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+//===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is the generic implementation of LoopInfo used for both Loops and
+// MachineLoops.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LOOPINFOIMPL_H
+#define LLVM_ANALYSIS_LOOPINFOIMPL_H
+
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/Dominators.h"
+
+namespace llvm {
+
+//===----------------------------------------------------------------------===//
+// APIs for simple analysis of the loop. See header notes.
+
+/// getExitingBlocks - Return all blocks inside the loop that have successors
+/// outside of the loop.  These are the blocks _inside of the current loop_
+/// which branch out.  The returned list is always unique.
+///
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::getExitingBlocks(
+    SmallVectorImpl<BlockT *> &ExitingBlocks) const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  for (const auto BB : blocks())
+    for (const auto &Succ : children<BlockT *>(BB))
+      if (!contains(Succ)) {
+        // Not in current loop? It must be an exit block.
+        ExitingBlocks.push_back(BB);
+        break;
+      }
+}
+
+/// getExitingBlock - If getExitingBlocks would return exactly one block,
+/// return that block. Otherwise return null.
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getExitingBlock() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  SmallVector<BlockT *, 8> ExitingBlocks;
+  getExitingBlocks(ExitingBlocks);
+  if (ExitingBlocks.size() == 1)
+    return ExitingBlocks[0];
+  return nullptr;
+}
+
+/// getExitBlocks - Return all of the successor blocks of this loop.  These
+/// are the blocks _outside of the current loop_ which are branched to.
+///
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::getExitBlocks(
+    SmallVectorImpl<BlockT *> &ExitBlocks) const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  for (const auto BB : blocks())
+    for (const auto &Succ : children<BlockT *>(BB))
+      if (!contains(Succ))
+        // Not in current loop? It must be an exit block.
+        ExitBlocks.push_back(Succ);
+}
+
+/// getExitBlock - If getExitBlocks would return exactly one block,
+/// return that block. Otherwise return null.
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  SmallVector<BlockT *, 8> ExitBlocks;
+  getExitBlocks(ExitBlocks);
+  if (ExitBlocks.size() == 1)
+    return ExitBlocks[0];
+  return nullptr;
+}
+
+/// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::getExitEdges(
+    SmallVectorImpl<Edge> &ExitEdges) const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  for (const auto BB : blocks())
+    for (const auto &Succ : children<BlockT *>(BB))
+      if (!contains(Succ))
+        // Not in current loop? It must be an exit block.
+        ExitEdges.emplace_back(BB, Succ);
+}
+
+/// getLoopPreheader - If there is a preheader for this loop, return it.  A
+/// loop has a preheader if there is only one edge to the header of the loop
+/// from outside of the loop and it is legal to hoist instructions into the
+/// predecessor. If this is the case, the block branching to the header of the
+/// loop is the preheader node.
+///
+/// This method returns null if there is no preheader for the loop.
+///
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  // Keep track of nodes outside the loop branching to the header...
+  BlockT *Out = getLoopPredecessor();
+  if (!Out)
+    return nullptr;
+
+  // Make sure we are allowed to hoist instructions into the predecessor.
+  if (!Out->isLegalToHoistInto())
+    return nullptr;
+
+  // Make sure there is only one exit out of the preheader.
+  typedef GraphTraits<BlockT *> BlockTraits;
+  typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
+  ++SI;
+  if (SI != BlockTraits::child_end(Out))
+    return nullptr; // Multiple exits from the block, must not be a preheader.
+
+  // The predecessor has exactly one successor, so it is a preheader.
+  return Out;
+}
+
+/// getLoopPredecessor - If the given loop's header has exactly one unique
+/// predecessor outside the loop, return it. Otherwise return null.
+/// This is less strict that the loop "preheader" concept, which requires
+/// the predecessor to have exactly one successor.
+///
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  // Keep track of nodes outside the loop branching to the header...
+  BlockT *Out = nullptr;
+
+  // Loop over the predecessors of the header node...
+  BlockT *Header = getHeader();
+  for (const auto Pred : children<Inverse<BlockT *>>(Header)) {
+    if (!contains(Pred)) { // If the block is not in the loop...
+      if (Out && Out != Pred)
+        return nullptr; // Multiple predecessors outside the loop
+      Out = Pred;
+    }
+  }
+
+  // Make sure there is only one exit out of the preheader.
+  assert(Out && "Header of loop has no predecessors from outside loop?");
+  return Out;
+}
+
+/// getLoopLatch - If there is a single latch block for this loop, return it.
+/// A latch block is a block that contains a branch back to the header.
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  BlockT *Header = getHeader();
+  BlockT *Latch = nullptr;
+  for (const auto Pred : children<Inverse<BlockT *>>(Header)) {
+    if (contains(Pred)) {
+      if (Latch)
+        return nullptr;
+      Latch = Pred;
+    }
+  }
+
+  return Latch;
+}
+
+//===----------------------------------------------------------------------===//
+// APIs for updating loop information after changing the CFG
+//
+
+/// addBasicBlockToLoop - This method is used by other analyses to update loop
+/// information.  NewBB is set to be a new member of the current loop.
+/// Because of this, it is added as a member of all parent loops, and is added
+/// to the specified LoopInfo object as being in the current basic block.  It
+/// is not valid to replace the loop header with this method.
+///
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::addBasicBlockToLoop(
+    BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) {
+  assert(!isInvalid() && "Loop not in a valid state!");
+#ifndef NDEBUG
+  if (!Blocks.empty()) {
+    auto SameHeader = LIB[getHeader()];
+    assert(contains(SameHeader) && getHeader() == SameHeader->getHeader() &&
+           "Incorrect LI specified for this loop!");
+  }
+#endif
+  assert(NewBB && "Cannot add a null basic block to the loop!");
+  assert(!LIB[NewBB] && "BasicBlock already in the loop!");
+
+  LoopT *L = static_cast<LoopT *>(this);
+
+  // Add the loop mapping to the LoopInfo object...
+  LIB.BBMap[NewBB] = L;
+
+  // Add the basic block to this loop and all parent loops...
+  while (L) {
+    L->addBlockEntry(NewBB);
+    L = L->getParentLoop();
+  }
+}
+
+/// replaceChildLoopWith - This is used when splitting loops up.  It replaces
+/// the OldChild entry in our children list with NewChild, and updates the
+/// parent pointer of OldChild to be null and the NewChild to be this loop.
+/// This updates the loop depth of the new child.
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::replaceChildLoopWith(LoopT *OldChild,
+                                                   LoopT *NewChild) {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  assert(OldChild->ParentLoop == this && "This loop is already broken!");
+  assert(!NewChild->ParentLoop && "NewChild already has a parent!");
+  typename std::vector<LoopT *>::iterator I = find(SubLoops, OldChild);
+  assert(I != SubLoops.end() && "OldChild not in loop!");
+  *I = NewChild;
+  OldChild->ParentLoop = nullptr;
+  NewChild->ParentLoop = static_cast<LoopT *>(this);
+}
+
+/// verifyLoop - Verify loop structure
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::verifyLoop() const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+#ifndef NDEBUG
+  assert(!Blocks.empty() && "Loop header is missing");
+
+  // Setup for using a depth-first iterator to visit every block in the loop.
+  SmallVector<BlockT *, 8> ExitBBs;
+  getExitBlocks(ExitBBs);
+  df_iterator_default_set<BlockT *> VisitSet;
+  VisitSet.insert(ExitBBs.begin(), ExitBBs.end());
+  df_ext_iterator<BlockT *, df_iterator_default_set<BlockT *>>
+      BI = df_ext_begin(getHeader(), VisitSet),
+      BE = df_ext_end(getHeader(), VisitSet);
+
+  // Keep track of the BBs visited.
+  SmallPtrSet<BlockT *, 8> VisitedBBs;
+
+  // Check the individual blocks.
+  for (; BI != BE; ++BI) {
+    BlockT *BB = *BI;
+
+    assert(std::any_of(GraphTraits<BlockT *>::child_begin(BB),
+                       GraphTraits<BlockT *>::child_end(BB),
+                       [&](BlockT *B) { return contains(B); }) &&
+           "Loop block has no in-loop successors!");
+
+    assert(std::any_of(GraphTraits<Inverse<BlockT *>>::child_begin(BB),
+                       GraphTraits<Inverse<BlockT *>>::child_end(BB),
+                       [&](BlockT *B) { return contains(B); }) &&
+           "Loop block has no in-loop predecessors!");
+
+    SmallVector<BlockT *, 2> OutsideLoopPreds;
+    std::for_each(GraphTraits<Inverse<BlockT *>>::child_begin(BB),
+                  GraphTraits<Inverse<BlockT *>>::child_end(BB),
+                  [&](BlockT *B) {
+                    if (!contains(B))
+                      OutsideLoopPreds.push_back(B);
+                  });
+
+    if (BB == getHeader()) {
+      assert(!OutsideLoopPreds.empty() && "Loop is unreachable!");
+    } else if (!OutsideLoopPreds.empty()) {
+      // A non-header loop shouldn't be reachable from outside the loop,
+      // though it is permitted if the predecessor is not itself actually
+      // reachable.
+      BlockT *EntryBB = &BB->getParent()->front();
+      for (BlockT *CB : depth_first(EntryBB))
+        for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i)
+          assert(CB != OutsideLoopPreds[i] &&
+                 "Loop has multiple entry points!");
+    }
+    assert(BB != &getHeader()->getParent()->front() &&
+           "Loop contains function entry block!");
+
+    VisitedBBs.insert(BB);
+  }
+
+  if (VisitedBBs.size() != getNumBlocks()) {
+    dbgs() << "The following blocks are unreachable in the loop: ";
+    for (auto BB : Blocks) {
+      if (!VisitedBBs.count(BB)) {
+        dbgs() << *BB << "\n";
+      }
+    }
+    assert(false && "Unreachable block in loop");
+  }
+
+  // Check the subloops.
+  for (iterator I = begin(), E = end(); I != E; ++I)
+    // Each block in each subloop should be contained within this loop.
+    for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end();
+         BI != BE; ++BI) {
+      assert(contains(*BI) &&
+             "Loop does not contain all the blocks of a subloop!");
+    }
+
+  // Check the parent loop pointer.
+  if (ParentLoop) {
+    assert(is_contained(*ParentLoop, this) &&
+           "Loop is not a subloop of its parent!");
+  }
+#endif
+}
+
+/// verifyLoop - Verify loop structure of this loop and all nested loops.
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::verifyLoopNest(
+    DenseSet<const LoopT *> *Loops) const {
+  assert(!isInvalid() && "Loop not in a valid state!");
+  Loops->insert(static_cast<const LoopT *>(this));
+  // Verify this loop.
+  verifyLoop();
+  // Verify the subloops.
+  for (iterator I = begin(), E = end(); I != E; ++I)
+    (*I)->verifyLoopNest(Loops);
+}
+
+template <class BlockT, class LoopT>
+void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth,
+                                    bool Verbose) const {
+  OS.indent(Depth * 2) << "Loop at depth " << getLoopDepth() << " containing: ";
+
+  BlockT *H = getHeader();
+  for (unsigned i = 0; i < getBlocks().size(); ++i) {
+    BlockT *BB = getBlocks()[i];
+    if (!Verbose) {
+      if (i)
+        OS << ",";
+      BB->printAsOperand(OS, false);
+    } else
+      OS << "\n";
+
+    if (BB == H)
+      OS << "<header>";
+    if (isLoopLatch(BB))
+      OS << "<latch>";
+    if (isLoopExiting(BB))
+      OS << "<exiting>";
+    if (Verbose)
+      BB->print(OS);
+  }
+  OS << "\n";
+
+  for (iterator I = begin(), E = end(); I != E; ++I)
+    (*I)->print(OS, Depth + 2);
+}
+
+//===----------------------------------------------------------------------===//
+/// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the
+/// result does / not depend on use list (block predecessor) order.
+///
+
+/// Discover a subloop with the specified backedges such that: All blocks within
+/// this loop are mapped to this loop or a subloop. And all subloops within this
+/// loop have their parent loop set to this loop or a subloop.
+template <class BlockT, class LoopT>
+static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT *> Backedges,
+                                  LoopInfoBase<BlockT, LoopT> *LI,
+                                  const DomTreeBase<BlockT> &DomTree) {
+  typedef GraphTraits<Inverse<BlockT *>> InvBlockTraits;
+
+  unsigned NumBlocks = 0;
+  unsigned NumSubloops = 0;
+
+  // Perform a backward CFG traversal using a worklist.
+  std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end());
+  while (!ReverseCFGWorklist.empty()) {
+    BlockT *PredBB = ReverseCFGWorklist.back();
+    ReverseCFGWorklist.pop_back();
+
+    LoopT *Subloop = LI->getLoopFor(PredBB);
+    if (!Subloop) {
+      if (!DomTree.isReachableFromEntry(PredBB))
+        continue;
+
+      // This is an undiscovered block. Map it to the current loop.
+      LI->changeLoopFor(PredBB, L);
+      ++NumBlocks;
+      if (PredBB == L->getHeader())
+        continue;
+      // Push all block predecessors on the worklist.
+      ReverseCFGWorklist.insert(ReverseCFGWorklist.end(),
+                                InvBlockTraits::child_begin(PredBB),
+                                InvBlockTraits::child_end(PredBB));
+    } else {
+      // This is a discovered block. Find its outermost discovered loop.
+      while (LoopT *Parent = Subloop->getParentLoop())
+        Subloop = Parent;
+
+      // If it is already discovered to be a subloop of this loop, continue.
+      if (Subloop == L)
+        continue;
+
+      // Discover a subloop of this loop.
+      Subloop->setParentLoop(L);
+      ++NumSubloops;
+      NumBlocks += Subloop->getBlocksVector().capacity();
+      PredBB = Subloop->getHeader();
+      // Continue traversal along predecessors that are not loop-back edges from
+      // within this subloop tree itself. Note that a predecessor may directly
+      // reach another subloop that is not yet discovered to be a subloop of
+      // this loop, which we must traverse.
+      for (const auto Pred : children<Inverse<BlockT *>>(PredBB)) {
+        if (LI->getLoopFor(Pred) != Subloop)
+          ReverseCFGWorklist.push_back(Pred);
+      }
+    }
+  }
+  L->getSubLoopsVector().reserve(NumSubloops);
+  L->reserveBlocks(NumBlocks);
+}
+
+/// Populate all loop data in a stable order during a single forward DFS.
+template <class BlockT, class LoopT> class PopulateLoopsDFS {
+  typedef GraphTraits<BlockT *> BlockTraits;
+  typedef typename BlockTraits::ChildIteratorType SuccIterTy;
+
+  LoopInfoBase<BlockT, LoopT> *LI;
+
+public:
+  PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li) : LI(li) {}
+
+  void traverse(BlockT *EntryBlock);
+
+protected:
+  void insertIntoLoop(BlockT *Block);
+};
+
+/// Top-level driver for the forward DFS within the loop.
+template <class BlockT, class LoopT>
+void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) {
+  for (BlockT *BB : post_order(EntryBlock))
+    insertIntoLoop(BB);
+}
+
+/// Add a single Block to its ancestor loops in PostOrder. If the block is a
+/// subloop header, add the subloop to its parent in PostOrder, then reverse the
+/// Block and Subloop vectors of the now complete subloop to achieve RPO.
+template <class BlockT, class LoopT>
+void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) {
+  LoopT *Subloop = LI->getLoopFor(Block);
+  if (Subloop && Block == Subloop->getHeader()) {
+    // We reach this point once per subloop after processing all the blocks in
+    // the subloop.
+    if (Subloop->getParentLoop())
+      Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop);
+    else
+      LI->addTopLevelLoop(Subloop);
+
+    // For convenience, Blocks and Subloops are inserted in postorder. Reverse
+    // the lists, except for the loop header, which is always at the beginning.
+    Subloop->reverseBlock(1);
+    std::reverse(Subloop->getSubLoopsVector().begin(),
+                 Subloop->getSubLoopsVector().end());
+
+    Subloop = Subloop->getParentLoop();
+  }
+  for (; Subloop; Subloop = Subloop->getParentLoop())
+    Subloop->addBlockEntry(Block);
+}
+
+/// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal
+/// interleaved with backward CFG traversals within each subloop
+/// (discoverAndMapSubloop). The backward traversal skips inner subloops, so
+/// this part of the algorithm is linear in the number of CFG edges. Subloop and
+/// Block vectors are then populated during a single forward CFG traversal
+/// (PopulateLoopDFS).
+///
+/// During the two CFG traversals each block is seen three times:
+/// 1) Discovered and mapped by a reverse CFG traversal.
+/// 2) Visited during a forward DFS CFG traversal.
+/// 3) Reverse-inserted in the loop in postorder following forward DFS.
+///
+/// The Block vectors are inclusive, so step 3 requires loop-depth number of
+/// insertions per block.
+template <class BlockT, class LoopT>
+void LoopInfoBase<BlockT, LoopT>::analyze(const DomTreeBase<BlockT> &DomTree) {
+  // Postorder traversal of the dominator tree.
+  const DomTreeNodeBase<BlockT> *DomRoot = DomTree.getRootNode();
+  for (auto DomNode : post_order(DomRoot)) {
+
+    BlockT *Header = DomNode->getBlock();
+    SmallVector<BlockT *, 4> Backedges;
+
+    // Check each predecessor of the potential loop header.
+    for (const auto Backedge : children<Inverse<BlockT *>>(Header)) {
+      // If Header dominates predBB, this is a new loop. Collect the backedges.
+      if (DomTree.dominates(Header, Backedge) &&
+          DomTree.isReachableFromEntry(Backedge)) {
+        Backedges.push_back(Backedge);
+      }
+    }
+    // Perform a backward CFG traversal to discover and map blocks in this loop.
+    if (!Backedges.empty()) {
+      LoopT *L = AllocateLoop(Header);
+      discoverAndMapSubloop(L, ArrayRef<BlockT *>(Backedges), this, DomTree);
+    }
+  }
+  // Perform a single forward CFG traversal to populate block and subloop
+  // vectors for all loops.
+  PopulateLoopsDFS<BlockT, LoopT> DFS(this);
+  DFS.traverse(DomRoot->getBlock());
+}
+
+template <class BlockT, class LoopT>
+SmallVector<LoopT *, 4> LoopInfoBase<BlockT, LoopT>::getLoopsInPreorder() {
+  SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
+  // The outer-most loop actually goes into the result in the same relative
+  // order as we walk it. But LoopInfo stores the top level loops in reverse
+  // program order so for here we reverse it to get forward program order.
+  // FIXME: If we change the order of LoopInfo we will want to remove the
+  // reverse here.
+  for (LoopT *RootL : reverse(*this)) {
+    assert(PreOrderWorklist.empty() &&
+           "Must start with an empty preorder walk worklist.");
+    PreOrderWorklist.push_back(RootL);
+    do {
+      LoopT *L = PreOrderWorklist.pop_back_val();
+      // Sub-loops are stored in forward program order, but will process the
+      // worklist backwards so append them in reverse order.
+      PreOrderWorklist.append(L->rbegin(), L->rend());
+      PreOrderLoops.push_back(L);
+    } while (!PreOrderWorklist.empty());
+  }
+
+  return PreOrderLoops;
+}
+
+template <class BlockT, class LoopT>
+SmallVector<LoopT *, 4>
+LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() {
+  SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
+  // The outer-most loop actually goes into the result in the same relative
+  // order as we walk it. LoopInfo stores the top level loops in reverse
+  // program order so we walk in order here.
+  // FIXME: If we change the order of LoopInfo we will want to add a reverse
+  // here.
+  for (LoopT *RootL : *this) {
+    assert(PreOrderWorklist.empty() &&
+           "Must start with an empty preorder walk worklist.");
+    PreOrderWorklist.push_back(RootL);
+    do {
+      LoopT *L = PreOrderWorklist.pop_back_val();
+      // Sub-loops are stored in forward program order, but will process the
+      // worklist backwards so we can just append them in order.
+      PreOrderWorklist.append(L->begin(), L->end());
+      PreOrderLoops.push_back(L);
+    } while (!PreOrderWorklist.empty());
+  }
+
+  return PreOrderLoops;
+}
+
+// Debugging
+template <class BlockT, class LoopT>
+void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const {
+  for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
+    TopLevelLoops[i]->print(OS);
+#if 0
+  for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(),
+         E = BBMap.end(); I != E; ++I)
+    OS << "BB '" << I->first->getName() << "' level = "
+       << I->second->getLoopDepth() << "\n";
+#endif
+}
+
+template <typename T>
+bool compareVectors(std::vector<T> &BB1, std::vector<T> &BB2) {
+  std::sort(BB1.begin(), BB1.end());
+  std::sort(BB2.begin(), BB2.end());
+  return BB1 == BB2;
+}
+
+template <class BlockT, class LoopT>
+void addInnerLoopsToHeadersMap(DenseMap<BlockT *, const LoopT *> &LoopHeaders,
+                               const LoopInfoBase<BlockT, LoopT> &LI,
+                               const LoopT &L) {
+  LoopHeaders[L.getHeader()] = &L;
+  for (LoopT *SL : L)
+    addInnerLoopsToHeadersMap(LoopHeaders, LI, *SL);
+}
+
+#ifndef NDEBUG
+template <class BlockT, class LoopT>
+static void compareLoops(const LoopT *L, const LoopT *OtherL,
+                         DenseMap<BlockT *, const LoopT *> &OtherLoopHeaders) {
+  BlockT *H = L->getHeader();
+  BlockT *OtherH = OtherL->getHeader();
+  assert(H == OtherH &&
+         "Mismatched headers even though found in the same map entry!");
+
+  assert(L->getLoopDepth() == OtherL->getLoopDepth() &&
+         "Mismatched loop depth!");
+  const LoopT *ParentL = L, *OtherParentL = OtherL;
+  do {
+    assert(ParentL->getHeader() == OtherParentL->getHeader() &&
+           "Mismatched parent loop headers!");
+    ParentL = ParentL->getParentLoop();
+    OtherParentL = OtherParentL->getParentLoop();
+  } while (ParentL);
+
+  for (const LoopT *SubL : *L) {
+    BlockT *SubH = SubL->getHeader();
+    const LoopT *OtherSubL = OtherLoopHeaders.lookup(SubH);
+    assert(OtherSubL && "Inner loop is missing in computed loop info!");
+    OtherLoopHeaders.erase(SubH);
+    compareLoops(SubL, OtherSubL, OtherLoopHeaders);
+  }
+
+  std::vector<BlockT *> BBs = L->getBlocks();
+  std::vector<BlockT *> OtherBBs = OtherL->getBlocks();
+  assert(compareVectors(BBs, OtherBBs) &&
+         "Mismatched basic blocks in the loops!");
+}
+#endif
+
+template <class BlockT, class LoopT>
+void LoopInfoBase<BlockT, LoopT>::verify(
+    const DomTreeBase<BlockT> &DomTree) const {
+  DenseSet<const LoopT *> Loops;
+  for (iterator I = begin(), E = end(); I != E; ++I) {
+    assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
+    (*I)->verifyLoopNest(&Loops);
+  }
+
+// Verify that blocks are mapped to valid loops.
+#ifndef NDEBUG
+  for (auto &Entry : BBMap) {
+    const BlockT *BB = Entry.first;
+    LoopT *L = Entry.second;
+    assert(Loops.count(L) && "orphaned loop");
+    assert(L->contains(BB) && "orphaned block");
+  }
+
+  // Recompute LoopInfo to verify loops structure.
+  LoopInfoBase<BlockT, LoopT> OtherLI;
+  OtherLI.analyze(DomTree);
+
+  // Build a map we can use to move from our LI to the computed one. This
+  // allows us to ignore the particular order in any layer of the loop forest
+  // while still comparing the structure.
+  DenseMap<BlockT *, const LoopT *> OtherLoopHeaders;
+  for (LoopT *L : OtherLI)
+    addInnerLoopsToHeadersMap(OtherLoopHeaders, OtherLI, *L);
+
+  // Walk the top level loops and ensure there is a corresponding top-level
+  // loop in the computed version and then recursively compare those loop
+  // nests.
+  for (LoopT *L : *this) {
+    BlockT *Header = L->getHeader();
+    const LoopT *OtherL = OtherLoopHeaders.lookup(Header);
+    assert(OtherL && "Top level loop is missing in computed loop info!");
+    // Now that we've matched this loop, erase its header from the map.
+    OtherLoopHeaders.erase(Header);
+    // And recursively compare these loops.
+    compareLoops(L, OtherL, OtherLoopHeaders);
+  }
+
+  // Any remaining entries in the map are loops which were found when computing
+  // a fresh LoopInfo but not present in the current one.
+  if (!OtherLoopHeaders.empty()) {
+    for (const auto &HeaderAndLoop : OtherLoopHeaders)
+      dbgs() << "Found new loop: " << *HeaderAndLoop.second << "\n";
+    llvm_unreachable("Found new loops when recomputing LoopInfo!");
+  }
+#endif
+}
+
+} // End llvm namespace
+
+#endif