NodesCodegen.cpp

/*
*  Copyright (C) 1999-2002 Harri Porten (porten@kde.org)
*  Copyright (C) 2001 Peter Kelly (pmk@post.com)
*  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
*  Copyright (C) 2007 Cameron Zwarich (cwzwarich@uwaterloo.ca)
*  Copyright (C) 2007 Maks Orlovich
*  Copyright (C) 2007 Eric Seidel <eric@webkit.org>
*
*  This library is free software; you can redistribute it and/or
*  modify it under the terms of the GNU Library General Public
*  License as published by the Free Software Foundation; either
*  version 2 of the License, or (at your option) any later version.
*
*  This library is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
*  Library General Public License for more details.
*
*  You should have received a copy of the GNU Library General Public License
*  along with this library; see the file COPYING.LIB.  If not, write to
*  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
*  Boston, MA 02110-1301, USA.
*
*/

#include "config.h"
#include "Nodes.h"
#include "NodeConstructors.h"

#include "BytecodeGenerator.h"
#include "CallFrame.h"
#include "Debugger.h"
#include "JIT.h"
#include "JSFunction.h"
#include "JSGlobalObject.h"
#include "JSStaticScopeObject.h"
#include "LabelScope.h"
#include "Lexer.h"
#include "Operations.h"
#include "Parser.h"
#include "PropertyNameArray.h"
#include "RegExpCache.h"
#include "RegExpObject.h"
#include "SamplingTool.h"
#include "UStringConcatenate.h"
#include <wtf/Assertions.h>
#include <wtf/RefCountedLeakCounter.h>
#include <wtf/Threading.h>

using namespace WTF;

namespace JSC {

/*
    Details of the emitBytecode function.

    Return value: The register holding the production's value.
             dst: An optional parameter specifying the most efficient destination at
                  which to store the production's value. The callee must honor dst.

    The dst argument provides for a crude form of copy propagation. For example,

        x = 1

    becomes
    
        load r[x], 1
    
    instead of 

        load r0, 1
        mov r[x], r0
    
    because the assignment node, "x =", passes r[x] as dst to the number node, "1".
*/

// ------------------------------ ThrowableExpressionData --------------------------------

RegisterID* ThrowableExpressionData::emitThrowReferenceError(BytecodeGenerator& generator, const UString& message)
{
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    generator.emitThrowReferenceError(message);
    return generator.newTemporary();
}

// ------------------------------ NullNode -------------------------------------

RegisterID* NullNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitLoad(dst, jsNull());
}

// ------------------------------ BooleanNode ----------------------------------

RegisterID* BooleanNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitLoad(dst, m_value);
}

// ------------------------------ NumberNode -----------------------------------

RegisterID* NumberNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitLoad(dst, m_value);
}

// ------------------------------ StringNode -----------------------------------

RegisterID* StringNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitLoad(dst, m_value);
}

// ------------------------------ RegExpNode -----------------------------------

RegisterID* RegExpNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitNewRegExp(generator.finalDestination(dst), RegExp::create(generator.globalData(), m_pattern.ustring(), regExpFlags(m_flags.ustring())));
}

// ------------------------------ ThisNode -------------------------------------

RegisterID* ThisNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult())
        return 0;
    return generator.moveToDestinationIfNeeded(dst, generator.thisRegister());
}

// ------------------------------ ResolveNode ----------------------------------

bool ResolveNode::isPure(BytecodeGenerator& generator) const
{
    return generator.isLocal(m_ident);
}

RegisterID* ResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (RegisterID* local = generator.registerFor(m_ident)) {
        if (dst == generator.ignoredResult())
            return 0;
        return generator.moveToDestinationIfNeeded(dst, local);
    }
    
    generator.emitExpressionInfo(m_startOffset + m_ident.length(), m_ident.length(), 0);
    return generator.emitResolve(generator.finalDestination(dst), m_ident);
}

// ------------------------------ ArrayNode ------------------------------------

RegisterID* ArrayNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    // FIXME: Should we put all of this code into emitNewArray?

    unsigned length = 0;
    ElementNode* firstPutElement;
    for (firstPutElement = m_element; firstPutElement; firstPutElement = firstPutElement->next()) {
        if (firstPutElement->elision())
            break;
        ++length;
    }

    if (!firstPutElement && !m_elision)
        return generator.emitNewArray(generator.finalDestination(dst), m_element, length);

    RefPtr<RegisterID> array = generator.emitNewArray(generator.tempDestination(dst), m_element, length);

    for (ElementNode* n = firstPutElement; n; n = n->next()) {
        RegisterID* value = generator.emitNode(n->value());
        length += n->elision();
        generator.emitPutByIndex(array.get(), length++, value);
    }

    if (m_elision) {
        RegisterID* value = generator.emitLoad(0, jsNumber(m_elision + length));
        generator.emitPutById(array.get(), generator.propertyNames().length, value);
    }

    return generator.moveToDestinationIfNeeded(dst, array.get());
}

bool ArrayNode::isSimpleArray() const
{
    if (m_elision || m_optional)
        return false;
    for (ElementNode* ptr = m_element; ptr; ptr = ptr->next()) {
        if (ptr->elision())
            return false;
    }
    return true;
}

ArgumentListNode* ArrayNode::toArgumentList(JSGlobalData* globalData) const
{
    ASSERT(!m_elision && !m_optional);
    ElementNode* ptr = m_element;
    if (!ptr)
        return 0;
    ArgumentListNode* head = new (globalData) ArgumentListNode(globalData, ptr->value());
    ArgumentListNode* tail = head;
    ptr = ptr->next();
    for (; ptr; ptr = ptr->next()) {
        ASSERT(!ptr->elision());
        tail = new (globalData) ArgumentListNode(globalData, tail, ptr->value());
    }
    return head;
}

// ------------------------------ ObjectLiteralNode ----------------------------

RegisterID* ObjectLiteralNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
     if (!m_list) {
         if (dst == generator.ignoredResult())
             return 0;
         return generator.emitNewObject(generator.finalDestination(dst));
     }
     return generator.emitNode(dst, m_list);
}

// ------------------------------ PropertyListNode -----------------------------

RegisterID* PropertyListNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> newObj = generator.tempDestination(dst);
    
    generator.emitNewObject(newObj.get());
    
    for (PropertyListNode* p = this; p; p = p->m_next) {
        RegisterID* value = generator.emitNode(p->m_node->m_assign);
        
        switch (p->m_node->m_type) {
            case PropertyNode::Constant: {
                generator.emitDirectPutById(newObj.get(), p->m_node->name(), value);
                break;
            }
            case PropertyNode::Getter: {
                generator.emitPutGetter(newObj.get(), p->m_node->name(), value);
                break;
            }
            case PropertyNode::Setter: {
                generator.emitPutSetter(newObj.get(), p->m_node->name(), value);
                break;
            }
            default:
                ASSERT_NOT_REACHED();
        }
    }
    
    return generator.moveToDestinationIfNeeded(dst, newObj.get());
}

// ------------------------------ BracketAccessorNode --------------------------------

RegisterID* BracketAccessorNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (m_base->isResolveNode() && generator.willResolveToArguments(static_cast<ResolveNode*>(m_base)->identifier())) {
        RegisterID* property = generator.emitNode(m_subscript);
        generator.emitExpressionInfo(divot(), startOffset(), endOffset());    
        return generator.emitGetArgumentByVal(generator.finalDestination(dst), generator.uncheckedRegisterForArguments(), property);
    }

    RefPtr<RegisterID> base = generator.emitNodeForLeftHandSide(m_base, m_subscriptHasAssignments, m_subscript->isPure(generator));
    RegisterID* property = generator.emitNode(m_subscript);
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    return generator.emitGetByVal(generator.finalDestination(dst), base.get(), property);
}

// ------------------------------ DotAccessorNode --------------------------------

RegisterID* DotAccessorNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (m_ident == generator.propertyNames().length) {
        if (!m_base->isResolveNode())
            goto nonArgumentsPath;
        ResolveNode* resolveNode = static_cast<ResolveNode*>(m_base);
        if (!generator.willResolveToArguments(resolveNode->identifier()))
            goto nonArgumentsPath;
        generator.emitExpressionInfo(divot(), startOffset(), endOffset());    
        return generator.emitGetArgumentsLength(generator.finalDestination(dst), generator.uncheckedRegisterForArguments());
    }

nonArgumentsPath:
    RegisterID* base = generator.emitNode(m_base);
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    return generator.emitGetById(generator.finalDestination(dst), base, m_ident);
}

// ------------------------------ ArgumentListNode -----------------------------

RegisterID* ArgumentListNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    ASSERT(m_expr);
    return generator.emitNode(dst, m_expr);
}

// ------------------------------ NewExprNode ----------------------------------

RegisterID* NewExprNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> func = generator.emitNode(m_expr);
    CallArguments callArguments(generator, m_args);
    return generator.emitConstruct(generator.finalDestinationOrIgnored(dst), func.get(), callArguments, divot(), startOffset(), endOffset());
}

CallArguments::CallArguments(BytecodeGenerator& generator, ArgumentsNode* argumentsNode)
    : m_argumentsNode(argumentsNode)
{
    if (generator.shouldEmitProfileHooks())
        m_profileHookRegister = generator.newTemporary();
    m_argv.append(generator.newTemporary());
    if (argumentsNode) {
        for (ArgumentListNode* n = argumentsNode->m_listNode; n; n = n->m_next) {
            m_argv.append(generator.newTemporary());
            // op_call requires the arguments to be a sequential range of registers
            ASSERT(m_argv[m_argv.size() - 1]->index() == m_argv[m_argv.size() - 2]->index() + 1);
        }
    }
}

// ------------------------------ EvalFunctionCallNode ----------------------------------

RegisterID* EvalFunctionCallNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> func = generator.tempDestination(dst);
    CallArguments callArguments(generator, m_args);
    generator.emitExpressionInfo(divot() - startOffset() + 4, 4, 0);
    generator.emitResolveWithBase(callArguments.thisRegister(), func.get(), generator.propertyNames().eval);
    return generator.emitCallEval(generator.finalDestination(dst, func.get()), func.get(), callArguments, divot(), startOffset(), endOffset());
}

// ------------------------------ FunctionCallValueNode ----------------------------------

RegisterID* FunctionCallValueNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> func = generator.emitNode(m_expr);
    CallArguments callArguments(generator, m_args);
    generator.emitLoad(callArguments.thisRegister(), jsUndefined());
    return generator.emitCall(generator.finalDestinationOrIgnored(dst, func.get()), func.get(), callArguments, divot(), startOffset(), endOffset());
}

// ------------------------------ FunctionCallResolveNode ----------------------------------

RegisterID* FunctionCallResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (RefPtr<RegisterID> local = generator.registerFor(m_ident)) {
        CallArguments callArguments(generator, m_args);
        generator.emitLoad(callArguments.thisRegister(), jsUndefined());
        return generator.emitCall(generator.finalDestinationOrIgnored(dst, callArguments.thisRegister()), local.get(), callArguments, divot(), startOffset(), endOffset());
    }

    int index = 0;
    size_t depth = 0;
    JSObject* globalObject = 0;
    bool requiresDynamicChecks = false;
    if (generator.findScopedProperty(m_ident, index, depth, false, requiresDynamicChecks, globalObject) && index != missingSymbolMarker() && !requiresDynamicChecks) {
        RefPtr<RegisterID> func = generator.emitGetScopedVar(generator.newTemporary(), depth, index, globalObject);
        CallArguments callArguments(generator, m_args);
        generator.emitLoad(callArguments.thisRegister(), jsUndefined());
        return generator.emitCall(generator.finalDestinationOrIgnored(dst, func.get()), func.get(), callArguments, divot(), startOffset(), endOffset());
    }

    RefPtr<RegisterID> func = generator.newTemporary();
    CallArguments callArguments(generator, m_args);
    int identifierStart = divot() - startOffset();
    generator.emitExpressionInfo(identifierStart + m_ident.length(), m_ident.length(), 0);
    generator.emitResolveWithBase(callArguments.thisRegister(), func.get(), m_ident);
    return generator.emitCall(generator.finalDestinationOrIgnored(dst, func.get()), func.get(), callArguments, divot(), startOffset(), endOffset());
}

// ------------------------------ FunctionCallBracketNode ----------------------------------

RegisterID* FunctionCallBracketNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    RegisterID* property = generator.emitNode(m_subscript);
    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    RefPtr<RegisterID> function = generator.emitGetByVal(generator.tempDestination(dst), base.get(), property);
    CallArguments callArguments(generator, m_args);
    generator.emitMove(callArguments.thisRegister(), base.get());
    return generator.emitCall(generator.finalDestinationOrIgnored(dst, function.get()), function.get(), callArguments, divot(), startOffset(), endOffset());
}

// ------------------------------ FunctionCallDotNode ----------------------------------

RegisterID* FunctionCallDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> function = generator.tempDestination(dst);
    CallArguments callArguments(generator, m_args);
    generator.emitNode(callArguments.thisRegister(), m_base);
    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    generator.emitMethodCheck();
    generator.emitGetById(function.get(), callArguments.thisRegister(), m_ident);
    return generator.emitCall(generator.finalDestinationOrIgnored(dst, function.get()), function.get(), callArguments, divot(), startOffset(), endOffset());
}

RegisterID* CallFunctionCallDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<Label> realCall = generator.newLabel();
    RefPtr<Label> end = generator.newLabel();
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    RefPtr<RegisterID> function = generator.emitGetById(generator.tempDestination(dst), base.get(), m_ident);
    RefPtr<RegisterID> finalDestinationOrIgnored = generator.finalDestinationOrIgnored(dst, function.get());
    generator.emitJumpIfNotFunctionCall(function.get(), realCall.get());
    {
        if (m_args->m_listNode && m_args->m_listNode->m_expr) {
            ArgumentListNode* oldList = m_args->m_listNode;
            m_args->m_listNode = m_args->m_listNode->m_next;

            RefPtr<RegisterID> realFunction = generator.emitMove(generator.tempDestination(dst), base.get());
            CallArguments callArguments(generator, m_args);
            generator.emitNode(callArguments.thisRegister(), oldList->m_expr);
            generator.emitCall(finalDestinationOrIgnored.get(), realFunction.get(), callArguments, divot(), startOffset(), endOffset());
            generator.emitJump(end.get());

            m_args->m_listNode = oldList;

        } else {
            RefPtr<RegisterID> realFunction = generator.emitMove(generator.tempDestination(dst), base.get());
            CallArguments callArguments(generator, m_args);
            generator.emitLoad(callArguments.thisRegister(), jsUndefined());
            generator.emitCall(finalDestinationOrIgnored.get(), realFunction.get(), callArguments, divot(), startOffset(), endOffset());
            generator.emitJump(end.get());
        }
    }
    generator.emitLabel(realCall.get());
    {
        CallArguments callArguments(generator, m_args);
        generator.emitMove(callArguments.thisRegister(), base.get());
        generator.emitCall(finalDestinationOrIgnored.get(), function.get(), callArguments, divot(), startOffset(), endOffset());
    }
    generator.emitLabel(end.get());
    return finalDestinationOrIgnored.get();
}

static bool areTrivialApplyArguments(ArgumentsNode* args)
{
    return !args->m_listNode || !args->m_listNode->m_expr || !args->m_listNode->m_next
        || (!args->m_listNode->m_next->m_next && args->m_listNode->m_next->m_expr->isSimpleArray());
}

RegisterID* ApplyFunctionCallDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    // A few simple cases can be trivially handled as ordinary function calls.
    // function.apply(), function.apply(arg) -> identical to function.call
    // function.apply(thisArg, [arg0, arg1, ...]) -> can be trivially coerced into function.call(thisArg, arg0, arg1, ...) and saves object allocation
    bool mayBeCall = areTrivialApplyArguments(m_args);

    RefPtr<Label> realCall = generator.newLabel();
    RefPtr<Label> end = generator.newLabel();
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    RefPtr<RegisterID> function = generator.emitGetById(generator.tempDestination(dst), base.get(), m_ident);
    RefPtr<RegisterID> finalDestinationOrIgnored = generator.finalDestinationOrIgnored(dst, function.get());
    generator.emitJumpIfNotFunctionApply(function.get(), realCall.get());
    {
        if (mayBeCall) {
            if (m_args->m_listNode && m_args->m_listNode->m_expr) {
                ArgumentListNode* oldList = m_args->m_listNode;
                if (m_args->m_listNode->m_next) {
                    ASSERT(m_args->m_listNode->m_next->m_expr->isSimpleArray());
                    ASSERT(!m_args->m_listNode->m_next->m_next);
                    m_args->m_listNode = static_cast<ArrayNode*>(m_args->m_listNode->m_next->m_expr)->toArgumentList(generator.globalData());
                    RefPtr<RegisterID> realFunction = generator.emitMove(generator.tempDestination(dst), base.get());
                    CallArguments callArguments(generator, m_args);
                    generator.emitNode(callArguments.thisRegister(), oldList->m_expr);
                    generator.emitCall(finalDestinationOrIgnored.get(), realFunction.get(), callArguments, divot(), startOffset(), endOffset());
                } else {
                    m_args->m_listNode = m_args->m_listNode->m_next;
                    RefPtr<RegisterID> realFunction = generator.emitMove(generator.tempDestination(dst), base.get());
                    CallArguments callArguments(generator, m_args);
                    generator.emitNode(callArguments.thisRegister(), oldList->m_expr);
                    generator.emitCall(finalDestinationOrIgnored.get(), realFunction.get(), callArguments, divot(), startOffset(), endOffset());
                }
                m_args->m_listNode = oldList;
            } else {
                RefPtr<RegisterID> realFunction = generator.emitMove(generator.tempDestination(dst), base.get());
                CallArguments callArguments(generator, m_args);
                generator.emitLoad(callArguments.thisRegister(), jsUndefined());
                generator.emitCall(finalDestinationOrIgnored.get(), realFunction.get(), callArguments, divot(), startOffset(), endOffset());
            }
        } else {
            ASSERT(m_args->m_listNode && m_args->m_listNode->m_next);
            RefPtr<RegisterID> realFunction = generator.emitMove(generator.newTemporary(), base.get());
            RefPtr<RegisterID> argsCountRegister = generator.newTemporary();
            RefPtr<RegisterID> thisRegister = generator.newTemporary();
            RefPtr<RegisterID> argsRegister = generator.newTemporary();
            generator.emitNode(thisRegister.get(), m_args->m_listNode->m_expr);
            ArgumentListNode* args = m_args->m_listNode->m_next;
            bool isArgumentsApply = false;
            if (args->m_expr->isResolveNode()) {
                ResolveNode* resolveNode = static_cast<ResolveNode*>(args->m_expr);
                isArgumentsApply = generator.willResolveToArguments(resolveNode->identifier());
                if (isArgumentsApply)
                    generator.emitMove(argsRegister.get(), generator.uncheckedRegisterForArguments());
            }
            if (!isArgumentsApply)
                generator.emitNode(argsRegister.get(), args->m_expr);
            while ((args = args->m_next))
                generator.emitNode(args->m_expr);

            generator.emitLoadVarargs(argsCountRegister.get(), thisRegister.get(), argsRegister.get());
            generator.emitCallVarargs(finalDestinationOrIgnored.get(), realFunction.get(), thisRegister.get(), argsCountRegister.get(), divot(), startOffset(), endOffset());
        }
        generator.emitJump(end.get());
    }
    generator.emitLabel(realCall.get());
    {
        CallArguments callArguments(generator, m_args);
        generator.emitMove(callArguments.thisRegister(), base.get());
        generator.emitCall(finalDestinationOrIgnored.get(), function.get(), callArguments, divot(), startOffset(), endOffset());
    }
    generator.emitLabel(end.get());
    return finalDestinationOrIgnored.get();
}

// ------------------------------ PostfixResolveNode ----------------------------------

static RegisterID* emitPreIncOrDec(BytecodeGenerator& generator, RegisterID* srcDst, Operator oper)
{
    return (oper == OpPlusPlus) ? generator.emitPreInc(srcDst) : generator.emitPreDec(srcDst);
}

static RegisterID* emitPostIncOrDec(BytecodeGenerator& generator, RegisterID* dst, RegisterID* srcDst, Operator oper)
{
    if (srcDst == dst)
        return generator.emitToJSNumber(dst, srcDst);
    return (oper == OpPlusPlus) ? generator.emitPostInc(dst, srcDst) : generator.emitPostDec(dst, srcDst);
}

RegisterID* PostfixResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (RegisterID* local = generator.registerFor(m_ident)) {
        if (generator.isLocalConstant(m_ident)) {
            if (dst == generator.ignoredResult())
                return 0;
            return generator.emitToJSNumber(generator.finalDestination(dst), local);
        }

        if (dst == generator.ignoredResult())
            return emitPreIncOrDec(generator, local, m_operator);
        return emitPostIncOrDec(generator, generator.finalDestination(dst), local, m_operator);
    }

    int index = 0;
    size_t depth = 0;
    JSObject* globalObject = 0;
    bool requiresDynamicChecks = false;
    if (generator.findScopedProperty(m_ident, index, depth, true, requiresDynamicChecks, globalObject) && index != missingSymbolMarker() && !requiresDynamicChecks) {
        RefPtr<RegisterID> value = generator.emitGetScopedVar(generator.newTemporary(), depth, index, globalObject);
        RegisterID* oldValue;
        if (dst == generator.ignoredResult()) {
            oldValue = 0;
            emitPreIncOrDec(generator, value.get(), m_operator);
        } else {
            oldValue = emitPostIncOrDec(generator, generator.finalDestination(dst), value.get(), m_operator);
        }
        generator.emitPutScopedVar(depth, index, value.get(), globalObject);
        return oldValue;
    }

    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    RefPtr<RegisterID> value = generator.newTemporary();
    RefPtr<RegisterID> base = generator.emitResolveWithBase(generator.newTemporary(), value.get(), m_ident);
    RegisterID* oldValue;
    if (dst == generator.ignoredResult()) {
        oldValue = 0;
        emitPreIncOrDec(generator, value.get(), m_operator);
    } else {
        oldValue = emitPostIncOrDec(generator, generator.finalDestination(dst), value.get(), m_operator);
    }
    generator.emitPutById(base.get(), m_ident, value.get());
    return oldValue;
}

// ------------------------------ PostfixBracketNode ----------------------------------

RegisterID* PostfixBracketNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    RefPtr<RegisterID> property = generator.emitNode(m_subscript);

    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    RefPtr<RegisterID> value = generator.emitGetByVal(generator.newTemporary(), base.get(), property.get());
    RegisterID* oldValue;
    if (dst == generator.ignoredResult()) {
        oldValue = 0;
        if (m_operator == OpPlusPlus)
            generator.emitPreInc(value.get());
        else
            generator.emitPreDec(value.get());
    } else {
        oldValue = (m_operator == OpPlusPlus) ? generator.emitPostInc(generator.finalDestination(dst), value.get()) : generator.emitPostDec(generator.finalDestination(dst), value.get());
    }
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    generator.emitPutByVal(base.get(), property.get(), value.get());
    return oldValue;
}

// ------------------------------ PostfixDotNode ----------------------------------

RegisterID* PostfixDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> base = generator.emitNode(m_base);

    generator.emitExpressionInfo(divot() - m_subexpressionDivotOffset, startOffset() - m_subexpressionDivotOffset, m_subexpressionEndOffset);
    RefPtr<RegisterID> value = generator.emitGetById(generator.newTemporary(), base.get(), m_ident);
    RegisterID* oldValue;
    if (dst == generator.ignoredResult()) {
        oldValue = 0;
        if (m_operator == OpPlusPlus)
            generator.emitPreInc(value.get());
        else
            generator.emitPreDec(value.get());
    } else {
        oldValue = (m_operator == OpPlusPlus) ? generator.emitPostInc(generator.finalDestination(dst), value.get()) : generator.emitPostDec(generator.finalDestination(dst), value.get());
    }
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    generator.emitPutById(base.get(), m_ident, value.get());
    return oldValue;
}

// ------------------------------ PostfixErrorNode -----------------------------------

RegisterID* PostfixErrorNode::emitBytecode(BytecodeGenerator& generator, RegisterID*)
{
    return emitThrowReferenceError(generator, m_operator == OpPlusPlus
        ? "Postfix ++ operator applied to value that is not a reference."
        : "Postfix -- operator applied to value that is not a reference.");
}

// ------------------------------ DeleteResolveNode -----------------------------------

RegisterID* DeleteResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (generator.registerFor(m_ident))
        return generator.emitLoad(generator.finalDestination(dst), false);

    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    RegisterID* base = generator.emitResolveBase(generator.tempDestination(dst), m_ident);
    return generator.emitDeleteById(generator.finalDestination(dst, base), base, m_ident);
}

// ------------------------------ DeleteBracketNode -----------------------------------

RegisterID* DeleteBracketNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> r0 = generator.emitNode(m_base);
    RegisterID* r1 = generator.emitNode(m_subscript);

    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    return generator.emitDeleteByVal(generator.finalDestination(dst), r0.get(), r1);
}

// ------------------------------ DeleteDotNode -----------------------------------

RegisterID* DeleteDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RegisterID* r0 = generator.emitNode(m_base);

    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    return generator.emitDeleteById(generator.finalDestination(dst), r0, m_ident);
}

// ------------------------------ DeleteValueNode -----------------------------------

RegisterID* DeleteValueNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    generator.emitNode(generator.ignoredResult(), m_expr);

    // delete on a non-location expression ignores the value and returns true
    return generator.emitLoad(generator.finalDestination(dst), true);
}

// ------------------------------ VoidNode -------------------------------------

RegisterID* VoidNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult()) {
        generator.emitNode(generator.ignoredResult(), m_expr);
        return 0;
    }
    RefPtr<RegisterID> r0 = generator.emitNode(m_expr);
    return generator.emitLoad(dst, jsUndefined());
}

// ------------------------------ TypeOfValueNode -----------------------------------

RegisterID* TypeOfResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (RegisterID* local = generator.registerFor(m_ident)) {
        if (dst == generator.ignoredResult())
            return 0;
        return generator.emitTypeOf(generator.finalDestination(dst), local);
    }

    RefPtr<RegisterID> scratch = generator.emitResolveBase(generator.tempDestination(dst), m_ident);
    generator.emitGetById(scratch.get(), scratch.get(), m_ident);
    if (dst == generator.ignoredResult())
        return 0;
    return generator.emitTypeOf(generator.finalDestination(dst, scratch.get()), scratch.get());
}

// ------------------------------ TypeOfValueNode -----------------------------------

RegisterID* TypeOfValueNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (dst == generator.ignoredResult()) {
        generator.emitNode(generator.ignoredResult(), m_expr);
        return 0;
    }
    RefPtr<RegisterID> src = generator.emitNode(m_expr);
    return generator.emitTypeOf(generator.finalDestination(dst), src.get());
}

// ------------------------------ PrefixResolveNode ----------------------------------

RegisterID* PrefixResolveNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (RegisterID* local = generator.registerFor(m_ident)) {
        if (generator.isLocalConstant(m_ident)) {
            if (dst == generator.ignoredResult())
                return 0;
            RefPtr<RegisterID> r0 = generator.emitLoad(generator.finalDestination(dst), (m_operator == OpPlusPlus) ? 1.0 : -1.0);
            return generator.emitBinaryOp(op_add, r0.get(), local, r0.get(), OperandTypes());
        }

        emitPreIncOrDec(generator, local, m_operator);
        return generator.moveToDestinationIfNeeded(dst, local);
    }

    int index = 0;
    size_t depth = 0;
    JSObject* globalObject = 0;
    bool requiresDynamicChecks = false;
    if (generator.findScopedProperty(m_ident, index, depth, false, requiresDynamicChecks, globalObject) && index != missingSymbolMarker() && !requiresDynamicChecks) {
        RefPtr<RegisterID> propDst = generator.emitGetScopedVar(generator.tempDestination(dst), depth, index, globalObject);
        emitPreIncOrDec(generator, propDst.get(), m_operator);
        generator.emitPutScopedVar(depth, index, propDst.get(), globalObject);
        return generator.moveToDestinationIfNeeded(dst, propDst.get());
    }

    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    RefPtr<RegisterID> propDst = generator.tempDestination(dst);
    RefPtr<RegisterID> base = generator.emitResolveWithBase(generator.newTemporary(), propDst.get(), m_ident);
    emitPreIncOrDec(generator, propDst.get(), m_operator);
    generator.emitPutById(base.get(), m_ident, propDst.get());
    return generator.moveToDestinationIfNeeded(dst, propDst.get());
}

// ------------------------------ PrefixBracketNode ----------------------------------

RegisterID* PrefixBracketNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    RefPtr<RegisterID> property = generator.emitNode(m_subscript);
    RefPtr<RegisterID> propDst = generator.tempDestination(dst);

    generator.emitExpressionInfo(divot() + m_subexpressionDivotOffset, m_subexpressionStartOffset, endOffset() - m_subexpressionDivotOffset);
    RegisterID* value = generator.emitGetByVal(propDst.get(), base.get(), property.get());
    if (m_operator == OpPlusPlus)
        generator.emitPreInc(value);
    else
        generator.emitPreDec(value);
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    generator.emitPutByVal(base.get(), property.get(), value);
    return generator.moveToDestinationIfNeeded(dst, propDst.get());
}

// ------------------------------ PrefixDotNode ----------------------------------

RegisterID* PrefixDotNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> base = generator.emitNode(m_base);
    RefPtr<RegisterID> propDst = generator.tempDestination(dst);

    generator.emitExpressionInfo(divot() + m_subexpressionDivotOffset, m_subexpressionStartOffset, endOffset() - m_subexpressionDivotOffset);
    RegisterID* value = generator.emitGetById(propDst.get(), base.get(), m_ident);
    if (m_operator == OpPlusPlus)
        generator.emitPreInc(value);
    else
        generator.emitPreDec(value);
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    generator.emitPutById(base.get(), m_ident, value);
    return generator.moveToDestinationIfNeeded(dst, propDst.get());
}

// ------------------------------ PrefixErrorNode -----------------------------------

RegisterID* PrefixErrorNode::emitBytecode(BytecodeGenerator& generator, RegisterID*)
{
    return emitThrowReferenceError(generator, m_operator == OpPlusPlus
        ? "Prefix ++ operator applied to value that is not a reference."
        : "Prefix -- operator applied to value that is not a reference.");
}

// ------------------------------ Unary Operation Nodes -----------------------------------

RegisterID* UnaryOpNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RegisterID* src = generator.emitNode(m_expr);
    return generator.emitUnaryOp(opcodeID(), generator.finalDestination(dst), src);
}


// ------------------------------ LogicalNotNode -----------------------------------

void LogicalNotNode::emitBytecodeInConditionContext(BytecodeGenerator& generator, Label* trueTarget, Label* falseTarget, bool fallThroughMeansTrue)
{
    ASSERT(expr()->hasConditionContextCodegen());

    // reverse the true and false targets
    generator.emitNodeInConditionContext(expr(), falseTarget, trueTarget, !fallThroughMeansTrue);
}


// ------------------------------ Binary Operation Nodes -----------------------------------

// BinaryOpNode::emitStrcat:
//
// This node generates an op_strcat operation.  This opcode can handle concatenation of three or
// more values, where we can determine a set of separate op_add operations would be operating on
// string values.
//
// This function expects to be operating on a graph of AST nodes looking something like this:
//
//     (a)...     (b)
//          \   /
//           (+)     (c)
//              \   /
//      [d]     ((+))
//         \    /
//          [+=]
//
// The assignment operation is optional, if it exists the register holding the value on the
// lefthand side of the assignment should be passing as the optional 'lhs' argument.
//
// The method should be called on the node at the root of the tree of regular binary add
// operations (marked in the diagram with a double set of parentheses).  This node must
// be performing a string concatenation (determined by statically detecting that at least
// one child must be a string).  
//
// Since the minimum number of values being concatenated together is expected to be 3, if
// a lhs to a concatenating assignment is not provided then the  root add should have at
// least one left child that is also an add that can be determined to be operating on strings.
//
RegisterID* BinaryOpNode::emitStrcat(BytecodeGenerator& generator, RegisterID* dst, RegisterID* lhs, ReadModifyResolveNode* emitExpressionInfoForMe)
{
    ASSERT(isAdd());
    ASSERT(resultDescriptor().definitelyIsString());

    // Create a list of expressions for all the adds in the tree of nodes we can convert into
    // a string concatenation.  The rightmost node (c) is added first.  The rightmost node is
    // added first, and the leftmost child is never added, so the vector produced for the
    // example above will be [ c, b ].
    Vector<ExpressionNode*, 16> reverseExpressionList;
    reverseExpressionList.append(m_expr2);

    // Examine the left child of the add.  So long as this is a string add, add its right-child
    // to the list, and keep processing along the left fork.
    ExpressionNode* leftMostAddChild = m_expr1;
    while (leftMostAddChild->isAdd() && leftMostAddChild->resultDescriptor().definitelyIsString()) {
        reverseExpressionList.append(static_cast<AddNode*>(leftMostAddChild)->m_expr2);
        leftMostAddChild = static_cast<AddNode*>(leftMostAddChild)->m_expr1;
    }

    Vector<RefPtr<RegisterID>, 16> temporaryRegisters;

    // If there is an assignment, allocate a temporary to hold the lhs after conversion.
    // We could possibly avoid this (the lhs is converted last anyway, we could let the
    // op_strcat node handle its conversion if required).
    if (lhs)
        temporaryRegisters.append(generator.newTemporary());

    // Emit code for the leftmost node ((a) in the example).
    temporaryRegisters.append(generator.newTemporary());
    RegisterID* leftMostAddChildTempRegister = temporaryRegisters.last().get();
    generator.emitNode(leftMostAddChildTempRegister, leftMostAddChild);

    // Note on ordering of conversions:
    //
    // We maintain the same ordering of conversions as we would see if the concatenations
    // was performed as a sequence of adds (otherwise this optimization could change
    // behaviour should an object have been provided a valueOf or toString method).
    //
    // Considering the above example, the sequnce of execution is:
    //     * evaluate operand (a)
    //     * evaluate operand (b)
    //     * convert (a) to primitive   <-  (this would be triggered by the first add)
    //     * convert (b) to primitive   <-  (ditto)
    //     * evaluate operand (c)
    //     * convert (c) to primitive   <-  (this would be triggered by the second add)
    // And optionally, if there is an assignment:
    //     * convert (d) to primitive   <-  (this would be triggered by the assigning addition)
    //
    // As such we do not plant an op to convert the leftmost child now.  Instead, use
    // 'leftMostAddChildTempRegister' as a flag to trigger generation of the conversion
    // once the second node has been generated.  However, if the leftmost child is an
    // immediate we can trivially determine that no conversion will be required.
    // If this is the case
    if (leftMostAddChild->isString())
        leftMostAddChildTempRegister = 0;

    while (reverseExpressionList.size()) {
        ExpressionNode* node = reverseExpressionList.last();
        reverseExpressionList.removeLast();

        // Emit the code for the current node.
        temporaryRegisters.append(generator.newTemporary());
        generator.emitNode(temporaryRegisters.last().get(), node);

        // On the first iteration of this loop, when we first reach this point we have just
        // generated the second node, which means it is time to convert the leftmost operand.
        if (leftMostAddChildTempRegister) {
            generator.emitToPrimitive(leftMostAddChildTempRegister, leftMostAddChildTempRegister);
            leftMostAddChildTempRegister = 0; // Only do this once.
        }
        // Plant a conversion for this node, if necessary.
        if (!node->isString())
            generator.emitToPrimitive(temporaryRegisters.last().get(), temporaryRegisters.last().get());
    }
    ASSERT(temporaryRegisters.size() >= 3);

    // Certain read-modify nodes require expression info to be emitted *after* m_right has been generated.
    // If this is required the node is passed as 'emitExpressionInfoForMe'; do so now.
    if (emitExpressionInfoForMe)
        generator.emitExpressionInfo(emitExpressionInfoForMe->divot(), emitExpressionInfoForMe->startOffset(), emitExpressionInfoForMe->endOffset());

    // If there is an assignment convert the lhs now.  This will also copy lhs to
    // the temporary register we allocated for it.
    if (lhs)
        generator.emitToPrimitive(temporaryRegisters[0].get(), lhs);

    return generator.emitStrcat(generator.finalDestination(dst, temporaryRegisters[0].get()), temporaryRegisters[0].get(), temporaryRegisters.size());
}

RegisterID* BinaryOpNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    OpcodeID opcodeID = this->opcodeID();

    if (opcodeID == op_add && m_expr1->isAdd() && m_expr1->resultDescriptor().definitelyIsString())
        return emitStrcat(generator, dst);

    if (opcodeID == op_neq) {
        if (m_expr1->isNull() || m_expr2->isNull()) {
            RefPtr<RegisterID> src = generator.tempDestination(dst);
            generator.emitNode(src.get(), m_expr1->isNull() ? m_expr2 : m_expr1);
            return generator.emitUnaryOp(op_neq_null, generator.finalDestination(dst, src.get()), src.get());
        }
    }

    RefPtr<RegisterID> src1 = generator.emitNodeForLeftHandSide(m_expr1, m_rightHasAssignments, m_expr2->isPure(generator));
    RegisterID* src2 = generator.emitNode(m_expr2);
    return generator.emitBinaryOp(opcodeID, generator.finalDestination(dst, src1.get()), src1.get(), src2, OperandTypes(m_expr1->resultDescriptor(), m_expr2->resultDescriptor()));
}

RegisterID* EqualNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    if (m_expr1->isNull() || m_expr2->isNull()) {
        RefPtr<RegisterID> src = generator.tempDestination(dst);
        generator.emitNode(src.get(), m_expr1->isNull() ? m_expr2 : m_expr1);
        return generator.emitUnaryOp(op_eq_null, generator.finalDestination(dst, src.get()), src.get());
    }

    RefPtr<RegisterID> src1 = generator.emitNodeForLeftHandSide(m_expr1, m_rightHasAssignments, m_expr2->isPure(generator));
    RegisterID* src2 = generator.emitNode(m_expr2);
    return generator.emitEqualityOp(op_eq, generator.finalDestination(dst, src1.get()), src1.get(), src2);
}

RegisterID* StrictEqualNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> src1 = generator.emitNodeForLeftHandSide(m_expr1, m_rightHasAssignments, m_expr2->isPure(generator));
    RegisterID* src2 = generator.emitNode(m_expr2);
    return generator.emitEqualityOp(op_stricteq, generator.finalDestination(dst, src1.get()), src1.get(), src2);
}

RegisterID* ReverseBinaryOpNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> src1 = generator.emitNodeForLeftHandSide(m_expr1, m_rightHasAssignments, m_expr2->isPure(generator));
    RegisterID* src2 = generator.emitNode(m_expr2);
    return generator.emitBinaryOp(opcodeID(), generator.finalDestination(dst, src1.get()), src2, src1.get(), OperandTypes(m_expr2->resultDescriptor(), m_expr1->resultDescriptor()));
}

RegisterID* ThrowableBinaryOpNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
{
    RefPtr<RegisterID> src1 = generator.emitNodeForLeftHandSide(m_expr1, m_rightHasAssignments, m_expr2->isPure(generator));
    RegisterID* src2 = generator.emitNode(m_expr2);
    generator.emitExpressionInfo(divot(), startOffset(), endOffset());
    return generator.emitBinaryOp(opcodeID(), generator.finalDestination(dst, src1.get()), src1.get(), src2, OperandTypes(m_expr1->resultDescriptor(), m_expr2->resultDescriptor()));