/*

  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/Semantics.h>

#include <libyul/optimiser/OptimiserStep.h>

namespace solidity::yul

{

/**

 * Loop-invariant code motion.

 *

 * This optimization moves movable SSA variable declarations outside the loop.

 *

 * Only statements at the top level in a loop's body or post block are considered, i.e variable

 * declarations inside conditional branches will not be moved out of the loop.

 *

 * Requirements:

 * - The Disambiguator, ForLoopInitRewriter and FunctionHoister must be run upfront.

 * - Expression splitter and SSA transform should be run upfront to obtain better result.

 */

class LoopInvariantCodeMotion: public ASTModifier

{

public:

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

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

  void operator()(Block& _block) override;

private:

  explicit LoopInvariantCodeMotion(

    Dialect const& _dialect,

    std::set<YulString> const& _ssaVariables,

    std::map<YulString, SideEffects> const& _functionSideEffects,

    bool _containsMSize

  ):

    m_containsMSize(_containsMSize),

    m_dialect(_dialect),

    m_ssaVariables(_ssaVariables),

    m_functionSideEffects(_functionSideEffects)

  { }

  /// @returns true if the given variable declaration can be moved to in front of the loop.

  bool canBePromoted(

    VariableDeclaration const& _varDecl,

    std::set<YulString> const& _varsDefinedInCurrentScope,

    SideEffects const& _forLoopSideEffects

  ) const;

  std::optional<std::vector<Statement>> rewriteLoop(ForLoop& _for);

  bool m_containsMSize = true;

  Dialect const& m_dialect;

  std::set<YulString> const& m_ssaVariables;

  std::map<YulString, SideEffects> const& m_functionSideEffects;

};

}