Egraphs are for optimization passes, which operate on the same IR, and (without egraphs) may undo and/or prevent each other and are repeated for more optimization.

Nanopass is compiler passes, which each have their own IR, and run once in a fixed sequence.

Egraphs also require the IR to be defined a specific way, which prevents some optimizations. My understanding of https://github.com/bytecodealliance/rfcs/blob/main/accepted/... is that cranelift’s egraph optimizations are pure expression reordering/duplication/deduplication and rewrite rules.