code: def save_used_registers(self):
          
          used = self.used_registers[:]
          del self.used_registers[:]
          self.used_registers_stack.append(used[:])
          used.sort()
          for reg in used:
              self.newline_text("PUSH\t%s" % SharedData.REGISTERS[reg], True)
          self.free_registers.extend(used)
          self.free_registers.sort(reverse = True)
docs: Pushes all used working registers before function call