Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -640,6 +640,13 @@
   // iterations. This function adds the appropriate CFG connections.
   BasicBlock *InsertBot = UseEpilogRemainder ? Exit : PrologExit;
   BasicBlock *InsertTop = UseEpilogRemainder ? EpilogPreHeader : PrologPreHeader;
+  // Cloning the loop basic blocks requires that one of the targets of the Latch
+  // be the (single) exit block out of the loop. This needs to be guaranteed by
+  // the callers of UnrollRuntimeLoopRemainder.
+  BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
+  assert(LatchBR->getSuccessor(0) == Exit ||
+         LatchBR->getSuccessor(1) == Exit && "loop latch successor should be "
+                                             "exit block!");
   CloneLoopBlocks(L, ModVal, CreateRemainderLoop, UseEpilogRemainder, InsertTop,
                   InsertBot, NewPreHeader, NewBlocks, LoopBlocks, VMap, DT, LI);