List all of the slithir variables (non SSA)

def slithir_variables(self):
        '''
            List all of the slithir variables (non SSA)
        '''
        slithir_variables = [f.slithir_variables for f in self.functions + self.modifiers]
        slithir_variables = [item for sublist in slithir_variables for item in sublist]
        return list(set(slithir_variables))