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/*
    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/>.
*/
/**
 * Optimiser component that turns complex expressions into multiple variable
 * declarations.
 */
#pragma once

#include <libyul/AsmDataForward.h>

#include <libyul/optimiser/ASTWalker.h>
#include <libyul/optimiser/NameDispenser.h>

#include <vector>

namespace yul
{

class NameCollector;


/**
 * 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:
    explicit ExpressionSplitter(NameDispenser& _nameDispenser):
        m_nameDispenser(_nameDispenser)
    { }

    void operator()(FunctionalInstruction&) override;
    void operator()(FunctionCall&) override;
    void operator()(If&) override;
    void operator()(Switch&) override;
    void operator()(ForLoop&) override;
    void operator()(Block& _block) override;

private:
    /// 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;
    NameDispenser& m_nameDispenser;
};

}