Add unique identifier field to Composite Types and Format.

llvm-svn: 189593

llvm/docs/SourceLevelDebugging.rst

@@ -462,9 +462,10 @@ Composite type descriptors
     i32,      ;; Flags
     metadata, ;; Reference to type derived from
     metadata, ;; Reference to array of member descriptors
-    i32       ;; Runtime languages
+    i32,      ;; Runtime languages
     metadata, ;; Base type containing the vtable pointer for this type
-    metadata  ;; Template parameters
+    metadata, ;; Template parameters
+    metadata  ;; A unique identifier for type uniquing purpose (may be null)
   }
 
 These descriptors are used to define types that are composed of 0 or more