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//===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- 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 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/PostOrderIterator.h"

#include "llvm/ADT/STLExtras.h"

#include "llvm/ADT/SetOperations.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 (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!");

  auto notInLoop = [&](BlockT *BB) { return !contains(BB); };

  auto isExitBlock = [&](BlockT *BB, bool AllowRepeats) -> BlockT * {

    assert(!AllowRepeats && "Unexpected parameter value.");

    // Child not in current loop?  It must be an exit block.

    return any_of(children<BlockT *>(BB), notInLoop) ? BB : nullptr;

  };

  return find_singleton<BlockT>(blocks(), isExitBlock);

}

/// 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 (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>

std::pair<BlockT *, bool> getExitBlockHelper(const LoopBase<BlockT, LoopT> *L,

                                             bool Unique) {

  assert(!L->isInvalid() && "Loop not in a valid state!");

  auto notInLoop = [&](BlockT *BB,

                       bool AllowRepeats) -> std::pair<BlockT *, bool> {

    assert(AllowRepeats == Unique && "Unexpected parameter value.");

    return {!L->contains(BB) ? BB : nullptr, false};

  };

  auto singleExitBlock = [&](BlockT *BB,

                             bool AllowRepeats) -> std::pair<BlockT *, bool> {

    assert(AllowRepeats == Unique && "Unexpected parameter value.");

    return find_singleton_nested<BlockT>(children<BlockT *>(BB), notInLoop,

                                         AllowRepeats);

  };

  return find_singleton_nested<BlockT>(L->blocks(), singleExitBlock, Unique);

}

template <class BlockT, class LoopT>

bool LoopBase<BlockT, LoopT>::hasNoExitBlocks() const {

  auto RC = getExitBlockHelper(this, false);

  if (RC.second)

    // found multiple exit blocks

    return false;

  // return true if there is no exit block

  return !RC.first;

}

/// 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 {

  return getExitBlockHelper(this, false).first;

}

template <class BlockT, class LoopT>

bool LoopBase<BlockT, LoopT>::hasDedicatedExits() const {

  // Each predecessor of each exit block of a normal loop is contained

  // within the loop.

  SmallVector<BlockT *, 4> UniqueExitBlocks;

  getUniqueExitBlocks(UniqueExitBlocks);

  for (BlockT *EB : UniqueExitBlocks)

    for (BlockT *Predecessor : children<Inverse<BlockT *>>(EB))

      if (!contains(Predecessor))

        return false;

  // All the requirements are met.

  return true;

}

// Helper function to get unique loop exits. Pred is a predicate pointing to

// BasicBlocks in a loop which should be considered to find loop exits.

template <class BlockT, class LoopT, typename PredicateT>

void getUniqueExitBlocksHelper(const LoopT *L,

                               SmallVectorImpl<BlockT *> &ExitBlocks,

                               PredicateT Pred) {

  assert(!L->isInvalid() && "Loop not in a valid state!");

  SmallPtrSet<BlockT *, 32> Visited;

  auto Filtered = make_filter_range(L->blocks(), Pred);

  for (BlockT *BB : Filtered)

    for (BlockT *Successor : children<BlockT *>(BB))

      if (!L->contains(Successor))

        if (Visited.insert(Successor).second)

          ExitBlocks.push_back(Successor);

}

template <class BlockT, class LoopT>

void LoopBase<BlockT, LoopT>::getUniqueExitBlocks(

    SmallVectorImpl<BlockT *> &ExitBlocks) const {

  getUniqueExitBlocksHelper(this, ExitBlocks,

                            [](const BlockT *BB) { return true; });

}

template <class BlockT, class LoopT>

void LoopBase<BlockT, LoopT>::getUniqueNonLatchExitBlocks(

    SmallVectorImpl<BlockT *> &ExitBlocks) const {

  const BlockT *Latch = getLoopLatch();

  assert(Latch && "Latch block must exists");

  getUniqueExitBlocksHelper(this, ExitBlocks,

                            [Latch](const BlockT *BB) { return BB != Latch; });

}

template <class BlockT, class LoopT>

BlockT *LoopBase<BlockT, LoopT>::getUniqueExitBlock() const {

  return getExitBlockHelper(this, true).first;

}

/// 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 (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;

    }

  }

  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());

  // Keep track of the BBs visited.

  SmallPtrSet<BlockT *, 8> VisitedBBs;

  // Check the individual blocks.

  for (BlockT *BB : depth_first_ext(getHeader(), VisitSet)) {

    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;

    for (BlockT *B :

         llvm::make_range(GraphTraits<Inverse<BlockT *>>::child_begin(BB),

                          GraphTraits<Inverse<BlockT *>>::child_end(BB)))

      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, bool Verbose,

                                    bool PrintNested, unsigned Depth) const {

  OS.indent(Depth * 2);

  if (static_cast<const LoopT *>(this)->isAnnotatedParallel())

    OS << "Parallel ";

  OS << "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);

  }

  if (PrintNested) {

    OS << "\n";

    for (iterator I = begin(), E = end(); I != E; ++I)

      (*I)->print(OS, /*Verbose*/ false, PrintNested, 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.

      Subloop = Subloop->getOutermostLoop();

      // 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->isOutermost())

      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() const {

  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)) {

    auto PreOrderLoopsInRootL = RootL->getLoopsInPreorder();

    PreOrderLoops.append(PreOrderLoopsInRootL.begin(),

                         PreOrderLoopsInRootL.end());

  }

  return PreOrderLoops;

}

template <class BlockT, class LoopT>

SmallVector<LoopT *, 4>

LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() const {

  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) {

  llvm::sort(BB1);

  llvm::sort(BB2);

  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!");

  const SmallPtrSetImpl<const BlockT *> &BlocksSet = L->getBlocksSet();

  const SmallPtrSetImpl<const BlockT *> &OtherBlocksSet =

      OtherL->getBlocksSet();

  assert(BlocksSet.size() == OtherBlocksSet.size() &&

         llvm::set_is_subset(BlocksSet, OtherBlocksSet) &&

         "Mismatched basic blocks in BlocksSets!");

}

#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)->isOutermost() && "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");