Change the definition of marray::size() to return NumElements

[fknorr]

The spec defines marray::size() to return the number of bytes in the marray instead of the number of elements. This is at odds with every other definition of a member named size() in SYCL, where size() would return the number of elements stored / accessed, and where applicable, a corresponding byte_size() function is provided to obtain the number of bytes.

I propose to change the definition to return the number of elements instead to avoid confusion and give the user a method of querying the element count without resorting to metaprogramming:

• Change marray::size() to read "Returns NumElements."
• (optionally) Add marray::byte_size() that reads "Returns the size of this SYCL marray in bytes.".

(Accidental) prior art:

• DPC++ already implements this in the manner proposed
• The CTS assumes any SYCL type with size() and operator[] members to behave in the proposed way, and will fail a SYCL implementation that adheres to the spec for this member.

[illuhad]

The definition in the spec indeed does seem counterintuitive to me.

For what it's worth, AdaptiveCpp also implements marray in the manner you propose, with the size() function returning NumElements: https://github.com/AdaptiveCpp/AdaptiveCpp/blob/2333dc631b38510f43e1c59f23ffc8e05d13daa6/include/hipSYCL/sycl/libkernel/marray.hpp#L112

This means that all implementations agree to disagree with the spec here. We should change the spec.

[gmlueck]

Yes, that's a good catch. I also think the spec should be changed.

[tomdeakin]

PR needed. CTS also assumes this returns NumElements.