/*

  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

/**

 * @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 <libevmasm/AssemblyItem.h>

#include <libsolutil/Common.h>

#include <memory>

#include <unordered_set>

#include <vector>

namespace solidity::langutil

{

struct SourceLocation;

}

namespace solidity::evmasm

{

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;

    struct ExpressionHash

    {

      std::size_t operator()(Expression const& _expression) 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.

  size_t 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(langutil::DebugData::ConstPtr _debugData);

  /// @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.

  Id tryToSimplify(Expression const& _expr);

  /// 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::unordered_set<Expression, Expression::ExpressionHash> m_expressions;

  std::vector<std::shared_ptr<AssemblyItem>> m_spareAssemblyItems;

};

}