chriseth
10 years ago
21 changed files with 513 additions and 46 deletions
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/*
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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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@ -0,0 +1,66 @@ |
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/*
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This file is part of cpp-ethereum. |
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|
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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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|
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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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|
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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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#pragma once |
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#include <set> |
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#include <vector> |
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#include <memory> |
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#include <libevmasm/GasMeter.h> |
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namespace dev |
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{ |
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namespace eth |
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{ |
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class KnownState; |
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struct GasPath |
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{ |
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size_t index = 0; |
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std::shared_ptr<KnownState> state; |
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u256 largestMemoryAccess; |
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GasMeter::GasConsumption gas; |
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std::set<size_t> visitedJumpdests; |
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}; |
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/**
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* Computes an upper bound on the gas usage of a computation starting at a certain position in |
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* a list of AssemblyItems in a given state until the computation stops. |
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* Can be used to estimate the gas usage of functions on any given input. |
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*/ |
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class PathGasMeter |
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{ |
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public: |
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PathGasMeter(AssemblyItems const& _items); |
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GasMeter::GasConsumption estimateMax(size_t _startIndex, std::shared_ptr<KnownState> const& _state); |
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private: |
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GasMeter::GasConsumption handleQueueItem(); |
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std::vector<std::unique_ptr<GasPath>> m_queue; |
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std::map<u256, size_t> m_tagPositions; |
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AssemblyItems const& m_items; |
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}; |
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} |
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} |
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