if 0 <= n && n <= 30 { // not 31
			return arm64.REG_R0 + n, true
		}
	case "V":
		if 0 <= n && n <= 31 {
			return arm64.REG_V0 + n, true
		}
	}
	return 0, false
}

// ARM64RegisterShift constructs an ARM64 register with shift operation.
func ARM64RegisterShift(reg, op, count int16) (int64, error) {
	// the base register of shift operations must be general register.
	if reg > arm64.REG_R31 || reg < arm64.REG_R0 {