/*

  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 unused variables and functions.

 */

#pragma once

#include <libyul/optimiser/ASTWalker.h>

#include <libyul/optimiser/OptimiserStep.h>

#include <libyul/YulString.h>

#include <map>

#include <set>

namespace solidity::yul

{

struct Dialect;

struct SideEffects;

/**

 * Optimisation stage that removes unused variables and functions and also

 * removes side-effect-free expression statements.

 *

 * If msize is used, we cannot remove any statements that access memory.

 * Because of that, the Unused Pruner should only be invoked on full ASTs,

 * such that it can check for the presence of msize itself, or

 * the `_allowMSizeOptimization` needs to be passed.

 *

 * Note that this does not remove circular references.

 *

 * Prerequisite: Disambiguator

 */

class UnusedPruner: public ASTModifier

{

public:

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

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

  using ASTModifier::operator();

  void operator()(Block& _block) override;

  // @returns true iff the code changed in the previous run.

  bool shouldRunAgain() const { return m_shouldRunAgain; }

  // Run the pruner until the code does not change anymore.

  static void runUntilStabilised(

    Dialect const& _dialect,

    Block& _ast,

    bool _allowMSizeOptimization,

    std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,

    std::set<YulString> const& _externallyUsedFunctions = {}

  );

  static void run(

    Dialect const& _dialect,

    Block& _ast,

    std::set<YulString> const& _externallyUsedFunctions = {}

  )

  {

    runUntilStabilisedOnFullAST(_dialect, _ast, _externallyUsedFunctions);

  }

  /// Run the pruner until the code does not change anymore.

  /// The provided block has to be a full AST.

  /// The pruner itself determines if msize is used and which user-defined functions

  /// are side-effect free.

  static void runUntilStabilisedOnFullAST(

    Dialect const& _dialect,

    Block& _ast,

    std::set<YulString> const& _externallyUsedFunctions = {}

  );

  // Run the pruner until the code does not change anymore.

  // Only run on the given function.

  // @param _allowMSizeOptimization if true, allows to remove instructions

  //        whose only side-effect is a potential change of the return value of

  //        the msize instruction.

  static void runUntilStabilised(

    Dialect const& _dialect,

    FunctionDefinition& _functionDefinition,

    bool _allowMSizeOptimization,

    std::set<YulString> const& _externallyUsedFunctions = {}

  );

private:

  UnusedPruner(

    Dialect const& _dialect,

    Block& _ast,

    bool _allowMSizeOptimization,

    std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,

    std::set<YulString> const& _externallyUsedFunctions = {}

  );

  UnusedPruner(

    Dialect const& _dialect,

    FunctionDefinition& _function,

    bool _allowMSizeOptimization,

    std::set<YulString> const& _externallyUsedFunctions = {}

  );

  bool used(YulString _name) const;

  void subtractReferences(std::map<YulString, size_t> const& _subtrahend);

  Dialect const& m_dialect;

  bool m_allowMSizeOptimization = false;

  std::map<YulString, SideEffects> const* m_functionSideEffects = nullptr;

  bool m_shouldRunAgain = false;

  std::map<YulString, size_t> m_references;

};

}