[SYCL] Add structure to pass references to ranges

[Alexandr-Konovalov]

This allows to have single entry point for all dimentions and keep reference to user-provided range data, not copy them.

[uditagarwal97]

Just thinking out load, would it be better to call this class ranges_ref_view? Since this class is just a "view" over the user-provided range and doesn't own the lifetime of the underlying range object. Similar to how string_view or ranges::ref_view (https://www.en.cppreference.com/w/cpp/ranges/ref_view.html) works.

[Alexandr-Konovalov]

Sounds good, done.

[Alexandr-Konovalov]

Issue probably related to the test fail: Reduction/reduction_internal_nd_range_1dim.cpp sporadically fails in pre-commit BMG&L0 #19767

[vinser52]

I am not sure that it is the best name. We have sycl::range and someone might assume that ranges_ref_view is a view to the sycl::range. Also it is not lear what _ref_ means in the name. Why not just nd_range_view?

[Alexandr-Konovalov]

View has strong connotation to views from C++20, that may be or may be not good.

Alternatively, it can be nd_range_ref. I don't know.

Also it is not lear what ref means in the name.

That's for "reference", I hope.

[vinser52]

I vote for nd_range_view.

@sergey-semenov, @aelovikov-intel, @slawekptak what do you think?

[aelovikov-intel]

I'll copy my sketch from the offline group chat:

struct range_storage { std::array<size_t, 3> r; };

struct range_view {
  range_storage &s;
  size_t Dims;

  range_view(const range_base&);
  range_view(const range_storage&, size_t);

  operator range_base();

  // define all range interfaces;
};

struct range_base : range_storage { size_t Dims; 
// All interfaces delegate to range_view(*this).interface(...);
}
template <size_t> range : range_base {};

struct nd_range_base {
  size_t Dims;
  range_storage global;
  ...
};

[uditagarwal97]

The testing logic for 1,2 and 3 dimensions ranges_ref_view is the same. Would it be possible to abstract out the testing logic in a function, templated over the dimension parameter?
For example:

template <int dims>
void TestNDRangesRefView(sycl::ranges<dims> global, sycl::ranges<dims> local, sycl::id<dims> offset) {
sycl::nd_range<dims> nd_range{global, local, offset};
  {
    sycl::detail::ranges_ref_view r{nd_range};
     ASSERT_EQ(r.Dims, size_t{dims}); // I guess this can be a compile-time static assert?
     for (int d = 0, d < dims, d++) {
        ASSERT_EQ(r.GlobalSize[d], global_range[d]);
        ASSERT_EQ(r.LocalSize[d], local_range[d]);
        ASSERT_EQ(r.GlobalOffset[d], offset[d]);
     }
  }
 ...
}

And then this function can be called thrice, once for each dimension, 1, 2, 3. That should reduce code duplication and would be easier to update it, if something changes in ranges_ref_view

[Alexandr-Konovalov]

Thanks, that's much better!

Unfortunately I can't use static_assert for the dimension check, constness should be improved.