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diff --git a/Source/JavaScriptCore/bytecode/BytecodeKills.h b/Source/JavaScriptCore/bytecode/BytecodeKills.h
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+++ b/Source/JavaScriptCore/bytecode/BytecodeKills.h
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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. AND ITS CONTRIBUTORS ``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 ITS 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
+
+#include "CodeBlock.h"
+#include <wtf/FastBitVector.h>
+
+namespace JSC {
+
+class BytecodeLivenessAnalysis;
+
+class BytecodeKills {
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    BytecodeKills()
+        : m_codeBlock(nullptr)
+    {
+    }
+    
+    // By convention, we say that non-local operands are never killed.
+    bool operandIsKilled(unsigned bytecodeIndex, int operand) const
+    {
+        ASSERT_WITH_SECURITY_IMPLICATION(bytecodeIndex < m_codeBlock->instructions().size());
+        VirtualRegister reg(operand);
+        if (reg.isLocal())
+            return m_killSets[bytecodeIndex].contains(operand);
+        return false;
+    }
+    
+    bool operandIsKilled(Instruction* instruction, int operand) const
+    {
+        return operandIsKilled(instruction - m_codeBlock->instructions().begin(), operand);
+    }
+    
+    template<typename Functor>
+    void forEachOperandKilledAt(unsigned bytecodeIndex, const Functor& functor) const
+    {
+        ASSERT_WITH_SECURITY_IMPLICATION(bytecodeIndex < m_codeBlock->instructions().size());
+        m_killSets[bytecodeIndex].forEachLocal(
+            [&] (unsigned local) {
+                functor(virtualRegisterForLocal(local));
+            });
+    }
+    
+    template<typename Functor>
+    void forEachOperandKilledAt(Instruction* pc, const Functor& functor) const
+    {
+        forEachOperandKilledAt(pc - m_codeBlock->instructions().begin(), functor);
+    }
+    
+private:
+    friend class BytecodeLivenessAnalysis;
+
+    class KillSet {
+    public:
+        KillSet()
+            : m_word(0)
+        {
+        }
+
+        ~KillSet()
+        {
+            if (hasVector())
+                delete vector();
+        }
+        
+        void add(unsigned local)
+        {
+            if (isEmpty()) {
+                setOneItem(local);
+                return;
+            }
+            if (hasOneItem()) {
+                ASSERT(oneItem() != local);
+                Vector<unsigned>* vector = new Vector<unsigned>();
+                vector->append(oneItem());
+                vector->append(local);
+                setVector(vector);
+                return;
+            }
+            ASSERT(!vector()->contains(local));
+            vector()->append(local);
+        }
+        
+        template<typename Functor>
+        void forEachLocal(const Functor& functor)
+        {
+            if (isEmpty())
+                return;
+            if (hasOneItem()) {
+                functor(oneItem());
+                return;
+            }
+            for (unsigned local : *vector())
+                functor(local);
+        }
+        
+        bool contains(unsigned expectedLocal)
+        {
+            if (isEmpty())
+                return false;
+            if (hasOneItem())
+                return oneItem() == expectedLocal;
+            for (unsigned local : *vector()) {
+                if (local == expectedLocal)
+                    return true;
+            }
+            return false;
+        }
+        
+    private:
+        bool isEmpty() const
+        {
+            return !m_word;
+        }
+        
+        bool hasOneItem() const
+        {
+            return m_word & 1;
+        }
+        
+        unsigned oneItem() const
+        {
+            return m_word >> 1;
+        }
+        
+        void setOneItem(unsigned value)
+        {
+            m_word = (value << 1) | 1;
+        }
+        
+        bool hasVector() const
+        {
+            return !isEmpty() && !hasOneItem();
+        }
+        
+        Vector<unsigned>* vector()
+        {
+            return bitwise_cast<Vector<unsigned>*>(m_word);
+        }
+        
+        void setVector(Vector<unsigned>* value)
+        {
+            m_word = bitwise_cast<uintptr_t>(value);
+        }
+        
+        uintptr_t m_word;
+    };
+    
+    CodeBlock* m_codeBlock;
+    std::unique_ptr<KillSet[]> m_killSets;
+};
+
+} // namespace JSC