Function rustc_middle::mir::pretty::write_allocation_bytes

fn write_allocation_bytes<'tcx, Prov: Provenance, Extra>(
    tcx: TyCtxt<'tcx>,
    alloc: &Allocation<Prov, Extra>,
    w: &mut dyn Write,
    prefix: &str
) -> Result

The prefix argument allows callers to add an arbitrary prefix before each line (even if there is only one line). Note that your prefix should contain a trailing space as the lines are printed directly after it.