BytecodeGenerator.cpp

/*
 * Copyright (C) 2008, 2009, 2012, 2013 Apple Inc. All rights reserved.
 * Copyright (C) 2008 Cameron Zwarich <cwzwarich@uwaterloo.ca>
 * Copyright (C) 2012 Igalia, S.L.
 *
 * 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.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE 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 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.
 */

#include "config.h"
#include "BytecodeGenerator.h"

#include "Interpreter.h"
#include "JSActivation.h"
#include "JSFunction.h"
#include "JSNameScope.h"
#include "LowLevelInterpreter.h"
#include "Operations.h"
#include "Options.h"
#include "StrongInlines.h"
#include "UnlinkedCodeBlock.h"
#include <wtf/StdLibExtras.h>
#include <wtf/text/WTFString.h>

using namespace std;

namespace JSC {

void Label::setLocation(unsigned location)
{
    m_location = location;
    
    unsigned size = m_unresolvedJumps.size();
    for (unsigned i = 0; i < size; ++i)
        m_generator->m_instructions[m_unresolvedJumps[i].second].u.operand = m_location - m_unresolvedJumps[i].first;
}

ParserError BytecodeGenerator::generate()
{
    SamplingRegion samplingRegion("Bytecode Generation");
    
    m_codeBlock->setThisRegister(m_thisRegister.virtualRegister());

    m_scopeNode->emitBytecode(*this);

    m_staticPropertyAnalyzer.kill();

    for (unsigned i = 0; i < m_tryRanges.size(); ++i) {
        TryRange& range = m_tryRanges[i];
        int start = range.start->bind();
        int end = range.end->bind();
        
        // This will happen for empty try blocks and for some cases of finally blocks:
        //
        // try {
        //    try {
        //    } finally {
        //        return 42;
        //        // *HERE*
        //    }
        // } finally {
        //    print("things");
        // }
        //
        // The return will pop scopes to execute the outer finally block. But this includes
        // popping the try context for the inner try. The try context is live in the fall-through
        // part of the finally block not because we will emit a handler that overlaps the finally,
        // but because we haven't yet had a chance to plant the catch target. Then when we finish
        // emitting code for the outer finally block, we repush the try contex, this time with a
        // new start index. But that means that the start index for the try range corresponding
        // to the inner-finally-following-the-return (marked as "*HERE*" above) will be greater
        // than the end index of the try block. This is harmless since end < start handlers will
        // never get matched in our logic, but we do the runtime a favor and choose to not emit
        // such handlers at all.
        if (end <= start)
            continue;
        
        ASSERT(range.tryData->targetScopeDepth != UINT_MAX);
        UnlinkedHandlerInfo info = {
            static_cast<uint32_t>(start), static_cast<uint32_t>(end),
            static_cast<uint32_t>(range.tryData->target->bind()),
            range.tryData->targetScopeDepth
        };
        m_codeBlock->addExceptionHandler(info);
    }
    
    m_codeBlock->instructions() = RefCountedArray<UnlinkedInstruction>(m_instructions);

    m_codeBlock->shrinkToFit();

    if (m_expressionTooDeep)
        return ParserError(ParserError::OutOfMemory);
    return ParserError(ParserError::ErrorNone);
}

bool BytecodeGenerator::addVar(const Identifier& ident, bool isConstant, RegisterID*& r0)
{
    ConcurrentJITLocker locker(symbolTable().m_lock);
    int index = virtualRegisterForLocal(m_calleeRegisters.size()).offset();
    SymbolTableEntry newEntry(index, isConstant ? ReadOnly : 0);
    SymbolTable::Map::AddResult result = symbolTable().add(locker, ident.impl(), newEntry);

    if (!result.isNewEntry) {
        r0 = &registerFor(result.iterator->value.getIndex());
        return false;
    }

    r0 = addVar();
    return true;
}

void BytecodeGenerator::preserveLastVar()
{
    if ((m_firstConstantIndex = m_calleeRegisters.size()) != 0)
        m_lastVar = &m_calleeRegisters.last();
}

BytecodeGenerator::BytecodeGenerator(VM& vm, ProgramNode* programNode, UnlinkedProgramCodeBlock* codeBlock, DebuggerMode debuggerMode, ProfilerMode profilerMode)
    : m_shouldEmitDebugHooks(debuggerMode == DebuggerOn)
    , m_shouldEmitProfileHooks(profilerMode == ProfilerOn)
    , m_symbolTable(0)
    , m_scopeNode(programNode)
    , m_codeBlock(vm, codeBlock)
    , m_thisRegister(CallFrame::thisArgumentOffset())
    , m_emptyValueRegister(0)
    , m_globalObjectRegister(0)
    , m_finallyDepth(0)
    , m_localScopeDepth(0)
    , m_codeType(GlobalCode)
    , m_nextConstantOffset(0)
    , m_globalConstantIndex(0)
    , m_hasCreatedActivation(true)
    , m_firstLazyFunction(0)
    , m_lastLazyFunction(0)
    , m_staticPropertyAnalyzer(&m_instructions)
    , m_vm(&vm)
    , m_lastOpcodeID(op_end)
#ifndef NDEBUG
    , m_lastOpcodePosition(0)
#endif
    , m_stack(vm, wtfThreadData().stack())
    , m_usesExceptions(false)
    , m_expressionTooDeep(false)
{
    if (m_shouldEmitDebugHooks)
        m_codeBlock->setNeedsFullScopeChain(true);

    m_codeBlock->setNumParameters(1); // Allocate space for "this"

    emitOpcode(op_enter);

    const VarStack& varStack = programNode->varStack();
    const FunctionStack& functionStack = programNode->functionStack();

    for (size_t i = 0; i < functionStack.size(); ++i) {
        FunctionBodyNode* function = functionStack[i];
        UnlinkedFunctionExecutable* unlinkedFunction = makeFunction(function);
        codeBlock->addFunctionDeclaration(*m_vm, function->ident(), unlinkedFunction);
    }

    for (size_t i = 0; i < varStack.size(); ++i)
        codeBlock->addVariableDeclaration(varStack[i].first, !!(varStack[i].second & DeclarationStacks::IsConstant));

}

BytecodeGenerator::BytecodeGenerator(VM& vm, FunctionBodyNode* functionBody, UnlinkedFunctionCodeBlock* codeBlock, DebuggerMode debuggerMode, ProfilerMode profilerMode)
    : m_shouldEmitDebugHooks(debuggerMode == DebuggerOn)
    , m_shouldEmitProfileHooks(profilerMode == ProfilerOn)
    , m_symbolTable(codeBlock->symbolTable())
    , m_scopeNode(functionBody)
    , m_codeBlock(vm, codeBlock)
    , m_activationRegister(0)
    , m_emptyValueRegister(0)
    , m_globalObjectRegister(0)
    , m_finallyDepth(0)
    , m_localScopeDepth(0)
    , m_codeType(FunctionCode)
    , m_nextConstantOffset(0)
    , m_globalConstantIndex(0)
    , m_hasCreatedActivation(false)
    , m_firstLazyFunction(0)
    , m_lastLazyFunction(0)
    , m_staticPropertyAnalyzer(&m_instructions)
    , m_vm(&vm)
    , m_lastOpcodeID(op_end)
#ifndef NDEBUG
    , m_lastOpcodePosition(0)
#endif
    , m_stack(vm, wtfThreadData().stack())
    , m_usesExceptions(false)
    , m_expressionTooDeep(false)
{
    if (m_shouldEmitDebugHooks)
        m_codeBlock->setNeedsFullScopeChain(true);

    m_symbolTable->setUsesNonStrictEval(codeBlock->usesEval() && !codeBlock->isStrictMode());
    Vector<Identifier> boundParameterProperties;
    FunctionParameters& parameters = *functionBody->parameters();
    for (size_t i = 0; i < parameters.size(); i++) {
        auto pattern = parameters.at(i);
        if (pattern->isBindingNode())
            continue;
        pattern->collectBoundIdentifiers(boundParameterProperties);
        continue;
    }
    m_symbolTable->setParameterCountIncludingThis(functionBody->parameters()->size() + 1);

    emitOpcode(op_enter);
    if (m_codeBlock->needsFullScopeChain()) {
        m_activationRegister = addVar();
        emitInitLazyRegister(m_activationRegister);
        m_codeBlock->setActivationRegister(m_activationRegister->virtualRegister());
    }

    m_symbolTable->setCaptureStart(virtualRegisterForLocal(m_codeBlock->m_numVars).offset());

    if (functionBody->usesArguments() || codeBlock->usesEval()) { // May reify arguments object.
        RegisterID* unmodifiedArgumentsRegister = addVar(); // Anonymous, so it can't be modified by user code.
        RegisterID* argumentsRegister = addVar(propertyNames().arguments, false); // Can be changed by assigning to 'arguments'.

        // We can save a little space by hard-coding the knowledge that the two
        // 'arguments' values are stored in consecutive registers, and storing
        // only the index of the assignable one.
        codeBlock->setArgumentsRegister(argumentsRegister->virtualRegister());
        ASSERT_UNUSED(unmodifiedArgumentsRegister, unmodifiedArgumentsRegister->virtualRegister() == JSC::unmodifiedArgumentsRegister(codeBlock->argumentsRegister()));

        emitInitLazyRegister(argumentsRegister);
        emitInitLazyRegister(unmodifiedArgumentsRegister);
        
        if (shouldTearOffArgumentsEagerly()) {
            emitOpcode(op_create_arguments);
            instructions().append(argumentsRegister->index());
        }
    }

    bool shouldCaptureAllTheThings = m_shouldEmitDebugHooks || codeBlock->usesEval();

    bool capturesAnyArgumentByName = false;
    Vector<RegisterID*, 0, UnsafeVectorOverflow> capturedArguments;
    if (functionBody->hasCapturedVariables() || shouldCaptureAllTheThings) {
        FunctionParameters& parameters = *functionBody->parameters();
        capturedArguments.resize(parameters.size());
        for (size_t i = 0; i < parameters.size(); ++i) {
            capturedArguments[i] = 0;
            auto pattern = parameters.at(i);
            if (!pattern->isBindingNode())
                continue;
            const Identifier& ident = static_cast<const BindingNode*>(pattern)->boundProperty();
            if (!functionBody->captures(ident) && !shouldCaptureAllTheThings)
                continue;
            capturesAnyArgumentByName = true;
            capturedArguments[i] = addVar();
        }
    }

    if (capturesAnyArgumentByName && !shouldTearOffArgumentsEagerly()) {
        size_t parameterCount = m_symbolTable->parameterCount();
        auto slowArguments = std::make_unique<SlowArgument[]>(parameterCount);
        for (size_t i = 0; i < parameterCount; ++i) {
            if (!capturedArguments[i]) {
                ASSERT(slowArguments[i].status == SlowArgument::Normal);
                slowArguments[i].index = CallFrame::argumentOffset(i);
                continue;
            }
            slowArguments[i].status = SlowArgument::Captured;
            slowArguments[i].index = capturedArguments[i]->index();
        }
        m_symbolTable->setSlowArguments(std::move(slowArguments));
    }

    RegisterID* calleeRegister = resolveCallee(functionBody); // May push to the scope chain and/or add a captured var.

    const DeclarationStacks::FunctionStack& functionStack = functionBody->functionStack();
    const DeclarationStacks::VarStack& varStack = functionBody->varStack();

    // Captured variables and functions go first so that activations don't have
    // to step over the non-captured locals to mark them.
    m_hasCreatedActivation = false;
    if (functionBody->hasCapturedVariables()) {
        for (size_t i = 0; i < functionStack.size(); ++i) {
            FunctionBodyNode* function = functionStack[i];
            const Identifier& ident = function->ident();
            if (functionBody->captures(ident)) {
                if (!m_hasCreatedActivation) {
                    m_hasCreatedActivation = true;
                    emitOpcode(op_create_activation);
                    instructions().append(m_activationRegister->index());
                }
                m_functions.add(ident.impl());
                emitNewFunction(addVar(ident, false), function);
            }
        }
        for (size_t i = 0; i < varStack.size(); ++i) {
            const Identifier& ident = varStack[i].first;
            if (functionBody->captures(ident))
                addVar(ident, varStack[i].second & DeclarationStacks::IsConstant);
        }
    }
    bool canLazilyCreateFunctions = !functionBody->needsActivationForMoreThanVariables() && !m_shouldEmitDebugHooks;
    if (!canLazilyCreateFunctions && !m_hasCreatedActivation) {
        m_hasCreatedActivation = true;
        emitOpcode(op_create_activation);
        instructions().append(m_activationRegister->index());
    }

    m_symbolTable->setCaptureEnd(virtualRegisterForLocal(codeBlock->m_numVars).offset());

    m_firstLazyFunction = codeBlock->m_numVars;
    for (size_t i = 0; i < functionStack.size(); ++i) {
        FunctionBodyNode* function = functionStack[i];
        const Identifier& ident = function->ident();
        if (!functionBody->captures(ident)) {
            m_functions.add(ident.impl());
            RefPtr<RegisterID> reg = addVar(ident, false);
            // Don't lazily create functions that override the name 'arguments'
            // as this would complicate lazy instantiation of actual arguments.
            if (!canLazilyCreateFunctions || ident == propertyNames().arguments)
                emitNewFunction(reg.get(), function);
            else {
                emitInitLazyRegister(reg.get());
                m_lazyFunctions.set(reg->virtualRegister().toLocal(), function);
            }
        }
    }
    m_lastLazyFunction = canLazilyCreateFunctions ? codeBlock->m_numVars : m_firstLazyFunction;
    for (size_t i = 0; i < varStack.size(); ++i) {
        const Identifier& ident = varStack[i].first;
        if (!functionBody->captures(ident))
            addVar(ident, varStack[i].second & DeclarationStacks::IsConstant);
    }

    if (shouldCaptureAllTheThings)
        m_symbolTable->setCaptureEnd(virtualRegisterForLocal(codeBlock->m_numVars).offset());

    m_parameters.grow(parameters.size() + 1); // reserve space for "this"

    // Add "this" as a parameter
    int nextParameterIndex = CallFrame::thisArgumentOffset();
    m_thisRegister.setIndex(nextParameterIndex++);
    m_codeBlock->addParameter();
    Vector<std::pair<RegisterID*, const DeconstructionPatternNode*>> deconstructedParameters;
    for (size_t i = 0; i < parameters.size(); ++i, ++nextParameterIndex) {
        int index = nextParameterIndex;
        auto pattern = parameters.at(i);
        if (!pattern->isBindingNode()) {
            m_codeBlock->addParameter();
            RegisterID& parameter = registerFor(index);
            parameter.setIndex(index);
            deconstructedParameters.append(make_pair(&parameter, pattern));
            continue;
        }
        auto simpleParameter = static_cast<const BindingNode*>(pattern);
        if (capturedArguments.size() && capturedArguments[i]) {
            ASSERT((functionBody->hasCapturedVariables() && functionBody->captures(simpleParameter->boundProperty())) || shouldCaptureAllTheThings);
            index = capturedArguments[i]->index();
            RegisterID original(nextParameterIndex);
            emitMove(capturedArguments[i], &original);
        }
        addParameter(simpleParameter->boundProperty(), index);
    }
    preserveLastVar();

    // We declare the callee's name last because it should lose to a var, function, and/or parameter declaration.
    addCallee(functionBody, calleeRegister);

    if (isConstructor()) {
        emitCreateThis(&m_thisRegister);
    } else if (functionBody->usesThis() || codeBlock->usesEval() || m_shouldEmitDebugHooks) {
        m_codeBlock->addPropertyAccessInstruction(instructions().size());
        emitOpcode(op_to_this);
        instructions().append(kill(&m_thisRegister));
        instructions().append(0);
    }
    for (size_t i = 0; i < deconstructedParameters.size(); i++) {
        auto& entry = deconstructedParameters[i];
        entry.second->bindValue(*this, entry.first);
    }
}

BytecodeGenerator::BytecodeGenerator(VM& vm, EvalNode* evalNode, UnlinkedEvalCodeBlock* codeBlock, DebuggerMode debuggerMode, ProfilerMode profilerMode)
    : m_shouldEmitDebugHooks(debuggerMode == DebuggerOn)
    , m_shouldEmitProfileHooks(profilerMode == ProfilerOn)
    , m_symbolTable(codeBlock->symbolTable())
    , m_scopeNode(evalNode)
    , m_codeBlock(vm, codeBlock)
    , m_thisRegister(CallFrame::thisArgumentOffset())
    , m_emptyValueRegister(0)
    , m_globalObjectRegister(0)
    , m_finallyDepth(0)
    , m_localScopeDepth(0)
    , m_codeType(EvalCode)
    , m_nextConstantOffset(0)
    , m_globalConstantIndex(0)
    , m_hasCreatedActivation(true)
    , m_firstLazyFunction(0)
    , m_lastLazyFunction(0)
    , m_staticPropertyAnalyzer(&m_instructions)
    , m_vm(&vm)
    , m_lastOpcodeID(op_end)
#ifndef NDEBUG
    , m_lastOpcodePosition(0)
#endif
    , m_stack(vm, wtfThreadData().stack())
    , m_usesExceptions(false)
    , m_expressionTooDeep(false)
{
    m_codeBlock->setNeedsFullScopeChain(true);

    m_symbolTable->setUsesNonStrictEval(codeBlock->usesEval() && !codeBlock->isStrictMode());
    m_codeBlock->setNumParameters(1);

    emitOpcode(op_enter);

    const DeclarationStacks::FunctionStack& functionStack = evalNode->functionStack();
    for (size_t i = 0; i < functionStack.size(); ++i)
        m_codeBlock->addFunctionDecl(makeFunction(functionStack[i]));

    const DeclarationStacks::VarStack& varStack = evalNode->varStack();
    unsigned numVariables = varStack.size();
    Vector<Identifier, 0, UnsafeVectorOverflow> variables;
    variables.reserveCapacity(numVariables);
    for (size_t i = 0; i < numVariables; ++i) {
        ASSERT(varStack[i].first.impl()->isIdentifier());
        variables.append(varStack[i].first);
    }
    codeBlock->adoptVariables(variables);
    preserveLastVar();
}

BytecodeGenerator::~BytecodeGenerator()
{
}

RegisterID* BytecodeGenerator::emitInitLazyRegister(RegisterID* reg)
{
    emitOpcode(op_init_lazy_reg);
    instructions().append(reg->index());
    return reg;
}

RegisterID* BytecodeGenerator::resolveCallee(FunctionBodyNode* functionBodyNode)
{
    if (functionBodyNode->ident().isNull() || !functionBodyNode->functionNameIsInScope())
        return 0;

    m_calleeRegister.setIndex(JSStack::Callee);

    // If non-strict eval is in play, we use a separate object in the scope chain for the callee's name.
    if ((m_codeBlock->usesEval() && !m_codeBlock->isStrictMode()) || m_shouldEmitDebugHooks)
        emitPushNameScope(functionBodyNode->ident(), &m_calleeRegister, ReadOnly | DontDelete);

    if (!functionBodyNode->captures(functionBodyNode->ident()))
        return &m_calleeRegister;

    // Move the callee into the captured section of the stack.
    return emitMove(addVar(), &m_calleeRegister);
}

void BytecodeGenerator::addCallee(FunctionBodyNode* functionBodyNode, RegisterID* calleeRegister)
{
    if (functionBodyNode->ident().isNull() || !functionBodyNode->functionNameIsInScope())
        return;

    // If non-strict eval is in play, we use a separate object in the scope chain for the callee's name.
    if ((m_codeBlock->usesEval() && !m_codeBlock->isStrictMode()) || m_shouldEmitDebugHooks)
        return;

    ASSERT(calleeRegister);
    symbolTable().add(functionBodyNode->ident().impl(), SymbolTableEntry(calleeRegister->index(), ReadOnly));
}

void BytecodeGenerator::addParameter(const Identifier& ident, int parameterIndex)
{
    // Parameters overwrite var declarations, but not function declarations.
    StringImpl* rep = ident.impl();
    if (!m_functions.contains(rep)) {
        symbolTable().set(rep, parameterIndex);
        RegisterID& parameter = registerFor(parameterIndex);
        parameter.setIndex(parameterIndex);
    }

    // To maintain the calling convention, we have to allocate unique space for
    // each parameter, even if the parameter doesn't make it into the symbol table.
    m_codeBlock->addParameter();
}

bool BytecodeGenerator::willResolveToArguments(const Identifier& ident)
{
    if (ident != propertyNames().arguments)
        return false;
    
    if (!shouldOptimizeLocals())
        return false;
    
    SymbolTableEntry entry = symbolTable().get(ident.impl());
    if (entry.isNull())
        return false;

    if (m_codeBlock->usesArguments() && m_codeType == FunctionCode)
        return true;
    
    return false;
}

RegisterID* BytecodeGenerator::uncheckedRegisterForArguments()
{
    ASSERT(willResolveToArguments(propertyNames().arguments));

    SymbolTableEntry entry = symbolTable().get(propertyNames().arguments.impl());
    ASSERT(!entry.isNull());
    return &registerFor(entry.getIndex());
}

RegisterID* BytecodeGenerator::createLazyRegisterIfNecessary(RegisterID* reg)
{
    if (!reg->virtualRegister().isLocal())
        return reg;

    int localVariableNumber = reg->virtualRegister().toLocal();

    if (m_lastLazyFunction <= localVariableNumber || localVariableNumber < m_firstLazyFunction)
        return reg;
    emitLazyNewFunction(reg, m_lazyFunctions.get(localVariableNumber));
    return reg;
}

RegisterID* BytecodeGenerator::newRegister()
{
    m_calleeRegisters.append(virtualRegisterForLocal(m_calleeRegisters.size()));
    m_codeBlock->m_numCalleeRegisters = max<int>(m_codeBlock->m_numCalleeRegisters, m_calleeRegisters.size());
    return &m_calleeRegisters.last();
}

RegisterID* BytecodeGenerator::newTemporary()
{
    // Reclaim free register IDs.
    while (m_calleeRegisters.size() && !m_calleeRegisters.last().refCount())
        m_calleeRegisters.removeLast();
        
    RegisterID* result = newRegister();
    result->setTemporary();
    return result;
}

LabelScopePtr BytecodeGenerator::newLabelScope(LabelScope::Type type, const Identifier* name)
{
    // Reclaim free label scopes.
    while (m_labelScopes.size() && !m_labelScopes.last().refCount())
        m_labelScopes.removeLast();

    // Allocate new label scope.
    LabelScope scope(type, name, scopeDepth(), newLabel(), type == LabelScope::Loop ? newLabel() : PassRefPtr<Label>()); // Only loops have continue targets.
    m_labelScopes.append(scope);
    return LabelScopePtr(&m_labelScopes, m_labelScopes.size() - 1);
}

PassRefPtr<Label> BytecodeGenerator::newLabel()
{
    // Reclaim free label IDs.
    while (m_labels.size() && !m_labels.last().refCount())
        m_labels.removeLast();

    // Allocate new label ID.
    m_labels.append(this);
    return &m_labels.last();
}

PassRefPtr<Label> BytecodeGenerator::emitLabel(Label* l0)
{
    unsigned newLabelIndex = instructions().size();
    l0->setLocation(newLabelIndex);

    if (m_codeBlock->numberOfJumpTargets()) {
        unsigned lastLabelIndex = m_codeBlock->lastJumpTarget();
        ASSERT(lastLabelIndex <= newLabelIndex);
        if (newLabelIndex == lastLabelIndex) {
            // Peephole optimizations have already been disabled by emitting the last label
            return l0;
        }
    }

    m_codeBlock->addJumpTarget(newLabelIndex);

    // This disables peephole optimizations when an instruction is a jump target
    m_lastOpcodeID = op_end;
    return l0;
}

void BytecodeGenerator::emitOpcode(OpcodeID opcodeID)
{
#ifndef NDEBUG
    size_t opcodePosition = instructions().size();
    ASSERT(opcodePosition - m_lastOpcodePosition == opcodeLength(m_lastOpcodeID) || m_lastOpcodeID == op_end);
    m_lastOpcodePosition = opcodePosition;
#endif
    instructions().append(opcodeID);
    m_lastOpcodeID = opcodeID;
}

UnlinkedArrayProfile BytecodeGenerator::newArrayProfile()
{
#if ENABLE(VALUE_PROFILER)
    return m_codeBlock->addArrayProfile();
#else
    return 0;
#endif
}

UnlinkedArrayAllocationProfile BytecodeGenerator::newArrayAllocationProfile()
{
#if ENABLE(VALUE_PROFILER)
    return m_codeBlock->addArrayAllocationProfile();
#else
    return 0;
#endif
}

UnlinkedObjectAllocationProfile BytecodeGenerator::newObjectAllocationProfile()
{
    return m_codeBlock->addObjectAllocationProfile();
}

UnlinkedValueProfile BytecodeGenerator::emitProfiledOpcode(OpcodeID opcodeID)
{
#if ENABLE(VALUE_PROFILER)
    UnlinkedValueProfile result = m_codeBlock->addValueProfile();
#else
    UnlinkedValueProfile result = 0;
#endif
    emitOpcode(opcodeID);
    return result;
}

void BytecodeGenerator::emitLoopHint()
{
    emitOpcode(op_loop_hint);
}

void BytecodeGenerator::retrieveLastBinaryOp(int& dstIndex, int& src1Index, int& src2Index)
{
    ASSERT(instructions().size() >= 4);
    size_t size = instructions().size();
    dstIndex = instructions().at(size - 3).u.operand;
    src1Index = instructions().at(size - 2).u.operand;
    src2Index = instructions().at(size - 1).u.operand;
}

void BytecodeGenerator::retrieveLastUnaryOp(int& dstIndex, int& srcIndex)
{
    ASSERT(instructions().size() >= 3);
    size_t size = instructions().size();
    dstIndex = instructions().at(size - 2).u.operand;
    srcIndex = instructions().at(size - 1).u.operand;
}

void ALWAYS_INLINE BytecodeGenerator::rewindBinaryOp()
{
    ASSERT(instructions().size() >= 4);
    instructions().shrink(instructions().size() - 4);
    m_lastOpcodeID = op_end;
}

void ALWAYS_INLINE BytecodeGenerator::rewindUnaryOp()
{
    ASSERT(instructions().size() >= 3);
    instructions().shrink(instructions().size() - 3);
    m_lastOpcodeID = op_end;
}

PassRefPtr<Label> BytecodeGenerator::emitJump(Label* target)
{
    size_t begin = instructions().size();
    emitOpcode(op_jmp);
    instructions().append(target->bind(begin, instructions().size()));
    return target;
}

PassRefPtr<Label> BytecodeGenerator::emitJumpIfTrue(RegisterID* cond, Label* target)
{
    if (m_lastOpcodeID == op_less) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jless);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_lesseq) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jlesseq);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_greater) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jgreater);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_greatereq) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jgreatereq);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_eq_null && target->isForward()) {
        int dstIndex;
        int srcIndex;

        retrieveLastUnaryOp(dstIndex, srcIndex);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindUnaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jeq_null);
            instructions().append(srcIndex);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_neq_null && target->isForward()) {
        int dstIndex;
        int srcIndex;

        retrieveLastUnaryOp(dstIndex, srcIndex);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindUnaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jneq_null);
            instructions().append(srcIndex);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    }

    size_t begin = instructions().size();

    emitOpcode(op_jtrue);
    instructions().append(cond->index());
    instructions().append(target->bind(begin, instructions().size()));
    return target;
}

PassRefPtr<Label> BytecodeGenerator::emitJumpIfFalse(RegisterID* cond, Label* target)
{
    if (m_lastOpcodeID == op_less && target->isForward()) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jnless);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_lesseq && target->isForward()) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jnlesseq);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_greater && target->isForward()) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jngreater);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_greatereq && target->isForward()) {
        int dstIndex;
        int src1Index;
        int src2Index;

        retrieveLastBinaryOp(dstIndex, src1Index, src2Index);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindBinaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jngreatereq);
            instructions().append(src1Index);
            instructions().append(src2Index);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_not) {
        int dstIndex;
        int srcIndex;

        retrieveLastUnaryOp(dstIndex, srcIndex);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindUnaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jtrue);
            instructions().append(srcIndex);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_eq_null && target->isForward()) {
        int dstIndex;
        int srcIndex;

        retrieveLastUnaryOp(dstIndex, srcIndex);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindUnaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jneq_null);
            instructions().append(srcIndex);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    } else if (m_lastOpcodeID == op_neq_null && target->isForward()) {
        int dstIndex;
        int srcIndex;

        retrieveLastUnaryOp(dstIndex, srcIndex);

        if (cond->index() == dstIndex && cond->isTemporary() && !cond->refCount()) {
            rewindUnaryOp();

            size_t begin = instructions().size();
            emitOpcode(op_jeq_null);
            instructions().append(srcIndex);
            instructions().append(target->bind(begin, instructions().size()));
            return target;
        }
    }

    size_t begin = instructions().size();
    emitOpcode(op_jfalse);
    instructions().append(cond->index());
    instructions().append(target->bind(begin, instructions().size()));
    return target;
}

PassRefPtr<Label> BytecodeGenerator::emitJumpIfNotFunctionCall(RegisterID* cond, Label* target)
{
    size_t begin = instructions().size();

    emitOpcode(op_jneq_ptr);
    instructions().append(cond->index());
    instructions().append(Special::CallFunction);
    instructions().append(target->bind(begin, instructions().size()));
    return target;
}

PassRefPtr<Label> BytecodeGenerator::emitJumpIfNotFunctionApply(RegisterID* cond, Label* target)
{
    size_t begin = instructions().size();

    emitOpcode(op_jneq_ptr);
    instructions().append(cond->index());
    instructions().append(Special::ApplyFunction);
    instructions().append(target->bind(begin, instructions().size()));
    return target;
}

unsigned BytecodeGenerator::addConstant(const Identifier& ident)
{
    StringImpl* rep = ident.impl();
    IdentifierMap::AddResult result = m_identifierMap.add(rep, m_codeBlock->numberOfIdentifiers());
    if (result.isNewEntry)
        m_codeBlock->addIdentifier(ident);

    return result.iterator->value;
}

// We can't hash JSValue(), so we use a dedicated data member to cache it.
RegisterID* BytecodeGenerator::addConstantEmptyValue()
{
    if (!m_emptyValueRegister) {
        int index = m_nextConstantOffset;
        m_constantPoolRegisters.append(FirstConstantRegisterIndex + m_nextConstantOffset);
        ++m_nextConstantOffset;
        m_codeBlock->addConstant(JSValue());
        m_emptyValueRegister = &m_constantPoolRegisters[index];
    }

    return m_emptyValueRegister;
}

RegisterID* BytecodeGenerator::addConstantValue(JSValue v)
{
    if (!v)
        return addConstantEmptyValue();

    int index = m_nextConstantOffset;
    JSValueMap::AddResult result = m_jsValueMap.add(JSValue::encode(v), m_nextConstantOffset);
    if (result.isNewEntry) {
        m_constantPoolRegisters.append(FirstConstantRegisterIndex + m_nextConstantOffset);
        ++m_nextConstantOffset;
        m_codeBlock->addConstant(v);
    } else
        index = result.iterator->value;
    return &m_constantPoolRegisters[index];
}

unsigned BytecodeGenerator::addRegExp(RegExp* r)
{
    return m_codeBlock->addRegExp(r);
}

RegisterID* BytecodeGenerator::emitMove(RegisterID* dst, RegisterID* src)