a.Index = arm64.REG_SXTW + Rnum
			} else {
				a.Reg = arm64.REG_SXTW + Rnum
			}
		case "SXTX":
			if a.Type == obj.TYPE_MEM {
				a.Index = arm64.REG_SXTX + Rnum
			} else {
				a.Reg = arm64.REG_SXTX + Rnum
			}
		case "LSL":
			a.Index = arm64.REG_LSL + Rnum
		default:
			return errors.New("unsupported general register extension type: " + ext)

		}
	} else if reg <= arm64.REG_V31 && reg >= arm64.REG_V0 {