1 files changed, 41 insertions, 0 deletions
diff --git a/gcc-4.9/libstdc++-v3/include/ext/aligned_buffer.h b/gcc-4.9/libstdc++-v3/include/ext/aligned_buffer.h
index 861de5be3..99c4575c5 100644
--- a/gcc-4.9/libstdc++-v3/include/ext/aligned_buffer.h
+++ b/gcc-4.9/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>
     {