/*

  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 uses the simplification rules to simplify expressions.

 */

#include <libyul/optimiser/ExpressionSimplifier.h>

#include <libyul/optimiser/SimplificationRules.h>

#include <libyul/optimiser/OptimiserStep.h>

#include <libyul/optimiser/OptimizerUtilities.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

#include <libevmasm/SemanticInformation.h>

using namespace std;

using namespace solidity;

using namespace solidity::yul;

void ExpressionSimplifier::run(OptimiserStepContext& _context, Block& _ast)

{

  ExpressionSimplifier{_context.dialect}(_ast);

}

void ExpressionSimplifier::visit(Expression& _expression)

{

  ASTModifier::visit(_expression);

  while (auto const* match = SimplificationRules::findFirstMatch(

    _expression,

    m_dialect,

    [this](YulString _var) { return variableValue(_var); }

  ))

    _expression = match->action().toExpression(debugDataOf(_expression));

  if (auto* functionCall = get_if<FunctionCall>(&_expression))

    if (optional<evmasm::Instruction> instruction = toEVMInstruction(m_dialect, functionCall->functionName.name))

      for (auto op: evmasm::SemanticInformation::readWriteOperations(*instruction))

        if (op.startParameter && op.lengthParameter)

        {

          Expression& startArgument = functionCall->arguments.at(*op.startParameter);

          Expression const& lengthArgument = functionCall->arguments.at(*op.lengthParameter);

          if (

            knownToBeZero(lengthArgument) &&

            !knownToBeZero(startArgument) &&

            !holds_alternative<FunctionCall>(startArgument)

          )

            startArgument = Literal{debugDataOf(startArgument), LiteralKind::Number, "0"_yulstring, {}};

        }

}

bool ExpressionSimplifier::knownToBeZero(Expression const& _expression) const

{

  if (auto const* literal = get_if<Literal>(&_expression))

    return valueOfLiteral(*literal) == 0;

  else if (auto const* identifier = get_if<Identifier>(&_expression))

    return valueOfIdentifier(identifier->name) == 0;

  else

    return false;

}