diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.h b/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 0de20c76e11..b42232b5d13 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -173,6 +173,9 @@ class DwarfDebug {
   /// (at the end of the module) as DW_AT_inline.
   SmallPtrSet<DIE *, 4> InlinedSubprogramDIEs;
 
+  /// ContainingTypeMap - This map is used to keep track of subprogram DIEs that
+  /// need DW_AT_containing_type attribute. This attribute points to a DIE that
+  /// corresponds to the MDNode mapped with the subprogram DIE.
   DenseMap<DIE *, MDNode *> ContainingTypeMap;
 
   typedef SmallVector<DbgScope *, 2> ScopeVector;