libyul/optimiser/Rematerialiser.cpp


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/*(
    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 variables by their most recently assigned expressions.
 */

#include <libyul/optimiser/Rematerialiser.h>

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

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

void Rematerialiser::run(Block& _ast)
{
    Rematerialiser{_ast}(_ast);
}

Rematerialiser::Rematerialiser(Block& _ast):
    m_referenceCounts(ReferencesCounter::countReferences(_ast))
{
}

void Rematerialiser::visit(Expression& _e)
{
    if (_e.type() == typeid(Identifier))
    {
        Identifier& identifier = boost::get<Identifier>(_e);
        if (m_value.count(identifier.name))
        {
            YulString name = identifier.name;
            assertThrow(m_value.at(name), OptimizerException, "");
            auto const& value = *m_value.at(name);
            size_t refs = m_referenceCounts[name];
            size_t cost = CodeCost::codeCost(value);
            if (refs <= 1 || cost == 0 || (refs <= 5 && cost <= 1))
            {
                assertThrow(m_referenceCounts[name] > 0, OptimizerException, "");
                for (auto const& ref: m_references[name])
                    assertThrow(inScope(ref), OptimizerException, "");
                // update reference counts
                m_referenceCounts[name]--;
                for (auto const& ref: ReferencesCounter::countReferences(value))
                    m_referenceCounts[ref.first] += ref.second;
                _e = (ASTCopier{}).translate(value);
            }
        }
    }
    DataFlowAnalyzer::visit(_e);
}