path: root/libevmasm/JumpdestRemover.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 Alex Beregszaszi
 * Removes unused JUMPDESTs.
 */

#include "JumpdestRemover.h"

#include <libevmasm/AssemblyItem.h>

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


bool JumpdestRemover::optimise(set<size_t> const& _tagsReferencedFromOutside)
{
    set<size_t> references{referencedTags(m_items, -1)};
    references.insert(_tagsReferencedFromOutside.begin(), _tagsReferencedFromOutside.end());

    size_t initialSize = m_items.size();
    /// Remove tags which are never referenced.
    auto pend = remove_if(
        m_items.begin(),
        m_items.end(),
        [&](AssemblyItem const& _item)
        {
            if (_item.type() != Tag)
                return false;
            auto asmIdAndTag = _item.splitForeignPushTag();
            assertThrow(asmIdAndTag.first == size_t(-1), OptimizerException, "Sub-assembly tag used as label.");
            size_t tag = asmIdAndTag.second;
            return !references.count(tag);
        }
    );
    m_items.erase(pend, m_items.end());
    return m_items.size() != initialSize;
}

set<size_t> JumpdestRemover::referencedTags(AssemblyItems const& _items, size_t _subId)
{
    set<size_t> ret;
    for (auto const& item: _items)
        if (item.type() == PushTag)
        {
            auto subAndTag = item.splitForeignPushTag();
            if (subAndTag.first == _subId)
                ret.insert(subAndTag.second);
        }
    return ret;
}