This is an optional SYCL feature and should be used accordingly. It's a part of the reduce-then-scan algorithm.
There is a warning when using it with acpp - a real use-case when it is not supported:
include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl_reduce_then_scan.h:1526:70: warning: unknown attribute 'reqd_sub_group_size' ignored [-Wunknown-attributes]
1526 | __nd_range, [=, *this](sycl::nd_item<1> __ndi) [[sycl::reqd_sub_group_size(__sub_group_size)]] {
This is an optional SYCL feature and should be used accordingly. It's a part of the reduce-then-scan algorithm.
There is a warning when using it with
acpp- a real use-case when it is not supported: