The prof and gprof commands provide different levels of run-time profile reports, which you can examine to find performance bottlenecks and identify the subprograms that are called most or least often. This information can help you decide where to concentrate performance-tuning efforts.
See -p Option for information on compiling for profiling and an example of the sequence of commands.
The -qipa Option allows you to feed profiling information back into subsequent compilations to enhance optimization.