Fix/implement new write barrier for x64.

src/write-buffer-inl.h

Index: src/write-buffer-inl.h
===================================================================
--- src/write-buffer-inl.h	(revision 0)
+++ src/write-buffer-inl.h	(revision 0)
@@ -0,0 +1,56 @@
+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_WRITE_BARRIER_INL_H_
+#define V8_WRITE_BARRIER_INL_H_
+
+#include "v8.h"
+#include "write-buffer.h"
+
+namespace v8 {
+namespace internal {
+
+Address WriteBuffer::TopAddress() {
+  return reinterpret_cast<Address>(Heap::write_buffer_top_address());
+}
+
+
+void WriteBuffer::Mark(Address addr) {
+  Address* top = reinterpret_cast<Address*>(Heap::write_buffer_top());
+  *top++ = addr;
+  Heap::public_set_write_buffer_top(top);
+  if ((reinterpret_cast<uintptr_t>(top) & kWriteBufferOverflowBit) != 0) {
+    ASSERT(top == limit_);
+    Compact();
+  } else {
+    ASSERT(top < limit_);
+  }
+}
+
+} }  // namespace v8::internal
+
+#endif  // V8_WRITE_BARRIER_INL_H_