Yikes. Now you're pushing my memory. I believe there was a profiler built into Visual Studio and we had some external tool, too. We had some sort of system set up with serial cable to debug and profile. The EXE would download onto our test PC next to us.
Problem for id is that you have no sane way of profiling the DOS port on NeXT.
Visual Studio? The first released Visual Studio (Boston) was released in 1997. Doom was developed during 1993 :P !
He may well be thinking of Microsoft Visual C++, which dates back to 1993 and evolved into Visual Studio. It had a profiler.