rustc-dev-guide/src/profiling.md

Profiling the compiler

This discussion talks about how profile the compiler and find out where it spends its time. If you just want to get a general overview, it is often a good idea to just add -Zself-profile option to the rustc command line. This will break down time spent into various categories. But if you want a more detailed look, you probably want to break out a custom profiler.