I may have bad news for you on how compilers typically work.

I use them everywhere since the late 1990's, it is called managed runtime.

I think it's technically possible to achieve determinism with LLM output. The LLM makers typically make them non-deterministic by default but it's not inherent to them.

Well I've been seeing on HN how everyone else feels about it and I'm terrified.

A compiler that can turn cash into improved code without round tripping a human is very cool though. As those steps can get longer and succeed more often in more difficult circumstances, what it means to be a software engineer changes a lot.