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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/>.
*/
/**
 * @file ExpressionClasses.h
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Container for equivalence classes of expressions for use in common subexpression elimination.
 */

#pragma once

#include <vector>
#include <map>
#include <memory>
#include <libdevcore/Common.h>
#include <libevmasm/AssemblyItem.h>

namespace dev
{
namespace eth
{

class Pattern;
struct ExpressionTemplate;

/**
 * Collection of classes of equivalent expressions that can also determine the class of an expression.
 * Identifiers are contiguously assigned to new classes starting from zero.
 */
class ExpressionClasses
{
public:
    using Id = unsigned;
    using Ids = std::vector<Id>;

    struct Expression
    {
        Id id;
        AssemblyItem const* item = nullptr;
        Ids arguments;
        /// Storage modification sequence, only used for storage and memory operations.
        unsigned sequenceNumber = 0;
        /// Behaves as if this was a tuple of (item->type(), item->data(), arguments, sequenceNumber).
        bool operator<(Expression const& _other) const;
    };

    /// Retrieves the id of the expression equivalence class resulting from the given item applied to the
    /// given classes, might also create a new one.
    /// @param _copyItem if true, copies the assembly item to an internal storage instead of just
    /// keeping a pointer.
    /// The @a _sequenceNumber indicates the current storage or memory access sequence.
    Id find(
        AssemblyItem const& _item,
        Ids const& _arguments = {},
        bool _copyItem = true,
        unsigned _sequenceNumber = 0
    );
    /// @returns the canonical representative of an expression class.
    Expression const& representative(Id _id) const { return m_representatives.at(_id); }
    /// @returns the number of classes.
    Id size() const { return m_representatives.size(); }

    /// Forces the given @a _item with @a _arguments to the class @a _id. This can be used to
    /// add prior knowledge e.g. about CALLDATA, but has to be used with caution. Will not work as
    /// expected if @a _item applied to @a _arguments already exists.
    void forceEqual(Id _id, AssemblyItem const& _item, Ids const& _arguments, bool _copyItem = true);

    /// @returns the id of a new class which is different to all other classes.
    Id newClass(SourceLocation const& _location);

    /// @returns true if the values of the given classes are known to be different (on every input).
    /// @note that this function might still return false for some different inputs.
    bool knownToBeDifferent(Id _a, Id _b);
    /// Similar to @a knownToBeDifferent but require that abs(_a - b) >= 32.
    bool knownToBeDifferentBy32(Id _a, Id _b);
    /// @returns true if the value of the given class is known to be zero.
    /// @note that this is not the negation of knownNonZero
    bool knownZero(Id _c);
    /// @returns true if the value of the given class is known to be nonzero.
    /// @note that this is not the negation of knownZero
    bool knownNonZero(Id _c);
    /// @returns a pointer to the value if the given class is known to be a constant,
    /// and a nullptr otherwise.
    u256 const* knownConstant(Id _c);

    /// Stores a copy of the given AssemblyItem and returns a pointer to the copy that is valid for
    /// the lifetime of the ExpressionClasses object.
    AssemblyItem const* storeItem(AssemblyItem const& _item);

    std::string fullDAGToString(Id _id) const;

private:
    /// Tries to simplify the given expression.
    /// @returns its class if it possible or Id(-1) otherwise.
    /// @param _secondRun is set to true for the second run where arguments of commutative expressions are reversed
    Id tryToSimplify(Expression const& _expr, bool _secondRun = false);

    /// Rebuilds an expression from a (matched) pattern.
    Id rebuildExpression(ExpressionTemplate const& _template);

    std::vector<std::pair<Pattern, std::function<Pattern()>>> createRules() const;

    /// Expression equivalence class representatives - we only store one item of an equivalence.
    std::vector<Expression> m_representatives;
    /// All expression ever encountered.
    std::set<Expression> m_expressions;
    std::vector<std::shared_ptr<AssemblyItem>> m_spareAssemblyItems;
};

}
}