[mfranc42]

I don't remember using PGO like ever. And even if you do use it, isn't it like breaking compilation into two phases that are themselves deterministic?

It is pretty useful picture in my eyes, because that's what I've been observing since like forever. Non-deterministic compiler would be pretty hard to test or reason about.

It might be a banal observation, but an important one if you want to contrast a compiler with something like an OS kernel or most modern programming projects that interact heavily with outside world. When you throw hardware, network traffic, or users into the mix, it gets crazy.