from armv8.c:1413
static struct reg_data_type_union_field aarch64_union_fields_vns[] = {
{"f", aarch64_fpu_vector + 3, aarch64_union_fields_vns + 1},
{"u", aarch64_fpu_vector + 4, aarch64_union_fields_vns + 2},
{"s", aarch64_fpu_vector + 5, NULL},
};