/*

  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/backends/evm/EVMDialect.h>

#include <libyul/optimiser/SimplificationRules.h>

#include <libyul/optimiser/OptimiserStep.h>

#include <libyul/optimiser/OptimizerUtilities.h>

#include <libyul/optimiser/Semantics.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

#include <libevmasm/SemanticInformation.h>

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](YulName const& _var) -> AssignedValue const* {

      AssignedValue const* value = variableValue(_var);

      if (!value || !value->value)

        return nullptr;

      // check that all variables in the value expression are in current scope

      MovableChecker const checker(m_dialect, *value->value);

      for (YulName const& referencedVar: checker.referencedVariables())

        if (!inScope(referencedVar))

          return nullptr;  // don't substitute if any referenced var is out of scope

      return value;

    }

  ))

  {

    auto const* evmDialect = dynamic_cast<EVMDialect const*>(&m_dialect);

    yulAssert(evmDialect);

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

  }

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

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

      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) &&

            !std::holds_alternative<FunctionCall>(startArgument)

          )

            startArgument = Literal{debugDataOf(startArgument), LiteralKind::Number, LiteralValue{0, std::nullopt}};

        }

}

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

{

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

    return literal->value.value() == 0;

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

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

  else

    return false;

}