1 //===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===//
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 is the generic implementation of LoopInfo used for both Loops and
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ANALYSIS_LOOPINFOIMPL_H
16 #define LLVM_ANALYSIS_LOOPINFOIMPL_H
18 #include "llvm/ADT/DepthFirstIterator.h"
19 #include "llvm/ADT/PostOrderIterator.h"
20 #include "llvm/ADT/SetVector.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/IR/Dominators.h"
27 //===----------------------------------------------------------------------===//
28 // APIs for simple analysis of the loop. See header notes.
30 /// getExitingBlocks - Return all blocks inside the loop that have successors
31 /// outside of the loop. These are the blocks _inside of the current loop_
32 /// which branch out. The returned list is always unique.
34 template<class BlockT, class LoopT>
35 void LoopBase<BlockT, LoopT>::
36 getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const {
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);
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 SmallVector<BlockT*, 8> ExitingBlocks;
51 getExitingBlocks(ExitingBlocks);
52 if (ExitingBlocks.size() == 1)
53 return ExitingBlocks[0];
57 /// getExitBlocks - Return all of the successor blocks of this loop. These
58 /// are the blocks _outside of the current loop_ which are branched to.
60 template<class BlockT, class LoopT>
61 void LoopBase<BlockT, LoopT>::
62 getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const {
63 for (const auto BB : blocks())
64 for (const auto Succ : children<BlockT*>(BB))
66 // Not in current loop? It must be an exit block.
67 ExitBlocks.push_back(Succ);
70 /// getExitBlock - If getExitBlocks would return exactly one block,
71 /// return that block. Otherwise return null.
72 template<class BlockT, class LoopT>
73 BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const {
74 SmallVector<BlockT*, 8> ExitBlocks;
75 getExitBlocks(ExitBlocks);
76 if (ExitBlocks.size() == 1)
81 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
82 template<class BlockT, class LoopT>
83 void LoopBase<BlockT, LoopT>::
84 getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const {
85 for (const auto BB : blocks())
86 for (const auto Succ : children<BlockT*>(BB))
88 // Not in current loop? It must be an exit block.
89 ExitEdges.emplace_back(BB, Succ);
92 /// getLoopPreheader - If there is a preheader for this loop, return it. A
93 /// loop has a preheader if there is only one edge to the header of the loop
94 /// from outside of the loop. If this is the case, the block branching to the
95 /// header of the loop is the preheader node.
97 /// This method returns null if there is no preheader for the loop.
99 template<class BlockT, class LoopT>
100 BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const {
101 // Keep track of nodes outside the loop branching to the header...
102 BlockT *Out = getLoopPredecessor();
103 if (!Out) return nullptr;
105 // Make sure there is only one exit out of the preheader.
106 typedef GraphTraits<BlockT*> BlockTraits;
107 typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
109 if (SI != BlockTraits::child_end(Out))
110 return nullptr; // Multiple exits from the block, must not be a preheader.
112 // The predecessor has exactly one successor, so it is a preheader.
116 /// getLoopPredecessor - If the given loop's header has exactly one unique
117 /// predecessor outside the loop, return it. Otherwise return null.
118 /// This is less strict that the loop "preheader" concept, which requires
119 /// the predecessor to have exactly one successor.
121 template<class BlockT, class LoopT>
122 BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const {
123 // Keep track of nodes outside the loop branching to the header...
124 BlockT *Out = nullptr;
126 // Loop over the predecessors of the header node...
127 BlockT *Header = getHeader();
128 for (const auto Pred : children<Inverse<BlockT*>>(Header)) {
129 if (!contains(Pred)) { // If the block is not in the loop...
130 if (Out && Out != Pred)
131 return nullptr; // Multiple predecessors outside the loop
136 // Make sure there is only one exit out of the preheader.
137 assert(Out && "Header of loop has no predecessors from outside loop?");
141 /// getLoopLatch - If there is a single latch block for this loop, return it.
142 /// A latch block is a block that contains a branch back to the header.
143 template<class BlockT, class LoopT>
144 BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const {
145 BlockT *Header = getHeader();
146 BlockT *Latch = nullptr;
147 for (const auto Pred : children<Inverse<BlockT*>>(Header)) {
148 if (contains(Pred)) {
149 if (Latch) return nullptr;
157 //===----------------------------------------------------------------------===//
158 // APIs for updating loop information after changing the CFG
161 /// addBasicBlockToLoop - This method is used by other analyses to update loop
162 /// information. NewBB is set to be a new member of the current loop.
163 /// Because of this, it is added as a member of all parent loops, and is added
164 /// to the specified LoopInfo object as being in the current basic block. It
165 /// is not valid to replace the loop header with this method.
167 template<class BlockT, class LoopT>
168 void LoopBase<BlockT, LoopT>::
169 addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) {
171 if (!Blocks.empty()) {
172 auto SameHeader = LIB[getHeader()];
173 assert(contains(SameHeader) && getHeader() == SameHeader->getHeader()
174 && "Incorrect LI specified for this loop!");
177 assert(NewBB && "Cannot add a null basic block to the loop!");
178 assert(!LIB[NewBB] && "BasicBlock already in the loop!");
180 LoopT *L = static_cast<LoopT *>(this);
182 // Add the loop mapping to the LoopInfo object...
183 LIB.BBMap[NewBB] = L;
185 // Add the basic block to this loop and all parent loops...
187 L->addBlockEntry(NewBB);
188 L = L->getParentLoop();
192 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
193 /// the OldChild entry in our children list with NewChild, and updates the
194 /// parent pointer of OldChild to be null and the NewChild to be this loop.
195 /// This updates the loop depth of the new child.
196 template<class BlockT, class LoopT>
197 void LoopBase<BlockT, LoopT>::
198 replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild) {
199 assert(OldChild->ParentLoop == this && "This loop is already broken!");
200 assert(!NewChild->ParentLoop && "NewChild already has a parent!");
201 typename std::vector<LoopT *>::iterator I = find(SubLoops, OldChild);
202 assert(I != SubLoops.end() && "OldChild not in loop!");
204 OldChild->ParentLoop = nullptr;
205 NewChild->ParentLoop = static_cast<LoopT *>(this);
208 /// verifyLoop - Verify loop structure
209 template<class BlockT, class LoopT>
210 void LoopBase<BlockT, LoopT>::verifyLoop() const {
212 assert(!Blocks.empty() && "Loop header is missing");
214 // Setup for using a depth-first iterator to visit every block in the loop.
215 SmallVector<BlockT*, 8> ExitBBs;
216 getExitBlocks(ExitBBs);
217 df_iterator_default_set<BlockT*> VisitSet;
218 VisitSet.insert(ExitBBs.begin(), ExitBBs.end());
219 df_ext_iterator<BlockT*, df_iterator_default_set<BlockT*>>
220 BI = df_ext_begin(getHeader(), VisitSet),
221 BE = df_ext_end(getHeader(), VisitSet);
223 // Keep track of the number of BBs visited.
224 unsigned NumVisited = 0;
226 // Check the individual blocks.
227 for ( ; BI != BE; ++BI) {
230 assert(std::any_of(GraphTraits<BlockT*>::child_begin(BB),
231 GraphTraits<BlockT*>::child_end(BB),
232 [&](BlockT *B){return contains(B);}) &&
233 "Loop block has no in-loop successors!");
235 assert(std::any_of(GraphTraits<Inverse<BlockT*> >::child_begin(BB),
236 GraphTraits<Inverse<BlockT*> >::child_end(BB),
237 [&](BlockT *B){return contains(B);}) &&
238 "Loop block has no in-loop predecessors!");
240 SmallVector<BlockT *, 2> OutsideLoopPreds;
241 std::for_each(GraphTraits<Inverse<BlockT*> >::child_begin(BB),
242 GraphTraits<Inverse<BlockT*> >::child_end(BB),
243 [&](BlockT *B){if (!contains(B))
244 OutsideLoopPreds.push_back(B);
247 if (BB == getHeader()) {
248 assert(!OutsideLoopPreds.empty() && "Loop is unreachable!");
249 } else if (!OutsideLoopPreds.empty()) {
250 // A non-header loop shouldn't be reachable from outside the loop,
251 // though it is permitted if the predecessor is not itself actually
253 BlockT *EntryBB = &BB->getParent()->front();
254 for (BlockT *CB : depth_first(EntryBB))
255 for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i)
256 assert(CB != OutsideLoopPreds[i] &&
257 "Loop has multiple entry points!");
259 assert(BB != &getHeader()->getParent()->front() &&
260 "Loop contains function entry block!");
265 assert(NumVisited == getNumBlocks() && "Unreachable block in loop");
267 // Check the subloops.
268 for (iterator I = begin(), E = end(); I != E; ++I)
269 // Each block in each subloop should be contained within this loop.
270 for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end();
272 assert(contains(*BI) &&
273 "Loop does not contain all the blocks of a subloop!");
276 // Check the parent loop pointer.
278 assert(is_contained(*ParentLoop, this) &&
279 "Loop is not a subloop of its parent!");
284 /// verifyLoop - Verify loop structure of this loop and all nested loops.
285 template<class BlockT, class LoopT>
286 void LoopBase<BlockT, LoopT>::verifyLoopNest(
287 DenseSet<const LoopT*> *Loops) const {
288 Loops->insert(static_cast<const LoopT *>(this));
291 // Verify the subloops.
292 for (iterator I = begin(), E = end(); I != E; ++I)
293 (*I)->verifyLoopNest(Loops);
296 template<class BlockT, class LoopT>
297 void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth,
298 bool Verbose) const {
299 OS.indent(Depth*2) << "Loop at depth " << getLoopDepth()
302 BlockT *H = getHeader();
303 for (unsigned i = 0; i < getBlocks().size(); ++i) {
304 BlockT *BB = getBlocks()[i];
307 BB->printAsOperand(OS, false);
310 if (BB == H) OS << "<header>";
311 if (isLoopLatch(BB)) OS << "<latch>";
312 if (isLoopExiting(BB)) OS << "<exiting>";
318 for (iterator I = begin(), E = end(); I != E; ++I)
319 (*I)->print(OS, Depth+2);
322 //===----------------------------------------------------------------------===//
323 /// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the
324 /// result does / not depend on use list (block predecessor) order.
327 /// Discover a subloop with the specified backedges such that: All blocks within
328 /// this loop are mapped to this loop or a subloop. And all subloops within this
329 /// loop have their parent loop set to this loop or a subloop.
330 template<class BlockT, class LoopT>
331 static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT*> Backedges,
332 LoopInfoBase<BlockT, LoopT> *LI,
333 const DominatorTreeBase<BlockT> &DomTree) {
334 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
336 unsigned NumBlocks = 0;
337 unsigned NumSubloops = 0;
339 // Perform a backward CFG traversal using a worklist.
340 std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end());
341 while (!ReverseCFGWorklist.empty()) {
342 BlockT *PredBB = ReverseCFGWorklist.back();
343 ReverseCFGWorklist.pop_back();
345 LoopT *Subloop = LI->getLoopFor(PredBB);
347 if (!DomTree.isReachableFromEntry(PredBB))
350 // This is an undiscovered block. Map it to the current loop.
351 LI->changeLoopFor(PredBB, L);
353 if (PredBB == L->getHeader())
355 // Push all block predecessors on the worklist.
356 ReverseCFGWorklist.insert(ReverseCFGWorklist.end(),
357 InvBlockTraits::child_begin(PredBB),
358 InvBlockTraits::child_end(PredBB));
361 // This is a discovered block. Find its outermost discovered loop.
362 while (LoopT *Parent = Subloop->getParentLoop())
365 // If it is already discovered to be a subloop of this loop, continue.
369 // Discover a subloop of this loop.
370 Subloop->setParentLoop(L);
372 NumBlocks += Subloop->getBlocks().capacity();
373 PredBB = Subloop->getHeader();
374 // Continue traversal along predecessors that are not loop-back edges from
375 // within this subloop tree itself. Note that a predecessor may directly
376 // reach another subloop that is not yet discovered to be a subloop of
377 // this loop, which we must traverse.
378 for (const auto Pred : children<Inverse<BlockT*>>(PredBB)) {
379 if (LI->getLoopFor(Pred) != Subloop)
380 ReverseCFGWorklist.push_back(Pred);
384 L->getSubLoopsVector().reserve(NumSubloops);
385 L->reserveBlocks(NumBlocks);
388 /// Populate all loop data in a stable order during a single forward DFS.
389 template<class BlockT, class LoopT>
390 class PopulateLoopsDFS {
391 typedef GraphTraits<BlockT*> BlockTraits;
392 typedef typename BlockTraits::ChildIteratorType SuccIterTy;
394 LoopInfoBase<BlockT, LoopT> *LI;
396 PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li):
399 void traverse(BlockT *EntryBlock);
402 void insertIntoLoop(BlockT *Block);
405 /// Top-level driver for the forward DFS within the loop.
406 template<class BlockT, class LoopT>
407 void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) {
408 for (BlockT *BB : post_order(EntryBlock))
412 /// Add a single Block to its ancestor loops in PostOrder. If the block is a
413 /// subloop header, add the subloop to its parent in PostOrder, then reverse the
414 /// Block and Subloop vectors of the now complete subloop to achieve RPO.
415 template<class BlockT, class LoopT>
416 void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) {
417 LoopT *Subloop = LI->getLoopFor(Block);
418 if (Subloop && Block == Subloop->getHeader()) {
419 // We reach this point once per subloop after processing all the blocks in
421 if (Subloop->getParentLoop())
422 Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop);
424 LI->addTopLevelLoop(Subloop);
426 // For convenience, Blocks and Subloops are inserted in postorder. Reverse
427 // the lists, except for the loop header, which is always at the beginning.
428 Subloop->reverseBlock(1);
429 std::reverse(Subloop->getSubLoopsVector().begin(),
430 Subloop->getSubLoopsVector().end());
432 Subloop = Subloop->getParentLoop();
434 for (; Subloop; Subloop = Subloop->getParentLoop())
435 Subloop->addBlockEntry(Block);
438 /// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal
439 /// interleaved with backward CFG traversals within each subloop
440 /// (discoverAndMapSubloop). The backward traversal skips inner subloops, so
441 /// this part of the algorithm is linear in the number of CFG edges. Subloop and
442 /// Block vectors are then populated during a single forward CFG traversal
443 /// (PopulateLoopDFS).
445 /// During the two CFG traversals each block is seen three times:
446 /// 1) Discovered and mapped by a reverse CFG traversal.
447 /// 2) Visited during a forward DFS CFG traversal.
448 /// 3) Reverse-inserted in the loop in postorder following forward DFS.
450 /// The Block vectors are inclusive, so step 3 requires loop-depth number of
451 /// insertions per block.
452 template<class BlockT, class LoopT>
453 void LoopInfoBase<BlockT, LoopT>::
454 analyze(const DominatorTreeBase<BlockT> &DomTree) {
456 // Postorder traversal of the dominator tree.
457 const DomTreeNodeBase<BlockT> *DomRoot = DomTree.getRootNode();
458 for (auto DomNode : post_order(DomRoot)) {
460 BlockT *Header = DomNode->getBlock();
461 SmallVector<BlockT *, 4> Backedges;
463 // Check each predecessor of the potential loop header.
464 for (const auto Backedge : children<Inverse<BlockT*>>(Header)) {
465 // If Header dominates predBB, this is a new loop. Collect the backedges.
466 if (DomTree.dominates(Header, Backedge)
467 && DomTree.isReachableFromEntry(Backedge)) {
468 Backedges.push_back(Backedge);
471 // Perform a backward CFG traversal to discover and map blocks in this loop.
472 if (!Backedges.empty()) {
473 LoopT *L = new LoopT(Header);
474 discoverAndMapSubloop(L, ArrayRef<BlockT*>(Backedges), this, DomTree);
477 // Perform a single forward CFG traversal to populate block and subloop
478 // vectors for all loops.
479 PopulateLoopsDFS<BlockT, LoopT> DFS(this);
480 DFS.traverse(DomRoot->getBlock());
483 template <class BlockT, class LoopT>
484 SmallVector<LoopT *, 4> LoopInfoBase<BlockT, LoopT>::getLoopsInPreorder() {
485 SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
486 // The outer-most loop actually goes into the result in the same relative
487 // order as we walk it. But LoopInfo stores the top level loops in reverse
488 // program order so for here we reverse it to get forward program order.
489 // FIXME: If we change the order of LoopInfo we will want to remove the
491 for (LoopT *RootL : reverse(*this)) {
492 assert(PreOrderWorklist.empty() &&
493 "Must start with an empty preorder walk worklist.");
494 PreOrderWorklist.push_back(RootL);
496 LoopT *L = PreOrderWorklist.pop_back_val();
497 // Sub-loops are stored in forward program order, but will process the
498 // worklist backwards so append them in reverse order.
499 PreOrderWorklist.append(L->rbegin(), L->rend());
500 PreOrderLoops.push_back(L);
501 } while (!PreOrderWorklist.empty());
504 return PreOrderLoops;
507 template <class BlockT, class LoopT>
508 SmallVector<LoopT *, 4>
509 LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() {
510 SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
511 // The outer-most loop actually goes into the result in the same relative
512 // order as we walk it. LoopInfo stores the top level loops in reverse
513 // program order so we walk in order here.
514 // FIXME: If we change the order of LoopInfo we will want to add a reverse
516 for (LoopT *RootL : *this) {
517 assert(PreOrderWorklist.empty() &&
518 "Must start with an empty preorder walk worklist.");
519 PreOrderWorklist.push_back(RootL);
521 LoopT *L = PreOrderWorklist.pop_back_val();
522 // Sub-loops are stored in forward program order, but will process the
523 // worklist backwards so we can just append them in order.
524 PreOrderWorklist.append(L->begin(), L->end());
525 PreOrderLoops.push_back(L);
526 } while (!PreOrderWorklist.empty());
529 return PreOrderLoops;
533 template<class BlockT, class LoopT>
534 void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const {
535 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
536 TopLevelLoops[i]->print(OS);
538 for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(),
539 E = BBMap.end(); I != E; ++I)
540 OS << "BB '" << I->first->getName() << "' level = "
541 << I->second->getLoopDepth() << "\n";
545 template <typename T>
546 bool compareVectors(std::vector<T> &BB1, std::vector<T> &BB2) {
547 std::sort(BB1.begin(), BB1.end());
548 std::sort(BB2.begin(), BB2.end());
552 template <class BlockT, class LoopT>
553 void addInnerLoopsToHeadersMap(DenseMap<BlockT *, const LoopT *> &LoopHeaders,
554 const LoopInfoBase<BlockT, LoopT> &LI,
556 LoopHeaders[L.getHeader()] = &L;
558 addInnerLoopsToHeadersMap(LoopHeaders, LI, *SL);
562 template <class BlockT, class LoopT>
563 static void compareLoops(const LoopT *L, const LoopT *OtherL,
564 DenseMap<BlockT *, const LoopT *> &OtherLoopHeaders) {
565 BlockT *H = L->getHeader();
566 BlockT *OtherH = OtherL->getHeader();
567 assert(H == OtherH &&
568 "Mismatched headers even though found in the same map entry!");
570 assert(L->getLoopDepth() == OtherL->getLoopDepth() &&
571 "Mismatched loop depth!");
572 const LoopT *ParentL = L, *OtherParentL = OtherL;
574 assert(ParentL->getHeader() == OtherParentL->getHeader() &&
575 "Mismatched parent loop headers!");
576 ParentL = ParentL->getParentLoop();
577 OtherParentL = OtherParentL->getParentLoop();
580 for (const LoopT *SubL : *L) {
581 BlockT *SubH = SubL->getHeader();
582 const LoopT *OtherSubL = OtherLoopHeaders.lookup(SubH);
583 assert(OtherSubL && "Inner loop is missing in computed loop info!");
584 OtherLoopHeaders.erase(SubH);
585 compareLoops(SubL, OtherSubL, OtherLoopHeaders);
588 std::vector<BlockT *> BBs = L->getBlocks();
589 std::vector<BlockT *> OtherBBs = OtherL->getBlocks();
590 assert(compareVectors(BBs, OtherBBs) &&
591 "Mismatched basic blocks in the loops!");
595 template <class BlockT, class LoopT>
596 void LoopInfoBase<BlockT, LoopT>::verify(
597 const DominatorTreeBase<BlockT> &DomTree) const {
598 DenseSet<const LoopT*> Loops;
599 for (iterator I = begin(), E = end(); I != E; ++I) {
600 assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
601 (*I)->verifyLoopNest(&Loops);
604 // Verify that blocks are mapped to valid loops.
606 for (auto &Entry : BBMap) {
607 const BlockT *BB = Entry.first;
608 LoopT *L = Entry.second;
609 assert(Loops.count(L) && "orphaned loop");
610 assert(L->contains(BB) && "orphaned block");
613 // Recompute LoopInfo to verify loops structure.
614 LoopInfoBase<BlockT, LoopT> OtherLI;
615 OtherLI.analyze(DomTree);
617 // Build a map we can use to move from our LI to the computed one. This
618 // allows us to ignore the particular order in any layer of the loop forest
619 // while still comparing the structure.
620 DenseMap<BlockT *, const LoopT *> OtherLoopHeaders;
621 for (LoopT *L : OtherLI)
622 addInnerLoopsToHeadersMap(OtherLoopHeaders, OtherLI, *L);
624 // Walk the top level loops and ensure there is a corresponding top-level
625 // loop in the computed version and then recursively compare those loop
627 for (LoopT *L : *this) {
628 BlockT *Header = L->getHeader();
629 const LoopT *OtherL = OtherLoopHeaders.lookup(Header);
630 assert(OtherL && "Top level loop is missing in computed loop info!");
631 // Now that we've matched this loop, erase its header from the map.
632 OtherLoopHeaders.erase(Header);
633 // And recursively compare these loops.
634 compareLoops(L, OtherL, OtherLoopHeaders);
637 // Any remaining entries in the map are loops which were found when computing
638 // a fresh LoopInfo but not present in the current one.
639 if (!OtherLoopHeaders.empty()) {
640 for (const auto &HeaderAndLoop : OtherLoopHeaders)
641 dbgs() << "Found new loop: " << *HeaderAndLoop.second << "\n";
642 llvm_unreachable("Found new loops when recomputing LoopInfo!");
647 } // End llvm namespace