path: root/libsolidity/codegen/CompilerUtils.cpp

/*
    This file is part of solidity.

    solidity 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.

    solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2014
 * Routines used by both the compiler and the expression compiler.
 */

#include <libsolidity/codegen/CompilerUtils.h>
#include <libsolidity/ast/AST.h>
#include <libevmasm/Instruction.h>
#include <libsolidity/codegen/ArrayUtils.h>
#include <libsolidity/codegen/LValue.h>

using namespace std;

namespace dev
{
namespace solidity
{

const unsigned CompilerUtils::dataStartOffset = 4;
const size_t CompilerUtils::freeMemoryPointer = 64;
const unsigned CompilerUtils::identityContractAddress = 4;

void CompilerUtils::initialiseFreeMemoryPointer()
{
    m_context << u256(freeMemoryPointer + 32);
    storeFreeMemoryPointer();
}

void CompilerUtils::fetchFreeMemoryPointer()
{
    m_context << u256(freeMemoryPointer) << Instruction::MLOAD;
}

void CompilerUtils::storeFreeMemoryPointer()
{
    m_context << u256(freeMemoryPointer) << Instruction::MSTORE;
}

void CompilerUtils::allocateMemory()
{
    fetchFreeMemoryPointer();
    m_context << Instruction::SWAP1 << Instruction::DUP2 << Instruction::ADD;
    storeFreeMemoryPointer();
}

void CompilerUtils::toSizeAfterFreeMemoryPointer()
{
    fetchFreeMemoryPointer();
    m_context << Instruction::DUP1 << Instruction::SWAP2 << Instruction::SUB;
    m_context << Instruction::SWAP1;
}

unsigned CompilerUtils::loadFromMemory(
    unsigned _offset,
    Type const& _type,
    bool _fromCalldata,
    bool _padToWordBoundaries
)
{
    solAssert(_type.category() != Type::Category::Array, "Unable to statically load dynamic type.");
    m_context << u256(_offset);
    return loadFromMemoryHelper(_type, _fromCalldata, _padToWordBoundaries);
}

void CompilerUtils::loadFromMemoryDynamic(
    Type const& _type,
    bool _fromCalldata,
    bool _padToWordBoundaries,
    bool _keepUpdatedMemoryOffset
)
{       
    if (_keepUpdatedMemoryOffset)
        m_context << Instruction::DUP1;

    if (auto arrayType = dynamic_cast<ArrayType const*>(&_type))
    {
        solAssert(!arrayType->isDynamicallySized(), "");
        solAssert(!_fromCalldata, "");
        solAssert(_padToWordBoundaries, "");
        if (_keepUpdatedMemoryOffset)
            m_context << arrayType->memorySize() << Instruction::ADD;
    }
    else
    {
        unsigned numBytes = loadFromMemoryHelper(_type, _fromCalldata, _padToWordBoundaries);
        if (_keepUpdatedMemoryOffset)
        {
            // update memory counter
            moveToStackTop(_type.sizeOnStack());
            m_context << u256(numBytes) << Instruction::ADD;
        }
    }
}

void CompilerUtils::storeInMemory(unsigned _offset)
{
    unsigned numBytes = prepareMemoryStore(IntegerType(256), true);
    if (numBytes > 0)
        m_context << u256(_offset) << Instruction::MSTORE;
}

void CompilerUtils::storeInMemoryDynamic(Type const& _type, bool _padToWordBoundaries)
{
    if (auto ref = dynamic_cast<ReferenceType const*>(&_type))
    {
        solAssert(ref->location() == DataLocation::Memory, "");
        storeInMemoryDynamic(IntegerType(256), _padToWordBoundaries);
    }
    else if (auto str = dynamic_cast<StringLiteralType const*>(&_type))
    {
        m_context << Instruction::DUP1;
        storeStringData(bytesConstRef(str->value()));
        if (_padToWordBoundaries)
            m_context << u256(((str->value().size() + 31) / 32) * 32);
        else
            m_context << u256(str->value().size());
        m_context << Instruction::ADD;
    }
    else if (
        _type.category() == Type::Category::Function &&
        dynamic_cast<FunctionType const&>(_type).kind() == FunctionType::Kind::External
    )
    {
        solUnimplementedAssert(_padToWordBoundaries, "Non-padded store for function not implemented.");
        combineExternalFunctionType(true);
        m_context << Instruction::DUP2 << Instruction::MSTORE;
        m_context << u256(_padToWordBoundaries ? 32 : 24) << Instruction::ADD;
    }
    else
    {
        unsigned numBytes = prepareMemoryStore(_type, _padToWordBoundaries);
        if (numBytes > 0)
        {
            solUnimplementedAssert(
                _type.sizeOnStack() == 1,
                "Memory store of types with stack size != 1 not implemented."
            );
            m_context << Instruction::DUP2 << Instruction::MSTORE;
            m_context << u256(numBytes) << Instruction::ADD;
        }
    }
}

void CompilerUtils::encodeToMemory(
    TypePointers const& _givenTypes,
    TypePointers const& _targetTypes,
    bool _padToWordBoundaries,
    bool _copyDynamicDataInPlace,
    bool _encodeAsLibraryTypes
)
{
    // stack: <v1> <v2> ... <vn> <mem>
    TypePointers targetTypes = _targetTypes.empty() ? _givenTypes : _targetTypes;
    solAssert(targetTypes.size() == _givenTypes.size(), "");
    for (TypePointer& t: targetTypes)
    {
        solUnimplementedAssert(
            t->mobileType() &&
            t->mobileType()->interfaceType(_encodeAsLibraryTypes) &&
            t->mobileType()->interfaceType(_encodeAsLibraryTypes)->encodingType(),
            "Encoding type \"" + t->toString() + "\" not yet implemented."
        );
        t = t->mobileType()->interfaceType(_encodeAsLibraryTypes)->encodingType();
    }

    // Stack during operation:
    // <v1> <v2> ... <vn> <mem_start> <dyn_head_1> ... <dyn_head_r> <end_of_mem>
    // The values dyn_head_i are added during the first loop and they point to the head part
    // of the ith dynamic parameter, which is filled once the dynamic parts are processed.

    // store memory start pointer
    m_context << Instruction::DUP1;

    unsigned argSize = CompilerUtils::sizeOnStack(_givenTypes);
    unsigned stackPos = 0; // advances through the argument values
    unsigned dynPointers = 0; // number of dynamic head pointers on the stack
    for (size_t i = 0; i < _givenTypes.size(); ++i)
    {
        TypePointer targetType = targetTypes[i];
        solAssert(!!targetType, "Externalable type expected.");
        if (targetType->isDynamicallySized() && !_copyDynamicDataInPlace)
        {
            // leave end_of_mem as dyn head pointer
            m_context << Instruction::DUP1 << u256(32) << Instruction::ADD;
            dynPointers++;
            solAssert((argSize + dynPointers) < 16, "Stack too deep, try using less variables.");
        }
        else
        {
            copyToStackTop(argSize - stackPos + dynPointers + 2, _givenTypes[i]->sizeOnStack());
            solAssert(!!targetType, "Externalable type expected.");
            TypePointer type = targetType;
            if (_givenTypes[i]->dataStoredIn(DataLocation::Storage) && targetType->isValueType())
            {
                // special case: convert storage reference type to value type - this is only
                // possible for library calls where we just forward the storage reference
                solAssert(_encodeAsLibraryTypes, "");
                solAssert(_givenTypes[i]->sizeOnStack() == 1, "");
            }
            else if (
                _givenTypes[i]->dataStoredIn(DataLocation::Storage) ||
                _givenTypes[i]->dataStoredIn(DataLocation::CallData) ||
                _givenTypes[i]->category() == Type::Category::StringLiteral ||
                _givenTypes[i]->category() == Type::Category::Function
            )
                type = _givenTypes[i]; // delay conversion
            else
                convertType(*_givenTypes[i], *targetType, true);
            if (auto arrayType = dynamic_cast<ArrayType const*>(type.get()))
                ArrayUtils(m_context).copyArrayToMemory(*arrayType, _padToWordBoundaries);
            else
                storeInMemoryDynamic(*type, _padToWordBoundaries);
        }
        stackPos += _givenTypes[i]->sizeOnStack();
    }

    // now copy the dynamic part
    // Stack: <v1> <v2> ... <vn> <mem_start> <dyn_head_1> ... <dyn_head_r> <end_of_mem>
    stackPos = 0;
    unsigned thisDynPointer = 0;
    for (size_t i = 0; i < _givenTypes.size(); ++i)
    {
        TypePointer targetType = targetTypes[i];
        solAssert(!!targetType, "Externalable type expected.");
        if (targetType->isDynamicallySized() && !_copyDynamicDataInPlace)
        {
            // copy tail pointer (=mem_end - mem_start) to memory
            m_context << dupInstruction(2 + dynPointers) << Instruction::DUP2;
            m_context << Instruction::SUB;
            m_context << dupInstruction(2 + dynPointers - thisDynPointer);
            m_context << Instruction::MSTORE;
            // stack: ... <end_of_mem>
            if (_givenTypes[i]->category() == Type::Category::StringLiteral)
            {
                auto const& strType = dynamic_cast<StringLiteralType const&>(*_givenTypes[i]);
                m_context << u256(strType.value().size());
                storeInMemoryDynamic(IntegerType(256), true);
                // stack: ... <end_of_mem'>
                storeInMemoryDynamic(strType, _padToWordBoundaries);
            }
            else
            {
                solAssert(_givenTypes[i]->category() == Type::Category::Array, "Unknown dynamic type.");
                auto const& arrayType = dynamic_cast<ArrayType const&>(*_givenTypes[i]);
                // now copy the array
                copyToStackTop(argSize - stackPos + dynPointers + 2, arrayType.sizeOnStack());
                // stack: ... <end_of_mem> <value...>
                // copy length to memory
                m_context << dupInstruction(1 + arrayType.sizeOnStack());
                ArrayUtils(m_context).retrieveLength(arrayType, 1);
                // stack: ... <end_of_mem> <value...> <end_of_mem'> <length>
                storeInMemoryDynamic(IntegerType(256), true);
                // stack: ... <end_of_mem> <value...> <end_of_mem''>
                // copy the new memory pointer
                m_context << swapInstruction(arrayType.sizeOnStack() + 1) << Instruction::POP;
                // stack: ... <end_of_mem''> <value...>
                // copy data part
                ArrayUtils(m_context).copyArrayToMemory(arrayType, _padToWordBoundaries);
                // stack: ... <end_of_mem'''>
            }

            thisDynPointer++;
        }
        stackPos += _givenTypes[i]->sizeOnStack();
    }

    // remove unneeded stack elements (and retain memory pointer)
    m_context << swapInstruction(argSize + dynPointers + 1);
    popStackSlots(argSize + dynPointers + 1);
}

void CompilerUtils::zeroInitialiseMemoryArray(ArrayType const& _type)
{
    auto repeat = m_context.newTag();
    m_context << repeat;
    pushZeroValue(*_type.baseType());
    storeInMemoryDynamic(*_type.baseType());
    m_context << Instruction::SWAP1 << u256(1) << Instruction::SWAP1;
    m_context << Instruction::SUB << Instruction::SWAP1;
    m_context << Instruction::DUP2;
    m_context.appendConditionalJumpTo(repeat);
    m_context << Instruction::SWAP1 << Instruction::POP;
}

void CompilerUtils::memoryCopy32()
{
    // Stack here: size target source

    m_context.appendInlineAssembly(R"(
        {
        jumpi(end, eq(len, 0))
        start:
        mstore(dst, mload(src))
        jumpi(end, iszero(gt(len, 32)))
        dst := add(dst, 32)
        src := add(src, 32)
        len := sub(len, 32)
        jump(start)
        end:
        }
    )",
        { "len", "dst", "src" }
    );
    m_context << Instruction::POP << Instruction::POP << Instruction::POP;
}

void CompilerUtils::memoryCopy()
{
    // Stack here: size target source

    m_context.appendInlineAssembly(R"(
        {
        // copy 32 bytes at once
        start32:
        jumpi(end32, lt(len, 32))
        mstore(dst, mload(src))
        dst := add(dst, 32)
        src := add(src, 32)
        len := sub(len, 32)
        jump(start32)
        end32:

        // copy the remainder (0 < len < 32)
        let mask := sub(exp(256, sub(32, len)), 1)
        let srcpart := and(mload(src), not(mask))
        let dstpart := and(mload(dst), mask)
        mstore(dst, or(srcpart, dstpart))
        }
    )",
        { "len", "dst", "src" }
    );
    m_context << Instruction::POP << Instruction::POP << Instruction::POP;
}

void CompilerUtils::splitExternalFunctionType(bool _leftAligned)
{
    // We have to split the left-aligned <address><function identifier> into two stack slots:
    // address (right aligned), function identifier (right aligned)
    if (_leftAligned)
    {
        m_context << Instruction::DUP1 << (u256(1) << (64 + 32)) << Instruction::SWAP1 << Instruction::DIV;
        // <input> <address>
        m_context << Instruction::SWAP1 << (u256(1) << 64) << Instruction::SWAP1 << Instruction::DIV;
    }
    else
    {
        m_context << Instruction::DUP1 << (u256(1) << 32) << Instruction::SWAP1 << Instruction::DIV;
        m_context << ((u256(1) << 160) - 1) << Instruction::AND << Instruction::SWAP1;
    }
    m_context << u256(0xffffffffUL) << Instruction::AND;
}

void CompilerUtils::combineExternalFunctionType(bool _leftAligned)
{
    // <address> <function_id>
    m_context << u256(0xffffffffUL) << Instruction::AND << Instruction::SWAP1;
    if (!_leftAligned)
        m_context << ((u256(1) << 160) - 1) << Instruction::AND;
    m_context << (u256(1) << 32) << Instruction::MUL;
    m_context << Instruction::OR;
    if (_leftAligned)
        m_context << (u256(1) << 64) << Instruction::MUL;
}

void CompilerUtils::pushCombinedFunctionEntryLabel(Declaration const& _function)
{
    m_context << m_context.functionEntryLabel(_function).pushTag();
    // If there is a runtime context, we have to merge both labels into the same
    // stack slot in case we store it in storage.
    if (CompilerContext* rtc = m_context.runtimeContext())
        m_context <<
            (u256(1) << 32) <<
            Instruction::MUL <<
            rtc->functionEntryLabel(_function).toSubAssemblyTag(m_context.runtimeSub()) <<
            Instruction::OR;
}

void CompilerUtils::convertType(Type const& _typeOnStack, Type const& _targetType, bool _cleanupNeeded, bool _chopSignBits)
{
    // 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.category();
    Type::Category targetTypeCategory = _targetType.category();

    bool enumOverflowCheckPending = (targetTypeCategory == Type::Category::Enum || stackTypeCategory == Type::Category::Enum);
    bool chopSignBitsPending = _chopSignBits && targetTypeCategory == Type::Category::Integer;
    if (chopSignBitsPending)
    {
        const IntegerType& targetIntegerType = dynamic_cast<const IntegerType &>(_targetType);
        chopSignBitsPending = targetIntegerType.isSigned();
    }

    switch (stackTypeCategory)
    {
    case Type::Category::FixedBytes:
    {
        FixedBytesType const& typeOnStack = dynamic_cast<FixedBytesType const&>(_typeOnStack);
        if (targetTypeCategory == Type::Category::Integer)
        {
            // conversion from bytes to integer. no need to clean the high bit
            // only to shift right because of opposite alignment
            IntegerType const& targetIntegerType = dynamic_cast<IntegerType const&>(_targetType);
            m_context << (u256(1) << (256 - typeOnStack.numBytes() * 8)) << Instruction::SWAP1 << Instruction::DIV;
            if (targetIntegerType.numBits() < typeOnStack.numBytes() * 8)
                convertType(IntegerType(typeOnStack.numBytes() * 8), _targetType, _cleanupNeeded);
        }
        else
        {
            // clear for conversion to longer bytes
            solAssert(targetTypeCategory == Type::Category::FixedBytes, "Invalid type conversion requested.");
            FixedBytesType const& targetType = dynamic_cast<FixedBytesType const&>(_targetType);
            if (targetType.numBytes() > typeOnStack.numBytes() || _cleanupNeeded)
            {
                if (typeOnStack.numBytes() == 0)
                    m_context << Instruction::POP << u256(0);
                else
                {
                    m_context << ((u256(1) << (256 - typeOnStack.numBytes() * 8)) - 1);
                    m_context << Instruction::NOT << Instruction::AND;
                }
            }
        }
    }
        break;
    case Type::Category::Enum:
        solAssert(_targetType == _typeOnStack || targetTypeCategory == Type::Category::Integer, "");
        if (enumOverflowCheckPending)
        {
            EnumType const& enumType = dynamic_cast<decltype(enumType)>(_typeOnStack);
            solAssert(enumType.numberOfMembers() > 0, "empty enum should have caused a parser error.");
            m_context << u256(enumType.numberOfMembers() - 1) << Instruction::DUP2 << Instruction::GT;
            m_context.appendConditionalInvalid();
            enumOverflowCheckPending = false;
        }
        break;
    case Type::Category::FixedPoint:
        solUnimplemented("Not yet implemented - FixedPointType.");
    case Type::Category::Integer:
    case Type::Category::Contract:
    case Type::Category::RationalNumber:
        if (targetTypeCategory == Type::Category::FixedBytes)
        {
            solAssert(stackTypeCategory == Type::Category::Integer || stackTypeCategory == Type::Category::RationalNumber,
                "Invalid conversion to FixedBytesType requested.");
            // conversion from bytes to string. no need to clean the high bit
            // only to shift left because of opposite alignment
            FixedBytesType const& targetBytesType = dynamic_cast<FixedBytesType const&>(_targetType);
            if (auto typeOnStack = dynamic_cast<IntegerType const*>(&_typeOnStack))
                if (targetBytesType.numBytes() * 8 > typeOnStack->numBits())
                    cleanHigherOrderBits(*typeOnStack);
            m_context << (u256(1) << (256 - targetBytesType.numBytes() * 8)) << Instruction::MUL;
        }
        else if (targetTypeCategory == Type::Category::Enum)
        {
            solAssert(_typeOnStack.mobileType(), "");
            // just clean
            convertType(_typeOnStack, *_typeOnStack.mobileType(), true);
            EnumType const& enumType = dynamic_cast<decltype(enumType)>(_targetType);
            solAssert(enumType.numberOfMembers() > 0, "empty enum should have caused a parser error.");
            m_context << u256(enumType.numberOfMembers() - 1) << Instruction::DUP2 << Instruction::GT;
            m_context.appendConditionalInvalid();
            enumOverflowCheckPending = false;
        }
        else if (targetTypeCategory == Type::Category::FixedPoint)
        {
            solAssert(
                stackTypeCategory == Type::Category::Integer || 
                stackTypeCategory == Type::Category::RationalNumber ||
                stackTypeCategory == Type::Category::FixedPoint,
                "Invalid conversion to FixedMxNType requested."
            );
            //shift all integer bits onto the left side of the fixed type
            FixedPointType const& targetFixedPointType = dynamic_cast<FixedPointType const&>(_targetType);
            if (auto typeOnStack = dynamic_cast<IntegerType const*>(&_typeOnStack))
                if (targetFixedPointType.integerBits() > typeOnStack->numBits())
                    cleanHigherOrderBits(*typeOnStack);
            solUnimplemented("Not yet implemented - FixedPointType.");
        }
        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::RationalNumber)
            {
                RationalNumberType const& constType = dynamic_cast<RationalNumberType const&>(_typeOnStack);
                // We know that the stack is clean, we only have to clean for a narrowing conversion
                // where cleanup is forced.
                solUnimplementedAssert(!constType.isFractional(), "Not yet implemented - FixedPointType.");
                if (targetType.numBits() < constType.integerType()->numBits() && _cleanupNeeded)
                    cleanHigherOrderBits(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.numBits() > typeOnStack.numBits())
                    cleanHigherOrderBits(typeOnStack);
                else if (_cleanupNeeded)
                    cleanHigherOrderBits(targetType);
                if (chopSignBitsPending)
                {
                    if (typeOnStack.numBits() < 256)
                        m_context
                            << ((u256(1) << typeOnStack.numBits()) - 1)
                            << Instruction::AND;
                    chopSignBitsPending = false;
                }
            }
        }
        break;
    case Type::Category::StringLiteral:
    {
        auto const& literalType = dynamic_cast<StringLiteralType const&>(_typeOnStack);
        string const& value = literalType.value();
        bytesConstRef data(value);
        if (targetTypeCategory == Type::Category::FixedBytes)
        {
            solAssert(data.size() <= 32, "");
            m_context << h256::Arith(h256(data, h256::AlignLeft));
        }
        else if (targetTypeCategory == Type::Category::Array)
        {
            auto const& arrayType = dynamic_cast<ArrayType const&>(_targetType);
            solAssert(arrayType.isByteArray(), "");
            u256 storageSize(32 + ((data.size() + 31) / 32) * 32);
            m_context << storageSize;
            allocateMemory();
            // stack: mempos
            m_context << Instruction::DUP1 << u256(data.size());
            storeInMemoryDynamic(IntegerType(256));
            // stack: mempos datapos
            storeStringData(data);
            break;
        }
        else
            solAssert(
                false,
                "Invalid conversion from string literal to " + _targetType.toString(false) + " requested."
            );
        break;
    }
    case Type::Category::Array:
    {
        solAssert(targetTypeCategory == stackTypeCategory, "");
        ArrayType const& typeOnStack = dynamic_cast<ArrayType const&>(_typeOnStack);
        ArrayType const& targetType = dynamic_cast<ArrayType const&>(_targetType);
        switch (targetType.location())
        {
        case DataLocation::Storage:
            // Other cases are done explicitly in LValue::storeValue, and only possible by assignment.
            solAssert(
                (targetType.isPointer() || (typeOnStack.isByteArray() && targetType.isByteArray())) &&
                typeOnStack.location() == DataLocation::Storage,
                "Invalid conversion to storage type."
            );
            break;
        case DataLocation::Memory:
        {
            // Copy the array to a free position in memory, unless it is already in memory.
            if (typeOnStack.location() != DataLocation::Memory)
            {
                // stack: <source ref> (variably sized)
                unsigned stackSize = typeOnStack.sizeOnStack();
                ArrayUtils(m_context).retrieveLength(typeOnStack);

                // allocate memory
                // stack: <source ref> (variably sized) <length>
                m_context << Instruction::DUP1;
                ArrayUtils(m_context).convertLengthToSize(targetType, true);
                // stack: <source ref> (variably sized) <length> <size>
                if (targetType.isDynamicallySized())
                    m_context << u256(0x20) << Instruction::ADD;
                allocateMemory();
                // stack: <source ref> (variably sized) <length> <mem start>
                m_context << Instruction::DUP1;
                moveIntoStack(2 + stackSize);
                if (targetType.isDynamicallySized())
                {
                    m_context << Instruction::DUP2;
                    storeInMemoryDynamic(IntegerType(256));
                }
                // stack: <mem start> <source ref> (variably sized) <length> <mem data pos>
                if (targetType.baseType()->isValueType())
                {
                    solAssert(typeOnStack.baseType()->isValueType(), "");
                    copyToStackTop(2 + stackSize, stackSize);
                    ArrayUtils(m_context).copyArrayToMemory(typeOnStack);
                }
                else
                {
                    m_context << u256(0) << Instruction::SWAP1;
                    // stack: <mem start> <source ref> (variably sized) <length> <counter> <mem data pos>
                    auto repeat = m_context.newTag();
                    m_context << repeat;
                    m_context << Instruction::DUP3 << Instruction::DUP3;
                    m_context << Instruction::LT << Instruction::ISZERO;
                    auto loopEnd = m_context.appendConditionalJump();
                    copyToStackTop(3 + stackSize, stackSize);
                    copyToStackTop(2 + stackSize, 1);
                    ArrayUtils(m_context).accessIndex(typeOnStack, false);
                    if (typeOnStack.location() == DataLocation::Storage)
                        StorageItem(m_context, *typeOnStack.baseType()).retrieveValue(SourceLocation(), true);
                    convertType(*typeOnStack.baseType(), *targetType.baseType(), _cleanupNeeded);
                    storeInMemoryDynamic(*targetType.baseType(), true);
                    m_context << Instruction::SWAP1 << u256(1) << Instruction::ADD;
                    m_context << Instruction::SWAP1;
                    m_context.appendJumpTo(repeat);
                    m_context << loopEnd;
                    m_context << Instruction::POP;
                }
                // stack: <mem start> <source ref> (variably sized) <length> <mem data pos updated>
                popStackSlots(2 + stackSize);
                // Stack: <mem start>
            }
            break;
        }
        case DataLocation::CallData:
            solAssert(
                    targetType.isByteArray() &&
                    typeOnStack.isByteArray() &&
                    typeOnStack.location() == DataLocation::CallData,
                "Invalid conversion to calldata type.");
            break;
        default:
            solAssert(
                false,
                "Invalid type conversion " +
                _typeOnStack.toString(false) +
                " to " +
                _targetType.toString(false) +
                " requested."
            );
        }
        break;
    }
    case Type::Category::Struct:
    {
        solAssert(targetTypeCategory == stackTypeCategory, "");
        auto& targetType = dynamic_cast<StructType const&>(_targetType);
        auto& typeOnStack = dynamic_cast<StructType const&>(_typeOnStack);
        solAssert(
            targetType.location() != DataLocation::CallData &&
            typeOnStack.location() != DataLocation::CallData
        , "");
        switch (targetType.location())
        {
        case DataLocation::Storage:
            // Other cases are done explicitly in LValue::storeValue, and only possible by assignment.
            solAssert(
                targetType.isPointer() &&
                typeOnStack.location() == DataLocation::Storage,
                "Invalid conversion to storage type."
            );
            break;
        case DataLocation::Memory:
            // Copy the array to a free position in memory, unless it is already in memory.
            if (typeOnStack.location() != DataLocation::Memory)
            {
                solAssert(typeOnStack.location() == DataLocation::Storage, "");
                // stack: <source ref>
                m_context << typeOnStack.memorySize();
                allocateMemory();
                m_context << Instruction::SWAP1 << Instruction::DUP2;
                // stack: <memory ptr> <source ref> <memory ptr>
                for (auto const& member: typeOnStack.members(nullptr))
                {
                    if (!member.type->canLiveOutsideStorage())
                        continue;
                    pair<u256, unsigned> const& offsets = typeOnStack.storageOffsetsOfMember(member.name);
                    m_context << offsets.first << Instruction::DUP3 << Instruction::ADD;
                    m_context << u256(offsets.second);
                    StorageItem(m_context, *member.type).retrieveValue(SourceLocation(), true);
                    TypePointer targetMemberType = targetType.memberType(member.name);
                    solAssert(!!targetMemberType, "Member not found in target type.");
                    convertType(*member.type, *targetMemberType, true);
                    storeInMemoryDynamic(*targetMemberType, true);
                }
                m_context << Instruction::POP << Instruction::POP;
            }
            break;
        case DataLocation::CallData:
            solAssert(false, "Invalid type conversion target location CallData.");
            break;
        }
        break;
    }
    case Type::Category::Tuple:
    {
        TupleType const& sourceTuple = dynamic_cast<TupleType const&>(_typeOnStack);
        TupleType const& targetTuple = dynamic_cast<TupleType const&>(_targetType);
        // fillRight: remove excess values at right side, !fillRight: remove eccess values at left side
        bool fillRight = !targetTuple.components().empty() && (
            !targetTuple.components().back() ||
            targetTuple.components().front()
        );
        unsigned depth = sourceTuple.sizeOnStack();
        for (size_t i = 0; i < sourceTuple.components().size(); ++i)
        {
            TypePointer sourceType = sourceTuple.components()[i];
            TypePointer targetType;
            if (fillRight && i < targetTuple.components().size())
                targetType = targetTuple.components()[i];
            else if (!fillRight && targetTuple.components().size() + i >= sourceTuple.components().size())
                targetType = targetTuple.components()[targetTuple.components().size() - (sourceTuple.components().size() - i)];
            if (!sourceType)
            {
                solAssert(!targetType, "");
                continue;
            }
            unsigned sourceSize = sourceType->sizeOnStack();
            unsigned targetSize = targetType ? targetType->sizeOnStack() : 0;
            if (!targetType || *sourceType != *targetType || _cleanupNeeded)
            {
                if (targetType)
                {
                    if (sourceSize > 0)
                        copyToStackTop(depth, sourceSize);
                    convertType(*sourceType, *targetType, _cleanupNeeded);
                }
                if (sourceSize > 0 || targetSize > 0)
                {
                    // Move it back into its place.
                    for (unsigned j = 0; j < min(sourceSize, targetSize); ++j)
                        m_context <<
                            swapInstruction(depth + targetSize - sourceSize) <<
                            Instruction::POP;
                    // Value shrank
                    for (unsigned j = targetSize; j < sourceSize; ++j)
                    {
                        moveToStackTop(depth - 1, 1);
                        m_context << Instruction::POP;
                    }
                    // Value grew
                    if (targetSize > sourceSize)
                        moveIntoStack(depth + targetSize - sourceSize - 1, targetSize - sourceSize);
                }
            }
            depth -= sourceSize;
        }
        break;
    }
    case Type::Category::Bool:
        solAssert(_targetType == _typeOnStack, "Invalid conversion for bool.");
        if (_cleanupNeeded)
            m_context << Instruction::ISZERO << Instruction::ISZERO;
        break;
    case Type::Category::Function:
    {
        if (targetTypeCategory == Type::Category::Integer)
        {
            IntegerType const& targetType = dynamic_cast<IntegerType const&>(_targetType);
            solAssert(targetType.isAddress(), "Function type can only be converted to address.");
            FunctionType const& typeOnStack = dynamic_cast<FunctionType const&>(_typeOnStack);
            solAssert(typeOnStack.kind() == FunctionType::Kind::External, "Only external function type can be converted.");

            // stack: <address> <function_id>
            m_context << Instruction::POP;
            break;
        }
    }
    default:
        // All other types should not be convertible to non-equal types.
        solAssert(_typeOnStack == _targetType, "Invalid type conversion requested.");
        if (_cleanupNeeded && _targetType.canBeStored() && _targetType.storageBytes() < 32)
                m_context
                    << ((u256(1) << (8 * _targetType.storageBytes())) - 1)
                    << Instruction::AND;
        break;
    }

    solAssert(!enumOverflowCheckPending, "enum overflow checking missing.");
    solAssert(!chopSignBitsPending, "forgot to chop the sign bits.");
}

void CompilerUtils::pushZeroValue(Type const& _type)
{
    if (auto const* funType = dynamic_cast<FunctionType const*>(&_type))
    {
        if (funType->kind() == FunctionType::Kind::Internal)
        {
            m_context << m_context.lowLevelFunctionTag("$invalidFunction", 0, 0, [](CompilerContext& _context) {
                _context.appendInvalid();
            });
            return;
        }
    }
    auto const* referenceType = dynamic_cast<ReferenceType const*>(&_type);
    if (!referenceType || referenceType->location() == DataLocation::Storage)
    {
        for (size_t i = 0; i < _type.sizeOnStack(); ++i)
            m_context << u256(0);
        return;
    }
    solAssert(referenceType->location() == DataLocation::Memory, "");

    TypePointer type = _type.shared_from_this();
    m_context.callLowLevelFunction(
        "$pushZeroValue_" + referenceType->identifier(),
        0,
        1,
        [type](CompilerContext& _context) {
            CompilerUtils utils(_context);
            _context << u256(max(32u, type->calldataEncodedSize()));
            utils.allocateMemory();
            _context << Instruction::DUP1;

            if (auto structType = dynamic_cast<StructType const*>(type.get()))
                for (auto const& member: structType->members(nullptr))
                {
                    utils.pushZeroValue(*member.type);
                    utils.storeInMemoryDynamic(*member.type);
                }
            else if (auto arrayType = dynamic_cast<ArrayType const*>(type.get()))
            {
                if (arrayType->isDynamicallySized())
                {
                    // zero length
                    _context << u256(0);
                    utils.storeInMemoryDynamic(IntegerType(256));
                }
                else if (arrayType->length() > 0)
                {
                    _context << arrayType->length() << Instruction::SWAP1;
                    // stack: items_to_do memory_pos
                    utils.zeroInitialiseMemoryArray(*arrayType);
                    // stack: updated_memory_pos
                }
            }
            else
                solAssert(false, "Requested initialisation for unknown type: " + type->toString());

            // remove the updated memory pointer
            _context << Instruction::POP;
        }
    );
}

void CompilerUtils::moveToStackVariable(VariableDeclaration const& _variable)
{
    unsigned const stackPosition = m_context.baseToCurrentStackOffset(m_context.baseStackOffsetOfVariable(_variable));
    unsigned const size = _variable.annotation().type->sizeOnStack();
    solAssert(stackPosition >= size, "Variable size and position mismatch.");
    // move variable starting from its top end in the stack
    if (stackPosition - size + 1 > 16)
        BOOST_THROW_EXCEPTION(
            CompilerError() <<
            errinfo_sourceLocation(_variable.location()) <<
            errinfo_comment("Stack too deep, try removing local variables.")
        );
    for (unsigned i = 0; i < size; ++i)
        m_context << swapInstruction(stackPosition - size + 1) << Instruction::POP;
}

void CompilerUtils::copyToStackTop(unsigned _stackDepth, unsigned _itemSize)
{
    solAssert(_stackDepth <= 16, "Stack too deep, try removing local variables.");
    for (unsigned i = 0; i < _itemSize; ++i)
        m_context << dupInstruction(_stackDepth);
}

void CompilerUtils::moveToStackTop(unsigned _stackDepth, unsigned _itemSize)
{
    moveIntoStack(_itemSize, _stackDepth);
}

void CompilerUtils::moveIntoStack(unsigned _stackDepth, unsigned _itemSize)
{
    if (_stackDepth <= _itemSize)
        for (unsigned i = 0; i < _stackDepth; ++i)
            rotateStackDown(_stackDepth + _itemSize);
    else
        for (unsigned i = 0; i < _itemSize; ++i)
            rotateStackUp(_stackDepth + _itemSize);
}

void CompilerUtils::rotateStackUp(unsigned _items)
{
    solAssert(_items - 1 <= 16, "Stack too deep, try removing local variables.");
    for (unsigned i = 1; i < _items; ++i)
        m_context << swapInstruction(_items - i);
}

void CompilerUtils::rotateStackDown(unsigned _items)
{
    solAssert(_items - 1 <= 16, "Stack too deep, try removing local variables.");
    for (unsigned i = 1; i < _items; ++i)
        m_context << swapInstruction(i);
}

void CompilerUtils::popStackElement(Type const& _type)
{
    popStackSlots(_type.sizeOnStack());
}

void CompilerUtils::popStackSlots(size_t _amount)
{
    for (size_t i = 0; i < _amount; ++i)
        m_context << Instruction::POP;
}

unsigned CompilerUtils::sizeOnStack(vector<shared_ptr<Type const>> const& _variableTypes)
{
    unsigned size = 0;
    for (shared_ptr<Type const> const& type: _variableTypes)
        size += type->sizeOnStack();
    return size;
}

void CompilerUtils::computeHashStatic()
{
    storeInMemory(0);
    m_context << u256(32) << u256(0) << Instruction::SHA3;
}

void CompilerUtils::storeStringData(bytesConstRef _data)
{
    //@todo provide both alternatives to the optimiser
    // stack: mempos
    if (_data.size() <= 128)
    {
        for (unsigned i = 0; i < _data.size(); i += 32)
        {
            m_context << h256::Arith(h256(_data.cropped(i), h256::AlignLeft));
            storeInMemoryDynamic(IntegerType(256));
        }
        m_context << Instruction::POP;
    }
    else
    {
        // stack: mempos mempos_data
        m_context.appendData(_data.toBytes());
        m_context << u256(_data.size()) << Instruction::SWAP2;
        m_context << Instruction::CODECOPY;
    }
}

unsigned CompilerUtils::loadFromMemoryHelper(Type const& _type, bool _fromCalldata, bool _padToWords)
{
    unsigned numBytes = _type.calldataEncodedSize(_padToWords);
    bool isExternalFunctionType = false;
    if (auto const* funType = dynamic_cast<FunctionType const*>(&_type))
        if (funType->kind() == FunctionType::Kind::External)
            isExternalFunctionType = true;
    if (numBytes == 0)
    {
        m_context << Instruction::POP << u256(0);
        return numBytes;
    }
    solAssert(numBytes <= 32, "Static memory load of more than 32 bytes requested.");
    m_context << (_fromCalldata ? Instruction::CALLDATALOAD : Instruction::MLOAD);
    if (isExternalFunctionType)
        splitExternalFunctionType(true);
    else if (numBytes != 32)
    {
        bool leftAligned = _type.category() == Type::Category::FixedBytes;
        // add leading or trailing zeros by dividing/multiplying depending on alignment
        u256 shiftFactor = u256(1) << ((32 - numBytes) * 8);
        m_context << shiftFactor << Instruction::SWAP1 << Instruction::DIV;
        if (leftAligned)
            m_context << shiftFactor << Instruction::MUL;
    }
    if (_fromCalldata)
        convertType(_type, _type, true);

    return numBytes;
}

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

unsigned CompilerUtils::prepareMemoryStore(Type const& _type, bool _padToWords)
{
    unsigned numBytes = _type.calldataEncodedSize(_padToWords);
    bool leftAligned = _type.category() == Type::Category::FixedBytes;
    if (numBytes == 0)
        m_context << Instruction::POP;
    else
    {
        solAssert(numBytes <= 32, "Memory store of more than 32 bytes requested.");
        convertType(_type, _type, true);
        if (numBytes != 32 && !leftAligned && !_padToWords)
            // shift the value accordingly before storing
            m_context << (u256(1) << ((32 - numBytes) * 8)) << Instruction::MUL;
    }
    return numBytes;
}

}
}