Oilpan: like Vector<T>, restrict Deque<T> to certain part objects.

Source/wtf/Deque.h

 /*
  * Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 208 matching lines @@
         // postfix ++ intentionally omitted
         Iterator& operator--() { Base::decrement(); return *this; }
         // postfix -- intentionally omitted
     };
 
     template<typename T, size_t inlineCapacity, typename Allocator>
     inline Deque<T, inlineCapacity, Allocator>::Deque()
         : m_start(0)
         , m_end(0)
     {
+        // Unused buffer slots are initialized to zero so that the visitor and the
+        // finalizer can visit them safely. canInitializeWithMemset tells us
+        // that the class does not expect matching constructor and
+        // destructor calls as long as the memory is zeroed.

[haraken, 2015/04/22 05:29:40]

Or can we add these static_assert to Vector::trace (or
HeapVectorBacking::trace)? Then we don't need to duplicate the static_asserts
between Vector and Deque.

[sof, 2015/04/22 16:05:21]

It makes some sense to keep it associated with the declaration of the collection
type, rather than where it is traced.

+        static_assert(!Allocator::isGarbageCollected || !VectorTraits<T>::needsDestruction || VectorTraits<T>::canInitializeWithMemset, "class has problems with finalizers called on cleared memory");
+        static_assert(!WTF::IsPolymorphic<T>::value || !VectorTraits<T>::canInitializeWithMemset, "cannot initialize with memset if there is a vtable");
     }
 
     template<typename T, size_t inlineCapacity, typename Allocator>
     inline Deque<T, inlineCapacity, Allocator>::Deque(const Deque<T, inlineCapacity, Allocator>& other)
         : m_buffer(other.m_buffer.capacity())
         , m_start(other.m_start)
         , m_end(other.m_end)
     {
         const T* otherBuffer = other.m_buffer.buffer();
         if (m_start <= m_end)
@@ skipping 327 matching lines @@
     struct NeedsTracing<Deque<T, N>> {
         static const bool value = false;
     };
 #endif
 
 } // namespace WTF
 
 using WTF::Deque;
 
 #endif // WTF_Deque_h