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 //===- GenericLoopInfo - Generic Loop Info for graphs -----------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the LoopInfoBase class that is used to identify natural
 // loops and determine the loop depth of various nodes in a generic graph of
 // blocks.  A natural loop has exactly one entry-point, which is called the
 // header. Note that natural loops may actually be several loops that share the
 // same header node.
 //
 // This analysis calculates the nesting structure of loops in a function.  For
 // each natural loop identified, this analysis identifies natural loops
 // contained entirely within the loop and the basic blocks that make up the
 // loop.
 //
 // It can calculate on the fly various bits of information, for example:
 //
 //  * whether there is a preheader for the loop
 //  * the number of back edges to the header
 //  * whether or not a particular block branches out of the loop
 //  * the successor blocks of the loop
 //  * the loop depth
 //  * etc...
 //
 // Note that this analysis specifically identifies *Loops* not cycles or SCCs
 // in the graph.  There can be strongly connected components in the graph which
 // this analysis will not recognize and that will not be represented by a Loop
 // instance.  In particular, a Loop might be inside such a non-loop SCC, or a
 // non-loop SCC might contain a sub-SCC which is a Loop.
 //
 // For an overview of terminology used in this API (and thus all of our loop
 // analyses or transforms), see docs/LoopTerminology.rst.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_GENERICLOOPINFO_H
 #define LLVM_SUPPORT_GENERICLOOPINFO_H
 
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetOperations.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/GenericDomTree.h"
 
 namespace llvm {
 
 template <class N, class M> class LoopInfoBase;
 template <class N, class M> class LoopBase;
 
 //===----------------------------------------------------------------------===//
 /// Instances of this class are used to represent loops that are detected in the
 /// flow graph.
 ///
 template <class BlockT, class LoopT> class LoopBase {
   LoopT *ParentLoop;
   // Loops contained entirely within this one.
   std::vector<LoopT *> SubLoops;
 
   // The list of blocks in this loop. First entry is the header node.
   std::vector<BlockT *> Blocks;
 
   SmallPtrSet<const BlockT *, 8> DenseBlockSet;
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   /// Indicator that this loop is no longer a valid loop.
   bool IsInvalid = false;
 #endif
 
   LoopBase(const LoopBase<BlockT, LoopT> &) = delete;
   const LoopBase<BlockT, LoopT> &
   operator=(const LoopBase<BlockT, LoopT> &) = delete;
 
 public:
   /// Return the nesting level of this loop.  An outer-most loop has depth 1,
   /// for consistency with loop depth values used for basic blocks, where depth
   /// 0 is used for blocks not inside any loops.
   unsigned getLoopDepth() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     unsigned D = 1;
     for (const LoopT *CurLoop = ParentLoop; CurLoop;
          CurLoop = CurLoop->ParentLoop)
       ++D;
     return D;
   }
   BlockT *getHeader() const { return getBlocks().front(); }
   /// Return the parent loop if it exists or nullptr for top
   /// level loops.
 
   /// A loop is either top-level in a function (that is, it is not
   /// contained in any other loop) or it is entirely enclosed in
   /// some other loop.
   /// If a loop is top-level, it has no parent, otherwise its
   /// parent is the innermost loop in which it is enclosed.
   LoopT *getParentLoop() const { return ParentLoop; }
 
   /// Get the outermost loop in which this loop is contained.
   /// This may be the loop itself, if it already is the outermost loop.
   const LoopT *getOutermostLoop() const {
     const LoopT *L = static_cast<const LoopT *>(this);
     while (L->ParentLoop)
       L = L->ParentLoop;
     return L;
   }
 
   LoopT *getOutermostLoop() {
     LoopT *L = static_cast<LoopT *>(this);
     while (L->ParentLoop)
       L = L->ParentLoop;
     return L;
   }
 
   /// This is a raw interface for bypassing addChildLoop.
   void setParentLoop(LoopT *L) {
     assert(!isInvalid() && "Loop not in a valid state!");
     ParentLoop = L;
   }
 
   /// Return true if the specified loop is contained within in this loop.
   bool contains(const LoopT *L) const {
     assert(!isInvalid() && "Loop not in a valid state!");
     if (L == this)
       return true;
     if (!L)
       return false;
     return contains(L->getParentLoop());
   }
 
   /// Return true if the specified basic block is in this loop.
   bool contains(const BlockT *BB) const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return DenseBlockSet.count(BB);
   }
 
   /// Return true if the specified instruction is in this loop.
   template <class InstT> bool contains(const InstT *Inst) const {
     return contains(Inst->getParent());
   }
 
   /// Return the loops contained entirely within this loop.
   const std::vector<LoopT *> &getSubLoops() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return SubLoops;
   }
   std::vector<LoopT *> &getSubLoopsVector() {
     assert(!isInvalid() && "Loop not in a valid state!");
     return SubLoops;
   }
   typedef typename std::vector<LoopT *>::const_iterator iterator;
   typedef
       typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
   iterator begin() const { return getSubLoops().begin(); }
   iterator end() const { return getSubLoops().end(); }
   reverse_iterator rbegin() const { return getSubLoops().rbegin(); }
   reverse_iterator rend() const { return getSubLoops().rend(); }
 
   // LoopInfo does not detect irreducible control flow, just natural
   // loops. That is, it is possible that there is cyclic control
   // flow within the "innermost loop" or around the "outermost
   // loop".
 
   /// Return true if the loop does not contain any (natural) loops.
   bool isInnermost() const { return getSubLoops().empty(); }
   /// Return true if the loop does not have a parent (natural) loop
   // (i.e. it is outermost, which is the same as top-level).
   bool isOutermost() const { return getParentLoop() == nullptr; }
 
   /// Get a list of the basic blocks which make up this loop.
   ArrayRef<BlockT *> getBlocks() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return Blocks;
   }
   typedef typename ArrayRef<BlockT *>::const_iterator block_iterator;
   block_iterator block_begin() const { return getBlocks().begin(); }
   block_iterator block_end() const { return getBlocks().end(); }
   inline iterator_range<block_iterator> blocks() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return make_range(block_begin(), block_end());
   }
 
   /// Get the number of blocks in this loop in constant time.
   /// Invalidate the loop, indicating that it is no longer a loop.
   unsigned getNumBlocks() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return Blocks.size();
   }
 
   /// Return a direct, mutable handle to the blocks vector so that we can
   /// mutate it efficiently with techniques like `std::remove`.
   std::vector<BlockT *> &getBlocksVector() {
     assert(!isInvalid() && "Loop not in a valid state!");
     return Blocks;
   }
   /// Return a direct, mutable handle to the blocks set so that we can
   /// mutate it efficiently.
   SmallPtrSetImpl<const BlockT *> &getBlocksSet() {
     assert(!isInvalid() && "Loop not in a valid state!");
     return DenseBlockSet;
   }
 
   /// Return a direct, immutable handle to the blocks set.
   const SmallPtrSetImpl<const BlockT *> &getBlocksSet() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return DenseBlockSet;
   }
 
   /// Return true if this loop is no longer valid.  The only valid use of this
   /// helper is "assert(L.isInvalid())" or equivalent, since IsInvalid is set to
   /// true by the destructor.  In other words, if this accessor returns true,
   /// the caller has already triggered UB by calling this accessor; and so it
   /// can only be called in a context where a return value of true indicates a
   /// programmer error.
   bool isInvalid() const {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     return IsInvalid;
 #else
     return false;
 #endif
   }
 
   /// True if terminator in the block can branch to another block that is
   /// outside of the current loop. \p BB must be inside the loop.
   bool isLoopExiting(const BlockT *BB) const {
     assert(!isInvalid() && "Loop not in a valid state!");
     assert(contains(BB) && "Exiting block must be part of the loop");
     for (const auto *Succ : children<const BlockT *>(BB)) {
       if (!contains(Succ))
         return true;
     }
     return false;
   }
 
   /// Returns true if \p BB is a loop-latch.
   /// A latch block is a block that contains a branch back to the header.
   /// This function is useful when there are multiple latches in a loop
   /// because \fn getLoopLatch will return nullptr in that case.
   bool isLoopLatch(const BlockT *BB) const {
     assert(!isInvalid() && "Loop not in a valid state!");
     assert(contains(BB) && "block does not belong to the loop");
     return llvm::is_contained(inverse_children<BlockT *>(getHeader()), BB);
   }
 
   /// Calculate the number of back edges to the loop header.
   unsigned getNumBackEdges() const {
     assert(!isInvalid() && "Loop not in a valid state!");
     return llvm::count_if(inverse_children<BlockT *>(getHeader()),
                           [&](BlockT *Pred) { return contains(Pred); });
   }
 
   //===--------------------------------------------------------------------===//
   // APIs for simple analysis of the loop.
   //
   // Note that all of these methods can fail on general loops (ie, there may not
   // be a preheader, etc).  For best success, the loop simplification and
   // induction variable canonicalization pass should be used to normalize loops
   // for easy analysis.  These methods assume canonical loops.
 
   /// 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.
   void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const;
 
   /// If getExitingBlocks would return exactly one block, return that block.
   /// Otherwise return null.
   BlockT *getExitingBlock() const;
 
   /// Return all of the successor blocks of this loop. These are the blocks
   /// _outside of the current loop_ which are branched to.
   void getExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
 
   /// If getExitBlocks would return exactly one block, return that block.
   /// Otherwise return null.
   BlockT *getExitBlock() const;
 
   /// Return true if no exit block for the loop has a predecessor that is
   /// outside the loop.
   bool hasDedicatedExits() const;
 
   /// Return all unique successor blocks of this loop.
   /// These are the blocks _outside of the current loop_ which are branched to.
   void getUniqueExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
 
   /// Return all unique successor blocks of this loop except successors from
   /// Latch block are not considered. If the exit comes from Latch has also
   /// non Latch predecessor in a loop it will be added to ExitBlocks.
   /// These are the blocks _outside of the current loop_ which are branched to.
   void getUniqueNonLatchExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
 
   /// If getUniqueExitBlocks would return exactly one block, return that block.
   /// Otherwise return null.
   BlockT *getUniqueExitBlock() const;
 
   /// Return the unique exit block for the latch, or null if there are multiple
   /// different exit blocks or the latch is not exiting.
   BlockT *getUniqueLatchExitBlock() const;
 
   /// Return true if this loop does not have any exit blocks.
   bool hasNoExitBlocks() const;
 
   /// Edge type.
   typedef std::pair<BlockT *, BlockT *> Edge;
 
   /// Return all pairs of (_inside_block_,_outside_block_).
   void getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const;
 
   /// 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. 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.
   BlockT *getLoopPreheader() const;
 
   /// 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.
   BlockT *getLoopPredecessor() const;
 
   /// 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.
   BlockT *getLoopLatch() const;
 
   /// Return all loop latch blocks of this loop. A latch block is a block that
   /// contains a branch back to the header.
   void getLoopLatches(SmallVectorImpl<BlockT *> &LoopLatches) const {
     assert(!isInvalid() && "Loop not in a valid state!");
     BlockT *H = getHeader();
     for (const auto Pred : inverse_children<BlockT *>(H))
       if (contains(Pred))
         LoopLatches.push_back(Pred);
   }
 
   /// Return all inner loops in the loop nest rooted by the loop in preorder,
   /// with siblings in forward program order.
   template <class Type>
   static void getInnerLoopsInPreorder(const LoopT &L,
                                       SmallVectorImpl<Type> &PreOrderLoops) {
     SmallVector<LoopT *, 4> PreOrderWorklist;
     PreOrderWorklist.append(L.rbegin(), L.rend());
 
     while (!PreOrderWorklist.empty()) {
       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);
     }
   }
 
   /// Return all loops in the loop nest rooted by the loop in preorder, with
   /// siblings in forward program order.
   SmallVector<const LoopT *, 4> getLoopsInPreorder() const {
     SmallVector<const LoopT *, 4> PreOrderLoops;
     const LoopT *CurLoop = static_cast<const LoopT *>(this);
     PreOrderLoops.push_back(CurLoop);
     getInnerLoopsInPreorder(*CurLoop, PreOrderLoops);
     return PreOrderLoops;
   }
   SmallVector<LoopT *, 4> getLoopsInPreorder() {
     SmallVector<LoopT *, 4> PreOrderLoops;
     LoopT *CurLoop = static_cast<LoopT *>(this);
     PreOrderLoops.push_back(CurLoop);
     getInnerLoopsInPreorder(*CurLoop, PreOrderLoops);
     return PreOrderLoops;
   }
 
   //===--------------------------------------------------------------------===//
   // APIs for updating loop information after changing the CFG
   //
 
   /// 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.
   void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI);
 
   /// 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.
   void replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild);
 
   /// Add the specified loop to be a child of this loop.
   /// This updates the loop depth of the new child.
   void addChildLoop(LoopT *NewChild) {
     assert(!isInvalid() && "Loop not in a valid state!");
     assert(!NewChild->ParentLoop && "NewChild already has a parent!");
     NewChild->ParentLoop = static_cast<LoopT *>(this);
     SubLoops.push_back(NewChild);
   }
 
   /// This removes the specified child from being a subloop of this loop. The
   /// loop is not deleted, as it will presumably be inserted into another loop.
   LoopT *removeChildLoop(iterator I) {
     assert(!isInvalid() && "Loop not in a valid state!");
     assert(I != SubLoops.end() && "Cannot remove end iterator!");
     LoopT *Child = *I;
     assert(Child->ParentLoop == this && "Child is not a child of this loop!");
     SubLoops.erase(SubLoops.begin() + (I - begin()));
     Child->ParentLoop = nullptr;
     return Child;
   }
 
   /// This removes the specified child from being a subloop of this loop. The
   /// loop is not deleted, as it will presumably be inserted into another loop.
   LoopT *removeChildLoop(LoopT *Child) {
     return removeChildLoop(llvm::find(*this, Child));
   }
 
   /// This adds a basic block directly to the basic block list.
   /// This should only be used by transformations that create new loops.  Other
   /// transformations should use addBasicBlockToLoop.
   void addBlockEntry(BlockT *BB) {
     assert(!isInvalid() && "Loop not in a valid state!");
     Blocks.push_back(BB);
     DenseBlockSet.insert(BB);
   }
 
   /// interface to reverse Blocks[from, end of loop] in this loop
   void reverseBlock(unsigned from) {
     assert(!isInvalid() && "Loop not in a valid state!");
     std::reverse(Blocks.begin() + from, Blocks.end());
   }
 
   /// interface to do reserve() for Blocks
   void reserveBlocks(unsigned size) {
     assert(!isInvalid() && "Loop not in a valid state!");
     Blocks.reserve(size);
   }
 
   /// This method is used to move BB (which must be part of this loop) to be the
   /// loop header of the loop (the block that dominates all others).
   void moveToHeader(BlockT *BB) {
     assert(!isInvalid() && "Loop not in a valid state!");
     if (Blocks[0] == BB)
       return;
     for (unsigned i = 0;; ++i) {
       assert(i != Blocks.size() && "Loop does not contain BB!");
       if (Blocks[i] == BB) {
         Blocks[i] = Blocks[0];
         Blocks[0] = BB;
         return;
       }
     }
   }
 
   /// This removes the specified basic block from the current loop, updating the
   /// Blocks as appropriate. This does not update the mapping in the LoopInfo
   /// class.
   void removeBlockFromLoop(BlockT *BB) {
     assert(!isInvalid() && "Loop not in a valid state!");
     auto I = find(Blocks, BB);
     assert(I != Blocks.end() && "N is not in this list!");
     Blocks.erase(I);
 
     DenseBlockSet.erase(BB);
   }
 
   /// Verify loop structure
   void verifyLoop() const;
 
   /// Verify loop structure of this loop and all nested loops.
   void verifyLoopNest(DenseSet<const LoopT *> *Loops) const;
 
   /// Returns true if the loop is annotated parallel.
   ///
   /// Derived classes can override this method using static template
   /// polymorphism.
   bool isAnnotatedParallel() const { return false; }
 
   /// Print loop with all the BBs inside it.
   void print(raw_ostream &OS, bool Verbose = false, bool PrintNested = true,
              unsigned Depth = 0) const;
 
 protected:
   friend class LoopInfoBase<BlockT, LoopT>;
 
   /// This creates an empty loop.
   LoopBase() : ParentLoop(nullptr) {}
 
   explicit LoopBase(BlockT *BB) : ParentLoop(nullptr) {
     Blocks.push_back(BB);
     DenseBlockSet.insert(BB);
   }
 
   // Since loop passes like SCEV are allowed to key analysis results off of
   // `Loop` pointers, we cannot re-use pointers within a loop pass manager.
   // This means loop passes should not be `delete` ing `Loop` objects directly
   // (and risk a later `Loop` allocation re-using the address of a previous one)
   // but should be using LoopInfo::markAsRemoved, which keeps around the `Loop`
   // pointer till the end of the lifetime of the `LoopInfo` object.
   //
   // To make it easier to follow this rule, we mark the destructor as
   // non-public.
   ~LoopBase() {
     for (auto *SubLoop : SubLoops)
       SubLoop->~LoopT();
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     IsInvalid = true;
 #endif
     SubLoops.clear();
     Blocks.clear();
     DenseBlockSet.clear();
     ParentLoop = nullptr;
   }
 };
 
 template <class BlockT, class LoopT>
 raw_ostream &operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) {
   Loop.print(OS);
   return OS;
 }
 
 //===----------------------------------------------------------------------===//
 /// This class builds and contains all of the top-level loop
 /// structures in the specified function.
 ///
 
 template <class BlockT, class LoopT> class LoopInfoBase {
   // BBMap - Mapping of basic blocks to the inner most loop they occur in
   DenseMap<const BlockT *, LoopT *> BBMap;
   std::vector<LoopT *> TopLevelLoops;
   BumpPtrAllocator LoopAllocator;
 
   friend class LoopBase<BlockT, LoopT>;
   friend class LoopInfo;
 
   void operator=(const LoopInfoBase &) = delete;
   LoopInfoBase(const LoopInfoBase &) = delete;
 
 public:
   LoopInfoBase() = default;
   ~LoopInfoBase() { releaseMemory(); }
 
   LoopInfoBase(LoopInfoBase &&Arg)
       : BBMap(std::move(Arg.BBMap)),
         TopLevelLoops(std::move(Arg.TopLevelLoops)),
         LoopAllocator(std::move(Arg.LoopAllocator)) {
     // We have to clear the arguments top level loops as we've taken ownership.
     Arg.TopLevelLoops.clear();
   }
   LoopInfoBase &operator=(LoopInfoBase &&RHS) {
     BBMap = std::move(RHS.BBMap);
 
     for (auto *L : TopLevelLoops)
       L->~LoopT();
 
     TopLevelLoops = std::move(RHS.TopLevelLoops);
     LoopAllocator = std::move(RHS.LoopAllocator);
     RHS.TopLevelLoops.clear();
     return *this;
   }
 
   void releaseMemory() {
     BBMap.clear();
 
     for (auto *L : TopLevelLoops)
       L->~LoopT();
     TopLevelLoops.clear();
     LoopAllocator.Reset();
   }
 
   template <typename... ArgsTy> LoopT *AllocateLoop(ArgsTy &&...Args) {
     LoopT *Storage = LoopAllocator.Allocate<LoopT>();
     return new (Storage) LoopT(std::forward<ArgsTy>(Args)...);
   }
 
   /// iterator/begin/end - The interface to the top-level loops in the current
   /// function.
   ///
   typedef typename std::vector<LoopT *>::const_iterator iterator;
   typedef
       typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
   iterator begin() const { return TopLevelLoops.begin(); }
   iterator end() const { return TopLevelLoops.end(); }
   reverse_iterator rbegin() const { return TopLevelLoops.rbegin(); }
   reverse_iterator rend() const { return TopLevelLoops.rend(); }
   bool empty() const { return TopLevelLoops.empty(); }
 
   /// Return all of the loops in the function in preorder across the loop
   /// nests, with siblings in forward program order.
   ///
   /// Note that because loops form a forest of trees, preorder is equivalent to
   /// reverse postorder.
   SmallVector<LoopT *, 4> getLoopsInPreorder() const;
 
   /// Return all of the loops in the function in preorder across the loop
   /// nests, with siblings in *reverse* program order.
   ///
   /// Note that because loops form a forest of trees, preorder is equivalent to
   /// reverse postorder.
   ///
   /// Also note that this is *not* a reverse preorder. Only the siblings are in
   /// reverse program order.
   SmallVector<LoopT *, 4> getLoopsInReverseSiblingPreorder() const;
 
   /// Return the inner most loop that BB lives in. If a basic block is in no
   /// loop (for example the entry node), null is returned.
   LoopT *getLoopFor(const BlockT *BB) const { return BBMap.lookup(BB); }
 
   /// Same as getLoopFor.
   const LoopT *operator[](const BlockT *BB) const { return getLoopFor(BB); }
 
   /// Return the loop nesting level of the specified block. A depth of 0 means
   /// the block is not inside any loop.
   unsigned getLoopDepth(const BlockT *BB) const {
     const LoopT *L = getLoopFor(BB);
     return L ? L->getLoopDepth() : 0;
   }
 
   // True if the block is a loop header node
   bool isLoopHeader(const BlockT *BB) const {
     const LoopT *L = getLoopFor(BB);
     return L && L->getHeader() == BB;
   }
 
   /// Return the top-level loops.
   const std::vector<LoopT *> &getTopLevelLoops() const { return TopLevelLoops; }
 
   /// Return the top-level loops.
   std::vector<LoopT *> &getTopLevelLoopsVector() { return TopLevelLoops; }
 
   /// This removes the specified top-level loop from this loop info object.
   /// The loop is not deleted, as it will presumably be inserted into
   /// another loop.
   LoopT *removeLoop(iterator I) {
     assert(I != end() && "Cannot remove end iterator!");
     LoopT *L = *I;
     assert(L->isOutermost() && "Not a top-level loop!");
     TopLevelLoops.erase(TopLevelLoops.begin() + (I - begin()));
     return L;
   }
 
   /// Change the top-level loop that contains BB to the specified loop.
   /// This should be used by transformations that restructure the loop hierarchy
   /// tree.
   void changeLoopFor(BlockT *BB, LoopT *L) {
     if (!L) {
       BBMap.erase(BB);
       return;
     }
     BBMap[BB] = L;
   }
 
   /// Replace the specified loop in the top-level loops list with the indicated
   /// loop.
   void changeTopLevelLoop(LoopT *OldLoop, LoopT *NewLoop) {
     auto I = find(TopLevelLoops, OldLoop);
     assert(I != TopLevelLoops.end() && "Old loop not at top level!");
     *I = NewLoop;
     assert(!NewLoop->ParentLoop && !OldLoop->ParentLoop &&
            "Loops already embedded into a subloop!");
   }
 
   /// This adds the specified loop to the collection of top-level loops.
   void addTopLevelLoop(LoopT *New) {
     assert(New->isOutermost() && "Loop already in subloop!");
     TopLevelLoops.push_back(New);
   }
 
   /// This method completely removes BB from all data structures,
   /// including all of the Loop objects it is nested in and our mapping from
   /// BasicBlocks to loops.
   void removeBlock(BlockT *BB) {
     auto I = BBMap.find(BB);
     if (I != BBMap.end()) {
       for (LoopT *L = I->second; L; L = L->getParentLoop())
         L->removeBlockFromLoop(BB);
 
       BBMap.erase(I);
     }
   }
 
   // Internals
 
   static bool isNotAlreadyContainedIn(const LoopT *SubLoop,
                                       const LoopT *ParentLoop) {
     if (!SubLoop)
       return true;
     if (SubLoop == ParentLoop)
       return false;
     return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
   }
 
   /// Create the loop forest using a stable algorithm.
   void analyze(const DominatorTreeBase<BlockT, false> &DomTree);
 
   // Debugging
   void print(raw_ostream &OS) const;
 
   void verify(const DominatorTreeBase<BlockT, false> &DomTree) const;
 
   /// Destroy a loop that has been removed from the `LoopInfo` nest.
   ///
   /// This runs the destructor of the loop object making it invalid to
   /// reference afterward. The memory is retained so that the *pointer* to the
   /// loop remains valid.
   ///
   /// The caller is responsible for removing this loop from the loop nest and
   /// otherwise disconnecting it from the broader `LoopInfo` data structures.
   /// Callers that don't naturally handle this themselves should probably call
   /// `erase' instead.
   void destroy(LoopT *L) {
     L->~LoopT();
 
     // Since LoopAllocator is a BumpPtrAllocator, this Deallocate only poisons
     // \c L, but the pointer remains valid for non-dereferencing uses.
     LoopAllocator.Deallocate(L);
   }
 };
 
 } // namespace llvm
 
 #endif // LLVM_SUPPORT_GENERICLOOPINFO_H

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