/*

  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

#pragma once

#include <libyul/optimiser/ASTWalker.h>

#include <libyul/optimiser/OptimiserStep.h>

namespace solidity::yul

{

class AssignmentCounter;

/**

 * Reverses the SSA transformation.

 *

 * In particular, the SSA transform will rewrite

 *

 *     a := E

 *

 * to

 *

 *     let a_1 := E

 *     a := a_1

 *

 * To undo this kind of transformation, the SSAReverser changes this back to

 *

 *     a := E

 *     let a_1 := a

 *

 * In the special case

 *     let a := E

 *     a := a

 *

 * the redundant assignment "a := a" is removed.

 *

 *

 * Secondly, the SSA transform will rewrite

 *

 *     let a := E

 * to

 *

 *     let a_1 := E

 *     let a := a_1

 *

 * To undo this kind of transformation, the SSAReverser changes this back to

 *

 *     let a := E

 *     let a_1 := a

 *

 * After that the CSE can replace references of a_1 by references to a,

 * after which the unused pruner can remove the declaration of a_1.

 *

 * Prerequisites: Disambiguator

 *

 */

class SSAReverser: public ASTModifier

{

public:

  static constexpr char const* name{"SSAReverser"};

  static void run(OptimiserStepContext& _context, Block& _ast);

  using ASTModifier::operator();

  void operator()(Block& _block) override;

private:

  explicit SSAReverser(AssignmentCounter const& _assignmentCounter): m_assignmentCounter(_assignmentCounter) {}

  AssignmentCounter const& m_assignmentCounter;

};

}