mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
129 lines
3.9 KiB
C++
129 lines
3.9 KiB
C++
/*
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This file is part of cpp-ethereum.
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cpp-ethereum is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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cpp-ethereum is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
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*/
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/** @file PathGasMeter.cpp
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* @author Christian <c@ethdev.com>
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* @date 2015
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*/
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#include "PathGasMeter.h"
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#include <libevmasm/KnownState.h>
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#include <libevmasm/SemanticInformation.h>
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using namespace std;
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using namespace dev;
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using namespace dev::eth;
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PathGasMeter::PathGasMeter(AssemblyItems const& _items):
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m_items(_items)
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{
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for (size_t i = 0; i < m_items.size(); ++i)
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if (m_items[i].type() == Tag)
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m_tagPositions[m_items[i].data()] = i;
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}
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GasMeter::GasConsumption PathGasMeter::estimateMax(
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size_t _startIndex,
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shared_ptr<KnownState> const& _state
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)
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{
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auto path = unique_ptr<GasPath>(new GasPath());
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path->index = _startIndex;
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path->state = _state->copy();
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m_queue.push_back(move(path));
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GasMeter::GasConsumption gas;
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while (!m_queue.empty() && !gas.isInfinite)
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gas = max(gas, handleQueueItem());
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return gas;
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}
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GasMeter::GasConsumption PathGasMeter::handleQueueItem()
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{
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assertThrow(!m_queue.empty(), OptimizerException, "");
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unique_ptr<GasPath> path = move(m_queue.back());
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m_queue.pop_back();
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shared_ptr<KnownState> state = path->state;
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GasMeter meter(state, path->largestMemoryAccess);
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ExpressionClasses& classes = state->expressionClasses();
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GasMeter::GasConsumption gas = path->gas;
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size_t index = path->index;
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if (index >= m_items.size() || (index > 0 && m_items.at(index).type() != Tag))
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// Invalid jump usually provokes an out-of-gas exception, but we want to give an upper
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// bound on the gas that is needed without changing the behaviour, so it is fine to
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// return the current gas value.
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return gas;
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set<u256> jumpTags;
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for (; index < m_items.size() && !gas.isInfinite; ++index)
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{
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bool branchStops = false;
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jumpTags.clear();
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AssemblyItem const& item = m_items.at(index);
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if (item.type() == Tag || item == AssemblyItem(eth::Instruction::JUMPDEST))
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{
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// Do not allow any backwards jump. This is quite restrictive but should work for
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// the simplest things.
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if (path->visitedJumpdests.count(index))
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return GasMeter::GasConsumption::infinite();
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path->visitedJumpdests.insert(index);
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}
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else if (item == AssemblyItem(eth::Instruction::JUMP))
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{
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branchStops = true;
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jumpTags = state->tagsInExpression(state->relativeStackElement(0));
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if (jumpTags.empty()) // unknown jump destination
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return GasMeter::GasConsumption::infinite();
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}
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else if (item == AssemblyItem(eth::Instruction::JUMPI))
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{
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ExpressionClasses::Id condition = state->relativeStackElement(-1);
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if (classes.knownNonZero(condition) || !classes.knownZero(condition))
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{
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jumpTags = state->tagsInExpression(state->relativeStackElement(0));
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if (jumpTags.empty()) // unknown jump destination
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return GasMeter::GasConsumption::infinite();
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}
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branchStops = classes.knownNonZero(condition);
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}
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else if (SemanticInformation::altersControlFlow(item))
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branchStops = true;
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gas += meter.estimateMax(item);
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for (u256 const& tag: jumpTags)
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{
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auto newPath = unique_ptr<GasPath>(new GasPath());
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newPath->index = m_items.size();
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if (m_tagPositions.count(tag))
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newPath->index = m_tagPositions.at(tag);
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newPath->gas = gas;
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newPath->largestMemoryAccess = meter.largestMemoryAccess();
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newPath->state = state->copy();
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newPath->visitedJumpdests = path->visitedJumpdests;
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m_queue.push_back(move(newPath));
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}
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if (branchStops)
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break;
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}
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return gas;
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}
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