Index: lib/Transforms/Utils/CloneFunction.cpp
===================================================================
--- lib/Transforms/Utils/CloneFunction.cpp
+++ lib/Transforms/Utils/CloneFunction.cpp
@@ -310,10 +310,11 @@
       // the basic block.
       if (Value *V =
               SimplifyInstruction(NewInst, BB->getModule()->getDataLayout())) {
-        // On the off-chance that this simplifies to an instruction in the old
-        // function, map it back into the new function.
-        if (Value *MappedV = VMap.lookup(V))
-          V = MappedV;
+        assert((dyn_cast<Instruction>(V) == nullptr ||
+                dyn_cast<Instruction>(V)->getParent() == nullptr ||
+                dyn_cast<Instruction>(V)->getFunction() != OldFunc ||
+                OldFunc == NewFunc) &&
+               "Simplified Instruction should not be in the old function.");
 
         if (!NewInst->mayHaveSideEffects()) {
           VMap[&*II] = V;
@@ -453,7 +454,7 @@
   //
   // Defer PHI resolution until rest of function is resolved.
   SmallVector<const PHINode*, 16> PHIToResolve;
-  for (const BasicBlock &BI : *OldFunc) {
+  for (const BasicBlock &BI : make_range(OldFunc->begin(), OldFunc->end())) {
     Value *V = VMap.lookup(&BI);
     BasicBlock *NewBB = cast_or_null<BasicBlock>(V);
     if (!NewBB) continue;  // Dead block.