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diff --git a/Source/JavaScriptCore/dfg/DFGClobberSet.h b/Source/JavaScriptCore/dfg/DFGClobberSet.h
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+/*
+ * Copyright (C) 2013 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. 
+ */
+
+#ifndef DFGClobberSet_h
+#define DFGClobberSet_h
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGAbstractHeap.h"
+#include <wtf/HashMap.h>
+#include <wtf/HashSet.h>
+#include <wtf/PrintStream.h>
+
+namespace JSC { namespace DFG {
+
+class Graph;
+struct Node;
+
+// FIXME: If we ever want to compare if two nodes clobber each other, we should
+// have a SmallClobberSet, which just keeps an array of the AbstractHeaps and
+// satisfies overlaps() requests by looping over all of them. This will probably
+// be faster than a full HashMap in a lot of cases. Or, maybe, we could have
+// ClobberSet be smart and use a vector so long as it was small.
+
+class ClobberSet {
+public:
+    ClobberSet();
+    ~ClobberSet();
+    
+    bool isEmpty() const { return m_clobbers.isEmpty(); }
+    
+    void add(AbstractHeap);
+    void addAll(const ClobberSet&);
+    bool contains(AbstractHeap) const;
+    bool overlaps(AbstractHeap) const;
+    void clear();
+    
+    // Calls useful for debugging the ClobberSet.
+    
+    HashSet<AbstractHeap> direct() const;
+    HashSet<AbstractHeap> super() const;
+    
+    void dump(PrintStream&) const;
+    
+private:
+    HashSet<AbstractHeap> setOf(bool direct) const;
+    
+    // Maps heap to:
+    // true --> it's a direct clobber
+    // false --> it's just a supertype of a direct clobber
+    HashMap<AbstractHeap, bool> m_clobbers;
+};
+
+class ClobberSetAdd {
+public:
+    ClobberSetAdd(ClobberSet& set)
+        : m_set(set)
+    {
+    }
+    
+    void operator()(AbstractHeap heap) const
+    {
+        m_set.add(heap);
+    }
+private:
+    ClobberSet& m_set;
+};
+
+class ClobberSetOverlaps {
+public:
+    ClobberSetOverlaps(const ClobberSet& set)
+        : m_set(set)
+        , m_result(false)
+    {
+    }
+    
+    void operator()(AbstractHeap heap) const
+    {
+        m_result |= m_set.overlaps(heap);
+    }
+    
+    bool result() const { return m_result; }
+    
+private:
+    const ClobberSet& m_set;
+    mutable bool m_result;
+};
+
+void addReads(Graph&, Node*, ClobberSet&);
+void addWrites(Graph&, Node*, ClobberSet&);
+void addReadsAndWrites(Graph&, Node*, ClobberSet& reads, ClobberSet& writes);
+
+bool readsOverlap(Graph&, Node*, ClobberSet&);
+bool writesOverlap(Graph&, Node*, ClobberSet&);
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+
+#endif // DFGClobberSet_h
+