src/llvm/lib/Analysis/LoopInfo.cpp

   1 //===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file defines the LoopInfo class that is used to identify natural loops
  11 // and determine the loop depth of various nodes of the CFG.  Note that the
  12 // loops identified may actually be several natural loops that share the same
  13 // header node... not just a single natural loop.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/Analysis/LoopInfo.h"
  18 #include "llvm/ADT/DepthFirstIterator.h"
  19 #include "llvm/ADT/SmallPtrSet.h"
  20 #include "llvm/Analysis/Dominators.h"
  21 #include "llvm/Analysis/LoopInfoImpl.h"
  22 #include "llvm/Analysis/LoopIterator.h"
  23 #include "llvm/Analysis/ValueTracking.h"
  24 #include "llvm/Assembly/Writer.h"
  25 #include "llvm/IR/Constants.h"
  26 #include "llvm/IR/Instructions.h"
  27 #include "llvm/IR/Metadata.h"
  28 #include "llvm/Support/CFG.h"
  29 #include "llvm/Support/CommandLine.h"
  30 #include "llvm/Support/Debug.h"
  31 #include <algorithm>
  32 using namespace llvm;
  33
  34 // Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
  35 template class llvm::LoopBase<BasicBlock, Loop>;
  36 template class llvm::LoopInfoBase<BasicBlock, Loop>;
  37
  38 // Always verify loopinfo if expensive checking is enabled.
  39 #ifdef XDEBUG
  40 static bool VerifyLoopInfo = true;
  41 #else
  42 static bool VerifyLoopInfo = false;
  43 #endif
  44 static cl::opt<bool,true>
  45 VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
  46                 cl::desc("Verify loop info (time consuming)"));
  47
  48 char LoopInfo::ID = 0;
  49 INITIALIZE_PASS_BEGIN(LoopInfo, "loops", "Natural Loop Information", true, true)
  50 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
  51 INITIALIZE_PASS_END(LoopInfo, "loops", "Natural Loop Information", true, true)
  52
  53 //===----------------------------------------------------------------------===//
  54 // Loop implementation
  55 //
  56
  57 /// isLoopInvariant - Return true if the specified value is loop invariant
  58 ///
  59 bool Loop::isLoopInvariant(Value *V) const {
  60   if (Instruction *I = dyn_cast<Instruction>(V))
  61     return !contains(I);
  62   return true;  // All non-instructions are loop invariant
  63 }
  64
  65 /// hasLoopInvariantOperands - Return true if all the operands of the
  66 /// specified instruction are loop invariant.
  67 bool Loop::hasLoopInvariantOperands(Instruction *I) const {
  68   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
  69     if (!isLoopInvariant(I->getOperand(i)))
  70       return false;
  71
  72   return true;
  73 }
  74
  75 /// makeLoopInvariant - If the given value is an instruciton inside of the
  76 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
  77 /// Return true if the value after any hoisting is loop invariant. This
  78 /// function can be used as a slightly more aggressive replacement for
  79 /// isLoopInvariant.
  80 ///
  81 /// If InsertPt is specified, it is the point to hoist instructions to.
  82 /// If null, the terminator of the loop preheader is used.
  83 ///
  84 bool Loop::makeLoopInvariant(Value *V, bool &Changed,
  85                              Instruction *InsertPt) const {
  86   if (Instruction *I = dyn_cast<Instruction>(V))
  87     return makeLoopInvariant(I, Changed, InsertPt);
  88   return true;  // All non-instructions are loop-invariant.
  89 }
  90
  91 /// makeLoopInvariant - If the given instruction is inside of the
  92 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
  93 /// Return true if the instruction after any hoisting is loop invariant. This
  94 /// function can be used as a slightly more aggressive replacement for
  95 /// isLoopInvariant.
  96 ///
  97 /// If InsertPt is specified, it is the point to hoist instructions to.
  98 /// If null, the terminator of the loop preheader is used.
  99 ///
 100 bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
 101                              Instruction *InsertPt) const {
 102   // Test if the value is already loop-invariant.
 103   if (isLoopInvariant(I))
 104     return true;
 105   if (!isSafeToSpeculativelyExecute(I))
 106     return false;
 107   if (I->mayReadFromMemory())
 108     return false;
 109   // The landingpad instruction is immobile.
 110   if (isa<LandingPadInst>(I))
 111     return false;
 112   // Determine the insertion point, unless one was given.
 113   if (!InsertPt) {
 114     BasicBlock *Preheader = getLoopPreheader();
 115     // Without a preheader, hoisting is not feasible.
 116     if (!Preheader)
 117       return false;
 118     InsertPt = Preheader->getTerminator();
 119   }
 120   // Don't hoist instructions with loop-variant operands.
 121   for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
 122     if (!makeLoopInvariant(I->getOperand(i), Changed, InsertPt))
 123       return false;
 124
 125   // Hoist.
 126   I->moveBefore(InsertPt);
 127   Changed = true;
 128   return true;
 129 }
 130
 131 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
 132 /// induction variable: an integer recurrence that starts at 0 and increments
 133 /// by one each time through the loop.  If so, return the phi node that
 134 /// corresponds to it.
 135 ///
 136 /// The IndVarSimplify pass transforms loops to have a canonical induction
 137 /// variable.
 138 ///
 139 PHINode *Loop::getCanonicalInductionVariable() const {
 140   BasicBlock *H = getHeader();
 141
 142   BasicBlock *Incoming = 0, *Backedge = 0;
 143   pred_iterator PI = pred_begin(H);
 144   assert(PI != pred_end(H) &&
 145          "Loop must have at least one backedge!");
 146   Backedge = *PI++;
 147   if (PI == pred_end(H)) return 0;  // dead loop
 148   Incoming = *PI++;
 149   if (PI != pred_end(H)) return 0;  // multiple backedges?
 150
 151   if (contains(Incoming)) {
 152     if (contains(Backedge))
 153       return 0;
 154     std::swap(Incoming, Backedge);
 155   } else if (!contains(Backedge))
 156     return 0;
 157
 158   // Loop over all of the PHI nodes, looking for a canonical indvar.
 159   for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
 160     PHINode *PN = cast<PHINode>(I);
 161     if (ConstantInt *CI =
 162         dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
 163       if (CI->isNullValue())
 164         if (Instruction *Inc =
 165             dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
 166           if (Inc->getOpcode() == Instruction::Add &&
 167                 Inc->getOperand(0) == PN)
 168             if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
 169               if (CI->equalsInt(1))
 170                 return PN;
 171   }
 172   return 0;
 173 }
 174
 175 /// isLCSSAForm - Return true if the Loop is in LCSSA form
 176 bool Loop::isLCSSAForm(DominatorTree &DT) const {
 177   // Sort the blocks vector so that we can use binary search to do quick
 178   // lookups.
 179   SmallPtrSet<BasicBlock*, 16> LoopBBs(block_begin(), block_end());
 180
 181   for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) {
 182     BasicBlock *BB = *BI;
 183     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;++I)
 184       for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
 185            ++UI) {
 186         User *U = *UI;
 187         BasicBlock *UserBB = cast<Instruction>(U)->getParent();
 188         if (PHINode *P = dyn_cast<PHINode>(U))
 189           UserBB = P->getIncomingBlock(UI);
 190
 191         // Check the current block, as a fast-path, before checking whether
 192         // the use is anywhere in the loop.  Most values are used in the same
 193         // block they are defined in.  Also, blocks not reachable from the
 194         // entry are special; uses in them don't need to go through PHIs.
 195         if (UserBB != BB &&
 196             !LoopBBs.count(UserBB) &&
 197             DT.isReachableFromEntry(UserBB))
 198           return false;
 199       }
 200   }
 201
 202   return true;
 203 }
 204
 205 /// isLoopSimplifyForm - Return true if the Loop is in the form that
 206 /// the LoopSimplify form transforms loops to, which is sometimes called
 207 /// normal form.
 208 bool Loop::isLoopSimplifyForm() const {
 209   // Normal-form loops have a preheader, a single backedge, and all of their
 210   // exits have all their predecessors inside the loop.
 211   return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
 212 }
 213
 214 /// isSafeToClone - Return true if the loop body is safe to clone in practice.
 215 /// Routines that reform the loop CFG and split edges often fail on indirectbr.
 216 bool Loop::isSafeToClone() const {
 217   // Return false if any loop blocks contain indirectbrs, or there are any calls
 218   // to noduplicate functions.
 219   for (Loop::block_iterator I = block_begin(), E = block_end(); I != E; ++I) {
 220     if (isa<IndirectBrInst>((*I)->getTerminator())) {
 221       return false;
 222     } else if (const InvokeInst *II = dyn_cast<InvokeInst>((*I)->getTerminator())) {
 223       if (II->hasFnAttr(Attribute::NoDuplicate))
 224         return false;
 225     }
 226
 227     for (BasicBlock::iterator BI = (*I)->begin(), BE = (*I)->end(); BI != BE; ++BI) {
 228       if (const CallInst *CI = dyn_cast<CallInst>(BI)) {
 229         if (CI->hasFnAttr(Attribute::NoDuplicate))
 230           return false;
 231       }
 232     }
 233   }
 234   return true;
 235 }
 236
 237 bool Loop::isAnnotatedParallel() const {
 238
 239   BasicBlock *latch = getLoopLatch();
 240   if (latch == NULL)
 241     return false;
 242
 243   MDNode *desiredLoopIdMetadata =
 244     latch->getTerminator()->getMetadata("llvm.loop.parallel");
 245
 246   if (!desiredLoopIdMetadata)
 247       return false;
 248
 249   // The loop branch contains the parallel loop metadata. In order to ensure
 250   // that any parallel-loop-unaware optimization pass hasn't added loop-carried
 251   // dependencies (thus converted the loop back to a sequential loop), check
 252   // that all the memory instructions in the loop contain parallelism metadata
 253   // that point to the same unique "loop id metadata" the loop branch does.
 254   for (block_iterator BB = block_begin(), BE = block_end(); BB != BE; ++BB) {
 255     for (BasicBlock::iterator II = (*BB)->begin(), EE = (*BB)->end();
 256          II != EE; II++) {
 257
 258       if (!II->mayReadOrWriteMemory())
 259         continue;
 260
 261       if (!II->getMetadata("llvm.mem.parallel_loop_access"))
 262         return false;
 263
 264       // The memory instruction can refer to the loop identifier metadata
 265       // directly or indirectly through another list metadata (in case of
 266       // nested parallel loops). The loop identifier metadata refers to
 267       // itself so we can check both cases with the same routine.
 268       MDNode *loopIdMD =
 269           dyn_cast<MDNode>(II->getMetadata("llvm.mem.parallel_loop_access"));
 270       bool loopIdMDFound = false;
 271       for (unsigned i = 0, e = loopIdMD->getNumOperands(); i < e; ++i) {
 272         if (loopIdMD->getOperand(i) == desiredLoopIdMetadata) {
 273           loopIdMDFound = true;
 274           break;
 275         }
 276       }
 277
 278       if (!loopIdMDFound)
 279         return false;
 280     }
 281   }
 282   return true;
 283 }
 284
 285
 286 /// hasDedicatedExits - Return true if no exit block for the loop
 287 /// has a predecessor that is outside the loop.
 288 bool Loop::hasDedicatedExits() const {
 289   // Sort the blocks vector so that we can use binary search to do quick
 290   // lookups.
 291   SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end());
 292   // Each predecessor of each exit block of a normal loop is contained
 293   // within the loop.
 294   SmallVector<BasicBlock *, 4> ExitBlocks;
 295   getExitBlocks(ExitBlocks);
 296   for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
 297     for (pred_iterator PI = pred_begin(ExitBlocks[i]),
 298          PE = pred_end(ExitBlocks[i]); PI != PE; ++PI)
 299       if (!LoopBBs.count(*PI))
 300         return false;
 301   // All the requirements are met.
 302   return true;
 303 }
 304
 305 /// getUniqueExitBlocks - Return all unique successor blocks of this loop.
 306 /// These are the blocks _outside of the current loop_ which are branched to.
 307 /// This assumes that loop exits are in canonical form.
 308 ///
 309 void
 310 Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
 311   assert(hasDedicatedExits() &&
 312          "getUniqueExitBlocks assumes the loop has canonical form exits!");
 313
 314   // Sort the blocks vector so that we can use binary search to do quick
 315   // lookups.
 316   SmallVector<BasicBlock *, 128> LoopBBs(block_begin(), block_end());
 317   std::sort(LoopBBs.begin(), LoopBBs.end());
 318
 319   SmallVector<BasicBlock *, 32> switchExitBlocks;
 320
 321   for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
 322
 323     BasicBlock *current = *BI;
 324     switchExitBlocks.clear();
 325
 326     for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I) {
 327       // If block is inside the loop then it is not a exit block.
 328       if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
 329         continue;
 330
 331       pred_iterator PI = pred_begin(*I);
 332       BasicBlock *firstPred = *PI;
 333
 334       // If current basic block is this exit block's first predecessor
 335       // then only insert exit block in to the output ExitBlocks vector.
 336       // This ensures that same exit block is not inserted twice into
 337       // ExitBlocks vector.
 338       if (current != firstPred)
 339         continue;
 340
 341       // If a terminator has more then two successors, for example SwitchInst,
 342       // then it is possible that there are multiple edges from current block
 343       // to one exit block.
 344       if (std::distance(succ_begin(current), succ_end(current)) <= 2) {
 345         ExitBlocks.push_back(*I);
 346         continue;
 347       }
 348
 349       // In case of multiple edges from current block to exit block, collect
 350       // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
 351       // duplicate edges.
 352       if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I)
 353           == switchExitBlocks.end()) {
 354         switchExitBlocks.push_back(*I);
 355         ExitBlocks.push_back(*I);
 356       }
 357     }
 358   }
 359 }
 360
 361 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
 362 /// block, return that block. Otherwise return null.
 363 BasicBlock *Loop::getUniqueExitBlock() const {
 364   SmallVector<BasicBlock *, 8> UniqueExitBlocks;
 365   getUniqueExitBlocks(UniqueExitBlocks);
 366   if (UniqueExitBlocks.size() == 1)
 367     return UniqueExitBlocks[0];
 368   return 0;
 369 }
 370
 371 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 372 void Loop::dump() const {
 373   print(dbgs());
 374 }
 375 #endif
 376
 377 //===----------------------------------------------------------------------===//
 378 // UnloopUpdater implementation
 379 //
 380
 381 namespace {
 382 /// Find the new parent loop for all blocks within the "unloop" whose last
 383 /// backedges has just been removed.
 384 class UnloopUpdater {
 385   Loop *Unloop;
 386   LoopInfo *LI;
 387
 388   LoopBlocksDFS DFS;
 389
 390   // Map unloop's immediate subloops to their nearest reachable parents. Nested
 391   // loops within these subloops will not change parents. However, an immediate
 392   // subloop's new parent will be the nearest loop reachable from either its own
 393   // exits *or* any of its nested loop's exits.
 394   DenseMap<Loop*, Loop*> SubloopParents;
 395
 396   // Flag the presence of an irreducible backedge whose destination is a block
 397   // directly contained by the original unloop.
 398   bool FoundIB;
 399
 400 public:
 401   UnloopUpdater(Loop *UL, LoopInfo *LInfo) :
 402     Unloop(UL), LI(LInfo), DFS(UL), FoundIB(false) {}
 403
 404   void updateBlockParents();
 405
 406   void removeBlocksFromAncestors();
 407
 408   void updateSubloopParents();
 409
 410 protected:
 411   Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
 412 };
 413 } // end anonymous namespace
 414
 415 /// updateBlockParents - Update the parent loop for all blocks that are directly
 416 /// contained within the original "unloop".
 417 void UnloopUpdater::updateBlockParents() {
 418   if (Unloop->getNumBlocks()) {
 419     // Perform a post order CFG traversal of all blocks within this loop,
 420     // propagating the nearest loop from sucessors to predecessors.
 421     LoopBlocksTraversal Traversal(DFS, LI);
 422     for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
 423            POE = Traversal.end(); POI != POE; ++POI) {
 424
 425       Loop *L = LI->getLoopFor(*POI);
 426       Loop *NL = getNearestLoop(*POI, L);
 427
 428       if (NL != L) {
 429         // For reducible loops, NL is now an ancestor of Unloop.
 430         assert((NL != Unloop && (!NL || NL->contains(Unloop))) &&
 431                "uninitialized successor");
 432         LI->changeLoopFor(*POI, NL);
 433       }
 434       else {
 435         // Or the current block is part of a subloop, in which case its parent
 436         // is unchanged.
 437         assert((FoundIB || Unloop->contains(L)) && "uninitialized successor");
 438       }
 439     }
 440   }
 441   // Each irreducible loop within the unloop induces a round of iteration using
 442   // the DFS result cached by Traversal.
 443   bool Changed = FoundIB;
 444   for (unsigned NIters = 0; Changed; ++NIters) {
 445     assert(NIters < Unloop->getNumBlocks() && "runaway iterative algorithm");
 446
 447     // Iterate over the postorder list of blocks, propagating the nearest loop
 448     // from successors to predecessors as before.
 449     Changed = false;
 450     for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
 451            POE = DFS.endPostorder(); POI != POE; ++POI) {
 452
 453       Loop *L = LI->getLoopFor(*POI);
 454       Loop *NL = getNearestLoop(*POI, L);
 455       if (NL != L) {
 456         assert(NL != Unloop && (!NL || NL->contains(Unloop)) &&
 457                "uninitialized successor");
 458         LI->changeLoopFor(*POI, NL);
 459         Changed = true;
 460       }
 461     }
 462   }
 463 }
 464
 465 /// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below
 466 /// their new parents.
 467 void UnloopUpdater::removeBlocksFromAncestors() {
 468   // Remove all unloop's blocks (including those in nested subloops) from
 469   // ancestors below the new parent loop.
 470   for (Loop::block_iterator BI = Unloop->block_begin(),
 471          BE = Unloop->block_end(); BI != BE; ++BI) {
 472     Loop *OuterParent = LI->getLoopFor(*BI);
 473     if (Unloop->contains(OuterParent)) {
 474       while (OuterParent->getParentLoop() != Unloop)
 475         OuterParent = OuterParent->getParentLoop();
 476       OuterParent = SubloopParents[OuterParent];
 477     }
 478     // Remove blocks from former Ancestors except Unloop itself which will be
 479     // deleted.
 480     for (Loop *OldParent = Unloop->getParentLoop(); OldParent != OuterParent;
 481          OldParent = OldParent->getParentLoop()) {
 482       assert(OldParent && "new loop is not an ancestor of the original");
 483       OldParent->removeBlockFromLoop(*BI);
 484     }
 485   }
 486 }
 487
 488 /// updateSubloopParents - Update the parent loop for all subloops directly
 489 /// nested within unloop.
 490 void UnloopUpdater::updateSubloopParents() {
 491   while (!Unloop->empty()) {
 492     Loop *Subloop = *llvm::prior(Unloop->end());
 493     Unloop->removeChildLoop(llvm::prior(Unloop->end()));
 494
 495     assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
 496     if (Loop *Parent = SubloopParents[Subloop])
 497       Parent->addChildLoop(Subloop);
 498     else
 499       LI->addTopLevelLoop(Subloop);
 500   }
 501 }
 502
 503 /// getNearestLoop - Return the nearest parent loop among this block's
 504 /// successors. If a successor is a subloop header, consider its parent to be
 505 /// the nearest parent of the subloop's exits.
 506 ///
 507 /// For subloop blocks, simply update SubloopParents and return NULL.
 508 Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
 509
 510   // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
 511   // is considered uninitialized.
 512   Loop *NearLoop = BBLoop;
 513
 514   Loop *Subloop = 0;
 515   if (NearLoop != Unloop && Unloop->contains(NearLoop)) {
 516     Subloop = NearLoop;
 517     // Find the subloop ancestor that is directly contained within Unloop.
 518     while (Subloop->getParentLoop() != Unloop) {
 519       Subloop = Subloop->getParentLoop();
 520       assert(Subloop && "subloop is not an ancestor of the original loop");
 521     }
 522     // Get the current nearest parent of the Subloop exits, initially Unloop.
 523     NearLoop =
 524       SubloopParents.insert(std::make_pair(Subloop, Unloop)).first->second;
 525   }
 526
 527   succ_iterator I = succ_begin(BB), E = succ_end(BB);
 528   if (I == E) {
 529     assert(!Subloop && "subloop blocks must have a successor");
 530     NearLoop = 0; // unloop blocks may now exit the function.
 531   }
 532   for (; I != E; ++I) {
 533     if (*I == BB)
 534       continue; // self loops are uninteresting
 535
 536     Loop *L = LI->getLoopFor(*I);
 537     if (L == Unloop) {
 538       // This successor has not been processed. This path must lead to an
 539       // irreducible backedge.
 540       assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
 541       FoundIB = true;
 542     }
 543     if (L != Unloop && Unloop->contains(L)) {
 544       // Successor is in a subloop.
 545       if (Subloop)
 546         continue; // Branching within subloops. Ignore it.
 547
 548       // BB branches from the original into a subloop header.
 549       assert(L->getParentLoop() == Unloop && "cannot skip into nested loops");
 550
 551       // Get the current nearest parent of the Subloop's exits.
 552       L = SubloopParents[L];
 553       // L could be Unloop if the only exit was an irreducible backedge.
 554     }
 555     if (L == Unloop) {
 556       continue;
 557     }
 558     // Handle critical edges from Unloop into a sibling loop.
 559     if (L && !L->contains(Unloop)) {
 560       L = L->getParentLoop();
 561     }
 562     // Remember the nearest parent loop among successors or subloop exits.
 563     if (NearLoop == Unloop || !NearLoop || NearLoop->contains(L))
 564       NearLoop = L;
 565   }
 566   if (Subloop) {
 567     SubloopParents[Subloop] = NearLoop;
 568     return BBLoop;
 569   }
 570   return NearLoop;
 571 }
 572
 573 //===----------------------------------------------------------------------===//
 574 // LoopInfo implementation
 575 //
 576 bool LoopInfo::runOnFunction(Function &) {
 577   releaseMemory();
 578   LI.Analyze(getAnalysis<DominatorTree>().getBase());
 579   return false;
 580 }
 581
 582 /// updateUnloop - The last backedge has been removed from a loop--now the
 583 /// "unloop". Find a new parent for the blocks contained within unloop and
 584 /// update the loop tree. We don't necessarily have valid dominators at this
 585 /// point, but LoopInfo is still valid except for the removal of this loop.
 586 ///
 587 /// Note that Unloop may now be an empty loop. Calling Loop::getHeader without
 588 /// checking first is illegal.
 589 void LoopInfo::updateUnloop(Loop *Unloop) {
 590
 591   // First handle the special case of no parent loop to simplify the algorithm.
 592   if (!Unloop->getParentLoop()) {
 593     // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
 594     for (Loop::block_iterator I = Unloop->block_begin(),
 595          E = Unloop->block_end(); I != E; ++I) {
 596
 597       // Don't reparent blocks in subloops.
 598       if (getLoopFor(*I) != Unloop)
 599         continue;
 600
 601       // Blocks no longer have a parent but are still referenced by Unloop until
 602       // the Unloop object is deleted.
 603       LI.changeLoopFor(*I, 0);
 604     }
 605
 606     // Remove the loop from the top-level LoopInfo object.
 607     for (LoopInfo::iterator I = LI.begin();; ++I) {
 608       assert(I != LI.end() && "Couldn't find loop");
 609       if (*I == Unloop) {
 610         LI.removeLoop(I);
 611         break;
 612       }
 613     }
 614
 615     // Move all of the subloops to the top-level.
 616     while (!Unloop->empty())
 617       LI.addTopLevelLoop(Unloop->removeChildLoop(llvm::prior(Unloop->end())));
 618
 619     return;
 620   }
 621
 622   // Update the parent loop for all blocks within the loop. Blocks within
 623   // subloops will not change parents.
 624   UnloopUpdater Updater(Unloop, this);
 625   Updater.updateBlockParents();
 626
 627   // Remove blocks from former ancestor loops.
 628   Updater.removeBlocksFromAncestors();
 629
 630   // Add direct subloops as children in their new parent loop.
 631   Updater.updateSubloopParents();
 632
 633   // Remove unloop from its parent loop.
 634   Loop *ParentLoop = Unloop->getParentLoop();
 635   for (Loop::iterator I = ParentLoop->begin();; ++I) {
 636     assert(I != ParentLoop->end() && "Couldn't find loop");
 637     if (*I == Unloop) {
 638       ParentLoop->removeChildLoop(I);
 639       break;
 640     }
 641   }
 642 }
 643
 644 void LoopInfo::verifyAnalysis() const {
 645   // LoopInfo is a FunctionPass, but verifying every loop in the function
 646   // each time verifyAnalysis is called is very expensive. The
 647   // -verify-loop-info option can enable this. In order to perform some
 648   // checking by default, LoopPass has been taught to call verifyLoop
 649   // manually during loop pass sequences.
 650
 651   if (!VerifyLoopInfo) return;
 652
 653   DenseSet<const Loop*> Loops;
 654   for (iterator I = begin(), E = end(); I != E; ++I) {
 655     assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
 656     (*I)->verifyLoopNest(&Loops);
 657   }
 658
 659   // Verify that blocks are mapped to valid loops.
 660   for (DenseMap<BasicBlock*, Loop*>::const_iterator I = LI.BBMap.begin(),
 661          E = LI.BBMap.end(); I != E; ++I) {
 662     assert(Loops.count(I->second) && "orphaned loop");
 663     assert(I->second->contains(I->first) && "orphaned block");
 664   }
 665 }
 666
 667 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
 668   AU.setPreservesAll();
 669   AU.addRequired<DominatorTree>();
 670 }
 671
 672 void LoopInfo::print(raw_ostream &OS, const Module*) const {
 673   LI.print(OS);
 674 }
 675
 676 //===----------------------------------------------------------------------===//
 677 // LoopBlocksDFS implementation
 678 //
 679
 680 /// Traverse the loop blocks and store the DFS result.
 681 /// Useful for clients that just want the final DFS result and don't need to
 682 /// visit blocks during the initial traversal.
 683 void LoopBlocksDFS::perform(LoopInfo *LI) {
 684   LoopBlocksTraversal Traversal(*this, LI);
 685   for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
 686          POE = Traversal.end(); POI != POE; ++POI) ;
 687 }