# Profile-Guided Optimization Report

The PGO report can help identify where and how the compiler used profile information to optimize the source code. The PGO report can also identify where profile information was discarded due to source code changes made between the time of instrumentation and feedback steps. The PGO report is most useful when combined with the PGO compilation steps outlined in the topic, Profile an Application with Instrumentation. Without the profiling data generated during the application profiling process the report will generally not provide useful information.

Combine the final PGO step with the reporting options by including -prof-use (Linux* and macOS) or /Qprof-use (Windows*). The following syntax examples demonstrate how to run the report using the combined options.

Operating System | Syntax Examples
--- | ---
Linux* | `icpc -prof-use -qopt-report-phase=pgo pgotools_sample.c`
macOS | `icpc -prof-use -qopt-report-phase=pgo pgotools_sample.c`
Windows* | `icl /Qprof-use /Qopt-report-phase:pgo pgotools_sample.c`

By default the PGO report generates a medium level of detail (where the [q or Q]opt-report argument n=2). You can use the -qopt-report=n (Linux and macOS) or /Qopt-report:n option along with the [q or Q]opt-report-phase option if you want a greater or lesser level of diagnostic detail.

The output, by default, comes out to a file with the same name as the object file but with an .optrpt extension and is written into the same directory as the object file. Using the entries in the example above, the output file will be pgotools_sample.optrpt. Use the -qopt-report-file (Linux and macOS) or the /Qopt-report-file (Windows) option to specify any other name for the output file that captures the report results, or to specify that the output should go to `stdout` or `stderr`.

Parent topic: Profile-Guided Optimization (PGO)

## See Also

qopt-report-phase, Qopt-report-phase compiler option
qopt-report, Qopt-report compiler option
qopt-report-file, Qopt-report-file compiler option
prof-use, Qprof-use compiler option
Profile an Application