Add description for GPU code generation pass in DFG2LLVM_OpenCL.cpp

hpvm/lib/Transforms/DFG2LLVM_OpenCL/DFG2LLVM_OpenCL.cpp

@@ -6,6 +6,14 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+// 
+// This pass is responsible for generating code for kernel code and code for 
+// launching kernels for GPU target using HPVM dataflow graph. The kernels are
+// generated into a separate file which is the C-Backend uses to generate 
+// OpenCL kernels with.
+//
+//===----------------------------------------------------------------------===//
+
 
 #define ENABLE_ASSERTS
 #define TARGET_PTX 64