Add a note about a missing optimization in the case of virtual
inheritance.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153722 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/NOTES.txt b/NOTES.txt
index 9f7ed4b..ca46d1c 100644
--- a/NOTES.txt
+++ b/NOTES.txt
@@ -101,3 +101,14 @@
 metaprogramming.
 
 //===---------------------------------------------------------------------===//
+
+We can still apply a modified version of the constructor/destructor
+delegation optimization in cases of virtual inheritance where:
+  - there is no function-try-block,
+  - the constructor signature is not variadic, and
+  - the parameter variables can safely be copied and repassed
+    to the base constructor because either
+    - they have not had their addresses taken by the vbase initializers or
+    - they were passed indirectly.
+
+//===---------------------------------------------------------------------===//