Index: include/llvm/Transforms/Utils/Cloning.h
===================================================================
--- include/llvm/Transforms/Utils/Cloning.h
+++ include/llvm/Transforms/Utils/Cloning.h
@@ -221,6 +221,7 @@
 ///
 /// Updates LoopInfo and DominatorTree assuming the loop is dominated by block
 /// \p LoopDomBB.  Insert the new blocks before block specified in \p Before.
+/// TODO: Support cloning loops with other loops inside it.
 Loop *cloneLoopWithPreheader(BasicBlock *Before, BasicBlock *LoopDomBB,
                              Loop *OrigLoop, ValueToValueMapTy &VMap,
                              const Twine &NameSuffix, LoopInfo *LI,
Index: lib/Transforms/Utils/CloneFunction.cpp
===================================================================
--- lib/Transforms/Utils/CloneFunction.cpp
+++ lib/Transforms/Utils/CloneFunction.cpp
@@ -702,11 +702,14 @@
 ///
 /// Updates LoopInfo and DominatorTree assuming the loop is dominated by block
 /// \p LoopDomBB.  Insert the new blocks before block specified in \p Before.
+/// TODO: Support cloning loops with other loops inside it.
 Loop *llvm::cloneLoopWithPreheader(BasicBlock *Before, BasicBlock *LoopDomBB,
                                    Loop *OrigLoop, ValueToValueMapTy &VMap,
                                    const Twine &NameSuffix, LoopInfo *LI,
                                    DominatorTree *DT,
                                    SmallVectorImpl<BasicBlock *> &Blocks) {
+  assert(OrigLoop->getSubLoops().empty() && 
+         "Loop to be cloned cannot have inner loop");
   Function *F = OrigLoop->getHeader()->getParent();
   Loop *ParentLoop = OrigLoop->getParentLoop();