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/*
This file is part of cpp-ethereum.
cpp-ethereum 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.
cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file BlockDeduplicator.cpp
* @author Christian <c@ethdev.com>
* @date 2015
* Unifies basic blocks that share content.
*/
#include <libevmasm/BlockDeduplicator.h>
#include <functional>
#include <libevmasm/AssemblyItem.h>
#include <libevmasm/SemanticInformation.h>
using namespace std;
using namespace dev;
using namespace dev::eth;
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();
BlockIterator first(m_items.begin() + _i, m_items.end(), &pushFirstTag, &pushSelf);
BlockIterator second(m_items.begin() + _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);
map<u256, u256> tagReplacement;
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
tagReplacement[m_items.at(i).data()] = m_items.at(*it).data();
}
bool changed = false;
for (AssemblyItem& item: m_items)
if (item.type() == PushTag && tagReplacement.count(item.data()))
{
changed = true;
item.setData(tagReplacement.at(item.data()));
}
if (!changed)
break;
}
return iterations > 0;
}
BlockDeduplicator::BlockIterator& BlockDeduplicator::BlockIterator::operator++()
{
if (it == end)
return *this;
if (SemanticInformation::altersControlFlow(*it) && *it != AssemblyItem(eth::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;
}
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