Profiling the DMD Compiler Itself

[Walter Bright]

If the dmd builder builds dmd with the ENABLE_PROFILE=1, the resulting compiler 
will profile itself compiling a program. The results of the profile will be 
emitted to the file trace.log, which is described here:

https://www.digitalmars.com/ctg/trace.html

Yes, dmd inherited the profiler from the Digital Mars C++ profiler.

It works by inserting code into the prolog and epilog of each function, 
calculating the time it takes the function to execute. It turns out that this 
takes a disastrously long time to run, so it is only useful for profiling with 
fairly short programs. Trying to profile dmd itself will likely have to wait 
until the sun becomes a red giant before it finishes.

But anyhow, profiling compiles of smaller programs can work out nicely, and with 
the report in trace.log one can see where the problems are.

Happy profiling!