Comment by exDM69

Doing many passes seems to be working very well in LLVM, which is definitely not targeted at or implemented with functional languages and is not a toy compiler framework for educational purposes but a full-blown industrial strength compiler framework.

Yes, you need to take care of garbage collection (in one way or another) when you're manipulating tree and graph structures.

I can't share your opinion about "ending badly". This has been shown to be a good strategy in practice.