Oilpan: Support polymorphic objects in HeapVectorBackings

Source/wtf/Vector.h

 /*
  *  Copyright (C) 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Library General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, 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
@@ skipping 72 matching lines @@
         static void clear(T*, T*) { }
 #if ENABLE(ASSERT)
         static void checkCleared(const T*, const T*) { }
 #endif
     };
 
     template<typename T>
     struct VectorUnusedSlotClearer<true, T> {
         static void clear(T* begin, T* end)
         {
-            memset(begin, 0, sizeof(T) * (end - begin));
+            char* array = reinterpret_cast<char*>(begin);
+            for (size_t i = 0; i < sizeof(T) * (end - begin); i++)
+                array[i] = 0;

[haraken, 2015/04/27 06:57:57]

We cannot now use memset here because clang complains that we should not use
memset for slots that contain vtables. Yeah, but we do want to do that here :)

[sof, 2015/04/30 21:15:47]

It might rewrite that loop to a memset() application internally -- I seem to
remember some amusing breakage we had in the past which ran into this (kouhei
fixed it, iirc.)

Wouldn't it work to do memset(reinterpret_cast<void*>(begin), ...) ? 

[haraken, 2015/04/30 23:40:20]

Thanks, it works.

         }
 
 #if ENABLE(ASSERT)
         static void checkCleared(const T* begin, const T* end)
         {
             const unsigned char* unusedArea = reinterpret_cast<const unsigned char*>(begin);
             const unsigned char* endAddress = reinterpret_cast<const unsigned char*>(end);
             ASSERT(endAddress >= unusedArea);
             for (int i = 0; i < endAddress - unusedArea; ++i)
                 ASSERT(!unusedArea[i]);
@@ skipping 1219 matching lines @@
     struct NeedsTracing<Vector<T, N>> {
         static const bool value = false;
     };
 #endif
 
 } // namespace WTF
 
 using WTF::Vector;
 
 #endif // WTF_Vector_h