Implement subroutines for yul functions.

libsolidity/codegen/CompilerContext.cpp

@@ -132,6 +132,7 @@ void CompilerContext::callLowLevelFunction(
 
 	*this << lowLevelFunctionTag(_name, _inArgs, _outArgs, _generator);
 
+	// TODO could use jumpsub?
 	appendJump(evmasm::AssemblyItem::JumpType::IntoFunction);
 	adjustStackOffset(static_cast<int>(_outArgs) - 1 - static_cast<int>(_inArgs));
 	*this << retTag.tag();

libsolidity/codegen/ContractCompiler.cpp

@@ -505,6 +505,7 @@ void ContractCompiler::appendFunctionSelector(ContractDefinition const& _contrac
 			m_context << Instruction::DUP1 << Instruction::CALLDATASIZE << Instruction::SUB;
 			CompilerUtils(m_context).abiDecode(functionType->parameterTypes());
 		}
+		// TODO could use JUMPSUB?
 		m_context.appendJumpTo(
 			m_context.functionEntryLabel(functionType->declaration()),
 			evmasm::AssemblyItem::JumpType::IntoFunction

libsolidity/codegen/ExpressionCompiler.cpp

@@ -614,6 +614,7 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 				// Extract the runtime part.
 				m_context << ((u256(1) << 32) - 1) << Instruction::AND;
 
+			// TODO could use jumpsub
 			m_context.appendJump(evmasm::AssemblyItem::JumpType::IntoFunction);
 			m_context << returnLabel;