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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/>.
*/
#include <libyul/optimiser/SSAReverser.h>
#include <libyul/AsmData.h>
#include <libdevcore/CommonData.h>

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

void SSAReverser::operator()(Block& _block)
{
    walkVector(_block.statements);
    iterateReplacingWindow<2>(
        _block.statements,
        [&](Statement& _stmt1, Statement& _stmt2) -> boost::optional<vector<Statement>>
        {
            // Replaces
            //   let a_1 := E
            //   a := a_1
            // with
            //   a := E
            //   let a_1 := a

            auto* varDecl = boost::get<VariableDeclaration>(&_stmt1);
            auto* assignment = boost::get<Assignment>(&_stmt2);

            if (!varDecl || !assignment)
                return {};

            auto* identifier = boost::get<Identifier>(assignment->value.get());

            if (
                varDecl->variables.size() == 1 &&
                varDecl->value &&
                assignment->variableNames.size() == 1 &&
                identifier &&
                identifier->name == varDecl->variables.front().name
            )
            {
                vector<Statement> result;
                result.emplace_back(Assignment{
                    std::move(assignment->location),
                    assignment->variableNames,
                    std::move(varDecl->value)
                });
                result.emplace_back(VariableDeclaration{
                            std::move(varDecl->location),
                            std::move(varDecl->variables),
                            std::make_unique<Expression>(std::move(assignment->variableNames.front()))
                });
                return { std::move(result) };
            }
            return {};
        }
    );
}