1 //===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the LoopInfo class that is used to identify natural loops
10 // and determine the loop depth of various nodes of the CFG. Note that the
11 // loops identified may actually be several natural loops that share the same
12 // header node... not just a single natural loop.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/ADT/DepthFirstIterator.h"
18 #include "llvm/ADT/ScopeExit.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/Analysis/IVDescriptors.h"
21 #include "llvm/Analysis/LoopInfoImpl.h"
22 #include "llvm/Analysis/LoopIterator.h"
23 #include "llvm/Analysis/MemorySSA.h"
24 #include "llvm/Analysis/MemorySSAUpdater.h"
25 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
26 #include "llvm/Analysis/ValueTracking.h"
27 #include "llvm/Config/llvm-config.h"
28 #include "llvm/IR/CFG.h"
29 #include "llvm/IR/Constants.h"
30 #include "llvm/IR/DebugLoc.h"
31 #include "llvm/IR/Dominators.h"
32 #include "llvm/IR/IRPrintingPasses.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/LLVMContext.h"
35 #include "llvm/IR/Metadata.h"
36 #include "llvm/IR/PassManager.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
40 #include <algorithm>
41 using namespace llvm;
42
43 // Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
44 template class llvm::LoopBase<BasicBlock, Loop>;
45 template class llvm::LoopInfoBase<BasicBlock, Loop>;
46
47 // Always verify loopinfo if expensive checking is enabled.
48 #ifdef EXPENSIVE_CHECKS
49 bool llvm::VerifyLoopInfo = true;
50 #else
51 bool llvm::VerifyLoopInfo = false;
52 #endif
53 static cl::opt<bool, true>
54 VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
55 cl::Hidden, cl::desc("Verify loop info (time consuming)"));
56
57 //===----------------------------------------------------------------------===//
58 // Loop implementation
59 //
60
isLoopInvariant(const Value * V) const61 bool Loop::isLoopInvariant(const Value *V) const {
62 if (const Instruction *I = dyn_cast<Instruction>(V))
63 return !contains(I);
64 return true; // All non-instructions are loop invariant
65 }
66
hasLoopInvariantOperands(const Instruction * I) const67 bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
68 return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
69 }
70
makeLoopInvariant(Value * V,bool & Changed,Instruction * InsertPt,MemorySSAUpdater * MSSAU) const71 bool Loop::makeLoopInvariant(Value *V, bool &Changed, Instruction *InsertPt,
72 MemorySSAUpdater *MSSAU) const {
73 if (Instruction *I = dyn_cast<Instruction>(V))
74 return makeLoopInvariant(I, Changed, InsertPt, MSSAU);
75 return true; // All non-instructions are loop-invariant.
76 }
77
makeLoopInvariant(Instruction * I,bool & Changed,Instruction * InsertPt,MemorySSAUpdater * MSSAU) const78 bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
79 Instruction *InsertPt,
80 MemorySSAUpdater *MSSAU) const {
81 // Test if the value is already loop-invariant.
82 if (isLoopInvariant(I))
83 return true;
84 if (!isSafeToSpeculativelyExecute(I))
85 return false;
86 if (I->mayReadFromMemory())
87 return false;
88 // EH block instructions are immobile.
89 if (I->isEHPad())
90 return false;
91 // Determine the insertion point, unless one was given.
92 if (!InsertPt) {
93 BasicBlock *Preheader = getLoopPreheader();
94 // Without a preheader, hoisting is not feasible.
95 if (!Preheader)
96 return false;
97 InsertPt = Preheader->getTerminator();
98 }
99 // Don't hoist instructions with loop-variant operands.
100 for (Value *Operand : I->operands())
101 if (!makeLoopInvariant(Operand, Changed, InsertPt, MSSAU))
102 return false;
103
104 // Hoist.
105 I->moveBefore(InsertPt);
106 if (MSSAU)
107 if (auto *MUD = MSSAU->getMemorySSA()->getMemoryAccess(I))
108 MSSAU->moveToPlace(MUD, InsertPt->getParent(), MemorySSA::End);
109
110 // There is possibility of hoisting this instruction above some arbitrary
111 // condition. Any metadata defined on it can be control dependent on this
112 // condition. Conservatively strip it here so that we don't give any wrong
113 // information to the optimizer.
114 I->dropUnknownNonDebugMetadata();
115
116 Changed = true;
117 return true;
118 }
119
getIncomingAndBackEdge(BasicBlock * & Incoming,BasicBlock * & Backedge) const120 bool Loop::getIncomingAndBackEdge(BasicBlock *&Incoming,
121 BasicBlock *&Backedge) const {
122 BasicBlock *H = getHeader();
123
124 Incoming = nullptr;
125 Backedge = nullptr;
126 pred_iterator PI = pred_begin(H);
127 assert(PI != pred_end(H) && "Loop must have at least one backedge!");
128 Backedge = *PI++;
129 if (PI == pred_end(H))
130 return false; // dead loop
131 Incoming = *PI++;
132 if (PI != pred_end(H))
133 return false; // multiple backedges?
134
135 if (contains(Incoming)) {
136 if (contains(Backedge))
137 return false;
138 std::swap(Incoming, Backedge);
139 } else if (!contains(Backedge))
140 return false;
141
142 assert(Incoming && Backedge && "expected non-null incoming and backedges");
143 return true;
144 }
145
getCanonicalInductionVariable() const146 PHINode *Loop::getCanonicalInductionVariable() const {
147 BasicBlock *H = getHeader();
148
149 BasicBlock *Incoming = nullptr, *Backedge = nullptr;
150 if (!getIncomingAndBackEdge(Incoming, Backedge))
151 return nullptr;
152
153 // Loop over all of the PHI nodes, looking for a canonical indvar.
154 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
155 PHINode *PN = cast<PHINode>(I);
156 if (ConstantInt *CI =
157 dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
158 if (CI->isZero())
159 if (Instruction *Inc =
160 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
161 if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
162 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
163 if (CI->isOne())
164 return PN;
165 }
166 return nullptr;
167 }
168
169 /// Get the latch condition instruction.
getLatchCmpInst(const Loop & L)170 static ICmpInst *getLatchCmpInst(const Loop &L) {
171 if (BasicBlock *Latch = L.getLoopLatch())
172 if (BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator()))
173 if (BI->isConditional())
174 return dyn_cast<ICmpInst>(BI->getCondition());
175
176 return nullptr;
177 }
178
179 /// Return the final value of the loop induction variable if found.
findFinalIVValue(const Loop & L,const PHINode & IndVar,const Instruction & StepInst)180 static Value *findFinalIVValue(const Loop &L, const PHINode &IndVar,
181 const Instruction &StepInst) {
182 ICmpInst *LatchCmpInst = getLatchCmpInst(L);
183 if (!LatchCmpInst)
184 return nullptr;
185
186 Value *Op0 = LatchCmpInst->getOperand(0);
187 Value *Op1 = LatchCmpInst->getOperand(1);
188 if (Op0 == &IndVar || Op0 == &StepInst)
189 return Op1;
190
191 if (Op1 == &IndVar || Op1 == &StepInst)
192 return Op0;
193
194 return nullptr;
195 }
196
getBounds(const Loop & L,PHINode & IndVar,ScalarEvolution & SE)197 Optional<Loop::LoopBounds> Loop::LoopBounds::getBounds(const Loop &L,
198 PHINode &IndVar,
199 ScalarEvolution &SE) {
200 InductionDescriptor IndDesc;
201 if (!InductionDescriptor::isInductionPHI(&IndVar, &L, &SE, IndDesc))
202 return None;
203
204 Value *InitialIVValue = IndDesc.getStartValue();
205 Instruction *StepInst = IndDesc.getInductionBinOp();
206 if (!InitialIVValue || !StepInst)
207 return None;
208
209 const SCEV *Step = IndDesc.getStep();
210 Value *StepInstOp1 = StepInst->getOperand(1);
211 Value *StepInstOp0 = StepInst->getOperand(0);
212 Value *StepValue = nullptr;
213 if (SE.getSCEV(StepInstOp1) == Step)
214 StepValue = StepInstOp1;
215 else if (SE.getSCEV(StepInstOp0) == Step)
216 StepValue = StepInstOp0;
217
218 Value *FinalIVValue = findFinalIVValue(L, IndVar, *StepInst);
219 if (!FinalIVValue)
220 return None;
221
222 return LoopBounds(L, *InitialIVValue, *StepInst, StepValue, *FinalIVValue,
223 SE);
224 }
225
226 using Direction = Loop::LoopBounds::Direction;
227
getCanonicalPredicate() const228 ICmpInst::Predicate Loop::LoopBounds::getCanonicalPredicate() const {
229 BasicBlock *Latch = L.getLoopLatch();
230 assert(Latch && "Expecting valid latch");
231
232 BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator());
233 assert(BI && BI->isConditional() && "Expecting conditional latch branch");
234
235 ICmpInst *LatchCmpInst = dyn_cast<ICmpInst>(BI->getCondition());
236 assert(LatchCmpInst &&
237 "Expecting the latch compare instruction to be a CmpInst");
238
239 // Need to inverse the predicate when first successor is not the loop
240 // header
241 ICmpInst::Predicate Pred = (BI->getSuccessor(0) == L.getHeader())
242 ? LatchCmpInst->getPredicate()
243 : LatchCmpInst->getInversePredicate();
244
245 if (LatchCmpInst->getOperand(0) == &getFinalIVValue())
246 Pred = ICmpInst::getSwappedPredicate(Pred);
247
248 // Need to flip strictness of the predicate when the latch compare instruction
249 // is not using StepInst
250 if (LatchCmpInst->getOperand(0) == &getStepInst() ||
251 LatchCmpInst->getOperand(1) == &getStepInst())
252 return Pred;
253
254 // Cannot flip strictness of NE and EQ
255 if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
256 return ICmpInst::getFlippedStrictnessPredicate(Pred);
257
258 Direction D = getDirection();
259 if (D == Direction::Increasing)
260 return ICmpInst::ICMP_SLT;
261
262 if (D == Direction::Decreasing)
263 return ICmpInst::ICMP_SGT;
264
265 // If cannot determine the direction, then unable to find the canonical
266 // predicate
267 return ICmpInst::BAD_ICMP_PREDICATE;
268 }
269
getDirection() const270 Direction Loop::LoopBounds::getDirection() const {
271 if (const SCEVAddRecExpr *StepAddRecExpr =
272 dyn_cast<SCEVAddRecExpr>(SE.getSCEV(&getStepInst())))
273 if (const SCEV *StepRecur = StepAddRecExpr->getStepRecurrence(SE)) {
274 if (SE.isKnownPositive(StepRecur))
275 return Direction::Increasing;
276 if (SE.isKnownNegative(StepRecur))
277 return Direction::Decreasing;
278 }
279
280 return Direction::Unknown;
281 }
282
getBounds(ScalarEvolution & SE) const283 Optional<Loop::LoopBounds> Loop::getBounds(ScalarEvolution &SE) const {
284 if (PHINode *IndVar = getInductionVariable(SE))
285 return LoopBounds::getBounds(*this, *IndVar, SE);
286
287 return None;
288 }
289
getInductionVariable(ScalarEvolution & SE) const290 PHINode *Loop::getInductionVariable(ScalarEvolution &SE) const {
291 if (!isLoopSimplifyForm())
292 return nullptr;
293
294 BasicBlock *Header = getHeader();
295 assert(Header && "Expected a valid loop header");
296 ICmpInst *CmpInst = getLatchCmpInst(*this);
297 if (!CmpInst)
298 return nullptr;
299
300 Instruction *LatchCmpOp0 = dyn_cast<Instruction>(CmpInst->getOperand(0));
301 Instruction *LatchCmpOp1 = dyn_cast<Instruction>(CmpInst->getOperand(1));
302
303 for (PHINode &IndVar : Header->phis()) {
304 InductionDescriptor IndDesc;
305 if (!InductionDescriptor::isInductionPHI(&IndVar, this, &SE, IndDesc))
306 continue;
307
308 Instruction *StepInst = IndDesc.getInductionBinOp();
309
310 // case 1:
311 // IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
312 // StepInst = IndVar + step
313 // cmp = StepInst < FinalValue
314 if (StepInst == LatchCmpOp0 || StepInst == LatchCmpOp1)
315 return &IndVar;
316
317 // case 2:
318 // IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
319 // StepInst = IndVar + step
320 // cmp = IndVar < FinalValue
321 if (&IndVar == LatchCmpOp0 || &IndVar == LatchCmpOp1)
322 return &IndVar;
323 }
324
325 return nullptr;
326 }
327
getInductionDescriptor(ScalarEvolution & SE,InductionDescriptor & IndDesc) const328 bool Loop::getInductionDescriptor(ScalarEvolution &SE,
329 InductionDescriptor &IndDesc) const {
330 if (PHINode *IndVar = getInductionVariable(SE))
331 return InductionDescriptor::isInductionPHI(IndVar, this, &SE, IndDesc);
332
333 return false;
334 }
335
isAuxiliaryInductionVariable(PHINode & AuxIndVar,ScalarEvolution & SE) const336 bool Loop::isAuxiliaryInductionVariable(PHINode &AuxIndVar,
337 ScalarEvolution &SE) const {
338 // Located in the loop header
339 BasicBlock *Header = getHeader();
340 if (AuxIndVar.getParent() != Header)
341 return false;
342
343 // No uses outside of the loop
344 for (User *U : AuxIndVar.users())
345 if (const Instruction *I = dyn_cast<Instruction>(U))
346 if (!contains(I))
347 return false;
348
349 InductionDescriptor IndDesc;
350 if (!InductionDescriptor::isInductionPHI(&AuxIndVar, this, &SE, IndDesc))
351 return false;
352
353 // The step instruction opcode should be add or sub.
354 if (IndDesc.getInductionOpcode() != Instruction::Add &&
355 IndDesc.getInductionOpcode() != Instruction::Sub)
356 return false;
357
358 // Incremented by a loop invariant step for each loop iteration
359 return SE.isLoopInvariant(IndDesc.getStep(), this);
360 }
361
isCanonical(ScalarEvolution & SE) const362 bool Loop::isCanonical(ScalarEvolution &SE) const {
363 InductionDescriptor IndDesc;
364 if (!getInductionDescriptor(SE, IndDesc))
365 return false;
366
367 ConstantInt *Init = dyn_cast_or_null<ConstantInt>(IndDesc.getStartValue());
368 if (!Init || !Init->isZero())
369 return false;
370
371 if (IndDesc.getInductionOpcode() != Instruction::Add)
372 return false;
373
374 ConstantInt *Step = IndDesc.getConstIntStepValue();
375 if (!Step || !Step->isOne())
376 return false;
377
378 return true;
379 }
380
381 // Check that 'BB' doesn't have any uses outside of the 'L'
isBlockInLCSSAForm(const Loop & L,const BasicBlock & BB,DominatorTree & DT)382 static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
383 DominatorTree &DT) {
384 for (const Instruction &I : BB) {
385 // Tokens can't be used in PHI nodes and live-out tokens prevent loop
386 // optimizations, so for the purposes of considered LCSSA form, we
387 // can ignore them.
388 if (I.getType()->isTokenTy())
389 continue;
390
391 for (const Use &U : I.uses()) {
392 const Instruction *UI = cast<Instruction>(U.getUser());
393 const BasicBlock *UserBB = UI->getParent();
394 if (const PHINode *P = dyn_cast<PHINode>(UI))
395 UserBB = P->getIncomingBlock(U);
396
397 // Check the current block, as a fast-path, before checking whether
398 // the use is anywhere in the loop. Most values are used in the same
399 // block they are defined in. Also, blocks not reachable from the
400 // entry are special; uses in them don't need to go through PHIs.
401 if (UserBB != &BB && !L.contains(UserBB) &&
402 DT.isReachableFromEntry(UserBB))
403 return false;
404 }
405 }
406 return true;
407 }
408
isLCSSAForm(DominatorTree & DT) const409 bool Loop::isLCSSAForm(DominatorTree &DT) const {
410 // For each block we check that it doesn't have any uses outside of this loop.
411 return all_of(this->blocks(), [&](const BasicBlock *BB) {
412 return isBlockInLCSSAForm(*this, *BB, DT);
413 });
414 }
415
isRecursivelyLCSSAForm(DominatorTree & DT,const LoopInfo & LI) const416 bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const {
417 // For each block we check that it doesn't have any uses outside of its
418 // innermost loop. This process will transitively guarantee that the current
419 // loop and all of the nested loops are in LCSSA form.
420 return all_of(this->blocks(), [&](const BasicBlock *BB) {
421 return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
422 });
423 }
424
isLoopSimplifyForm() const425 bool Loop::isLoopSimplifyForm() const {
426 // Normal-form loops have a preheader, a single backedge, and all of their
427 // exits have all their predecessors inside the loop.
428 return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
429 }
430
431 // Routines that reform the loop CFG and split edges often fail on indirectbr.
isSafeToClone() const432 bool Loop::isSafeToClone() const {
433 // Return false if any loop blocks contain indirectbrs, or there are any calls
434 // to noduplicate functions.
435 // FIXME: it should be ok to clone CallBrInst's if we correctly update the
436 // operand list to reflect the newly cloned labels.
437 for (BasicBlock *BB : this->blocks()) {
438 if (isa<IndirectBrInst>(BB->getTerminator()) ||
439 isa<CallBrInst>(BB->getTerminator()))
440 return false;
441
442 for (Instruction &I : *BB)
443 if (auto CS = CallSite(&I))
444 if (CS.cannotDuplicate())
445 return false;
446 }
447 return true;
448 }
449
getLoopID() const450 MDNode *Loop::getLoopID() const {
451 MDNode *LoopID = nullptr;
452
453 // Go through the latch blocks and check the terminator for the metadata.
454 SmallVector<BasicBlock *, 4> LatchesBlocks;
455 getLoopLatches(LatchesBlocks);
456 for (BasicBlock *BB : LatchesBlocks) {
457 Instruction *TI = BB->getTerminator();
458 MDNode *MD = TI->getMetadata(LLVMContext::MD_loop);
459
460 if (!MD)
461 return nullptr;
462
463 if (!LoopID)
464 LoopID = MD;
465 else if (MD != LoopID)
466 return nullptr;
467 }
468 if (!LoopID || LoopID->getNumOperands() == 0 ||
469 LoopID->getOperand(0) != LoopID)
470 return nullptr;
471 return LoopID;
472 }
473
setLoopID(MDNode * LoopID) const474 void Loop::setLoopID(MDNode *LoopID) const {
475 assert((!LoopID || LoopID->getNumOperands() > 0) &&
476 "Loop ID needs at least one operand");
477 assert((!LoopID || LoopID->getOperand(0) == LoopID) &&
478 "Loop ID should refer to itself");
479
480 SmallVector<BasicBlock *, 4> LoopLatches;
481 getLoopLatches(LoopLatches);
482 for (BasicBlock *BB : LoopLatches)
483 BB->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
484 }
485
setLoopAlreadyUnrolled()486 void Loop::setLoopAlreadyUnrolled() {
487 LLVMContext &Context = getHeader()->getContext();
488
489 MDNode *DisableUnrollMD =
490 MDNode::get(Context, MDString::get(Context, "llvm.loop.unroll.disable"));
491 MDNode *LoopID = getLoopID();
492 MDNode *NewLoopID = makePostTransformationMetadata(
493 Context, LoopID, {"llvm.loop.unroll."}, {DisableUnrollMD});
494 setLoopID(NewLoopID);
495 }
496
isAnnotatedParallel() const497 bool Loop::isAnnotatedParallel() const {
498 MDNode *DesiredLoopIdMetadata = getLoopID();
499
500 if (!DesiredLoopIdMetadata)
501 return false;
502
503 MDNode *ParallelAccesses =
504 findOptionMDForLoop(this, "llvm.loop.parallel_accesses");
505 SmallPtrSet<MDNode *, 4>
506 ParallelAccessGroups; // For scalable 'contains' check.
507 if (ParallelAccesses) {
508 for (const MDOperand &MD : drop_begin(ParallelAccesses->operands(), 1)) {
509 MDNode *AccGroup = cast<MDNode>(MD.get());
510 assert(isValidAsAccessGroup(AccGroup) &&
511 "List item must be an access group");
512 ParallelAccessGroups.insert(AccGroup);
513 }
514 }
515
516 // The loop branch contains the parallel loop metadata. In order to ensure
517 // that any parallel-loop-unaware optimization pass hasn't added loop-carried
518 // dependencies (thus converted the loop back to a sequential loop), check
519 // that all the memory instructions in the loop belong to an access group that
520 // is parallel to this loop.
521 for (BasicBlock *BB : this->blocks()) {
522 for (Instruction &I : *BB) {
523 if (!I.mayReadOrWriteMemory())
524 continue;
525
526 if (MDNode *AccessGroup = I.getMetadata(LLVMContext::MD_access_group)) {
527 auto ContainsAccessGroup = [&ParallelAccessGroups](MDNode *AG) -> bool {
528 if (AG->getNumOperands() == 0) {
529 assert(isValidAsAccessGroup(AG) && "Item must be an access group");
530 return ParallelAccessGroups.count(AG);
531 }
532
533 for (const MDOperand &AccessListItem : AG->operands()) {
534 MDNode *AccGroup = cast<MDNode>(AccessListItem.get());
535 assert(isValidAsAccessGroup(AccGroup) &&
536 "List item must be an access group");
537 if (ParallelAccessGroups.count(AccGroup))
538 return true;
539 }
540 return false;
541 };
542
543 if (ContainsAccessGroup(AccessGroup))
544 continue;
545 }
546
547 // The memory instruction can refer to the loop identifier metadata
548 // directly or indirectly through another list metadata (in case of
549 // nested parallel loops). The loop identifier metadata refers to
550 // itself so we can check both cases with the same routine.
551 MDNode *LoopIdMD =
552 I.getMetadata(LLVMContext::MD_mem_parallel_loop_access);
553
554 if (!LoopIdMD)
555 return false;
556
557 bool LoopIdMDFound = false;
558 for (const MDOperand &MDOp : LoopIdMD->operands()) {
559 if (MDOp == DesiredLoopIdMetadata) {
560 LoopIdMDFound = true;
561 break;
562 }
563 }
564
565 if (!LoopIdMDFound)
566 return false;
567 }
568 }
569 return true;
570 }
571
getStartLoc() const572 DebugLoc Loop::getStartLoc() const { return getLocRange().getStart(); }
573
getLocRange() const574 Loop::LocRange Loop::getLocRange() const {
575 // If we have a debug location in the loop ID, then use it.
576 if (MDNode *LoopID = getLoopID()) {
577 DebugLoc Start;
578 // We use the first DebugLoc in the header as the start location of the loop
579 // and if there is a second DebugLoc in the header we use it as end location
580 // of the loop.
581 for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
582 if (DILocation *L = dyn_cast<DILocation>(LoopID->getOperand(i))) {
583 if (!Start)
584 Start = DebugLoc(L);
585 else
586 return LocRange(Start, DebugLoc(L));
587 }
588 }
589
590 if (Start)
591 return LocRange(Start);
592 }
593
594 // Try the pre-header first.
595 if (BasicBlock *PHeadBB = getLoopPreheader())
596 if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
597 return LocRange(DL);
598
599 // If we have no pre-header or there are no instructions with debug
600 // info in it, try the header.
601 if (BasicBlock *HeadBB = getHeader())
602 return LocRange(HeadBB->getTerminator()->getDebugLoc());
603
604 return LocRange();
605 }
606
607 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const608 LLVM_DUMP_METHOD void Loop::dump() const { print(dbgs()); }
609
dumpVerbose() const610 LLVM_DUMP_METHOD void Loop::dumpVerbose() const {
611 print(dbgs(), /*Depth=*/0, /*Verbose=*/true);
612 }
613 #endif
614
615 //===----------------------------------------------------------------------===//
616 // UnloopUpdater implementation
617 //
618
619 namespace {
620 /// Find the new parent loop for all blocks within the "unloop" whose last
621 /// backedges has just been removed.
622 class UnloopUpdater {
623 Loop &Unloop;
624 LoopInfo *LI;
625
626 LoopBlocksDFS DFS;
627
628 // Map unloop's immediate subloops to their nearest reachable parents. Nested
629 // loops within these subloops will not change parents. However, an immediate
630 // subloop's new parent will be the nearest loop reachable from either its own
631 // exits *or* any of its nested loop's exits.
632 DenseMap<Loop *, Loop *> SubloopParents;
633
634 // Flag the presence of an irreducible backedge whose destination is a block
635 // directly contained by the original unloop.
636 bool FoundIB;
637
638 public:
UnloopUpdater(Loop * UL,LoopInfo * LInfo)639 UnloopUpdater(Loop *UL, LoopInfo *LInfo)
640 : Unloop(*UL), LI(LInfo), DFS(UL), FoundIB(false) {}
641
642 void updateBlockParents();
643
644 void removeBlocksFromAncestors();
645
646 void updateSubloopParents();
647
648 protected:
649 Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
650 };
651 } // end anonymous namespace
652
653 /// Update the parent loop for all blocks that are directly contained within the
654 /// original "unloop".
updateBlockParents()655 void UnloopUpdater::updateBlockParents() {
656 if (Unloop.getNumBlocks()) {
657 // Perform a post order CFG traversal of all blocks within this loop,
658 // propagating the nearest loop from successors to predecessors.
659 LoopBlocksTraversal Traversal(DFS, LI);
660 for (BasicBlock *POI : Traversal) {
661
662 Loop *L = LI->getLoopFor(POI);
663 Loop *NL = getNearestLoop(POI, L);
664
665 if (NL != L) {
666 // For reducible loops, NL is now an ancestor of Unloop.
667 assert((NL != &Unloop && (!NL || NL->contains(&Unloop))) &&
668 "uninitialized successor");
669 LI->changeLoopFor(POI, NL);
670 } else {
671 // Or the current block is part of a subloop, in which case its parent
672 // is unchanged.
673 assert((FoundIB || Unloop.contains(L)) && "uninitialized successor");
674 }
675 }
676 }
677 // Each irreducible loop within the unloop induces a round of iteration using
678 // the DFS result cached by Traversal.
679 bool Changed = FoundIB;
680 for (unsigned NIters = 0; Changed; ++NIters) {
681 assert(NIters < Unloop.getNumBlocks() && "runaway iterative algorithm");
682
683 // Iterate over the postorder list of blocks, propagating the nearest loop
684 // from successors to predecessors as before.
685 Changed = false;
686 for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
687 POE = DFS.endPostorder();
688 POI != POE; ++POI) {
689
690 Loop *L = LI->getLoopFor(*POI);
691 Loop *NL = getNearestLoop(*POI, L);
692 if (NL != L) {
693 assert(NL != &Unloop && (!NL || NL->contains(&Unloop)) &&
694 "uninitialized successor");
695 LI->changeLoopFor(*POI, NL);
696 Changed = true;
697 }
698 }
699 }
700 }
701
702 /// Remove unloop's blocks from all ancestors below their new parents.
removeBlocksFromAncestors()703 void UnloopUpdater::removeBlocksFromAncestors() {
704 // Remove all unloop's blocks (including those in nested subloops) from
705 // ancestors below the new parent loop.
706 for (Loop::block_iterator BI = Unloop.block_begin(), BE = Unloop.block_end();
707 BI != BE; ++BI) {
708 Loop *OuterParent = LI->getLoopFor(*BI);
709 if (Unloop.contains(OuterParent)) {
710 while (OuterParent->getParentLoop() != &Unloop)
711 OuterParent = OuterParent->getParentLoop();
712 OuterParent = SubloopParents[OuterParent];
713 }
714 // Remove blocks from former Ancestors except Unloop itself which will be
715 // deleted.
716 for (Loop *OldParent = Unloop.getParentLoop(); OldParent != OuterParent;
717 OldParent = OldParent->getParentLoop()) {
718 assert(OldParent && "new loop is not an ancestor of the original");
719 OldParent->removeBlockFromLoop(*BI);
720 }
721 }
722 }
723
724 /// Update the parent loop for all subloops directly nested within unloop.
updateSubloopParents()725 void UnloopUpdater::updateSubloopParents() {
726 while (!Unloop.empty()) {
727 Loop *Subloop = *std::prev(Unloop.end());
728 Unloop.removeChildLoop(std::prev(Unloop.end()));
729
730 assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
731 if (Loop *Parent = SubloopParents[Subloop])
732 Parent->addChildLoop(Subloop);
733 else
734 LI->addTopLevelLoop(Subloop);
735 }
736 }
737
738 /// Return the nearest parent loop among this block's successors. If a successor
739 /// is a subloop header, consider its parent to be the nearest parent of the
740 /// subloop's exits.
741 ///
742 /// For subloop blocks, simply update SubloopParents and return NULL.
getNearestLoop(BasicBlock * BB,Loop * BBLoop)743 Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
744
745 // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
746 // is considered uninitialized.
747 Loop *NearLoop = BBLoop;
748
749 Loop *Subloop = nullptr;
750 if (NearLoop != &Unloop && Unloop.contains(NearLoop)) {
751 Subloop = NearLoop;
752 // Find the subloop ancestor that is directly contained within Unloop.
753 while (Subloop->getParentLoop() != &Unloop) {
754 Subloop = Subloop->getParentLoop();
755 assert(Subloop && "subloop is not an ancestor of the original loop");
756 }
757 // Get the current nearest parent of the Subloop exits, initially Unloop.
758 NearLoop = SubloopParents.insert({Subloop, &Unloop}).first->second;
759 }
760
761 succ_iterator I = succ_begin(BB), E = succ_end(BB);
762 if (I == E) {
763 assert(!Subloop && "subloop blocks must have a successor");
764 NearLoop = nullptr; // unloop blocks may now exit the function.
765 }
766 for (; I != E; ++I) {
767 if (*I == BB)
768 continue; // self loops are uninteresting
769
770 Loop *L = LI->getLoopFor(*I);
771 if (L == &Unloop) {
772 // This successor has not been processed. This path must lead to an
773 // irreducible backedge.
774 assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
775 FoundIB = true;
776 }
777 if (L != &Unloop && Unloop.contains(L)) {
778 // Successor is in a subloop.
779 if (Subloop)
780 continue; // Branching within subloops. Ignore it.
781
782 // BB branches from the original into a subloop header.
783 assert(L->getParentLoop() == &Unloop && "cannot skip into nested loops");
784
785 // Get the current nearest parent of the Subloop's exits.
786 L = SubloopParents[L];
787 // L could be Unloop if the only exit was an irreducible backedge.
788 }
789 if (L == &Unloop) {
790 continue;
791 }
792 // Handle critical edges from Unloop into a sibling loop.
793 if (L && !L->contains(&Unloop)) {
794 L = L->getParentLoop();
795 }
796 // Remember the nearest parent loop among successors or subloop exits.
797 if (NearLoop == &Unloop || !NearLoop || NearLoop->contains(L))
798 NearLoop = L;
799 }
800 if (Subloop) {
801 SubloopParents[Subloop] = NearLoop;
802 return BBLoop;
803 }
804 return NearLoop;
805 }
806
LoopInfo(const DomTreeBase<BasicBlock> & DomTree)807 LoopInfo::LoopInfo(const DomTreeBase<BasicBlock> &DomTree) { analyze(DomTree); }
808
invalidate(Function & F,const PreservedAnalyses & PA,FunctionAnalysisManager::Invalidator &)809 bool LoopInfo::invalidate(Function &F, const PreservedAnalyses &PA,
810 FunctionAnalysisManager::Invalidator &) {
811 // Check whether the analysis, all analyses on functions, or the function's
812 // CFG have been preserved.
813 auto PAC = PA.getChecker<LoopAnalysis>();
814 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
815 PAC.preservedSet<CFGAnalyses>());
816 }
817
erase(Loop * Unloop)818 void LoopInfo::erase(Loop *Unloop) {
819 assert(!Unloop->isInvalid() && "Loop has already been erased!");
820
821 auto InvalidateOnExit = make_scope_exit([&]() { destroy(Unloop); });
822
823 // First handle the special case of no parent loop to simplify the algorithm.
824 if (!Unloop->getParentLoop()) {
825 // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
826 for (Loop::block_iterator I = Unloop->block_begin(),
827 E = Unloop->block_end();
828 I != E; ++I) {
829
830 // Don't reparent blocks in subloops.
831 if (getLoopFor(*I) != Unloop)
832 continue;
833
834 // Blocks no longer have a parent but are still referenced by Unloop until
835 // the Unloop object is deleted.
836 changeLoopFor(*I, nullptr);
837 }
838
839 // Remove the loop from the top-level LoopInfo object.
840 for (iterator I = begin();; ++I) {
841 assert(I != end() && "Couldn't find loop");
842 if (*I == Unloop) {
843 removeLoop(I);
844 break;
845 }
846 }
847
848 // Move all of the subloops to the top-level.
849 while (!Unloop->empty())
850 addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
851
852 return;
853 }
854
855 // Update the parent loop for all blocks within the loop. Blocks within
856 // subloops will not change parents.
857 UnloopUpdater Updater(Unloop, this);
858 Updater.updateBlockParents();
859
860 // Remove blocks from former ancestor loops.
861 Updater.removeBlocksFromAncestors();
862
863 // Add direct subloops as children in their new parent loop.
864 Updater.updateSubloopParents();
865
866 // Remove unloop from its parent loop.
867 Loop *ParentLoop = Unloop->getParentLoop();
868 for (Loop::iterator I = ParentLoop->begin();; ++I) {
869 assert(I != ParentLoop->end() && "Couldn't find loop");
870 if (*I == Unloop) {
871 ParentLoop->removeChildLoop(I);
872 break;
873 }
874 }
875 }
876
877 AnalysisKey LoopAnalysis::Key;
878
run(Function & F,FunctionAnalysisManager & AM)879 LoopInfo LoopAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
880 // FIXME: Currently we create a LoopInfo from scratch for every function.
881 // This may prove to be too wasteful due to deallocating and re-allocating
882 // memory each time for the underlying map and vector datastructures. At some
883 // point it may prove worthwhile to use a freelist and recycle LoopInfo
884 // objects. I don't want to add that kind of complexity until the scope of
885 // the problem is better understood.
886 LoopInfo LI;
887 LI.analyze(AM.getResult<DominatorTreeAnalysis>(F));
888 return LI;
889 }
890
run(Function & F,FunctionAnalysisManager & AM)891 PreservedAnalyses LoopPrinterPass::run(Function &F,
892 FunctionAnalysisManager &AM) {
893 AM.getResult<LoopAnalysis>(F).print(OS);
894 return PreservedAnalyses::all();
895 }
896
printLoop(Loop & L,raw_ostream & OS,const std::string & Banner)897 void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
898
899 if (forcePrintModuleIR()) {
900 // handling -print-module-scope
901 OS << Banner << " (loop: ";
902 L.getHeader()->printAsOperand(OS, false);
903 OS << ")\n";
904
905 // printing whole module
906 OS << *L.getHeader()->getModule();
907 return;
908 }
909
910 OS << Banner;
911
912 auto *PreHeader = L.getLoopPreheader();
913 if (PreHeader) {
914 OS << "\n; Preheader:";
915 PreHeader->print(OS);
916 OS << "\n; Loop:";
917 }
918
919 for (auto *Block : L.blocks())
920 if (Block)
921 Block->print(OS);
922 else
923 OS << "Printing <null> block";
924
925 SmallVector<BasicBlock *, 8> ExitBlocks;
926 L.getExitBlocks(ExitBlocks);
927 if (!ExitBlocks.empty()) {
928 OS << "\n; Exit blocks";
929 for (auto *Block : ExitBlocks)
930 if (Block)
931 Block->print(OS);
932 else
933 OS << "Printing <null> block";
934 }
935 }
936
findOptionMDForLoopID(MDNode * LoopID,StringRef Name)937 MDNode *llvm::findOptionMDForLoopID(MDNode *LoopID, StringRef Name) {
938 // No loop metadata node, no loop properties.
939 if (!LoopID)
940 return nullptr;
941
942 // First operand should refer to the metadata node itself, for legacy reasons.
943 assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
944 assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
945
946 // Iterate over the metdata node operands and look for MDString metadata.
947 for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
948 MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
949 if (!MD || MD->getNumOperands() < 1)
950 continue;
951 MDString *S = dyn_cast<MDString>(MD->getOperand(0));
952 if (!S)
953 continue;
954 // Return the operand node if MDString holds expected metadata.
955 if (Name.equals(S->getString()))
956 return MD;
957 }
958
959 // Loop property not found.
960 return nullptr;
961 }
962
findOptionMDForLoop(const Loop * TheLoop,StringRef Name)963 MDNode *llvm::findOptionMDForLoop(const Loop *TheLoop, StringRef Name) {
964 return findOptionMDForLoopID(TheLoop->getLoopID(), Name);
965 }
966
isValidAsAccessGroup(MDNode * Node)967 bool llvm::isValidAsAccessGroup(MDNode *Node) {
968 return Node->getNumOperands() == 0 && Node->isDistinct();
969 }
970
makePostTransformationMetadata(LLVMContext & Context,MDNode * OrigLoopID,ArrayRef<StringRef> RemovePrefixes,ArrayRef<MDNode * > AddAttrs)971 MDNode *llvm::makePostTransformationMetadata(LLVMContext &Context,
972 MDNode *OrigLoopID,
973 ArrayRef<StringRef> RemovePrefixes,
974 ArrayRef<MDNode *> AddAttrs) {
975 // First remove any existing loop metadata related to this transformation.
976 SmallVector<Metadata *, 4> MDs;
977
978 // Reserve first location for self reference to the LoopID metadata node.
979 TempMDTuple TempNode = MDNode::getTemporary(Context, None);
980 MDs.push_back(TempNode.get());
981
982 // Remove metadata for the transformation that has been applied or that became
983 // outdated.
984 if (OrigLoopID) {
985 for (unsigned i = 1, ie = OrigLoopID->getNumOperands(); i < ie; ++i) {
986 bool IsVectorMetadata = false;
987 Metadata *Op = OrigLoopID->getOperand(i);
988 if (MDNode *MD = dyn_cast<MDNode>(Op)) {
989 const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
990 if (S)
991 IsVectorMetadata =
992 llvm::any_of(RemovePrefixes, [S](StringRef Prefix) -> bool {
993 return S->getString().startswith(Prefix);
994 });
995 }
996 if (!IsVectorMetadata)
997 MDs.push_back(Op);
998 }
999 }
1000
1001 // Add metadata to avoid reapplying a transformation, such as
1002 // llvm.loop.unroll.disable and llvm.loop.isvectorized.
1003 MDs.append(AddAttrs.begin(), AddAttrs.end());
1004
1005 MDNode *NewLoopID = MDNode::getDistinct(Context, MDs);
1006 // Replace the temporary node with a self-reference.
1007 NewLoopID->replaceOperandWith(0, NewLoopID);
1008 return NewLoopID;
1009 }
1010
1011 //===----------------------------------------------------------------------===//
1012 // LoopInfo implementation
1013 //
1014
1015 char LoopInfoWrapperPass::ID = 0;
1016 INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",
1017 true, true)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)1018 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
1019 INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",
1020 true, true)
1021
1022 bool LoopInfoWrapperPass::runOnFunction(Function &) {
1023 releaseMemory();
1024 LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
1025 return false;
1026 }
1027
verifyAnalysis() const1028 void LoopInfoWrapperPass::verifyAnalysis() const {
1029 // LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
1030 // function each time verifyAnalysis is called is very expensive. The
1031 // -verify-loop-info option can enable this. In order to perform some
1032 // checking by default, LoopPass has been taught to call verifyLoop manually
1033 // during loop pass sequences.
1034 if (VerifyLoopInfo) {
1035 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1036 LI.verify(DT);
1037 }
1038 }
1039
getAnalysisUsage(AnalysisUsage & AU) const1040 void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
1041 AU.setPreservesAll();
1042 AU.addRequiredTransitive<DominatorTreeWrapperPass>();
1043 }
1044
print(raw_ostream & OS,const Module *) const1045 void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
1046 LI.print(OS);
1047 }
1048
run(Function & F,FunctionAnalysisManager & AM)1049 PreservedAnalyses LoopVerifierPass::run(Function &F,
1050 FunctionAnalysisManager &AM) {
1051 LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
1052 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
1053 LI.verify(DT);
1054 return PreservedAnalyses::all();
1055 }
1056
1057 //===----------------------------------------------------------------------===//
1058 // LoopBlocksDFS implementation
1059 //
1060
1061 /// Traverse the loop blocks and store the DFS result.
1062 /// Useful for clients that just want the final DFS result and don't need to
1063 /// visit blocks during the initial traversal.
perform(LoopInfo * LI)1064 void LoopBlocksDFS::perform(LoopInfo *LI) {
1065 LoopBlocksTraversal Traversal(*this, LI);
1066 for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
1067 POE = Traversal.end();
1068 POI != POE; ++POI)
1069 ;
1070 }
1071