include/llvm/Analysis/LoopInfoImpl.h

   1 //===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This is the generic implementation of LoopInfo used for both Loops and
  10 // MachineLoops.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_ANALYSIS_LOOPINFOIMPL_H
  15 #define LLVM_ANALYSIS_LOOPINFOIMPL_H
  16
  17 #include "llvm/ADT/DepthFirstIterator.h"
  18 #include "llvm/ADT/PostOrderIterator.h"
  19 #include "llvm/ADT/STLExtras.h"
  20 #include "llvm/ADT/SetVector.h"
  21 #include "llvm/Analysis/LoopInfo.h"
  22 #include "llvm/IR/Dominators.h"
  23
  24 namespace llvm {
  25
  26 //===----------------------------------------------------------------------===//
  27 // APIs for simple analysis of the loop. See header notes.
  28
  29 /// getExitingBlocks - Return all blocks inside the loop that have successors
  30 /// outside of the loop.  These are the blocks _inside of the current loop_
  31 /// which branch out.  The returned list is always unique.
  32 ///
  33 template <class BlockT, class LoopT>
  34 void LoopBase<BlockT, LoopT>::getExitingBlocks(
  35     SmallVectorImpl<BlockT *> &ExitingBlocks) const {
  36   assert(!isInvalid() && "Loop not in a valid state!");
  37   for (const auto BB : blocks())
  38     for (const auto &Succ : children<BlockT *>(BB))
  39       if (!contains(Succ)) {
  40         // Not in current loop? It must be an exit block.
  41         ExitingBlocks.push_back(BB);
  42         break;
  43       }
  44 }
  45
  46 /// getExitingBlock - If getExitingBlocks would return exactly one block,
  47 /// return that block. Otherwise return null.
  48 template <class BlockT, class LoopT>
  49 BlockT *LoopBase<BlockT, LoopT>::getExitingBlock() const {
  50   assert(!isInvalid() && "Loop not in a valid state!");
  51   SmallVector<BlockT *, 8> ExitingBlocks;
  52   getExitingBlocks(ExitingBlocks);
  53   if (ExitingBlocks.size() == 1)
  54     return ExitingBlocks[0];
  55   return nullptr;
  56 }
  57
  58 /// getExitBlocks - Return all of the successor blocks of this loop.  These
  59 /// are the blocks _outside of the current loop_ which are branched to.
  60 ///
  61 template <class BlockT, class LoopT>
  62 void LoopBase<BlockT, LoopT>::getExitBlocks(
  63     SmallVectorImpl<BlockT *> &ExitBlocks) const {
  64   assert(!isInvalid() && "Loop not in a valid state!");
  65   for (const auto BB : blocks())
  66     for (const auto &Succ : children<BlockT *>(BB))
  67       if (!contains(Succ))
  68         // Not in current loop? It must be an exit block.
  69         ExitBlocks.push_back(Succ);
  70 }
  71
  72 /// getExitBlock - If getExitBlocks would return exactly one block,
  73 /// return that block. Otherwise return null.
  74 template <class BlockT, class LoopT>
  75 BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const {
  76   assert(!isInvalid() && "Loop not in a valid state!");
  77   SmallVector<BlockT *, 8> ExitBlocks;
  78   getExitBlocks(ExitBlocks);
  79   if (ExitBlocks.size() == 1)
  80     return ExitBlocks[0];
  81   return nullptr;
  82 }
  83
  84 template <class BlockT, class LoopT>
  85 bool LoopBase<BlockT, LoopT>::hasDedicatedExits() const {
  86   // Each predecessor of each exit block of a normal loop is contained
  87   // within the loop.
  88   SmallVector<BlockT *, 4> ExitBlocks;
  89   getExitBlocks(ExitBlocks);
  90   for (BlockT *EB : ExitBlocks)
  91     for (BlockT *Predecessor : children<Inverse<BlockT *>>(EB))
  92       if (!contains(Predecessor))
  93         return false;
  94   // All the requirements are met.
  95   return true;
  96 }
  97
  98 template <class BlockT, class LoopT>
  99 void LoopBase<BlockT, LoopT>::getUniqueExitBlocks(
 100     SmallVectorImpl<BlockT *> &ExitBlocks) const {
 101   typedef GraphTraits<BlockT *> BlockTraits;
 102   typedef GraphTraits<Inverse<BlockT *>> InvBlockTraits;
 103
 104   assert(hasDedicatedExits() &&
 105          "getUniqueExitBlocks assumes the loop has canonical form exits!");
 106
 107   SmallVector<BlockT *, 32> SwitchExitBlocks;
 108   for (BlockT *Block : this->blocks()) {
 109     SwitchExitBlocks.clear();
 110     for (BlockT *Successor : children<BlockT *>(Block)) {
 111       // If block is inside the loop then it is not an exit block.
 112       if (contains(Successor))
 113         continue;
 114
 115       BlockT *FirstPred = *InvBlockTraits::child_begin(Successor);
 116
 117       // If current basic block is this exit block's first predecessor then only
 118       // insert exit block in to the output ExitBlocks vector. This ensures that
 119       // same exit block is not inserted twice into ExitBlocks vector.
 120       if (Block != FirstPred)
 121         continue;
 122
 123       // If a terminator has more then two successors, for example SwitchInst,
 124       // then it is possible that there are multiple edges from current block to
 125       // one exit block.
 126       if (std::distance(BlockTraits::child_begin(Block),
 127                         BlockTraits::child_end(Block)) <= 2) {
 128         ExitBlocks.push_back(Successor);
 129         continue;
 130       }
 131
 132       // In case of multiple edges from current block to exit block, collect
 133       // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
 134       // duplicate edges.
 135       if (!is_contained(SwitchExitBlocks, Successor)) {
 136         SwitchExitBlocks.push_back(Successor);
 137         ExitBlocks.push_back(Successor);
 138       }
 139     }
 140   }
 141 }
 142
 143 template <class BlockT, class LoopT>
 144 BlockT *LoopBase<BlockT, LoopT>::getUniqueExitBlock() const {
 145   SmallVector<BlockT *, 8> UniqueExitBlocks;
 146   getUniqueExitBlocks(UniqueExitBlocks);
 147   if (UniqueExitBlocks.size() == 1)
 148     return UniqueExitBlocks[0];
 149   return nullptr;
 150 }
 151
 152 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
 153 template <class BlockT, class LoopT>
 154 void LoopBase<BlockT, LoopT>::getExitEdges(
 155     SmallVectorImpl<Edge> &ExitEdges) const {
 156   assert(!isInvalid() && "Loop not in a valid state!");
 157   for (const auto BB : blocks())
 158     for (const auto &Succ : children<BlockT *>(BB))
 159       if (!contains(Succ))
 160         // Not in current loop? It must be an exit block.
 161         ExitEdges.emplace_back(BB, Succ);
 162 }
 163
 164 /// getLoopPreheader - If there is a preheader for this loop, return it.  A
 165 /// loop has a preheader if there is only one edge to the header of the loop
 166 /// from outside of the loop and it is legal to hoist instructions into the
 167 /// predecessor. If this is the case, the block branching to the header of the
 168 /// loop is the preheader node.
 169 ///
 170 /// This method returns null if there is no preheader for the loop.
 171 ///
 172 template <class BlockT, class LoopT>
 173 BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const {
 174   assert(!isInvalid() && "Loop not in a valid state!");
 175   // Keep track of nodes outside the loop branching to the header...
 176   BlockT *Out = getLoopPredecessor();
 177   if (!Out)
 178     return nullptr;
 179
 180   // Make sure we are allowed to hoist instructions into the predecessor.
 181   if (!Out->isLegalToHoistInto())
 182     return nullptr;
 183
 184   // Make sure there is only one exit out of the preheader.
 185   typedef GraphTraits<BlockT *> BlockTraits;
 186   typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
 187   ++SI;
 188   if (SI != BlockTraits::child_end(Out))
 189     return nullptr; // Multiple exits from the block, must not be a preheader.
 190
 191   // The predecessor has exactly one successor, so it is a preheader.
 192   return Out;
 193 }
 194
 195 /// getLoopPredecessor - If the given loop's header has exactly one unique
 196 /// predecessor outside the loop, return it. Otherwise return null.
 197 /// This is less strict that the loop "preheader" concept, which requires
 198 /// the predecessor to have exactly one successor.
 199 ///
 200 template <class BlockT, class LoopT>
 201 BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const {
 202   assert(!isInvalid() && "Loop not in a valid state!");
 203   // Keep track of nodes outside the loop branching to the header...
 204   BlockT *Out = nullptr;
 205
 206   // Loop over the predecessors of the header node...
 207   BlockT *Header = getHeader();
 208   for (const auto Pred : children<Inverse<BlockT *>>(Header)) {
 209     if (!contains(Pred)) { // If the block is not in the loop...
 210       if (Out && Out != Pred)
 211         return nullptr; // Multiple predecessors outside the loop
 212       Out = Pred;
 213     }
 214   }
 215
 216   // Make sure there is only one exit out of the preheader.
 217   assert(Out && "Header of loop has no predecessors from outside loop?");
 218   return Out;
 219 }
 220
 221 /// getLoopLatch - If there is a single latch block for this loop, return it.
 222 /// A latch block is a block that contains a branch back to the header.
 223 template <class BlockT, class LoopT>
 224 BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const {
 225   assert(!isInvalid() && "Loop not in a valid state!");
 226   BlockT *Header = getHeader();
 227   BlockT *Latch = nullptr;
 228   for (const auto Pred : children<Inverse<BlockT *>>(Header)) {
 229     if (contains(Pred)) {
 230       if (Latch)
 231         return nullptr;
 232       Latch = Pred;
 233     }
 234   }
 235
 236   return Latch;
 237 }
 238
 239 //===----------------------------------------------------------------------===//
 240 // APIs for updating loop information after changing the CFG
 241 //
 242
 243 /// addBasicBlockToLoop - This method is used by other analyses to update loop
 244 /// information.  NewBB is set to be a new member of the current loop.
 245 /// Because of this, it is added as a member of all parent loops, and is added
 246 /// to the specified LoopInfo object as being in the current basic block.  It
 247 /// is not valid to replace the loop header with this method.
 248 ///
 249 template <class BlockT, class LoopT>
 250 void LoopBase<BlockT, LoopT>::addBasicBlockToLoop(
 251     BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) {
 252   assert(!isInvalid() && "Loop not in a valid state!");
 253 #ifndef NDEBUG
 254   if (!Blocks.empty()) {
 255     auto SameHeader = LIB[getHeader()];
 256     assert(contains(SameHeader) && getHeader() == SameHeader->getHeader() &&
 257            "Incorrect LI specified for this loop!");
 258   }
 259 #endif
 260   assert(NewBB && "Cannot add a null basic block to the loop!");
 261   assert(!LIB[NewBB] && "BasicBlock already in the loop!");
 262
 263   LoopT *L = static_cast<LoopT *>(this);
 264
 265   // Add the loop mapping to the LoopInfo object...
 266   LIB.BBMap[NewBB] = L;
 267
 268   // Add the basic block to this loop and all parent loops...
 269   while (L) {
 270     L->addBlockEntry(NewBB);
 271     L = L->getParentLoop();
 272   }
 273 }
 274
 275 /// replaceChildLoopWith - This is used when splitting loops up.  It replaces
 276 /// the OldChild entry in our children list with NewChild, and updates the
 277 /// parent pointer of OldChild to be null and the NewChild to be this loop.
 278 /// This updates the loop depth of the new child.
 279 template <class BlockT, class LoopT>
 280 void LoopBase<BlockT, LoopT>::replaceChildLoopWith(LoopT *OldChild,
 281                                                    LoopT *NewChild) {
 282   assert(!isInvalid() && "Loop not in a valid state!");
 283   assert(OldChild->ParentLoop == this && "This loop is already broken!");
 284   assert(!NewChild->ParentLoop && "NewChild already has a parent!");
 285   typename std::vector<LoopT *>::iterator I = find(SubLoops, OldChild);
 286   assert(I != SubLoops.end() && "OldChild not in loop!");
 287   *I = NewChild;
 288   OldChild->ParentLoop = nullptr;
 289   NewChild->ParentLoop = static_cast<LoopT *>(this);
 290 }
 291
 292 /// verifyLoop - Verify loop structure
 293 template <class BlockT, class LoopT>
 294 void LoopBase<BlockT, LoopT>::verifyLoop() const {
 295   assert(!isInvalid() && "Loop not in a valid state!");
 296 #ifndef NDEBUG
 297   assert(!Blocks.empty() && "Loop header is missing");
 298
 299   // Setup for using a depth-first iterator to visit every block in the loop.
 300   SmallVector<BlockT *, 8> ExitBBs;
 301   getExitBlocks(ExitBBs);
 302   df_iterator_default_set<BlockT *> VisitSet;
 303   VisitSet.insert(ExitBBs.begin(), ExitBBs.end());
 304   df_ext_iterator<BlockT *, df_iterator_default_set<BlockT *>>
 305       BI = df_ext_begin(getHeader(), VisitSet),
 306       BE = df_ext_end(getHeader(), VisitSet);
 307
 308   // Keep track of the BBs visited.
 309   SmallPtrSet<BlockT *, 8> VisitedBBs;
 310
 311   // Check the individual blocks.
 312   for (; BI != BE; ++BI) {
 313     BlockT *BB = *BI;
 314
 315     assert(std::any_of(GraphTraits<BlockT *>::child_begin(BB),
 316                        GraphTraits<BlockT *>::child_end(BB),
 317                        [&](BlockT *B) { return contains(B); }) &&
 318            "Loop block has no in-loop successors!");
 319
 320     assert(std::any_of(GraphTraits<Inverse<BlockT *>>::child_begin(BB),
 321                        GraphTraits<Inverse<BlockT *>>::child_end(BB),
 322                        [&](BlockT *B) { return contains(B); }) &&
 323            "Loop block has no in-loop predecessors!");
 324
 325     SmallVector<BlockT *, 2> OutsideLoopPreds;
 326     std::for_each(GraphTraits<Inverse<BlockT *>>::child_begin(BB),
 327                   GraphTraits<Inverse<BlockT *>>::child_end(BB),
 328                   [&](BlockT *B) {
 329                     if (!contains(B))
 330                       OutsideLoopPreds.push_back(B);
 331                   });
 332
 333     if (BB == getHeader()) {
 334       assert(!OutsideLoopPreds.empty() && "Loop is unreachable!");
 335     } else if (!OutsideLoopPreds.empty()) {
 336       // A non-header loop shouldn't be reachable from outside the loop,
 337       // though it is permitted if the predecessor is not itself actually
 338       // reachable.
 339       BlockT *EntryBB = &BB->getParent()->front();
 340       for (BlockT *CB : depth_first(EntryBB))
 341         for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i)
 342           assert(CB != OutsideLoopPreds[i] &&
 343                  "Loop has multiple entry points!");
 344     }
 345     assert(BB != &getHeader()->getParent()->front() &&
 346            "Loop contains function entry block!");
 347
 348     VisitedBBs.insert(BB);
 349   }
 350
 351   if (VisitedBBs.size() != getNumBlocks()) {
 352     dbgs() << "The following blocks are unreachable in the loop: ";
 353     for (auto BB : Blocks) {
 354       if (!VisitedBBs.count(BB)) {
 355         dbgs() << *BB << "\n";
 356       }
 357     }
 358     assert(false && "Unreachable block in loop");
 359   }
 360
 361   // Check the subloops.
 362   for (iterator I = begin(), E = end(); I != E; ++I)
 363     // Each block in each subloop should be contained within this loop.
 364     for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end();
 365          BI != BE; ++BI) {
 366       assert(contains(*BI) &&
 367              "Loop does not contain all the blocks of a subloop!");
 368     }
 369
 370   // Check the parent loop pointer.
 371   if (ParentLoop) {
 372     assert(is_contained(*ParentLoop, this) &&
 373            "Loop is not a subloop of its parent!");
 374   }
 375 #endif
 376 }
 377
 378 /// verifyLoop - Verify loop structure of this loop and all nested loops.
 379 template <class BlockT, class LoopT>
 380 void LoopBase<BlockT, LoopT>::verifyLoopNest(
 381     DenseSet<const LoopT *> *Loops) const {
 382   assert(!isInvalid() && "Loop not in a valid state!");
 383   Loops->insert(static_cast<const LoopT *>(this));
 384   // Verify this loop.
 385   verifyLoop();
 386   // Verify the subloops.
 387   for (iterator I = begin(), E = end(); I != E; ++I)
 388     (*I)->verifyLoopNest(Loops);
 389 }
 390
 391 template <class BlockT, class LoopT>
 392 void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth,
 393                                     bool Verbose) const {
 394   OS.indent(Depth * 2);
 395   if (static_cast<const LoopT *>(this)->isAnnotatedParallel())
 396     OS << "Parallel ";
 397   OS << "Loop at depth " << getLoopDepth() << " containing: ";
 398
 399   BlockT *H = getHeader();
 400   for (unsigned i = 0; i < getBlocks().size(); ++i) {
 401     BlockT *BB = getBlocks()[i];
 402     if (!Verbose) {
 403       if (i)
 404         OS << ",";
 405       BB->printAsOperand(OS, false);
 406     } else
 407       OS << "\n";
 408
 409     if (BB == H)
 410       OS << "<header>";
 411     if (isLoopLatch(BB))
 412       OS << "<latch>";
 413     if (isLoopExiting(BB))
 414       OS << "<exiting>";
 415     if (Verbose)
 416       BB->print(OS);
 417   }
 418   OS << "\n";
 419
 420   for (iterator I = begin(), E = end(); I != E; ++I)
 421     (*I)->print(OS, Depth + 2);
 422 }
 423
 424 //===----------------------------------------------------------------------===//
 425 /// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the
 426 /// result does / not depend on use list (block predecessor) order.
 427 ///
 428
 429 /// Discover a subloop with the specified backedges such that: All blocks within
 430 /// this loop are mapped to this loop or a subloop. And all subloops within this
 431 /// loop have their parent loop set to this loop or a subloop.
 432 template <class BlockT, class LoopT>
 433 static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT *> Backedges,
 434                                   LoopInfoBase<BlockT, LoopT> *LI,
 435                                   const DomTreeBase<BlockT> &DomTree) {
 436   typedef GraphTraits<Inverse<BlockT *>> InvBlockTraits;
 437
 438   unsigned NumBlocks = 0;
 439   unsigned NumSubloops = 0;
 440
 441   // Perform a backward CFG traversal using a worklist.
 442   std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end());
 443   while (!ReverseCFGWorklist.empty()) {
 444     BlockT *PredBB = ReverseCFGWorklist.back();
 445     ReverseCFGWorklist.pop_back();
 446
 447     LoopT *Subloop = LI->getLoopFor(PredBB);
 448     if (!Subloop) {
 449       if (!DomTree.isReachableFromEntry(PredBB))
 450         continue;
 451
 452       // This is an undiscovered block. Map it to the current loop.
 453       LI->changeLoopFor(PredBB, L);
 454       ++NumBlocks;
 455       if (PredBB == L->getHeader())
 456         continue;
 457       // Push all block predecessors on the worklist.
 458       ReverseCFGWorklist.insert(ReverseCFGWorklist.end(),
 459                                 InvBlockTraits::child_begin(PredBB),
 460                                 InvBlockTraits::child_end(PredBB));
 461     } else {
 462       // This is a discovered block. Find its outermost discovered loop.
 463       while (LoopT *Parent = Subloop->getParentLoop())
 464         Subloop = Parent;
 465
 466       // If it is already discovered to be a subloop of this loop, continue.
 467       if (Subloop == L)
 468         continue;
 469
 470       // Discover a subloop of this loop.
 471       Subloop->setParentLoop(L);
 472       ++NumSubloops;
 473       NumBlocks += Subloop->getBlocksVector().capacity();
 474       PredBB = Subloop->getHeader();
 475       // Continue traversal along predecessors that are not loop-back edges from
 476       // within this subloop tree itself. Note that a predecessor may directly
 477       // reach another subloop that is not yet discovered to be a subloop of
 478       // this loop, which we must traverse.
 479       for (const auto Pred : children<Inverse<BlockT *>>(PredBB)) {
 480         if (LI->getLoopFor(Pred) != Subloop)
 481           ReverseCFGWorklist.push_back(Pred);
 482       }
 483     }
 484   }
 485   L->getSubLoopsVector().reserve(NumSubloops);
 486   L->reserveBlocks(NumBlocks);
 487 }
 488
 489 /// Populate all loop data in a stable order during a single forward DFS.
 490 template <class BlockT, class LoopT> class PopulateLoopsDFS {
 491   typedef GraphTraits<BlockT *> BlockTraits;
 492   typedef typename BlockTraits::ChildIteratorType SuccIterTy;
 493
 494   LoopInfoBase<BlockT, LoopT> *LI;
 495
 496 public:
 497   PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li) : LI(li) {}
 498
 499   void traverse(BlockT *EntryBlock);
 500
 501 protected:
 502   void insertIntoLoop(BlockT *Block);
 503 };
 504
 505 /// Top-level driver for the forward DFS within the loop.
 506 template <class BlockT, class LoopT>
 507 void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) {
 508   for (BlockT *BB : post_order(EntryBlock))
 509     insertIntoLoop(BB);
 510 }
 511
 512 /// Add a single Block to its ancestor loops in PostOrder. If the block is a
 513 /// subloop header, add the subloop to its parent in PostOrder, then reverse the
 514 /// Block and Subloop vectors of the now complete subloop to achieve RPO.
 515 template <class BlockT, class LoopT>
 516 void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) {
 517   LoopT *Subloop = LI->getLoopFor(Block);
 518   if (Subloop && Block == Subloop->getHeader()) {
 519     // We reach this point once per subloop after processing all the blocks in
 520     // the subloop.
 521     if (Subloop->getParentLoop())
 522       Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop);
 523     else
 524       LI->addTopLevelLoop(Subloop);
 525
 526     // For convenience, Blocks and Subloops are inserted in postorder. Reverse
 527     // the lists, except for the loop header, which is always at the beginning.
 528     Subloop->reverseBlock(1);
 529     std::reverse(Subloop->getSubLoopsVector().begin(),
 530                  Subloop->getSubLoopsVector().end());
 531
 532     Subloop = Subloop->getParentLoop();
 533   }
 534   for (; Subloop; Subloop = Subloop->getParentLoop())
 535     Subloop->addBlockEntry(Block);
 536 }
 537
 538 /// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal
 539 /// interleaved with backward CFG traversals within each subloop
 540 /// (discoverAndMapSubloop). The backward traversal skips inner subloops, so
 541 /// this part of the algorithm is linear in the number of CFG edges. Subloop and
 542 /// Block vectors are then populated during a single forward CFG traversal
 543 /// (PopulateLoopDFS).
 544 ///
 545 /// During the two CFG traversals each block is seen three times:
 546 /// 1) Discovered and mapped by a reverse CFG traversal.
 547 /// 2) Visited during a forward DFS CFG traversal.
 548 /// 3) Reverse-inserted in the loop in postorder following forward DFS.
 549 ///
 550 /// The Block vectors are inclusive, so step 3 requires loop-depth number of
 551 /// insertions per block.
 552 template <class BlockT, class LoopT>
 553 void LoopInfoBase<BlockT, LoopT>::analyze(const DomTreeBase<BlockT> &DomTree) {
 554   // Postorder traversal of the dominator tree.
 555   const DomTreeNodeBase<BlockT> *DomRoot = DomTree.getRootNode();
 556   for (auto DomNode : post_order(DomRoot)) {
 557
 558     BlockT *Header = DomNode->getBlock();
 559     SmallVector<BlockT *, 4> Backedges;
 560
 561     // Check each predecessor of the potential loop header.
 562     for (const auto Backedge : children<Inverse<BlockT *>>(Header)) {
 563       // If Header dominates predBB, this is a new loop. Collect the backedges.
 564       if (DomTree.dominates(Header, Backedge) &&
 565           DomTree.isReachableFromEntry(Backedge)) {
 566         Backedges.push_back(Backedge);
 567       }
 568     }
 569     // Perform a backward CFG traversal to discover and map blocks in this loop.
 570     if (!Backedges.empty()) {
 571       LoopT *L = AllocateLoop(Header);
 572       discoverAndMapSubloop(L, ArrayRef<BlockT *>(Backedges), this, DomTree);
 573     }
 574   }
 575   // Perform a single forward CFG traversal to populate block and subloop
 576   // vectors for all loops.
 577   PopulateLoopsDFS<BlockT, LoopT> DFS(this);
 578   DFS.traverse(DomRoot->getBlock());
 579 }
 580
 581 template <class BlockT, class LoopT>
 582 SmallVector<LoopT *, 4> LoopInfoBase<BlockT, LoopT>::getLoopsInPreorder() {
 583   SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
 584   // The outer-most loop actually goes into the result in the same relative
 585   // order as we walk it. But LoopInfo stores the top level loops in reverse
 586   // program order so for here we reverse it to get forward program order.
 587   // FIXME: If we change the order of LoopInfo we will want to remove the
 588   // reverse here.
 589   for (LoopT *RootL : reverse(*this)) {
 590     assert(PreOrderWorklist.empty() &&
 591            "Must start with an empty preorder walk worklist.");
 592     PreOrderWorklist.push_back(RootL);
 593     do {
 594       LoopT *L = PreOrderWorklist.pop_back_val();
 595       // Sub-loops are stored in forward program order, but will process the
 596       // worklist backwards so append them in reverse order.
 597       PreOrderWorklist.append(L->rbegin(), L->rend());
 598       PreOrderLoops.push_back(L);
 599     } while (!PreOrderWorklist.empty());
 600   }
 601
 602   return PreOrderLoops;
 603 }
 604
 605 template <class BlockT, class LoopT>
 606 SmallVector<LoopT *, 4>
 607 LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() {
 608   SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
 609   // The outer-most loop actually goes into the result in the same relative
 610   // order as we walk it. LoopInfo stores the top level loops in reverse
 611   // program order so we walk in order here.
 612   // FIXME: If we change the order of LoopInfo we will want to add a reverse
 613   // here.
 614   for (LoopT *RootL : *this) {
 615     assert(PreOrderWorklist.empty() &&
 616            "Must start with an empty preorder walk worklist.");
 617     PreOrderWorklist.push_back(RootL);
 618     do {
 619       LoopT *L = PreOrderWorklist.pop_back_val();
 620       // Sub-loops are stored in forward program order, but will process the
 621       // worklist backwards so we can just append them in order.
 622       PreOrderWorklist.append(L->begin(), L->end());
 623       PreOrderLoops.push_back(L);
 624     } while (!PreOrderWorklist.empty());
 625   }
 626
 627   return PreOrderLoops;
 628 }
 629
 630 // Debugging
 631 template <class BlockT, class LoopT>
 632 void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const {
 633   for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
 634     TopLevelLoops[i]->print(OS);
 635 #if 0
 636   for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(),
 637          E = BBMap.end(); I != E; ++I)
 638     OS << "BB '" << I->first->getName() << "' level = "
 639        << I->second->getLoopDepth() << "\n";
 640 #endif
 641 }
 642
 643 template <typename T>
 644 bool compareVectors(std::vector<T> &BB1, std::vector<T> &BB2) {
 645   llvm::sort(BB1);
 646   llvm::sort(BB2);
 647   return BB1 == BB2;
 648 }
 649
 650 template <class BlockT, class LoopT>
 651 void addInnerLoopsToHeadersMap(DenseMap<BlockT *, const LoopT *> &LoopHeaders,
 652                                const LoopInfoBase<BlockT, LoopT> &LI,
 653                                const LoopT &L) {
 654   LoopHeaders[L.getHeader()] = &L;
 655   for (LoopT *SL : L)
 656     addInnerLoopsToHeadersMap(LoopHeaders, LI, *SL);
 657 }
 658
 659 #ifndef NDEBUG
 660 template <class BlockT, class LoopT>
 661 static void compareLoops(const LoopT *L, const LoopT *OtherL,
 662                          DenseMap<BlockT *, const LoopT *> &OtherLoopHeaders) {
 663   BlockT *H = L->getHeader();
 664   BlockT *OtherH = OtherL->getHeader();
 665   assert(H == OtherH &&
 666          "Mismatched headers even though found in the same map entry!");
 667
 668   assert(L->getLoopDepth() == OtherL->getLoopDepth() &&
 669          "Mismatched loop depth!");
 670   const LoopT *ParentL = L, *OtherParentL = OtherL;
 671   do {
 672     assert(ParentL->getHeader() == OtherParentL->getHeader() &&
 673            "Mismatched parent loop headers!");
 674     ParentL = ParentL->getParentLoop();
 675     OtherParentL = OtherParentL->getParentLoop();
 676   } while (ParentL);
 677
 678   for (const LoopT *SubL : *L) {
 679     BlockT *SubH = SubL->getHeader();
 680     const LoopT *OtherSubL = OtherLoopHeaders.lookup(SubH);
 681     assert(OtherSubL && "Inner loop is missing in computed loop info!");
 682     OtherLoopHeaders.erase(SubH);
 683     compareLoops(SubL, OtherSubL, OtherLoopHeaders);
 684   }
 685
 686   std::vector<BlockT *> BBs = L->getBlocks();
 687   std::vector<BlockT *> OtherBBs = OtherL->getBlocks();
 688   assert(compareVectors(BBs, OtherBBs) &&
 689          "Mismatched basic blocks in the loops!");
 690
 691   const SmallPtrSetImpl<const BlockT *> &BlocksSet = L->getBlocksSet();
 692   const SmallPtrSetImpl<const BlockT *> &OtherBlocksSet = L->getBlocksSet();
 693   assert(BlocksSet.size() == OtherBlocksSet.size() &&
 694          std::all_of(BlocksSet.begin(), BlocksSet.end(),
 695                      [&OtherBlocksSet](const BlockT *BB) {
 696                        return OtherBlocksSet.count(BB);
 697                      }) &&
 698          "Mismatched basic blocks in BlocksSets!");
 699 }
 700 #endif
 701
 702 template <class BlockT, class LoopT>
 703 void LoopInfoBase<BlockT, LoopT>::verify(
 704     const DomTreeBase<BlockT> &DomTree) const {
 705   DenseSet<const LoopT *> Loops;
 706   for (iterator I = begin(), E = end(); I != E; ++I) {
 707     assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
 708     (*I)->verifyLoopNest(&Loops);
 709   }
 710
 711 // Verify that blocks are mapped to valid loops.
 712 #ifndef NDEBUG
 713   for (auto &Entry : BBMap) {
 714     const BlockT *BB = Entry.first;
 715     LoopT *L = Entry.second;
 716     assert(Loops.count(L) && "orphaned loop");
 717     assert(L->contains(BB) && "orphaned block");
 718     for (LoopT *ChildLoop : *L)
 719       assert(!ChildLoop->contains(BB) &&
 720              "BBMap should point to the innermost loop containing BB");
 721   }
 722
 723   // Recompute LoopInfo to verify loops structure.
 724   LoopInfoBase<BlockT, LoopT> OtherLI;
 725   OtherLI.analyze(DomTree);
 726
 727   // Build a map we can use to move from our LI to the computed one. This
 728   // allows us to ignore the particular order in any layer of the loop forest
 729   // while still comparing the structure.
 730   DenseMap<BlockT *, const LoopT *> OtherLoopHeaders;
 731   for (LoopT *L : OtherLI)
 732     addInnerLoopsToHeadersMap(OtherLoopHeaders, OtherLI, *L);
 733
 734   // Walk the top level loops and ensure there is a corresponding top-level
 735   // loop in the computed version and then recursively compare those loop
 736   // nests.
 737   for (LoopT *L : *this) {
 738     BlockT *Header = L->getHeader();
 739     const LoopT *OtherL = OtherLoopHeaders.lookup(Header);
 740     assert(OtherL && "Top level loop is missing in computed loop info!");
 741     // Now that we've matched this loop, erase its header from the map.
 742     OtherLoopHeaders.erase(Header);
 743     // And recursively compare these loops.
 744     compareLoops(L, OtherL, OtherLoopHeaders);
 745   }
 746
 747   // Any remaining entries in the map are loops which were found when computing
 748   // a fresh LoopInfo but not present in the current one.
 749   if (!OtherLoopHeaders.empty()) {
 750     for (const auto &HeaderAndLoop : OtherLoopHeaders)
 751       dbgs() << "Found new loop: " << *HeaderAndLoop.second << "\n";
 752     llvm_unreachable("Found new loops when recomputing LoopInfo!");
 753   }
 754 #endif
 755 }
 756
 757 } // End llvm namespace
 758
 759 #endif