Index: include/llvm/ADT/DepthFirstIterator.h
===================================================================
--- include/llvm/ADT/DepthFirstIterator.h
+++ include/llvm/ADT/DepthFirstIterator.h
@@ -107,7 +107,11 @@
       if (!Opt)
         Opt.emplace(GT::child_begin(Node));
 
-      for (NodeRef Next : make_range(*Opt, GT::child_end(Node))) {
+      // Notice that we use `auto &It =` here, as opposed to `auto It =` or
+      // range-based for loop, so that VisitStack.back().second actually gets
+      // updated.
+      for (auto &It = *Opt; It != GT::child_end(Node); ++It) {
+        NodeRef Next = *It;
         // Has our next sibling been visited?
         if (this->Visited.insert(Next).second) {
           // No, do it now.