[sanxiyn]

Well, OCaml Rust compiler also didn't use LLVM and used its own lightweight code generator and I think self-hosted Rust compiler frontend was in fact faster than OCaml Rust compiler frontend.

[parentheses]

With both projects, how much of the improvement is simply building for the second time?

[sanxiyn]

For Rust, I think improvement was almost entirely due to LLVM producing faster code. That's not applicable to Zig case, since both old and new compiler use LLVM. I don't know enough about Zig to answer.