[CyberDildonics]

That's not how it works. BOLT is mainly about figuring out the most likely instructions that will run after branches and putting them close together in the binary. Unlikely instructions like error and exception paths can be put at the end of the binary. Putting the most used instructions close together leverages prefetching and cache so that unused instructions aren't what is being prefetched and cached.

In short it is better memory access patterns for instructions.

[foota]

I suspect you know this based on the detail in your comment and just missed it, but parent is talking about FDO, not BOLT.

[mhh__]

Yes, but I'm not talking about BOLT