/*

  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 BlockDeduplicator.cpp

 * @author Christian <c@ethdev.com>

 * @date 2015

 * Unifies basic blocks that share content.

 */

#include <libevmasm/BlockDeduplicator.h>

#include <libevmasm/AssemblyItem.h>

#include <libevmasm/SemanticInformation.h>

#include <functional>

#include <set>

using namespace std;

using namespace solidity;

using namespace solidity::evmasm;

bool BlockDeduplicator::deduplicate()

{

  // Compares indices based on the suffix that starts there, ignoring tags and stopping at

  // opcodes that stop the control flow.

  // Virtual tag that signifies "the current block" and which is used to optimise loops.

  // We abort if this virtual tag actually exists.

  AssemblyItem pushSelf{PushTag, u256(-4)};

  if (

    std::count(m_items.cbegin(), m_items.cend(), pushSelf.tag()) ||

    std::count(m_items.cbegin(), m_items.cend(), pushSelf.pushTag())

  )

    return false;

  function<bool(size_t, size_t)> comparator = [&](size_t _i, size_t _j)

  {

    if (_i == _j)

      return false;

    // To compare recursive loops, we have to already unify PushTag opcodes of the

    // block's own tag.

    AssemblyItem pushFirstTag{pushSelf};

    AssemblyItem pushSecondTag{pushSelf};

    if (_i < m_items.size() && m_items.at(_i).type() == Tag)

      pushFirstTag = m_items.at(_i).pushTag();

    if (_j < m_items.size() && m_items.at(_j).type() == Tag)

      pushSecondTag = m_items.at(_j).pushTag();

    using diff_type = BlockIterator::difference_type;

    BlockIterator first{m_items.begin() + diff_type(_i), m_items.end(), &pushFirstTag, &pushSelf};

    BlockIterator second{m_items.begin() + diff_type(_j), m_items.end(), &pushSecondTag, &pushSelf};

    BlockIterator end{m_items.end(), m_items.end()};

    if (first != end && (*first).type() == Tag)

      ++first;

    if (second != end && (*second).type() == Tag)

      ++second;

    return std::lexicographical_compare(first, end, second, end);

  };

  size_t iterations = 0;

  for (; ; ++iterations)

  {

    //@todo this should probably be optimized.

    set<size_t, function<bool(size_t, size_t)>> blocksSeen(comparator);

    for (size_t i = 0; i < m_items.size(); ++i)

    {

      if (m_items.at(i).type() != Tag)

        continue;

      auto it = blocksSeen.find(i);

      if (it == blocksSeen.end())

        blocksSeen.insert(i);

      else

        m_replacedTags[m_items.at(i).data()] = m_items.at(*it).data();

    }

    if (!applyTagReplacement(m_items, m_replacedTags))

      break;

  }

  return iterations > 0;

}

bool BlockDeduplicator::applyTagReplacement(

  AssemblyItems& _items,

  map<u256, u256> const& _replacements,

  size_t _subId

)

{

  bool changed = false;

  for (AssemblyItem& item: _items)

    if (item.type() == PushTag)

    {

      size_t subId;

      size_t tagId;

      tie(subId, tagId) = item.splitForeignPushTag();

      if (subId != _subId)

        continue;

      auto it = _replacements.find(tagId);

      // Recursively look for the element replaced by tagId

      for (auto _it = it; _it != _replacements.end(); _it = _replacements.find(_it->second))

        it = _it;

      if (it != _replacements.end())

      {

        changed = true;

        item.setPushTagSubIdAndTag(subId, static_cast<size_t>(it->second));

      }

    }

  return changed;

}

BlockDeduplicator::BlockIterator& BlockDeduplicator::BlockIterator::operator++()

{

  if (it == end)

    return *this;

  if (SemanticInformation::altersControlFlow(*it) && *it != AssemblyItem{Instruction::JUMPI})

    it = end;

  else

  {

    ++it;

    while (it != end && it->type() == Tag)

      ++it;

  }

  return *this;

}

AssemblyItem const& BlockDeduplicator::BlockIterator::operator*() const

{

  if (replaceItem && replaceWith && *it == *replaceItem)

    return *replaceWith;

  else

    return *it;

}