If you found the video on Super Mario 64 being published with debug symbols interesting, check this out: After finding out about the debug symbols, a developer took a deeper dive through the codebase and optimized the ever living hell out of to get 60fps+.
FIXING the ENTIRE SM64 Source Code (INSANE N64 performance)
FIXING the ENTIRE SM64 Source Code (INSANE N64 performance)
https://www.youtube.com/watch?v=t_rzYnXEQlE