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diff --git a/Source/JavaScriptCore/dfg/DFGLiveCatchVariablePreservationPhase.cpp b/Source/JavaScriptCore/dfg/DFGLiveCatchVariablePreservationPhase.cpp
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+++ b/Source/JavaScriptCore/dfg/DFGLiveCatchVariablePreservationPhase.cpp
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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. 
+ */
+
+#include "config.h"
+#include "DFGLiveCatchVariablePreservationPhase.h"
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGBasicBlockInlines.h"
+#include "DFGGraph.h"
+#include "DFGInsertionSet.h"
+#include "DFGPhase.h"
+#include "FullBytecodeLiveness.h"
+#include "JSCInlines.h"
+
+namespace JSC { namespace DFG {
+
+class LiveCatchVariablePreservationPhase : public Phase {
+public:
+    LiveCatchVariablePreservationPhase(Graph& graph)
+        : Phase(graph, "live catch variable preservation phase")
+    {
+    }
+
+    bool run()
+    {
+        if (!m_graph.m_hasExceptionHandlers)
+            return true;
+
+        DFG_ASSERT(m_graph, nullptr, m_graph.m_form == LoadStore);
+
+        m_currentBlockLiveness.resize(m_graph.block(0)->variablesAtTail.numberOfLocals());
+
+        InsertionSet insertionSet(m_graph);
+        for (BasicBlock* block : m_graph.blocksInNaturalOrder()) {
+            handleBlock(block, insertionSet);
+            insertionSet.execute(block);
+        }
+
+        return true;
+    }
+
+    bool willCatchException(CodeOrigin origin)
+    {
+        unsigned bytecodeIndexToCheck = origin.bytecodeIndex;
+        m_currentBlockLiveness.clearAll();
+
+        while (1) {
+            InlineCallFrame* inlineCallFrame = origin.inlineCallFrame;
+            CodeBlock* codeBlock = m_graph.baselineCodeBlockFor(inlineCallFrame);
+            if (HandlerInfo* handler = codeBlock->handlerForBytecodeOffset(bytecodeIndexToCheck)) {
+                unsigned catchBytecodeIndex = handler->target;
+                m_graph.forAllLocalsLiveInBytecode(CodeOrigin(catchBytecodeIndex, inlineCallFrame), [&] (VirtualRegister operand) {
+                    m_currentBlockLiveness.set(operand.toLocal(), true); 
+                });
+                return true;
+            }
+
+            if (!inlineCallFrame)
+                return false;
+
+            bytecodeIndexToCheck = inlineCallFrame->directCaller.bytecodeIndex;
+            origin = inlineCallFrame->directCaller;
+        }
+    }
+
+    void handleBlock(BasicBlock* block, InsertionSet& insertionSet)
+    {
+        // Because precise jump targets ensures that the start of a "try" block is its
+        // own basic block, we will never have two "try" statements in the same DFG
+        // basic block. Therefore, checking the first node in the block is sufficient 
+        // to checking if we're in a try block.
+        if (!willCatchException(block->at(0)->origin.semantic))
+            return;
+
+        Operands<VariableAccessData*> currentBlockAccessData(block->variablesAtTail.numberOfArguments(), block->variablesAtTail.numberOfLocals(), nullptr);
+        HashSet<InlineCallFrame*> seenInlineCallFrames;
+
+        {
+            for (unsigned i = 0; i < block->size(); i++) {
+                Node* node = block->at(i);
+                bool isPrimordialSetArgument = node->op() == SetArgument && node->local().isArgument() && node == m_graph.m_arguments[node->local().toArgument()];
+                InlineCallFrame* inlineCallFrame = node->origin.semantic.inlineCallFrame;
+                if (inlineCallFrame)
+                    seenInlineCallFrames.add(inlineCallFrame);
+
+                if (node->op() == SetLocal || (node->op() == SetArgument && !isPrimordialSetArgument)) {
+                    VirtualRegister operand = node->local();
+
+                    int stackOffset = inlineCallFrame ? inlineCallFrame->stackOffset : 0;
+                    if ((operand.isLocal() && m_currentBlockLiveness.get(operand.toLocal()))
+                        || (operand.offset() == stackOffset + CallFrame::thisArgumentOffset())) {
+
+                        VariableAccessData* variableAccessData = currentBlockAccessData.operand(operand);
+                        if (!variableAccessData)
+                            variableAccessData = newVariableAccessData(operand);
+
+                        insertionSet.insertNode(i, SpecNone, 
+                            Flush, node->origin, OpInfo(variableAccessData));
+                    }
+                }
+
+                if (node->hasVariableAccessData(m_graph))
+                    currentBlockAccessData.operand(node->local()) = node->variableAccessData();
+            }
+        }
+
+        // Insert Flush for everything at the end of the block.
+        {
+            NodeOrigin origin = block->at(block->size() - 1)->origin;
+            auto preserveLivenessAtEndOfBlock = [&] (VirtualRegister operand, bool alwaysInsert) {
+                if ((operand.isLocal() && m_currentBlockLiveness.get(operand.toLocal())) 
+                    || operand.isArgument()
+                    || alwaysInsert) {
+                    VariableAccessData* accessData = currentBlockAccessData.operand(operand);
+                    if (!accessData)
+                        accessData = newVariableAccessData(operand);
+
+                    currentBlockAccessData.operand(operand) = accessData;
+
+                    insertionSet.insertNode(block->size(), SpecNone, 
+                        Flush, origin, OpInfo(accessData));
+                }
+            };
+            for (unsigned local = 0; local < block->variablesAtTail.numberOfLocals(); local++)
+                preserveLivenessAtEndOfBlock(virtualRegisterForLocal(local), false);
+            for (InlineCallFrame* inlineCallFrame : seenInlineCallFrames)
+                preserveLivenessAtEndOfBlock(VirtualRegister(inlineCallFrame->stackOffset + CallFrame::thisArgumentOffset()), true);
+            preserveLivenessAtEndOfBlock(VirtualRegister(CallFrame::thisArgumentOffset()), true);
+        }
+    }
+
+    VariableAccessData* newVariableAccessData(VirtualRegister operand)
+    {
+        ASSERT(!operand.isConstant());
+        
+        m_graph.m_variableAccessData.append(VariableAccessData(operand));
+        return &m_graph.m_variableAccessData.last();
+    }
+
+    FastBitVector m_currentBlockLiveness;
+};
+
+bool performLiveCatchVariablePreservationPhase(Graph& graph)
+{
+    SamplingRegion samplingRegion("DFG Live Catch Variables Preservation Phase");
+    return runPhase<LiveCatchVariablePreservationPhase>(graph);
+}
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)