/*

  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

/**

 * Optimisation stage that removes unreachable code.

 */

#include <libyul/optimiser/DeadCodeEliminator.h>

#include <libyul/optimiser/Semantics.h>

#include <libyul/optimiser/OptimiserStep.h>

#include <libyul/ControlFlowSideEffectsCollector.h>

#include <libyul/AST.h>

#include <libevmasm/SemanticInformation.h>

#include <algorithm>

#include <limits>

using namespace solidity;

using namespace solidity::util;

using namespace solidity::yul;

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

{

  ControlFlowSideEffectsCollector sideEffects(_context.dialect, _ast);

  DeadCodeEliminator{

    _context.dialect,

    sideEffects.functionSideEffectsNamed()

  }(_ast);

}

void DeadCodeEliminator::operator()(ForLoop& _for)

{

  yulAssert(_for.pre.statements.empty(), "DeadCodeEliminator needs ForLoopInitRewriter as a prerequisite.");

  ASTModifier::operator()(_for);

}

void DeadCodeEliminator::operator()(Block& _block)

{

  TerminationFinder::ControlFlow controlFlowChange;

  size_t index;

  std::tie(controlFlowChange, index) = TerminationFinder{m_dialect, &m_functionSideEffects}.firstUnconditionalControlFlowChange(_block.statements);

  // Erase everything after the terminating statement that is not a function definition.

  if (controlFlowChange != TerminationFinder::ControlFlow::FlowOut && index != std::numeric_limits<size_t>::max())

    _block.statements.erase(

      remove_if(

        _block.statements.begin() + static_cast<ptrdiff_t>(index) + 1,

        _block.statements.end(),

        [] (Statement const& _s) { return !std::holds_alternative<yul::FunctionDefinition>(_s); }

      ),

      _block.statements.end()

    );

  ASTModifier::operator()(_block);

}