I’m talking about passes which operate on either (a) CodeInfo - a high-level IR which is the data interface for Julia’s abstract interpretation based type infer

I’m talking about passes which operate on either (a) CodeInfo - a high-level IR which is the data interface for Julia’s abstract interpretation based type inference an (b) IRCode which is what Julia’s optimizer uses. Note: again, I haven’t looked recently —- but this is what I remember from a number of months ago. When I discussed writing passes, I was referring to interacting with these two phases of the compiler (abstract interpreter and optimization). In practice, these two phases are interlinked. Shuffling data between these two phases make a lot of assumptions which are mostly opaque to users. Like I said, you can hack it — but it’s hard to learn what you need to know, and there’s not a stable interface or a nice “this is how you write a transformation to operate on this IR” or “this is how you write a custom opt”. In any case, I’m not totally convinced that it’s a good idea to expose this stuff to user libraries. Or, at least, it needs to be carefully thought about. See some of the complaints about “magic” in this post for some of that. I’m just fascinated by this stuff for some weird reason.