
+	      __throw_exception_again;
+	    }
+	}
+
+#if _GLIBCXX_USE_DEPRECATED
+      // Special case for auto_ptr<_Tp> to provide the strong guarantee.
+      template<typename _Tp>
+        explicit
+	__shared_count(std::auto_ptr<_Tp>&& __r);
+#endif
+
+      // Special case for unique_ptr<_Tp,_Del> to provide the strong guarantee.
+      template<typename _Tp, typename _Del>
+        explicit
+	__shared_count(std::unique_ptr<_Tp, _Del>&& __r) : _M_pi(0)
+	{
+	  using _Ptr = typename unique_ptr<_Tp, _Del>::pointer;
+	  using _Del2 = typename conditional<is_reference<_Del>::value,
+	      reference_wrapper<typename remove_reference<_Del>::type>,
+	      _Del>::type;
+	  using _Sp_cd_type
+	    = _Sp_counted_deleter<_Ptr, _Del2, allocator<void>, _Lp>;
+	  using _Alloc = allocator<_Sp_cd_type>;
+	  using _Alloc_traits = allocator_traits<_Alloc>;
+	  _Alloc __a;
+	  _Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
+	  _Alloc_traits::construct(__a, __mem, __r.release(),
+				   __r.get_deleter());  // non-throwing
+	  _M_pi = __mem;
+	}
+
+      // Throw bad_weak_ptr when __r._M_get_use_count() == 0.
+      explicit __shared_count(const __weak_count<_Lp>& __r);
+
+      // Does not throw if __r._M_get_use_count() == 0, caller must check.
+      explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
+
+      ~__shared_count() noexcept
+      {
+	if (_M_pi != nullptr)
+	  _M_pi->_M_release();
+      }
+
+      __shared_count(const __shared_count& __r) noexcept
+      : _M_pi(__r._M_pi)
+      {
+	if (_M_pi != 0)
+	  _M_pi->_M_add_ref_copy();
+      }
+
+      __shared_count&
+      operator=(const __shared_count& __r) noexcept
+      {
+	_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
+	if (__tmp != _M_pi)
+	  {
+	    if (__tmp != 0)
+	      __tmp->_M_add_ref_copy();
+	    if (_M_pi != 0)
+	      _M_pi->_M_release();
+	    _M_pi = __tmp;
+	  }
+	return *this;
+      }
+
+      void
+      _M_swap(__shared_count& __r) noexcept
+      {
+	_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
+	__r._M_pi = _M_pi;
+	_M_pi = __tmp;
+      }
+
+      long
+      _M_get_use_count() const noexcept
+      { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
+
+      bool
+      _M_unique() const noexcept
+      { return this->_M_get_use_count() == 1; }
+
+      void*
+      _M_get_deleter(const std::type_info& __ti) const noexcept
+      { return _M_pi ? _M_pi->_M_get_deleter(__ti) : nullptr; }
+
+      bool
+      _M_less(const __shared_count& __rhs) const noexcept
+      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
+
+      bool
+      _M_less(const __weak_count<_Lp>& __rhs) const noexcept
+      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
+
+      // Friend function injected into enclosing namespace and found by ADL
+      friend inline bool
+      operator==(const __shared_count& __a, const __shared_count& __b) noexcept
+      { return __a._M_pi == __b._M_pi; }
+
+    private:
+      friend class __weak_count<_Lp>;
+
+      _Sp_counted_base<_Lp>*  _M_pi;
+    };
+
+
+  template<_Lock_policy _Lp>
+    class __weak_count
+    {
+    public:
+      constexpr __weak_count() noexcept : _M_pi(0)
+      { }
+
+      __weak_count(const __shared_count<_Lp>& __r) noexcept
+      : _M_pi(__r._M_pi)
+      {
+	if (_M_pi != 0)
+	  _M_pi->_M_weak_add_ref();
+      }
+
+      __weak_count(const __weak_count<_Lp>& __r) noexcept
+      : _M_pi(__r._M_pi)
+      {
+	if (_M_pi != 0)
+	  _M_pi->_M_weak_add_ref();
+      }
+
+      ~__weak_count() noexcept
+      {
+	if (_M_pi != 0)
+	  _M_pi->_M_weak_release();
+      }
+
+      __weak_count<_Lp>&
+      operator=(const __shared_count<_Lp>& __r) noexcept
+      {
+	_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
+	if (__tmp != 0)
+	  __tmp->_M_weak_add_ref();
+	if (_M_pi != 0)
+	  _M_pi->_M_weak_release();
+	_M_pi = __tmp;
+	return *this;
+      }
+
+      __weak_count<_Lp>&
+      operator=(const __weak_count<_Lp>& __r) noexcept
+      {
+	_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
+	if (__tmp != 0)
+	  __tmp->_M_weak_add_ref();
+	if (_M_pi != 0)
+	  _M_pi->_M_weak_release();
+	_M_pi = __tmp;
+	return *this;
+      }
+
+      void
+      _M_swap(__weak_count<_Lp>& __r) noexcept
+      {
+	_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
+	__r._M_pi = _M_pi;
+	_M_pi = __tmp;
+      }
+
+      long
+      _M_get_use_count() const noexcept
+      { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
+
+      bool
+      _M_less(const __weak_count& __rhs) const noexcept
+      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
+
+      bool
+      _M_less(const __shared_count<_Lp>& __rhs) const noexcept
+      { return std::less<_Sp_counted_base<_Lp>*>()(this->_M_pi, __rhs._M_pi); }
+
+      // Friend function injected into enclosing namespace and found by ADL
+      friend inline bool
+      operator==(const __weak_count& __a, const __weak_count& __b) noexcept
+      { return __a._M_pi == __b._M_pi; }
+
+    private:
+      friend class __shared_count<_Lp>;
+
+      _Sp_counted_base<_Lp>*  _M_pi;
+    };
+
+  // Now that __weak_count is defined we can define this constructor:
+  template<_Lock_policy _Lp>
+    inline
+    __shared_count<_Lp>::__shared_count(const __weak_count<_Lp>& __r)
+    : _M_pi(__r._M_pi)
+    {
+      if (_M_pi != nullptr)
+	_M_pi->_M_add_ref_lock();
+      else
+	__throw_bad_weak_ptr();
+    }
+
+  // Now that __weak_count is defined we can define this constructor:
+  template<_Lock_policy _Lp>
+    inline
+    __shared_count<_Lp>::
+    __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
+    : _M_pi(__r._M_pi)
+    {
+      if (_M_pi != nullptr)
+	if (!_M_pi->_M_add_ref_lock_nothrow())
+	  _M_pi = nullptr;
+    }
+
+  // Support for enable_shared_from_this.
+
+  // Friend of __enable_shared_from_this.
+  template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
+    void
+    __enable_shared_from_this_helper(const __shared_count<_Lp>&,
+				     const __enable_shared_from_this<_Tp1,
+				     _Lp>*, const _Tp2*) noexcept;
+
+  // Friend of enable_shared_from_this.
+  template<typename _Tp1, typename _Tp2>
+    void
+    __enable_shared_from_this_helper(const __shared_count<>&,
+				     const enable_shared_from_this<_Tp1>*,
+				     const _Tp2*) noexcept;
+
+  template<_Lock_policy _Lp>
+    inline void
+    __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
+    { }
+
+
+  template<typename _Tp, _Lock_policy _Lp>
+    class __shared_ptr
+    {
+    public:
+      typedef _Tp   element_type;
+
+      constexpr __shared_ptr() noexcept
+      : _M_ptr(0), _M_refcount()
+      { }
+
+      template<typename _Tp1>
+	explicit __shared_ptr(_Tp1* __p)
+        : _M_ptr(__p), _M_refcount(__p)
+	{
+	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
+	  static_assert( !is_void<_Tp>::value, "incomplete type" );
+	  static_assert( sizeof(_Tp1) > 0, "incomplete type" );
+	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	}
+
+      template<typename _Tp1, typename _Deleter>
+	__shared_ptr(_Tp1* __p, _Deleter __d)
+	: _M_ptr(__p), _M_refcount(__p, __d)
+	{
+	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
+	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
+	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	}
+
+      template<typename _Tp1, typename _Deleter, typename _Alloc>
+	__shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
+	: _M_ptr(__p), _M_refcount(__p, __d, std::move(__a))
+	{
+	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
+	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
+	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	}
+
+      template<typename _Deleter>
+	__shared_ptr(nullptr_t __p, _Deleter __d)
+	: _M_ptr(0), _M_refcount(__p, __d)
+	{ }
+
+      template<typename _Deleter, typename _Alloc>
+        __shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
+	: _M_ptr(0), _M_refcount(__p, __d, std::move(__a))
+	{ }
+
+      template<typename _Tp1>
+	__shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r, _Tp* __p) noexcept
+	: _M_ptr(__p), _M_refcount(__r._M_refcount) // never throws
+	{ }
+
+      __shared_ptr(const __shared_ptr&) noexcept = default;
+      __shared_ptr& operator=(const __shared_ptr&) noexcept = default;
+      ~__shared_ptr() = default;
+
+      template<typename _Tp1, typename = typename
+	       std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
+	__shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+	: _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
+	{ }
+
+      __shared_ptr(__shared_ptr&& __r) noexcept
+      : _M_ptr(__r._M_ptr), _M_refcount()
+      {
+	_M_refcount._M_swap(__r._M_refcount);
+	__r._M_ptr = 0;
+      }
+
+      template<typename _Tp1, typename = typename
+	       std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
+	__shared_ptr(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
+	: _M_ptr(__r._M_ptr), _M_refcount()
+	{
+	  _M_refcount._M_swap(__r._M_refcount);
+	  __r._M_ptr = 0;
+	}
+
+      template<typename _Tp1>
+	explicit __shared_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
+	: _M_refcount(__r._M_refcount) // may throw
+	{
+	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
+
+	  // It is now safe to copy __r._M_ptr, as
+	  // _M_refcount(__r._M_refcount) did not throw.
+	  _M_ptr = __r._M_ptr;
+	}
+
+      // If an exception is thrown this constructor has no effect.
+      template<typename _Tp1, typename _Del>
+	__shared_ptr(std::unique_ptr<_Tp1, _Del>&& __r)
+	: _M_ptr(__r.get()), _M_refcount()
+	{
+	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
+	  auto __raw = _S_raw_ptr(__r.get());
+	  _M_refcount = __shared_count<_Lp>(std::move(__r));
+	  __enable_shared_from_this_helper(_M_refcount, __raw, __raw);
+	}
+
+#if _GLIBCXX_USE_DEPRECATED
+      // Postcondition: use_count() == 1 and __r.get() == 0
+      template<typename _Tp1>
+	__shared_ptr(std::auto_ptr<_Tp1>&& __r);
+#endif
+
+      /* TODO: use delegating constructor */
+      constexpr __shared_ptr(nullptr_t) noexcept
+      : _M_ptr(0), _M_refcount()
+      { }
+
+      template<typename _Tp1>
+	__shared_ptr&
+	operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+	{
+	  _M_ptr = __r._M_ptr;
+	  _M_refcount = __r._M_refcount; // __shared_count::op= doesn't throw
+	  return *this;
+	}
+
+#if _GLIBCXX_USE_DEPRECATED
+      template<typename _Tp1>
+	__shared_ptr&
+	operator=(std::auto_ptr<_Tp1>&& __r)
+	{
+	  __shared_ptr(std::move(__r)).swap(*this);
+	  return *this;
+	}
+#endif
+
+      __shared_ptr&
+      operator=(__shared_ptr&& __r) noexcept
+      {
+	__shared_ptr(std::move(__r)).swap(*this);
+	return *this;
+      }
+
+      template<class _Tp1>
+	__shared_ptr&
+	operator=(__shared_ptr<_Tp1, _Lp>&& __r) noexcept
+	{
+	  __shared_ptr(std::move(__r)).swap(*this);
+	  return *this;
+	}
+
+      template<typename _Tp1, typename _Del>
+	__shared_ptr&
+	operator=(std::unique_ptr<_Tp1, _Del>&& __r)
+	{
+	  __shared_ptr(std::move(__r)).swap(*this);
+	  return *this;
+	}
+
+      void
+      reset() noexcept
+      { __shared_ptr().swap(*this); }
+
+      template<typename _Tp1>
+	void
+	reset(_Tp1* __p) // _Tp1 must be complete.
+	{
+	  // Catch self-reset errors.
+	  _GLIBCXX_DEBUG_ASSERT(__p == 0 || __p != _M_ptr);
+	  __shared_ptr(__p).swap(*this);
+	}
+
+      template<typename _Tp1, typename _Deleter>
+	void
+	reset(_Tp1* __p, _Deleter __d)
+	{ __shared_ptr(__p, __d).swap(*this); }
+
+      template<typename _Tp1, typename _Deleter, typename _Alloc>
+	void
+        reset(_Tp1* __p, _Deleter __d, _Alloc __a)
+        { __shared_ptr(__p, __d, std::move(__a)).swap(*this); }
+
+      // Allow class instantiation when _Tp is [cv-qual] void.
+      typename std::add_lvalue_reference<_Tp>::type
+      operator*() const noexcept
+      {
+	_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
+	return *_M_ptr;
+      }
+
+      _Tp*
+      operator->() const noexcept
+      {
+	_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
+	return _M_ptr;
+      }
+
+      _Tp*
+      get() const noexcept
+      { return _M_ptr; }
+
+      explicit operator bool() const // never throws
+      { return _M_ptr == 0 ? false : true; }
+
+      bool
+      unique() const noexcept
+      { return _M_refcount._M_unique(); }
+
+      long
+      use_count() const noexcept
+      { return _M_refcount._M_get_use_count(); }
+
+      void
+      swap(__shared_ptr<_Tp, _Lp>& __other) noexcept
+      {
+	std::swap(_M_ptr, __other._M_ptr);
+	_M_refcount._M_swap(__other._M_refcount);
+      }
+
+      template<typename _Tp1>
+	bool
+	owner_before(__shared_ptr<_Tp1, _Lp> const& __rhs) const
+	{ return _M_refcount._M_less(__rhs._M_refcount); }
+
+      template<typename _Tp1>
+	bool
+	owner_before(__weak_ptr<_Tp1, _Lp> const& __rhs) const
+	{ return _M_refcount._M_less(__rhs._M_refcount); }
+
+#ifdef __GXX_RTTI
+    protected:
+      // This constructor is non-standard, it is used by allocate_shared.
+      template<typename _Alloc, typename... _Args>
+	__shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
+		     _Args&&... __args)
+	: _M_ptr(), _M_refcount(__tag, (_Tp*)0, __a,
+				std::forward<_Args>(__args)...)
+	{
+	  // _M_ptr needs to point to the newly constructed object.
+	  // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
+	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
+	  _M_ptr = static_cast<_Tp*>(__p);
+	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
+	}
+#else
+      template<typename _Alloc>
+        struct _Deleter
+        {
+          void operator()(_Tp* __ptr)
+          {
+	    typedef allocator_traits<_Alloc> _Alloc_traits;
+	    _Alloc_traits::destroy(_M_alloc, __ptr);
+	    _Alloc_traits::deallocate(_M_alloc, __ptr, 1);
+          }
+          _Alloc _M_alloc;
+        };
+
+      template<typename _Alloc, typename... _Args>
+	__shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
+		     _Args&&... __args)
+	: _M_ptr(), _M_refcount()
+        {
+	  typedef typename _Alloc::template rebind<_Tp>::other _Alloc2;
+          _Deleter<_Alloc2> __del = { _Alloc2(__a) };
+	  typedef allocator_traits<_Alloc2> __traits;
+          _M_ptr = __traits::allocate(__del._M_alloc, 1);
+	  __try
+	    {
+	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
+	      // 2070. allocate_shared should use allocator_traits<A>::construct
+	      __traits::construct(__del._M_alloc, _M_ptr,
+		                  std::forward<_Args>(__args)...);
+	    }
+	  __catch(...)
+	    {
+	      __traits::deallocate(__del._M_alloc, _M_ptr, 1);
+	      __throw_exception_again;
+	    }
+          __shared_count<_Lp> __count(_M_ptr, __del, __del._M_alloc);
+          _M_refcount._M_swap(__count);
+	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
+        }
+#endif
+
+      template<typename _Tp1, _Lock_policy _Lp1, typename _Alloc,
+	       typename... _Args>
+	friend __shared_ptr<_Tp1, _Lp1>
+	__allocate_shared(const _Alloc& __a, _Args&&... __args);
+
+      // This constructor is used by __weak_ptr::lock() and
+      // shared_ptr::shared_ptr(const weak_ptr&, std::nothrow_t).
+      __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
+      : _M_refcount(__r._M_refcount, std::nothrow)
+      {
+	_M_ptr = _M_refcount._M_get_use_count() ? __r._M_ptr : nullptr;
+      }
+
+      friend class __weak_ptr<_Tp, _Lp>;
+
+    private:
+      void*
+      _M_get_deleter(const std::type_info& __ti) const noexcept
+      { return _M_refcount._M_get_deleter(__ti); }
+
+      template<typename _Tp1>
+	static _Tp1*
+	_S_raw_ptr(_Tp1* __ptr)
+	{ return __ptr; }
+
+      template<typename _Tp1>
+	static auto
+	_S_raw_ptr(_Tp1 __ptr) -> decltype(std::__addressof(*__ptr))
+	{ return std::__addressof(*__ptr); }
+
+      template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
+      template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
+
+      template<typename _Del, typename _Tp1, _Lock_policy _Lp1>
+	friend _Del* get_deleter(const __shared_ptr<_Tp1, _Lp1>&) noexcept;
+
+      _Tp*	   	   _M_ptr;         // Contained pointer.
+      __shared_count<_Lp>  _M_refcount;    // Reference counter.
+    };
+
+
+  // 20.7.2.2.7 shared_ptr comparisons
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator==(const __shared_ptr<_Tp1, _Lp>& __a,
+	       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    { return __a.get() == __b.get(); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return !__a; }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return !__a; }
+
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator!=(const __shared_ptr<_Tp1, _Lp>& __a,
+	       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    { return __a.get() != __b.get(); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator!=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return (bool)__a; }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator!=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return (bool)__a; }
+
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator<(const __shared_ptr<_Tp1, _Lp>& __a,
+	      const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    {
+      typedef typename std::common_type<_Tp1*, _Tp2*>::type _CT;
+      return std::less<_CT>()(__a.get(), __b.get());
+    }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator<(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return std::less<_Tp*>()(__a.get(), nullptr); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator<(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return std::less<_Tp*>()(nullptr, __a.get()); }
+
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator<=(const __shared_ptr<_Tp1, _Lp>& __a,
+	       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    { return !(__b < __a); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator<=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return !(nullptr < __a); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator<=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return !(__a < nullptr); }
+
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator>(const __shared_ptr<_Tp1, _Lp>& __a,
+	      const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    { return (__b < __a); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return std::less<_Tp*>()(nullptr, __a.get()); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator>(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return std::less<_Tp*>()(__a.get(), nullptr); }
+
+  template<typename _Tp1, typename _Tp2, _Lock_policy _Lp>
+    inline bool
+    operator>=(const __shared_ptr<_Tp1, _Lp>& __a,
+	       const __shared_ptr<_Tp2, _Lp>& __b) noexcept
+    { return !(__a < __b); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator>=(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    { return !(__a < nullptr); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline bool
+    operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
+    { return !(nullptr < __a); }
+
+  template<typename _Sp>
+    struct _Sp_less : public binary_function<_Sp, _Sp, bool>
+    {
+      bool
+      operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
+      {
+	typedef typename _Sp::element_type element_type;
+	return std::less<element_type*>()(__lhs.get(), __rhs.get());
+      }
+    };
+
+  template<typename _Tp, _Lock_policy _Lp>
+    struct less<__shared_ptr<_Tp, _Lp>>
+    : public _Sp_less<__shared_ptr<_Tp, _Lp>>
+    { };
+
+  // 20.7.2.2.8 shared_ptr specialized algorithms.
+  template<typename _Tp, _Lock_policy _Lp>
+    inline void
+    swap(__shared_ptr<_Tp, _Lp>& __a, __shared_ptr<_Tp, _Lp>& __b) noexcept
+    { __a.swap(__b); }
+
+  // 20.7.2.2.9 shared_ptr casts
+
+  // The seemingly equivalent code:
+  // shared_ptr<_Tp, _Lp>(static_cast<_Tp*>(__r.get()))
+  // will eventually result in undefined behaviour, attempting to
+  // delete the same object twice.
+  /// static_pointer_cast
+  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
+    inline __shared_ptr<_Tp, _Lp>
+    static_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+    { return __shared_ptr<_Tp, _Lp>(__r, static_cast<_Tp*>(__r.get())); }
+
+  // The seemingly equivalent code:
+  // shared_ptr<_Tp, _Lp>(const_cast<_Tp*>(__r.get()))
+  // will eventually result in undefined behaviour, attempting to
+  // delete the same object twice.
+  /// const_pointer_cast
+  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
+    inline __shared_ptr<_Tp, _Lp>
+    const_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+    { return __shared_ptr<_Tp, _Lp>(__r, const_cast<_Tp*>(__r.get())); }
+
+  // The seemingly equivalent code:
+  // shared_ptr<_Tp, _Lp>(dynamic_cast<_Tp*>(__r.get()))
+  // will eventually result in undefined behaviour, attempting to
+  // delete the same object twice.
+  /// dynamic_pointer_cast
+  template<typename _Tp, typename _Tp1, _Lock_policy _Lp>
+    inline __shared_ptr<_Tp, _Lp>
+    dynamic_pointer_cast(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+    {
+      if (_Tp* __p = dynamic_cast<_Tp*>(__r.get()))
+	return __shared_ptr<_Tp, _Lp>(__r, __p);
+      return __shared_ptr<_Tp, _Lp>();
+    }
+
+
+  template<typename _Tp, _Lock_policy _Lp>
+    class __weak_ptr
+    {
+    public:
+      typedef _Tp element_type;
+
+      constexpr __weak_ptr() noexcept
+      : _M_ptr(0), _M_refcount()
+      { }
+
+      __weak_ptr(const __weak_ptr&) noexcept = default;
+      __weak_ptr& operator=(const __weak_ptr&) noexcept = default;
+      ~__weak_ptr() = default;
+
+      // The "obvious" converting constructor implementation:
+      //
+      //  template<typename _Tp1>
+      //    __weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r)
+      //    : _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount) // never throws
+      //    { }
+      //
+      // has a serious problem.
+      //
+      //  __r._M_ptr may already have been invalidated. The _M_ptr(__r._M_ptr)
+      //  conversion may require access to *__r._M_ptr (virtual inheritance).
+      //
+      // It is not possible to avoid spurious access violations since
+      // in multithreaded programs __r._M_ptr may be invalidated at any point.
+      template<typename _Tp1, typename = typename
+	       std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
+	__weak_ptr(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
+	: _M_refcount(__r._M_refcount)
+        { _M_ptr = __r.lock().get(); }
+
+      template<typename _Tp1, typename = typename
+	       std::enable_if<std::is_convertible<_Tp1*, _Tp*>::value>::type>
+	__weak_ptr(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+	: _M_ptr(__r._M_ptr), _M_refcount(__r._M_refcount)
+	{ }
+
+      template<typename _Tp1>
+	__weak_ptr&
+	operator=(const __weak_ptr<_Tp1, _Lp>& __r) noexcept
+	{
+	  _M_ptr = __r.lock().get();
+	  _M_refcount = __r._M_refcount;
+	  return *this;
+	}
+
+      template<typename _Tp1>
+	__weak_ptr&
+	operator=(const __shared_ptr<_Tp1, _Lp>& __r) noexcept
+	{
+	  _M_ptr = __r._M_ptr;
+	  _M_refcount = __r._M_refcount;
+	  return *this;
+	}
+
+      __shared_ptr<_Tp, _Lp>
+      lock() const noexcept
+      { return __shared_ptr<element_type, _Lp>(*this, std::nothrow); }
+
+      long
+      use_count() const noexcept
+      { return _M_refcount._M_get_use_count(); }
+
+      bool
+      expired() const noexcept
+      { return _M_refcount._M_get_use_count() == 0; }
+
+      template<typename _Tp1>
+	bool
+	owner_before(const __shared_ptr<_Tp1, _Lp>& __rhs) const
+	{ return _M_refcount._M_less(__rhs._M_refcount); }
+
+      template<typename _Tp1>
+	bool
+	owner_before(const __weak_ptr<_Tp1, _Lp>& __rhs) const
+	{ return _M_refcount._M_less(__rhs._M_refcount); }
+
+      void
+      reset() noexcept
+      { __weak_ptr().swap(*this); }
+
+      void
+      swap(__weak_ptr& __s) noexcept
+      {
+	std::swap(_M_ptr, __s._M_ptr);
+	_M_refcount._M_swap(__s._M_refcount);
+      }
+
+    private:
+      // Used by __enable_shared_from_this.
+      void
+      _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
+      {
+	_M_ptr = __ptr;
+	_M_refcount = __refcount;
+      }
+
+      template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
+      template<typename _Tp1, _Lock_policy _Lp1> friend class __weak_ptr;
+      friend class __enable_shared_from_this<_Tp, _Lp>;
+      friend class enable_shared_from_this<_Tp>;
+
+      _Tp*	 	 _M_ptr;         // Contained pointer.
+      __weak_count<_Lp>  _M_refcount;    // Reference counter.
+    };
+
+  // 20.7.2.3.6 weak_ptr specialized algorithms.
+  template<typename _Tp, _Lock_policy _Lp>
+    inline void
+    swap(__weak_ptr<_Tp, _Lp>& __a, __weak_ptr<_Tp, _Lp>& __b) noexcept
+    { __a.swap(__b); }
+
+  template<typename _Tp, typename _Tp1>
+    struct _Sp_owner_less : public binary_function<_Tp, _Tp, bool>
+    {
+      bool
+      operator()(const _Tp& __lhs, const _Tp& __rhs) const
+      { return __lhs.owner_before(__rhs); }
+
+      bool
+      operator()(const _Tp& __lhs, const _Tp1& __rhs) const
+      { return __lhs.owner_before(__rhs); }
+
+      bool
+      operator()(const _Tp1& __lhs, const _Tp& __rhs) const
+      { return __lhs.owner_before(__rhs); }
+    };
+
+  template<typename _Tp, _Lock_policy _Lp>
+    struct owner_less<__shared_ptr<_Tp, _Lp>>
+    : public _Sp_owner_less<__shared_ptr<_Tp, _Lp>, __weak_ptr<_Tp, _Lp>>
+    { };
+
+  template<typename _Tp, _Lock_policy _Lp>
+    struct owner_less<__weak_ptr<_Tp, _Lp>>
+    : public _Sp_owner_less<__weak_ptr<_Tp, _Lp>, __shared_ptr<_Tp, _Lp>>
+    { };
+
+
+  template<typename _Tp, _Lock_policy _Lp>
+    class __enable_shared_from_this
+    {
+    protected:
+      constexpr __enable_shared_from_this() noexcept { }
+
+      __enable_shared_from_this(const __enable_shared_from_this&) noexcept { }
+
+      __enable_shared_from_this&
+      operator=(const __enable_shared_from_this&) noexcept
+      { return *this; }
+
+      ~__enable_shared_from_this() { }
+
+    public:
+      __shared_ptr<_Tp, _Lp>
+      shared_from_this()
+      { return __shared_ptr<_Tp, _Lp>(this->_M_weak_this); }
+
+      __shared_ptr<const _Tp, _Lp>
+      shared_from_this() const
+      { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
+
+    private:
+      template<typename _Tp1>
+	void
+	_M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
+	{ _M_weak_this._M_assign(__p, __n); }
+
+      template<typename _Tp1>
+	friend void
+	__enable_shared_from_this_helper(const __shared_count<_Lp>& __pn,
+					 const __enable_shared_from_this* __pe,
+					 const _Tp1* __px) noexcept
+	{
+	  if (__pe != 0)
+	    __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
+	}
+
+      mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
+    };
+
+
+  template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
+    inline __shared_ptr<_Tp, _Lp>
+    __allocate_shared(const _Alloc& __a, _Args&&... __args)
+    {
+      return __shared_ptr<_Tp, _Lp>(_Sp_make_shared_tag(), __a,
+				    std::forward<_Args>(__args)...);
+    }
+
+  template<typename _Tp, _Lock_policy _Lp, typename... _Args>
+    inline __shared_ptr<_Tp, _Lp>
+    __make_shared(_Args&&... __args)
+    {
+      typedef typename std::remove_const<_Tp>::type _Tp_nc;
+      return std::__allocate_shared<_Tp, _Lp>(std::allocator<_Tp_nc>(),
+					      std::forward<_Args>(__args)...);
+    }
+
+  /// std::hash specialization for __shared_ptr.
+  template<typename _Tp, _Lock_policy _Lp>
+    struct hash<__shared_ptr<_Tp, _Lp>>
+    : public __hash_base<size_t, __shared_ptr<_Tp, _Lp>>
+    {
+      size_t
+      operator()(const __shared_ptr<_Tp, _Lp>& __s) const noexcept
+      { return std::hash<_Tp*>()(__s.get()); }
+    };
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+
+#endif // _SHARED_PTR_BASE_H