The biggest bottleneck in Zig's case is LLVM. That's why they implement fast alternative backends for development. See: https://kristoff.it/blog/zig-new-relationship-llvm/

looks like the project's now abandonned :

https://github.com/ziglang/zig/projects/2

This comment suggests otherwise:

https://github.com/ziglang/zig/issues/89#issuecomment-122118...

Although I'm not sure the "self hosted compiler" is the same as "llvm free backend".

It's not. The self-hosted compiler still uses llvm, and it's still slow because of it.

"self-hosted compiler" in this case means moving all the non-LLVM code (which was previously in C++) to Zig itself.

One thing I hate about LLVM is that once you get into the ecosystem to get “another alternative” or “abandon LLVM” it’s like hell, you get all these nice cool features then implementing a custom compiler for debugging can be much much harder than that