REG_FN_TEST_BASE
[REG_FN_TEST_BASE + 0] = test_8,
[REG_FN_TEST_BASE + 1] = test_16,
[REG_FN_TEST_BASE + 3] = test_32,
unsigned int fn = REG_FN_TEST_BASE + (subgroup->reg_width >> 3) - 1;