Multiple copies of same subroutine in single source file

I am working with a legacy Fortran program originally written on the IBM Mainframe. The single source file has several copies of the same subroutine. How can I determine which copy is used by the compiler?  Is this behavior the same for all compilers? What I really need is how the IBM Mainframe compiler handle this condition so I can identify and remove the duplicate subroutine that was ignored by the compiler used during the development of the code.

Thanks….