1# Using Profile Guided Optimizations to identify compiler optimization failures 2 3When using Clang, the `-Rpass-missed` flag enables the verbose log of failed 4compiler optimizations. However, the extensive log messages can obscure 5potential optimization opportunities. 6 7Use the following steps to generate a more transparent optimization report 8using a previously created PGO profile file. The report also includes code 9hotness diagnostics: 10 11```bash 12$ ../libvpx/configure --use-profile=perf.profdata \ 13 --extra-cflags="-fsave-optimization-record -fdiagnostics-show-hotness" 14``` 15 16Convert the generated YAML files into a detailed HTML report using the 17[optviewer2](https://github.com/OfekShilon/optview2) tool: 18 19```bash 20$ opt-viewer.py --output-dir=out/ --source-dir=libvpx . 21``` 22 23The HTML report displays each code line's relative hotness, cross-referenced 24with the failed compiler optimizations. 25