[SYCL][DOC] Move SPIR-V and OpenCL extensions (#5578)

The SPIR-V and OpenCL extensions are not SYCL extensions, rather they
are extensions to underlying components used by DPC++.  Therefore, we
consider them part of the design, so move them to "doc/design".

Our policy is to remove SPIR-V and OpenCL extension specifications from
this repo once they are added to the Khronos registry.  The
"SPV_INTEL_arbitrary_precision_int" extension was already added there,
so remove it from this repo.

Author: gmlueck

sycl/ReleaseNotes.md

@@ -1185,7 +1185,7 @@ Release notes for commit range 5976ff0..1fc0e4f
     [c4c3494]
 
 ### Documentation
-  - Added documentation for [`SPV_INTEL_usm_storage_classes`](doc/extensions/SPIRV/SPV_INTEL_usm_storage_classes.asciidoc)
+  - Added documentation for [`SPV_INTEL_usm_storage_classes`](doc/design/spirv-extensions/SPV_INTEL_usm_storage_classes.asciidoc)
     and [SYCL_INTEL_usm_address_spaces](doc/extensions/supported/SYCL_EXT_INTEL_USM_ADDRESS_SPACES.asciidoc) [781fbfc]
   - Fixed SPIR-V format name spelling [6e9bf3b]
   - Added extension [LocalMemory](doc/extensions/supported/SYCL_EXT_ONEAPI_LOCAL_MEMORY.asciidoc) draft specification [4b5308a]

sycl/doc/conf.py

@@ -49,6 +49,8 @@
 exclude_patterns = [
     # Extensions are mostly in asciidoc which has poor support in Sphinx.
     'extensions/*',
+    'design/opencl-extensions/*',
+    'design/spirv-extensions/*',
 
     # Sphinx complains about syntax errors in these files.
     'design/DeviceLibExtensions.rst',

sycl/doc/design/DeviceGlobal.md

@@ -403,7 +403,7 @@ has the `implement_in_csr` property).  See the
 [SPV\_INTEL\_global\_variable\_decorations][6] SPIR-V extension for details
 about all of these decorations.
 
-[6]: <../extensions/DeviceGlobal/SPV_INTEL_global_variable_decorations.asciidoc>
+[6]: <spirv-extensions/SPV_INTEL_global_variable_decorations.asciidoc>
 
 The `sycl-post-link` tool also create a "SYCL/device globals" property set for
 each device code module that contains at least one device global variable.
@@ -614,7 +614,7 @@ The OpenCL backend has a proposed extension
 which can be easily used to implement these PI interfaces.  This DPC++ design
 depends upon implementation of that OpenCL extension.
 
-[10]: <../extensions/DeviceGlobal/cl_intel_global_variable_access.asciidoc>
+[10]: <opencl-extensions/cl_intel_global_variable_access.asciidoc>
 
 The CUDA backend has existing APIs `cudaMemcpyToSymbol()` and
 `cudaMemcpyFromSymbol()` which can be used to implement these PI interfaces.

sycl/doc/design/opencl-extensions/README.md

@@ -0,0 +1,8 @@
+# Draft OpenCL Extensions
+
+This directory contains draft OpenCL extensions that are used as part of the
+DPC++ design.  Once these extensions become fully mature, they are moved to the
+[Khronos OpenCL Registry][1].  Therefore, look there also for OpenCL extensions
+that are used by DPC++.
+
+[1]: <https://www.khronos.org/registry/OpenCL>

sycl/doc/extensions/DeviceGlobal/cl_intel_global_variable_access.asciidoc renamed to sycl/doc/design/opencl-extensions/cl_intel_global_variable_access.asciidoc

@@ -0,0 +1,8 @@
+# Draft SPIR-V Extensions
+
+This directory contains draft SPIR-V extensions that are used as part of the
+DPC++ design.  Once these extensions become fully mature, they are moved to the
+[Khronos SPIR-V Registry][1].  Therefore, look there also for SPIR-V extensions
+that are used by DPC++.
+
+[1]: <https://github.com/KhronosGroup/SPIRV-Registry>