Function compile 

pub fn compile(
    source: &Func,
    names: &mut Interner,
    machine: &Machine,
    flags: Flags,
) -> Result<Func, Unsupported>

Compiles one function, from the IR the middle end produced to machine instructions.

Errors

The first thing in it this cannot lower, which is what lower::func reports and is the only pass here that can refuse a function. Everything after lowering works on machine instructions that exist, so it either runs or it is a bug in this crate.