[PATCH] D94188: [OpenCL] add documentation for experimental C++ libraries support

[Anastasia Stulova via Phabricator via cfe-commits]

Anastasia created this revision.
Anastasia added a reviewer: mantognini.
Herald added subscribers: ebevhan, yaxunl.
Anastasia requested review of this revision.

Started a new doc section about the OpenCL experimental features and described ongoing work on C++ libraries e.g. type traits.


https://reviews.llvm.org/D94188

Files:
  clang/docs/OpenCLSupport.rst


Index: clang/docs/OpenCLSupport.rst
===================================================================
--- clang/docs/OpenCLSupport.rst
+++ clang/docs/OpenCLSupport.rst
@@ -96,3 +96,56 @@
 +------------------------------+--------------------------------------------------------------+----------------------+---------------------------------------------------------------------------+
 | New functionality            | Atomic mem scopes: subgroup, all devices including functions | :part:`worked on`    | https://reviews.llvm.org/D92004 (functions only)                          |
 +------------------------------+--------------------------------------------------------------+----------------------+---------------------------------------------------------------------------+
+
+Experimental features
+=====================
+
+Clang provides the following new WIP features for the developers to experiment
+with and provide early feedback or contribute with further improvements.
+Feel free to contact us on `cfe-dev
+<https://lists.llvm.org/mailman/listinfo/cfe-dev>`_ or via `Bugzilla
+<https://bugs.llvm.org/>`_.
+
+C++ libraries for OpenCL
+------------------------
+
+There is ongoing work to support C++ standard libraries from `LLVM's libcxx
+<https://libcxx.llvm.org/>`_ in OpenCL kernel code using C++ for OpenCL mode.
+
+It is currently possible to use `type_traits` from C++17 in the kernel sources
+if the following clang extensions are enabled ``__cl_clang_function_pointers``
+and ``__cl_clang_variadic_functions``, see :doc:`LanguageExtensions` for more
+details. The use of non-conformant features enabled by the extensions does not
+expose non-conformant behavior beyond the compilation i.e. does not get
+generated in IR or binary.  The extension only appear in metaprogramming
+mechanism to identify or verify the properties of types. This allows to provide
+the full C++ functionality without a loss of portability. To avoid unsafe use
+of the extensions it is recommended that the extensions are disabled directly
+after the header include.
+
+**Example of Use**:
+
+The example of kernel code with `type_traits` is illustrated here.
+
+.. code-block:: c++
+
+  #pragma OPENCL EXTENSION __cl_clang_function_pointers : enable
+  #pragma OPENCL EXTENSION __cl_clang_variadic_functions : enable
+  #include "type_traits"
+  #pragma OPENCL EXTENSION __cl_clang_function_pointers : disable
+  #pragma OPENCL EXTENSION __cl_clang_variadic_functions : disable
+ 
+  typedef std::make_signed<unsigned int>::type sint_t;
+        
+  __kernel void foo() {
+    static_assert(!std::is_same<sint_t, unsigned int>::value);
+  }
+
+The possible clang invocation to compile the example is as follows:
+
+   .. code-block:: console
+
+     $ clang -cl-std=clc++  -I<path to libcxx checkout or installation>/include test.cl
+
+Note that `type_traits` is a header only library and therefore no extra
+linking step for the standard libraries is required.


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