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diff --git a/Source/JavaScriptCore/heap/CellState.h b/Source/JavaScriptCore/heap/CellState.h
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+++ b/Source/JavaScriptCore/heap/CellState.h
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+/*
+ * Copyright (C) 2015 Apple 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.
+ * 2. 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS 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 APPLE INC. OR ITS 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 CellState_h
+#define CellState_h
+
+namespace JSC {
+
+enum class CellState : uint8_t {
+    // The object is black as far as this GC is concerned. When not in GC, this just means that it's an
+    // old gen object. Note that we deliberately arrange OldBlack to be zero, so that the store barrier on
+    // a target object "from" is just:
+    //
+    // if (!from->cellState())
+    //     slowPath(from);
+    //
+    // There is a bunch of code in the LLInt and JITs that rely on this being the case. You'd have to
+    // change a lot of code if you ever wanted the store barrier to be anything but a non-zero check on
+    // cellState.
+    OldBlack = 0,
+    
+    // The object is in eden. During GC, this means that the object has not been marked yet.
+    NewWhite = 1,
+
+    // The object is grey - i.e. it will be scanned - but it either belongs to old gen (if this is eden
+    // GC) or it is grey a second time in this current GC (because a concurrent store barrier requested
+    // re-greying).
+    OldGrey = 2,
+
+    // The object is grey - i.e. it will be scanned - and this is the first time in this GC that we are
+    // going to scan it. If this is an eden GC, this also means that the object is in eden.
+    NewGrey = 3
+};
+
+} // namespace JSC
+
+#endif // CellState_h
+