Backport r223811 from gcc-5-branch:

    PR libstdc++/66017
    * include/bits/stl_tree.h (_Rb_tree_node): Use __aligned_membuf.
    (_Rb_tree_iterator, _Rb_tree_const_iterator): Support construction
    from _Base_ptr.
    (_Rb_tree_const_iterator::_M_const_cast): Remove static_cast.
    (_Rb_tree::begin, _Rb_tree::end): Remove static_cast.
    * include/ext/aligned_buffer.h (__aligned_membuf): New type using
    alignment of _Tp as a member subobject, not as a complete object.
    * python/libstdcxx/v6/printers.py (StdRbtreeIteratorPrinter): Lookup
    _Link_type manually as it might not be in the debug info.




git-svn-id: https://gcc.gnu.org/svn/gcc/branches/google/gcc-4_9-mobile@228098 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 53 insertions, 21 deletions

diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h
index 61156dbf73d..00ff1ac83f0 100644
--- a/libstdc++-v3/include/bits/stl_tree.h
+++ b/libstdc++-v3/include/bits/stl_tree.h
@@ -144,7 +144,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _M_valptr() const
       { return std::__addressof(_M_value_field); }
 #else
-      __gnu_cxx::__aligned_buffer<_Val> _M_storage;
+      __gnu_cxx::__aligned_membuf<_Val> _M_storage;
 
       _Val*
       _M_valptr()
@@ -186,7 +186,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _M_node() { }
 
       explicit
-      _Rb_tree_iterator(_Link_type __x) _GLIBCXX_NOEXCEPT
+      _Rb_tree_iterator(_Base_ptr __x) _GLIBCXX_NOEXCEPT
       : _M_node(__x) { }
 
       reference
@@ -258,7 +258,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _M_node() { }
 
       explicit
-      _Rb_tree_const_iterator(_Link_type __x) _GLIBCXX_NOEXCEPT
+      _Rb_tree_const_iterator(_Base_ptr __x) _GLIBCXX_NOEXCEPT
       : _M_node(__x) { }
 
       _Rb_tree_const_iterator(const iterator& __it) _GLIBCXX_NOEXCEPT
@@ -266,8 +266,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       iterator
       _M_const_cast() const _GLIBCXX_NOEXCEPT
-      { return iterator(static_cast<typename iterator::_Link_type>
-			(const_cast<typename iterator::_Base_ptr>(_M_node))); }
+      { return iterator(const_cast<typename iterator::_Base_ptr>(_M_node)); }
 
       reference
       operator*() const _GLIBCXX_NOEXCEPT
@@ -764,28 +763,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       iterator
       begin() _GLIBCXX_NOEXCEPT
-      { 
-	return iterator(static_cast<_Link_type>
-			(this->_M_impl._M_header._M_left));
-      }
+      { return iterator(this->_M_impl._M_header._M_left); }
 
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
-      { 
-	return const_iterator(static_cast<_Const_Link_type>
-			      (this->_M_impl._M_header._M_left));
-      }
+      { return const_iterator(this->_M_impl._M_header._M_left); }
 
       iterator
       end() _GLIBCXX_NOEXCEPT
-      { return iterator(static_cast<_Link_type>(&this->_M_impl._M_header)); }
+      { return iterator(&this->_M_impl._M_header); }
 
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
-      { 
-	return const_iterator(static_cast<_Const_Link_type>
-			      (&this->_M_impl._M_header));
-      }
+      { return const_iterator(&this->_M_impl._M_header); }
 
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
diff --git a/libstdc++-v3/include/ext/aligned_buffer.h b/libstdc++-v3/include/ext/aligned_buffer.h
index 861de5be331..99c4575c5ee 100644
--- a/libstdc++-v3/include/ext/aligned_buffer.h
+++ b/libstdc++-v3/include/ext/aligned_buffer.h
@@ -39,7 +39,48 @@
 
 namespace __gnu_cxx
 {
+  // A utility type containing a POD object that can hold an object of type
+  // _Tp initialized via placement new or allocator_traits::construct.
+  // Intended for use as a data member subobject, use __aligned_buffer for
+  // complete objects.
   template<typename _Tp>
+  struct __aligned_membuf
+  {
+    // Target macro ADJUST_FIELD_ALIGN can produce different alignment for
+    // types when used as class members. __aligned_membuf is intended
+    // for use as a class member, so align the buffer as for a class member.
+    struct _Tp2 { _Tp _M_t; };
+
+    alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
+
+    __aligned_membuf() = default;
+
+    // Can be used to avoid value-initialization zeroing _M_storage.
+    __aligned_membuf(std::nullptr_t) { }
+
+    void*
+    _M_addr() noexcept
+    { return static_cast<void*>(&_M_storage); }
+
+    const void*
+    _M_addr() const noexcept
+    { return static_cast<const void*>(&_M_storage); }
+
+    _Tp*
+    _M_ptr() noexcept
+    { return static_cast<_Tp*>(_M_addr()); }
+
+    const _Tp*
+    _M_ptr() const noexcept
+    { return static_cast<const _Tp*>(_M_addr()); }
+  };
+
+  // Similar to __aligned_membuf but aligned for complete objects, not members.
+  // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
+  // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
+  // instead, as it has smaller size for some types on some targets.
+  // This type is still used to avoid an ABI change.
+    template<typename _Tp>
     struct __aligned_buffer
     : std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>
     {
diff --git a/libstdc++-v3/python/libstdcxx/v6/printers.py b/libstdc++-v3/python/libstdcxx/v6/printers.py
index 1fa08fbd572..65b8a935823 100644
--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -443,11 +443,12 @@ class StdRbtreeIteratorPrinter:
 
     def __init__ (self, typename, val):
         self.val = val
+        valtype = self.val.type.template_argument(0).strip_typedefs()
+        nodetype = gdb.lookup_type('std::_Rb_tree_node<' + str(valtype) + '>')
+        self.link_type = nodetype.strip_typedefs().pointer()
 
     def to_string (self):
-        typename = str(self.val.type.strip_typedefs()) + '::_Link_type'
-        nodetype = gdb.lookup_type(typename).strip_typedefs()
-        node = self.val.cast(nodetype).dereference()
+        node = self.val['_M_node'].cast(self.link_type).dereference()
         return get_value_from_Rb_tree_node(node)
 
 class StdDebugIteratorPrinter: