Function entry 

pub fn entry(
    out: &mut Func,
    block: Block,
    params: &[Param],
    conv: &CallRegs,
    names: &mut Interner,
    save: Option<Area>,
) -> Result<Arrived, (usize, Missing)>

Binds a function’s parameters to where the convention says they arrive.

Errors

The first parameter this cannot bring in, and why. A function with one is reported rather than compiled, because the alternative is a function that reads an argument from wherever the last one happened to leave a register.