Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -545,6 +545,15 @@
   BasicBlock *Header = L->getHeader();
 
   BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
+
+  if (!LatchBR || LatchBR->isUnconditional()) {
+    // The loop-rotate pass can be helpful to avoid this in many cases.
+    LLVM_DEBUG(
+        dbgs()
+        << "Can't unroll; loop not terminated by a conditional branch.\n");
+    return false;
+  }
+
   unsigned ExitIndex = LatchBR->getSuccessor(0) == Header ? 1 : 0;
   BasicBlock *LatchExit = LatchBR->getSuccessor(ExitIndex);
   // Cloning the loop basic blocks (`CloneLoopBlocks`) requires that one of the