/*

  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/>.

*/

// SPDX-License-Identifier: GPL-3.0

/**

 * Optimisation stage that removes mstore and sstore operations if they store the same

 * value that is already known to be in that slot.

 */

#include <libyul/optimiser/EqualStoreEliminator.h>

#include <libyul/optimiser/CallGraphGenerator.h>

#include <libyul/optimiser/OptimizerUtilities.h>

#include <libyul/optimiser/Semantics.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

using namespace solidity;

using namespace solidity::util;

using namespace solidity::evmasm;

using namespace solidity::yul;

void EqualStoreEliminator::run(OptimiserStepContext const& _context, Block& _ast)

{

  EqualStoreEliminator eliminator{

    _context.dialect,

    SideEffectsPropagator::sideEffects(_context.dialect, CallGraphGenerator::callGraph(_ast))

  };

  eliminator(_ast);

  StatementRemover remover{eliminator.m_pendingRemovals};

  remover(_ast);

}

void EqualStoreEliminator::visit(Statement& _statement)

{

  // No need to consider potential changes through complex arguments since

  // isSimpleStore only returns something if the arguments are identifiers.

  if (ExpressionStatement const* expression = std::get_if<ExpressionStatement>(&_statement))

  {

    if (auto vars = isSimpleStore(StoreLoadLocation::Storage, *expression))

    {

      if (std::optional<YulName> currentValue = storageValue(vars->first))

        if (*currentValue == vars->second)

          m_pendingRemovals.insert(&_statement);

    }

    else if (auto vars = isSimpleStore(StoreLoadLocation::Memory, *expression))

    {

      if (std::optional<YulName> currentValue = memoryValue(vars->first))

        if (*currentValue == vars->second)

          m_pendingRemovals.insert(&_statement);

    }

  }

  DataFlowAnalyzer::visit(_statement);

}