/*

  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

/**

 * Class that can answer questions about values of variables and their relations.

 */

#include <libyul/optimiser/KnowledgeBase.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

#include <libyul/optimiser/SimplificationRules.h>

#include <libyul/optimiser/DataFlowAnalyzer.h>

#include <libsolutil/CommonData.h>

#include <variant>

using namespace std;

using namespace solidity;

using namespace solidity::yul;

bool KnowledgeBase::knownToBeDifferent(YulString _a, YulString _b)

{

  // Try to use the simplification rules together with the

  // current values to turn `sub(_a, _b)` into a nonzero constant.

  // If that fails, try `eq(_a, _b)`.

  if (optional<u256> difference = differenceIfKnownConstant(_a, _b))

    return difference != 0;

  Expression expr2 = simplify(FunctionCall{{}, {{}, "eq"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});

  if (holds_alternative<Literal>(expr2))

    return valueOfLiteral(std::get<Literal>(expr2)) == 0;

  return false;

}

optional<u256> KnowledgeBase::differenceIfKnownConstant(YulString _a, YulString _b)

{

  // Try to use the simplification rules together with the

  // current values to turn `sub(_a, _b)` into a constant.

  Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});

  if (Literal const* value = get_if<Literal>(&expr1))

    return valueOfLiteral(*value);

  return {};

}

bool KnowledgeBase::knownToBeDifferentByAtLeast32(YulString _a, YulString _b)

{

  // Try to use the simplification rules together with the

  // current values to turn `sub(_a, _b)` into a constant whose absolute value is at least 32.

  if (optional<u256> difference = differenceIfKnownConstant(_a, _b))

    return difference >= 32 && difference <= u256(0) - 32;

  return false;

}

bool KnowledgeBase::knownToBeZero(YulString _a)

{

  return valueIfKnownConstant(_a) == u256{};

}

optional<u256> KnowledgeBase::valueIfKnownConstant(YulString _a)

{

  if (AssignedValue const* value = m_variableValues(_a))

    if (Literal const* literal = get_if<Literal>(value->value))

      return valueOfLiteral(*literal);

  return {};

}

Expression KnowledgeBase::simplify(Expression _expression)

{

  m_counter = 0;

  return simplifyRecursively(move(_expression));

}

Expression KnowledgeBase::simplifyRecursively(Expression _expression)

{

  if (m_counter++ > 100)

    return _expression;

  if (holds_alternative<FunctionCall>(_expression))

    for (Expression& arg: std::get<FunctionCall>(_expression).arguments)

      arg = simplifyRecursively(arg);

  if (auto match = SimplificationRules::findFirstMatch(_expression, m_dialect, m_variableValues))

    return simplifyRecursively(match->action().toExpression(debugDataOf(_expression)));

  return _expression;

}