def <<( reg )
      raise "not reg #{reg}" unless reg.is_a?(RegisterValue)
      reg_to_slot = Risc.reg_to_slot("#{reg.class_name} -> #{register.class_name}[#{index}]" , reg , register, index)
      builder.add_code(reg_to_slot) if builder
      reg_to_slot
    end
def <<( reg )
      raise "not reg #{reg}" unless reg.is_a?(RegisterValue)
      reg_to_slot = Risc.reg_to_slot("#{reg.class_name} -> #{register.class_name}[#{index}]" , reg , register, index)
      builder.add_code(reg_to_slot) if builder
      reg_to_slot
    end
fullfil the objects purpose by creating a RegToSlot instruction from
 itself (the slot) and the register given