Gas estimation taking known state into account.

libevmasm/Assembly.cpp

@@ -431,6 +431,7 @@ bytes Assembly::assemble() const
 		case PushSubSize:
 		{
 			auto s = m_data[i.data()].size();
+			i.setPushedValue(u256(s));
 			byte b = max<unsigned>(1, dev::bytesRequired(s));
 			ret.push_back((byte)Instruction::PUSH1 - 1 + b);
 			ret.resize(ret.size() + b);

libevmasm/AssemblyItem.h

@@ -84,11 +84,17 @@ public:
 	JumpType getJumpType() const { return m_jumpType; }
 	std::string getJumpTypeAsString() const;
 
+	void setPushedValue(u256 const& _value) const { m_pushedValue = std::make_shared<u256>(_value); }
+	u256 const* pushedValue() const { return m_pushedValue.get(); }
+
 private:
 	AssemblyItemType m_type;
 	u256 m_data;
 	SourceLocation m_location;
 	JumpType m_jumpType = JumpType::Ordinary;
+	/// Pushed value for operations with data to be determined during assembly stage,
+	/// e.g. PushSubSize, PushTag, PushSub, etc.
+	mutable std::shared_ptr<u256> m_pushedValue;
 };
 
 using AssemblyItems = std::vector<AssemblyItem>;

libevmasm/GasMeter.cpp

@@ -20,6 +20,7 @@
  */
 
 #include "GasMeter.h"
+#include <libevmasm/KnownState.h>
 #include <libevmcore/Params.h>
 
 using namespace std;
@@ -41,55 +42,162 @@ GasMeter::GasConsumption& GasMeter::GasConsumption::operator+=(GasConsumption co
 
 GasMeter::GasConsumption GasMeter::estimateMax(AssemblyItem const& _item)
 {
-	switch (_item.type()) {
+	GasConsumption gas;
+	switch (_item.type())
+	{
 	case Push:
 	case PushTag:
-		return runGas(Instruction::PUSH1);
+	case PushData:
+	case PushString:
+	case PushSub:
+	case PushSubSize:
+	case PushProgramSize:
+		gas = runGas(Instruction::PUSH1);
+		break;
 	case Tag:
-		return runGas(Instruction::JUMPDEST);
+		gas = runGas(Instruction::JUMPDEST);
+		break;
 	case Operation:
 	{
-		GasConsumption gas = runGas(_item.instruction());
+		ExpressionClasses& classes = m_state->expressionClasses();
+		gas = runGas(_item.instruction());
 		switch (_item.instruction())
 		{
 		case Instruction::SSTORE:
-			// @todo logic can be improved
+		{
-			gas += c_sstoreSetGas;
+			ExpressionClasses::Id slot = m_state->relativeStackElement(0);
+			ExpressionClasses::Id value = m_state->relativeStackElement(-1);
+			if (classes.knownZero(value) || (
+				m_state->storageContent().count(slot) &&
+				classes.knownNonZero(m_state->storageContent().at(slot))
+			))
+				gas += c_sstoreResetGas; //@todo take refunds into account
+			else
+				gas += c_sstoreSetGas;
 			break;
+		}
 		case Instruction::SLOAD:
 			gas += c_sloadGas;
 			break;
+		case Instruction::RETURN:
+			gas += memoryGas(0, -1);
+			break;
+		case Instruction::MLOAD:
 		case Instruction::MSTORE:
+			gas += memoryGas(classes.find(eth::Instruction::ADD, {
+				m_state->relativeStackElement(0),
+				classes.find(AssemblyItem(32))
+			}));
+			break;
 		case Instruction::MSTORE8:
-		case Instruction::MLOAD:
+			gas += memoryGas(classes.find(eth::Instruction::ADD, {
-		case Instruction::RETURN:
+				m_state->relativeStackElement(0),
+				classes.find(AssemblyItem(1))
+			}));
+			break;
 		case Instruction::SHA3:
+			gas = c_sha3Gas;
+			gas += wordGas(c_sha3WordGas, m_state->relativeStackElement(-1));
+			gas += memoryGas(0, -1);
+			break;
 		case Instruction::CALLDATACOPY:
 		case Instruction::CODECOPY:
+			gas += memoryGas(0, -2);
+			gas += wordGas(c_copyGas, m_state->relativeStackElement(-2));
+			break;
 		case Instruction::EXTCODECOPY:
+			gas += memoryGas(-1, -3);
+			gas += wordGas(c_copyGas, m_state->relativeStackElement(-3));
+			break;
 		case Instruction::LOG0:
 		case Instruction::LOG1:
 		case Instruction::LOG2:
 		case Instruction::LOG3:
 		case Instruction::LOG4:
+		{
+			unsigned n = unsigned(_item.instruction()) - unsigned(Instruction::LOG0);
+			gas = c_logGas + c_logTopicGas * n;
+			gas += memoryGas(0, -1);
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
+				gas += c_logDataGas * (*value);
+			else
+				gas = GasConsumption::infinite();
+			break;
+		}
 		case Instruction::CALL:
 		case Instruction::CALLCODE:
+			gas = c_callGas;
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(0)))
+				gas += (*value);
+			else
+				gas = GasConsumption::infinite();
+			if (_item.instruction() != Instruction::CALLCODE)
+				gas += c_callNewAccountGas; // We very rarely know whether the address exists.
+			if (!classes.knownZero(m_state->relativeStackElement(-2)))
+				gas += c_callValueTransferGas;
+			gas += memoryGas(-3, -4);
+			gas += memoryGas(-5, -6);
+			break;
 		case Instruction::CREATE:
+			gas = c_createGas;
+			gas += memoryGas(-1, -2);
+			break;
 		case Instruction::EXP:
-			// @todo logic can be improved
+			gas = c_expGas;
-			gas = GasConsumption::infinite();
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
+				gas += c_expByteGas * (32 - (h256(*value).firstBitSet() / 8));
+			else
+				gas = GasConsumption::infinite();
 			break;
 		default:
 			break;
 		}
-		return gas;
 		break;
 	}
 	default:
+		gas = GasConsumption::infinite();
 		break;
 	}
 
-	return GasConsumption::infinite();
+	m_state->feedItem(_item);
+	return gas;
+}
+
+GasMeter::GasConsumption GasMeter::wordGas(u256 const& _multiplier, ExpressionClasses::Id _position)
+{
+	u256 const* value = m_state->expressionClasses().knownConstant(_position);
+	if (!value)
+		return GasConsumption::infinite();
+	return GasConsumption(_multiplier * ((*value + 31) / 32));
+}
+
+GasMeter::GasConsumption GasMeter::memoryGas(ExpressionClasses::Id _position)
+{
+	u256 const* value = m_state->expressionClasses().knownConstant(_position);
+	if (!value)
+		return GasConsumption::infinite();
+	if (*value < m_largestMemoryAccess)
+		return GasConsumption(u256(0));
+	u256 previous = m_largestMemoryAccess;
+	m_largestMemoryAccess = *value;
+	auto memGas = [](u256 const& pos) -> u256
+	{
+		u256 size = (pos + 31) / 32;
+		return c_memoryGas * size + size * size / c_quadCoeffDiv;
+	};
+	return memGas(*value) - memGas(previous);
+}
+
+GasMeter::GasConsumption GasMeter::memoryGas(int _stackPosOffset, int _stackPosSize)
+{
+	ExpressionClasses& classes = m_state->expressionClasses();
+	if (classes.knownZero(m_state->relativeStackElement(_stackPosSize)))
+		return GasConsumption(0);
+	else
+		return memoryGas(classes.find(eth::Instruction::ADD, {
+			m_state->relativeStackElement(_stackPosOffset),
+			m_state->relativeStackElement(_stackPosSize)
+		}));
 }
 
 GasMeter::GasConsumption GasMeter::runGas(Instruction _instruction)

libevmasm/GasMeter.h

@@ -22,6 +22,7 @@
 #pragma once
 
 #include <ostream>
+#include <libevmasm/ExpressionClasses.h>
 #include <libevmasm/AssemblyItem.h>
 
 namespace dev
@@ -29,8 +30,13 @@ namespace dev
 namespace eth
 {
 
+class KnownState;
+
 /**
  * Class that helps computing the maximum gas consumption for instructions.
+ * Has to be initialized with a certain known state that will be automatically updated for
+ * each call to estimateMax. These calls have to supply strictly subsequent AssemblyItems.
+ * A new gas meter has to be constructed (with a new state) for control flow changes.
  */
 class GasMeter
 {
@@ -47,11 +53,28 @@ public:
 		bool isInfinite;
 	};
 
-	/// Returns an upper bound on the gas consumed by the given instruction.
+	/// Constructs a new gas meter given the current state.
+	GasMeter(std::shared_ptr<KnownState> const& _state): m_state(_state) {}
+
+	/// @returns an upper bound on the gas consumed by the given instruction and updates
+	/// the state.
 	GasConsumption estimateMax(AssemblyItem const& _item);
 
 private:
+	/// @returns _multiplier * (_value + 31) / 32, if _value is a known constant and infinite otherwise.
+	GasConsumption wordGas(u256 const& _multiplier, ExpressionClasses::Id _value);
+	/// @returns the gas needed to access the given memory position.
+	/// @todo this assumes that memory was never accessed before and thus over-estimates gas usage.
+	GasConsumption memoryGas(ExpressionClasses::Id _position);
+	/// @returns the memory gas for accessing the memory at a specific offset for a number of bytes
+	/// given as values on the stack at the given relative positions.
+	GasConsumption memoryGas(int _stackPosOffset, int _stackPosSize);
+
 	static GasConsumption runGas(Instruction _instruction);
+
+	std::shared_ptr<KnownState> m_state;
+	/// Largest point where memory was accessed since the creation of this object.
+	u256 m_largestMemoryAccess;
 };
 
 inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption const& _consumption)
@@ -59,7 +82,7 @@ inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption con
 	if (_consumption.isInfinite)
 		return _str << "inf";
 	else
-		return _str << _consumption.value;
+		return _str << std::dec << _consumption.value;
 }
 
 

libevmasm/KnownState.cpp

@@ -92,7 +92,11 @@ KnownState::StoreOperation KnownState::feedItem(AssemblyItem const& _item, bool
 	else if (_item.type() != Operation)
 	{
 		assertThrow(_item.deposit() == 1, InvalidDeposit, "");
-		setStackElement(++m_stackHeight, m_expressionClasses->find(_item, {}, _copyItem));
+		if (_item.pushedValue())
+			// only available after assembly stage, should not be used for optimisation
+			setStackElement(++m_stackHeight, m_expressionClasses->find(*_item.pushedValue()));
+		else
+			setStackElement(++m_stackHeight, m_expressionClasses->find(_item, {}, _copyItem));
 	}
 	else
 	{
@@ -230,7 +234,12 @@ ExpressionClasses::Id KnownState::stackElement(int _stackHeight, SourceLocation
 		return m_stackElements.at(_stackHeight);
 	// Stack element not found (not assigned yet), create new unknown equivalence class.
 	return m_stackElements[_stackHeight] =
-		m_expressionClasses->find(AssemblyItem(UndefinedItem, _stackHeight, _location));
+			m_expressionClasses->find(AssemblyItem(UndefinedItem, _stackHeight, _location));
+}
+
+KnownState::Id KnownState::relativeStackElement(int _stackOffset, SourceLocation const& _location)
+{
+	return stackElement(m_stackHeight + _stackOffset, _location);
 }
 
 void KnownState::clearTagUnions()

libevmasm/KnownState.h

@@ -111,6 +111,8 @@ public:
 	/// Retrieves the current equivalence class fo the given stack element (or generates a new
 	/// one if it does not exist yet).
 	Id stackElement(int _stackHeight, SourceLocation const& _location);
+	/// @returns the stackElement relative to the current stack height.
+	Id relativeStackElement(int _stackOffset, SourceLocation const& _location = SourceLocation());
 
 	/// @returns its set of tags if the given expression class is a known tag union; returns a set
 	/// containing the tag if it is a PushTag expression and the empty set otherwise.
@@ -123,6 +125,8 @@ public:
 	std::map<int, Id> const& stackElements() const { return m_stackElements; }
 	ExpressionClasses& expressionClasses() const { return *m_expressionClasses; }
 
+	std::map<Id, Id> const& storageContent() const { return m_storageContent; }
+
 private:
 	/// Assigns a new equivalence class to the next sequence number of the given stack element.
 	void setStackElement(int _stackHeight, Id _class);

libsolidity/ASTVisitor.h

@@ -220,6 +220,26 @@ protected:
 	virtual void endVisitNode(ASTNode const&) { }
 };
 
+/**
+ * Utility class that accepts std::functions and calls them for visitNode and endVisitNode.
+ */
+class SimpleASTVisitor: public ASTConstVisitor
+{
+public:
+	SimpleASTVisitor(
+		std::function<bool(ASTNode const&)> _onVisit,
+		std::function<void(ASTNode const&)> _onEndVisit
+	): m_onVisit(_onVisit), m_onEndVisit(_onEndVisit) {}
+
+protected:
+	virtual bool visitNode(ASTNode const& _n) override { return m_onVisit ? m_onVisit(_n) : true; }
+	virtual void endVisitNode(ASTNode const& _n) override { m_onEndVisit(_n); }
+
+private:
+	std::function<bool(ASTNode const&)> m_onVisit;
+	std::function<void(ASTNode const&)> m_onEndVisit;
+};
+
 /**
  * Utility class that visits the AST in depth-first order and calls a function on each node and each edge.
  * Child nodes are only visited if the node callback of the parent returns true.

libsolidity/CompilerStack.cpp

@@ -55,12 +55,29 @@ const map<string, string> StandardSources = map<string, string>{
 };
 
 CompilerStack::CompilerStack(bool _addStandardSources):
-	m_addStandardSources(_addStandardSources), m_parseSuccessful(false)
+	m_parseSuccessful(false)
 {
-	if (m_addStandardSources)
+	if (_addStandardSources)
 		addSources(StandardSources, true); // add them as libraries
 }
 
+void CompilerStack::reset(bool _keepSources, bool _addStandardSources)
+{
+	m_parseSuccessful = false;
+	if (_keepSources)
+		for (auto sourcePair: m_sources)
+			sourcePair.second.reset();
+	else
+	{
+		m_sources.clear();
+		if (_addStandardSources)
+			addSources(StandardSources, true);
+	}
+	m_globalContext.reset();
+	m_sourceOrder.clear();
+	m_contracts.clear();
+}
+
 bool CompilerStack::addSource(string const& _name, string const& _content, bool _isLibrary)
 {
 	bool existed = m_sources.count(_name) != 0;
@@ -269,23 +286,6 @@ tuple<int, int, int, int> CompilerStack::positionFromSourceLocation(SourceLocati
 	return make_tuple(++startLine, ++startColumn, ++endLine, ++endColumn);
 }
 
-void CompilerStack::reset(bool _keepSources)
-{
-	m_parseSuccessful = false;
-	if (_keepSources)
-		for (auto sourcePair: m_sources)
-			sourcePair.second.reset();
-	else
-	{
-		m_sources.clear();
-		if (m_addStandardSources)
-			addSources(StandardSources, true);
-	}
-	m_globalContext.reset();
-	m_sourceOrder.clear();
-	m_contracts.clear();
-}
-
 void CompilerStack::resolveImports()
 {
 	// topological sorting (depth first search) of the import graph, cutting potential cycles

libsolidity/CompilerStack.h

@@ -72,6 +72,9 @@ public:
 	/// Creates a new compiler stack. Adds standard sources if @a _addStandardSources.
 	explicit CompilerStack(bool _addStandardSources = true);
 
+	/// Resets the compiler to a state where the sources are not parsed or even removed.
+	void reset(bool _keepSources = false, bool _addStandardSources = true);
+
 	/// Adds a source object (e.g. file) to the parser. After this, parse has to be called again.
 	/// @returns true if a source object by the name already existed and was replaced.
 	void addSources(StringMap const& _nameContents, bool _isLibrary = false) { for (auto const& i: _nameContents) addSource(i.first, i.second, _isLibrary); }
@@ -165,13 +168,11 @@ private:
 		Contract();
 	};
 
-	void reset(bool _keepSources = false);
 	void resolveImports();
 
 	Contract const& getContract(std::string const& _contractName = "") const;
 	Source const& getSource(std::string const& _sourceName = "") const;
 
-	bool m_addStandardSources; ///< If true, standard sources are added.
 	bool m_parseSuccessful;
 	std::map<std::string const, Source> m_sources;
 	std::shared_ptr<GlobalContext> m_globalContext;

libsolidity/StructuralGasEstimator.cpp

@@ -23,6 +23,9 @@
 #include "StructuralGasEstimator.h"
 #include <map>
 #include <functional>
+#include <memory>
+#include <libevmasm/ControlFlowGraph.h>
+#include <libevmasm/KnownState.h>
 #include <libsolidity/AST.h>
 #include <libsolidity/ASTVisitor.h>
 
@@ -38,14 +41,23 @@ StructuralGasEstimator::ASTGasConsumptionSelfAccumulated StructuralGasEstimator:
 {
 	solAssert(std::count(_ast.begin(), _ast.end(), nullptr) == 0, "");
 	map<SourceLocation, GasMeter::GasConsumption> particularCosts;
-	GasMeter meter;
 
-	for (auto const& item: _items)
+	ControlFlowGraph cfg(_items);
-		particularCosts[item.getLocation()] += meter.estimateMax(item);
+	for (BasicBlock const& block: cfg.optimisedBlocks())
+	{
+		assertThrow(!!block.startState, OptimizerException, "");
+		GasMeter meter(block.startState->copy());
+		auto const end = _items.begin() + block.end;
+		for (auto iter = _items.begin() + block.begin; iter != end; ++iter)
+			particularCosts[iter->getLocation()] += meter.estimateMax(*iter);
+	}
 
+	set<ASTNode const*> finestNodes = finestNodesAtLocation(_ast);
 	ASTGasConsumptionSelfAccumulated gasCosts;
 	auto onNode = [&](ASTNode const& _node)
 	{
+		if (!finestNodes.count(&_node))
+			return true;
 		gasCosts[&_node][0] = gasCosts[&_node][1] = particularCosts[_node.getLocation()];
 		return true;
 	};
@@ -108,3 +120,24 @@ map<ASTNode const*, GasMeter::GasConsumption> StructuralGasEstimator::breakToSta
 	// gasCosts should only contain non-overlapping locations
 	return gasCosts;
 }
+
+set<ASTNode const*> StructuralGasEstimator::finestNodesAtLocation(
+	vector<ASTNode const*> const& _roots
+)
+{
+	map<SourceLocation, ASTNode const*> locations;
+	set<ASTNode const*> nodes;
+	SimpleASTVisitor visitor(function<bool(ASTNode const&)>(), [&](ASTNode const& _n)
+	{
+		if (!locations.count(_n.getLocation()))
+		{
+			locations[_n.getLocation()] = &_n;
+			nodes.insert(&_n);
+		}
+	});
+
+	for (ASTNode const* root: _roots)
+		root->accept(visitor);
+	return nodes;
+}
+

libsolidity/StructuralGasEstimator.h

@@ -56,6 +56,10 @@ public:
 		ASTGasConsumptionSelfAccumulated const& _gasCosts,
 		std::vector<ASTNode const*> const& _roots
 	);
+
+private:
+	/// @returns the set of AST nodes which are the finest nodes at their location.
+	std::set<ASTNode const*> finestNodesAtLocation(std::vector<ASTNode const*> const& _roots);
 };
 
 }

test/GasMeter.cpp → test/libsolidity/GasMeter.cpp

@@ -21,6 +21,8 @@
  */
 
 #include <test/libsolidity/solidityExecutionFramework.h>
+#include <libevmasm/GasMeter.h>
+#include <libevmasm/KnownState.h>
 #include <libsolidity/AST.h>
 #include <libsolidity/StructuralGasEstimator.h>
 #include <libsolidity/SourceReferenceFormatter.h>
@@ -55,8 +57,21 @@ public:
 		);
 	}
 
+	void testCreationTimeGas(string const& _sourceCode, string const& _contractName = "")
+	{
+		compileAndRun(_sourceCode);
+		auto state = make_shared<KnownState>();
+		GasMeter meter(state);
+		GasMeter::GasConsumption gas;
+		for (AssemblyItem const& item: *m_compiler.getAssemblyItems(_contractName))
+			gas += meter.estimateMax(item);
+		u256 bytecodeSize(m_compiler.getRuntimeBytecode(_contractName).size());
+		gas += bytecodeSize * c_createDataGas;
+		BOOST_REQUIRE(!gas.isInfinite);
+		BOOST_CHECK(gas.value == m_gasUsed);
+	}
+
 protected:
-	dev::solidity::CompilerStack m_compiler;
 	map<ASTNode const*, eth::GasMeter::GasConsumption> m_gasCosts;
 };
 
@@ -91,6 +106,49 @@ BOOST_AUTO_TEST_CASE(non_overlapping_filtered_costs)
 	}
 }
 
+BOOST_AUTO_TEST_CASE(simple_contract)
+{
+	// Tests a simple "deploy contract" code without constructor. The actual contract is not relevant.
+	char const* sourceCode = R"(
+		contract test {
+			bytes32 public shaValue;
+			function f(uint a) {
+				shaValue = sha3(a);
+			}
+		}
+	)";
+	testCreationTimeGas(sourceCode);
+}
+
+BOOST_AUTO_TEST_CASE(store_sha3)
+{
+	char const* sourceCode = R"(
+		contract test {
+			bytes32 public shaValue;
+			function test(uint a) {
+				shaValue = sha3(a);
+			}
+		}
+	)";
+	testCreationTimeGas(sourceCode);
+}
+
+BOOST_AUTO_TEST_CASE(updating_store)
+{
+	char const* sourceCode = R"(
+		contract test {
+			uint data;
+			uint data2;
+			function test() {
+				data = 1;
+				data = 2;
+				data2 = 0;
+			}
+		}
+	)";
+	testCreationTimeGas(sourceCode);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }

test/libsolidity/solidityExecutionFramework.h

@@ -44,11 +44,11 @@ public:
 
 	bytes const& compileAndRun(std::string const& _sourceCode, u256 const& _value = 0, std::string const& _contractName = "")
 	{
-		dev::solidity::CompilerStack compiler(m_addStandardSources);
+		m_compiler.reset(false, m_addStandardSources);
-		compiler.addSource("", _sourceCode);
+		m_compiler.addSource("", _sourceCode);
-		ETH_TEST_REQUIRE_NO_THROW(compiler.compile(m_optimize), "Compiling contract failed");
+		ETH_TEST_REQUIRE_NO_THROW(m_compiler.compile(m_optimize), "Compiling contract failed");
 
-		bytes code = compiler.getBytecode(_contractName);
+		bytes code = m_compiler.getBytecode(_contractName);
 		sendMessage(code, true, _value);
 		BOOST_REQUIRE(!m_output.empty());
 		return m_output;
@@ -160,12 +160,14 @@ protected:
 		BOOST_REQUIRE(executive.go());
 		m_state.noteSending(m_sender);
 		executive.finalize();
+		m_gasUsed = executive.gasUsed();
 		m_output = executive.out().toVector();
 		m_logs = executive.logs();
 	}
 
 	bool m_optimize = false;
 	bool m_addStandardSources = false;
+	dev::solidity::CompilerStack m_compiler;
 	Address m_sender;
 	Address m_contractAddress;
 	eth::State m_state;
@@ -173,6 +175,7 @@ protected:
 	u256 const m_gas = 100000000;
 	bytes m_output;
 	eth::LogEntries m_logs;
+	u256 m_gasUsed;
 };
 
 }