Fallback takes constant amount of gas, and send to gas with send.

libsolidity/Compiler.cpp

@@ -174,6 +174,16 @@ void Compiler::appendFunctionSelector(ContractDefinition const& _contract)
 	map<FixedHash<4>, FunctionTypePointer> interfaceFunctions = _contract.getInterfaceFunctions();
 	map<FixedHash<4>, const eth::AssemblyItem> callDataUnpackerEntryPoints;
 
+	FunctionDefinition const* fallback = _contract.getFallbackFunction();
+	eth::AssemblyItem notFound = m_context.newTag();
+	// shortcut messages without data if we have many functions in order to be able to receive
+	// ether with constant gas
+	if (interfaceFunctions.size() > 5 || fallback)
+	{
+		m_context << eth::Instruction::CALLDATASIZE << eth::Instruction::ISZERO;
+		m_context.appendConditionalJumpTo(notFound);
+	}
+
 	// retrieve the function signature hash from the calldata
 	if (!interfaceFunctions.empty())
 		CompilerUtils(m_context).loadFromMemory(0, IntegerType(CompilerUtils::dataStartOffset * 8), true);
@@ -185,7 +195,10 @@ void Compiler::appendFunctionSelector(ContractDefinition const& _contract)
 		m_context << eth::dupInstruction(1) << u256(FixedHash<4>::Arith(it.first)) << eth::Instruction::EQ;
 		m_context.appendConditionalJumpTo(callDataUnpackerEntryPoints.at(it.first));
 	}
-	if (FunctionDefinition const* fallback = _contract.getFallbackFunction())
+	m_context.appendJumpTo(notFound);
+
+	m_context << notFound;
+	if (fallback)
 	{
 		eth::AssemblyItem returnTag = m_context.pushNewTag();
 		fallback->accept(*this);
@@ -194,6 +207,7 @@ void Compiler::appendFunctionSelector(ContractDefinition const& _contract)
 	}
 	else
 		m_context << eth::Instruction::STOP; // function not found
+
 	for (auto const& it: interfaceFunctions)
 	{
 		FunctionTypePointer const& functionType = it.second;

libsolidity/ExpressionCompiler.cpp

@@ -521,6 +521,7 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			break;
 		case Location::Send:
 			_functionCall.getExpression().accept(*this);
+			m_context << u256(0); // do not send gas (there still is the stipend)
 			arguments.front()->accept(*this);
 			appendTypeConversion(*arguments.front()->getType(),
 								 *function.getParameterTypes().front(), true);
@@ -532,7 +533,7 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 					strings(),
 					Location::Bare,
 					false,
-					false,
+					true,
 					true
 				),
 				{}