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diff --git a/Source/JavaScriptCore/dfg/DFGCombinedLiveness.cpp b/Source/JavaScriptCore/dfg/DFGCombinedLiveness.cpp
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+++ b/Source/JavaScriptCore/dfg/DFGCombinedLiveness.cpp
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+/*
+ * Copyright (C) 2015-2016 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. 
+ */
+
+#include "config.h"
+#include "DFGCombinedLiveness.h"
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGAvailabilityMap.h"
+#include "DFGBlockMapInlines.h"
+#include "FullBytecodeLiveness.h"
+#include "JSCInlines.h"
+
+namespace JSC { namespace DFG {
+
+HashSet<Node*> liveNodesAtHead(Graph& graph, BasicBlock* block)
+{
+    HashSet<Node*> seen;
+    for (NodeFlowProjection node : block->ssa->liveAtHead) {
+        if (node.kind() == NodeFlowProjection::Primary)
+            seen.add(node.node());
+    }
+    
+    AvailabilityMap& availabilityMap = block->ssa->availabilityAtHead;
+    graph.forAllLocalsLiveInBytecode(
+        block->at(0)->origin.forExit,
+        [&] (VirtualRegister reg) {
+            availabilityMap.closeStartingWithLocal(
+                reg,
+                [&] (Node* node) -> bool {
+                    return seen.contains(node);
+                },
+                [&] (Node* node) -> bool {
+                    return seen.add(node).isNewEntry;
+                });
+        });
+    
+    return seen;
+}
+
+CombinedLiveness::CombinedLiveness(Graph& graph)
+    : liveAtHead(graph)
+    , liveAtTail(graph)
+{
+    // First compute the liveAtHead for each block.
+    for (BasicBlock* block : graph.blocksInNaturalOrder())
+        liveAtHead[block] = liveNodesAtHead(graph, block);
+    
+    // Now compute the liveAtTail by unifying the liveAtHead of the successors.
+    for (BasicBlock* block : graph.blocksInNaturalOrder()) {
+        for (BasicBlock* successor : block->successors()) {
+            for (Node* node : liveAtHead[successor])
+                liveAtTail[block].add(node);
+        }
+    }
+}
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+