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diff --git a/Source/JavaScriptCore/dfg/DFGEpoch.h b/Source/JavaScriptCore/dfg/DFGEpoch.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. ``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 <wtf/PrintStream.h>
+
+namespace JSC { namespace DFG {
+
+// Utility class for epoch-based analyses.
+
+class Epoch {
+public:
+    Epoch()
+        : m_epoch(s_none)
+    {
+    }
+    
+    static Epoch fromUnsigned(unsigned value)
+    {
+        Epoch result;
+        result.m_epoch = value;
+        return result;
+    }
+    
+    unsigned toUnsigned() const
+    {
+        return m_epoch;
+    }
+    
+    static Epoch first()
+    {
+        Epoch result;
+        result.m_epoch = s_first;
+        return result;
+    }
+    
+    bool operator!() const
+    {
+        return m_epoch == s_none;
+    }
+    
+    Epoch next() const
+    {
+        Epoch result;
+        result.m_epoch = m_epoch + 1;
+        return result;
+    }
+    
+    void bump()
+    {
+        *this = next();
+    }
+    
+    bool operator==(const Epoch& other) const
+    {
+        return m_epoch == other.m_epoch;
+    }
+    
+    bool operator!=(const Epoch& other) const
+    {
+        return !(*this == other);
+    }
+    
+    bool operator<(const Epoch& other) const
+    {
+        return m_epoch < other.m_epoch;
+    }
+    
+    bool operator>(const Epoch& other) const
+    {
+        return other < *this;
+    }
+    
+    bool operator<=(const Epoch& other) const
+    {
+        return !(*this > other);
+    }
+    
+    bool operator>=(const Epoch& other) const
+    {
+        return !(*this < other);
+    }
+    
+    void dump(PrintStream&) const;
+    
+private:
+    static const unsigned s_none = 0;
+    static const unsigned s_first = 1;
+    
+    unsigned m_epoch;
+};
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)