AMDGPU: Add implicitarg.ptr intrinsic.

Points to the start of implicit arguments (appended after explicit arguments)

Differential Revision: http://reviews.llvm.org/D20297

llvm-svn: 273317
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
index ecf69f8..d4b3766 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
@@ -201,8 +201,9 @@
                                        unsigned Reg, EVT VT) const;
 
   enum ImplicitParameter {
-    GRID_DIM,
-    GRID_OFFSET
+    FIRST_IMPLICIT,
+    GRID_DIM = FIRST_IMPLICIT,
+    GRID_OFFSET,
   };
 
   /// \brief Helper function that returns the byte offset of the given