/*

  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

/**

 * Optimiser component that turns complex expressions into multiple variable

 * declarations.

 */

#pragma once

#include <libyul/ASTForward.h>

#include <libyul/optimiser/ASTWalker.h>

#include <libyul/optimiser/NameDispenser.h>

#include <vector>

namespace solidity::yul

{

struct Dialect;

struct OptimiserStepContext;

class TypeInfo;

/**

 * Optimiser component that modifies an AST in place, turning complex

 * expressions into simple expressions and multiple variable declarations.

 *

 * Code of the form

 *

 * sstore(mul(x, 4), mload(y))

 *

 * is transformed into

 *

 * let a1 := mload(y)

 * let a2 := mul(x, 4)

 * sstore(a2, a1)

 *

 * The transformation is not applied to loop conditions, because the loop control flow

 * does not allow "outlining" the inner expressions in all cases.

 *

 * The final program should be in a form such that with the exception of a loop condition,

 * function calls can only appear in the right-hand side of a variable declaration,

 * assignments or expression statements and all arguments have to be constants or variables.

 */

class ExpressionSplitter: public ASTModifier

{

public:

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

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

  void operator()(FunctionCall&) override;

  void operator()(If&) override;

  void operator()(Switch&) override;

  void operator()(ForLoop&) override;

  void operator()(Block& _block) override;

private:

  explicit ExpressionSplitter(

    Dialect const& _dialect,

    NameDispenser& _nameDispenser,

    TypeInfo& _typeInfo

  ):

    m_dialect(_dialect),

    m_nameDispenser(_nameDispenser),

    m_typeInfo(_typeInfo)

  { }

  /// Replaces the expression by a variable if it is a function call or functional

  /// instruction. The declaration of the variable is appended to m_statementsToPrefix.

  /// Recurses via visit().

  void outlineExpression(Expression& _expr);

  /// List of statements that should go in front of the currently visited AST element,

  /// at the statement level.

  std::vector<Statement> m_statementsToPrefix;

  Dialect const& m_dialect;

  NameDispenser& m_nameDispenser;

  TypeInfo& m_typeInfo;

};

}