diff --git a/llvm/lib/Transforms/Scalar/NewGVN.cpp b/llvm/lib/Transforms/Scalar/NewGVN.cpp
--- a/llvm/lib/Transforms/Scalar/NewGVN.cpp
+++ b/llvm/lib/Transforms/Scalar/NewGVN.cpp
@@ -859,6 +859,7 @@
   // Utilities.
   void cleanupTables();
   std::pair<unsigned, unsigned> assignDFSNumbers(BasicBlock *, unsigned);
+  unsigned updateDFSNumbers(unsigned);
   void updateProcessedCount(const Value *V);
   void verifyMemoryCongruency() const;
   void verifyIterationSettled(Function &F);
@@ -3011,6 +3012,16 @@
   return std::make_pair(Start, End);
 }
 
+unsigned NewGVN::updateDFSNumbers(unsigned ICount) {
+  for (auto DTN : depth_first(DT->getRootNode())) {
+    BasicBlock *B = DTN->getBlock();
+    const auto &BlockRange = assignDFSNumbers(B, ICount);
+    BlockInstRange.insert({B, BlockRange});
+    ICount += BlockRange.second - BlockRange.first;
+  }
+  return ICount;
+}
+
 void NewGVN::updateProcessedCount(const Value *V) {
 #ifndef NDEBUG
   if (ProcessedCount.count(V) == 0) {
@@ -3449,12 +3460,7 @@
   }
 
   // Now a standard depth first ordering of the domtree is equivalent to RPO.
-  for (auto DTN : depth_first(DT->getRootNode())) {
-    BasicBlock *B = DTN->getBlock();
-    const auto &BlockRange = assignDFSNumbers(B, ICount);
-    BlockInstRange.insert({B, BlockRange});
-    ICount += BlockRange.second - BlockRange.first;
-  }
+  ICount = updateDFSNumbers(ICount);
   initializeCongruenceClasses(F);
 
   TouchedInstructions.resize(ICount);