This makes sense for a verifiable task like a regex engine - but those are clearly defined and I doubt an LLM will have a meaningful speed increase over current human regex engines.

Anything else kind of just feels like "make GTA 6, make no mistakes". The ability for you to write fast and correct software is really going to depend on well you can specify your problem, and having the ability to specify correct programs in such detail an LLM can reasonably performance tune it is a big enough reason for me to believe there will still be slow software