Merge pull request #2478 from ethereum/fallback-dispatcher

Optimise the fallback dispatcher by removing a useless jump

Changelog.md

@@ -2,6 +2,7 @@
 
 Features:
  * C API (``jsonCompiler``): Export the ``license`` method.
+ * Code Generator: Optimise the fallback function, by removing a useless jump.
  * Inline Assembly: Show useful error message if trying to access calldata variables.
  * Inline Assembly: Support variable declaration without initial value (defaults to 0).
  * Metadata: Only include files which were used to compile the given contract.

libsolidity/analysis/TypeChecker.cpp

@@ -93,7 +93,7 @@ bool TypeChecker::visit(ContractDefinition const& _contract)
 	FunctionDefinition const* fallbackFunction = nullptr;
 	for (FunctionDefinition const* function: _contract.definedFunctions())
 	{
-		if (function->name().empty())
+		if (function->isFallback())
 		{
 			if (fallbackFunction)
 			{
@@ -482,7 +482,7 @@ bool TypeChecker::visit(FunctionDefinition const& _function)
 	{
 		if (isLibraryFunction)
 			m_errorReporter.typeError(_function.location(), "Library functions cannot be payable.");
-		if (!_function.isConstructor() && !_function.name().empty() && !_function.isPartOfExternalInterface())
+		if (!_function.isConstructor() && !_function.isFallback() && !_function.isPartOfExternalInterface())
 			m_errorReporter.typeError(_function.location(), "Internal functions cannot be payable.");
 		if (_function.isDeclaredConst())
 			m_errorReporter.typeError(_function.location(), "Functions cannot be constant and payable at the same time.");

libsolidity/ast/AST.cpp

@@ -162,7 +162,7 @@ FunctionDefinition const* ContractDefinition::fallbackFunction() const
 {
 	for (ContractDefinition const* contract: annotation().linearizedBaseContracts)
 		for (FunctionDefinition const* f: contract->definedFunctions())
-			if (f->name().empty())
+			if (f->isFallback())
 				return f;
 	return nullptr;
 }

libsolidity/ast/AST.h

@@ -589,6 +589,7 @@ public:
 	virtual void accept(ASTConstVisitor& _visitor) const override;
 
 	bool isConstructor() const { return m_isConstructor; }
+	bool isFallback() const { return name().empty(); }
 	bool isDeclaredConst() const { return m_isDeclaredConst; }
 	bool isPayable() const { return m_isPayable; }
 	std::vector<ASTPointer<ModifierInvocation>> const& modifiers() const { return m_functionModifiers; }
@@ -596,9 +597,9 @@ public:
 	Block const& body() const { solAssert(m_body, ""); return *m_body; }
 	virtual bool isVisibleInContract() const override
 	{
-		return Declaration::isVisibleInContract() && !isConstructor() && !name().empty();
+		return Declaration::isVisibleInContract() && !isConstructor() && !isFallback();
 	}
-	virtual bool isPartOfExternalInterface() const override { return isPublic() && !m_isConstructor && !name().empty(); }
+	virtual bool isPartOfExternalInterface() const override { return isPublic() && !isConstructor() && !isFallback(); }
 
 	/// @returns the external signature of the function
 	/// That consists of the name of the function followed by the types of the

libsolidity/ast/Types.cpp

@@ -2524,6 +2524,7 @@ bool FunctionType::isBareCall() const
 string FunctionType::externalSignature() const
 {
 	solAssert(m_declaration != nullptr, "External signature of function needs declaration");
+	solAssert(!m_declaration->name().empty(), "Fallback function has no signature.");
 
 	bool _inLibrary = dynamic_cast<ContractDefinition const&>(*m_declaration->scope()).isLibrary();
 

libsolidity/codegen/ContractCompiler.cpp

@@ -267,18 +267,13 @@ void ContractCompiler::appendFunctionSelector(ContractDefinition const& _contrac
 	m_context << notFound;
 	if (fallback)
 	{
-		m_context.setStackOffset(0);
 		if (!fallback->isPayable())
 			appendCallValueCheck();
 
-		// Return tag is used to jump out of the function.
+		solAssert(fallback->isFallback(), "");
-		eth::AssemblyItem returnTag = m_context.pushNewTag();
-		fallback->accept(*this);
-		m_context << returnTag;
 		solAssert(FunctionType(*fallback).parameterTypes().empty(), "");
 		solAssert(FunctionType(*fallback).returnParameterTypes().empty(), "");
-		// Return tag gets consumed.
+		fallback->accept(*this);
-		m_context.adjustStackOffset(-1);
 		m_context << Instruction::STOP;
 	}
 	else
@@ -536,7 +531,8 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 
 	m_context.adjustStackOffset(-(int)c_returnValuesSize);
 
-	if (!_function.isConstructor())
+	/// The constructor and the fallback function doesn't to jump out.
+	if (!_function.isConstructor() && !_function.isFallback())
 		m_context.appendJump(eth::AssemblyItem::JumpType::OutOfFunction);
 	return false;
 }

libsolidity/interface/CompilerStack.cpp

@@ -935,7 +935,7 @@ Json::Value CompilerStack::gasEstimates(string const& _contractName) const
 		for (auto const& it: contract.definedFunctions())
 		{
 			/// Exclude externally visible functions, constructor and the fallback function
-			if (it->isPartOfExternalInterface() || it->isConstructor() || it->name().empty())
+			if (it->isPartOfExternalInterface() || it->isConstructor() || it->isFallback())
 				continue;
 
 			size_t entry = functionEntryPoint(_contractName, *it);
@@ -943,12 +943,14 @@ Json::Value CompilerStack::gasEstimates(string const& _contractName) const
 			if (entry > 0)
 				gas = GasEstimator::functionalEstimation(*items, entry, *it);
 
+			/// TODO: This could move into a method shared with externalSignature()
 			FunctionType type(*it);
 			string sig = it->name() + "(";
 			auto paramTypes = type.parameterTypes();
 			for (auto it = paramTypes.begin(); it != paramTypes.end(); ++it)
 				sig += (*it)->toString() + (it + 1 == paramTypes.end() ? "" : ",");
 			sig += ")";
+
 			internalFunctions[sig] = gasToJson(gas);
 		}