Function rustc_middle::mir::pretty::write_allocation_bytes

fn write_allocation_bytes<Tag: Provenance, Extra, 'tcx>(
    tcx: TyCtxt<'tcx>, 
    alloc: &Allocation<Tag, 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.