[tnh]

Agree this difficulty is the biggest obstacle to PGO's success. A language/ecosystem that works out how to integrate this as smoothly as testing would have a sizeable performance boost in practice.

The default profile is a nice hack. We do this by default for C++ builds at [company], it works great. Teams that care can build a custom profile which performs better, but most don't.

> I'd like compiler writers to embed a 'default profile' into the compiler, which uses data from as much opensource code as they can find all over github etc.

Working out how to build, let alone profile all that code is no joke. And the result will be large, and maybe not that much overlap with the average program. As a sibling points out, maybe using ML to recognize patterns instead of concrete code would help?

I'd settle for profiling of the standard library. In an ecosystem like Rust, per-crate default profiles that you could stitch together would be amazing.