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Follow highest gas usage only for gas estimation.

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This commit is contained in:
chriseth 2018-05-04 17:18:02 +02:00
parent 10792dbc90
commit fba7e055d9
3 changed files with 25 additions and 5 deletions
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1
Changelog.md
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@ -3,6 +3,7 @@
Features:
* Build System: Update internal dependency of jsoncpp to 1.8.4, which introduces more strictness and reduces memory usage.
* Code Generator: Use native shift instructions on target Constantinople.
* Gas Estimator: Only explore paths with higher gas costs. This reduces accuracy but greatly improves the speed of gas estimation.
* Optimizer: Remove unnecessary masking of the result of known short instructions (``ADDRESS``, ``CALLER``, ``ORIGIN`` and ``COINBASE``).
* Type Checker: Deprecate the ``years`` unit denomination and raise a warning for it (or an error as experimental 0.5.0 feature).
* Type Checker: Make literals (without explicit type casting) an error for tight packing as experimental 0.5.0 feature.

19
libevmasm/PathGasMeter.cpp
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@ -43,7 +43,7 @@ GasMeter::GasConsumption PathGasMeter::estimateMax(
auto path = unique_ptr<GasPath>(new GasPath());
path->index = _startIndex;
path->state = _state->copy();
m_queue.push_back(move(path));
queue(move(path));
GasMeter::GasConsumption gas;
while (!m_queue.empty() && !gas.isInfinite)
@ -51,12 +51,23 @@ GasMeter::GasConsumption PathGasMeter::estimateMax(
return gas;
}
void PathGasMeter::queue(std::unique_ptr<GasPath>&& _newPath)
{
if (
m_highestGasUsagePerJumpdest.count(_newPath->index) &&
_newPath->gas < m_highestGasUsagePerJumpdest.at(_newPath->index)
)
return;
m_highestGasUsagePerJumpdest[_newPath->index] = _newPath->gas;
m_queue[_newPath->index] = move(_newPath);
}
GasMeter::GasConsumption PathGasMeter::handleQueueItem()
{
assertThrow(!m_queue.empty(), OptimizerException, "");
unique_ptr<GasPath> path = move(m_queue.back());
m_queue.pop_back();
unique_ptr<GasPath> path = move(m_queue.rbegin()->second);
m_queue.erase(--m_queue.end());
shared_ptr<KnownState> state = path->state;
GasMeter meter(state, m_evmVersion, path->largestMemoryAccess);
@ -117,7 +128,7 @@ GasMeter::GasConsumption PathGasMeter::handleQueueItem()
newPath->largestMemoryAccess = meter.largestMemoryAccess();
newPath->state = state->copy();
newPath->visitedJumpdests = path->visitedJumpdests;
m_queue.push_back(move(newPath));
queue(move(newPath));
}
if (branchStops)

10
libevmasm/PathGasMeter.h
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@ -58,9 +58,17 @@ public:
GasMeter::GasConsumption estimateMax(size_t _startIndex, std::shared_ptr<KnownState> const& _state);
private:
/// Adds a new path item to the queue, but only if we do not already have
/// a higher gas usage at that point.
/// This is not exact as different state might influence higher gas costs at a later
/// point in time, but it greatly reduces computational overhead.
void queue(std::unique_ptr<GasPath>&& _newPath);
GasMeter::GasConsumption handleQueueItem();
std::vector<std::unique_ptr<GasPath>> m_queue;
/// Map of jumpdest -> gas path, so not really a queue. We only have one queued up
/// item per jumpdest, because of the behaviour of `queue` above.
std::map<size_t, std::unique_ptr<GasPath>> m_queue;
std::map<size_t, GasMeter::GasConsumption> m_highestGasUsagePerJumpdest;
std::map<u256, size_t> m_tagPositions;
AssemblyItems const& m_items;
solidity::EVMVersion m_evmVersion;