[SYCL] Half type in global scope

[Ruyk]

The line below:

llvm/sycl/include/CL/sycl/half_type.hpp

Line 223 in c72cbc4

using half = cl::sycl::detail::half_impl::half;

defines Half type in global scope, but that is not required by the SYCL specification. Is there any reason this is there?

It causes conflicts with CUDA headers, which define also the half type in global scope.

[Ruyk]

In case someone arrives here from finding this error in SYCL for CUDA code: the CUDA_NO_HALF definition removes the half type in CUDA.

[bader]

@Fznamznon, you seem to commit the original code. Do you recall the reason?

[bader]

Might be related to this spec issue: KhronosGroup/SYCL-Docs#40. At some point half was defined as fundamental type. It might be just an artifact of old implementation.

[Fznamznon]

Might be related to this spec issue: KhronosGroup/SYCL-Docs#40. At some point half was defined as fundamental type. It might be just an artifact of old implementation.

Yes, you are right. half was defined in global scope because CTS tests were checking it without any namespaces. If tests are fixed, we can remove this definition.

[bader]

Can we make it in reverse order? Let's remove the global scope declaration and test it against the latest SYCL-CTS. If tests fail, we fix both the implementation and the tests.

[pvchupin]

@AlexeySachkov, can you please take a look?

[bader]

Fixed by #2624.