/*

  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 replaces variables by their most recently assigned expressions.

 */

#pragma once

#include <libyul/optimiser/DataFlowAnalyzer.h>

#include <libyul/optimiser/OptimiserStep.h>

namespace solidity::yul

{

/**

 * Optimisation stage that replaces variable references by those expressions

 * that are most recently assigned to the referenced variables,

 * but only if the expression is movable and one of the following holds:

 *  - the variable is referenced exactly once (and definition-to-reference does not cross a loop boundary)

 *  - the value is extremely cheap ("cost" of zero like ``caller()``)

 *  - the variable is referenced at most 5 times and the value is rather cheap

 *    ("cost" of at most 1 like a constant up to 0xff) and we are not in a loop

 *

 * Prerequisite: Disambiguator, ForLoopInitRewriter.

 */

class Rematerialiser: public DataFlowAnalyzer

{

public:

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

  static void run(

    OptimiserStepContext& _context,

    Block& _ast

  ) { run(_context.dialect, _ast); }

  static void run(

    Dialect const& _dialect,

    Block& _ast,

    std::set<YulName> _varsToAlwaysRematerialize = {},

    bool _onlySelectedVariables = false

  );

protected:

  Rematerialiser(

    Dialect const& _dialect,

    Block& _ast,

    std::set<YulName> _varsToAlwaysRematerialize = {},

    bool _onlySelectedVariables = false

  );

  using DataFlowAnalyzer::operator();

  using ASTModifier::visit;

  void visit(Expression& _e) override;

  std::map<YulName, size_t> m_referenceCounts;

  std::set<YulName> m_varsToAlwaysRematerialize;

  bool m_onlySelectedVariables = false;

};

/**

 * If a variable is referenced that is known to have a literal

 * value at that point, replace it by a literal.

 *

 * This is mostly used so that other components do not have to rely

 * on the data flow analyzer.

 *

 * Prerequisite: Disambiguator, ForLoopInitRewriter.

 */

class LiteralRematerialiser: public DataFlowAnalyzer

{

public:

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

  static void run(

    OptimiserStepContext& _context,

    Block& _ast

  ) { LiteralRematerialiser{_context.dialect}(_ast); }

  using ASTModifier::visit;

  void visit(Expression& _e) override;

private:

  LiteralRematerialiser(Dialect const& _dialect):

    DataFlowAnalyzer(_dialect, MemoryAndStorage::Ignore)

  {}

};

}