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/Constants.h" 19 #include "llvm/Instructions.h" 20 #include "llvm/Analysis/Dominators.h" 21 #include "llvm/Analysis/LoopIterator.h" 22 #include "llvm/Assembly/Writer.h" 23 #include "llvm/Support/CFG.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Debug.h" 26 #include "llvm/ADT/DepthFirstIterator.h" 27 #include "llvm/ADT/SmallPtrSet.h" 28 #include <algorithm> 29 using namespace llvm; 30 31 // Always verify loopinfo if expensive checking is enabled. 32 #ifdef XDEBUG 33 static bool VerifyLoopInfo = true; 34 #else 35 static bool VerifyLoopInfo = false; 36 #endif 37 static cl::opt<bool,true> 38 VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo), 39 cl::desc("Verify loop info (time consuming)")); 40 41 char LoopInfo::ID = 0; 42 INITIALIZE_PASS_BEGIN(LoopInfo, "loops", "Natural Loop Information", true, true) 43 INITIALIZE_PASS_DEPENDENCY(DominatorTree) 44 INITIALIZE_PASS_END(LoopInfo, "loops", "Natural Loop Information", true, true) 45 46 //===----------------------------------------------------------------------===// 47 // Loop implementation 48 // 49 50 /// isLoopInvariant - Return true if the specified value is loop invariant 51 /// 52 bool Loop::isLoopInvariant(Value *V) const { 53 if (Instruction *I = dyn_cast<Instruction>(V)) 54 return !contains(I); 55 return true; // All non-instructions are loop invariant 56 } 57 58 /// hasLoopInvariantOperands - Return true if all the operands of the 59 /// specified instruction are loop invariant. 60 bool Loop::hasLoopInvariantOperands(Instruction *I) const { 61 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 62 if (!isLoopInvariant(I->getOperand(i))) 63 return false; 64 65 return true; 66 } 67 68 /// makeLoopInvariant - If the given value is an instruciton inside of the 69 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 70 /// Return true if the value after any hoisting is loop invariant. This 71 /// function can be used as a slightly more aggressive replacement for 72 /// isLoopInvariant. 73 /// 74 /// If InsertPt is specified, it is the point to hoist instructions to. 75 /// If null, the terminator of the loop preheader is used. 76 /// 77 bool Loop::makeLoopInvariant(Value *V, bool &Changed, 78 Instruction *InsertPt) const { 79 if (Instruction *I = dyn_cast<Instruction>(V)) 80 return makeLoopInvariant(I, Changed, InsertPt); 81 return true; // All non-instructions are loop-invariant. 82 } 83 84 /// makeLoopInvariant - If the given instruction is inside of the 85 /// loop and it can be hoisted, do so to make it trivially loop-invariant. 86 /// Return true if the instruction after any hoisting is loop invariant. This 87 /// function can be used as a slightly more aggressive replacement for 88 /// isLoopInvariant. 89 /// 90 /// If InsertPt is specified, it is the point to hoist instructions to. 91 /// If null, the terminator of the loop preheader is used. 92 /// 93 bool Loop::makeLoopInvariant(Instruction *I, bool &Changed, 94 Instruction *InsertPt) const { 95 // Test if the value is already loop-invariant. 96 if (isLoopInvariant(I)) 97 return true; 98 if (!I->isSafeToSpeculativelyExecute()) 99 return false; 100 if (I->mayReadFromMemory()) 101 return false; 102 // The landingpad instruction is immobile. 103 if (isa<LandingPadInst>(I)) 104 return false; 105 // Determine the insertion point, unless one was given. 106 if (!InsertPt) { 107 BasicBlock *Preheader = getLoopPreheader(); 108 // Without a preheader, hoisting is not feasible. 109 if (!Preheader) 110 return false; 111 InsertPt = Preheader->getTerminator(); 112 } 113 // Don't hoist instructions with loop-variant operands. 114 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 115 if (!makeLoopInvariant(I->getOperand(i), Changed, InsertPt)) 116 return false; 117 118 // Hoist. 119 I->moveBefore(InsertPt); 120 Changed = true; 121 return true; 122 } 123 124 /// getCanonicalInductionVariable - Check to see if the loop has a canonical 125 /// induction variable: an integer recurrence that starts at 0 and increments 126 /// by one each time through the loop. If so, return the phi node that 127 /// corresponds to it. 128 /// 129 /// The IndVarSimplify pass transforms loops to have a canonical induction 130 /// variable. 131 /// 132 PHINode *Loop::getCanonicalInductionVariable() const { 133 BasicBlock *H = getHeader(); 134 135 BasicBlock *Incoming = 0, *Backedge = 0; 136 pred_iterator PI = pred_begin(H); 137 assert(PI != pred_end(H) && 138 "Loop must have at least one backedge!"); 139 Backedge = *PI++; 140 if (PI == pred_end(H)) return 0; // dead loop 141 Incoming = *PI++; 142 if (PI != pred_end(H)) return 0; // multiple backedges? 143 144 if (contains(Incoming)) { 145 if (contains(Backedge)) 146 return 0; 147 std::swap(Incoming, Backedge); 148 } else if (!contains(Backedge)) 149 return 0; 150 151 // Loop over all of the PHI nodes, looking for a canonical indvar. 152 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) { 153 PHINode *PN = cast<PHINode>(I); 154 if (ConstantInt *CI = 155 dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming))) 156 if (CI->isNullValue()) 157 if (Instruction *Inc = 158 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge))) 159 if (Inc->getOpcode() == Instruction::Add && 160 Inc->getOperand(0) == PN) 161 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1))) 162 if (CI->equalsInt(1)) 163 return PN; 164 } 165 return 0; 166 } 167 168 /// getTripCount - Return a loop-invariant LLVM value indicating the number of 169 /// times the loop will be executed. Note that this means that the backedge 170 /// of the loop executes N-1 times. If the trip-count cannot be determined, 171 /// this returns null. 172 /// 173 /// The IndVarSimplify pass transforms loops to have a form that this 174 /// function easily understands. 175 /// 176 Value *Loop::getTripCount() const { 177 // Canonical loops will end with a 'cmp ne I, V', where I is the incremented 178 // canonical induction variable and V is the trip count of the loop. 179 PHINode *IV = getCanonicalInductionVariable(); 180 if (IV == 0 || IV->getNumIncomingValues() != 2) return 0; 181 182 bool P0InLoop = contains(IV->getIncomingBlock(0)); 183 Value *Inc = IV->getIncomingValue(!P0InLoop); 184 BasicBlock *BackedgeBlock = IV->getIncomingBlock(!P0InLoop); 185 186 if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator())) 187 if (BI->isConditional()) { 188 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) { 189 if (ICI->getOperand(0) == Inc) { 190 if (BI->getSuccessor(0) == getHeader()) { 191 if (ICI->getPredicate() == ICmpInst::ICMP_NE) 192 return ICI->getOperand(1); 193 } else if (ICI->getPredicate() == ICmpInst::ICMP_EQ) { 194 return ICI->getOperand(1); 195 } 196 } 197 } 198 } 199 200 return 0; 201 } 202 203 /// getSmallConstantTripCount - Returns the trip count of this loop as a 204 /// normal unsigned value, if possible. Returns 0 if the trip count is unknown 205 /// or not constant. Will also return 0 if the trip count is very large 206 /// (>= 2^32) 207 unsigned Loop::getSmallConstantTripCount() const { 208 Value* TripCount = this->getTripCount(); 209 if (TripCount) { 210 if (ConstantInt *TripCountC = dyn_cast<ConstantInt>(TripCount)) { 211 // Guard against huge trip counts. 212 if (TripCountC->getValue().getActiveBits() <= 32) { 213 return (unsigned)TripCountC->getZExtValue(); 214 } 215 } 216 } 217 return 0; 218 } 219 220 /// getSmallConstantTripMultiple - Returns the largest constant divisor of the 221 /// trip count of this loop as a normal unsigned value, if possible. This 222 /// means that the actual trip count is always a multiple of the returned 223 /// value (don't forget the trip count could very well be zero as well!). 224 /// 225 /// Returns 1 if the trip count is unknown or not guaranteed to be the 226 /// multiple of a constant (which is also the case if the trip count is simply 227 /// constant, use getSmallConstantTripCount for that case), Will also return 1 228 /// if the trip count is very large (>= 2^32). 229 unsigned Loop::getSmallConstantTripMultiple() const { 230 Value* TripCount = this->getTripCount(); 231 // This will hold the ConstantInt result, if any 232 ConstantInt *Result = NULL; 233 if (TripCount) { 234 // See if the trip count is constant itself 235 Result = dyn_cast<ConstantInt>(TripCount); 236 // if not, see if it is a multiplication 237 if (!Result) 238 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TripCount)) { 239 switch (BO->getOpcode()) { 240 case BinaryOperator::Mul: 241 Result = dyn_cast<ConstantInt>(BO->getOperand(1)); 242 break; 243 case BinaryOperator::Shl: 244 if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) 245 if (CI->getValue().getActiveBits() <= 5) 246 return 1u << CI->getZExtValue(); 247 break; 248 default: 249 break; 250 } 251 } 252 } 253 // Guard against huge trip counts. 254 if (Result && Result->getValue().getActiveBits() <= 32) { 255 return (unsigned)Result->getZExtValue(); 256 } else { 257 return 1; 258 } 259 } 260 261 /// isLCSSAForm - Return true if the Loop is in LCSSA form 262 bool Loop::isLCSSAForm(DominatorTree &DT) const { 263 // Sort the blocks vector so that we can use binary search to do quick 264 // lookups. 265 SmallPtrSet<BasicBlock*, 16> LoopBBs(block_begin(), block_end()); 266 267 for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) { 268 BasicBlock *BB = *BI; 269 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;++I) 270 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 271 ++UI) { 272 User *U = *UI; 273 BasicBlock *UserBB = cast<Instruction>(U)->getParent(); 274 if (PHINode *P = dyn_cast<PHINode>(U)) 275 UserBB = P->getIncomingBlock(UI); 276 277 // Check the current block, as a fast-path, before checking whether 278 // the use is anywhere in the loop. Most values are used in the same 279 // block they are defined in. Also, blocks not reachable from the 280 // entry are special; uses in them don't need to go through PHIs. 281 if (UserBB != BB && 282 !LoopBBs.count(UserBB) && 283 DT.isReachableFromEntry(UserBB)) 284 return false; 285 } 286 } 287 288 return true; 289 } 290 291 /// isLoopSimplifyForm - Return true if the Loop is in the form that 292 /// the LoopSimplify form transforms loops to, which is sometimes called 293 /// normal form. 294 bool Loop::isLoopSimplifyForm() const { 295 // Normal-form loops have a preheader, a single backedge, and all of their 296 // exits have all their predecessors inside the loop. 297 return getLoopPreheader() && getLoopLatch() && hasDedicatedExits(); 298 } 299 300 /// hasDedicatedExits - Return true if no exit block for the loop 301 /// has a predecessor that is outside the loop. 302 bool Loop::hasDedicatedExits() const { 303 // Sort the blocks vector so that we can use binary search to do quick 304 // lookups. 305 SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end()); 306 // Each predecessor of each exit block of a normal loop is contained 307 // within the loop. 308 SmallVector<BasicBlock *, 4> ExitBlocks; 309 getExitBlocks(ExitBlocks); 310 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) 311 for (pred_iterator PI = pred_begin(ExitBlocks[i]), 312 PE = pred_end(ExitBlocks[i]); PI != PE; ++PI) 313 if (!LoopBBs.count(*PI)) 314 return false; 315 // All the requirements are met. 316 return true; 317 } 318 319 /// getUniqueExitBlocks - Return all unique successor blocks of this loop. 320 /// These are the blocks _outside of the current loop_ which are branched to. 321 /// This assumes that loop exits are in canonical form. 322 /// 323 void 324 Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const { 325 assert(hasDedicatedExits() && 326 "getUniqueExitBlocks assumes the loop has canonical form exits!"); 327 328 // Sort the blocks vector so that we can use binary search to do quick 329 // lookups. 330 SmallVector<BasicBlock *, 128> LoopBBs(block_begin(), block_end()); 331 std::sort(LoopBBs.begin(), LoopBBs.end()); 332 333 SmallVector<BasicBlock *, 32> switchExitBlocks; 334 335 for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) { 336 337 BasicBlock *current = *BI; 338 switchExitBlocks.clear(); 339 340 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I) { 341 // If block is inside the loop then it is not a exit block. 342 if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) 343 continue; 344 345 pred_iterator PI = pred_begin(*I); 346 BasicBlock *firstPred = *PI; 347 348 // If current basic block is this exit block's first predecessor 349 // then only insert exit block in to the output ExitBlocks vector. 350 // This ensures that same exit block is not inserted twice into 351 // ExitBlocks vector. 352 if (current != firstPred) 353 continue; 354 355 // If a terminator has more then two successors, for example SwitchInst, 356 // then it is possible that there are multiple edges from current block 357 // to one exit block. 358 if (std::distance(succ_begin(current), succ_end(current)) <= 2) { 359 ExitBlocks.push_back(*I); 360 continue; 361 } 362 363 // In case of multiple edges from current block to exit block, collect 364 // only one edge in ExitBlocks. Use switchExitBlocks to keep track of 365 // duplicate edges. 366 if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I) 367 == switchExitBlocks.end()) { 368 switchExitBlocks.push_back(*I); 369 ExitBlocks.push_back(*I); 370 } 371 } 372 } 373 } 374 375 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one 376 /// block, return that block. Otherwise return null. 377 BasicBlock *Loop::getUniqueExitBlock() const { 378 SmallVector<BasicBlock *, 8> UniqueExitBlocks; 379 getUniqueExitBlocks(UniqueExitBlocks); 380 if (UniqueExitBlocks.size() == 1) 381 return UniqueExitBlocks[0]; 382 return 0; 383 } 384 385 void Loop::dump() const { 386 print(dbgs()); 387 } 388 389 //===----------------------------------------------------------------------===// 390 // UnloopUpdater implementation 391 // 392 393 namespace { 394 /// Find the new parent loop for all blocks within the "unloop" whose last 395 /// backedges has just been removed. 396 class UnloopUpdater { 397 Loop *Unloop; 398 LoopInfo *LI; 399 400 LoopBlocksDFS DFS; 401 402 // Map unloop's immediate subloops to their nearest reachable parents. Nested 403 // loops within these subloops will not change parents. However, an immediate 404 // subloop's new parent will be the nearest loop reachable from either its own 405 // exits *or* any of its nested loop's exits. 406 DenseMap<Loop*, Loop*> SubloopParents; 407 408 // Flag the presence of an irreducible backedge whose destination is a block 409 // directly contained by the original unloop. 410 bool FoundIB; 411 412 public: 413 UnloopUpdater(Loop *UL, LoopInfo *LInfo) : 414 Unloop(UL), LI(LInfo), DFS(UL), FoundIB(false) {} 415 416 void updateBlockParents(); 417 418 void removeBlocksFromAncestors(); 419 420 void updateSubloopParents(); 421 422 protected: 423 Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop); 424 }; 425 } // end anonymous namespace 426 427 /// updateBlockParents - Update the parent loop for all blocks that are directly 428 /// contained within the original "unloop". 429 void UnloopUpdater::updateBlockParents() { 430 if (Unloop->getNumBlocks()) { 431 // Perform a post order CFG traversal of all blocks within this loop, 432 // propagating the nearest loop from sucessors to predecessors. 433 LoopBlocksTraversal Traversal(DFS, LI); 434 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(), 435 POE = Traversal.end(); POI != POE; ++POI) { 436 437 Loop *L = LI->getLoopFor(*POI); 438 Loop *NL = getNearestLoop(*POI, L); 439 440 if (NL != L) { 441 // For reducible loops, NL is now an ancestor of Unloop. 442 assert((NL != Unloop && (!NL || NL->contains(Unloop))) && 443 "uninitialized successor"); 444 LI->changeLoopFor(*POI, NL); 445 } 446 else { 447 // Or the current block is part of a subloop, in which case its parent 448 // is unchanged. 449 assert((FoundIB || Unloop->contains(L)) && "uninitialized successor"); 450 } 451 } 452 } 453 // Each irreducible loop within the unloop induces a round of iteration using 454 // the DFS result cached by Traversal. 455 bool Changed = FoundIB; 456 for (unsigned NIters = 0; Changed; ++NIters) { 457 assert(NIters < Unloop->getNumBlocks() && "runaway iterative algorithm"); 458 459 // Iterate over the postorder list of blocks, propagating the nearest loop 460 // from successors to predecessors as before. 461 Changed = false; 462 for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(), 463 POE = DFS.endPostorder(); POI != POE; ++POI) { 464 465 Loop *L = LI->getLoopFor(*POI); 466 Loop *NL = getNearestLoop(*POI, L); 467 if (NL != L) { 468 assert(NL != Unloop && (!NL || NL->contains(Unloop)) && 469 "uninitialized successor"); 470 LI->changeLoopFor(*POI, NL); 471 Changed = true; 472 } 473 } 474 } 475 } 476 477 /// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below 478 /// their new parents. 479 void UnloopUpdater::removeBlocksFromAncestors() { 480 // Remove unloop's blocks from all ancestors below their new parents. 481 for (Loop::block_iterator BI = Unloop->block_begin(), 482 BE = Unloop->block_end(); BI != BE; ++BI) { 483 Loop *NewParent = LI->getLoopFor(*BI); 484 // If this block is an immediate subloop, remove all blocks (including 485 // nested subloops) from ancestors below the new parent loop. 486 // Otherwise, if this block is in a nested subloop, skip it. 487 if (SubloopParents.count(NewParent)) 488 NewParent = SubloopParents[NewParent]; 489 else if (Unloop->contains(NewParent)) 490 continue; 491 492 // Remove blocks from former Ancestors except Unloop itself which will be 493 // deleted. 494 for (Loop *OldParent = Unloop->getParentLoop(); OldParent != NewParent; 495 OldParent = OldParent->getParentLoop()) { 496 assert(OldParent && "new loop is not an ancestor of the original"); 497 OldParent->removeBlockFromLoop(*BI); 498 } 499 } 500 } 501 502 /// updateSubloopParents - Update the parent loop for all subloops directly 503 /// nested within unloop. 504 void UnloopUpdater::updateSubloopParents() { 505 while (!Unloop->empty()) { 506 Loop *Subloop = *llvm::prior(Unloop->end()); 507 Unloop->removeChildLoop(llvm::prior(Unloop->end())); 508 509 assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop"); 510 if (SubloopParents[Subloop]) 511 SubloopParents[Subloop]->addChildLoop(Subloop); 512 else 513 LI->addTopLevelLoop(Subloop); 514 } 515 } 516 517 /// getNearestLoop - Return the nearest parent loop among this block's 518 /// successors. If a successor is a subloop header, consider its parent to be 519 /// the nearest parent of the subloop's exits. 520 /// 521 /// For subloop blocks, simply update SubloopParents and return NULL. 522 Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) { 523 524 // Initially for blocks directly contained by Unloop, NearLoop == Unloop and 525 // is considered uninitialized. 526 Loop *NearLoop = BBLoop; 527 528 Loop *Subloop = 0; 529 if (NearLoop != Unloop && Unloop->contains(NearLoop)) { 530 Subloop = NearLoop; 531 // Find the subloop ancestor that is directly contained within Unloop. 532 while (Subloop->getParentLoop() != Unloop) { 533 Subloop = Subloop->getParentLoop(); 534 assert(Subloop && "subloop is not an ancestor of the original loop"); 535 } 536 // Get the current nearest parent of the Subloop exits, initially Unloop. 537 if (!SubloopParents.count(Subloop)) 538 SubloopParents[Subloop] = Unloop; 539 NearLoop = SubloopParents[Subloop]; 540 } 541 542 succ_iterator I = succ_begin(BB), E = succ_end(BB); 543 if (I == E) { 544 assert(!Subloop && "subloop blocks must have a successor"); 545 NearLoop = 0; // unloop blocks may now exit the function. 546 } 547 for (; I != E; ++I) { 548 if (*I == BB) 549 continue; // self loops are uninteresting 550 551 Loop *L = LI->getLoopFor(*I); 552 if (L == Unloop) { 553 // This successor has not been processed. This path must lead to an 554 // irreducible backedge. 555 assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB"); 556 FoundIB = true; 557 } 558 if (L != Unloop && Unloop->contains(L)) { 559 // Successor is in a subloop. 560 if (Subloop) 561 continue; // Branching within subloops. Ignore it. 562 563 // BB branches from the original into a subloop header. 564 assert(L->getParentLoop() == Unloop && "cannot skip into nested loops"); 565 566 // Get the current nearest parent of the Subloop's exits. 567 L = SubloopParents[L]; 568 // L could be Unloop if the only exit was an irreducible backedge. 569 } 570 if (L == Unloop) { 571 continue; 572 } 573 // Handle critical edges from Unloop into a sibling loop. 574 if (L && !L->contains(Unloop)) { 575 L = L->getParentLoop(); 576 } 577 // Remember the nearest parent loop among successors or subloop exits. 578 if (NearLoop == Unloop || !NearLoop || NearLoop->contains(L)) 579 NearLoop = L; 580 } 581 if (Subloop) { 582 SubloopParents[Subloop] = NearLoop; 583 return BBLoop; 584 } 585 return NearLoop; 586 } 587 588 //===----------------------------------------------------------------------===// 589 // LoopInfo implementation 590 // 591 bool LoopInfo::runOnFunction(Function &) { 592 releaseMemory(); 593 LI.Calculate(getAnalysis<DominatorTree>().getBase()); // Update 594 return false; 595 } 596 597 /// updateUnloop - The last backedge has been removed from a loop--now the 598 /// "unloop". Find a new parent for the blocks contained within unloop and 599 /// update the loop tree. We don't necessarily have valid dominators at this 600 /// point, but LoopInfo is still valid except for the removal of this loop. 601 /// 602 /// Note that Unloop may now be an empty loop. Calling Loop::getHeader without 603 /// checking first is illegal. 604 void LoopInfo::updateUnloop(Loop *Unloop) { 605 606 // First handle the special case of no parent loop to simplify the algorithm. 607 if (!Unloop->getParentLoop()) { 608 // Since BBLoop had no parent, Unloop blocks are no longer in a loop. 609 for (Loop::block_iterator I = Unloop->block_begin(), 610 E = Unloop->block_end(); I != E; ++I) { 611 612 // Don't reparent blocks in subloops. 613 if (getLoopFor(*I) != Unloop) 614 continue; 615 616 // Blocks no longer have a parent but are still referenced by Unloop until 617 // the Unloop object is deleted. 618 LI.changeLoopFor(*I, 0); 619 } 620 621 // Remove the loop from the top-level LoopInfo object. 622 for (LoopInfo::iterator I = LI.begin();; ++I) { 623 assert(I != LI.end() && "Couldn't find loop"); 624 if (*I == Unloop) { 625 LI.removeLoop(I); 626 break; 627 } 628 } 629 630 // Move all of the subloops to the top-level. 631 while (!Unloop->empty()) 632 LI.addTopLevelLoop(Unloop->removeChildLoop(llvm::prior(Unloop->end()))); 633 634 return; 635 } 636 637 // Update the parent loop for all blocks within the loop. Blocks within 638 // subloops will not change parents. 639 UnloopUpdater Updater(Unloop, this); 640 Updater.updateBlockParents(); 641 642 // Remove blocks from former ancestor loops. 643 Updater.removeBlocksFromAncestors(); 644 645 // Add direct subloops as children in their new parent loop. 646 Updater.updateSubloopParents(); 647 648 // Remove unloop from its parent loop. 649 Loop *ParentLoop = Unloop->getParentLoop(); 650 for (Loop::iterator I = ParentLoop->begin();; ++I) { 651 assert(I != ParentLoop->end() && "Couldn't find loop"); 652 if (*I == Unloop) { 653 ParentLoop->removeChildLoop(I); 654 break; 655 } 656 } 657 } 658 659 void LoopInfo::verifyAnalysis() const { 660 // LoopInfo is a FunctionPass, but verifying every loop in the function 661 // each time verifyAnalysis is called is very expensive. The 662 // -verify-loop-info option can enable this. In order to perform some 663 // checking by default, LoopPass has been taught to call verifyLoop 664 // manually during loop pass sequences. 665 666 if (!VerifyLoopInfo) return; 667 668 DenseSet<const Loop*> Loops; 669 for (iterator I = begin(), E = end(); I != E; ++I) { 670 assert(!(*I)->getParentLoop() && "Top-level loop has a parent!"); 671 (*I)->verifyLoopNest(&Loops); 672 } 673 674 // Verify that blocks are mapped to valid loops. 675 // 676 // FIXME: With an up-to-date DFS (see LoopIterator.h) and DominatorTree, we 677 // could also verify that the blocks are still in the correct loops. 678 for (DenseMap<BasicBlock*, Loop*>::const_iterator I = LI.BBMap.begin(), 679 E = LI.BBMap.end(); I != E; ++I) { 680 assert(Loops.count(I->second) && "orphaned loop"); 681 assert(I->second->contains(I->first) && "orphaned block"); 682 } 683 } 684 685 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { 686 AU.setPreservesAll(); 687 AU.addRequired<DominatorTree>(); 688 } 689 690 void LoopInfo::print(raw_ostream &OS, const Module*) const { 691 LI.print(OS); 692 } 693 694 //===----------------------------------------------------------------------===// 695 // LoopBlocksDFS implementation 696 // 697 698 /// Traverse the loop blocks and store the DFS result. 699 /// Useful for clients that just want the final DFS result and don't need to 700 /// visit blocks during the initial traversal. 701 void LoopBlocksDFS::perform(LoopInfo *LI) { 702 LoopBlocksTraversal Traversal(*this, LI); 703 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(), 704 POE = Traversal.end(); POI != POE; ++POI) ; 705 } 706