1 //===- LoopDistribute.cpp - Loop Distribution Pass ------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the Loop Distribution Pass. Its main focus is to
11 // distribute loops that cannot be vectorized due to dependence cycles. It
12 // tries to isolate the offending dependences into a new loop allowing
13 // vectorization of the remaining parts.
15 // For dependence analysis, the pass uses the LoopVectorizer's
16 // LoopAccessAnalysis. Because this analysis presumes no change in the order of
17 // memory operations, special care is taken to preserve the lexical order of
20 // Similarly to the Vectorizer, the pass also supports loop versioning to
21 // run-time disambiguate potentially overlapping arrays.
23 //===----------------------------------------------------------------------===//
25 #include "llvm/Transforms/Scalar/LoopDistribute.h"
26 #include "llvm/ADT/DepthFirstIterator.h"
27 #include "llvm/ADT/EquivalenceClasses.h"
28 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/ADT/Statistic.h"
30 #include "llvm/Analysis/BlockFrequencyInfo.h"
31 #include "llvm/Analysis/GlobalsModRef.h"
32 #include "llvm/Analysis/LoopAccessAnalysis.h"
33 #include "llvm/Analysis/LoopInfo.h"
34 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
35 #include "llvm/IR/DiagnosticInfo.h"
36 #include "llvm/IR/Dominators.h"
37 #include "llvm/Pass.h"
38 #include "llvm/Support/CommandLine.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Transforms/Scalar/LoopPassManager.h"
41 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
42 #include "llvm/Transforms/Utils/Cloning.h"
43 #include "llvm/Transforms/Utils/LoopUtils.h"
44 #include "llvm/Transforms/Utils/LoopVersioning.h"
47 #define LDIST_NAME "loop-distribute"
48 #define DEBUG_TYPE LDIST_NAME
53 LDistVerify("loop-distribute-verify", cl::Hidden,
54 cl::desc("Turn on DominatorTree and LoopInfo verification "
55 "after Loop Distribution"),
58 static cl::opt<bool> DistributeNonIfConvertible(
59 "loop-distribute-non-if-convertible", cl::Hidden,
60 cl::desc("Whether to distribute into a loop that may not be "
61 "if-convertible by the loop vectorizer"),
64 static cl::opt<unsigned> DistributeSCEVCheckThreshold(
65 "loop-distribute-scev-check-threshold", cl::init(8), cl::Hidden,
66 cl::desc("The maximum number of SCEV checks allowed for Loop "
69 static cl::opt<unsigned> PragmaDistributeSCEVCheckThreshold(
70 "loop-distribute-scev-check-threshold-with-pragma", cl::init(128),
73 "The maximum number of SCEV checks allowed for Loop "
74 "Distribution for loop marked with #pragma loop distribute(enable)"));
76 static cl::opt<bool> EnableLoopDistribute(
77 "enable-loop-distribute", cl::Hidden,
78 cl::desc("Enable the new, experimental LoopDistribution Pass"),
81 STATISTIC(NumLoopsDistributed, "Number of loops distributed");
84 /// \brief Maintains the set of instructions of the loop for a partition before
85 /// cloning. After cloning, it hosts the new loop.
87 typedef SmallPtrSet<Instruction *, 8> InstructionSet;
90 InstPartition(Instruction *I, Loop *L, bool DepCycle = false)
91 : DepCycle(DepCycle), OrigLoop(L), ClonedLoop(nullptr) {
95 /// \brief Returns whether this partition contains a dependence cycle.
96 bool hasDepCycle() const { return DepCycle; }
98 /// \brief Adds an instruction to this partition.
99 void add(Instruction *I) { Set.insert(I); }
101 /// \brief Collection accessors.
102 InstructionSet::iterator begin() { return Set.begin(); }
103 InstructionSet::iterator end() { return Set.end(); }
104 InstructionSet::const_iterator begin() const { return Set.begin(); }
105 InstructionSet::const_iterator end() const { return Set.end(); }
106 bool empty() const { return Set.empty(); }
108 /// \brief Moves this partition into \p Other. This partition becomes empty
110 void moveTo(InstPartition &Other) {
111 Other.Set.insert(Set.begin(), Set.end());
113 Other.DepCycle |= DepCycle;
116 /// \brief Populates the partition with a transitive closure of all the
117 /// instructions that the seeded instructions dependent on.
118 void populateUsedSet() {
119 // FIXME: We currently don't use control-dependence but simply include all
120 // blocks (possibly empty at the end) and let simplifycfg mostly clean this
122 for (auto *B : OrigLoop->getBlocks())
123 Set.insert(B->getTerminator());
125 // Follow the use-def chains to form a transitive closure of all the
126 // instructions that the originally seeded instructions depend on.
127 SmallVector<Instruction *, 8> Worklist(Set.begin(), Set.end());
128 while (!Worklist.empty()) {
129 Instruction *I = Worklist.pop_back_val();
130 // Insert instructions from the loop that we depend on.
131 for (Value *V : I->operand_values()) {
132 auto *I = dyn_cast<Instruction>(V);
133 if (I && OrigLoop->contains(I->getParent()) && Set.insert(I).second)
134 Worklist.push_back(I);
139 /// \brief Clones the original loop.
141 /// Updates LoopInfo and DominatorTree using the information that block \p
142 /// LoopDomBB dominates the loop.
143 Loop *cloneLoopWithPreheader(BasicBlock *InsertBefore, BasicBlock *LoopDomBB,
144 unsigned Index, LoopInfo *LI,
146 ClonedLoop = ::cloneLoopWithPreheader(InsertBefore, LoopDomBB, OrigLoop,
147 VMap, Twine(".ldist") + Twine(Index),
148 LI, DT, ClonedLoopBlocks);
152 /// \brief The cloned loop. If this partition is mapped to the original loop,
154 const Loop *getClonedLoop() const { return ClonedLoop; }
156 /// \brief Returns the loop where this partition ends up after distribution.
157 /// If this partition is mapped to the original loop then use the block from
159 const Loop *getDistributedLoop() const {
160 return ClonedLoop ? ClonedLoop : OrigLoop;
163 /// \brief The VMap that is populated by cloning and then used in
164 /// remapinstruction to remap the cloned instructions.
165 ValueToValueMapTy &getVMap() { return VMap; }
167 /// \brief Remaps the cloned instructions using VMap.
168 void remapInstructions() {
169 remapInstructionsInBlocks(ClonedLoopBlocks, VMap);
172 /// \brief Based on the set of instructions selected for this partition,
173 /// removes the unnecessary ones.
174 void removeUnusedInsts() {
175 SmallVector<Instruction *, 8> Unused;
177 for (auto *Block : OrigLoop->getBlocks())
178 for (auto &Inst : *Block)
179 if (!Set.count(&Inst)) {
180 Instruction *NewInst = &Inst;
182 NewInst = cast<Instruction>(VMap[NewInst]);
184 assert(!isa<BranchInst>(NewInst) &&
185 "Branches are marked used early on");
186 Unused.push_back(NewInst);
189 // Delete the instructions backwards, as it has a reduced likelihood of
190 // having to update as many def-use and use-def chains.
191 for (auto *Inst : reverse(Unused)) {
192 if (!Inst->use_empty())
193 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
194 Inst->eraseFromParent();
200 dbgs() << " (cycle)\n";
202 // Prefix with the block name.
203 dbgs() << " " << I->getParent()->getName() << ":" << *I << "\n";
206 void printBlocks() const {
207 for (auto *BB : getDistributedLoop()->getBlocks())
212 /// \brief Instructions from OrigLoop selected for this partition.
215 /// \brief Whether this partition contains a dependence cycle.
218 /// \brief The original loop.
221 /// \brief The cloned loop. If this partition is mapped to the original loop,
225 /// \brief The blocks of ClonedLoop including the preheader. If this
226 /// partition is mapped to the original loop, this is empty.
227 SmallVector<BasicBlock *, 8> ClonedLoopBlocks;
229 /// \brief These gets populated once the set of instructions have been
230 /// finalized. If this partition is mapped to the original loop, these are not
232 ValueToValueMapTy VMap;
235 /// \brief Holds the set of Partitions. It populates them, merges them and then
236 /// clones the loops.
237 class InstPartitionContainer {
238 typedef DenseMap<Instruction *, int> InstToPartitionIdT;
241 InstPartitionContainer(Loop *L, LoopInfo *LI, DominatorTree *DT)
242 : L(L), LI(LI), DT(DT) {}
244 /// \brief Returns the number of partitions.
245 unsigned getSize() const { return PartitionContainer.size(); }
247 /// \brief Adds \p Inst into the current partition if that is marked to
248 /// contain cycles. Otherwise start a new partition for it.
249 void addToCyclicPartition(Instruction *Inst) {
250 // If the current partition is non-cyclic. Start a new one.
251 if (PartitionContainer.empty() || !PartitionContainer.back().hasDepCycle())
252 PartitionContainer.emplace_back(Inst, L, /*DepCycle=*/true);
254 PartitionContainer.back().add(Inst);
257 /// \brief Adds \p Inst into a partition that is not marked to contain
258 /// dependence cycles.
260 // Initially we isolate memory instructions into as many partitions as
261 // possible, then later we may merge them back together.
262 void addToNewNonCyclicPartition(Instruction *Inst) {
263 PartitionContainer.emplace_back(Inst, L);
266 /// \brief Merges adjacent non-cyclic partitions.
268 /// The idea is that we currently only want to isolate the non-vectorizable
269 /// partition. We could later allow more distribution among these partition
271 void mergeAdjacentNonCyclic() {
272 mergeAdjacentPartitionsIf(
273 [](const InstPartition *P) { return !P->hasDepCycle(); });
276 /// \brief If a partition contains only conditional stores, we won't vectorize
277 /// it. Try to merge it with a previous cyclic partition.
278 void mergeNonIfConvertible() {
279 mergeAdjacentPartitionsIf([&](const InstPartition *Partition) {
280 if (Partition->hasDepCycle())
283 // Now, check if all stores are conditional in this partition.
284 bool seenStore = false;
286 for (auto *Inst : *Partition)
287 if (isa<StoreInst>(Inst)) {
289 if (!LoopAccessInfo::blockNeedsPredication(Inst->getParent(), L, DT))
296 /// \brief Merges the partitions according to various heuristics.
297 void mergeBeforePopulating() {
298 mergeAdjacentNonCyclic();
299 if (!DistributeNonIfConvertible)
300 mergeNonIfConvertible();
303 /// \brief Merges partitions in order to ensure that no loads are duplicated.
305 /// We can't duplicate loads because that could potentially reorder them.
306 /// LoopAccessAnalysis provides dependency information with the context that
307 /// the order of memory operation is preserved.
309 /// Return if any partitions were merged.
310 bool mergeToAvoidDuplicatedLoads() {
311 typedef DenseMap<Instruction *, InstPartition *> LoadToPartitionT;
312 typedef EquivalenceClasses<InstPartition *> ToBeMergedT;
314 LoadToPartitionT LoadToPartition;
315 ToBeMergedT ToBeMerged;
317 // Step through the partitions and create equivalence between partitions
318 // that contain the same load. Also put partitions in between them in the
319 // same equivalence class to avoid reordering of memory operations.
320 for (PartitionContainerT::iterator I = PartitionContainer.begin(),
321 E = PartitionContainer.end();
325 // If a load occurs in two partitions PartI and PartJ, merge all
326 // partitions (PartI, PartJ] into PartI.
327 for (Instruction *Inst : *PartI)
328 if (isa<LoadInst>(Inst)) {
330 LoadToPartitionT::iterator LoadToPart;
332 std::tie(LoadToPart, NewElt) =
333 LoadToPartition.insert(std::make_pair(Inst, PartI));
335 DEBUG(dbgs() << "Merging partitions due to this load in multiple "
336 << "partitions: " << PartI << ", "
337 << LoadToPart->second << "\n" << *Inst << "\n");
342 ToBeMerged.unionSets(PartI, &*PartJ);
343 } while (&*PartJ != LoadToPart->second);
347 if (ToBeMerged.empty())
350 // Merge the member of an equivalence class into its class leader. This
351 // makes the members empty.
352 for (ToBeMergedT::iterator I = ToBeMerged.begin(), E = ToBeMerged.end();
357 auto PartI = I->getData();
358 for (auto PartJ : make_range(std::next(ToBeMerged.member_begin(I)),
359 ToBeMerged.member_end())) {
360 PartJ->moveTo(*PartI);
364 // Remove the empty partitions.
365 PartitionContainer.remove_if(
366 [](const InstPartition &P) { return P.empty(); });
371 /// \brief Sets up the mapping between instructions to partitions. If the
372 /// instruction is duplicated across multiple partitions, set the entry to -1.
373 void setupPartitionIdOnInstructions() {
375 for (const auto &Partition : PartitionContainer) {
376 for (Instruction *Inst : Partition) {
378 InstToPartitionIdT::iterator Iter;
380 std::tie(Iter, NewElt) =
381 InstToPartitionId.insert(std::make_pair(Inst, PartitionID));
389 /// \brief Populates the partition with everything that the seeding
390 /// instructions require.
391 void populateUsedSet() {
392 for (auto &P : PartitionContainer)
396 /// \brief This performs the main chunk of the work of cloning the loops for
399 BasicBlock *OrigPH = L->getLoopPreheader();
400 // At this point the predecessor of the preheader is either the memcheck
401 // block or the top part of the original preheader.
402 BasicBlock *Pred = OrigPH->getSinglePredecessor();
403 assert(Pred && "Preheader does not have a single predecessor");
404 BasicBlock *ExitBlock = L->getExitBlock();
405 assert(ExitBlock && "No single exit block");
408 assert(!PartitionContainer.empty() && "at least two partitions expected");
409 // We're cloning the preheader along with the loop so we already made sure
411 assert(&*OrigPH->begin() == OrigPH->getTerminator() &&
412 "preheader not empty");
414 // Create a loop for each partition except the last. Clone the original
415 // loop before PH along with adding a preheader for the cloned loop. Then
416 // update PH to point to the newly added preheader.
417 BasicBlock *TopPH = OrigPH;
418 unsigned Index = getSize() - 1;
419 for (auto I = std::next(PartitionContainer.rbegin()),
420 E = PartitionContainer.rend();
421 I != E; ++I, --Index, TopPH = NewLoop->getLoopPreheader()) {
424 NewLoop = Part->cloneLoopWithPreheader(TopPH, Pred, Index, LI, DT);
426 Part->getVMap()[ExitBlock] = TopPH;
427 Part->remapInstructions();
429 Pred->getTerminator()->replaceUsesOfWith(OrigPH, TopPH);
431 // Now go in forward order and update the immediate dominator for the
432 // preheaders with the exiting block of the previous loop. Dominance
433 // within the loop is updated in cloneLoopWithPreheader.
434 for (auto Curr = PartitionContainer.cbegin(),
435 Next = std::next(PartitionContainer.cbegin()),
436 E = PartitionContainer.cend();
437 Next != E; ++Curr, ++Next)
438 DT->changeImmediateDominator(
439 Next->getDistributedLoop()->getLoopPreheader(),
440 Curr->getDistributedLoop()->getExitingBlock());
443 /// \brief Removes the dead instructions from the cloned loops.
444 void removeUnusedInsts() {
445 for (auto &Partition : PartitionContainer)
446 Partition.removeUnusedInsts();
449 /// \brief For each memory pointer, it computes the partitionId the pointer is
452 /// This returns an array of int where the I-th entry corresponds to I-th
453 /// entry in LAI.getRuntimePointerCheck(). If the pointer is used in multiple
454 /// partitions its entry is set to -1.
456 computePartitionSetForPointers(const LoopAccessInfo &LAI) {
457 const RuntimePointerChecking *RtPtrCheck = LAI.getRuntimePointerChecking();
459 unsigned N = RtPtrCheck->Pointers.size();
460 SmallVector<int, 8> PtrToPartitions(N);
461 for (unsigned I = 0; I < N; ++I) {
462 Value *Ptr = RtPtrCheck->Pointers[I].PointerValue;
464 LAI.getInstructionsForAccess(Ptr, RtPtrCheck->Pointers[I].IsWritePtr);
466 int &Partition = PtrToPartitions[I];
467 // First set it to uninitialized.
469 for (Instruction *Inst : Instructions) {
470 // Note that this could be -1 if Inst is duplicated across multiple
472 int ThisPartition = this->InstToPartitionId[Inst];
474 Partition = ThisPartition;
475 // -1 means belonging to multiple partitions.
476 else if (Partition == -1)
478 else if (Partition != (int)ThisPartition)
481 assert(Partition != -2 && "Pointer not belonging to any partition");
484 return PtrToPartitions;
487 void print(raw_ostream &OS) const {
489 for (const auto &P : PartitionContainer) {
490 OS << "Partition " << Index++ << " (" << &P << "):\n";
495 void dump() const { print(dbgs()); }
498 friend raw_ostream &operator<<(raw_ostream &OS,
499 const InstPartitionContainer &Partitions) {
500 Partitions.print(OS);
505 void printBlocks() const {
507 for (const auto &P : PartitionContainer) {
508 dbgs() << "\nPartition " << Index++ << " (" << &P << "):\n";
514 typedef std::list<InstPartition> PartitionContainerT;
516 /// \brief List of partitions.
517 PartitionContainerT PartitionContainer;
519 /// \brief Mapping from Instruction to partition Id. If the instruction
520 /// belongs to multiple partitions the entry contains -1.
521 InstToPartitionIdT InstToPartitionId;
527 /// \brief The control structure to merge adjacent partitions if both satisfy
528 /// the \p Predicate.
529 template <class UnaryPredicate>
530 void mergeAdjacentPartitionsIf(UnaryPredicate Predicate) {
531 InstPartition *PrevMatch = nullptr;
532 for (auto I = PartitionContainer.begin(); I != PartitionContainer.end();) {
533 auto DoesMatch = Predicate(&*I);
534 if (PrevMatch == nullptr && DoesMatch) {
537 } else if (PrevMatch != nullptr && DoesMatch) {
538 I->moveTo(*PrevMatch);
539 I = PartitionContainer.erase(I);
548 /// \brief For each memory instruction, this class maintains difference of the
549 /// number of unsafe dependences that start out from this instruction minus
550 /// those that end here.
552 /// By traversing the memory instructions in program order and accumulating this
553 /// number, we know whether any unsafe dependence crosses over a program point.
554 class MemoryInstructionDependences {
555 typedef MemoryDepChecker::Dependence Dependence;
560 unsigned NumUnsafeDependencesStartOrEnd;
562 Entry(Instruction *Inst) : Inst(Inst), NumUnsafeDependencesStartOrEnd(0) {}
565 typedef SmallVector<Entry, 8> AccessesType;
567 AccessesType::const_iterator begin() const { return Accesses.begin(); }
568 AccessesType::const_iterator end() const { return Accesses.end(); }
570 MemoryInstructionDependences(
571 const SmallVectorImpl<Instruction *> &Instructions,
572 const SmallVectorImpl<Dependence> &Dependences) {
573 Accesses.append(Instructions.begin(), Instructions.end());
575 DEBUG(dbgs() << "Backward dependences:\n");
576 for (auto &Dep : Dependences)
577 if (Dep.isPossiblyBackward()) {
578 // Note that the designations source and destination follow the program
579 // order, i.e. source is always first. (The direction is given by the
581 ++Accesses[Dep.Source].NumUnsafeDependencesStartOrEnd;
582 --Accesses[Dep.Destination].NumUnsafeDependencesStartOrEnd;
584 DEBUG(Dep.print(dbgs(), 2, Instructions));
589 AccessesType Accesses;
592 /// \brief The actual class performing the per-loop work.
593 class LoopDistributeForLoop {
595 LoopDistributeForLoop(Loop *L, Function *F, LoopInfo *LI, DominatorTree *DT,
596 ScalarEvolution *SE, OptimizationRemarkEmitter *ORE)
597 : L(L), F(F), LI(LI), LAI(nullptr), DT(DT), SE(SE), ORE(ORE) {
601 /// \brief Try to distribute an inner-most loop.
602 bool processLoop(std::function<const LoopAccessInfo &(Loop &)> &GetLAA) {
603 assert(L->empty() && "Only process inner loops.");
605 DEBUG(dbgs() << "\nLDist: In \"" << L->getHeader()->getParent()->getName()
606 << "\" checking " << *L << "\n");
608 if (!L->getExitBlock())
609 return fail("MultipleExitBlocks", "multiple exit blocks");
610 if (!L->isLoopSimplifyForm())
611 return fail("NotLoopSimplifyForm",
612 "loop is not in loop-simplify form");
614 BasicBlock *PH = L->getLoopPreheader();
616 // LAA will check that we only have a single exiting block.
619 // Currently, we only distribute to isolate the part of the loop with
620 // dependence cycles to enable partial vectorization.
621 if (LAI->canVectorizeMemory())
622 return fail("MemOpsCanBeVectorized",
623 "memory operations are safe for vectorization");
625 auto *Dependences = LAI->getDepChecker().getDependences();
626 if (!Dependences || Dependences->empty())
627 return fail("NoUnsafeDeps", "no unsafe dependences to isolate");
629 InstPartitionContainer Partitions(L, LI, DT);
631 // First, go through each memory operation and assign them to consecutive
632 // partitions (the order of partitions follows program order). Put those
633 // with unsafe dependences into "cyclic" partition otherwise put each store
634 // in its own "non-cyclic" partition (we'll merge these later).
636 // Note that a memory operation (e.g. Load2 below) at a program point that
637 // has an unsafe dependence (Store3->Load1) spanning over it must be
638 // included in the same cyclic partition as the dependent operations. This
639 // is to preserve the original program order after distribution. E.g.:
641 // NumUnsafeDependencesStartOrEnd NumUnsafeDependencesActive
643 // Load2 | /Unsafe/ 0 1
647 // NumUnsafeDependencesActive > 0 indicates this situation and in this case
648 // we just keep assigning to the same cyclic partition until
649 // NumUnsafeDependencesActive reaches 0.
650 const MemoryDepChecker &DepChecker = LAI->getDepChecker();
651 MemoryInstructionDependences MID(DepChecker.getMemoryInstructions(),
654 int NumUnsafeDependencesActive = 0;
655 for (auto &InstDep : MID) {
656 Instruction *I = InstDep.Inst;
657 // We update NumUnsafeDependencesActive post-instruction, catch the
658 // start of a dependence directly via NumUnsafeDependencesStartOrEnd.
659 if (NumUnsafeDependencesActive ||
660 InstDep.NumUnsafeDependencesStartOrEnd > 0)
661 Partitions.addToCyclicPartition(I);
663 Partitions.addToNewNonCyclicPartition(I);
664 NumUnsafeDependencesActive += InstDep.NumUnsafeDependencesStartOrEnd;
665 assert(NumUnsafeDependencesActive >= 0 &&
666 "Negative number of dependences active");
669 // Add partitions for values used outside. These partitions can be out of
670 // order from the original program order. This is OK because if the
671 // partition uses a load we will merge this partition with the original
672 // partition of the load that we set up in the previous loop (see
673 // mergeToAvoidDuplicatedLoads).
674 auto DefsUsedOutside = findDefsUsedOutsideOfLoop(L);
675 for (auto *Inst : DefsUsedOutside)
676 Partitions.addToNewNonCyclicPartition(Inst);
678 DEBUG(dbgs() << "Seeded partitions:\n" << Partitions);
679 if (Partitions.getSize() < 2)
680 return fail("CantIsolateUnsafeDeps",
681 "cannot isolate unsafe dependencies");
683 // Run the merge heuristics: Merge non-cyclic adjacent partitions since we
684 // should be able to vectorize these together.
685 Partitions.mergeBeforePopulating();
686 DEBUG(dbgs() << "\nMerged partitions:\n" << Partitions);
687 if (Partitions.getSize() < 2)
688 return fail("CantIsolateUnsafeDeps",
689 "cannot isolate unsafe dependencies");
691 // Now, populate the partitions with non-memory operations.
692 Partitions.populateUsedSet();
693 DEBUG(dbgs() << "\nPopulated partitions:\n" << Partitions);
695 // In order to preserve original lexical order for loads, keep them in the
696 // partition that we set up in the MemoryInstructionDependences loop.
697 if (Partitions.mergeToAvoidDuplicatedLoads()) {
698 DEBUG(dbgs() << "\nPartitions merged to ensure unique loads:\n"
700 if (Partitions.getSize() < 2)
701 return fail("CantIsolateUnsafeDeps",
702 "cannot isolate unsafe dependencies");
705 // Don't distribute the loop if we need too many SCEV run-time checks.
706 const SCEVUnionPredicate &Pred = LAI->getPSE().getUnionPredicate();
707 if (Pred.getComplexity() > (IsForced.getValueOr(false)
708 ? PragmaDistributeSCEVCheckThreshold
709 : DistributeSCEVCheckThreshold))
710 return fail("TooManySCEVRuntimeChecks",
711 "too many SCEV run-time checks needed.\n");
713 DEBUG(dbgs() << "\nDistributing loop: " << *L << "\n");
714 // We're done forming the partitions set up the reverse mapping from
715 // instructions to partitions.
716 Partitions.setupPartitionIdOnInstructions();
718 // To keep things simple have an empty preheader before we version or clone
719 // the loop. (Also split if this has no predecessor, i.e. entry, because we
720 // rely on PH having a predecessor.)
721 if (!PH->getSinglePredecessor() || &*PH->begin() != PH->getTerminator())
722 SplitBlock(PH, PH->getTerminator(), DT, LI);
724 // If we need run-time checks, version the loop now.
725 auto PtrToPartition = Partitions.computePartitionSetForPointers(*LAI);
726 const auto *RtPtrChecking = LAI->getRuntimePointerChecking();
727 const auto &AllChecks = RtPtrChecking->getChecks();
728 auto Checks = includeOnlyCrossPartitionChecks(AllChecks, PtrToPartition,
731 if (!Pred.isAlwaysTrue() || !Checks.empty()) {
732 DEBUG(dbgs() << "\nPointers:\n");
733 DEBUG(LAI->getRuntimePointerChecking()->printChecks(dbgs(), Checks));
734 LoopVersioning LVer(*LAI, L, LI, DT, SE, false);
735 LVer.setAliasChecks(std::move(Checks));
736 LVer.setSCEVChecks(LAI->getPSE().getUnionPredicate());
737 LVer.versionLoop(DefsUsedOutside);
738 LVer.annotateLoopWithNoAlias();
741 // Create identical copies of the original loop for each partition and hook
742 // them up sequentially.
743 Partitions.cloneLoops();
745 // Now, we remove the instruction from each loop that don't belong to that
747 Partitions.removeUnusedInsts();
748 DEBUG(dbgs() << "\nAfter removing unused Instrs:\n");
749 DEBUG(Partitions.printBlocks());
756 ++NumLoopsDistributed;
757 // Report the success.
758 ORE->emit(OptimizationRemark(LDIST_NAME, "Distribute", L->getStartLoc(),
760 << "distributed loop");
764 /// \brief Provide diagnostics then \return with false.
765 bool fail(StringRef RemarkName, StringRef Message) {
766 LLVMContext &Ctx = F->getContext();
767 bool Forced = isForced().getValueOr(false);
769 DEBUG(dbgs() << "Skipping; " << Message << "\n");
771 // With Rpass-missed report that distribution failed.
773 OptimizationRemarkMissed(LDIST_NAME, "NotDistributed", L->getStartLoc(),
775 << "loop not distributed: use -Rpass-analysis=loop-distribute for more "
778 // With Rpass-analysis report why. This is on by default if distribution
779 // was requested explicitly.
780 ORE->emit(OptimizationRemarkAnalysis(
781 Forced ? OptimizationRemarkAnalysis::AlwaysPrint : LDIST_NAME,
782 RemarkName, L->getStartLoc(), L->getHeader())
783 << "loop not distributed: " << Message);
785 // Also issue a warning if distribution was requested explicitly but it
788 Ctx.diagnose(DiagnosticInfoOptimizationFailure(
789 *F, L->getStartLoc(), "loop not distributed: failed "
790 "explicitly specified loop distribution"));
795 /// \brief Return if distribution forced to be enabled/disabled for the loop.
797 /// If the optional has a value, it indicates whether distribution was forced
798 /// to be enabled (true) or disabled (false). If the optional has no value
799 /// distribution was not forced either way.
800 const Optional<bool> &isForced() const { return IsForced; }
803 /// \brief Filter out checks between pointers from the same partition.
805 /// \p PtrToPartition contains the partition number for pointers. Partition
806 /// number -1 means that the pointer is used in multiple partitions. In this
807 /// case we can't safely omit the check.
808 SmallVector<RuntimePointerChecking::PointerCheck, 4>
809 includeOnlyCrossPartitionChecks(
810 const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &AllChecks,
811 const SmallVectorImpl<int> &PtrToPartition,
812 const RuntimePointerChecking *RtPtrChecking) {
813 SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks;
815 copy_if(AllChecks, std::back_inserter(Checks),
816 [&](const RuntimePointerChecking::PointerCheck &Check) {
817 for (unsigned PtrIdx1 : Check.first->Members)
818 for (unsigned PtrIdx2 : Check.second->Members)
819 // Only include this check if there is a pair of pointers
820 // that require checking and the pointers fall into
821 // separate partitions.
823 // (Note that we already know at this point that the two
824 // pointer groups need checking but it doesn't follow
825 // that each pair of pointers within the two groups need
828 // In other words we don't want to include a check just
829 // because there is a pair of pointers between the two
830 // pointer groups that require checks and a different
831 // pair whose pointers fall into different partitions.)
832 if (RtPtrChecking->needsChecking(PtrIdx1, PtrIdx2) &&
833 !RuntimePointerChecking::arePointersInSamePartition(
834 PtrToPartition, PtrIdx1, PtrIdx2))
842 /// \brief Check whether the loop metadata is forcing distribution to be
843 /// enabled/disabled.
845 Optional<const MDOperand *> Value =
846 findStringMetadataForLoop(L, "llvm.loop.distribute.enable");
850 const MDOperand *Op = *Value;
851 assert(Op && mdconst::hasa<ConstantInt>(*Op) && "invalid metadata");
852 IsForced = mdconst::extract<ConstantInt>(*Op)->getZExtValue();
860 const LoopAccessInfo *LAI;
863 OptimizationRemarkEmitter *ORE;
865 /// \brief Indicates whether distribution is forced to be enabled/disabled for
868 /// If the optional has a value, it indicates whether distribution was forced
869 /// to be enabled (true) or disabled (false). If the optional has no value
870 /// distribution was not forced either way.
871 Optional<bool> IsForced;
874 /// Shared implementation between new and old PMs.
875 static bool runImpl(Function &F, LoopInfo *LI, DominatorTree *DT,
876 ScalarEvolution *SE, OptimizationRemarkEmitter *ORE,
877 std::function<const LoopAccessInfo &(Loop &)> &GetLAA) {
878 // Build up a worklist of inner-loops to vectorize. This is necessary as the
879 // act of distributing a loop creates new loops and can invalidate iterators
881 SmallVector<Loop *, 8> Worklist;
883 for (Loop *TopLevelLoop : *LI)
884 for (Loop *L : depth_first(TopLevelLoop))
885 // We only handle inner-most loops.
887 Worklist.push_back(L);
889 // Now walk the identified inner loops.
890 bool Changed = false;
891 for (Loop *L : Worklist) {
892 LoopDistributeForLoop LDL(L, &F, LI, DT, SE, ORE);
894 // If distribution was forced for the specific loop to be
895 // enabled/disabled, follow that. Otherwise use the global flag.
896 if (LDL.isForced().getValueOr(EnableLoopDistribute))
897 Changed |= LDL.processLoop(GetLAA);
900 // Process each loop nest in the function.
904 /// \brief The pass class.
905 class LoopDistributeLegacy : public FunctionPass {
907 LoopDistributeLegacy() : FunctionPass(ID) {
908 // The default is set by the caller.
909 initializeLoopDistributeLegacyPass(*PassRegistry::getPassRegistry());
912 bool runOnFunction(Function &F) override {
916 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
917 auto *LAA = &getAnalysis<LoopAccessLegacyAnalysis>();
918 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
919 auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
920 auto *ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
921 std::function<const LoopAccessInfo &(Loop &)> GetLAA =
922 [&](Loop &L) -> const LoopAccessInfo & { return LAA->getInfo(&L); };
924 return runImpl(F, LI, DT, SE, ORE, GetLAA);
927 void getAnalysisUsage(AnalysisUsage &AU) const override {
928 AU.addRequired<ScalarEvolutionWrapperPass>();
929 AU.addRequired<LoopInfoWrapperPass>();
930 AU.addPreserved<LoopInfoWrapperPass>();
931 AU.addRequired<LoopAccessLegacyAnalysis>();
932 AU.addRequired<DominatorTreeWrapperPass>();
933 AU.addPreserved<DominatorTreeWrapperPass>();
934 AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
935 AU.addPreserved<GlobalsAAWrapperPass>();
940 } // anonymous namespace
942 PreservedAnalyses LoopDistributePass::run(Function &F,
943 FunctionAnalysisManager &AM) {
944 auto &LI = AM.getResult<LoopAnalysis>(F);
945 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
946 auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
947 auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
949 // We don't directly need these analyses but they're required for loop
950 // analyses so provide them below.
951 auto &AA = AM.getResult<AAManager>(F);
952 auto &AC = AM.getResult<AssumptionAnalysis>(F);
953 auto &TTI = AM.getResult<TargetIRAnalysis>(F);
954 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
956 auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
957 std::function<const LoopAccessInfo &(Loop &)> GetLAA =
958 [&](Loop &L) -> const LoopAccessInfo & {
959 LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI};
960 return LAM.getResult<LoopAccessAnalysis>(L, AR);
963 bool Changed = runImpl(F, &LI, &DT, &SE, &ORE, GetLAA);
965 return PreservedAnalyses::all();
966 PreservedAnalyses PA;
967 PA.preserve<LoopAnalysis>();
968 PA.preserve<DominatorTreeAnalysis>();
969 PA.preserve<GlobalsAA>();
973 char LoopDistributeLegacy::ID;
974 static const char ldist_name[] = "Loop Distribution";
976 INITIALIZE_PASS_BEGIN(LoopDistributeLegacy, LDIST_NAME, ldist_name, false,
978 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
979 INITIALIZE_PASS_DEPENDENCY(LoopAccessLegacyAnalysis)
980 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
981 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
982 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
983 INITIALIZE_PASS_END(LoopDistributeLegacy, LDIST_NAME, ldist_name, false, false)
986 FunctionPass *createLoopDistributePass() { return new LoopDistributeLegacy(); }