[SYCL] Enable shuffle tests on HIP AMD.

[jchlanda]

Even though gfx908 and gfx906 support halfs, libspirv is currently
built with tahiti as the target CPU, which means that clang rejects
AMD built-ins using halfs, for that reason half support has to stay
disabled.

[jchlanda]

Corresponding work in llvm repo: intel/llvm#4664

[Pennycook]

Half test is still xfail as neither gfx908 nor gfx906 supports it.

Sorry if this is a silly question -- is this something you could work around by forwarding to an integer shuffle, or does compilation for these platforms fail as soon as they see a half type in a kernel?

[npmiller]

Half test is still xfail as neither gfx908 nor gfx906 supports it.

Sorry if this is a silly question -- is this something you could work around by forwarding to an integer shuffle, or does compilation for these platforms fail as soon as they see a half type in a kernel?

To expand a bit on that gfx906 and gfx908 actually do support half as far as I understand it, the issue is that libspirv is currently built with tahiti as the target CPU, which means that clang rejects AMD built-ins using halfs, as tahiti doesn't support them.

This is definitely an issue we need to figure out in the libclc build, but it's broader than just the subgroup builtins here, so I'm not sure if it's worth doing a workaround just for this, I also ran into it in intel/llvm#4223 a while back.

[Pennycook]

This is definitely an issue we need to figure out in the libclc build, but it's broader than just the subgroup builtins here, so I'm not sure if it's worth doing a workaround just for this, I also ran into it in intel/llvm#4223 a while back.

Got it. Thanks for the explanation.

FWIW, this sort of thing also impacts the CUDA backend. The ability to generate floating-point atomics, for example (see intel/llvm#3276) depends on the SM architecture that libclc is being built for. A general solution for multi-versioning and/or controlling the architecture used by libclc would be useful to multiple backends.

[jchlanda]

To expand a bit on that gfx906 and gfx908 actually do support half as far as I understand it, the issue is that libspirv is currently built with tahiti as the target CPU, which means that clang rejects AMD built-ins using halfs, as tahiti doesn't support them.

Thanks @npmiller for the clarification, I'll update the comments to reflect that.