I’m a little confused reading this. Is MIR short for “machine intermediate representation” instead of “medium intermediate representation”? I generally expect IRs to be relatively platform-independent but it sounds like the “MIR” here is close to Aarch64 binary?

Zig has a couple of IR layers. Generally, Zig's compiler goes: AST → ZIR → AIR, and from there it'll either emit LLVM bitcode or one of its own, platform-specific "Machine IR"

Likely refers to Machine IR, a lower level representation that normal LLVM IR lowers to?

In rust it's mid-level IR.

Here's what that all means in rust terms [1]. I assume zig doing something similar.

[1] https://blog.rust-lang.org/2016/04/19/MIR/