hashtable_policy.h (__details::_Before_begin<>): New, combine a base node…

hashtable_policy.h (__details::_Before_begin<>): New, combine a base node instance and an allocator.

2012-11-01  François Dumont  <fdumont@gcc.gnu.org>

	* include/bits/hashtable_policy.h (__details::_Before_begin<>):
	New, combine a base node instance and an allocator.
	* include/bits/hashtable.h (_Hashtable<>::_M_node_allocator): Remove.
	(_Hashtable<>::_M_before_begin): Rename into _M_bbegin and type
	modified to __detail::_Before_begin<>.
	(_Hashtable<>::_M_node_allocator()): New, get the node allocator
	part of _M_bbegin.
	(_Hashtable<>::_M_before_begin()): New, get the before begin node
	part of _M_bbegin.
	(_Hashtable<>): Adapt to use latter.

From-SVN: r193068

libstdc++-v3/ChangeLog

+2012-11-01  François Dumont  <fdumont@gcc.gnu.org>
+
+	* include/bits/hashtable_policy.h (__details::_Before_begin<>):
+	New, combine a base node instance and an allocator.
+	* include/bits/hashtable.h (_Hashtable<>::_M_node_allocator): Remove.
+	(_Hashtable<>::_M_before_begin): Rename into _M_bbegin and type
+	modified to __detail::_Before_begin<>.
+	(_Hashtable<>::_M_node_allocator()): New, get the node allocator
+	part of _M_bbegin.
+	(_Hashtable<>::_M_before_begin()): New, get the before begin node
+	part of _M_bbegin.
+	(_Hashtable<>): Adapt to use latter.
+
 2012-11-01  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	* include/bits/forward_list.h (forward_list::assign): Dispatch to new

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

@@ -1708,6 +1708,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return true;
     }
 
+  /**
+   * This type is to combine a _Hash_node_base instance with an allocator
+   * instance through inheritance to benefit from EBO when possible.
+   */
+  template<typename _NodeAlloc>
+    struct _Before_begin : public _NodeAlloc
+    {
+      _Hash_node_base _M_node;
+
+      _Before_begin(const _Before_begin&) = default;
+      _Before_begin(_Before_begin&&) = default;
+
+      template<typename _Alloc>
+	_Before_begin(_Alloc&& __a)
+	  : _NodeAlloc(std::forward<_Alloc>(__a))
+	{ }
+    };
+
  //@} hashtable-detail
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace __detail