Index: llvm/include/llvm/Analysis/LoopInfo.h
===================================================================
--- llvm/include/llvm/Analysis/LoopInfo.h
+++ llvm/include/llvm/Analysis/LoopInfo.h
@@ -103,6 +103,9 @@
     return D;
   }
   BlockT *getHeader() const { return getBlocks().front(); }
+  // Return the parent loop of this loop (i.e. the loop in which
+  // this loop is entirely contained). If there's no such loop (i.e.
+  // this is a top level loop in the function), return null.
   LoopT *getParentLoop() const { return ParentLoop; }
 
   /// This is a raw interface for bypassing addChildLoop.