[clang] [SYCL] The sycl_kernel_entry_point attribute. (PR #111389)

[Erich Keane via cfe-commits]

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@@ -455,6 +455,174 @@ The SYCL kernel in the previous code sample meets these expectations.
   }];
 }
 
+def SYCLKernelEntryPointDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``sycl_kernel_entry_point`` attribute facilitates the generation of an
+offload kernel entry point, sometimes called a SYCL kernel caller function,
+suitable for invoking a SYCL kernel on an offload device. The attribute is
+intended for use in the implementation of SYCL kernel invocation functions
+like the ``single_task`` and ``parallel_for`` member functions of the
+``sycl::handler`` class specified in section 4.9.4, "Command group ``handler``
+class", of the SYCL 2020 specification.
+
+The attribute requires a single type argument that specifies a class type that
+meets the requirements for a SYCL kernel name as described in section 5.2,
+"Naming of kernels", of the SYCL 2020 specification. A unique kernel name type
+is required for each function declared with the attribute. The attribute may
+not first appear on a declaration that follows a definition of the function.
+
+The attribute only appertains to functions and only those that meet the
+following requirements.
+
+* Has a ``void`` return type.
+* Is not a non-static member function, constructor, or destructor.
+* Is not a C variadic function.
+* Is not a coroutine.
+* Is not defined as deleted or as defaulted.
+* Is not declared with the ``constexpr`` or ``consteval`` specifiers.
----------------
erichkeane wrote:

I don't see a good reason to limit it here, I think we should just implement it as support.  Particularly as the library isn't necessarily the only user of this.  Plus, it allows users to USE existing library functions.  That is, it is an artificial restriction on users who wnat to re-use existing code, even if we don't ever execute at constexpr time.

https://github.com/llvm/llvm-project/pull/111389