path: root/ExpressionCompiler.cpp

/*
    This file is part of cpp-ethereum.

    cpp-ethereum is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    cpp-ethereum 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with cpp-ethereum.  If not, see <http://www.gnu.org/licenses/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2014
 * Solidity AST to EVM bytecode compiler for expressions.
 */

#include <utility>
#include <numeric>
#include <boost/range/adaptor/reversed.hpp>
#include <libdevcore/Common.h>
#include <libdevcrypto/SHA3.h>
#include <libsolidity/AST.h>
#include <libsolidity/ExpressionCompiler.h>
#include <libsolidity/CompilerContext.h>
#include <libsolidity/CompilerUtils.h>

using namespace std;

namespace dev
{
namespace solidity
{

void ExpressionCompiler::compileExpression(CompilerContext& _context, Expression const& _expression, bool _optimize)
{
    ExpressionCompiler compiler(_context, _optimize);
    _expression.accept(compiler);
}

void ExpressionCompiler::appendTypeConversion(CompilerContext& _context, Type const& _typeOnStack,
                                              Type const& _targetType, bool _cleanupNeeded)
{
    ExpressionCompiler compiler(_context);
    compiler.appendTypeConversion(_typeOnStack, _targetType, _cleanupNeeded);
}

void ExpressionCompiler::appendStateVariableAccessor(CompilerContext& _context, VariableDeclaration const& _varDecl, bool _optimize)
{
    ExpressionCompiler compiler(_context, _optimize);
    compiler.appendStateVariableAccessor(_varDecl);
}

bool ExpressionCompiler::visit(Assignment const& _assignment)
{
    _assignment.getRightHandSide().accept(*this);
    if (_assignment.getType()->isValueType())
        appendTypeConversion(*_assignment.getRightHandSide().getType(), *_assignment.getType());
    _assignment.getLeftHandSide().accept(*this);
    solAssert(m_currentLValue.isValid(), "LValue not retrieved.");

    Token::Value op = _assignment.getAssignmentOperator();
    if (op != Token::Assign) // compound assignment
    {
        solAssert(_assignment.getType()->isValueType(), "Compound operators not implemented for non-value types.");
        if (m_currentLValue.storesReferenceOnStack())
            m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2;
        m_currentLValue.retrieveValue(_assignment.getLocation(), true);
        appendOrdinaryBinaryOperatorCode(Token::AssignmentToBinaryOp(op), *_assignment.getType());
        if (m_currentLValue.storesReferenceOnStack())
            m_context << eth::Instruction::SWAP1;
    }
    m_currentLValue.storeValue(*_assignment.getRightHandSide().getType(), _assignment.getLocation());
    m_currentLValue.reset();

    return false;
}

bool ExpressionCompiler::visit(UnaryOperation const& _unaryOperation)
{
    //@todo type checking and creating code for an operator should be in the same place:
    // the operator should know how to convert itself and to which types it applies, so
    // put this code together with "Type::acceptsBinary/UnaryOperator" into a class that
    // represents the operator
    if (_unaryOperation.getType()->getCategory() == Type::Category::IntegerConstant)
    {
        m_context << _unaryOperation.getType()->literalValue(nullptr);
        return false;
    }

    _unaryOperation.getSubExpression().accept(*this);

    switch (_unaryOperation.getOperator())
    {
    case Token::Not: // !
        m_context << eth::Instruction::ISZERO;
        break;
    case Token::BitNot: // ~
        m_context << eth::Instruction::NOT;
        break;
    case Token::Delete: // delete
        solAssert(m_currentLValue.isValid(), "LValue not retrieved.");
        m_currentLValue.setToZero(_unaryOperation.getLocation());
        m_currentLValue.reset();
        break;
    case Token::Inc: // ++ (pre- or postfix)
    case Token::Dec: // -- (pre- or postfix)
        solAssert(m_currentLValue.isValid(), "LValue not retrieved.");
        m_currentLValue.retrieveValue(_unaryOperation.getLocation());
        if (!_unaryOperation.isPrefixOperation())
        {
            if (m_currentLValue.storesReferenceOnStack())
                m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2;
            else
                m_context << eth::Instruction::DUP1;
        }
        m_context << u256(1);
        if (_unaryOperation.getOperator() == Token::Inc)
            m_context << eth::Instruction::ADD;
        else
            m_context << eth::Instruction::SWAP1 << eth::Instruction::SUB; // @todo avoid the swap
        // Stack for prefix: [ref] (*ref)+-1
        // Stack for postfix: *ref [ref] (*ref)+-1
        if (m_currentLValue.storesReferenceOnStack())
            m_context << eth::Instruction::SWAP1;
        m_currentLValue.storeValue(*_unaryOperation.getType(), _unaryOperation.getLocation(),
                                   !_unaryOperation.isPrefixOperation());
        m_currentLValue.reset();
        break;
    case Token::Add: // +
        // unary add, so basically no-op
        break;
    case Token::Sub: // -
        m_context << u256(0) << eth::Instruction::SUB;
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid unary operator: " +
                                                                         string(Token::toString(_unaryOperation.getOperator()))));
    }
    return false;
}

bool ExpressionCompiler::visit(BinaryOperation const& _binaryOperation)
{
    Expression const& leftExpression = _binaryOperation.getLeftExpression();
    Expression const& rightExpression = _binaryOperation.getRightExpression();
    Type const& commonType = _binaryOperation.getCommonType();
    Token::Value const c_op = _binaryOperation.getOperator();

    if (c_op == Token::And || c_op == Token::Or) // special case: short-circuiting
        appendAndOrOperatorCode(_binaryOperation);
    else if (commonType.getCategory() == Type::Category::IntegerConstant)
        m_context << commonType.literalValue(nullptr);
    else
    {
        bool cleanupNeeded = commonType.getCategory() == Type::Category::Integer &&
                                (Token::isCompareOp(c_op) || c_op == Token::Div || c_op == Token::Mod);

        // for commutative operators, push the literal as late as possible to allow improved optimization
        auto isLiteral = [](Expression const& _e)
        {
            return dynamic_cast<Literal const*>(&_e) || _e.getType()->getCategory() == Type::Category::IntegerConstant;
        };
        bool swap = m_optimize && Token::isCommutativeOp(c_op) && isLiteral(rightExpression) && !isLiteral(leftExpression);
        if (swap)
        {
            leftExpression.accept(*this);
            appendTypeConversion(*leftExpression.getType(), commonType, cleanupNeeded);
            rightExpression.accept(*this);
            appendTypeConversion(*rightExpression.getType(), commonType, cleanupNeeded);
        }
        else
        {
            rightExpression.accept(*this);
            appendTypeConversion(*rightExpression.getType(), commonType, cleanupNeeded);
            leftExpression.accept(*this);
            appendTypeConversion(*leftExpression.getType(), commonType, cleanupNeeded);
        }
        if (Token::isCompareOp(c_op))
            appendCompareOperatorCode(c_op, commonType);
        else
            appendOrdinaryBinaryOperatorCode(c_op, commonType);
    }

    // do not visit the child nodes, we already did that explicitly
    return false;
}

bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
{
    using Location = FunctionType::Location;
    if (_functionCall.isTypeConversion())
    {
        //@todo struct construction
        solAssert(_functionCall.getArguments().size() == 1, "");
        solAssert(_functionCall.getNames().empty(), "");
        Expression const& firstArgument = *_functionCall.getArguments().front();
        firstArgument.accept(*this);
        appendTypeConversion(*firstArgument.getType(), *_functionCall.getType());
    }
    else
    {
        FunctionType const& function = dynamic_cast<FunctionType const&>(*_functionCall.getExpression().getType());
        TypePointers const& parameterTypes = function.getParameterTypes();
        vector<ASTPointer<Expression const>> const& callArguments = _functionCall.getArguments();
        vector<ASTPointer<ASTString>> const& callArgumentNames = _functionCall.getNames();
        if (!function.takesArbitraryParameters())
            solAssert(callArguments.size() == parameterTypes.size(), "");

        vector<ASTPointer<Expression const>> arguments;
        if (callArgumentNames.empty())
            // normal arguments
            arguments = callArguments;
        else
            // named arguments
            for (auto const& parameterName: function.getParameterNames())
            {
                bool found = false;
                for (size_t j = 0; j < callArgumentNames.size() && !found; j++)
                    if ((found = (parameterName == *callArgumentNames[j])))
                        // we found the actual parameter position
                        arguments.push_back(callArguments[j]);
                solAssert(found, "");
            }

        switch (function.getLocation())
        {
        case Location::Internal:
        {
            // Calling convention: Caller pushes return address and arguments
            // Callee removes them and pushes return values

            eth::AssemblyItem returnLabel = m_context.pushNewTag();
            for (unsigned i = 0; i < arguments.size(); ++i)
            {
                arguments[i]->accept(*this);
                appendTypeConversion(*arguments[i]->getType(), *function.getParameterTypes()[i]);
            }
            _functionCall.getExpression().accept(*this);

            m_context.appendJump();
            m_context << returnLabel;

            unsigned returnParametersSize = CompilerUtils::getSizeOnStack(function.getReturnParameterTypes());
            // callee adds return parameters, but removes arguments and return label
            m_context.adjustStackOffset(returnParametersSize - CompilerUtils::getSizeOnStack(function.getParameterTypes()) - 1);

            // @todo for now, the return value of a function is its first return value, so remove
            // all others
            for (unsigned i = 1; i < function.getReturnParameterTypes().size(); ++i)
                CompilerUtils(m_context).popStackElement(*function.getReturnParameterTypes()[i]);
            break;
        }
        case Location::External:
        case Location::Bare:
            _functionCall.getExpression().accept(*this);
            appendExternalFunctionCall(function, arguments, function.getLocation() == Location::Bare);
            break;
        case Location::Creation:
        {
            _functionCall.getExpression().accept(*this);
            solAssert(!function.gasSet(), "Gas limit set for contract creation.");
            solAssert(function.getReturnParameterTypes().size() == 1, "");
            ContractDefinition const& contract = dynamic_cast<ContractType const&>(
                            *function.getReturnParameterTypes().front()).getContractDefinition();
            // copy the contract's code into memory
            bytes const& bytecode = m_context.getCompiledContract(contract);
            m_context << u256(bytecode.size());
            //@todo could be done by actually appending the Assembly, but then we probably need to compile
            // multiple times. Will revisit once external fuctions are inlined.
            m_context.appendData(bytecode);
            //@todo copy to memory position 0, shift as soon as we use memory
            m_context << u256(0) << eth::Instruction::CODECOPY;

            m_context << u256(bytecode.size());
            appendArgumentsCopyToMemory(arguments, function.getParameterTypes());
            // size, offset, endowment
            m_context << u256(0);
            if (function.valueSet())
                m_context << eth::dupInstruction(3);
            else
                m_context << u256(0);
            m_context << eth::Instruction::CREATE;
            if (function.valueSet())
                m_context << eth::swapInstruction(1) << eth::Instruction::POP;
            break;
        }
        case Location::SetGas:
        {
            // stack layout: contract_address function_id [gas] [value]
            _functionCall.getExpression().accept(*this);
            arguments.front()->accept(*this);
            appendTypeConversion(*arguments.front()->getType(), IntegerType(256), true);
            // Note that function is not the original function, but the ".gas" function.
            // Its values of gasSet and valueSet is equal to the original function's though.
            unsigned stackDepth = (function.gasSet() ? 1 : 0) + (function.valueSet() ? 1 : 0);
            if (stackDepth > 0)
                m_context << eth::swapInstruction(stackDepth);
            if (function.gasSet())
                m_context << eth::Instruction::POP;
            break;
        }
        case Location::SetValue:
            // stack layout: contract_address function_id [gas] [value]
            _functionCall.getExpression().accept(*this);
            // Note that function is not the original function, but the ".value" function.
            // Its values of gasSet and valueSet is equal to the original function's though.
            if (function.valueSet())
                m_context << eth::Instruction::POP;
            arguments.front()->accept(*this);
            break;
        case Location::Send:
            _functionCall.getExpression().accept(*this);
            m_context << u256(0); // 0 gas, we do not want to execute code
            arguments.front()->accept(*this);
            appendTypeConversion(*arguments.front()->getType(),
                                 *function.getParameterTypes().front(), true);
            appendExternalFunctionCall(FunctionType(TypePointers{}, TypePointers{},
                                                    Location::External, false, true, true), {}, true);
            break;
        case Location::Suicide:
            arguments.front()->accept(*this);
            appendTypeConversion(*arguments.front()->getType(), *function.getParameterTypes().front(), true);
            m_context << eth::Instruction::SUICIDE;
            break;
        case Location::SHA3:
        {
            m_context << u256(0);
            appendArgumentsCopyToMemory(arguments, TypePointers(), function.padArguments());
            m_context << u256(0) << eth::Instruction::SHA3;
            break;
        }
        case Location::Log0:
        case Location::Log1:
        case Location::Log2:
        case Location::Log3:
        case Location::Log4:
        {
            unsigned logNumber = int(function.getLocation()) - int(Location::Log0);
            for (unsigned arg = logNumber; arg > 0; --arg)
            {
                arguments[arg]->accept(*this);
                appendTypeConversion(*arguments[arg]->getType(), *function.getParameterTypes()[arg], true);
            }
            m_context << u256(0);
            appendExpressionCopyToMemory(*function.getParameterTypes().front(), *arguments.front());
            m_context << u256(0) << eth::logInstruction(logNumber);
            break;
        }
        case Location::Event:
        {
            _functionCall.getExpression().accept(*this);
            auto const& event = dynamic_cast<EventDefinition const&>(function.getDeclaration());
            unsigned numIndexed = 0;
            // All indexed arguments go to the stack
            for (unsigned arg = arguments.size(); arg > 0; --arg)
                if (event.getParameters()[arg - 1]->isIndexed())
                {
                    ++numIndexed;
                    arguments[arg - 1]->accept(*this);
                    appendTypeConversion(*arguments[arg - 1]->getType(),
                                         *function.getParameterTypes()[arg - 1], true);
                }
            m_context << u256(h256::Arith(dev::sha3(function.getCanonicalSignature(event.getName()))));
            ++numIndexed;
            solAssert(numIndexed <= 4, "Too many indexed arguments.");
            // Copy all non-indexed arguments to memory (data)
            m_context << u256(0);
            for (unsigned arg = 0; arg < arguments.size(); ++arg)
                if (!event.getParameters()[arg]->isIndexed())
                    appendExpressionCopyToMemory(*function.getParameterTypes()[arg], *arguments[arg]);
            m_context << u256(0) << eth::logInstruction(numIndexed);
            break;
        }
        case Location::BlockHash:
        {
            arguments[0]->accept(*this);
            appendTypeConversion(*arguments[0]->getType(), *function.getParameterTypes()[0], true);
            m_context << eth::Instruction::BLOCKHASH;
            break;
        }
        case Location::ECRecover:
        case Location::SHA256:
        case Location::RIPEMD160:
        {
            static const map<Location, u256> contractAddresses{{Location::ECRecover, 1},
                                                               {Location::SHA256, 2},
                                                               {Location::RIPEMD160, 3}};
            m_context << contractAddresses.find(function.getLocation())->second;
            appendExternalFunctionCall(function, arguments, true);
            break;
        }
        default:
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid function type."));
        }
    }
    return false;
}

bool ExpressionCompiler::visit(NewExpression const&)
{
    // code is created for the function call (CREATION) only
    return false;
}

void ExpressionCompiler::endVisit(MemberAccess const& _memberAccess)
{
    ASTString const& member = _memberAccess.getMemberName();
    switch (_memberAccess.getExpression().getType()->getCategory())
    {
    case Type::Category::Contract:
    {
        bool alsoSearchInteger = false;
        ContractType const& type = dynamic_cast<ContractType const&>(*_memberAccess.getExpression().getType());
        if (type.isSuper())
            m_context << m_context.getSuperFunctionEntryLabel(member, type.getContractDefinition()).pushTag();
        else
        {
            // ordinary contract type
            u256 identifier = type.getFunctionIdentifier(member);
            if (identifier != Invalid256)
            {
                appendTypeConversion(type, IntegerType(0, IntegerType::Modifier::Address), true);
                m_context << identifier;
            }
            else
                // not found in contract, search in members inherited from address
                alsoSearchInteger = true;
        }
        if (!alsoSearchInteger)
            break;
    }
    case Type::Category::Integer:
        if (member == "balance")
        {
            appendTypeConversion(*_memberAccess.getExpression().getType(),
                                 IntegerType(0, IntegerType::Modifier::Address), true);
            m_context << eth::Instruction::BALANCE;
        }
        else if (member == "send" || member.substr(0, min<size_t>(member.size(), 4)) == "call")
            appendTypeConversion(*_memberAccess.getExpression().getType(),
                                 IntegerType(0, IntegerType::Modifier::Address), true);
        else
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid member access to integer."));
        break;
    case Type::Category::Function:
        solAssert(!!_memberAccess.getExpression().getType()->getMemberType(member),
                 "Invalid member access to function.");
        break;
    case Type::Category::Magic:
        // we can ignore the kind of magic and only look at the name of the member
        if (member == "coinbase")
            m_context << eth::Instruction::COINBASE;
        else if (member == "timestamp")
            m_context << eth::Instruction::TIMESTAMP;
        else if (member == "difficulty")
            m_context << eth::Instruction::DIFFICULTY;
        else if (member == "number")
            m_context << eth::Instruction::NUMBER;
        else if (member == "gaslimit")
            m_context << eth::Instruction::GASLIMIT;
        else if (member == "sender")
            m_context << eth::Instruction::CALLER;
        else if (member == "value")
            m_context << eth::Instruction::CALLVALUE;
        else if (member == "origin")
            m_context << eth::Instruction::ORIGIN;
        else if (member == "gas")
            m_context << eth::Instruction::GAS;
        else if (member == "gasprice")
            m_context << eth::Instruction::GASPRICE;
        else if (member == "data")
        {
            // nothing to store on the stack
        }
        else
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown magic member."));
        break;
    case Type::Category::Struct:
    {
        StructType const& type = dynamic_cast<StructType const&>(*_memberAccess.getExpression().getType());
        m_context << type.getStorageOffsetOfMember(member) << eth::Instruction::ADD;
        m_currentLValue = LValue(m_context, LValue::LValueType::Storage, _memberAccess.getType());
        m_currentLValue.retrieveValueIfLValueNotRequested(_memberAccess);
        break;
    }
    case Type::Category::Enum:
    {
        EnumType const& type = dynamic_cast<EnumType const&>(*_memberAccess.getExpression().getType());
        m_context << type.getMemberValue(_memberAccess.getMemberName());
        break;
    }
    case Type::Category::TypeType:
    {
        TypeType const& type = dynamic_cast<TypeType const&>(*_memberAccess.getExpression().getType());
        if (!type.getMembers().getMemberType(member))
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid member access to " + type.toString()));

        if (auto contractType = dynamic_cast<ContractType const*>(type.getActualType().get()))
        {
            ContractDefinition const& contract = contractType->getContractDefinition();
            for (ASTPointer<FunctionDefinition> const& function: contract.getDefinedFunctions())
                if (function->getName() == member)
                {
                    m_context << m_context.getFunctionEntryLabel(*function).pushTag();
                    return;
                }
        }
        else if (auto enumType = dynamic_cast<EnumType const*>(type.getActualType().get()))
            m_context << enumType->getMemberValue(_memberAccess.getMemberName());
        break;
    }
    case Type::Category::ByteArray:
    {
        solAssert(member == "length", "Illegal bytearray member.");
        m_context << eth::Instruction::SLOAD;
        break;
    }
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Member access to unknown type."));
    }
}

bool ExpressionCompiler::visit(IndexAccess const& _indexAccess)
{
    _indexAccess.getBaseExpression().accept(*this);

    Type const& baseType = *_indexAccess.getBaseExpression().getType();
    solAssert(baseType.getCategory() == Type::Category::Mapping, "");
    Type const& keyType = *dynamic_cast<MappingType const&>(baseType).getKeyType();
    m_context << u256(0);
    appendExpressionCopyToMemory(keyType, _indexAccess.getIndexExpression());
    solAssert(baseType.getSizeOnStack() == 1,
              "Unexpected: Not exactly one stack slot taken by subscriptable expression.");
    m_context << eth::Instruction::SWAP1;
    appendTypeMoveToMemory(IntegerType(256));
    m_context << u256(0) << eth::Instruction::SHA3;

    m_currentLValue = LValue(m_context, LValue::LValueType::Storage, _indexAccess.getType());
    m_currentLValue.retrieveValueIfLValueNotRequested(_indexAccess);

    return false;
}

void ExpressionCompiler::endVisit(Identifier const& _identifier)
{
    Declaration const* declaration = _identifier.getReferencedDeclaration();
    if (MagicVariableDeclaration const* magicVar = dynamic_cast<MagicVariableDeclaration const*>(declaration))
    {
        if (magicVar->getType()->getCategory() == Type::Category::Contract)
            // "this" or "super"
            if (!dynamic_cast<ContractType const&>(*magicVar->getType()).isSuper())
                m_context << eth::Instruction::ADDRESS;
    }
    else if (FunctionDefinition const* functionDef = dynamic_cast<FunctionDefinition const*>(declaration))
        m_context << m_context.getVirtualFunctionEntryLabel(*functionDef).pushTag();
    else if (dynamic_cast<VariableDeclaration const*>(declaration))
    {
        m_currentLValue.fromIdentifier(_identifier, *declaration);
        m_currentLValue.retrieveValueIfLValueNotRequested(_identifier);
    }
    else if (dynamic_cast<ContractDefinition const*>(declaration))
    {
        // no-op
    }
    else if (dynamic_cast<EventDefinition const*>(declaration))
    {
        // no-op
    }
    else if (dynamic_cast<EnumDefinition const*>(declaration))
    {
        // no-op
    }
    else
    {
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Identifier type not expected in expression context."));
    }
}

void ExpressionCompiler::endVisit(Literal const& _literal)
{
    switch (_literal.getType()->getCategory())
    {
    case Type::Category::IntegerConstant:
    case Type::Category::Bool:
    case Type::Category::String:
        m_context << _literal.getType()->literalValue(&_literal);
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Only integer, boolean and string literals implemented for now."));
    }
}

void ExpressionCompiler::appendAndOrOperatorCode(BinaryOperation const& _binaryOperation)
{
    Token::Value const c_op = _binaryOperation.getOperator();
    solAssert(c_op == Token::Or || c_op == Token::And, "");

    _binaryOperation.getLeftExpression().accept(*this);
    m_context << eth::Instruction::DUP1;
    if (c_op == Token::And)
        m_context << eth::Instruction::ISZERO;
    eth::AssemblyItem endLabel = m_context.appendConditionalJump();
    m_context << eth::Instruction::POP;
    _binaryOperation.getRightExpression().accept(*this);
    m_context << endLabel;
}

void ExpressionCompiler::appendCompareOperatorCode(Token::Value _operator, Type const& _type)
{
    if (_operator == Token::Equal || _operator == Token::NotEqual)
    {
        m_context << eth::Instruction::EQ;
        if (_operator == Token::NotEqual)
            m_context << eth::Instruction::ISZERO;
    }
    else
    {
        IntegerType const& type = dynamic_cast<IntegerType const&>(_type);
        bool const c_isSigned = type.isSigned();

        switch (_operator)
        {
        case Token::GreaterThanOrEqual:
            m_context << (c_isSigned ? eth::Instruction::SLT : eth::Instruction::LT)
                      << eth::Instruction::ISZERO;
            break;
        case Token::LessThanOrEqual:
            m_context << (c_isSigned ? eth::Instruction::SGT : eth::Instruction::GT)
                      << eth::Instruction::ISZERO;
            break;
        case Token::GreaterThan:
            m_context << (c_isSigned ? eth::Instruction::SGT : eth::Instruction::GT);
            break;
        case Token::LessThan:
            m_context << (c_isSigned ? eth::Instruction::SLT : eth::Instruction::LT);
            break;
        default:
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown comparison operator."));
        }
    }
}

void ExpressionCompiler::appendOrdinaryBinaryOperatorCode(Token::Value _operator, Type const& _type)
{
    if (Token::isArithmeticOp(_operator))
        appendArithmeticOperatorCode(_operator, _type);
    else if (Token::isBitOp(_operator))
        appendBitOperatorCode(_operator);
    else if (Token::isShiftOp(_operator))
        appendShiftOperatorCode(_operator);
    else
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown binary operator."));
}

void ExpressionCompiler::appendArithmeticOperatorCode(Token::Value _operator, Type const& _type)
{
    IntegerType const& type = dynamic_cast<IntegerType const&>(_type);
    bool const c_isSigned = type.isSigned();

    switch (_operator)
    {
    case Token::Add:
        m_context << eth::Instruction::ADD;
        break;
    case Token::Sub:
        m_context << eth::Instruction::SUB;
        break;
    case Token::Mul:
        m_context << eth::Instruction::MUL;
        break;
    case Token::Div:
        m_context  << (c_isSigned ? eth::Instruction::SDIV : eth::Instruction::DIV);
        break;
    case Token::Mod:
        m_context << (c_isSigned ? eth::Instruction::SMOD : eth::Instruction::MOD);
        break;
    case Token::Exp:
        m_context << eth::Instruction::EXP;
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown arithmetic operator."));
    }
}

void ExpressionCompiler::appendBitOperatorCode(Token::Value _operator)
{
    switch (_operator)
    {
    case Token::BitOr:
        m_context << eth::Instruction::OR;
        break;
    case Token::BitAnd:
        m_context << eth::Instruction::AND;
        break;
    case Token::BitXor:
        m_context << eth::Instruction::XOR;
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown bit operator."));
    }
}

void ExpressionCompiler::appendShiftOperatorCode(Token::Value _operator)
{
    BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Shift operators not yet implemented."));
    switch (_operator)
    {
    case Token::SHL:
        break;
    case Token::SAR:
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown shift operator."));
    }
}

void ExpressionCompiler::appendTypeConversion(Type const& _typeOnStack, Type const& _targetType, bool _cleanupNeeded)
{
    // For a type extension, we need to remove all higher-order bits that we might have ignored in
    // previous operations.
    // @todo: store in the AST whether the operand might have "dirty" higher order bits

    if (_typeOnStack == _targetType && !_cleanupNeeded)
        return;
    Type::Category stackTypeCategory = _typeOnStack.getCategory();
    Type::Category targetTypeCategory = _targetType.getCategory();

    if (stackTypeCategory == Type::Category::String)
    {
        StaticStringType const& typeOnStack = dynamic_cast<StaticStringType const&>(_typeOnStack);
        if (targetTypeCategory == Type::Category::Integer)
        {
            // conversion from string to hash. no need to clean the high bit
            // only to shift right because of opposite alignment
            IntegerType const& targetIntegerType = dynamic_cast<IntegerType const&>(_targetType);
            solAssert(targetIntegerType.isHash(), "Only conversion between String and Hash is allowed.");
            solAssert(targetIntegerType.getNumBits() == typeOnStack.getNumBytes() * 8, "The size should be the same.");
            m_context << (u256(1) << (256 - typeOnStack.getNumBytes() * 8)) << eth::Instruction::SWAP1 << eth::Instruction::DIV;
        }
        else
        {
            // clear lower-order bytes for conversion to shorter strings - we always clean
            solAssert(targetTypeCategory == Type::Category::String, "Invalid type conversion requested.");
            StaticStringType const& targetType = dynamic_cast<StaticStringType const&>(_targetType);
            if (targetType.getNumBytes() < typeOnStack.getNumBytes())
            {
                if (targetType.getNumBytes() == 0)
                    m_context << eth::Instruction::DUP1 << eth::Instruction::XOR;
                else
                    m_context << (u256(1) << (256 - targetType.getNumBytes() * 8))
                              << eth::Instruction::DUP1 << eth::Instruction::SWAP2
                              << eth::Instruction::DIV << eth::Instruction::MUL;
            }
        }
    }
    else if (stackTypeCategory == Type::Category::Enum)
        solAssert(targetTypeCategory == Type::Category::Integer ||
            targetTypeCategory == Type::Category::Enum, "");
    else if (stackTypeCategory == Type::Category::Integer || stackTypeCategory == Type::Category::Contract ||
             stackTypeCategory == Type::Category::IntegerConstant)
    {
        if (targetTypeCategory == Type::Category::String && stackTypeCategory == Type::Category::Integer)
        {
            // conversion from hash to string. no need to clean the high bit
            // only to shift left because of opposite alignment
            StaticStringType const& targetStringType = dynamic_cast<StaticStringType const&>(_targetType);
            IntegerType const& typeOnStack = dynamic_cast<IntegerType const&>(_typeOnStack);
            solAssert(typeOnStack.isHash(), "Only conversion between String and Hash is allowed.");
            solAssert(typeOnStack.getNumBits() == targetStringType.getNumBytes() * 8, "The size should be the same.");
            m_context << (u256(1) << (256 - typeOnStack.getNumBits())) << eth::Instruction::MUL;
        }
        else if (targetTypeCategory == Type::Category::Enum)
            // just clean
            appendTypeConversion(_typeOnStack, *_typeOnStack.getRealType(), true);
        else
        {
            solAssert(targetTypeCategory == Type::Category::Integer || targetTypeCategory == Type::Category::Contract, "");
            IntegerType addressType(0, IntegerType::Modifier::Address);
            IntegerType const& targetType = targetTypeCategory == Type::Category::Integer
                                            ? dynamic_cast<IntegerType const&>(_targetType) : addressType;
            if (stackTypeCategory == Type::Category::IntegerConstant)
            {
                IntegerConstantType const& constType = dynamic_cast<IntegerConstantType const&>(_typeOnStack);
                // We know that the stack is clean, we only have to clean for a narrowing conversion
                // where cleanup is forced.
                if (targetType.getNumBits() < constType.getIntegerType()->getNumBits() && _cleanupNeeded)
                    appendHighBitsCleanup(targetType);
            }
            else
            {
                IntegerType const& typeOnStack = stackTypeCategory == Type::Category::Integer
                                                ? dynamic_cast<IntegerType const&>(_typeOnStack) : addressType;
                // Widening: clean up according to source type width
                // Non-widening and force: clean up according to target type bits
                if (targetType.getNumBits() > typeOnStack.getNumBits())
                    appendHighBitsCleanup(typeOnStack);
                else if (_cleanupNeeded)
                    appendHighBitsCleanup(targetType);
            }
        }
    }
    else if (_typeOnStack != _targetType)
        // All other types should not be convertible to non-equal types.
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid type conversion requested."));
}

void ExpressionCompiler::appendHighBitsCleanup(IntegerType const& _typeOnStack)
{
    if (_typeOnStack.getNumBits() == 256)
        return;
    else if (_typeOnStack.isSigned())
        m_context << u256(_typeOnStack.getNumBits() / 8 - 1) << eth::Instruction::SIGNEXTEND;
    else
        m_context << ((u256(1) << _typeOnStack.getNumBits()) - 1) << eth::Instruction::AND;
}

void ExpressionCompiler::appendExternalFunctionCall(FunctionType const& _functionType,
                                                    vector<ASTPointer<Expression const>> const& _arguments,
                                                    bool bare)
{
    solAssert(_functionType.takesArbitraryParameters() ||
              _arguments.size() == _functionType.getParameterTypes().size(), "");

    // Assumed stack content here:
    // <stack top>
    // value [if _functionType.valueSet()]
    // gas [if _functionType.gasSet()]
    // function identifier [unless bare]
    // contract address

    unsigned gasValueSize = (_functionType.gasSet() ? 1 : 0) + (_functionType.valueSet() ? 1 : 0);

    unsigned contractStackPos = m_context.currentToBaseStackOffset(1 + gasValueSize + (bare ? 0 : 1));
    unsigned gasStackPos = m_context.currentToBaseStackOffset(gasValueSize);
    unsigned valueStackPos = m_context.currentToBaseStackOffset(1);

    //@todo only return the first return value for now
    Type const* firstType = _functionType.getReturnParameterTypes().empty() ? nullptr :
                            _functionType.getReturnParameterTypes().front().get();
    unsigned retSize = firstType ? CompilerUtils::getPaddedSize(firstType->getCalldataEncodedSize()) : 0;
    m_context << u256(retSize) << u256(0);

    if (bare)
        m_context << u256(0);
    else
    {
        // copy function identifier
        m_context << eth::dupInstruction(gasValueSize + 3);
        CompilerUtils(m_context).storeInMemory(0, IntegerType(CompilerUtils::dataStartOffset * 8));
        m_context << u256(CompilerUtils::dataStartOffset);
    }

    // For bare call, activate "4 byte pad exception": If the first argument has exactly 4 bytes,
    // do not pad it to 32 bytes.
    appendArgumentsCopyToMemory(_arguments, _functionType.getParameterTypes(),
                                _functionType.padArguments(), bare);

    // CALL arguments: outSize, outOff, inSize, (already present up to here)
    // inOff, value, addr, gas (stack top)
    m_context << u256(0);
    if (_functionType.valueSet())
        m_context << eth::dupInstruction(m_context.baseToCurrentStackOffset(valueStackPos));
    else
        m_context << u256(0);
    m_context << eth::dupInstruction(m_context.baseToCurrentStackOffset(contractStackPos));

    if (_functionType.gasSet())
        m_context << eth::dupInstruction(m_context.baseToCurrentStackOffset(gasStackPos));
    else
        // send all gas except for the 21 needed to execute "SUB" and "CALL"
        m_context << u256(21) << eth::Instruction::GAS << eth::Instruction::SUB;
    m_context << eth::Instruction::CALL
              << eth::Instruction::POP; // @todo do not ignore failure indicator
    if (_functionType.valueSet())
        m_context << eth::Instruction::POP;
    if (_functionType.gasSet())
        m_context << eth::Instruction::POP;
    if (!bare)
        m_context << eth::Instruction::POP;
    m_context << eth::Instruction::POP; // pop contract address

    if (retSize > 0)
    {
        bool const c_leftAligned = firstType->getCategory() == Type::Category::String;
        CompilerUtils(m_context).loadFromMemory(0, retSize, c_leftAligned, false, true);
    }
}

void ExpressionCompiler::appendArgumentsCopyToMemory(vector<ASTPointer<Expression const>> const& _arguments,
                                                     TypePointers const& _types,
                                                     bool _padToWordBoundaries,
                                                     bool _padExceptionIfFourBytes)
{
    solAssert(_types.empty() || _types.size() == _arguments.size(), "");
    for (size_t i = 0; i < _arguments.size(); ++i)
    {
        _arguments[i]->accept(*this);
        TypePointer const& expectedType = _types.empty() ? _arguments[i]->getType()->getRealType() : _types[i];
        appendTypeConversion(*_arguments[i]->getType(), *expectedType, true);
        bool pad = _padToWordBoundaries;
        // Do not pad if the first argument has exactly four bytes
        if (i == 0 && pad && _padExceptionIfFourBytes && expectedType->getCalldataEncodedSize() == 4)
            pad = false;
        appendTypeMoveToMemory(*expectedType, pad);
    }
}

void ExpressionCompiler::appendTypeMoveToMemory(Type const& _type, bool _padToWordBoundaries)
{
    CompilerUtils(m_context).storeInMemoryDynamic(_type, _padToWordBoundaries);
}

void ExpressionCompiler::appendExpressionCopyToMemory(Type const& _expectedType, Expression const& _expression)
{
    _expression.accept(*this);
    appendTypeConversion(*_expression.getType(), _expectedType, true);
    appendTypeMoveToMemory(_expectedType);
}

void ExpressionCompiler::appendStateVariableAccessor(VariableDeclaration const& _varDecl)
{
    FunctionType accessorType(_varDecl);

    unsigned length = 0;
    TypePointers const& paramTypes = accessorType.getParameterTypes();
    // move arguments to memory
    for (TypePointer const& paramType: boost::adaptors::reverse(paramTypes))
        length += CompilerUtils(m_context).storeInMemory(length, *paramType, true);

    // retrieve the position of the variable
    m_context << m_context.getStorageLocationOfVariable(_varDecl);
    TypePointer returnType = _varDecl.getType();

    for (TypePointer const& paramType: paramTypes)
    {
        // move offset to memory
        CompilerUtils(m_context).storeInMemory(length);
        unsigned argLen = CompilerUtils::getPaddedSize(paramType->getCalldataEncodedSize());
        length -= argLen;
        m_context << u256(argLen + 32) << u256(length) << eth::Instruction::SHA3;

        returnType = dynamic_cast<MappingType const&>(*returnType).getValueType();
    }

    unsigned retSizeOnStack = 0;
    solAssert(accessorType.getReturnParameterTypes().size() >= 1, "");
    if (StructType const* structType = dynamic_cast<StructType const*>(returnType.get()))
    {
        auto const& names = accessorType.getReturnParameterNames();
        auto const& types = accessorType.getReturnParameterTypes();
        // struct
        for (size_t i = 0; i < names.size(); ++i)
        {
            m_context << eth::Instruction::DUP1
                      << structType->getStorageOffsetOfMember(names[i])
                      << eth::Instruction::ADD;
            m_currentLValue = LValue(m_context, LValue::LValueType::Storage, types[i]);
            m_currentLValue.retrieveValue(Location(), true);
            solAssert(types[i]->getSizeOnStack() == 1, "Returning struct elements with stack size != 1 not yet implemented.");
            m_context << eth::Instruction::SWAP1;
            retSizeOnStack += types[i]->getSizeOnStack();
        }
        m_context << eth::Instruction::POP;
    }
    else
    {
        // simple value
        solAssert(accessorType.getReturnParameterTypes().size() == 1, "");
        m_currentLValue = LValue(m_context, LValue::LValueType::Storage, returnType);
        m_currentLValue.retrieveValue(Location(), true);
        retSizeOnStack = returnType->getSizeOnStack();
    }
    solAssert(retSizeOnStack <= 15, "Stack too deep.");
    m_context << eth::dupInstruction(retSizeOnStack + 1) << eth::Instruction::JUMP;
}

ExpressionCompiler::LValue::LValue(CompilerContext& _compilerContext, LValueType _type,
                                   TypePointer const& _dataType, unsigned _baseStackOffset):
    m_context(&_compilerContext), m_type(_type), m_dataType(_dataType),
    m_baseStackOffset(_baseStackOffset)
{
    //@todo change the type cast for arrays
    solAssert(m_dataType->getStorageSize() <= numeric_limits<unsigned>::max(),
              "The storage size of " + m_dataType->toString() + " should fit in unsigned");
    if (m_type == LValueType::Storage)
        m_size = unsigned(m_dataType->getStorageSize());
    else
        m_size = unsigned(m_dataType->getSizeOnStack());
}

void ExpressionCompiler::LValue::fromIdentifier(Identifier const& _identifier, Declaration const& _declaration)
{
    if (m_context->isLocalVariable(&_declaration))
    {
        m_type = LValueType::Stack;
        m_dataType = _identifier.getType();
        m_size = m_dataType->getSizeOnStack();
        m_baseStackOffset = m_context->getBaseStackOffsetOfVariable(_declaration);
    }
    else if (m_context->isStateVariable(&_declaration))
    {
        *m_context << m_context->getStorageLocationOfVariable(_declaration);
        m_type = LValueType::Storage;
        m_dataType = _identifier.getType();
        solAssert(m_dataType->getStorageSize() <= numeric_limits<unsigned>::max(),
                  "The storage size of " + m_dataType->toString() + " should fit in an unsigned");
        m_size = unsigned(m_dataType->getStorageSize());    }
    else
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_identifier.getLocation())
                                                      << errinfo_comment("Identifier type not supported or identifier not found."));
}

void ExpressionCompiler::LValue::retrieveValue(Location const& _location, bool _remove) const
{
    switch (m_type)
    {
    case LValueType::Stack:
    {
        unsigned stackPos = m_context->baseToCurrentStackOffset(unsigned(m_baseStackOffset));
        if (stackPos >= 15) //@todo correct this by fetching earlier or moving to memory
            BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_location)
                                                  << errinfo_comment("Stack too deep."));
        for (unsigned i = 0; i < m_size; ++i)
            *m_context << eth::dupInstruction(stackPos + 1);
        break;
    }
    case LValueType::Storage:
        retrieveValueFromStorage(_remove);
        break;
    case LValueType::Memory:
        if (!m_dataType->isValueType())
            break; // no distinction between value and reference for non-value types
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Location type not yet implemented."));
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Unsupported location type."));
        break;
    }
}

void ExpressionCompiler::LValue::retrieveValueFromStorage(bool _remove) const
{
    if (!m_dataType->isValueType())
        return; // no distinction between value and reference for non-value types
    if (!_remove)
        *m_context << eth::Instruction::DUP1;
    if (m_size == 1)
        *m_context << eth::Instruction::SLOAD;
    else
        for (unsigned i = 0; i < m_size; ++i)
        {
            *m_context << eth::Instruction::DUP1 << eth::Instruction::SLOAD << eth::Instruction::SWAP1;
            if (i + 1 < m_size)
                *m_context << u256(1) << eth::Instruction::ADD;
            else
                *m_context << eth::Instruction::POP;
        }
}

void ExpressionCompiler::LValue::storeValue(Type const& _sourceType, Location const& _location, bool _move) const
{
    switch (m_type)
    {
    case LValueType::Stack:
    {
        unsigned stackDiff = m_context->baseToCurrentStackOffset(unsigned(m_baseStackOffset)) - m_size + 1;
        if (stackDiff > 16)
            BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_location)
                                                  << errinfo_comment("Stack too deep."));
        else if (stackDiff > 0)
            for (unsigned i = 0; i < m_size; ++i)
                *m_context << eth::swapInstruction(stackDiff) << eth::Instruction::POP;
        if (!_move)
            retrieveValue(_location);
        break;
    }
    case LValueType::Storage:
        // stack layout: value value ... value target_ref
        if (m_dataType->isValueType())
        {
            if (!_move) // copy values
            {
                if (m_size + 1 > 16)
                    BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_location)
                                                          << errinfo_comment("Stack too deep."));
                for (unsigned i = 0; i < m_size; ++i)
                    *m_context << eth::dupInstruction(m_size + 1) << eth::Instruction::SWAP1;
            }
            if (m_size > 0) // store high index value first
                *m_context << u256(m_size - 1) << eth::Instruction::ADD;
            for (unsigned i = 0; i < m_size; ++i)
            {
                if (i + 1 >= m_size)
                    *m_context << eth::Instruction::SSTORE;
                else
                    // stack here: value value ... value value (target_ref+offset)
                    *m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2
                               << eth::Instruction::SSTORE
                               << u256(1) << eth::Instruction::SWAP1 << eth::Instruction::SUB;
            }
        }
        else
        {
            solAssert(_sourceType.getCategory() == m_dataType->getCategory(), "");
            if (m_dataType->getCategory() == Type::Category::ByteArray)
                CompilerUtils(*m_context).copyByteArrayToStorage(
                            dynamic_cast<ByteArrayType const&>(*m_dataType),
                            dynamic_cast<ByteArrayType const&>(_sourceType));
            else if (m_dataType->getCategory() == Type::Category::Struct)
            {
                // stack layout: source_ref target_ref
                auto const& structType = dynamic_cast<StructType const&>(*m_dataType);
                solAssert(structType == _sourceType, "Struct assignment with conversion.");
                for (auto const& member: structType.getMembers())
                {
                    // assign each member that is not a mapping
                    TypePointer const& memberType = member.second;
                    if (memberType->getCategory() == Type::Category::Mapping)
                        continue;
                    *m_context << structType.getStorageOffsetOfMember(member.first)
                               << eth::Instruction::DUP3 << eth::Instruction::DUP2
                               << eth::Instruction::ADD;
                    LValue rightHandSide(*m_context, LValueType::Storage, memberType);
                    rightHandSide.retrieveValue(_location, true);
                    // stack: source_ref target_ref offset source_value...
                    *m_context << eth::dupInstruction(2 + memberType->getSizeOnStack())
                               << eth::dupInstruction(2 + memberType->getSizeOnStack())
                               << eth::Instruction::ADD;
                    LValue memberLValue(*m_context, LValueType::Storage, memberType);
                    memberLValue.storeValue(*memberType, _location, true);
                    *m_context << eth::Instruction::POP;
                }
                if (_move)
                    *m_context << eth::Instruction::POP;
                else
                    *m_context << eth::Instruction::SWAP1;
                *m_context << eth::Instruction::POP;
            }
            else
                BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                              << errinfo_comment("Invalid non-value type for assignment."));
        }
        break;
    case LValueType::Memory:
        if (!m_dataType->isValueType())
            break; // no distinction between value and reference for non-value types
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Location type not yet implemented."));
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Unsupported location type."));
        break;
    }
}

void ExpressionCompiler::LValue::setToZero(Location const& _location) const
{
    switch (m_type)
    {
    case LValueType::Stack:
    {
        unsigned stackDiff = m_context->baseToCurrentStackOffset(unsigned(m_baseStackOffset));
        if (stackDiff > 16)
            BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_location)
                                                  << errinfo_comment("Stack too deep."));
        solAssert(stackDiff >= m_size - 1, "");
        for (unsigned i = 0; i < m_size; ++i)
            *m_context << u256(0) << eth::swapInstruction(stackDiff + 1 - i)
                        << eth::Instruction::POP;
        break;
    }
    case LValueType::Storage:
        if (m_dataType->getCategory() == Type::Category::ByteArray)
            CompilerUtils(*m_context).clearByteArray(dynamic_cast<ByteArrayType const&>(*m_dataType));
        else
        {
            if (m_size == 0)
                *m_context << eth::Instruction::POP;
            for (unsigned i = 0; i < m_size; ++i)
                if (i + 1 >= m_size)
                    *m_context << u256(0) << eth::Instruction::SWAP1 << eth::Instruction::SSTORE;
                else
                    *m_context << u256(0) << eth::Instruction::DUP2 << eth::Instruction::SSTORE
                                << u256(1) << eth::Instruction::ADD;
        }
        break;
    case LValueType::Memory:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Location type not yet implemented."));
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_location)
                                                      << errinfo_comment("Unsupported location type."));
        break;
    }
}

void ExpressionCompiler::LValue::retrieveValueIfLValueNotRequested(Expression const& _expression)
{
    if (!_expression.lvalueRequested())
    {
        retrieveValue(_expression.getLocation(), true);
        reset();
    }
}

}
}