Function one 

pub fn one(
    program: &Program,
    id: FunctionId,
    code: EncodedInst,
    pc: Pc,
) -> String

One encoded instruction as crate::print::one renders it.

Bytes that do not decode print as <the reason>, with the reason Malformed gives — which is the one thing the readable printer has no way to say, because no Inst is malformed.