Giving an LLM a program that does a well defined thing correctly and asking it to make a faster version and a crapload of tests to show that it performs exactly the same task is a great way to burn through a bunch of tokens and getting a faster program in return.

I currently have one running working on a multi path problem trying to make an A* heuristic that produces the same or better score for search time, paths crossed, corners taken (plus a few other metrics, like proximity of opposite direction corners of unconnected paths.)

I have another where I'm testing how well it can iteratively rewrite the same program without regressions and successively stricter resource conditions. Instead of progressively adding lines of code to make an over engineered behemoth, starting over with the previous version as a template of functionality lets it consider the problem increasingly holistically

I would be genuinely interested to see how it evolves the same program over a large number of generations. Given a whole lot of software is more a collection of programs rather than a singular "program", I have to imagine that the outcomes would be vastly different in shape when dealing with smaller targeted, articulable-in-a-few-paragraphs programs vs many-years-of-business-domain layered programs.