[mathisfun123]

>As I understand it, MLIR is the new subsystem that the LLVM project is transitioning to in the long term, and LLVM IR is the old.

this is very much not a forgone conclusion and many people in LLVM would boo vociferously at the idea (see last year's LLVM US meeting where Johannes Doerfert actually argued the exact opposite - extending LLVM IR to do some/many of the things that MLIR does).

[Joky]

It depends what you mean by "new subsystem" and "transitioning to": what seems like a given is that the notion of "one size fits all" of LLVM IR is behind us and the need to multi-level IR is embraced. LLVM IR is evolving to accommodate this better, within reason (that is: it stay organized around a pretty well defined core instruction set and type system), and MLIR is just the fully extensible framework beyond this. It is to be seen if anyone would have the appetite to port LLVM IR (and the LLVM framework) to be a dialect, I think there are challenges for this.