新增加的那行代码 adds our pass by calling the createMyCustomMachinePass() 函数。然而,这个函数还没有被定义。We will add a new source file with the code of our pass and will take the opportunity to define this function as well. 为此,创建一个新的名为MachineCountPass.cpp 的文件(注意要保证它与新增加的那行代码 adds our pass by calling the createMyCust