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diff --git a/Source/JavaScriptCore/dfg/DFGFlowMap.h b/Source/JavaScriptCore/dfg/DFGFlowMap.h
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+++ b/Source/JavaScriptCore/dfg/DFGFlowMap.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 "DFGFlowIndexing.h"
+#include "DFGGraph.h"
+#include "DFGNode.h"
+
+namespace JSC { namespace DFG {
+
+// This is a mapping from nodes to values that is useful for flow-sensitive analysis. In such an
+// analysis, at every point in the program we need to consider the values of nodes plus the shadow
+// values of Phis. This makes it easy to do both of those things.
+template<typename T>
+class FlowMap {
+public:
+    FlowMap(Graph& graph)
+        : m_graph(graph)
+    {
+        resize();
+    }
+    
+    // Call this if the number of nodes in the graph has changed. Note that this does not reset any
+    // entries.
+    void resize()
+    {
+        m_map.resize(m_graph.maxNodeCount());
+        m_shadowMap.resize(m_graph.maxNodeCount());
+    }
+    
+    Graph& graph() const { return m_graph; }
+    
+    T& at(unsigned nodeIndex)
+    {
+        return m_map[nodeIndex];
+    }
+    
+    T& at(Node* node)
+    {
+        return at(node->index());
+    }
+    
+    T& atShadow(unsigned nodeIndex)
+    {
+        return m_shadowMap[nodeIndex];
+    }
+    
+    T& atShadow(Node* node)
+    {
+        return atShadow(node->index());
+    }
+    
+    T& at(unsigned nodeIndex, NodeFlowProjection::Kind kind)
+    {
+        switch (kind) {
+        case NodeFlowProjection::Primary:
+            return at(nodeIndex);
+        case NodeFlowProjection::Shadow:
+            return atShadow(nodeIndex);
+        }
+        RELEASE_ASSERT_NOT_REACHED();
+        return *bitwise_cast<T*>(nullptr);
+    }
+    
+    T& at(Node* node, NodeFlowProjection::Kind kind)
+    {
+        return at(node->index(), kind);
+    }
+    
+    T& at(NodeFlowProjection projection)
+    {
+        return at(projection.node(), projection.kind());
+    }
+    
+    const T& at(unsigned nodeIndex) const { return const_cast<FlowMap*>(this)->at(nodeIndex); }
+    const T& at(Node* node) const { return const_cast<FlowMap*>(this)->at(node); }
+    const T& atShadow(unsigned nodeIndex) const { return const_cast<FlowMap*>(this)->atShadow(nodeIndex); }
+    const T& atShadow(Node* node) const { return const_cast<FlowMap*>(this)->atShadow(node); }
+    const T& at(unsigned nodeIndex, NodeFlowProjection::Kind kind) const { return const_cast<FlowMap*>(this)->at(nodeIndex, kind); }
+    const T& at(Node* node, NodeFlowProjection::Kind kind) const { return const_cast<FlowMap*>(this)->at(node, kind); }
+    const T& at(NodeFlowProjection projection) const { return const_cast<FlowMap*>(this)->at(projection); }
+    
+private:
+    Graph& m_graph;
+    Vector<T, 0, UnsafeVectorOverflow> m_map;
+    Vector<T, 0, UnsafeVectorOverflow> m_shadowMap;
+};
+
+} } // namespace JSC::DFG
+
+namespace WTF {
+
+template<typename T>
+void printInternal(PrintStream& out, const JSC::DFG::FlowMap<T>& map)
+{
+    CommaPrinter comma;
+    for (unsigned i = 0; i < map.graph().maxNodeCount(); ++i) {
+        if (JSC::DFG::Node* node = map.graph().nodeAt(i)) {
+            if (const T& value = map.at(node))
+                out.print(comma, node, "=>", value);
+        }
+    }
+    for (unsigned i = 0; i < map.graph().maxNodeCount(); ++i) {
+        if (JSC::DFG::Node* node = map.graph().nodeAt(i)) {
+            if (const T& value = map.atShadow(node))
+                out.print(comma, "shadow(", node, ")=>", value);
+        }
+    }
+}
+
+} // namespace WTF
+
+#endif // ENABLE(DFG_JIT)
+