Hundreds of passes, sure. Guaranteed that they preserve correctness is a bit more dubious, that's pretty hard to establish for most transforms. Passes that make no assumptions about prior passes are tricky too since compilers tend to work in terms of a lowering pipeline.

If the compiler has N correct passes that can be combined in arbitrary order without compromising compiler termination, exponentially increasing code size or generally making the output much worse, then you've already built a really good compiler. The subtask of then shuffling the order of passes to see if you missed anything is trivial, using machine learning to control your sort & test loop doesn't seem very compelling here.

My hunch is that the low hanging fruit in compiler dev using LLM is driving a fuzz tester with one. Other things seem worthwhile but difficult.