diff --git a/llvm/include/llvm/Analysis/BranchProbabilityInfo.h b/llvm/include/llvm/Analysis/BranchProbabilityInfo.h
--- a/llvm/include/llvm/Analysis/BranchProbabilityInfo.h
+++ b/llvm/include/llvm/Analysis/BranchProbabilityInfo.h
@@ -62,7 +62,8 @@
   }
 
   BranchProbabilityInfo(BranchProbabilityInfo &&Arg)
-      : Probs(std::move(Arg.Probs)), LastF(Arg.LastF),
+      : Probs(std::move(Arg.Probs)), MaxSuccIdx(std::move(Arg.MaxSuccIdx)),
+        LastF(Arg.LastF),
         PostDominatedByUnreachable(std::move(Arg.PostDominatedByUnreachable)),
         PostDominatedByColdCall(std::move(Arg.PostDominatedByColdCall)) {}
 
@@ -72,6 +73,7 @@
   BranchProbabilityInfo &operator=(BranchProbabilityInfo &&RHS) {
     releaseMemory();
     Probs = std::move(RHS.Probs);
+    MaxSuccIdx = std::move(RHS.MaxSuccIdx);
     PostDominatedByColdCall = std::move(RHS.PostDominatedByColdCall);
     PostDominatedByUnreachable = std::move(RHS.PostDominatedByUnreachable);
     return *this;
@@ -273,6 +275,9 @@
 
   DenseMap<Edge, BranchProbability> Probs;
 
+  // The maximum successor index ever entered for a given basic block.
+  DenseMap<const BasicBlock *, unsigned> MaxSuccIdx;
+
   /// Track the last function we run over for printing.
   const Function *LastF = nullptr;
 
diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -1031,6 +1031,7 @@
 
 void BranchProbabilityInfo::releaseMemory() {
   Probs.clear();
+  MaxSuccIdx.clear();
   Handles.clear();
 }
 
@@ -1136,6 +1137,11 @@
   LLVM_DEBUG(dbgs() << "set edge " << Src->getName() << " -> "
                     << IndexInSuccessors << " successor probability to " << Prob
                     << "\n");
+
+  if (MaxSuccIdx.find(Src) == MaxSuccIdx.end())
+    MaxSuccIdx[Src] = IndexInSuccessors;
+  else
+    MaxSuccIdx[Src] = std::max(MaxSuccIdx[Src], IndexInSuccessors);
 }
 
 /// Set the edge probability for all edges at once.
@@ -1173,11 +1179,16 @@
 }
 
 void BranchProbabilityInfo::eraseBlock(const BasicBlock *BB) {
-  for (const_succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
-    auto MapI = Probs.find(std::make_pair(BB, I.getSuccessorIndex()));
+  auto It = MaxSuccIdx.find(BB);
+  if (It == MaxSuccIdx.end())
+    return;
+
+  for (unsigned I = 0, E = It->second; I <= E; ++I) {
+    auto MapI = Probs.find(std::make_pair(BB, I));
     if (MapI != Probs.end())
       Probs.erase(MapI);
   }
+  MaxSuccIdx.erase(BB);
 }
 
 void BranchProbabilityInfo::calculate(const Function &F, const LoopInfo &LI,