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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/ScopeExit.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/Analysis/LoopInfoImpl.h"
22 #include "llvm/Analysis/LoopIterator.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/Config/llvm-config.h"
25 #include "llvm/IR/CFG.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DebugLoc.h"
28 #include "llvm/IR/Dominators.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/LLVMContext.h"
31 #include "llvm/IR/Metadata.h"
32 #include "llvm/IR/PassManager.h"
33 #include "llvm/Support/CommandLine.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include <algorithm>
37 using namespace llvm;
38 
39 // Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
40 template class llvm::LoopBase<BasicBlock, Loop>;
41 template class llvm::LoopInfoBase<BasicBlock, Loop>;
42 
43 // Always verify loopinfo if expensive checking is enabled.
44 #ifdef EXPENSIVE_CHECKS
45 bool llvm::VerifyLoopInfo = true;
46 #else
47 bool llvm::VerifyLoopInfo = false;
48 #endif
49 static cl::opt<bool, true>
50     VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
51                     cl::Hidden, cl::desc("Verify loop info (time consuming)"));
52 
53 //===----------------------------------------------------------------------===//
54 // Loop implementation
55 //
56 
isLoopInvariant(const Value * V) const57 bool Loop::isLoopInvariant(const Value *V) const {
58   if (const Instruction *I = dyn_cast<Instruction>(V))
59     return !contains(I);
60   return true; // All non-instructions are loop invariant
61 }
62 
hasLoopInvariantOperands(const Instruction * I) const63 bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
64   return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
65 }
66 
makeLoopInvariant(Value * V,bool & Changed,Instruction * InsertPt) const67 bool Loop::makeLoopInvariant(Value *V, bool &Changed,
68                              Instruction *InsertPt) const {
69   if (Instruction *I = dyn_cast<Instruction>(V))
70     return makeLoopInvariant(I, Changed, InsertPt);
71   return true; // All non-instructions are loop-invariant.
72 }
73 
makeLoopInvariant(Instruction * I,bool & Changed,Instruction * InsertPt) const74 bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
75                              Instruction *InsertPt) const {
76   // Test if the value is already loop-invariant.
77   if (isLoopInvariant(I))
78     return true;
79   if (!isSafeToSpeculativelyExecute(I))
80     return false;
81   if (I->mayReadFromMemory())
82     return false;
83   // EH block instructions are immobile.
84   if (I->isEHPad())
85     return false;
86   // Determine the insertion point, unless one was given.
87   if (!InsertPt) {
88     BasicBlock *Preheader = getLoopPreheader();
89     // Without a preheader, hoisting is not feasible.
90     if (!Preheader)
91       return false;
92     InsertPt = Preheader->getTerminator();
93   }
94   // Don't hoist instructions with loop-variant operands.
95   for (Value *Operand : I->operands())
96     if (!makeLoopInvariant(Operand, Changed, InsertPt))
97       return false;
98 
99   // Hoist.
100   I->moveBefore(InsertPt);
101 
102   // There is possibility of hoisting this instruction above some arbitrary
103   // condition. Any metadata defined on it can be control dependent on this
104   // condition. Conservatively strip it here so that we don't give any wrong
105   // information to the optimizer.
106   I->dropUnknownNonDebugMetadata();
107 
108   Changed = true;
109   return true;
110 }
111 
getCanonicalInductionVariable() const112 PHINode *Loop::getCanonicalInductionVariable() const {
113   BasicBlock *H = getHeader();
114 
115   BasicBlock *Incoming = nullptr, *Backedge = nullptr;
116   pred_iterator PI = pred_begin(H);
117   assert(PI != pred_end(H) && "Loop must have at least one backedge!");
118   Backedge = *PI++;
119   if (PI == pred_end(H))
120     return nullptr; // dead loop
121   Incoming = *PI++;
122   if (PI != pred_end(H))
123     return nullptr; // multiple backedges?
124 
125   if (contains(Incoming)) {
126     if (contains(Backedge))
127       return nullptr;
128     std::swap(Incoming, Backedge);
129   } else if (!contains(Backedge))
130     return nullptr;
131 
132   // Loop over all of the PHI nodes, looking for a canonical indvar.
133   for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
134     PHINode *PN = cast<PHINode>(I);
135     if (ConstantInt *CI =
136             dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
137       if (CI->isZero())
138         if (Instruction *Inc =
139                 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
140           if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
141             if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
142               if (CI->isOne())
143                 return PN;
144   }
145   return nullptr;
146 }
147 
148 // Check that 'BB' doesn't have any uses outside of the 'L'
isBlockInLCSSAForm(const Loop & L,const BasicBlock & BB,DominatorTree & DT)149 static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
150                                DominatorTree &DT) {
151   for (const Instruction &I : BB) {
152     // Tokens can't be used in PHI nodes and live-out tokens prevent loop
153     // optimizations, so for the purposes of considered LCSSA form, we
154     // can ignore them.
155     if (I.getType()->isTokenTy())
156       continue;
157 
158     for (const Use &U : I.uses()) {
159       const Instruction *UI = cast<Instruction>(U.getUser());
160       const BasicBlock *UserBB = UI->getParent();
161       if (const PHINode *P = dyn_cast<PHINode>(UI))
162         UserBB = P->getIncomingBlock(U);
163 
164       // Check the current block, as a fast-path, before checking whether
165       // the use is anywhere in the loop.  Most values are used in the same
166       // block they are defined in.  Also, blocks not reachable from the
167       // entry are special; uses in them don't need to go through PHIs.
168       if (UserBB != &BB && !L.contains(UserBB) &&
169           DT.isReachableFromEntry(UserBB))
170         return false;
171     }
172   }
173   return true;
174 }
175 
isLCSSAForm(DominatorTree & DT) const176 bool Loop::isLCSSAForm(DominatorTree &DT) const {
177   // For each block we check that it doesn't have any uses outside of this loop.
178   return all_of(this->blocks(), [&](const BasicBlock *BB) {
179     return isBlockInLCSSAForm(*this, *BB, DT);
180   });
181 }
182 
isRecursivelyLCSSAForm(DominatorTree & DT,const LoopInfo & LI) const183 bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const {
184   // For each block we check that it doesn't have any uses outside of its
185   // innermost loop. This process will transitively guarantee that the current
186   // loop and all of the nested loops are in LCSSA form.
187   return all_of(this->blocks(), [&](const BasicBlock *BB) {
188     return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
189   });
190 }
191 
isLoopSimplifyForm() const192 bool Loop::isLoopSimplifyForm() const {
193   // Normal-form loops have a preheader, a single backedge, and all of their
194   // exits have all their predecessors inside the loop.
195   return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
196 }
197 
198 // Routines that reform the loop CFG and split edges often fail on indirectbr.
isSafeToClone() const199 bool Loop::isSafeToClone() const {
200   // Return false if any loop blocks contain indirectbrs, or there are any calls
201   // to noduplicate functions.
202   for (BasicBlock *BB : this->blocks()) {
203     if (isa<IndirectBrInst>(BB->getTerminator()))
204       return false;
205 
206     for (Instruction &I : *BB)
207       if (auto CS = CallSite(&I))
208         if (CS.cannotDuplicate())
209           return false;
210   }
211   return true;
212 }
213 
getLoopID() const214 MDNode *Loop::getLoopID() const {
215   MDNode *LoopID = nullptr;
216   if (BasicBlock *Latch = getLoopLatch()) {
217     LoopID = Latch->getTerminator()->getMetadata(LLVMContext::MD_loop);
218   } else {
219     assert(!getLoopLatch() &&
220            "The loop should have no single latch at this point");
221     // Go through each predecessor of the loop header and check the
222     // terminator for the metadata.
223     BasicBlock *H = getHeader();
224     for (BasicBlock *BB : this->blocks()) {
225       TerminatorInst *TI = BB->getTerminator();
226       MDNode *MD = nullptr;
227 
228       // Check if this terminator branches to the loop header.
229       for (BasicBlock *Successor : TI->successors()) {
230         if (Successor == H) {
231           MD = TI->getMetadata(LLVMContext::MD_loop);
232           break;
233         }
234       }
235       if (!MD)
236         return nullptr;
237 
238       if (!LoopID)
239         LoopID = MD;
240       else if (MD != LoopID)
241         return nullptr;
242     }
243   }
244   if (!LoopID || LoopID->getNumOperands() == 0 ||
245       LoopID->getOperand(0) != LoopID)
246     return nullptr;
247   return LoopID;
248 }
249 
setLoopID(MDNode * LoopID) const250 void Loop::setLoopID(MDNode *LoopID) const {
251   assert(LoopID && "Loop ID should not be null");
252   assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand");
253   assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself");
254 
255   if (BasicBlock *Latch = getLoopLatch()) {
256     Latch->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
257     return;
258   }
259 
260   assert(!getLoopLatch() &&
261          "The loop should have no single latch at this point");
262   BasicBlock *H = getHeader();
263   for (BasicBlock *BB : this->blocks()) {
264     TerminatorInst *TI = BB->getTerminator();
265     for (BasicBlock *Successor : TI->successors()) {
266       if (Successor == H)
267         TI->setMetadata(LLVMContext::MD_loop, LoopID);
268     }
269   }
270 }
271 
setLoopAlreadyUnrolled()272 void Loop::setLoopAlreadyUnrolled() {
273   MDNode *LoopID = getLoopID();
274   // First remove any existing loop unrolling metadata.
275   SmallVector<Metadata *, 4> MDs;
276   // Reserve first location for self reference to the LoopID metadata node.
277   MDs.push_back(nullptr);
278 
279   if (LoopID) {
280     for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
281       bool IsUnrollMetadata = false;
282       MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
283       if (MD) {
284         const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
285         IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
286       }
287       if (!IsUnrollMetadata)
288         MDs.push_back(LoopID->getOperand(i));
289     }
290   }
291 
292   // Add unroll(disable) metadata to disable future unrolling.
293   LLVMContext &Context = getHeader()->getContext();
294   SmallVector<Metadata *, 1> DisableOperands;
295   DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
296   MDNode *DisableNode = MDNode::get(Context, DisableOperands);
297   MDs.push_back(DisableNode);
298 
299   MDNode *NewLoopID = MDNode::get(Context, MDs);
300   // Set operand 0 to refer to the loop id itself.
301   NewLoopID->replaceOperandWith(0, NewLoopID);
302   setLoopID(NewLoopID);
303 }
304 
isAnnotatedParallel() const305 bool Loop::isAnnotatedParallel() const {
306   MDNode *DesiredLoopIdMetadata = getLoopID();
307 
308   if (!DesiredLoopIdMetadata)
309     return false;
310 
311   // The loop branch contains the parallel loop metadata. In order to ensure
312   // that any parallel-loop-unaware optimization pass hasn't added loop-carried
313   // dependencies (thus converted the loop back to a sequential loop), check
314   // that all the memory instructions in the loop contain parallelism metadata
315   // that point to the same unique "loop id metadata" the loop branch does.
316   for (BasicBlock *BB : this->blocks()) {
317     for (Instruction &I : *BB) {
318       if (!I.mayReadOrWriteMemory())
319         continue;
320 
321       // The memory instruction can refer to the loop identifier metadata
322       // directly or indirectly through another list metadata (in case of
323       // nested parallel loops). The loop identifier metadata refers to
324       // itself so we can check both cases with the same routine.
325       MDNode *LoopIdMD =
326           I.getMetadata(LLVMContext::MD_mem_parallel_loop_access);
327 
328       if (!LoopIdMD)
329         return false;
330 
331       bool LoopIdMDFound = false;
332       for (const MDOperand &MDOp : LoopIdMD->operands()) {
333         if (MDOp == DesiredLoopIdMetadata) {
334           LoopIdMDFound = true;
335           break;
336         }
337       }
338 
339       if (!LoopIdMDFound)
340         return false;
341     }
342   }
343   return true;
344 }
345 
getStartLoc() const346 DebugLoc Loop::getStartLoc() const { return getLocRange().getStart(); }
347 
getLocRange() const348 Loop::LocRange Loop::getLocRange() const {
349   // If we have a debug location in the loop ID, then use it.
350   if (MDNode *LoopID = getLoopID()) {
351     DebugLoc Start;
352     // We use the first DebugLoc in the header as the start location of the loop
353     // and if there is a second DebugLoc in the header we use it as end location
354     // of the loop.
355     for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
356       if (DILocation *L = dyn_cast<DILocation>(LoopID->getOperand(i))) {
357         if (!Start)
358           Start = DebugLoc(L);
359         else
360           return LocRange(Start, DebugLoc(L));
361       }
362     }
363 
364     if (Start)
365       return LocRange(Start);
366   }
367 
368   // Try the pre-header first.
369   if (BasicBlock *PHeadBB = getLoopPreheader())
370     if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
371       return LocRange(DL);
372 
373   // If we have no pre-header or there are no instructions with debug
374   // info in it, try the header.
375   if (BasicBlock *HeadBB = getHeader())
376     return LocRange(HeadBB->getTerminator()->getDebugLoc());
377 
378   return LocRange();
379 }
380 
381 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const382 LLVM_DUMP_METHOD void Loop::dump() const { print(dbgs()); }
383 
dumpVerbose() const384 LLVM_DUMP_METHOD void Loop::dumpVerbose() const {
385   print(dbgs(), /*Depth=*/0, /*Verbose=*/true);
386 }
387 #endif
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:
UnloopUpdater(Loop * UL,LoopInfo * LInfo)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 /// Update the parent loop for all blocks that are directly contained within the
428 /// original "unloop".
updateBlockParents()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 successors to predecessors.
433     LoopBlocksTraversal Traversal(DFS, LI);
434     for (BasicBlock *POI : Traversal) {
435 
436       Loop *L = LI->getLoopFor(POI);
437       Loop *NL = getNearestLoop(POI, L);
438 
439       if (NL != L) {
440         // For reducible loops, NL is now an ancestor of Unloop.
441         assert((NL != &Unloop && (!NL || NL->contains(&Unloop))) &&
442                "uninitialized successor");
443         LI->changeLoopFor(POI, NL);
444       } else {
445         // Or the current block is part of a subloop, in which case its parent
446         // is unchanged.
447         assert((FoundIB || Unloop.contains(L)) && "uninitialized successor");
448       }
449     }
450   }
451   // Each irreducible loop within the unloop induces a round of iteration using
452   // the DFS result cached by Traversal.
453   bool Changed = FoundIB;
454   for (unsigned NIters = 0; Changed; ++NIters) {
455     assert(NIters < Unloop.getNumBlocks() && "runaway iterative algorithm");
456 
457     // Iterate over the postorder list of blocks, propagating the nearest loop
458     // from successors to predecessors as before.
459     Changed = false;
460     for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
461                                    POE = DFS.endPostorder();
462          POI != POE; ++POI) {
463 
464       Loop *L = LI->getLoopFor(*POI);
465       Loop *NL = getNearestLoop(*POI, L);
466       if (NL != L) {
467         assert(NL != &Unloop && (!NL || NL->contains(&Unloop)) &&
468                "uninitialized successor");
469         LI->changeLoopFor(*POI, NL);
470         Changed = true;
471       }
472     }
473   }
474 }
475 
476 /// Remove unloop's blocks from all ancestors below their new parents.
removeBlocksFromAncestors()477 void UnloopUpdater::removeBlocksFromAncestors() {
478   // Remove all unloop's blocks (including those in nested subloops) from
479   // ancestors below the new parent loop.
480   for (Loop::block_iterator BI = Unloop.block_begin(), BE = Unloop.block_end();
481        BI != BE; ++BI) {
482     Loop *OuterParent = LI->getLoopFor(*BI);
483     if (Unloop.contains(OuterParent)) {
484       while (OuterParent->getParentLoop() != &Unloop)
485         OuterParent = OuterParent->getParentLoop();
486       OuterParent = SubloopParents[OuterParent];
487     }
488     // Remove blocks from former Ancestors except Unloop itself which will be
489     // deleted.
490     for (Loop *OldParent = Unloop.getParentLoop(); OldParent != OuterParent;
491          OldParent = OldParent->getParentLoop()) {
492       assert(OldParent && "new loop is not an ancestor of the original");
493       OldParent->removeBlockFromLoop(*BI);
494     }
495   }
496 }
497 
498 /// Update the parent loop for all subloops directly nested within unloop.
updateSubloopParents()499 void UnloopUpdater::updateSubloopParents() {
500   while (!Unloop.empty()) {
501     Loop *Subloop = *std::prev(Unloop.end());
502     Unloop.removeChildLoop(std::prev(Unloop.end()));
503 
504     assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
505     if (Loop *Parent = SubloopParents[Subloop])
506       Parent->addChildLoop(Subloop);
507     else
508       LI->addTopLevelLoop(Subloop);
509   }
510 }
511 
512 /// Return the nearest parent loop among this block's successors. If a successor
513 /// is a subloop header, consider its parent to be the nearest parent of the
514 /// subloop's exits.
515 ///
516 /// For subloop blocks, simply update SubloopParents and return NULL.
getNearestLoop(BasicBlock * BB,Loop * BBLoop)517 Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
518 
519   // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
520   // is considered uninitialized.
521   Loop *NearLoop = BBLoop;
522 
523   Loop *Subloop = nullptr;
524   if (NearLoop != &Unloop && Unloop.contains(NearLoop)) {
525     Subloop = NearLoop;
526     // Find the subloop ancestor that is directly contained within Unloop.
527     while (Subloop->getParentLoop() != &Unloop) {
528       Subloop = Subloop->getParentLoop();
529       assert(Subloop && "subloop is not an ancestor of the original loop");
530     }
531     // Get the current nearest parent of the Subloop exits, initially Unloop.
532     NearLoop = SubloopParents.insert({Subloop, &Unloop}).first->second;
533   }
534 
535   succ_iterator I = succ_begin(BB), E = succ_end(BB);
536   if (I == E) {
537     assert(!Subloop && "subloop blocks must have a successor");
538     NearLoop = nullptr; // unloop blocks may now exit the function.
539   }
540   for (; I != E; ++I) {
541     if (*I == BB)
542       continue; // self loops are uninteresting
543 
544     Loop *L = LI->getLoopFor(*I);
545     if (L == &Unloop) {
546       // This successor has not been processed. This path must lead to an
547       // irreducible backedge.
548       assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
549       FoundIB = true;
550     }
551     if (L != &Unloop && Unloop.contains(L)) {
552       // Successor is in a subloop.
553       if (Subloop)
554         continue; // Branching within subloops. Ignore it.
555 
556       // BB branches from the original into a subloop header.
557       assert(L->getParentLoop() == &Unloop && "cannot skip into nested loops");
558 
559       // Get the current nearest parent of the Subloop's exits.
560       L = SubloopParents[L];
561       // L could be Unloop if the only exit was an irreducible backedge.
562     }
563     if (L == &Unloop) {
564       continue;
565     }
566     // Handle critical edges from Unloop into a sibling loop.
567     if (L && !L->contains(&Unloop)) {
568       L = L->getParentLoop();
569     }
570     // Remember the nearest parent loop among successors or subloop exits.
571     if (NearLoop == &Unloop || !NearLoop || NearLoop->contains(L))
572       NearLoop = L;
573   }
574   if (Subloop) {
575     SubloopParents[Subloop] = NearLoop;
576     return BBLoop;
577   }
578   return NearLoop;
579 }
580 
LoopInfo(const DomTreeBase<BasicBlock> & DomTree)581 LoopInfo::LoopInfo(const DomTreeBase<BasicBlock> &DomTree) { analyze(DomTree); }
582 
invalidate(Function & F,const PreservedAnalyses & PA,FunctionAnalysisManager::Invalidator &)583 bool LoopInfo::invalidate(Function &F, const PreservedAnalyses &PA,
584                           FunctionAnalysisManager::Invalidator &) {
585   // Check whether the analysis, all analyses on functions, or the function's
586   // CFG have been preserved.
587   auto PAC = PA.getChecker<LoopAnalysis>();
588   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
589            PAC.preservedSet<CFGAnalyses>());
590 }
591 
erase(Loop * Unloop)592 void LoopInfo::erase(Loop *Unloop) {
593   assert(!Unloop->isInvalid() && "Loop has already been erased!");
594 
595   auto InvalidateOnExit = make_scope_exit([&]() { destroy(Unloop); });
596 
597   // First handle the special case of no parent loop to simplify the algorithm.
598   if (!Unloop->getParentLoop()) {
599     // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
600     for (Loop::block_iterator I = Unloop->block_begin(),
601                               E = Unloop->block_end();
602          I != E; ++I) {
603 
604       // Don't reparent blocks in subloops.
605       if (getLoopFor(*I) != Unloop)
606         continue;
607 
608       // Blocks no longer have a parent but are still referenced by Unloop until
609       // the Unloop object is deleted.
610       changeLoopFor(*I, nullptr);
611     }
612 
613     // Remove the loop from the top-level LoopInfo object.
614     for (iterator I = begin();; ++I) {
615       assert(I != end() && "Couldn't find loop");
616       if (*I == Unloop) {
617         removeLoop(I);
618         break;
619       }
620     }
621 
622     // Move all of the subloops to the top-level.
623     while (!Unloop->empty())
624       addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
625 
626     return;
627   }
628 
629   // Update the parent loop for all blocks within the loop. Blocks within
630   // subloops will not change parents.
631   UnloopUpdater Updater(Unloop, this);
632   Updater.updateBlockParents();
633 
634   // Remove blocks from former ancestor loops.
635   Updater.removeBlocksFromAncestors();
636 
637   // Add direct subloops as children in their new parent loop.
638   Updater.updateSubloopParents();
639 
640   // Remove unloop from its parent loop.
641   Loop *ParentLoop = Unloop->getParentLoop();
642   for (Loop::iterator I = ParentLoop->begin();; ++I) {
643     assert(I != ParentLoop->end() && "Couldn't find loop");
644     if (*I == Unloop) {
645       ParentLoop->removeChildLoop(I);
646       break;
647     }
648   }
649 }
650 
651 AnalysisKey LoopAnalysis::Key;
652 
run(Function & F,FunctionAnalysisManager & AM)653 LoopInfo LoopAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
654   // FIXME: Currently we create a LoopInfo from scratch for every function.
655   // This may prove to be too wasteful due to deallocating and re-allocating
656   // memory each time for the underlying map and vector datastructures. At some
657   // point it may prove worthwhile to use a freelist and recycle LoopInfo
658   // objects. I don't want to add that kind of complexity until the scope of
659   // the problem is better understood.
660   LoopInfo LI;
661   LI.analyze(AM.getResult<DominatorTreeAnalysis>(F));
662   return LI;
663 }
664 
run(Function & F,FunctionAnalysisManager & AM)665 PreservedAnalyses LoopPrinterPass::run(Function &F,
666                                        FunctionAnalysisManager &AM) {
667   AM.getResult<LoopAnalysis>(F).print(OS);
668   return PreservedAnalyses::all();
669 }
670 
printLoop(Loop & L,raw_ostream & OS,const std::string & Banner)671 void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
672 
673   if (forcePrintModuleIR()) {
674     // handling -print-module-scope
675     OS << Banner << " (loop: ";
676     L.getHeader()->printAsOperand(OS, false);
677     OS << ")\n";
678 
679     // printing whole module
680     OS << *L.getHeader()->getModule();
681     return;
682   }
683 
684   OS << Banner;
685 
686   auto *PreHeader = L.getLoopPreheader();
687   if (PreHeader) {
688     OS << "\n; Preheader:";
689     PreHeader->print(OS);
690     OS << "\n; Loop:";
691   }
692 
693   for (auto *Block : L.blocks())
694     if (Block)
695       Block->print(OS);
696     else
697       OS << "Printing <null> block";
698 
699   SmallVector<BasicBlock *, 8> ExitBlocks;
700   L.getExitBlocks(ExitBlocks);
701   if (!ExitBlocks.empty()) {
702     OS << "\n; Exit blocks";
703     for (auto *Block : ExitBlocks)
704       if (Block)
705         Block->print(OS);
706       else
707         OS << "Printing <null> block";
708   }
709 }
710 
711 //===----------------------------------------------------------------------===//
712 // LoopInfo implementation
713 //
714 
715 char LoopInfoWrapperPass::ID = 0;
716 INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",
717                       true, true)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)718 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
719 INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",
720                     true, true)
721 
722 bool LoopInfoWrapperPass::runOnFunction(Function &) {
723   releaseMemory();
724   LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
725   return false;
726 }
727 
verifyAnalysis() const728 void LoopInfoWrapperPass::verifyAnalysis() const {
729   // LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
730   // function each time verifyAnalysis is called is very expensive. The
731   // -verify-loop-info option can enable this. In order to perform some
732   // checking by default, LoopPass has been taught to call verifyLoop manually
733   // during loop pass sequences.
734   if (VerifyLoopInfo) {
735     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
736     LI.verify(DT);
737   }
738 }
739 
getAnalysisUsage(AnalysisUsage & AU) const740 void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
741   AU.setPreservesAll();
742   AU.addRequired<DominatorTreeWrapperPass>();
743 }
744 
print(raw_ostream & OS,const Module *) const745 void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
746   LI.print(OS);
747 }
748 
run(Function & F,FunctionAnalysisManager & AM)749 PreservedAnalyses LoopVerifierPass::run(Function &F,
750                                         FunctionAnalysisManager &AM) {
751   LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
752   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
753   LI.verify(DT);
754   return PreservedAnalyses::all();
755 }
756 
757 //===----------------------------------------------------------------------===//
758 // LoopBlocksDFS implementation
759 //
760 
761 /// Traverse the loop blocks and store the DFS result.
762 /// Useful for clients that just want the final DFS result and don't need to
763 /// visit blocks during the initial traversal.
perform(LoopInfo * LI)764 void LoopBlocksDFS::perform(LoopInfo *LI) {
765   LoopBlocksTraversal Traversal(*this, LI);
766   for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
767                                         POE = Traversal.end();
768        POI != POE; ++POI)
769     ;
770 }
771