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diff --git a/Source/JavaScriptCore/dfg/DFGFlowIndexing.h b/Source/JavaScriptCore/dfg/DFGFlowIndexing.h
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+++ b/Source/JavaScriptCore/dfg/DFGFlowIndexing.h
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+/*
+ * Copyright (C) 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 "DFGGraph.h"
+#include "DFGNodeFlowProjection.h"
+
+namespace JSC { namespace DFG {
+
+// This is a mapping from nodes to unique, dense indices that can be used for creating fast
+// Node-keyed maps. The special part is that it also allocated indices for the shadow values of Phi
+// nodes, which is needed for any flow-sensitive analysis.
+class FlowIndexing {
+public:
+    FlowIndexing(Graph&);
+    ~FlowIndexing();
+    
+    void recompute();
+    
+    Graph& graph() const { return m_graph; }
+    
+    unsigned numIndices() const { return m_numIndices; }
+    
+    unsigned index(unsigned nodeIndex) const { return nodeIndex; }
+    
+    unsigned index(Node* node) const { return index(node->index()); }
+    
+    unsigned shadowIndex(unsigned nodeIndex) const
+    {
+        return m_nodeIndexToShadowIndex[nodeIndex];
+    }
+    
+    unsigned shadowIndex(Node* node) const
+    {
+        DFG_ASSERT(m_graph, node, node->op() == Phi);
+        return shadowIndex(node->index());
+    }
+    
+    unsigned index(unsigned nodeIndex, NodeFlowProjection::Kind kind) const
+    {
+        switch (kind) {
+        case NodeFlowProjection::Primary:
+            return index(nodeIndex);
+        case NodeFlowProjection::Shadow:
+            return shadowIndex(nodeIndex);
+        }
+        RELEASE_ASSERT_NOT_REACHED();
+        return 0;
+    }
+    
+    unsigned index(Node *node, NodeFlowProjection::Kind kind) const
+    {
+        switch (kind) {
+        case NodeFlowProjection::Primary:
+            return index(node);
+        case NodeFlowProjection::Shadow:
+            return shadowIndex(node);
+        }
+        RELEASE_ASSERT_NOT_REACHED();
+        return 0;
+    }
+    
+    unsigned index(NodeFlowProjection projection) const
+    {
+        return index(projection.node(), projection.kind());
+    }
+    
+    NodeFlowProjection nodeProjection(unsigned index) const
+    {
+        if (index < m_nodeIndexToShadowIndex.size())
+            return NodeFlowProjection(m_graph.nodeAt(index));
+        return NodeFlowProjection(
+            m_graph.nodeAt(m_shadowIndexToNodeIndex[index - m_nodeIndexToShadowIndex.size()]),
+            NodeFlowProjection::Shadow);
+    }
+    
+private:
+    Graph& m_graph;
+    unsigned m_numIndices;
+    Vector<unsigned, 0, UnsafeVectorOverflow> m_nodeIndexToShadowIndex;
+    Vector<unsigned, 0, UnsafeVectorOverflow> m_shadowIndexToNodeIndex;
+};
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+