[SYCL] Define missing feature test macros

[ghost]

[SYCL] Define missing feature test macros

According to SYCL spec (6.3.3. Feature test macros), vendors are encouraged to
group a related set of extensions together into a "feature" and to predefine
a feature-test macro when the implementation supports the extensions in that
feature. The feature-test macro should have the following form to ensure it is
unique: SYCL_EXT__.

The patch defines the following feature test macros:

• SYCL_EXT_ONEAPI_ASSERT
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/Assert/SYCL_ONEAPI_ASSERT.asciidoc)
• SYCL_EXT_ONEAPI_FREE_FUNCTION_QUERIES
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/FreeFunctionQueries/SYCL_INTEL_free_function_queries.asciidoc)
• SYCL_EXT_ONEAPI_GROUP_ALGORITHMS
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/GroupAlgorithms/SYCL_INTEL_group_algorithms.asciidoc)
• SYCL_EXT_ONEAPI_GROUP_SORT
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/GroupAlgorithms/SYCL_INTEL_group_sort.asciidoc)
• SYCL_EXT_ONEAPI_LOCAL_MEMORY
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/LocalMemory/LocalMemory.asciidoc)
• SYCL_EXT_ONEAPI_ND_RANGE_REDUCTIONS
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/Reduction/Reduction.md)
• SYCL_EXT_ONEAPI_DEFAULT_CONTEXT
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/PlatformContext/PlatformContext.adoc)
• SYCL_EXT_ONEAPI_USE_PINNED_HOST_MEMORY_PROPERTY
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/UsePinnedMemoryProperty/UsePinnedMemoryPropery.adoc)
• SYCL_EXT_ONEAPI_SUB_GROUP
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/SubGroup/SYCL_INTEL_sub_group.asciidoc)
• SYCL_EXT_INTEL_BITCAST
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/Bitcast/SYCL_INTEL_bitcast.asciidoc)
• SYCL_EXT_INTEL_DATAFLOW_PIPES
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/DataFlowPipes/data_flow_pipes.asciidoc)
• SYCL_EXT_INTEL_EXTENDED_ATOMICS
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/ExtendedAtomics/SYCL_INTEL_extended_atomics.asciidoc)
• SYCL_EXT_INTEL_FPGA_DEVICE_SELECTOR
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/IntelFPGA/FPGASelector.md)
• SYCL_EXT_INTEL_FPGA_LSU
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/IntelFPGA/FPGALsu.md)
• SYCL_EXT_INTEL_FPGA_REG
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/IntelFPGA/FPGAReg.md)
• SYCL_EXT_INTEL_KERNEL_ARGS_RESTRICT
  (for https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/KernelRestrictAll/SYCL_INTEL_kernel_restrict_all.asciidoc)

The feature macros are defined for documented extensions only and the documentation is updated to mention the corresponding macros.

[gmlueck]

This specification already defines the feature test macro (see above around line 112). That existing section is the boilerplate we've been using for all new extensions, so please check the other files you've modified to see if they also have an existing feature test macro section.

Also, I think it would be better if all the specifications used the same boilerplate. I'd suggest using the format at line 112 for all extension specifications. If you don't like that existing format, I'm open to discussing alternatives, but I'd like all the specifications to use the same format. The reason we chose to add a table of values is to make it easier to extend these specifications in the future. If we add more functionality in the future, we can easily add a new row to the table (with a new macro value).

[ghost]

@gmlueck Thank you for review and the suggestion. I'll checked all the changed doc files and rewrite the Feature test macro sections using the same boilerplate as at line 112.

[ghost]

@gmlueck Greg, I've fixed the documentation about defined feature test macros using the proposed template.

[gmlueck]

Why do we have this macro to disable this one extension? None of the other extensions have a similar disable macro. Is there some particular reason why this extension should be different from the others? If not, I'd recommend removing the macro. Note that this macro does not seem to be documented anywhere, so I think it's not part of the extension's API.

[ghost]

I've just used the __DISABLE_SYCL_ONEAPI_GROUP_ALGORITHMS__ macro since the group_algorithm.hpp header is guarded by the #ifndef __DISABLE_SYCL_ONEAPI_GROUP_ALGORITHMS__ check, so if this macro is defined somewhere, we have no implementation for the extension.

The __DISABLE_SYCL_ONEAPI_GROUP_ALGORITHMS__ macro has been in the group_algorithm.hpp file since its birthday from commit 8bfa107c2346e304aca0355d9f3945a0233440a4 from @Pennycook co-authored by @rolandschulz and @AlexeySachkov. Colleagues, can you explain, why the macro was used and can/should we remove the #ifndef __DISABLE_SYCL_ONEAPI_GROUP_ALGORITHMS__ guard from both feature_test.hpp.in and group_algorithm.hpp files?

[Pennycook]

I think this is just a case of that extension predating the extension mechanism. I don't remember the specifics, but there was a lot of discussion about giving developers a way to enable and disable individual extensions, and this is what we went with.

We should probably define SYCL_EXT_ONEAPI_GROUP_ALGORITHMS similar to the other extensions, for the group algorithm interfaces defined in sycl::ext::oneapi::.

[ghost]

@Pennycook @gmlueck Well, I've added a commit that removes the __DISABLE_SYCL_ONEAPI_GROUP_ALGORITHMS__ guard from both headers. If any objections are there, the commit can just be reverted.

[gmlueck]

I think that makes sense. @Pennycook, any concerns?

[Pennycook]

Looks good to me. If this breaks something, we'll find out. :)

[ghost]

/summary:run

[alexbatashev]

lgtm