/*

  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 <boost/container_hash/hash.hpp>

#include <range/v3/algorithm/any_of.hpp>

#include <range/v3/algorithm/equal.hpp>

#include <unordered_set>

using namespace solidity;

using namespace solidity::evmasm;

bool BlockDeduplicator::deduplicate()

{

  // Group basic blocks by a content hash and dedup within each bucket.

  // The hash and equality both walk a BlockIterator that ignores tags and stops at

  // opcodes that terminate control flow, replacing the block's own self-push by a

  // virtual tag so that recursive loops match.

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

  // We abort if this virtual tag actually exists.

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

  {

    AssemblyItem const selfTag = pushSelf.tag();

    if (ranges::any_of(m_items, [&](AssemblyItem const& _item) { return _item == selfTag || _item == pushSelf; }))

      return false;

  }

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

  // yields a block iterator into the body of a block (skips `Tag` typed assembly items at `_blockBegin`)

  auto const blockBodyBegin = [&](std::size_t const _blockBegin, AssemblyItem const& _selfTagPush)

  {

    BlockIterator it{

      m_items.begin() + static_cast<BlockIterator::difference_type>(_blockBegin),

      m_items.end(),

      &_selfTagPush,

      &pushSelf

    };

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

      ++it;

    return it;

  };

  auto const hashBlockAt = [&](std::size_t const _i)

  {

    return boost::hash_range(blockBodyBegin(_i, m_items[_i].pushTag()), end);

  };

  auto const blocksAtEqual = [&](std::size_t const _i, std::size_t const _j)

  {

    return ranges::equal(

      blockBodyBegin(_i, m_items[_i].pushTag()), end,

      blockBodyBegin(_j, m_items[_j].pushTag()), end

    );

  };

  std::size_t iterations = 0;

  for (; ; ++iterations)

  {

    std::unordered_set<std::size_t, decltype(hashBlockAt), decltype(blocksAtEqual)> seen(0, hashBlockAt, blocksAtEqual);

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

    {

      if (m_items[i].type() != Tag)

        continue;

      auto const [it, inserted] = seen.insert(i);

      if (!inserted)

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

    }

    if (!applyTagReplacement(m_items, m_replacedTags))

      break;

  }

  return iterations > 0;

}

bool BlockDeduplicator::applyTagReplacement(

  AssemblyItems& _items,

  std::map<u256, u256> const& _replacements,

  SubAssemblyID _subId

)

{

  bool changed = false;

  for (AssemblyItem& item: _items)

    if (item.type() == PushTag)

    {

      SubAssemblyID subId;

      size_t tagId;

      std::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;

}