Function func 

pub fn func(
    source: &Func,
    names: &mut Interner,
    selector: &'static Selector,
    conv: &'static CallRegs,
    elsewhere: &Elsewhere,
) -> Result<Lowered, Unsupported>

The machine IR for that function, for the machine the selector describes.

Errors

The first instruction no rule fires on, which today is anything at a width the rule set is not written at, a parameter that does not arrive in a register this can read, or a call that passes something this cannot put where the convention wants it.