Index: include/llvm/IR/Instruction.h
===================================================================
--- include/llvm/IR/Instruction.h
+++ include/llvm/IR/Instruction.h
@@ -665,6 +665,10 @@
   /// instruction must be a terminator.
   void setSuccessor(unsigned Idx, BasicBlock *BB);
 
+  /// Change specified successor OldBB to point at the provided block.
+  /// This instruction must be a terminator.
+  void changeSuccessor(BasicBlock *OldBB, BasicBlock *NewBB);
+
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const Value *V) {
     return V->getValueID() >= Value::InstructionVal;
Index: lib/IR/Instruction.cpp
===================================================================
--- lib/IR/Instruction.cpp
+++ lib/IR/Instruction.cpp
@@ -675,6 +675,15 @@
   llvm_unreachable("not a terminator");
 }
 
+void Instruction::changeSuccessor(BasicBlock *OldBB, BasicBlock *NewBB) {
+  for (unsigned idx = 0, NumSuccessors = Instruction::getNumSuccessors();
+       idx != NumSuccessors; ++idx) {
+    BasicBlock *CurrSuccessor = getSuccessor(idx);
+    if (CurrSuccessor == OldBB)
+      setSuccessor(idx, NewBB);
+  }
+}
+
 Instruction *Instruction::cloneImpl() const {
   llvm_unreachable("Subclass of Instruction failed to implement cloneImpl");
 }
Index: lib/Transforms/Utils/LoopSimplify.cpp
===================================================================
--- lib/Transforms/Utils/LoopSimplify.cpp
+++ lib/Transforms/Utils/LoopSimplify.cpp
@@ -443,9 +443,7 @@
     if (!LoopMD)
       LoopMD = TI->getMetadata(LoopMDKind);
     TI->setMetadata(LoopMDKind, nullptr);
-    for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
-      if (TI->getSuccessor(Op) == Header)
-        TI->setSuccessor(Op, BEBlock);
+    TI->changeSuccessor(Header, BEBlock);
   }
   BEBlock->getTerminator()->setMetadata(LoopMDKind, LoopMD);