diff --git a/llvm/include/llvm/ADT/PointerUnion.h b/llvm/include/llvm/ADT/PointerUnion.h
--- a/llvm/include/llvm/ADT/PointerUnion.h
+++ b/llvm/include/llvm/ADT/PointerUnion.h
@@ -139,6 +139,9 @@
 
   explicit operator bool() const { return !isNull(); }
 
+  // FIXME: Replace the uses of is(), get() and dyn_cast() with
+  //        isa<T>, cast<T> and the llvm::dyn_cast<T>
+
   /// Test if the Union currently holds the type matching T.
   template <typename T> inline bool is() const { return isa<T>(*this); }