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diff --git a/Source/JavaScriptCore/dfg/DFGFrozenValue.h b/Source/JavaScriptCore/dfg/DFGFrozenValue.h
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+++ b/Source/JavaScriptCore/dfg/DFGFrozenValue.h
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+/*
+ * Copyright (C) 2014-2016 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. ``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
+ * 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. 
+ */
+
+#pragma once
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGValueStrength.h"
+#include "JSCell.h"
+#include "JSCJSValue.h"
+#include "Structure.h"
+
+namespace JSC { namespace DFG {
+
+class Graph;
+
+class FrozenValue {
+public:
+    FrozenValue()
+        : m_structure(nullptr)
+        , m_strength(WeakValue)
+    {
+    }
+    
+    FrozenValue(JSValue value)
+        : m_value(value)
+        , m_structure(nullptr)
+        , m_strength(WeakValue)
+    {
+        RELEASE_ASSERT(!value || !value.isCell());
+    }
+    
+    FrozenValue(JSValue value, Structure* structure, ValueStrength strength)
+        : m_value(value)
+        , m_structure(structure)
+        , m_strength(strength)
+    {
+        ASSERT((!!value && value.isCell()) == !!structure);
+        ASSERT(!value || !value.isCell() || value.asCell()->classInfo(*value.asCell()->vm()) == structure->classInfo());
+        ASSERT(!!structure || (strength == WeakValue));
+    }
+    
+    static FrozenValue* emptySingleton();
+    
+    bool operator!() const { return !m_value; }
+    
+    JSValue value() const { return m_value; }
+    JSCell* cell() const { return m_value.asCell(); }
+    
+    template<typename T>
+    T dynamicCast(VM& vm)
+    {
+        JSValue theValue = value();
+        if (!theValue)
+            return nullptr;
+        return jsDynamicCast<T>(vm, theValue);
+    }
+    template<typename T>
+    T cast()
+    {
+        return jsCast<T>(value());
+    }
+    
+    Structure* structure() const { return m_structure; }
+    
+    void strengthenTo(ValueStrength strength)
+    {
+        if (!!m_value && m_value.isCell())
+            m_strength = merge(m_strength, strength);
+    }
+    
+    bool pointsToHeap() const { return !!value() && value().isCell(); }
+    
+    // The strength of the value itself. The structure is almost always weak.
+    ValueStrength strength() const { return m_strength; }
+
+    String tryGetString(Graph&);
+    
+    void dumpInContext(PrintStream& out, DumpContext* context) const;
+    void dump(PrintStream& out) const;
+    
+private:
+    friend class Graph;
+    
+    // This is a utility method for DFG::Graph::freeze(). You should almost always call
+    // Graph::freeze() directly. Calling this instead of Graph::freeze() can result in
+    // the same constant being viewed as having different structures during the course
+    // of compilation, which can sometimes cause bad things to happen. For example, we
+    // may observe that one version of the constant has an unwatchable structure but
+    // then a later version may start to have a watchable structure due to a transition.
+    // The point of freezing is to ensure that we generally only see one version of
+    // constants, but that requires freezing through the Graph.
+    static FrozenValue freeze(JSValue value)
+    {
+        return FrozenValue(
+            value,
+            (!!value && value.isCell()) ? value.asCell()->structure() : nullptr,
+            WeakValue);
+    }
+
+    JSValue m_value;
+    Structure* m_structure;
+    ValueStrength m_strength;
+};
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)