path: root/libevmasm/SemanticInformation.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/>.
*/
/**
 * @file SemanticInformation.cpp
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Helper to provide semantic information about assembly items.
 */

#include <libevmasm/SemanticInformation.h>
#include <libevmasm/AssemblyItem.h>

using namespace std;
using namespace dev;
using namespace dev::eth;

bool SemanticInformation::breaksCSEAnalysisBlock(AssemblyItem const& _item)
{
    switch (_item.type())
    {
    default:
    case UndefinedItem:
    case Tag:
        return true;
    case Push:
    case PushString:
    case PushTag:
    case PushSub:
    case PushSubSize:
    case PushProgramSize:
    case PushData:
    case PushLibraryAddress:
        return false;
    case Operation:
    {
        if (isSwapInstruction(_item) || isDupInstruction(_item))
            return false;
        if (_item.instruction() == Instruction::GAS || _item.instruction() == Instruction::PC)
            return true; // GAS and PC assume a specific order of opcodes
        if (_item.instruction() == Instruction::MSIZE)
            return true; // msize is modified already by memory access, avoid that for now
        InstructionInfo info = instructionInfo(_item.instruction());
        if (_item.instruction() == Instruction::SSTORE)
            return false;
        if (_item.instruction() == Instruction::MSTORE)
            return false;
        //@todo: We do not handle the following memory instructions for now:
        // calldatacopy, codecopy, extcodecopy, mstore8,
        // msize (note that msize also depends on memory read access)

        // the second requirement will be lifted once it is implemented
        return info.sideEffects || info.args > 2;
    }
    }
}

bool SemanticInformation::isCommutativeOperation(AssemblyItem const& _item)
{
    if (_item.type() != Operation)
        return false;
    switch (_item.instruction())
    {
    case Instruction::ADD:
    case Instruction::MUL:
    case Instruction::EQ:
    case Instruction::AND:
    case Instruction::OR:
    case Instruction::XOR:
        return true;
    default:
        return false;
    }
}

bool SemanticInformation::isDupInstruction(AssemblyItem const& _item)
{
    if (_item.type() != Operation)
        return false;
    return Instruction::DUP1 <= _item.instruction() && _item.instruction() <= Instruction::DUP16;
}

bool SemanticInformation::isSwapInstruction(AssemblyItem const& _item)
{
    if (_item.type() != Operation)
        return false;
    return Instruction::SWAP1 <= _item.instruction() && _item.instruction() <= Instruction::SWAP16;
}

bool SemanticInformation::isJumpInstruction(AssemblyItem const& _item)
{
    return _item == AssemblyItem(Instruction::JUMP) || _item == AssemblyItem(Instruction::JUMPI);
}

bool SemanticInformation::altersControlFlow(AssemblyItem const& _item)
{
    if (_item.type() != Operation)
        return false;
    switch (_item.instruction())
    {
    // note that CALL, CALLCODE and CREATE do not really alter the control flow, because we
    // continue on the next instruction
    case Instruction::JUMP:
    case Instruction::JUMPI:
    case Instruction::RETURN:
    case Instruction::SUICIDE:
    case Instruction::STOP:
        return true;
    default:
        return false;
    }
}


bool SemanticInformation::isDeterministic(AssemblyItem const& _item)
{
    if (_item.type() != Operation)
        return true;

    switch (_item.instruction())
    {
    case Instruction::CALL:
    case Instruction::CALLCODE:
    case Instruction::DELEGATECALL:
    case Instruction::CREATE:
    case Instruction::GAS:
    case Instruction::PC:
    case Instruction::MSIZE: // depends on previous writes and reads, not only on content
    case Instruction::BALANCE: // depends on previous calls
    case Instruction::EXTCODESIZE:
        return false;
    default:
        return true;
    }
}

bool SemanticInformation::invalidatesMemory(Instruction _instruction)
{
    switch (_instruction)
    {
    case Instruction::CALLDATACOPY:
    case Instruction::CODECOPY:
    case Instruction::EXTCODECOPY:
    case Instruction::MSTORE:
    case Instruction::MSTORE8:
    case Instruction::CALL:
    case Instruction::CALLCODE:
    case Instruction::DELEGATECALL:
        return true;
    default:
        return false;
    }
}

bool SemanticInformation::invalidatesStorage(Instruction _instruction)
{
    switch (_instruction)
    {
    case Instruction::CALL:
    case Instruction::CALLCODE:
    case Instruction::DELEGATECALL:
    case Instruction::CREATE:
    case Instruction::SSTORE:
        return true;
    default:
        return false;
    }
}