When using Clang, the -Rpass-missed flag enables the verbose log of failed compiler optimizations. However, the extensive log messages can obscure potential optimization opportunities.
Use the following steps to generate a more transparent optimization report using a previously created PGO profile file. The report also includes code hotness diagnostics:
$ ../libvpx/configure --use-profile=perf.profdata \ --extra-cflags="-fsave-optimization-record -fdiagnostics-show-hotness"
Convert the generated YAML files into a detailed HTML report using the optviewer2 tool:
$ opt-viewer.py --output-dir=out/ --source-dir=libvpx .
The HTML report displays each code line's relative hotness, cross-referenced with the failed compiler optimizations.