path: root/libevmasm/PeepholeOptimiser.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 PeepholeOptimiser.h
 * Performs local optimising code changes to assembly.
 */

#include "PeepholeOptimiser.h"

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

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

// TODO: Extend this to use the tools from ExpressionClasses.cpp

struct Identity
{
    static size_t windowSize() { return 1; }
    static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
    {
        *_out = *_in;
        return true;
    }
};

struct PushPop
{
    static size_t windowSize() { return 2; }
    static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
    {
        auto t = _in[0].type();
        if (_in[1] == Instruction::POP && (
            SemanticInformation::isDupInstruction(_in[0]) ||
            t == Push || t == PushString || t == PushTag || t == PushSub ||
            t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
        ))
            return true;
        else
            return false;
    }
};

struct DoubleSwap
{
    static size_t windowSize() { return 2; }
    static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
    {
        if (_in[0] == _in[1] && SemanticInformation::isSwapInstruction(_in[0]))
            return true;
        else
            return false;
    }
};

struct JumpToNext
{
    static size_t windowSize() { return 3; }
    static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
    {
        if (
            _in[0].type() == PushTag &&
            (_in[1] == Instruction::JUMP || _in[1] == Instruction::JUMPI) &&
            _in[2].type() == Tag &&
            _in[0].data() == _in[2].data()
        )
        {
            if (_in[1] == Instruction::JUMPI)
                *_out = AssemblyItem(Instruction::POP, _in[1].location());
            *_out = _in[2];
            return true;
        }
        else
            return false;
    }
};

struct TagConjunctions
{
    static size_t windowSize() { return 3; }
    static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
    {
        if (
            _in[0].type() == PushTag &&
            _in[2] == Instruction::AND &&
            _in[1].type() == Push &&
            (_in[1].data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
        )
        {
            *_out = _in[0];
            return true;
        }
        else
            return false;
    }
};

struct OptimiserState
{
    AssemblyItems const& items;
    size_t i;
    std::back_insert_iterator<AssemblyItems> out;
};

void applyMethods(OptimiserState&)
{
    assertThrow(false, OptimizerException, "Peephole optimizer failed to apply identity.");
}

template <typename Method, typename... OtherMethods>
void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
{
    if (_state.i + Method::windowSize() <= _state.items.size() && Method::apply(_state.items.begin() + _state.i, _state.out))
        _state.i += Method::windowSize();
    else
        applyMethods(_state, _other...);
}

bool PeepholeOptimiser::optimise()
{
    OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
    while (state.i < m_items.size())
        applyMethods(state, PushPop(), DoubleSwap(), JumpToNext(), TagConjunctions(), Identity());
    if (m_optimisedItems.size() < m_items.size())
    {
        m_items = std::move(m_optimisedItems);
        return true;
    }
    else
        return false;

}