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 <libdevcore/Common.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)
{
    ExpressionCompiler compiler(_context);
    compiler.appendTypeConversion(_typeOnStack, _targetType);
}

bool ExpressionCompiler::visit(Assignment const& _assignment)
{
    _assignment.getRightHandSide().accept(*this);
    appendTypeConversion(*_assignment.getRightHandSide().getType(), *_assignment.getType());
    _assignment.getLeftHandSide().accept(*this);
    if (asserts(m_currentLValue.isValid()))
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("LValue not retrieved."));

    Token::Value op = _assignment.getAssignmentOperator();
    if (op != Token::ASSIGN) // compound assignment
    {
        if (m_currentLValue.storesReferenceOnStack())
            m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2;
        m_currentLValue.retrieveValue(_assignment, true);
        appendOrdinaryBinaryOperatorCode(Token::AssignmentToBinaryOp(op), *_assignment.getType());
    }
    m_currentLValue.storeValue(_assignment);
    m_currentLValue.reset();

    return false;
}

void ExpressionCompiler::endVisit(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
    switch (_unaryOperation.getOperator())
    {
    case Token::NOT: // !
        m_context << eth::Instruction::ISZERO;
        break;
    case Token::BIT_NOT: // ~
        m_context << eth::Instruction::NOT;
        break;
    case Token::DELETE: // delete
        // @todo semantics change for complex types
        if (asserts(m_currentLValue.isValid()))
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("LValue not retrieved."));

        m_context << u256(0);
        if (m_currentLValue.storesReferenceOnStack())
            m_context << eth::Instruction::SWAP1;
        m_currentLValue.storeValue(_unaryOperation);
        m_currentLValue.reset();
        break;
    case Token::INC: // ++ (pre- or postfix)
    case Token::DEC: // -- (pre- or postfix)
        if (asserts(m_currentLValue.isValid()))
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("LValue not retrieved."));
        m_currentLValue.retrieveValue(_unaryOperation);
        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, !_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()))));
    }
}

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

    if (op == Token::AND || op == Token::OR) // special case: short-circuiting
        appendAndOrOperatorCode(_binaryOperation);
    else
    {
        bool cleanupNeeded = false;
        if (commonType.getCategory() == Type::Category::INTEGER)
            if (Token::isCompareOp(op) || op == Token::DIV || op == Token::MOD)
                cleanupNeeded = true;

        // for commutative operators, push the literal as late as possible to allow improved optimization
        //@todo this has to be extended for literal expressions
        bool swap = (m_optimize && Token::isCommutativeOp(op) && dynamic_cast<Literal const*>(&rightExpression)
                     && !dynamic_cast<Literal const*>(&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(op))
            appendCompareOperatorCode(op, commonType);
        else
            appendOrdinaryBinaryOperatorCode(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
        if (asserts(_functionCall.getArguments().size() == 1))
            BOOST_THROW_EXCEPTION(InternalCompilerError());
        Expression const& firstArgument = *_functionCall.getArguments().front();
        firstArgument.accept(*this);
        if (firstArgument.getType()->getCategory() == Type::Category::CONTRACT &&
                _functionCall.getType()->getCategory() == Type::Category::INTEGER)
        {
            // explicit type conversion contract -> address, nothing to do.
        }
        else
            appendTypeConversion(*firstArgument.getType(), *_functionCall.getType());
    }
    else
    {
        FunctionType const& function = dynamic_cast<FunctionType const&>(*_functionCall.getExpression().getType());
        std::vector<ASTPointer<Expression const>> arguments = _functionCall.getArguments();
        if (asserts(arguments.size() == function.getParameterTypes().size()))
            BOOST_THROW_EXCEPTION(InternalCompilerError());

        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(arguments) - 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:
        {
            unsigned dataOffset = 1; // reserve one byte for the function index
            for (unsigned i = 0; i < arguments.size(); ++i)
            {
                arguments[i]->accept(*this);
                Type const& type = *function.getParameterTypes()[i];
                appendTypeConversion(*arguments[i]->getType(), type);
                unsigned const numBytes = type.getCalldataEncodedSize();
                if (numBytes == 0 || numBytes > 32)
                    BOOST_THROW_EXCEPTION(CompilerError()
                                          << errinfo_sourceLocation(arguments[i]->getLocation())
                                          << errinfo_comment("Type " + type.toString() + " not yet supported."));
                bool const leftAligned = type.getCategory() == Type::Category::STRING;
                CompilerUtils(m_context).storeInMemory(dataOffset, numBytes, leftAligned);
                dataOffset += numBytes;
            }
            //@todo only return the first return value for now
            Type const* firstType = function.getReturnParameterTypes().empty() ? nullptr :
                                    function.getReturnParameterTypes().front().get();
            unsigned retSize = firstType ? firstType->getCalldataEncodedSize() : 0;
            // CALL arguments: outSize, outOff, inSize, inOff, value, addr, gas (stack top)
            m_context << u256(retSize) << u256(0) << u256(dataOffset) << u256(0) << u256(0);
            _functionCall.getExpression().accept(*this); // pushes addr and function index
            m_context << u256(0) << eth::Instruction::MSTORE8
                      << u256(25) << eth::Instruction::GAS << eth::Instruction::SUB
                      << eth::Instruction::CALL
                      << eth::Instruction::POP; // @todo do not ignore failure indicator
            if (retSize > 0)
            {
                bool const leftAligned = firstType->getCategory() == Type::Category::STRING;
                CompilerUtils(m_context).loadFromMemory(0, retSize, leftAligned);
            }
            break;
        }
        case Location::SEND:
            m_context << u256(0) << u256(0) << u256(0) << u256(0);
            arguments.front()->accept(*this);
            //@todo might not be necessary
            appendTypeConversion(*arguments.front()->getType(), *function.getParameterTypes().front(), true);
            _functionCall.getExpression().accept(*this);
            m_context << u256(25) << eth::Instruction::GAS << eth::Instruction::SUB
                      << eth::Instruction::CALL
                      << eth::Instruction::POP;
            break;
        case Location::SUICIDE:
            arguments.front()->accept(*this);
            //@todo might not be necessary
            appendTypeConversion(*arguments.front()->getType(), *function.getParameterTypes().front(), true);
            m_context << eth::Instruction::SUICIDE;
            break;
        case Location::SHA3:
            arguments.front()->accept(*this);
            appendTypeConversion(*arguments.front()->getType(), *function.getParameterTypes().front(), true);
            // @todo move this once we actually use memory
            CompilerUtils(m_context).storeInMemory(0);
            m_context << u256(32) << u256(0) << eth::Instruction::SHA3;
            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}};
            u256 contractAddress = contractAddresses.find(function.getLocation())->second;
            // @todo later, combine this code with external function call
            for (unsigned i = 0; i < arguments.size(); ++i)
            {
                arguments[i]->accept(*this);
                appendTypeConversion(*arguments[i]->getType(), *function.getParameterTypes()[i], true);
                // @todo move this once we actually use memory
                CompilerUtils(m_context).storeInMemory(i * 32);
            }
            m_context << u256(32) << u256(0) << u256(arguments.size() * 32) << u256(0) << u256(0)
                      << contractAddress << u256(500) //@todo determine actual gas requirement
                      << eth::Instruction::CALL
                      << eth::Instruction::POP;
            CompilerUtils(m_context).loadFromMemory(0);
            break;
        }
        default:
            BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Invalid function type."));
        }
    }
    return false;
}

void ExpressionCompiler::endVisit(MemberAccess const& _memberAccess)
{
    ASTString const& member = _memberAccess.getMemberName();
    switch (_memberAccess.getExpression().getType()->getCategory())
    {
    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")
        {
            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::CONTRACT:
    {
        ContractType const& type = dynamic_cast<ContractType const&>(*_memberAccess.getExpression().getType());
        m_context << type.getFunctionIndex(member);
        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 == "prevhash")
            m_context << eth::Instruction::PREVHASH;
        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
            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::STORAGE, *_memberAccess.getType());
        m_currentLValue.retrieveValueIfLValueNotRequested(_memberAccess);
        break;
    }
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Member access to unknown type."));
    }
}

bool ExpressionCompiler::visit(IndexAccess const& _indexAccess)
{
    _indexAccess.getBaseExpression().accept(*this);
    _indexAccess.getIndexExpression().accept(*this);
    appendTypeConversion(*_indexAccess.getIndexExpression().getType(),
                         *dynamic_cast<MappingType const&>(*_indexAccess.getBaseExpression().getType()).getKeyType(),
                         true);
    // @todo move this once we actually use memory
    CompilerUtils(m_context).storeInMemory(0);
    CompilerUtils(m_context).storeInMemory(32);
    m_context << u256(64) << u256(0) << eth::Instruction::SHA3;

    m_currentLValue = LValue(m_context, LValue::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) // must be "this"
            m_context << eth::Instruction::ADDRESS;
        return;
    }
    if (FunctionDefinition const* functionDef = dynamic_cast<FunctionDefinition const*>(declaration))
    {
        m_context << m_context.getFunctionEntryLabel(*functionDef).pushTag();
        return;
    }
    if (dynamic_cast<VariableDeclaration const*>(declaration))
    {
        m_currentLValue.fromIdentifier(_identifier, *declaration);
        m_currentLValue.retrieveValueIfLValueNotRequested(_identifier);
        return;
    }
    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::INTEGER:
    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 op = _binaryOperation.getOperator();
    if (asserts(op == Token::OR || op == Token::AND))
        BOOST_THROW_EXCEPTION(InternalCompilerError());

    _binaryOperation.getLeftExpression().accept(*this);
    m_context << eth::Instruction::DUP1;
    if (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::EQ || _operator == Token::NE)
    {
        m_context << eth::Instruction::EQ;
        if (_operator == Token::NE)
            m_context << eth::Instruction::ISZERO;
    }
    else
    {
        IntegerType const& type = dynamic_cast<IntegerType const&>(_type);
        bool const isSigned = type.isSigned();

        switch (_operator)
        {
        case Token::GTE:
            m_context << (isSigned ? eth::Instruction::SLT : eth::Instruction::LT)
                      << eth::Instruction::ISZERO;
            break;
        case Token::LTE:
            m_context << (isSigned ? eth::Instruction::SGT : eth::Instruction::GT)
                      << eth::Instruction::ISZERO;
            break;
        case Token::GT:
            m_context << (isSigned ? eth::Instruction::SGT : eth::Instruction::GT);
            break;
        case Token::LT:
            m_context << (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 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  << (isSigned ? eth::Instruction::SDIV : eth::Instruction::DIV);
        break;
    case Token::MOD:
        m_context << (isSigned ? eth::Instruction::SMOD : eth::Instruction::MOD);
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_comment("Unknown arithmetic operator."));
    }
}

void ExpressionCompiler::appendBitOperatorCode(Token::Value _operator)
{
    switch (_operator)
    {
    case Token::BIT_OR:
        m_context << eth::Instruction::OR;
        break;
    case Token::BIT_AND:
        m_context << eth::Instruction::AND;
        break;
    case Token::BIT_XOR:
        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;
    if (_typeOnStack.getCategory() == Type::Category::INTEGER)
        appendHighBitsCleanup(dynamic_cast<IntegerType const&>(_typeOnStack));
    else if (_typeOnStack.getCategory() == Type::Category::STRING)
    {
        // nothing to do, strings are high-order-bit-aligned
        //@todo clear lower-order bytes if we allow explicit conversion to shorter strings
    }
    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;
}

ExpressionCompiler::LValue::LValue(CompilerContext& _compilerContext, LValueType _type, Type const& _dataType,
                                   unsigned _baseStackOffset):
    m_context(&_compilerContext), m_type(_type), m_baseStackOffset(_baseStackOffset),
    m_stackSize(_dataType.getSizeOnStack())
{
}

void ExpressionCompiler::LValue::retrieveValue(Expression const& _expression, bool _remove) const
{
    switch (m_type)
    {
    case 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(_expression.getLocation())
                                                  << errinfo_comment("Stack too deep."));
        for (unsigned i = 0; i < m_stackSize; ++i)
            *m_context << eth::dupInstruction(stackPos + 1);
        break;
    }
    case STORAGE:
        if (!_expression.getType()->isValueType())
            break; // no distinction between value and reference for non-value types
        if (!_remove)
            *m_context << eth::Instruction::DUP1;
        if (m_stackSize == 1)
            *m_context << eth::Instruction::SLOAD;
        else
            for (unsigned i = 0; i < m_stackSize; ++i)
            {
                *m_context << eth::Instruction::DUP1 << eth::Instruction::SLOAD << eth::Instruction::SWAP1;
                if (i + 1 < m_stackSize)
                     *m_context << u256(1) << eth::Instruction::ADD;
                else
                    *m_context << eth::Instruction::POP;
            }
        break;
    case MEMORY:
        if (!_expression.getType()->isValueType())
            break; // no distinction between value and reference for non-value types
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                      << errinfo_comment("Location type not yet implemented."));
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                      << errinfo_comment("Unsupported location type."));
        break;
    }
}

void ExpressionCompiler::LValue::storeValue(Expression const& _expression, bool _move) const
{
    switch (m_type)
    {
    case STACK:
    {
        unsigned stackDiff = m_context->baseToCurrentStackOffset(unsigned(m_baseStackOffset)) - m_stackSize + 1;
        if (stackDiff > 16)
            BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                  << errinfo_comment("Stack too deep."));
        else if (stackDiff > 0)
            for (unsigned i = 0; i < m_stackSize; ++i)
                *m_context << eth::swapInstruction(stackDiff) << eth::Instruction::POP;
        if (!_move)
            retrieveValue(_expression);
        break;
    }
    case LValue::STORAGE:
        if (!_expression.getType()->isValueType())
            break; // no distinction between value and reference for non-value types
        // stack layout: value value ... value ref
        if (!_move) // copy values
        {
            if (m_stackSize + 1 > 16)
                BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                      << errinfo_comment("Stack too deep."));
            for (unsigned i = 0; i < m_stackSize; ++i)
                *m_context << eth::dupInstruction(m_stackSize + 1) << eth::Instruction::SWAP1;
        }
        if (m_stackSize > 0) // store high index value first
            *m_context << u256(m_stackSize - 1) << eth::Instruction::ADD;
        for (unsigned i = 0; i < m_stackSize; ++i)
        {
            if (i + 1 >= m_stackSize)
                *m_context << eth::Instruction::SSTORE;
            else
                // v v ... v v r+x
                *m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2
                           << eth::Instruction::SSTORE
                           << u256(1) << eth::Instruction::SWAP1 << eth::Instruction::SUB;
        }
        break;
    case LValue::MEMORY:
        if (!_expression.getType()->isValueType())
            break; // no distinction between value and reference for non-value types
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                      << errinfo_comment("Location type not yet implemented."));
        break;
    default:
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_expression.getLocation())
                                                      << errinfo_comment("Unsupported location type."));
        break;
    }
}

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

void ExpressionCompiler::LValue::fromIdentifier(Identifier const& _identifier, Declaration const& _declaration)
{
    m_stackSize = _identifier.getType()->getSizeOnStack();
    if (m_context->isLocalVariable(&_declaration))
    {
        m_type = STACK;
        m_baseStackOffset = m_context->getBaseStackOffsetOfVariable(_declaration);
    }
    else if (m_context->isStateVariable(&_declaration))
    {
        m_type = STORAGE;
        *m_context << m_context->getStorageLocationOfVariable(_declaration);
    }
    else
        BOOST_THROW_EXCEPTION(InternalCompilerError() << errinfo_sourceLocation(_identifier.getLocation())
                                                      << errinfo_comment("Identifier type not supported or identifier not found."));
}

}
}