code: def _add_return_site(self, return_site):
          
          self._register_nodes(True, return_site)
  
          self._ret_sites.add(return_site)
          # A return site must be an endpoint of the function - you cannot continue execution of the current function
          # after returning
          self._add_endpoint(return_site, 'return')
docs: Registers a basic block as a site for control flow to return from this function.
  
          :param CodeNode return_site:     The block node that ends with a return.