1 //===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// This file defines ObjC ARC optimizations. ARC stands for Automatic
11 /// Reference Counting and is a system for managing reference counts for objects
14 /// The optimizations performed include elimination of redundant, partially
15 /// redundant, and inconsequential reference count operations, elimination of
16 /// redundant weak pointer operations, and numerous minor simplifications.
18 /// WARNING: This file knows about certain library functions. It recognizes them
19 /// by name, and hardwires knowledge of their semantics.
21 /// WARNING: This file knows about how certain Objective-C library functions are
22 /// used. Naive LLVM IR transformations which would otherwise be
23 /// behavior-preserving may break these assumptions.
25 //===----------------------------------------------------------------------===//
28 #include "ARCRuntimeEntryPoints.h"
29 #include "DependencyAnalysis.h"
30 #include "ObjCARCAliasAnalysis.h"
31 #include "ProvenanceAnalysis.h"
32 #include "llvm/ADT/DenseMap.h"
33 #include "llvm/ADT/DenseSet.h"
34 #include "llvm/ADT/STLExtras.h"
35 #include "llvm/ADT/SmallPtrSet.h"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/IR/CFG.h"
38 #include "llvm/IR/IRBuilder.h"
39 #include "llvm/IR/LLVMContext.h"
40 #include "llvm/Support/Debug.h"
41 #include "llvm/Support/raw_ostream.h"
44 using namespace llvm::objcarc;
46 #define DEBUG_TYPE "objc-arc-opts"
48 /// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
52 /// \brief An associative container with fast insertion-order (deterministic)
53 /// iteration over its elements. Plus the special blot operation.
54 template<class KeyT, class ValueT>
56 /// Map keys to indices in Vector.
57 typedef DenseMap<KeyT, size_t> MapTy;
60 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
65 typedef typename VectorTy::iterator iterator;
66 typedef typename VectorTy::const_iterator const_iterator;
67 iterator begin() { return Vector.begin(); }
68 iterator end() { return Vector.end(); }
69 const_iterator begin() const { return Vector.begin(); }
70 const_iterator end() const { return Vector.end(); }
74 assert(Vector.size() >= Map.size()); // May differ due to blotting.
75 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
77 assert(I->second < Vector.size());
78 assert(Vector[I->second].first == I->first);
80 for (typename VectorTy::const_iterator I = Vector.begin(),
81 E = Vector.end(); I != E; ++I)
83 (Map.count(I->first) &&
84 Map[I->first] == size_t(I - Vector.begin())));
88 ValueT &operator[](const KeyT &Arg) {
89 std::pair<typename MapTy::iterator, bool> Pair =
90 Map.insert(std::make_pair(Arg, size_t(0)));
92 size_t Num = Vector.size();
93 Pair.first->second = Num;
94 Vector.push_back(std::make_pair(Arg, ValueT()));
95 return Vector[Num].second;
97 return Vector[Pair.first->second].second;
100 std::pair<iterator, bool>
101 insert(const std::pair<KeyT, ValueT> &InsertPair) {
102 std::pair<typename MapTy::iterator, bool> Pair =
103 Map.insert(std::make_pair(InsertPair.first, size_t(0)));
105 size_t Num = Vector.size();
106 Pair.first->second = Num;
107 Vector.push_back(InsertPair);
108 return std::make_pair(Vector.begin() + Num, true);
110 return std::make_pair(Vector.begin() + Pair.first->second, false);
113 iterator find(const KeyT &Key) {
114 typename MapTy::iterator It = Map.find(Key);
115 if (It == Map.end()) return Vector.end();
116 return Vector.begin() + It->second;
119 const_iterator find(const KeyT &Key) const {
120 typename MapTy::const_iterator It = Map.find(Key);
121 if (It == Map.end()) return Vector.end();
122 return Vector.begin() + It->second;
125 /// This is similar to erase, but instead of removing the element from the
126 /// vector, it just zeros out the key in the vector. This leaves iterators
127 /// intact, but clients must be prepared for zeroed-out keys when iterating.
128 void blot(const KeyT &Key) {
129 typename MapTy::iterator It = Map.find(Key);
130 if (It == Map.end()) return;
131 Vector[It->second].first = KeyT();
144 /// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
147 /// \brief This is similar to GetRCIdentityRoot but it stops as soon
148 /// as it finds a value with multiple uses.
149 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
150 if (Arg->hasOneUse()) {
151 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
152 return FindSingleUseIdentifiedObject(BC->getOperand(0));
153 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
154 if (GEP->hasAllZeroIndices())
155 return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
156 if (IsForwarding(GetBasicInstructionClass(Arg)))
157 return FindSingleUseIdentifiedObject(
158 cast<CallInst>(Arg)->getArgOperand(0));
159 if (!IsObjCIdentifiedObject(Arg))
164 // If we found an identifiable object but it has multiple uses, but they are
165 // trivial uses, we can still consider this to be a single-use value.
166 if (IsObjCIdentifiedObject(Arg)) {
167 for (const User *U : Arg->users())
168 if (!U->use_empty() || GetRCIdentityRoot(U) != Arg)
177 /// This is a wrapper around getUnderlyingObjCPtr along the lines of
178 /// GetUnderlyingObjects except that it returns early when it sees the first
180 static inline bool AreAnyUnderlyingObjectsAnAlloca(const Value *V) {
181 SmallPtrSet<const Value *, 4> Visited;
182 SmallVector<const Value *, 4> Worklist;
183 Worklist.push_back(V);
185 const Value *P = Worklist.pop_back_val();
186 P = GetUnderlyingObjCPtr(P);
188 if (isa<AllocaInst>(P))
191 if (!Visited.insert(P).second)
194 if (const SelectInst *SI = dyn_cast<const SelectInst>(P)) {
195 Worklist.push_back(SI->getTrueValue());
196 Worklist.push_back(SI->getFalseValue());
200 if (const PHINode *PN = dyn_cast<const PHINode>(P)) {
201 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
202 Worklist.push_back(PN->getIncomingValue(i));
205 } while (!Worklist.empty());
213 /// \defgroup ARCOpt ARC Optimization.
216 // TODO: On code like this:
219 // stuff_that_cannot_release()
220 // objc_autorelease(%x)
221 // stuff_that_cannot_release()
223 // stuff_that_cannot_release()
224 // objc_autorelease(%x)
226 // The second retain and autorelease can be deleted.
228 // TODO: It should be possible to delete
229 // objc_autoreleasePoolPush and objc_autoreleasePoolPop
230 // pairs if nothing is actually autoreleased between them. Also, autorelease
231 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
232 // after inlining) can be turned into plain release calls.
234 // TODO: Critical-edge splitting. If the optimial insertion point is
235 // a critical edge, the current algorithm has to fail, because it doesn't
236 // know how to split edges. It should be possible to make the optimizer
237 // think in terms of edges, rather than blocks, and then split critical
240 // TODO: OptimizeSequences could generalized to be Interprocedural.
242 // TODO: Recognize that a bunch of other objc runtime calls have
243 // non-escaping arguments and non-releasing arguments, and may be
244 // non-autoreleasing.
246 // TODO: Sink autorelease calls as far as possible. Unfortunately we
247 // usually can't sink them past other calls, which would be the main
248 // case where it would be useful.
250 // TODO: The pointer returned from objc_loadWeakRetained is retained.
252 // TODO: Delete release+retain pairs (rare).
254 STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
255 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
256 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
257 STATISTIC(NumRets, "Number of return value forwarding "
258 "retain+autoreleases eliminated");
259 STATISTIC(NumRRs, "Number of retain+release paths eliminated");
260 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
262 STATISTIC(NumRetainsBeforeOpt,
263 "Number of retains before optimization");
264 STATISTIC(NumReleasesBeforeOpt,
265 "Number of releases before optimization");
266 STATISTIC(NumRetainsAfterOpt,
267 "Number of retains after optimization");
268 STATISTIC(NumReleasesAfterOpt,
269 "Number of releases after optimization");
275 /// \brief A sequence of states that a pointer may go through in which an
276 /// objc_retain and objc_release are actually needed.
279 S_Retain, ///< objc_retain(x).
280 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement.
281 S_Use, ///< any use of x.
282 S_Stop, ///< like S_Release, but code motion is stopped.
283 S_Release, ///< objc_release(x).
284 S_MovableRelease ///< objc_release(x), !clang.imprecise_release.
287 raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
288 LLVM_ATTRIBUTE_UNUSED;
289 raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
292 return OS << "S_None";
294 return OS << "S_Retain";
296 return OS << "S_CanRelease";
298 return OS << "S_Use";
300 return OS << "S_Release";
301 case S_MovableRelease:
302 return OS << "S_MovableRelease";
304 return OS << "S_Stop";
306 llvm_unreachable("Unknown sequence type.");
310 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
314 if (A == S_None || B == S_None)
317 if (A > B) std::swap(A, B);
319 // Choose the side which is further along in the sequence.
320 if ((A == S_Retain || A == S_CanRelease) &&
321 (B == S_CanRelease || B == S_Use))
324 // Choose the side which is further along in the sequence.
325 if ((A == S_Use || A == S_CanRelease) &&
326 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
328 // If both sides are releases, choose the more conservative one.
329 if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
331 if (A == S_Release && B == S_MovableRelease)
339 /// \brief Unidirectional information about either a
340 /// retain-decrement-use-release sequence or release-use-decrement-retain
341 /// reverse sequence.
343 /// After an objc_retain, the reference count of the referenced
344 /// object is known to be positive. Similarly, before an objc_release, the
345 /// reference count of the referenced object is known to be positive. If
346 /// there are retain-release pairs in code regions where the retain count
347 /// is known to be positive, they can be eliminated, regardless of any side
348 /// effects between them.
350 /// Also, a retain+release pair nested within another retain+release
351 /// pair all on the known same pointer value can be eliminated, regardless
352 /// of any intervening side effects.
354 /// KnownSafe is true when either of these conditions is satisfied.
357 /// True of the objc_release calls are all marked with the "tail" keyword.
358 bool IsTailCallRelease;
360 /// If the Calls are objc_release calls and they all have a
361 /// clang.imprecise_release tag, this is the metadata tag.
362 MDNode *ReleaseMetadata;
364 /// For a top-down sequence, the set of objc_retains or
365 /// objc_retainBlocks. For bottom-up, the set of objc_releases.
366 SmallPtrSet<Instruction *, 2> Calls;
368 /// The set of optimal insert positions for moving calls in the opposite
370 SmallPtrSet<Instruction *, 2> ReverseInsertPts;
372 /// If this is true, we cannot perform code motion but can still remove
373 /// retain/release pairs.
374 bool CFGHazardAfflicted;
377 KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(nullptr),
378 CFGHazardAfflicted(false) {}
382 /// Conservatively merge the two RRInfo. Returns true if a partial merge has
383 /// occurred, false otherwise.
384 bool Merge(const RRInfo &Other);
389 void RRInfo::clear() {
391 IsTailCallRelease = false;
392 ReleaseMetadata = nullptr;
394 ReverseInsertPts.clear();
395 CFGHazardAfflicted = false;
398 bool RRInfo::Merge(const RRInfo &Other) {
399 // Conservatively merge the ReleaseMetadata information.
400 if (ReleaseMetadata != Other.ReleaseMetadata)
401 ReleaseMetadata = nullptr;
403 // Conservatively merge the boolean state.
404 KnownSafe &= Other.KnownSafe;
405 IsTailCallRelease &= Other.IsTailCallRelease;
406 CFGHazardAfflicted |= Other.CFGHazardAfflicted;
408 // Merge the call sets.
409 Calls.insert(Other.Calls.begin(), Other.Calls.end());
411 // Merge the insert point sets. If there are any differences,
412 // that makes this a partial merge.
413 bool Partial = ReverseInsertPts.size() != Other.ReverseInsertPts.size();
414 for (Instruction *Inst : Other.ReverseInsertPts)
415 Partial |= ReverseInsertPts.insert(Inst).second;
420 /// \brief This class summarizes several per-pointer runtime properties which
421 /// are propogated through the flow graph.
423 /// True if the reference count is known to be incremented.
424 bool KnownPositiveRefCount;
426 /// True if we've seen an opportunity for partial RR elimination, such as
427 /// pushing calls into a CFG triangle or into one side of a CFG diamond.
430 /// The current position in the sequence.
431 unsigned char Seq : 8;
433 /// Unidirectional information about the current sequence.
437 PtrState() : KnownPositiveRefCount(false), Partial(false),
441 bool IsKnownSafe() const {
442 return RRI.KnownSafe;
445 void SetKnownSafe(const bool NewValue) {
446 RRI.KnownSafe = NewValue;
449 bool IsTailCallRelease() const {
450 return RRI.IsTailCallRelease;
453 void SetTailCallRelease(const bool NewValue) {
454 RRI.IsTailCallRelease = NewValue;
457 bool IsTrackingImpreciseReleases() const {
458 return RRI.ReleaseMetadata != nullptr;
461 const MDNode *GetReleaseMetadata() const {
462 return RRI.ReleaseMetadata;
465 void SetReleaseMetadata(MDNode *NewValue) {
466 RRI.ReleaseMetadata = NewValue;
469 bool IsCFGHazardAfflicted() const {
470 return RRI.CFGHazardAfflicted;
473 void SetCFGHazardAfflicted(const bool NewValue) {
474 RRI.CFGHazardAfflicted = NewValue;
477 void SetKnownPositiveRefCount() {
478 DEBUG(dbgs() << "Setting Known Positive.\n");
479 KnownPositiveRefCount = true;
482 void ClearKnownPositiveRefCount() {
483 DEBUG(dbgs() << "Clearing Known Positive.\n");
484 KnownPositiveRefCount = false;
487 bool HasKnownPositiveRefCount() const {
488 return KnownPositiveRefCount;
491 void SetSeq(Sequence NewSeq) {
492 DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
496 Sequence GetSeq() const {
497 return static_cast<Sequence>(Seq);
500 void ClearSequenceProgress() {
501 ResetSequenceProgress(S_None);
504 void ResetSequenceProgress(Sequence NewSeq) {
505 DEBUG(dbgs() << "Resetting sequence progress.\n");
511 void Merge(const PtrState &Other, bool TopDown);
513 void InsertCall(Instruction *I) {
517 void InsertReverseInsertPt(Instruction *I) {
518 RRI.ReverseInsertPts.insert(I);
521 void ClearReverseInsertPts() {
522 RRI.ReverseInsertPts.clear();
525 bool HasReverseInsertPts() const {
526 return !RRI.ReverseInsertPts.empty();
529 const RRInfo &GetRRInfo() const {
536 PtrState::Merge(const PtrState &Other, bool TopDown) {
537 Seq = MergeSeqs(GetSeq(), Other.GetSeq(), TopDown);
538 KnownPositiveRefCount &= Other.KnownPositiveRefCount;
540 // If we're not in a sequence (anymore), drop all associated state.
544 } else if (Partial || Other.Partial) {
545 // If we're doing a merge on a path that's previously seen a partial
546 // merge, conservatively drop the sequence, to avoid doing partial
547 // RR elimination. If the branch predicates for the two merge differ,
548 // mixing them is unsafe.
549 ClearSequenceProgress();
551 // Otherwise merge the other PtrState's RRInfo into our RRInfo. At this
552 // point, we know that currently we are not partial. Stash whether or not
553 // the merge operation caused us to undergo a partial merging of reverse
555 Partial = RRI.Merge(Other.RRI);
560 /// \brief Per-BasicBlock state.
562 /// The number of unique control paths from the entry which can reach this
564 unsigned TopDownPathCount;
566 /// The number of unique control paths to exits from this block.
567 unsigned BottomUpPathCount;
569 /// A type for PerPtrTopDown and PerPtrBottomUp.
570 typedef MapVector<const Value *, PtrState> MapTy;
572 /// The top-down traversal uses this to record information known about a
573 /// pointer at the bottom of each block.
576 /// The bottom-up traversal uses this to record information known about a
577 /// pointer at the top of each block.
578 MapTy PerPtrBottomUp;
580 /// Effective predecessors of the current block ignoring ignorable edges and
581 /// ignored backedges.
582 SmallVector<BasicBlock *, 2> Preds;
583 /// Effective successors of the current block ignoring ignorable edges and
584 /// ignored backedges.
585 SmallVector<BasicBlock *, 2> Succs;
588 static const unsigned OverflowOccurredValue;
590 BBState() : TopDownPathCount(0), BottomUpPathCount(0) { }
592 typedef MapTy::iterator ptr_iterator;
593 typedef MapTy::const_iterator ptr_const_iterator;
595 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
596 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
597 ptr_const_iterator top_down_ptr_begin() const {
598 return PerPtrTopDown.begin();
600 ptr_const_iterator top_down_ptr_end() const {
601 return PerPtrTopDown.end();
604 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
605 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
606 ptr_const_iterator bottom_up_ptr_begin() const {
607 return PerPtrBottomUp.begin();
609 ptr_const_iterator bottom_up_ptr_end() const {
610 return PerPtrBottomUp.end();
613 /// Mark this block as being an entry block, which has one path from the
614 /// entry by definition.
615 void SetAsEntry() { TopDownPathCount = 1; }
617 /// Mark this block as being an exit block, which has one path to an exit by
619 void SetAsExit() { BottomUpPathCount = 1; }
621 /// Attempt to find the PtrState object describing the top down state for
622 /// pointer Arg. Return a new initialized PtrState describing the top down
623 /// state for Arg if we do not find one.
624 PtrState &getPtrTopDownState(const Value *Arg) {
625 return PerPtrTopDown[Arg];
628 /// Attempt to find the PtrState object describing the bottom up state for
629 /// pointer Arg. Return a new initialized PtrState describing the bottom up
630 /// state for Arg if we do not find one.
631 PtrState &getPtrBottomUpState(const Value *Arg) {
632 return PerPtrBottomUp[Arg];
635 /// Attempt to find the PtrState object describing the bottom up state for
637 ptr_iterator findPtrBottomUpState(const Value *Arg) {
638 return PerPtrBottomUp.find(Arg);
641 void clearBottomUpPointers() {
642 PerPtrBottomUp.clear();
645 void clearTopDownPointers() {
646 PerPtrTopDown.clear();
649 void InitFromPred(const BBState &Other);
650 void InitFromSucc(const BBState &Other);
651 void MergePred(const BBState &Other);
652 void MergeSucc(const BBState &Other);
654 /// Compute the number of possible unique paths from an entry to an exit
655 /// which pass through this block. This is only valid after both the
656 /// top-down and bottom-up traversals are complete.
658 /// Returns true if overflow occurred. Returns false if overflow did not
660 bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
661 if (TopDownPathCount == OverflowOccurredValue ||
662 BottomUpPathCount == OverflowOccurredValue)
664 unsigned long long Product =
665 (unsigned long long)TopDownPathCount*BottomUpPathCount;
666 // Overflow occurred if any of the upper bits of Product are set or if all
667 // the lower bits of Product are all set.
668 return (Product >> 32) ||
669 ((PathCount = Product) == OverflowOccurredValue);
672 // Specialized CFG utilities.
673 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
674 edge_iterator pred_begin() const { return Preds.begin(); }
675 edge_iterator pred_end() const { return Preds.end(); }
676 edge_iterator succ_begin() const { return Succs.begin(); }
677 edge_iterator succ_end() const { return Succs.end(); }
679 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
680 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
682 bool isExit() const { return Succs.empty(); }
685 const unsigned BBState::OverflowOccurredValue = 0xffffffff;
688 void BBState::InitFromPred(const BBState &Other) {
689 PerPtrTopDown = Other.PerPtrTopDown;
690 TopDownPathCount = Other.TopDownPathCount;
693 void BBState::InitFromSucc(const BBState &Other) {
694 PerPtrBottomUp = Other.PerPtrBottomUp;
695 BottomUpPathCount = Other.BottomUpPathCount;
698 /// The top-down traversal uses this to merge information about predecessors to
699 /// form the initial state for a new block.
700 void BBState::MergePred(const BBState &Other) {
701 if (TopDownPathCount == OverflowOccurredValue)
704 // Other.TopDownPathCount can be 0, in which case it is either dead or a
705 // loop backedge. Loop backedges are special.
706 TopDownPathCount += Other.TopDownPathCount;
708 // In order to be consistent, we clear the top down pointers when by adding
709 // TopDownPathCount becomes OverflowOccurredValue even though "true" overflow
711 if (TopDownPathCount == OverflowOccurredValue) {
712 clearTopDownPointers();
716 // Check for overflow. If we have overflow, fall back to conservative
718 if (TopDownPathCount < Other.TopDownPathCount) {
719 TopDownPathCount = OverflowOccurredValue;
720 clearTopDownPointers();
724 // For each entry in the other set, if our set has an entry with the same key,
725 // merge the entries. Otherwise, copy the entry and merge it with an empty
727 for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
728 ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
729 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
730 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
734 // For each entry in our set, if the other set doesn't have an entry with the
735 // same key, force it to merge with an empty entry.
736 for (ptr_iterator MI = top_down_ptr_begin(),
737 ME = top_down_ptr_end(); MI != ME; ++MI)
738 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
739 MI->second.Merge(PtrState(), /*TopDown=*/true);
742 /// The bottom-up traversal uses this to merge information about successors to
743 /// form the initial state for a new block.
744 void BBState::MergeSucc(const BBState &Other) {
745 if (BottomUpPathCount == OverflowOccurredValue)
748 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
749 // loop backedge. Loop backedges are special.
750 BottomUpPathCount += Other.BottomUpPathCount;
752 // In order to be consistent, we clear the top down pointers when by adding
753 // BottomUpPathCount becomes OverflowOccurredValue even though "true" overflow
755 if (BottomUpPathCount == OverflowOccurredValue) {
756 clearBottomUpPointers();
760 // Check for overflow. If we have overflow, fall back to conservative
762 if (BottomUpPathCount < Other.BottomUpPathCount) {
763 BottomUpPathCount = OverflowOccurredValue;
764 clearBottomUpPointers();
768 // For each entry in the other set, if our set has an entry with the
769 // same key, merge the entries. Otherwise, copy the entry and merge
770 // it with an empty entry.
771 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
772 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
773 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
774 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
778 // For each entry in our set, if the other set doesn't have an entry
779 // with the same key, force it to merge with an empty entry.
780 for (ptr_iterator MI = bottom_up_ptr_begin(),
781 ME = bottom_up_ptr_end(); MI != ME; ++MI)
782 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
783 MI->second.Merge(PtrState(), /*TopDown=*/false);
786 // Only enable ARC Annotations if we are building a debug version of
789 #define ARC_ANNOTATIONS
792 // Define some macros along the lines of DEBUG and some helper functions to make
793 // it cleaner to create annotations in the source code and to no-op when not
794 // building in debug mode.
795 #ifdef ARC_ANNOTATIONS
797 #include "llvm/Support/CommandLine.h"
799 /// Enable/disable ARC sequence annotations.
801 EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false),
802 cl::desc("Enable emission of arc data flow analysis "
805 DisableCheckForCFGHazards("disable-objc-arc-checkforcfghazards", cl::init(false),
806 cl::desc("Disable check for cfg hazards when "
808 static cl::opt<std::string>
809 ARCAnnotationTargetIdentifier("objc-arc-annotation-target-identifier",
811 cl::desc("filter out all data flow annotations "
812 "but those that apply to the given "
813 "target llvm identifier."));
815 /// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
816 /// instruction so that we can track backwards when post processing via the llvm
817 /// arc annotation processor tool. If the function is an
818 static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
820 MDString *Hash = nullptr;
822 // If pointer is a result of an instruction and it does not have a source
823 // MDNode it, attach a new MDNode onto it. If pointer is a result of
824 // an instruction and does have a source MDNode attached to it, return a
825 // reference to said Node. Otherwise just return 0.
826 if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
828 if (!(Node = Inst->getMetadata(NodeId))) {
829 // We do not have any node. Generate and attatch the hash MDString to the
832 // We just use an MDString to ensure that this metadata gets written out
833 // of line at the module level and to provide a very simple format
834 // encoding the information herein. Both of these makes it simpler to
835 // parse the annotations by a simple external program.
837 raw_string_ostream os(Str);
838 os << "(" << Inst->getParent()->getParent()->getName() << ",%"
839 << Inst->getName() << ")";
841 Hash = MDString::get(Inst->getContext(), os.str());
842 Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
844 // We have a node. Grab its hash and return it.
845 assert(Node->getNumOperands() == 1 &&
846 "An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
847 Hash = cast<MDString>(Node->getOperand(0));
849 } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
851 raw_string_ostream os(str);
852 os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
854 Hash = MDString::get(Arg->getContext(), os.str());
860 static std::string SequenceToString(Sequence A) {
862 raw_string_ostream os(str);
867 /// Helper function to change a Sequence into a String object using our overload
868 /// for raw_ostream so we only have printing code in one location.
869 static MDString *SequenceToMDString(LLVMContext &Context,
871 return MDString::get(Context, SequenceToString(A));
874 /// A simple function to generate a MDNode which describes the change in state
875 /// for Value *Ptr caused by Instruction *Inst.
876 static void AppendMDNodeToInstForPtr(unsigned NodeId,
879 MDString *PtrSourceMDNodeID,
882 MDNode *Node = nullptr;
883 Metadata *tmp[3] = {PtrSourceMDNodeID,
884 SequenceToMDString(Inst->getContext(), OldSeq),
885 SequenceToMDString(Inst->getContext(), NewSeq)};
886 Node = MDNode::get(Inst->getContext(), tmp);
888 Inst->setMetadata(NodeId, Node);
891 /// Add to the beginning of the basic block llvm.ptr.annotations which show the
892 /// state of a pointer at the entrance to a basic block.
893 static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
894 Value *Ptr, Sequence Seq) {
895 // If we have a target identifier, make sure that we match it before
897 if(!ARCAnnotationTargetIdentifier.empty() &&
898 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
901 Module *M = BB->getParent()->getParent();
902 LLVMContext &C = M->getContext();
903 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
904 Type *I8XX = PointerType::getUnqual(I8X);
905 Type *Params[] = {I8XX, I8XX};
906 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C), Params,
908 Constant *Callee = M->getOrInsertFunction(Name, FTy);
910 IRBuilder<> Builder(BB, BB->getFirstInsertionPt());
913 StringRef Tmp = Ptr->getName();
914 if (nullptr == (PtrName = M->getGlobalVariable(Tmp, true))) {
915 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
917 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
918 cast<Constant>(ActualPtrName), Tmp);
922 std::string SeqStr = SequenceToString(Seq);
923 if (nullptr == (S = M->getGlobalVariable(SeqStr, true))) {
924 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
926 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
927 cast<Constant>(ActualPtrName), SeqStr);
930 Builder.CreateCall2(Callee, PtrName, S);
933 /// Add to the end of the basic block llvm.ptr.annotations which show the state
934 /// of the pointer at the bottom of the basic block.
935 static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
936 Value *Ptr, Sequence Seq) {
937 // If we have a target identifier, make sure that we match it before emitting
939 if(!ARCAnnotationTargetIdentifier.empty() &&
940 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
943 Module *M = BB->getParent()->getParent();
944 LLVMContext &C = M->getContext();
945 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
946 Type *I8XX = PointerType::getUnqual(I8X);
947 Type *Params[] = {I8XX, I8XX};
948 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C), Params,
950 Constant *Callee = M->getOrInsertFunction(Name, FTy);
952 IRBuilder<> Builder(BB, std::prev(BB->end()));
955 StringRef Tmp = Ptr->getName();
956 if (nullptr == (PtrName = M->getGlobalVariable(Tmp, true))) {
957 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
959 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
960 cast<Constant>(ActualPtrName), Tmp);
964 std::string SeqStr = SequenceToString(Seq);
965 if (nullptr == (S = M->getGlobalVariable(SeqStr, true))) {
966 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
968 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
969 cast<Constant>(ActualPtrName), SeqStr);
971 Builder.CreateCall2(Callee, PtrName, S);
974 /// Adds a source annotation to pointer and a state change annotation to Inst
975 /// referencing the source annotation and the old/new state of pointer.
976 static void GenerateARCAnnotation(unsigned InstMDId,
982 if (EnableARCAnnotations) {
983 // If we have a target identifier, make sure that we match it before
984 // emitting an annotation.
985 if(!ARCAnnotationTargetIdentifier.empty() &&
986 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
989 // First generate the source annotation on our pointer. This will return an
990 // MDString* if Ptr actually comes from an instruction implying we can put
991 // in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
992 // then we know that our pointer is from an Argument so we put a reference
993 // to the argument number.
995 // The point of this is to make it easy for the
996 // llvm-arc-annotation-processor tool to cross reference where the source
997 // pointer is in the LLVM IR since the LLVM IR parser does not submit such
998 // information via debug info for backends to use (since why would anyone
999 // need such a thing from LLVM IR besides in non-standard cases
1001 MDString *SourcePtrMDNode =
1002 AppendMDNodeToSourcePtr(PtrMDId, Ptr);
1003 AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
1008 // The actual interface for accessing the above functionality is defined via
1009 // some simple macros which are defined below. We do this so that the user does
1010 // not need to pass in what metadata id is needed resulting in cleaner code and
1011 // additionally since it provides an easy way to conditionally no-op all
1012 // annotation support in a non-debug build.
1014 /// Use this macro to annotate a sequence state change when processing
1015 /// instructions bottom up,
1016 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new) \
1017 GenerateARCAnnotation(ARCAnnotationBottomUpMDKind, \
1018 ARCAnnotationProvenanceSourceMDKind, (inst), \
1019 const_cast<Value*>(ptr), (old), (new))
1020 /// Use this macro to annotate a sequence state change when processing
1021 /// instructions top down.
1022 #define ANNOTATE_TOPDOWN(inst, ptr, old, new) \
1023 GenerateARCAnnotation(ARCAnnotationTopDownMDKind, \
1024 ARCAnnotationProvenanceSourceMDKind, (inst), \
1025 const_cast<Value*>(ptr), (old), (new))
1027 #define ANNOTATE_BB(_states, _bb, _name, _type, _direction) \
1029 if (EnableARCAnnotations) { \
1030 for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
1031 E = (_states)._direction##_ptr_end(); I != E; ++I) { \
1032 Value *Ptr = const_cast<Value*>(I->first); \
1033 Sequence Seq = I->second.GetSeq(); \
1034 GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq); \
1039 #define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock) \
1040 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
1041 Entrance, bottom_up)
1042 #define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock) \
1043 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend", \
1044 Terminator, bottom_up)
1045 #define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock) \
1046 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart", \
1048 #define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock) \
1049 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend", \
1050 Terminator, top_down)
1052 #else // !ARC_ANNOTATION
1053 // If annotations are off, noop.
1054 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
1055 #define ANNOTATE_TOPDOWN(inst, ptr, old, new)
1056 #define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
1057 #define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
1058 #define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
1059 #define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
1060 #endif // !ARC_ANNOTATION
1063 /// \brief The main ARC optimization pass.
1064 class ObjCARCOpt : public FunctionPass {
1066 ProvenanceAnalysis PA;
1067 ARCRuntimeEntryPoints EP;
1069 // This is used to track if a pointer is stored into an alloca.
1070 DenseSet<const Value *> MultiOwnersSet;
1072 /// A flag indicating whether this optimization pass should run.
1075 /// Flags which determine whether each of the interesting runtine functions
1076 /// is in fact used in the current function.
1077 unsigned UsedInThisFunction;
1079 /// The Metadata Kind for clang.imprecise_release metadata.
1080 unsigned ImpreciseReleaseMDKind;
1082 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
1083 unsigned CopyOnEscapeMDKind;
1085 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
1086 unsigned NoObjCARCExceptionsMDKind;
1088 #ifdef ARC_ANNOTATIONS
1089 /// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
1090 unsigned ARCAnnotationBottomUpMDKind;
1091 /// The Metadata Kind for llvm.arc.annotation.topdown metadata.
1092 unsigned ARCAnnotationTopDownMDKind;
1093 /// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
1094 unsigned ARCAnnotationProvenanceSourceMDKind;
1095 #endif // ARC_ANNOATIONS
1097 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
1098 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1099 InstructionClass &Class);
1100 void OptimizeIndividualCalls(Function &F);
1102 void CheckForCFGHazards(const BasicBlock *BB,
1103 DenseMap<const BasicBlock *, BBState> &BBStates,
1104 BBState &MyStates) const;
1105 bool VisitInstructionBottomUp(Instruction *Inst,
1107 MapVector<Value *, RRInfo> &Retains,
1109 bool VisitBottomUp(BasicBlock *BB,
1110 DenseMap<const BasicBlock *, BBState> &BBStates,
1111 MapVector<Value *, RRInfo> &Retains);
1112 bool VisitInstructionTopDown(Instruction *Inst,
1113 DenseMap<Value *, RRInfo> &Releases,
1115 bool VisitTopDown(BasicBlock *BB,
1116 DenseMap<const BasicBlock *, BBState> &BBStates,
1117 DenseMap<Value *, RRInfo> &Releases);
1118 bool Visit(Function &F,
1119 DenseMap<const BasicBlock *, BBState> &BBStates,
1120 MapVector<Value *, RRInfo> &Retains,
1121 DenseMap<Value *, RRInfo> &Releases);
1123 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
1124 MapVector<Value *, RRInfo> &Retains,
1125 DenseMap<Value *, RRInfo> &Releases,
1126 SmallVectorImpl<Instruction *> &DeadInsts,
1129 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
1130 MapVector<Value *, RRInfo> &Retains,
1131 DenseMap<Value *, RRInfo> &Releases,
1133 SmallVectorImpl<Instruction *> &NewRetains,
1134 SmallVectorImpl<Instruction *> &NewReleases,
1135 SmallVectorImpl<Instruction *> &DeadInsts,
1136 RRInfo &RetainsToMove,
1137 RRInfo &ReleasesToMove,
1140 bool &AnyPairsCompletelyEliminated);
1142 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
1143 MapVector<Value *, RRInfo> &Retains,
1144 DenseMap<Value *, RRInfo> &Releases,
1147 void OptimizeWeakCalls(Function &F);
1149 bool OptimizeSequences(Function &F);
1151 void OptimizeReturns(Function &F);
1154 void GatherStatistics(Function &F, bool AfterOptimization = false);
1157 void getAnalysisUsage(AnalysisUsage &AU) const override;
1158 bool doInitialization(Module &M) override;
1159 bool runOnFunction(Function &F) override;
1160 void releaseMemory() override;
1164 ObjCARCOpt() : FunctionPass(ID) {
1165 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
1170 char ObjCARCOpt::ID = 0;
1171 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
1172 "objc-arc", "ObjC ARC optimization", false, false)
1173 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
1174 INITIALIZE_PASS_END(ObjCARCOpt,
1175 "objc-arc", "ObjC ARC optimization", false, false)
1177 Pass *llvm::createObjCARCOptPass() {
1178 return new ObjCARCOpt();
1181 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
1182 AU.addRequired<ObjCARCAliasAnalysis>();
1183 AU.addRequired<AliasAnalysis>();
1184 // ARC optimization doesn't currently split critical edges.
1185 AU.setPreservesCFG();
1188 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
1189 /// not a return value. Or, if it can be paired with an
1190 /// objc_autoreleaseReturnValue, delete the pair and return true.
1192 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
1193 // Check for the argument being from an immediately preceding call or invoke.
1194 const Value *Arg = GetArgRCIdentityRoot(RetainRV);
1195 ImmutableCallSite CS(Arg);
1196 if (const Instruction *Call = CS.getInstruction()) {
1197 if (Call->getParent() == RetainRV->getParent()) {
1198 BasicBlock::const_iterator I = Call;
1200 while (IsNoopInstruction(I)) ++I;
1201 if (&*I == RetainRV)
1203 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
1204 BasicBlock *RetainRVParent = RetainRV->getParent();
1205 if (II->getNormalDest() == RetainRVParent) {
1206 BasicBlock::const_iterator I = RetainRVParent->begin();
1207 while (IsNoopInstruction(I)) ++I;
1208 if (&*I == RetainRV)
1214 // Check for being preceded by an objc_autoreleaseReturnValue on the same
1215 // pointer. In this case, we can delete the pair.
1216 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
1218 do --I; while (I != Begin && IsNoopInstruction(I));
1219 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
1220 GetArgRCIdentityRoot(I) == Arg) {
1224 DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
1225 << "Erasing " << *RetainRV << "\n");
1227 EraseInstruction(I);
1228 EraseInstruction(RetainRV);
1233 // Turn it to a plain objc_retain.
1237 DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
1238 "objc_retain since the operand is not a return value.\n"
1239 "Old = " << *RetainRV << "\n");
1241 Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
1242 cast<CallInst>(RetainRV)->setCalledFunction(NewDecl);
1244 DEBUG(dbgs() << "New = " << *RetainRV << "\n");
1249 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
1250 /// used as a return value.
1252 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1253 InstructionClass &Class) {
1254 // Check for a return of the pointer value.
1255 const Value *Ptr = GetArgRCIdentityRoot(AutoreleaseRV);
1256 SmallVector<const Value *, 2> Users;
1257 Users.push_back(Ptr);
1259 Ptr = Users.pop_back_val();
1260 for (const User *U : Ptr->users()) {
1261 if (isa<ReturnInst>(U) || GetBasicInstructionClass(U) == IC_RetainRV)
1263 if (isa<BitCastInst>(U))
1266 } while (!Users.empty());
1271 DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
1272 "objc_autorelease since its operand is not used as a return "
1274 "Old = " << *AutoreleaseRV << "\n");
1276 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
1277 Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Autorelease);
1278 AutoreleaseRVCI->setCalledFunction(NewDecl);
1279 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
1280 Class = IC_Autorelease;
1282 DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
1286 /// Visit each call, one at a time, and make simplifications without doing any
1287 /// additional analysis.
1288 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
1289 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
1290 // Reset all the flags in preparation for recomputing them.
1291 UsedInThisFunction = 0;
1293 // Visit all objc_* calls in F.
1294 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1295 Instruction *Inst = &*I++;
1297 InstructionClass Class = GetBasicInstructionClass(Inst);
1299 DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
1304 // Delete no-op casts. These function calls have special semantics, but
1305 // the semantics are entirely implemented via lowering in the front-end,
1306 // so by the time they reach the optimizer, they are just no-op calls
1307 // which return their argument.
1309 // There are gray areas here, as the ability to cast reference-counted
1310 // pointers to raw void* and back allows code to break ARC assumptions,
1311 // however these are currently considered to be unimportant.
1315 DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
1316 EraseInstruction(Inst);
1319 // If the pointer-to-weak-pointer is null, it's undefined behavior.
1322 case IC_LoadWeakRetained:
1324 case IC_DestroyWeak: {
1325 CallInst *CI = cast<CallInst>(Inst);
1326 if (IsNullOrUndef(CI->getArgOperand(0))) {
1328 Type *Ty = CI->getArgOperand(0)->getType();
1329 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1330 Constant::getNullValue(Ty),
1332 llvm::Value *NewValue = UndefValue::get(CI->getType());
1333 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1334 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1335 CI->replaceAllUsesWith(NewValue);
1336 CI->eraseFromParent();
1343 CallInst *CI = cast<CallInst>(Inst);
1344 if (IsNullOrUndef(CI->getArgOperand(0)) ||
1345 IsNullOrUndef(CI->getArgOperand(1))) {
1347 Type *Ty = CI->getArgOperand(0)->getType();
1348 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1349 Constant::getNullValue(Ty),
1352 llvm::Value *NewValue = UndefValue::get(CI->getType());
1353 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1354 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1356 CI->replaceAllUsesWith(NewValue);
1357 CI->eraseFromParent();
1363 if (OptimizeRetainRVCall(F, Inst))
1366 case IC_AutoreleaseRV:
1367 OptimizeAutoreleaseRVCall(F, Inst, Class);
1371 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
1372 if (IsAutorelease(Class) && Inst->use_empty()) {
1373 CallInst *Call = cast<CallInst>(Inst);
1374 const Value *Arg = Call->getArgOperand(0);
1375 Arg = FindSingleUseIdentifiedObject(Arg);
1380 // Create the declaration lazily.
1381 LLVMContext &C = Inst->getContext();
1383 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
1384 CallInst *NewCall = CallInst::Create(Decl, Call->getArgOperand(0), "",
1386 NewCall->setMetadata(ImpreciseReleaseMDKind, MDNode::get(C, None));
1388 DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
1389 "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
1390 << *NewCall << "\n");
1392 EraseInstruction(Call);
1398 // For functions which can never be passed stack arguments, add
1400 if (IsAlwaysTail(Class)) {
1402 DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
1403 "passed stack args: " << *Inst << "\n");
1404 cast<CallInst>(Inst)->setTailCall();
1407 // Ensure that functions that can never have a "tail" keyword due to the
1408 // semantics of ARC truly do not do so.
1409 if (IsNeverTail(Class)) {
1411 DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
1413 cast<CallInst>(Inst)->setTailCall(false);
1416 // Set nounwind as needed.
1417 if (IsNoThrow(Class)) {
1419 DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
1421 cast<CallInst>(Inst)->setDoesNotThrow();
1424 if (!IsNoopOnNull(Class)) {
1425 UsedInThisFunction |= 1 << Class;
1429 const Value *Arg = GetArgRCIdentityRoot(Inst);
1431 // ARC calls with null are no-ops. Delete them.
1432 if (IsNullOrUndef(Arg)) {
1435 DEBUG(dbgs() << "ARC calls with null are no-ops. Erasing: " << *Inst
1437 EraseInstruction(Inst);
1441 // Keep track of which of retain, release, autorelease, and retain_block
1442 // are actually present in this function.
1443 UsedInThisFunction |= 1 << Class;
1445 // If Arg is a PHI, and one or more incoming values to the
1446 // PHI are null, and the call is control-equivalent to the PHI, and there
1447 // are no relevant side effects between the PHI and the call, the call
1448 // could be pushed up to just those paths with non-null incoming values.
1449 // For now, don't bother splitting critical edges for this.
1450 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
1451 Worklist.push_back(std::make_pair(Inst, Arg));
1453 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
1457 const PHINode *PN = dyn_cast<PHINode>(Arg);
1460 // Determine if the PHI has any null operands, or any incoming
1462 bool HasNull = false;
1463 bool HasCriticalEdges = false;
1464 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1466 GetRCIdentityRoot(PN->getIncomingValue(i));
1467 if (IsNullOrUndef(Incoming))
1469 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
1470 .getNumSuccessors() != 1) {
1471 HasCriticalEdges = true;
1475 // If we have null operands and no critical edges, optimize.
1476 if (!HasCriticalEdges && HasNull) {
1477 SmallPtrSet<Instruction *, 4> DependingInstructions;
1478 SmallPtrSet<const BasicBlock *, 4> Visited;
1480 // Check that there is nothing that cares about the reference
1481 // count between the call and the phi.
1484 case IC_RetainBlock:
1485 // These can always be moved up.
1488 // These can't be moved across things that care about the retain
1490 FindDependencies(NeedsPositiveRetainCount, Arg,
1491 Inst->getParent(), Inst,
1492 DependingInstructions, Visited, PA);
1494 case IC_Autorelease:
1495 // These can't be moved across autorelease pool scope boundaries.
1496 FindDependencies(AutoreleasePoolBoundary, Arg,
1497 Inst->getParent(), Inst,
1498 DependingInstructions, Visited, PA);
1501 case IC_AutoreleaseRV:
1502 // Don't move these; the RV optimization depends on the autoreleaseRV
1503 // being tail called, and the retainRV being immediately after a call
1504 // (which might still happen if we get lucky with codegen layout, but
1505 // it's not worth taking the chance).
1508 llvm_unreachable("Invalid dependence flavor");
1511 if (DependingInstructions.size() == 1 &&
1512 *DependingInstructions.begin() == PN) {
1515 // Clone the call into each predecessor that has a non-null value.
1516 CallInst *CInst = cast<CallInst>(Inst);
1517 Type *ParamTy = CInst->getArgOperand(0)->getType();
1518 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1520 GetRCIdentityRoot(PN->getIncomingValue(i));
1521 if (!IsNullOrUndef(Incoming)) {
1522 CallInst *Clone = cast<CallInst>(CInst->clone());
1523 Value *Op = PN->getIncomingValue(i);
1524 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
1525 if (Op->getType() != ParamTy)
1526 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
1527 Clone->setArgOperand(0, Op);
1528 Clone->insertBefore(InsertPos);
1530 DEBUG(dbgs() << "Cloning "
1532 "And inserting clone at " << *InsertPos << "\n");
1533 Worklist.push_back(std::make_pair(Clone, Incoming));
1536 // Erase the original call.
1537 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
1538 EraseInstruction(CInst);
1542 } while (!Worklist.empty());
1546 /// If we have a top down pointer in the S_Use state, make sure that there are
1547 /// no CFG hazards by checking the states of various bottom up pointers.
1548 static void CheckForUseCFGHazard(const Sequence SuccSSeq,
1549 const bool SuccSRRIKnownSafe,
1551 bool &SomeSuccHasSame,
1552 bool &AllSuccsHaveSame,
1553 bool &NotAllSeqEqualButKnownSafe,
1554 bool &ShouldContinue) {
1556 case S_CanRelease: {
1557 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe) {
1558 S.ClearSequenceProgress();
1561 S.SetCFGHazardAfflicted(true);
1562 ShouldContinue = true;
1566 SomeSuccHasSame = true;
1570 case S_MovableRelease:
1571 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
1572 AllSuccsHaveSame = false;
1574 NotAllSeqEqualButKnownSafe = true;
1577 llvm_unreachable("bottom-up pointer in retain state!");
1579 llvm_unreachable("This should have been handled earlier.");
1583 /// If we have a Top Down pointer in the S_CanRelease state, make sure that
1584 /// there are no CFG hazards by checking the states of various bottom up
1586 static void CheckForCanReleaseCFGHazard(const Sequence SuccSSeq,
1587 const bool SuccSRRIKnownSafe,
1589 bool &SomeSuccHasSame,
1590 bool &AllSuccsHaveSame,
1591 bool &NotAllSeqEqualButKnownSafe) {
1594 SomeSuccHasSame = true;
1598 case S_MovableRelease:
1600 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
1601 AllSuccsHaveSame = false;
1603 NotAllSeqEqualButKnownSafe = true;
1606 llvm_unreachable("bottom-up pointer in retain state!");
1608 llvm_unreachable("This should have been handled earlier.");
1612 /// Check for critical edges, loop boundaries, irreducible control flow, or
1613 /// other CFG structures where moving code across the edge would result in it
1614 /// being executed more.
1616 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
1617 DenseMap<const BasicBlock *, BBState> &BBStates,
1618 BBState &MyStates) const {
1619 // If any top-down local-use or possible-dec has a succ which is earlier in
1620 // the sequence, forget it.
1621 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
1622 E = MyStates.top_down_ptr_end(); I != E; ++I) {
1623 PtrState &S = I->second;
1624 const Sequence Seq = I->second.GetSeq();
1626 // We only care about S_Retain, S_CanRelease, and S_Use.
1630 // Make sure that if extra top down states are added in the future that this
1631 // code is updated to handle it.
1632 assert((Seq == S_Retain || Seq == S_CanRelease || Seq == S_Use) &&
1633 "Unknown top down sequence state.");
1635 const Value *Arg = I->first;
1636 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
1637 bool SomeSuccHasSame = false;
1638 bool AllSuccsHaveSame = true;
1639 bool NotAllSeqEqualButKnownSafe = false;
1641 succ_const_iterator SI(TI), SE(TI, false);
1643 for (; SI != SE; ++SI) {
1644 // If VisitBottomUp has pointer information for this successor, take
1645 // what we know about it.
1646 const DenseMap<const BasicBlock *, BBState>::iterator BBI =
1648 assert(BBI != BBStates.end());
1649 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
1650 const Sequence SuccSSeq = SuccS.GetSeq();
1652 // If bottom up, the pointer is in an S_None state, clear the sequence
1653 // progress since the sequence in the bottom up state finished
1654 // suggesting a mismatch in between retains/releases. This is true for
1655 // all three cases that we are handling here: S_Retain, S_Use, and
1657 if (SuccSSeq == S_None) {
1658 S.ClearSequenceProgress();
1662 // If we have S_Use or S_CanRelease, perform our check for cfg hazard
1664 const bool SuccSRRIKnownSafe = SuccS.IsKnownSafe();
1666 // *NOTE* We do not use Seq from above here since we are allowing for
1667 // S.GetSeq() to change while we are visiting basic blocks.
1668 switch(S.GetSeq()) {
1670 bool ShouldContinue = false;
1671 CheckForUseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S, SomeSuccHasSame,
1672 AllSuccsHaveSame, NotAllSeqEqualButKnownSafe,
1678 case S_CanRelease: {
1679 CheckForCanReleaseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S,
1680 SomeSuccHasSame, AllSuccsHaveSame,
1681 NotAllSeqEqualButKnownSafe);
1688 case S_MovableRelease:
1693 // If the state at the other end of any of the successor edges
1694 // matches the current state, require all edges to match. This
1695 // guards against loops in the middle of a sequence.
1696 if (SomeSuccHasSame && !AllSuccsHaveSame) {
1697 S.ClearSequenceProgress();
1698 } else if (NotAllSeqEqualButKnownSafe) {
1699 // If we would have cleared the state foregoing the fact that we are known
1700 // safe, stop code motion. This is because whether or not it is safe to
1701 // remove RR pairs via KnownSafe is an orthogonal concept to whether we
1702 // are allowed to perform code motion.
1703 S.SetCFGHazardAfflicted(true);
1709 ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
1711 MapVector<Value *, RRInfo> &Retains,
1712 BBState &MyStates) {
1713 bool NestingDetected = false;
1714 InstructionClass Class = GetInstructionClass(Inst);
1715 const Value *Arg = nullptr;
1717 DEBUG(dbgs() << "Class: " << Class << "\n");
1721 Arg = GetArgRCIdentityRoot(Inst);
1723 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1725 // If we see two releases in a row on the same pointer. If so, make
1726 // a note, and we'll cicle back to revisit it after we've
1727 // hopefully eliminated the second release, which may allow us to
1728 // eliminate the first release too.
1729 // Theoretically we could implement removal of nested retain+release
1730 // pairs by making PtrState hold a stack of states, but this is
1731 // simple and avoids adding overhead for the non-nested case.
1732 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
1733 DEBUG(dbgs() << "Found nested releases (i.e. a release pair)\n");
1734 NestingDetected = true;
1737 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
1738 Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
1739 ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
1740 S.ResetSequenceProgress(NewSeq);
1741 S.SetReleaseMetadata(ReleaseMetadata);
1742 S.SetKnownSafe(S.HasKnownPositiveRefCount());
1743 S.SetTailCallRelease(cast<CallInst>(Inst)->isTailCall());
1745 S.SetKnownPositiveRefCount();
1748 case IC_RetainBlock:
1749 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1750 // objc_retainBlocks to objc_retains. Thus at this point any
1751 // objc_retainBlocks that we see are not optimizable.
1755 Arg = GetArgRCIdentityRoot(Inst);
1757 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1758 S.SetKnownPositiveRefCount();
1760 Sequence OldSeq = S.GetSeq();
1764 case S_MovableRelease:
1766 // If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
1767 // imprecise release, clear our reverse insertion points.
1768 if (OldSeq != S_Use || S.IsTrackingImpreciseReleases())
1769 S.ClearReverseInsertPts();
1772 // Don't do retain+release tracking for IC_RetainRV, because it's
1773 // better to let it remain as the first instruction after a call.
1774 if (Class != IC_RetainRV)
1775 Retains[Inst] = S.GetRRInfo();
1776 S.ClearSequenceProgress();
1781 llvm_unreachable("bottom-up pointer in retain state!");
1783 ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
1784 // A retain moving bottom up can be a use.
1787 case IC_AutoreleasepoolPop:
1788 // Conservatively, clear MyStates for all known pointers.
1789 MyStates.clearBottomUpPointers();
1790 return NestingDetected;
1791 case IC_AutoreleasepoolPush:
1793 // These are irrelevant.
1794 return NestingDetected;
1796 // If we have a store into an alloca of a pointer we are tracking, the
1797 // pointer has multiple owners implying that we must be more conservative.
1799 // This comes up in the context of a pointer being ``KnownSafe''. In the
1800 // presence of a block being initialized, the frontend will emit the
1801 // objc_retain on the original pointer and the release on the pointer loaded
1802 // from the alloca. The optimizer will through the provenance analysis
1803 // realize that the two are related, but since we only require KnownSafe in
1804 // one direction, will match the inner retain on the original pointer with
1805 // the guard release on the original pointer. This is fixed by ensuring that
1806 // in the presence of allocas we only unconditionally remove pointers if
1807 // both our retain and our release are KnownSafe.
1808 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
1809 if (AreAnyUnderlyingObjectsAnAlloca(SI->getPointerOperand())) {
1810 BBState::ptr_iterator I = MyStates.findPtrBottomUpState(
1811 GetRCIdentityRoot(SI->getValueOperand()));
1812 if (I != MyStates.bottom_up_ptr_end())
1813 MultiOwnersSet.insert(I->first);
1821 // Consider any other possible effects of this instruction on each
1822 // pointer being tracked.
1823 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
1824 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
1825 const Value *Ptr = MI->first;
1827 continue; // Handled above.
1828 PtrState &S = MI->second;
1829 Sequence Seq = S.GetSeq();
1831 // Check for possible releases.
1832 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
1833 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
1835 S.ClearKnownPositiveRefCount();
1838 S.SetSeq(S_CanRelease);
1839 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
1843 case S_MovableRelease:
1848 llvm_unreachable("bottom-up pointer in retain state!");
1852 // Check for possible direct uses.
1855 case S_MovableRelease:
1856 if (CanUse(Inst, Ptr, PA, Class)) {
1857 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
1859 assert(!S.HasReverseInsertPts());
1860 // If this is an invoke instruction, we're scanning it as part of
1861 // one of its successor blocks, since we can't insert code after it
1862 // in its own block, and we don't want to split critical edges.
1863 if (isa<InvokeInst>(Inst))
1864 S.InsertReverseInsertPt(BB->getFirstInsertionPt());
1866 S.InsertReverseInsertPt(std::next(BasicBlock::iterator(Inst)));
1868 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1869 } else if (Seq == S_Release && IsUser(Class)) {
1870 DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
1872 // Non-movable releases depend on any possible objc pointer use.
1874 ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
1875 assert(!S.HasReverseInsertPts());
1876 // As above; handle invoke specially.
1877 if (isa<InvokeInst>(Inst))
1878 S.InsertReverseInsertPt(BB->getFirstInsertionPt());
1880 S.InsertReverseInsertPt(std::next(BasicBlock::iterator(Inst)));
1884 if (CanUse(Inst, Ptr, PA, Class)) {
1885 DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
1888 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1896 llvm_unreachable("bottom-up pointer in retain state!");
1900 return NestingDetected;
1904 ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
1905 DenseMap<const BasicBlock *, BBState> &BBStates,
1906 MapVector<Value *, RRInfo> &Retains) {
1908 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
1910 bool NestingDetected = false;
1911 BBState &MyStates = BBStates[BB];
1913 // Merge the states from each successor to compute the initial state
1914 // for the current block.
1915 BBState::edge_iterator SI(MyStates.succ_begin()),
1916 SE(MyStates.succ_end());
1918 const BasicBlock *Succ = *SI;
1919 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
1920 assert(I != BBStates.end());
1921 MyStates.InitFromSucc(I->second);
1923 for (; SI != SE; ++SI) {
1925 I = BBStates.find(Succ);
1926 assert(I != BBStates.end());
1927 MyStates.MergeSucc(I->second);
1931 // If ARC Annotations are enabled, output the current state of pointers at the
1932 // bottom of the basic block.
1933 ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);
1935 // Visit all the instructions, bottom-up.
1936 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
1937 Instruction *Inst = std::prev(I);
1939 // Invoke instructions are visited as part of their successors (below).
1940 if (isa<InvokeInst>(Inst))
1943 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1945 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
1948 // If there's a predecessor with an invoke, visit the invoke as if it were
1949 // part of this block, since we can't insert code after an invoke in its own
1950 // block, and we don't want to split critical edges.
1951 for (BBState::edge_iterator PI(MyStates.pred_begin()),
1952 PE(MyStates.pred_end()); PI != PE; ++PI) {
1953 BasicBlock *Pred = *PI;
1954 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
1955 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
1958 // If ARC Annotations are enabled, output the current state of pointers at the
1959 // top of the basic block.
1960 ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);
1962 return NestingDetected;
1966 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
1967 DenseMap<Value *, RRInfo> &Releases,
1968 BBState &MyStates) {
1969 bool NestingDetected = false;
1970 InstructionClass Class = GetInstructionClass(Inst);
1971 const Value *Arg = nullptr;
1974 case IC_RetainBlock:
1975 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1976 // objc_retainBlocks to objc_retains. Thus at this point any
1977 // objc_retainBlocks that we see are not optimizable.
1981 Arg = GetArgRCIdentityRoot(Inst);
1983 PtrState &S = MyStates.getPtrTopDownState(Arg);
1985 // Don't do retain+release tracking for IC_RetainRV, because it's
1986 // better to let it remain as the first instruction after a call.
1987 if (Class != IC_RetainRV) {
1988 // If we see two retains in a row on the same pointer. If so, make
1989 // a note, and we'll cicle back to revisit it after we've
1990 // hopefully eliminated the second retain, which may allow us to
1991 // eliminate the first retain too.
1992 // Theoretically we could implement removal of nested retain+release
1993 // pairs by making PtrState hold a stack of states, but this is
1994 // simple and avoids adding overhead for the non-nested case.
1995 if (S.GetSeq() == S_Retain)
1996 NestingDetected = true;
1998 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
1999 S.ResetSequenceProgress(S_Retain);
2000 S.SetKnownSafe(S.HasKnownPositiveRefCount());
2004 S.SetKnownPositiveRefCount();
2006 // A retain can be a potential use; procede to the generic checking
2011 Arg = GetArgRCIdentityRoot(Inst);
2013 PtrState &S = MyStates.getPtrTopDownState(Arg);
2014 S.ClearKnownPositiveRefCount();
2016 Sequence OldSeq = S.GetSeq();
2018 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
2023 if (OldSeq == S_Retain || ReleaseMetadata != nullptr)
2024 S.ClearReverseInsertPts();
2027 S.SetReleaseMetadata(ReleaseMetadata);
2028 S.SetTailCallRelease(cast<CallInst>(Inst)->isTailCall());
2029 Releases[Inst] = S.GetRRInfo();
2030 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
2031 S.ClearSequenceProgress();
2037 case S_MovableRelease:
2038 llvm_unreachable("top-down pointer in release state!");
2042 case IC_AutoreleasepoolPop:
2043 // Conservatively, clear MyStates for all known pointers.
2044 MyStates.clearTopDownPointers();
2045 return NestingDetected;
2046 case IC_AutoreleasepoolPush:
2048 // These are irrelevant.
2049 return NestingDetected;
2054 // Consider any other possible effects of this instruction on each
2055 // pointer being tracked.
2056 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
2057 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
2058 const Value *Ptr = MI->first;
2060 continue; // Handled above.
2061 PtrState &S = MI->second;
2062 Sequence Seq = S.GetSeq();
2064 // Check for possible releases.
2065 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
2066 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
2068 S.ClearKnownPositiveRefCount();
2071 S.SetSeq(S_CanRelease);
2072 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
2073 assert(!S.HasReverseInsertPts());
2074 S.InsertReverseInsertPt(Inst);
2076 // One call can't cause a transition from S_Retain to S_CanRelease
2077 // and S_CanRelease to S_Use. If we've made the first transition,
2086 case S_MovableRelease:
2087 llvm_unreachable("top-down pointer in release state!");
2091 // Check for possible direct uses.
2094 if (CanUse(Inst, Ptr, PA, Class)) {
2095 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
2098 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_Use);
2107 case S_MovableRelease:
2108 llvm_unreachable("top-down pointer in release state!");
2112 return NestingDetected;
2116 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
2117 DenseMap<const BasicBlock *, BBState> &BBStates,
2118 DenseMap<Value *, RRInfo> &Releases) {
2119 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
2120 bool NestingDetected = false;
2121 BBState &MyStates = BBStates[BB];
2123 // Merge the states from each predecessor to compute the initial state
2124 // for the current block.
2125 BBState::edge_iterator PI(MyStates.pred_begin()),
2126 PE(MyStates.pred_end());
2128 const BasicBlock *Pred = *PI;
2129 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
2130 assert(I != BBStates.end());
2131 MyStates.InitFromPred(I->second);
2133 for (; PI != PE; ++PI) {
2135 I = BBStates.find(Pred);
2136 assert(I != BBStates.end());
2137 MyStates.MergePred(I->second);
2141 // If ARC Annotations are enabled, output the current state of pointers at the
2142 // top of the basic block.
2143 ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);
2145 // Visit all the instructions, top-down.
2146 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
2147 Instruction *Inst = I;
2149 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
2151 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
2154 // If ARC Annotations are enabled, output the current state of pointers at the
2155 // bottom of the basic block.
2156 ANNOTATE_TOPDOWN_BBEND(MyStates, BB);
2158 #ifdef ARC_ANNOTATIONS
2159 if (!(EnableARCAnnotations && DisableCheckForCFGHazards))
2161 CheckForCFGHazards(BB, BBStates, MyStates);
2162 return NestingDetected;
2166 ComputePostOrders(Function &F,
2167 SmallVectorImpl<BasicBlock *> &PostOrder,
2168 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
2169 unsigned NoObjCARCExceptionsMDKind,
2170 DenseMap<const BasicBlock *, BBState> &BBStates) {
2171 /// The visited set, for doing DFS walks.
2172 SmallPtrSet<BasicBlock *, 16> Visited;
2174 // Do DFS, computing the PostOrder.
2175 SmallPtrSet<BasicBlock *, 16> OnStack;
2176 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
2178 // Functions always have exactly one entry block, and we don't have
2179 // any other block that we treat like an entry block.
2180 BasicBlock *EntryBB = &F.getEntryBlock();
2181 BBState &MyStates = BBStates[EntryBB];
2182 MyStates.SetAsEntry();
2183 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
2184 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
2185 Visited.insert(EntryBB);
2186 OnStack.insert(EntryBB);
2189 BasicBlock *CurrBB = SuccStack.back().first;
2190 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
2191 succ_iterator SE(TI, false);
2193 while (SuccStack.back().second != SE) {
2194 BasicBlock *SuccBB = *SuccStack.back().second++;
2195 if (Visited.insert(SuccBB).second) {
2196 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
2197 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
2198 BBStates[CurrBB].addSucc(SuccBB);
2199 BBState &SuccStates = BBStates[SuccBB];
2200 SuccStates.addPred(CurrBB);
2201 OnStack.insert(SuccBB);
2205 if (!OnStack.count(SuccBB)) {
2206 BBStates[CurrBB].addSucc(SuccBB);
2207 BBStates[SuccBB].addPred(CurrBB);
2210 OnStack.erase(CurrBB);
2211 PostOrder.push_back(CurrBB);
2212 SuccStack.pop_back();
2213 } while (!SuccStack.empty());
2217 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
2218 // Functions may have many exits, and there also blocks which we treat
2219 // as exits due to ignored edges.
2220 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
2221 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
2222 BasicBlock *ExitBB = I;
2223 BBState &MyStates = BBStates[ExitBB];
2224 if (!MyStates.isExit())
2227 MyStates.SetAsExit();
2229 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
2230 Visited.insert(ExitBB);
2231 while (!PredStack.empty()) {
2232 reverse_dfs_next_succ:
2233 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
2234 while (PredStack.back().second != PE) {
2235 BasicBlock *BB = *PredStack.back().second++;
2236 if (Visited.insert(BB).second) {
2237 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
2238 goto reverse_dfs_next_succ;
2241 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
2246 // Visit the function both top-down and bottom-up.
2248 ObjCARCOpt::Visit(Function &F,
2249 DenseMap<const BasicBlock *, BBState> &BBStates,
2250 MapVector<Value *, RRInfo> &Retains,
2251 DenseMap<Value *, RRInfo> &Releases) {
2253 // Use reverse-postorder traversals, because we magically know that loops
2254 // will be well behaved, i.e. they won't repeatedly call retain on a single
2255 // pointer without doing a release. We can't use the ReversePostOrderTraversal
2256 // class here because we want the reverse-CFG postorder to consider each
2257 // function exit point, and we want to ignore selected cycle edges.
2258 SmallVector<BasicBlock *, 16> PostOrder;
2259 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
2260 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
2261 NoObjCARCExceptionsMDKind,
2264 // Use reverse-postorder on the reverse CFG for bottom-up.
2265 bool BottomUpNestingDetected = false;
2266 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2267 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
2269 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
2271 // Use reverse-postorder for top-down.
2272 bool TopDownNestingDetected = false;
2273 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2274 PostOrder.rbegin(), E = PostOrder.rend();
2276 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
2278 return TopDownNestingDetected && BottomUpNestingDetected;
2281 /// Move the calls in RetainsToMove and ReleasesToMove.
2282 void ObjCARCOpt::MoveCalls(Value *Arg,
2283 RRInfo &RetainsToMove,
2284 RRInfo &ReleasesToMove,
2285 MapVector<Value *, RRInfo> &Retains,
2286 DenseMap<Value *, RRInfo> &Releases,
2287 SmallVectorImpl<Instruction *> &DeadInsts,
2289 Type *ArgTy = Arg->getType();
2290 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
2292 DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
2294 // Insert the new retain and release calls.
2295 for (Instruction *InsertPt : ReleasesToMove.ReverseInsertPts) {
2296 Value *MyArg = ArgTy == ParamTy ? Arg :
2297 new BitCastInst(Arg, ParamTy, "", InsertPt);
2298 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
2299 CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
2300 Call->setDoesNotThrow();
2301 Call->setTailCall();
2303 DEBUG(dbgs() << "Inserting new Retain: " << *Call << "\n"
2304 "At insertion point: " << *InsertPt << "\n");
2306 for (Instruction *InsertPt : RetainsToMove.ReverseInsertPts) {
2307 Value *MyArg = ArgTy == ParamTy ? Arg :
2308 new BitCastInst(Arg, ParamTy, "", InsertPt);
2309 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
2310 CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
2311 // Attach a clang.imprecise_release metadata tag, if appropriate.
2312 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
2313 Call->setMetadata(ImpreciseReleaseMDKind, M);
2314 Call->setDoesNotThrow();
2315 if (ReleasesToMove.IsTailCallRelease)
2316 Call->setTailCall();
2318 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
2319 "At insertion point: " << *InsertPt << "\n");
2322 // Delete the original retain and release calls.
2323 for (Instruction *OrigRetain : RetainsToMove.Calls) {
2324 Retains.blot(OrigRetain);
2325 DeadInsts.push_back(OrigRetain);
2326 DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
2328 for (Instruction *OrigRelease : ReleasesToMove.Calls) {
2329 Releases.erase(OrigRelease);
2330 DeadInsts.push_back(OrigRelease);
2331 DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
2337 ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
2339 MapVector<Value *, RRInfo> &Retains,
2340 DenseMap<Value *, RRInfo> &Releases,
2342 SmallVectorImpl<Instruction *> &NewRetains,
2343 SmallVectorImpl<Instruction *> &NewReleases,
2344 SmallVectorImpl<Instruction *> &DeadInsts,
2345 RRInfo &RetainsToMove,
2346 RRInfo &ReleasesToMove,
2349 bool &AnyPairsCompletelyEliminated) {
2350 // If a pair happens in a region where it is known that the reference count
2351 // is already incremented, we can similarly ignore possible decrements unless
2352 // we are dealing with a retainable object with multiple provenance sources.
2353 bool KnownSafeTD = true, KnownSafeBU = true;
2354 bool MultipleOwners = false;
2355 bool CFGHazardAfflicted = false;
2357 // Connect the dots between the top-down-collected RetainsToMove and
2358 // bottom-up-collected ReleasesToMove to form sets of related calls.
2359 // This is an iterative process so that we connect multiple releases
2360 // to multiple retains if needed.
2361 unsigned OldDelta = 0;
2362 unsigned NewDelta = 0;
2363 unsigned OldCount = 0;
2364 unsigned NewCount = 0;
2365 bool FirstRelease = true;
2367 for (SmallVectorImpl<Instruction *>::const_iterator
2368 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
2369 Instruction *NewRetain = *NI;
2370 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
2371 assert(It != Retains.end());
2372 const RRInfo &NewRetainRRI = It->second;
2373 KnownSafeTD &= NewRetainRRI.KnownSafe;
2375 MultipleOwners || MultiOwnersSet.count(GetArgRCIdentityRoot(NewRetain));
2376 for (Instruction *NewRetainRelease : NewRetainRRI.Calls) {
2377 DenseMap<Value *, RRInfo>::const_iterator Jt =
2378 Releases.find(NewRetainRelease);
2379 if (Jt == Releases.end())
2381 const RRInfo &NewRetainReleaseRRI = Jt->second;
2383 // If the release does not have a reference to the retain as well,
2384 // something happened which is unaccounted for. Do not do anything.
2386 // This can happen if we catch an additive overflow during path count
2388 if (!NewRetainReleaseRRI.Calls.count(NewRetain))
2391 if (ReleasesToMove.Calls.insert(NewRetainRelease).second) {
2393 // If we overflow when we compute the path count, don't remove/move
2395 const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
2396 unsigned PathCount = BBState::OverflowOccurredValue;
2397 if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
2399 assert(PathCount != BBState::OverflowOccurredValue &&
2400 "PathCount at this point can not be "
2401 "OverflowOccurredValue.");
2402 OldDelta -= PathCount;
2404 // Merge the ReleaseMetadata and IsTailCallRelease values.
2406 ReleasesToMove.ReleaseMetadata =
2407 NewRetainReleaseRRI.ReleaseMetadata;
2408 ReleasesToMove.IsTailCallRelease =
2409 NewRetainReleaseRRI.IsTailCallRelease;
2410 FirstRelease = false;
2412 if (ReleasesToMove.ReleaseMetadata !=
2413 NewRetainReleaseRRI.ReleaseMetadata)
2414 ReleasesToMove.ReleaseMetadata = nullptr;
2415 if (ReleasesToMove.IsTailCallRelease !=
2416 NewRetainReleaseRRI.IsTailCallRelease)
2417 ReleasesToMove.IsTailCallRelease = false;
2420 // Collect the optimal insertion points.
2422 for (Instruction *RIP : NewRetainReleaseRRI.ReverseInsertPts) {
2423 if (ReleasesToMove.ReverseInsertPts.insert(RIP).second) {
2424 // If we overflow when we compute the path count, don't
2425 // remove/move anything.
2426 const BBState &RIPBBState = BBStates[RIP->getParent()];
2427 PathCount = BBState::OverflowOccurredValue;
2428 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
2430 assert(PathCount != BBState::OverflowOccurredValue &&
2431 "PathCount at this point can not be "
2432 "OverflowOccurredValue.");
2433 NewDelta -= PathCount;
2436 NewReleases.push_back(NewRetainRelease);
2441 if (NewReleases.empty()) break;
2443 // Back the other way.
2444 for (SmallVectorImpl<Instruction *>::const_iterator
2445 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
2446 Instruction *NewRelease = *NI;
2447 DenseMap<Value *, RRInfo>::const_iterator It =
2448 Releases.find(NewRelease);
2449 assert(It != Releases.end());
2450 const RRInfo &NewReleaseRRI = It->second;
2451 KnownSafeBU &= NewReleaseRRI.KnownSafe;
2452 CFGHazardAfflicted |= NewReleaseRRI.CFGHazardAfflicted;
2453 for (Instruction *NewReleaseRetain : NewReleaseRRI.Calls) {
2454 MapVector<Value *, RRInfo>::const_iterator Jt =
2455 Retains.find(NewReleaseRetain);
2456 if (Jt == Retains.end())
2458 const RRInfo &NewReleaseRetainRRI = Jt->second;
2460 // If the retain does not have a reference to the release as well,
2461 // something happened which is unaccounted for. Do not do anything.
2463 // This can happen if we catch an additive overflow during path count
2465 if (!NewReleaseRetainRRI.Calls.count(NewRelease))
2468 if (RetainsToMove.Calls.insert(NewReleaseRetain).second) {
2469 // If we overflow when we compute the path count, don't remove/move
2471 const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
2472 unsigned PathCount = BBState::OverflowOccurredValue;
2473 if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
2475 assert(PathCount != BBState::OverflowOccurredValue &&
2476 "PathCount at this point can not be "
2477 "OverflowOccurredValue.");
2478 OldDelta += PathCount;
2479 OldCount += PathCount;
2481 // Collect the optimal insertion points.
2483 for (Instruction *RIP : NewReleaseRetainRRI.ReverseInsertPts) {
2484 if (RetainsToMove.ReverseInsertPts.insert(RIP).second) {
2485 // If we overflow when we compute the path count, don't
2486 // remove/move anything.
2487 const BBState &RIPBBState = BBStates[RIP->getParent()];
2489 PathCount = BBState::OverflowOccurredValue;
2490 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
2492 assert(PathCount != BBState::OverflowOccurredValue &&
2493 "PathCount at this point can not be "
2494 "OverflowOccurredValue.");
2495 NewDelta += PathCount;
2496 NewCount += PathCount;
2499 NewRetains.push_back(NewReleaseRetain);
2503 NewReleases.clear();
2504 if (NewRetains.empty()) break;
2507 // If the pointer is known incremented in 1 direction and we do not have
2508 // MultipleOwners, we can safely remove the retain/releases. Otherwise we need
2509 // to be known safe in both directions.
2510 bool UnconditionallySafe = (KnownSafeTD && KnownSafeBU) ||
2511 ((KnownSafeTD || KnownSafeBU) && !MultipleOwners);
2512 if (UnconditionallySafe) {
2513 RetainsToMove.ReverseInsertPts.clear();
2514 ReleasesToMove.ReverseInsertPts.clear();
2517 // Determine whether the new insertion points we computed preserve the
2518 // balance of retain and release calls through the program.
2519 // TODO: If the fully aggressive solution isn't valid, try to find a
2520 // less aggressive solution which is.
2524 // At this point, we are not going to remove any RR pairs, but we still are
2525 // able to move RR pairs. If one of our pointers is afflicted with
2526 // CFGHazards, we cannot perform such code motion so exit early.
2527 const bool WillPerformCodeMotion = RetainsToMove.ReverseInsertPts.size() ||
2528 ReleasesToMove.ReverseInsertPts.size();
2529 if (CFGHazardAfflicted && WillPerformCodeMotion)
2533 // Determine whether the original call points are balanced in the retain and
2534 // release calls through the program. If not, conservatively don't touch
2536 // TODO: It's theoretically possible to do code motion in this case, as
2537 // long as the existing imbalances are maintained.
2541 #ifdef ARC_ANNOTATIONS
2542 // Do not move calls if ARC annotations are requested.
2543 if (EnableARCAnnotations)
2545 #endif // ARC_ANNOTATIONS
2548 assert(OldCount != 0 && "Unreachable code?");
2549 NumRRs += OldCount - NewCount;
2550 // Set to true if we completely removed any RR pairs.
2551 AnyPairsCompletelyEliminated = NewCount == 0;
2553 // We can move calls!
2557 /// Identify pairings between the retains and releases, and delete and/or move
2560 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
2562 MapVector<Value *, RRInfo> &Retains,
2563 DenseMap<Value *, RRInfo> &Releases,
2565 DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
2567 bool AnyPairsCompletelyEliminated = false;
2568 RRInfo RetainsToMove;
2569 RRInfo ReleasesToMove;
2570 SmallVector<Instruction *, 4> NewRetains;
2571 SmallVector<Instruction *, 4> NewReleases;
2572 SmallVector<Instruction *, 8> DeadInsts;
2574 // Visit each retain.
2575 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
2576 E = Retains.end(); I != E; ++I) {
2577 Value *V = I->first;
2578 if (!V) continue; // blotted
2580 Instruction *Retain = cast<Instruction>(V);
2582 DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
2584 Value *Arg = GetArgRCIdentityRoot(Retain);
2586 // If the object being released is in static or stack storage, we know it's
2587 // not being managed by ObjC reference counting, so we can delete pairs
2588 // regardless of what possible decrements or uses lie between them.
2589 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
2591 // A constant pointer can't be pointing to an object on the heap. It may
2592 // be reference-counted, but it won't be deleted.
2593 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
2594 if (const GlobalVariable *GV =
2595 dyn_cast<GlobalVariable>(
2596 GetRCIdentityRoot(LI->getPointerOperand())))
2597 if (GV->isConstant())
2600 // Connect the dots between the top-down-collected RetainsToMove and
2601 // bottom-up-collected ReleasesToMove to form sets of related calls.
2602 NewRetains.push_back(Retain);
2603 bool PerformMoveCalls =
2604 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
2605 NewReleases, DeadInsts, RetainsToMove,
2606 ReleasesToMove, Arg, KnownSafe,
2607 AnyPairsCompletelyEliminated);
2609 if (PerformMoveCalls) {
2610 // Ok, everything checks out and we're all set. Let's move/delete some
2612 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
2613 Retains, Releases, DeadInsts, M);
2616 // Clean up state for next retain.
2617 NewReleases.clear();
2619 RetainsToMove.clear();
2620 ReleasesToMove.clear();
2623 // Now that we're done moving everything, we can delete the newly dead
2624 // instructions, as we no longer need them as insert points.
2625 while (!DeadInsts.empty())
2626 EraseInstruction(DeadInsts.pop_back_val());
2628 return AnyPairsCompletelyEliminated;
2631 /// Weak pointer optimizations.
2632 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
2633 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
2635 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
2636 // itself because it uses AliasAnalysis and we need to do provenance
2638 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2639 Instruction *Inst = &*I++;
2641 DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
2643 InstructionClass Class = GetBasicInstructionClass(Inst);
2644 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
2647 // Delete objc_loadWeak calls with no users.
2648 if (Class == IC_LoadWeak && Inst->use_empty()) {
2649 Inst->eraseFromParent();
2653 // TODO: For now, just look for an earlier available version of this value
2654 // within the same block. Theoretically, we could do memdep-style non-local
2655 // analysis too, but that would want caching. A better approach would be to
2656 // use the technique that EarlyCSE uses.
2657 inst_iterator Current = std::prev(I);
2658 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
2659 for (BasicBlock::iterator B = CurrentBB->begin(),
2660 J = Current.getInstructionIterator();
2662 Instruction *EarlierInst = &*std::prev(J);
2663 InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
2664 switch (EarlierClass) {
2666 case IC_LoadWeakRetained: {
2667 // If this is loading from the same pointer, replace this load's value
2669 CallInst *Call = cast<CallInst>(Inst);
2670 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2671 Value *Arg = Call->getArgOperand(0);
2672 Value *EarlierArg = EarlierCall->getArgOperand(0);
2673 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2674 case AliasAnalysis::MustAlias:
2676 // If the load has a builtin retain, insert a plain retain for it.
2677 if (Class == IC_LoadWeakRetained) {
2678 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
2679 CallInst *CI = CallInst::Create(Decl, EarlierCall, "", Call);
2682 // Zap the fully redundant load.
2683 Call->replaceAllUsesWith(EarlierCall);
2684 Call->eraseFromParent();
2686 case AliasAnalysis::MayAlias:
2687 case AliasAnalysis::PartialAlias:
2689 case AliasAnalysis::NoAlias:
2696 // If this is storing to the same pointer and has the same size etc.
2697 // replace this load's value with the stored value.
2698 CallInst *Call = cast<CallInst>(Inst);
2699 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2700 Value *Arg = Call->getArgOperand(0);
2701 Value *EarlierArg = EarlierCall->getArgOperand(0);
2702 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2703 case AliasAnalysis::MustAlias:
2705 // If the load has a builtin retain, insert a plain retain for it.
2706 if (Class == IC_LoadWeakRetained) {
2707 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
2708 CallInst *CI = CallInst::Create(Decl, EarlierCall, "", Call);
2711 // Zap the fully redundant load.
2712 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
2713 Call->eraseFromParent();
2715 case AliasAnalysis::MayAlias:
2716 case AliasAnalysis::PartialAlias:
2718 case AliasAnalysis::NoAlias:
2725 // TOOD: Grab the copied value.
2727 case IC_AutoreleasepoolPush:
2729 case IC_IntrinsicUser:
2731 // Weak pointers are only modified through the weak entry points
2732 // (and arbitrary calls, which could call the weak entry points).
2735 // Anything else could modify the weak pointer.
2742 // Then, for each destroyWeak with an alloca operand, check to see if
2743 // the alloca and all its users can be zapped.
2744 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2745 Instruction *Inst = &*I++;
2746 InstructionClass Class = GetBasicInstructionClass(Inst);
2747 if (Class != IC_DestroyWeak)
2750 CallInst *Call = cast<CallInst>(Inst);
2751 Value *Arg = Call->getArgOperand(0);
2752 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
2753 for (User *U : Alloca->users()) {
2754 const Instruction *UserInst = cast<Instruction>(U);
2755 switch (GetBasicInstructionClass(UserInst)) {
2758 case IC_DestroyWeak:
2765 for (auto UI = Alloca->user_begin(), UE = Alloca->user_end(); UI != UE;) {
2766 CallInst *UserInst = cast<CallInst>(*UI++);
2767 switch (GetBasicInstructionClass(UserInst)) {
2770 // These functions return their second argument.
2771 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
2773 case IC_DestroyWeak:
2777 llvm_unreachable("alloca really is used!");
2779 UserInst->eraseFromParent();
2781 Alloca->eraseFromParent();
2787 /// Identify program paths which execute sequences of retains and releases which
2788 /// can be eliminated.
2789 bool ObjCARCOpt::OptimizeSequences(Function &F) {
2790 // Releases, Retains - These are used to store the results of the main flow
2791 // analysis. These use Value* as the key instead of Instruction* so that the
2792 // map stays valid when we get around to rewriting code and calls get
2793 // replaced by arguments.
2794 DenseMap<Value *, RRInfo> Releases;
2795 MapVector<Value *, RRInfo> Retains;
2797 // This is used during the traversal of the function to track the
2798 // states for each identified object at each block.
2799 DenseMap<const BasicBlock *, BBState> BBStates;
2801 // Analyze the CFG of the function, and all instructions.
2802 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
2805 bool AnyPairsCompletelyEliminated = PerformCodePlacement(BBStates, Retains,
2810 MultiOwnersSet.clear();
2812 return AnyPairsCompletelyEliminated && NestingDetected;
2815 /// Check if there is a dependent call earlier that does not have anything in
2816 /// between the Retain and the call that can affect the reference count of their
2817 /// shared pointer argument. Note that Retain need not be in BB.
2819 HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
2820 SmallPtrSetImpl<Instruction *> &DepInsts,
2821 SmallPtrSetImpl<const BasicBlock *> &Visited,
2822 ProvenanceAnalysis &PA) {
2823 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
2824 DepInsts, Visited, PA);
2825 if (DepInsts.size() != 1)
2829 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2831 // Check that the pointer is the return value of the call.
2832 if (!Call || Arg != Call)
2835 // Check that the call is a regular call.
2836 InstructionClass Class = GetBasicInstructionClass(Call);
2837 if (Class != IC_CallOrUser && Class != IC_Call)
2843 /// Find a dependent retain that precedes the given autorelease for which there
2844 /// is nothing in between the two instructions that can affect the ref count of
2847 FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
2848 Instruction *Autorelease,
2849 SmallPtrSetImpl<Instruction *> &DepInsts,
2850 SmallPtrSetImpl<const BasicBlock *> &Visited,
2851 ProvenanceAnalysis &PA) {
2852 FindDependencies(CanChangeRetainCount, Arg,
2853 BB, Autorelease, DepInsts, Visited, PA);
2854 if (DepInsts.size() != 1)
2858 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2860 // Check that we found a retain with the same argument.
2862 !IsRetain(GetBasicInstructionClass(Retain)) ||
2863 GetArgRCIdentityRoot(Retain) != Arg) {
2870 /// Look for an ``autorelease'' instruction dependent on Arg such that there are
2871 /// no instructions dependent on Arg that need a positive ref count in between
2872 /// the autorelease and the ret.
2874 FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
2876 SmallPtrSetImpl<Instruction *> &DepInsts,
2877 SmallPtrSetImpl<const BasicBlock *> &V,
2878 ProvenanceAnalysis &PA) {
2879 FindDependencies(NeedsPositiveRetainCount, Arg,
2880 BB, Ret, DepInsts, V, PA);
2881 if (DepInsts.size() != 1)
2884 CallInst *Autorelease =
2885 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2888 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
2889 if (!IsAutorelease(AutoreleaseClass))
2891 if (GetArgRCIdentityRoot(Autorelease) != Arg)
2897 /// Look for this pattern:
2899 /// %call = call i8* @something(...)
2900 /// %2 = call i8* @objc_retain(i8* %call)
2901 /// %3 = call i8* @objc_autorelease(i8* %2)
2904 /// And delete the retain and autorelease.
2905 void ObjCARCOpt::OptimizeReturns(Function &F) {
2906 if (!F.getReturnType()->isPointerTy())
2909 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
2911 SmallPtrSet<Instruction *, 4> DependingInstructions;
2912 SmallPtrSet<const BasicBlock *, 4> Visited;
2913 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
2914 BasicBlock *BB = FI;
2915 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
2917 DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
2922 const Value *Arg = GetRCIdentityRoot(Ret->getOperand(0));
2924 // Look for an ``autorelease'' instruction that is a predecessor of Ret and
2925 // dependent on Arg such that there are no instructions dependent on Arg
2926 // that need a positive ref count in between the autorelease and Ret.
2927 CallInst *Autorelease =
2928 FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
2929 DependingInstructions, Visited,
2931 DependingInstructions.clear();
2938 FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
2939 DependingInstructions, Visited, PA);
2940 DependingInstructions.clear();
2946 // Check that there is nothing that can affect the reference count
2947 // between the retain and the call. Note that Retain need not be in BB.
2948 bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
2949 DependingInstructions,
2951 DependingInstructions.clear();
2954 if (!HasSafePathToCall)
2957 // If so, we can zap the retain and autorelease.
2960 DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
2961 << *Autorelease << "\n");
2962 EraseInstruction(Retain);
2963 EraseInstruction(Autorelease);
2969 ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
2970 llvm::Statistic &NumRetains =
2971 AfterOptimization? NumRetainsAfterOpt : NumRetainsBeforeOpt;
2972 llvm::Statistic &NumReleases =
2973 AfterOptimization? NumReleasesAfterOpt : NumReleasesBeforeOpt;
2975 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2976 Instruction *Inst = &*I++;
2977 switch (GetBasicInstructionClass(Inst)) {
2991 bool ObjCARCOpt::doInitialization(Module &M) {
2995 // If nothing in the Module uses ARC, don't do anything.
2996 Run = ModuleHasARC(M);
3000 // Identify the imprecise release metadata kind.
3001 ImpreciseReleaseMDKind =
3002 M.getContext().getMDKindID("clang.imprecise_release");
3003 CopyOnEscapeMDKind =
3004 M.getContext().getMDKindID("clang.arc.copy_on_escape");
3005 NoObjCARCExceptionsMDKind =
3006 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
3007 #ifdef ARC_ANNOTATIONS
3008 ARCAnnotationBottomUpMDKind =
3009 M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
3010 ARCAnnotationTopDownMDKind =
3011 M.getContext().getMDKindID("llvm.arc.annotation.topdown");
3012 ARCAnnotationProvenanceSourceMDKind =
3013 M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
3014 #endif // ARC_ANNOTATIONS
3016 // Intuitively, objc_retain and others are nocapture, however in practice
3017 // they are not, because they return their argument value. And objc_release
3018 // calls finalizers which can have arbitrary side effects.
3020 // Initialize our runtime entry point cache.
3026 bool ObjCARCOpt::runOnFunction(Function &F) {
3030 // If nothing in the Module uses ARC, don't do anything.
3036 DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
3039 PA.setAA(&getAnalysis<AliasAnalysis>());
3042 if (AreStatisticsEnabled()) {
3043 GatherStatistics(F, false);
3047 // This pass performs several distinct transformations. As a compile-time aid
3048 // when compiling code that isn't ObjC, skip these if the relevant ObjC
3049 // library functions aren't declared.
3051 // Preliminary optimizations. This also computes UsedInThisFunction.
3052 OptimizeIndividualCalls(F);
3054 // Optimizations for weak pointers.
3055 if (UsedInThisFunction & ((1 << IC_LoadWeak) |
3056 (1 << IC_LoadWeakRetained) |
3057 (1 << IC_StoreWeak) |
3058 (1 << IC_InitWeak) |
3059 (1 << IC_CopyWeak) |
3060 (1 << IC_MoveWeak) |
3061 (1 << IC_DestroyWeak)))
3062 OptimizeWeakCalls(F);
3064 // Optimizations for retain+release pairs.
3065 if (UsedInThisFunction & ((1 << IC_Retain) |
3066 (1 << IC_RetainRV) |
3067 (1 << IC_RetainBlock)))
3068 if (UsedInThisFunction & (1 << IC_Release))
3069 // Run OptimizeSequences until it either stops making changes or
3070 // no retain+release pair nesting is detected.
3071 while (OptimizeSequences(F)) {}
3073 // Optimizations if objc_autorelease is used.
3074 if (UsedInThisFunction & ((1 << IC_Autorelease) |
3075 (1 << IC_AutoreleaseRV)))
3078 // Gather statistics after optimization.
3080 if (AreStatisticsEnabled()) {
3081 GatherStatistics(F, true);
3085 DEBUG(dbgs() << "\n");
3090 void ObjCARCOpt::releaseMemory() {