Index: llvm/lib/CodeGen/MachineVerifier.cpp
===================================================================
--- llvm/lib/CodeGen/MachineVerifier.cpp
+++ llvm/lib/CodeGen/MachineVerifier.cpp
@@ -2264,10 +2264,13 @@
   }
 
   // Iteratively push vregsPassed to successors.
+  DenseSet<const MachineBasicBlock *> Visited;
   while (!RPOWorklist.empty()) {
     auto Next = RPOWorklist.begin();
     const MachineBasicBlock *MBB = Next->second;
     RPOWorklist.erase(Next);
+    if (!Visited.insert(MBB).second)
+      continue;
     FilteringVRegSet &MSet = VRegsPassedSets[RPONumbers[MBB]];
     for (const MachineBasicBlock *Succ : MBB->successors()) {
       if (Succ == MBB)