Hm yes I was wrong about that. It looks like v8 and PyPy do it (which is apparent from some Googling and grepping of the code).

I have been reading some papers on JITs and I don't see escape analysis mentioned that often. In the PyPy paper (which is over a decade old) they mention it as future work.

Still, I actually tried PyPy on a string-based workload and it was slower than CPython and used more memory. I don't know why but that contributes to my feeling that JITs are bad for string-based workloads.

I'm interested in seeing any pointers to benchmarks that show the improvements resulting from escape analysis in JITs. I haven't seen anything like that and I've done a decent amount of research.

A cursory look at this blog post makes me think it's not super straightforward:

https://v8project.blogspot.com/2017/09/disabling-escape-anal...

That post is less than a year old! i.e. the fact that v8 has been around for 10+ years and they're still updating escape analysis makes me wonder what the issue with it is. Is it hard to implement or does it not produce that much speedup? I appreciate any pointers.