Index: include/llvm/Support/GenericDomTree.h
===================================================================
--- include/llvm/Support/GenericDomTree.h
+++ include/llvm/Support/GenericDomTree.h
@@ -247,7 +247,7 @@
     unsigned Parent;
     unsigned Semi;
     NodeT *Label;
-
+    SmallVector<NodeT *, 2> ReverseChildren;
     InfoRec() : DFSNum(0), Parent(0), Semi(0), Label(nullptr) {}
   };
 
Index: include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- include/llvm/Support/GenericDomTreeConstruction.h
+++ include/llvm/Support/GenericDomTreeConstruction.h
@@ -93,6 +93,8 @@
     typename GraphT::NodeRef Succ = *NextSucc;
 
     auto &SuccVInfo = DT.Info[Succ];
+    SuccVInfo.ReverseChildren.push_back(BB);
+
     if (SuccVInfo.Semi == 0) {
       SuccVInfo.Parent = BBDFSNum;
       Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
@@ -201,16 +203,10 @@
 
     // initialize the semi dominator to point to the parent node
     WInfo.Semi = WInfo.Parent;
-    typedef GraphTraits<Inverse<NodeT> > InvTraits;
-    for (typename InvTraits::ChildIteratorType CI =
-         InvTraits::child_begin(W),
-         E = InvTraits::child_end(W); CI != E; ++CI) {
-      typename InvTraits::NodeRef N = *CI;
-      if (DT.Info.count(N)) {  // Only if this predecessor is reachable!
+    for (auto *N : WInfo.ReverseChildren) {
         unsigned SemiU = DT.Info[Eval<GraphT>(DT, N, i + 1)].Semi;
         if (SemiU < WInfo.Semi)
           WInfo.Semi = SemiU;
-      }
     }
 
     // If V is a non-root vertex and sdom(V) = parent(V), then idom(V) is