[OpenCL] Add intel_reqd_sub_group_size attribute support

Summary:
Add intel_reqd_sub_group_size attribute support as intel extension  cl_intel_required_subgroup_size from
https://www.khronos.org/registry/OpenCL/extensions/intel/cl_intel_required_subgroup_size.txt

Reviewers: Anastasia, bader, hfinkel, pxli168

Reviewed By: Anastasia, bader, pxli168

Subscribers: cfe-commits, yaxunl

Differential Revision: https://reviews.llvm.org/D30805

llvm-svn: 302125
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index b696408..459841a 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1413,16 +1413,8 @@
   /// True if we need emit the life-time markers.
   const bool ShouldEmitLifetimeMarkers;
 
-  /// Add a kernel metadata node to the named metadata node 'opencl.kernels'.
-  /// In the kernel metadata node, reference the kernel function and metadata 
-  /// nodes for its optional attribute qualifiers (OpenCL 1.1 6.7.2):
-  /// - A node for the vec_type_hint(<type>) qualifier contains string
-  ///   "vec_type_hint", an undefined value of the <type> data type,
-  ///   and a Boolean that is true if the <type> is integer and signed.
-  /// - A node for the work_group_size_hint(X,Y,Z) qualifier contains string 
-  ///   "work_group_size_hint", and three 32-bit integers X, Y and Z.
-  /// - A node for the reqd_work_group_size(X,Y,Z) qualifier contains string 
-  ///   "reqd_work_group_size", and three 32-bit integers X, Y and Z.
+  /// Add OpenCL kernel arg metadata and the kernel attribute meatadata to
+  /// the function metadata.
   void EmitOpenCLKernelMetadata(const FunctionDecl *FD, 
                                 llvm::Function *Fn);