path: root/libyul/optimiser/CommonSubexpressionEliminator.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/>.
*/
/**
 * Optimisation stage that replaces expressions known to be the current value of a variable
 * in scope by a reference to that variable.
 */

#include <libyul/optimiser/CommonSubexpressionEliminator.h>

#include <libyul/optimiser/Metrics.h>
#include <libyul/optimiser/SyntacticalEquality.h>
#include <libyul/Exceptions.h>
#include <libyul/AsmData.h>

using namespace std;
using namespace dev;
using namespace yul;

void CommonSubexpressionEliminator::visit(Expression& _e)
{
    // We visit the inner expression first to first simplify inner expressions,
    // which hopefully allows more matches.
    // Note that the DataFlowAnalyzer itself only has code for visiting Statements,
    // so this basically invokes the AST walker directly and thus post-visiting
    // is also fine with regards to data flow analysis.
    DataFlowAnalyzer::visit(_e);

    if (_e.type() == typeid(Identifier))
    {
        Identifier& identifier = boost::get<Identifier>(_e);
        YulString name = identifier.name;
        if (m_value.count(name))
        {
            assertThrow(m_value.at(name), OptimizerException, "");
            if (m_value.at(name)->type() == typeid(Identifier))
            {
                YulString value = boost::get<Identifier>(*m_value.at(name)).name;
                assertThrow(inScope(value), OptimizerException, "");
                _e = Identifier{locationOf(_e), value};
            }
        }
    }
    else
    {
        // TODO this search is rather inefficient.
        for (auto const& var: m_value)
        {
            assertThrow(var.second, OptimizerException, "");
            assertThrow(inScope(var.first), OptimizerException, "");
            if (SyntacticalEqualityChecker::equal(_e, *var.second))
            {
                _e = Identifier{locationOf(_e), var.first};
                break;
            }
        }
    }
}