1 //===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/ADT/DepthFirstIterator.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/Analysis/LoopInfoImpl.h"
21 #include "llvm/Analysis/LoopIterator.h"
22 #include "llvm/Analysis/ValueTracking.h"
23 #include "llvm/IR/CFG.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DebugLoc.h"
26 #include "llvm/IR/Dominators.h"
27 #include "llvm/IR/Instructions.h"
28 #include "llvm/IR/LLVMContext.h"
29 #include "llvm/IR/Metadata.h"
30 #include "llvm/IR/PassManager.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/raw_ostream.h"
37 // Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
38 template class llvm::LoopBase<BasicBlock, Loop>;
39 template class llvm::LoopInfoBase<BasicBlock, Loop>;
41 // Always verify loopinfo if expensive checking is enabled.
42 #ifdef EXPENSIVE_CHECKS
43 static bool VerifyLoopInfo = true;
45 static bool VerifyLoopInfo = false;
47 static cl::opt<bool,true>
48 VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
49 cl::desc("Verify loop info (time consuming)"));
51 //===----------------------------------------------------------------------===//
52 // Loop implementation
55 bool Loop::isLoopInvariant(const Value *V) const {
56 if (const Instruction *I = dyn_cast<Instruction>(V))
58 return true; // All non-instructions are loop invariant
61 bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
62 return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
65 bool Loop::makeLoopInvariant(Value *V, bool &Changed,
66 Instruction *InsertPt) const {
67 if (Instruction *I = dyn_cast<Instruction>(V))
68 return makeLoopInvariant(I, Changed, InsertPt);
69 return true; // All non-instructions are loop-invariant.
72 bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
73 Instruction *InsertPt) const {
74 // Test if the value is already loop-invariant.
75 if (isLoopInvariant(I))
77 if (!isSafeToSpeculativelyExecute(I))
79 if (I->mayReadFromMemory())
81 // EH block instructions are immobile.
84 // Determine the insertion point, unless one was given.
86 BasicBlock *Preheader = getLoopPreheader();
87 // Without a preheader, hoisting is not feasible.
90 InsertPt = Preheader->getTerminator();
92 // Don't hoist instructions with loop-variant operands.
93 for (Value *Operand : I->operands())
94 if (!makeLoopInvariant(Operand, Changed, InsertPt))
98 I->moveBefore(InsertPt);
100 // There is possibility of hoisting this instruction above some arbitrary
101 // condition. Any metadata defined on it can be control dependent on this
102 // condition. Conservatively strip it here so that we don't give any wrong
103 // information to the optimizer.
104 I->dropUnknownNonDebugMetadata();
110 PHINode *Loop::getCanonicalInductionVariable() const {
111 BasicBlock *H = getHeader();
113 BasicBlock *Incoming = nullptr, *Backedge = nullptr;
114 pred_iterator PI = pred_begin(H);
115 assert(PI != pred_end(H) &&
116 "Loop must have at least one backedge!");
118 if (PI == pred_end(H)) return nullptr; // dead loop
120 if (PI != pred_end(H)) return nullptr; // multiple backedges?
122 if (contains(Incoming)) {
123 if (contains(Backedge))
125 std::swap(Incoming, Backedge);
126 } else if (!contains(Backedge))
129 // Loop over all of the PHI nodes, looking for a canonical indvar.
130 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
131 PHINode *PN = cast<PHINode>(I);
132 if (ConstantInt *CI =
133 dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
134 if (CI->isNullValue())
135 if (Instruction *Inc =
136 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
137 if (Inc->getOpcode() == Instruction::Add &&
138 Inc->getOperand(0) == PN)
139 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
140 if (CI->equalsInt(1))
146 // Check that 'BB' doesn't have any uses outside of the 'L'
147 static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
149 for (const Instruction &I : BB) {
150 // Tokens can't be used in PHI nodes and live-out tokens prevent loop
151 // optimizations, so for the purposes of considered LCSSA form, we
153 if (I.getType()->isTokenTy())
156 for (const Use &U : I.uses()) {
157 const Instruction *UI = cast<Instruction>(U.getUser());
158 const BasicBlock *UserBB = UI->getParent();
159 if (const PHINode *P = dyn_cast<PHINode>(UI))
160 UserBB = P->getIncomingBlock(U);
162 // Check the current block, as a fast-path, before checking whether
163 // the use is anywhere in the loop. Most values are used in the same
164 // block they are defined in. Also, blocks not reachable from the
165 // entry are special; uses in them don't need to go through PHIs.
166 if (UserBB != &BB && !L.contains(UserBB) &&
167 DT.isReachableFromEntry(UserBB))
174 bool Loop::isLCSSAForm(DominatorTree &DT) const {
175 // For each block we check that it doesn't have any uses outside of this loop.
176 return all_of(this->blocks(), [&](const BasicBlock *BB) {
177 return isBlockInLCSSAForm(*this, *BB, DT);
181 bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const {
182 // For each block we check that it doesn't have any uses outside of its
183 // innermost loop. This process will transitively guarantee that the current
184 // loop and all of the nested loops are in LCSSA form.
185 return all_of(this->blocks(), [&](const BasicBlock *BB) {
186 return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
190 bool Loop::isLoopSimplifyForm() const {
191 // Normal-form loops have a preheader, a single backedge, and all of their
192 // exits have all their predecessors inside the loop.
193 return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
196 // Routines that reform the loop CFG and split edges often fail on indirectbr.
197 bool Loop::isSafeToClone() const {
198 // Return false if any loop blocks contain indirectbrs, or there are any calls
199 // to noduplicate functions.
200 for (BasicBlock *BB : this->blocks()) {
201 if (isa<IndirectBrInst>(BB->getTerminator()))
204 for (Instruction &I : *BB)
205 if (auto CS = CallSite(&I))
206 if (CS.cannotDuplicate())
212 MDNode *Loop::getLoopID() const {
213 MDNode *LoopID = nullptr;
214 if (isLoopSimplifyForm()) {
215 LoopID = getLoopLatch()->getTerminator()->getMetadata(LLVMContext::MD_loop);
217 // Go through each predecessor of the loop header and check the
218 // terminator for the metadata.
219 BasicBlock *H = getHeader();
220 for (BasicBlock *BB : this->blocks()) {
221 TerminatorInst *TI = BB->getTerminator();
222 MDNode *MD = nullptr;
224 // Check if this terminator branches to the loop header.
225 for (BasicBlock *Successor : TI->successors()) {
226 if (Successor == H) {
227 MD = TI->getMetadata(LLVMContext::MD_loop);
236 else if (MD != LoopID)
240 if (!LoopID || LoopID->getNumOperands() == 0 ||
241 LoopID->getOperand(0) != LoopID)
246 void Loop::setLoopID(MDNode *LoopID) const {
247 assert(LoopID && "Loop ID should not be null");
248 assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand");
249 assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself");
251 if (isLoopSimplifyForm()) {
252 getLoopLatch()->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
256 BasicBlock *H = getHeader();
257 for (BasicBlock *BB : this->blocks()) {
258 TerminatorInst *TI = BB->getTerminator();
259 for (BasicBlock *Successor : TI->successors()) {
261 TI->setMetadata(LLVMContext::MD_loop, LoopID);
266 bool Loop::isAnnotatedParallel() const {
267 MDNode *DesiredLoopIdMetadata = getLoopID();
269 if (!DesiredLoopIdMetadata)
272 // The loop branch contains the parallel loop metadata. In order to ensure
273 // that any parallel-loop-unaware optimization pass hasn't added loop-carried
274 // dependencies (thus converted the loop back to a sequential loop), check
275 // that all the memory instructions in the loop contain parallelism metadata
276 // that point to the same unique "loop id metadata" the loop branch does.
277 for (BasicBlock *BB : this->blocks()) {
278 for (Instruction &I : *BB) {
279 if (!I.mayReadOrWriteMemory())
282 // The memory instruction can refer to the loop identifier metadata
283 // directly or indirectly through another list metadata (in case of
284 // nested parallel loops). The loop identifier metadata refers to
285 // itself so we can check both cases with the same routine.
287 I.getMetadata(LLVMContext::MD_mem_parallel_loop_access);
292 bool LoopIdMDFound = false;
293 for (const MDOperand &MDOp : LoopIdMD->operands()) {
294 if (MDOp == DesiredLoopIdMetadata) {
295 LoopIdMDFound = true;
307 DebugLoc Loop::getStartLoc() const {
308 return getLocRange().getStart();
311 Loop::LocRange Loop::getLocRange() const {
312 // If we have a debug location in the loop ID, then use it.
313 if (MDNode *LoopID = getLoopID()) {
315 // We use the first DebugLoc in the header as the start location of the loop
316 // and if there is a second DebugLoc in the header we use it as end location
318 for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
319 if (DILocation *L = dyn_cast<DILocation>(LoopID->getOperand(i))) {
323 return LocRange(Start, DebugLoc(L));
328 return LocRange(Start);
331 // Try the pre-header first.
332 if (BasicBlock *PHeadBB = getLoopPreheader())
333 if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
336 // If we have no pre-header or there are no instructions with debug
337 // info in it, try the header.
338 if (BasicBlock *HeadBB = getHeader())
339 return LocRange(HeadBB->getTerminator()->getDebugLoc());
344 bool Loop::hasDedicatedExits() const {
345 // Each predecessor of each exit block of a normal loop is contained
347 SmallVector<BasicBlock *, 4> ExitBlocks;
348 getExitBlocks(ExitBlocks);
349 for (BasicBlock *BB : ExitBlocks)
350 for (BasicBlock *Predecessor : predecessors(BB))
351 if (!contains(Predecessor))
353 // All the requirements are met.
358 Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
359 assert(hasDedicatedExits() &&
360 "getUniqueExitBlocks assumes the loop has canonical form exits!");
362 SmallVector<BasicBlock *, 32> SwitchExitBlocks;
363 for (BasicBlock *BB : this->blocks()) {
364 SwitchExitBlocks.clear();
365 for (BasicBlock *Successor : successors(BB)) {
366 // If block is inside the loop then it is not an exit block.
367 if (contains(Successor))
370 pred_iterator PI = pred_begin(Successor);
371 BasicBlock *FirstPred = *PI;
373 // If current basic block is this exit block's first predecessor
374 // then only insert exit block in to the output ExitBlocks vector.
375 // This ensures that same exit block is not inserted twice into
376 // ExitBlocks vector.
380 // If a terminator has more then two successors, for example SwitchInst,
381 // then it is possible that there are multiple edges from current block
382 // to one exit block.
383 if (std::distance(succ_begin(BB), succ_end(BB)) <= 2) {
384 ExitBlocks.push_back(Successor);
388 // In case of multiple edges from current block to exit block, collect
389 // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
391 if (!is_contained(SwitchExitBlocks, Successor)) {
392 SwitchExitBlocks.push_back(Successor);
393 ExitBlocks.push_back(Successor);
399 BasicBlock *Loop::getUniqueExitBlock() const {
400 SmallVector<BasicBlock *, 8> UniqueExitBlocks;
401 getUniqueExitBlocks(UniqueExitBlocks);
402 if (UniqueExitBlocks.size() == 1)
403 return UniqueExitBlocks[0];
407 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
408 LLVM_DUMP_METHOD void Loop::dump() const {
412 LLVM_DUMP_METHOD void Loop::dumpVerbose() const {
413 print(dbgs(), /*Depth=*/ 0, /*Verbose=*/ true);
417 //===----------------------------------------------------------------------===//
418 // UnloopUpdater implementation
422 /// Find the new parent loop for all blocks within the "unloop" whose last
423 /// backedges has just been removed.
424 class UnloopUpdater {
430 // Map unloop's immediate subloops to their nearest reachable parents. Nested
431 // loops within these subloops will not change parents. However, an immediate
432 // subloop's new parent will be the nearest loop reachable from either its own
433 // exits *or* any of its nested loop's exits.
434 DenseMap<Loop*, Loop*> SubloopParents;
436 // Flag the presence of an irreducible backedge whose destination is a block
437 // directly contained by the original unloop.
441 UnloopUpdater(Loop *UL, LoopInfo *LInfo) :
442 Unloop(*UL), LI(LInfo), DFS(UL), FoundIB(false) {}
444 void updateBlockParents();
446 void removeBlocksFromAncestors();
448 void updateSubloopParents();
451 Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
453 } // end anonymous namespace
455 /// Update the parent loop for all blocks that are directly contained within the
456 /// original "unloop".
457 void UnloopUpdater::updateBlockParents() {
458 if (Unloop.getNumBlocks()) {
459 // Perform a post order CFG traversal of all blocks within this loop,
460 // propagating the nearest loop from sucessors to predecessors.
461 LoopBlocksTraversal Traversal(DFS, LI);
462 for (BasicBlock *POI : Traversal) {
464 Loop *L = LI->getLoopFor(POI);
465 Loop *NL = getNearestLoop(POI, L);
468 // For reducible loops, NL is now an ancestor of Unloop.
469 assert((NL != &Unloop && (!NL || NL->contains(&Unloop))) &&
470 "uninitialized successor");
471 LI->changeLoopFor(POI, NL);
474 // Or the current block is part of a subloop, in which case its parent
476 assert((FoundIB || Unloop.contains(L)) && "uninitialized successor");
480 // Each irreducible loop within the unloop induces a round of iteration using
481 // the DFS result cached by Traversal.
482 bool Changed = FoundIB;
483 for (unsigned NIters = 0; Changed; ++NIters) {
484 assert(NIters < Unloop.getNumBlocks() && "runaway iterative algorithm");
486 // Iterate over the postorder list of blocks, propagating the nearest loop
487 // from successors to predecessors as before.
489 for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
490 POE = DFS.endPostorder(); POI != POE; ++POI) {
492 Loop *L = LI->getLoopFor(*POI);
493 Loop *NL = getNearestLoop(*POI, L);
495 assert(NL != &Unloop && (!NL || NL->contains(&Unloop)) &&
496 "uninitialized successor");
497 LI->changeLoopFor(*POI, NL);
504 /// Remove unloop's blocks from all ancestors below their new parents.
505 void UnloopUpdater::removeBlocksFromAncestors() {
506 // Remove all unloop's blocks (including those in nested subloops) from
507 // ancestors below the new parent loop.
508 for (Loop::block_iterator BI = Unloop.block_begin(),
509 BE = Unloop.block_end(); BI != BE; ++BI) {
510 Loop *OuterParent = LI->getLoopFor(*BI);
511 if (Unloop.contains(OuterParent)) {
512 while (OuterParent->getParentLoop() != &Unloop)
513 OuterParent = OuterParent->getParentLoop();
514 OuterParent = SubloopParents[OuterParent];
516 // Remove blocks from former Ancestors except Unloop itself which will be
518 for (Loop *OldParent = Unloop.getParentLoop(); OldParent != OuterParent;
519 OldParent = OldParent->getParentLoop()) {
520 assert(OldParent && "new loop is not an ancestor of the original");
521 OldParent->removeBlockFromLoop(*BI);
526 /// Update the parent loop for all subloops directly nested within unloop.
527 void UnloopUpdater::updateSubloopParents() {
528 while (!Unloop.empty()) {
529 Loop *Subloop = *std::prev(Unloop.end());
530 Unloop.removeChildLoop(std::prev(Unloop.end()));
532 assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
533 if (Loop *Parent = SubloopParents[Subloop])
534 Parent->addChildLoop(Subloop);
536 LI->addTopLevelLoop(Subloop);
540 /// Return the nearest parent loop among this block's successors. If a successor
541 /// is a subloop header, consider its parent to be the nearest parent of the
544 /// For subloop blocks, simply update SubloopParents and return NULL.
545 Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
547 // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
548 // is considered uninitialized.
549 Loop *NearLoop = BBLoop;
551 Loop *Subloop = nullptr;
552 if (NearLoop != &Unloop && Unloop.contains(NearLoop)) {
554 // Find the subloop ancestor that is directly contained within Unloop.
555 while (Subloop->getParentLoop() != &Unloop) {
556 Subloop = Subloop->getParentLoop();
557 assert(Subloop && "subloop is not an ancestor of the original loop");
559 // Get the current nearest parent of the Subloop exits, initially Unloop.
560 NearLoop = SubloopParents.insert({Subloop, &Unloop}).first->second;
563 succ_iterator I = succ_begin(BB), E = succ_end(BB);
565 assert(!Subloop && "subloop blocks must have a successor");
566 NearLoop = nullptr; // unloop blocks may now exit the function.
568 for (; I != E; ++I) {
570 continue; // self loops are uninteresting
572 Loop *L = LI->getLoopFor(*I);
574 // This successor has not been processed. This path must lead to an
575 // irreducible backedge.
576 assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
579 if (L != &Unloop && Unloop.contains(L)) {
580 // Successor is in a subloop.
582 continue; // Branching within subloops. Ignore it.
584 // BB branches from the original into a subloop header.
585 assert(L->getParentLoop() == &Unloop && "cannot skip into nested loops");
587 // Get the current nearest parent of the Subloop's exits.
588 L = SubloopParents[L];
589 // L could be Unloop if the only exit was an irreducible backedge.
594 // Handle critical edges from Unloop into a sibling loop.
595 if (L && !L->contains(&Unloop)) {
596 L = L->getParentLoop();
598 // Remember the nearest parent loop among successors or subloop exits.
599 if (NearLoop == &Unloop || !NearLoop || NearLoop->contains(L))
603 SubloopParents[Subloop] = NearLoop;
609 LoopInfo::LoopInfo(const DominatorTreeBase<BasicBlock> &DomTree) {
613 void LoopInfo::markAsRemoved(Loop *Unloop) {
614 assert(!Unloop->isInvalid() && "Loop has already been removed");
615 Unloop->invalidate();
616 RemovedLoops.push_back(Unloop);
618 // First handle the special case of no parent loop to simplify the algorithm.
619 if (!Unloop->getParentLoop()) {
620 // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
621 for (Loop::block_iterator I = Unloop->block_begin(),
622 E = Unloop->block_end();
625 // Don't reparent blocks in subloops.
626 if (getLoopFor(*I) != Unloop)
629 // Blocks no longer have a parent but are still referenced by Unloop until
630 // the Unloop object is deleted.
631 changeLoopFor(*I, nullptr);
634 // Remove the loop from the top-level LoopInfo object.
635 for (iterator I = begin();; ++I) {
636 assert(I != end() && "Couldn't find loop");
643 // Move all of the subloops to the top-level.
644 while (!Unloop->empty())
645 addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
650 // Update the parent loop for all blocks within the loop. Blocks within
651 // subloops will not change parents.
652 UnloopUpdater Updater(Unloop, this);
653 Updater.updateBlockParents();
655 // Remove blocks from former ancestor loops.
656 Updater.removeBlocksFromAncestors();
658 // Add direct subloops as children in their new parent loop.
659 Updater.updateSubloopParents();
661 // Remove unloop from its parent loop.
662 Loop *ParentLoop = Unloop->getParentLoop();
663 for (Loop::iterator I = ParentLoop->begin();; ++I) {
664 assert(I != ParentLoop->end() && "Couldn't find loop");
666 ParentLoop->removeChildLoop(I);
672 AnalysisKey LoopAnalysis::Key;
674 LoopInfo LoopAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
675 // FIXME: Currently we create a LoopInfo from scratch for every function.
676 // This may prove to be too wasteful due to deallocating and re-allocating
677 // memory each time for the underlying map and vector datastructures. At some
678 // point it may prove worthwhile to use a freelist and recycle LoopInfo
679 // objects. I don't want to add that kind of complexity until the scope of
680 // the problem is better understood.
682 LI.analyze(AM.getResult<DominatorTreeAnalysis>(F));
686 PreservedAnalyses LoopPrinterPass::run(Function &F,
687 FunctionAnalysisManager &AM) {
688 AM.getResult<LoopAnalysis>(F).print(OS);
689 return PreservedAnalyses::all();
692 void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
694 for (auto *Block : L.blocks())
698 OS << "Printing <null> block";
701 //===----------------------------------------------------------------------===//
702 // LoopInfo implementation
705 char LoopInfoWrapperPass::ID = 0;
706 INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",
708 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
709 INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",
712 bool LoopInfoWrapperPass::runOnFunction(Function &) {
714 LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
718 void LoopInfoWrapperPass::verifyAnalysis() const {
719 // LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
720 // function each time verifyAnalysis is called is very expensive. The
721 // -verify-loop-info option can enable this. In order to perform some
722 // checking by default, LoopPass has been taught to call verifyLoop manually
723 // during loop pass sequences.
724 if (VerifyLoopInfo) {
725 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
730 void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
731 AU.setPreservesAll();
732 AU.addRequired<DominatorTreeWrapperPass>();
735 void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
739 PreservedAnalyses LoopVerifierPass::run(Function &F,
740 FunctionAnalysisManager &AM) {
741 LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
742 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
744 return PreservedAnalyses::all();
747 //===----------------------------------------------------------------------===//
748 // LoopBlocksDFS implementation
751 /// Traverse the loop blocks and store the DFS result.
752 /// Useful for clients that just want the final DFS result and don't need to
753 /// visit blocks during the initial traversal.
754 void LoopBlocksDFS::perform(LoopInfo *LI) {
755 LoopBlocksTraversal Traversal(*this, LI);
756 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
757 POE = Traversal.end(); POI != POE; ++POI) ;