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 //===----------------------------------------------------------------------===//
27 #define DEBUG_TYPE "objc-arc-opts"
29 #include "DependencyAnalysis.h"
30 #include "ObjCARCAliasAnalysis.h"
31 #include "ProvenanceAnalysis.h"
32 #include "llvm/ADT/DenseMap.h"
33 #include "llvm/ADT/STLExtras.h"
34 #include "llvm/ADT/SmallPtrSet.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/IR/IRBuilder.h"
37 #include "llvm/IR/LLVMContext.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/raw_ostream.h"
43 using namespace llvm::objcarc;
45 /// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
49 /// \brief An associative container with fast insertion-order (deterministic)
50 /// iteration over its elements. Plus the special blot operation.
51 template<class KeyT, class ValueT>
53 /// Map keys to indices in Vector.
54 typedef DenseMap<KeyT, size_t> MapTy;
57 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
62 typedef typename VectorTy::iterator iterator;
63 typedef typename VectorTy::const_iterator const_iterator;
64 iterator begin() { return Vector.begin(); }
65 iterator end() { return Vector.end(); }
66 const_iterator begin() const { return Vector.begin(); }
67 const_iterator end() const { return Vector.end(); }
71 assert(Vector.size() >= Map.size()); // May differ due to blotting.
72 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
74 assert(I->second < Vector.size());
75 assert(Vector[I->second].first == I->first);
77 for (typename VectorTy::const_iterator I = Vector.begin(),
78 E = Vector.end(); I != E; ++I)
80 (Map.count(I->first) &&
81 Map[I->first] == size_t(I - Vector.begin())));
85 ValueT &operator[](const KeyT &Arg) {
86 std::pair<typename MapTy::iterator, bool> Pair =
87 Map.insert(std::make_pair(Arg, size_t(0)));
89 size_t Num = Vector.size();
90 Pair.first->second = Num;
91 Vector.push_back(std::make_pair(Arg, ValueT()));
92 return Vector[Num].second;
94 return Vector[Pair.first->second].second;
97 std::pair<iterator, bool>
98 insert(const std::pair<KeyT, ValueT> &InsertPair) {
99 std::pair<typename MapTy::iterator, bool> Pair =
100 Map.insert(std::make_pair(InsertPair.first, size_t(0)));
102 size_t Num = Vector.size();
103 Pair.first->second = Num;
104 Vector.push_back(InsertPair);
105 return std::make_pair(Vector.begin() + Num, true);
107 return std::make_pair(Vector.begin() + Pair.first->second, false);
110 const_iterator find(const KeyT &Key) const {
111 typename MapTy::const_iterator It = Map.find(Key);
112 if (It == Map.end()) return Vector.end();
113 return Vector.begin() + It->second;
116 /// This is similar to erase, but instead of removing the element from the
117 /// vector, it just zeros out the key in the vector. This leaves iterators
118 /// intact, but clients must be prepared for zeroed-out keys when iterating.
119 void blot(const KeyT &Key) {
120 typename MapTy::iterator It = Map.find(Key);
121 if (It == Map.end()) return;
122 Vector[It->second].first = KeyT();
135 /// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
138 /// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon
139 /// as it finds a value with multiple uses.
140 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
141 if (Arg->hasOneUse()) {
142 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
143 return FindSingleUseIdentifiedObject(BC->getOperand(0));
144 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
145 if (GEP->hasAllZeroIndices())
146 return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
147 if (IsForwarding(GetBasicInstructionClass(Arg)))
148 return FindSingleUseIdentifiedObject(
149 cast<CallInst>(Arg)->getArgOperand(0));
150 if (!IsObjCIdentifiedObject(Arg))
155 // If we found an identifiable object but it has multiple uses, but they are
156 // trivial uses, we can still consider this to be a single-use value.
157 if (IsObjCIdentifiedObject(Arg)) {
158 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
161 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
171 /// \brief Test whether the given retainable object pointer escapes.
173 /// This differs from regular escape analysis in that a use as an
174 /// argument to a call is not considered an escape.
176 static bool DoesRetainableObjPtrEscape(const User *Ptr) {
177 DEBUG(dbgs() << "DoesRetainableObjPtrEscape: Target: " << *Ptr << "\n");
179 // Walk the def-use chains.
180 SmallVector<const Value *, 4> Worklist;
181 Worklist.push_back(Ptr);
182 // If Ptr has any operands add them as well.
183 for (User::const_op_iterator I = Ptr->op_begin(), E = Ptr->op_end(); I != E;
185 Worklist.push_back(*I);
188 // Ensure we do not visit any value twice.
189 SmallPtrSet<const Value *, 8> VisitedSet;
192 const Value *V = Worklist.pop_back_val();
194 DEBUG(dbgs() << "Visiting: " << *V << "\n");
196 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
198 const User *UUser = *UI;
200 DEBUG(dbgs() << "User: " << *UUser << "\n");
202 // Special - Use by a call (callee or argument) is not considered
204 switch (GetBasicInstructionClass(UUser)) {
209 case IC_AutoreleaseRV: {
210 DEBUG(dbgs() << "User copies pointer arguments. Pointer Escapes!\n");
211 // These special functions make copies of their pointer arguments.
214 case IC_IntrinsicUser:
215 // Use by the use intrinsic is not an escape.
219 // Use by an instruction which copies the value is an escape if the
220 // result is an escape.
221 if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) ||
222 isa<PHINode>(UUser) || isa<SelectInst>(UUser)) {
224 if (VisitedSet.insert(UUser)) {
225 DEBUG(dbgs() << "User copies value. Ptr escapes if result escapes."
226 " Adding to list.\n");
227 Worklist.push_back(UUser);
229 DEBUG(dbgs() << "Already visited node.\n");
233 // Use by a load is not an escape.
234 if (isa<LoadInst>(UUser))
236 // Use by a store is not an escape if the use is the address.
237 if (const StoreInst *SI = dyn_cast<StoreInst>(UUser))
238 if (V != SI->getValueOperand())
242 // Regular calls and other stuff are not considered escapes.
245 // Otherwise, conservatively assume an escape.
246 DEBUG(dbgs() << "Assuming ptr escapes.\n");
249 } while (!Worklist.empty());
252 DEBUG(dbgs() << "Ptr does not escape.\n");
258 /// \defgroup ARCOpt ARC Optimization.
261 // TODO: On code like this:
264 // stuff_that_cannot_release()
265 // objc_autorelease(%x)
266 // stuff_that_cannot_release()
268 // stuff_that_cannot_release()
269 // objc_autorelease(%x)
271 // The second retain and autorelease can be deleted.
273 // TODO: It should be possible to delete
274 // objc_autoreleasePoolPush and objc_autoreleasePoolPop
275 // pairs if nothing is actually autoreleased between them. Also, autorelease
276 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
277 // after inlining) can be turned into plain release calls.
279 // TODO: Critical-edge splitting. If the optimial insertion point is
280 // a critical edge, the current algorithm has to fail, because it doesn't
281 // know how to split edges. It should be possible to make the optimizer
282 // think in terms of edges, rather than blocks, and then split critical
285 // TODO: OptimizeSequences could generalized to be Interprocedural.
287 // TODO: Recognize that a bunch of other objc runtime calls have
288 // non-escaping arguments and non-releasing arguments, and may be
289 // non-autoreleasing.
291 // TODO: Sink autorelease calls as far as possible. Unfortunately we
292 // usually can't sink them past other calls, which would be the main
293 // case where it would be useful.
295 // TODO: The pointer returned from objc_loadWeakRetained is retained.
297 // TODO: Delete release+retain pairs (rare).
299 STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
300 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
301 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
302 STATISTIC(NumRets, "Number of return value forwarding "
303 "retain+autoreleaes eliminated");
304 STATISTIC(NumRRs, "Number of retain+release paths eliminated");
305 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
306 STATISTIC(NumRetainsBeforeOpt,
307 "Number of retains before optimization.");
308 STATISTIC(NumReleasesBeforeOpt,
309 "Number of releases before optimization.");
311 STATISTIC(NumRetainsAfterOpt,
312 "Number of retains after optimization.");
313 STATISTIC(NumReleasesAfterOpt,
314 "Number of releases after optimization.");
320 /// \brief A sequence of states that a pointer may go through in which an
321 /// objc_retain and objc_release are actually needed.
324 S_Retain, ///< objc_retain(x).
325 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement.
326 S_Use, ///< any use of x.
327 S_Stop, ///< like S_Release, but code motion is stopped.
328 S_Release, ///< objc_release(x).
329 S_MovableRelease ///< objc_release(x), !clang.imprecise_release.
332 raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
333 LLVM_ATTRIBUTE_UNUSED;
334 raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
337 return OS << "S_None";
339 return OS << "S_Retain";
341 return OS << "S_CanRelease";
343 return OS << "S_Use";
345 return OS << "S_Release";
346 case S_MovableRelease:
347 return OS << "S_MovableRelease";
349 return OS << "S_Stop";
351 llvm_unreachable("Unknown sequence type.");
355 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
359 if (A == S_None || B == S_None)
362 if (A > B) std::swap(A, B);
364 // Choose the side which is further along in the sequence.
365 if ((A == S_Retain || A == S_CanRelease) &&
366 (B == S_CanRelease || B == S_Use))
369 // Choose the side which is further along in the sequence.
370 if ((A == S_Use || A == S_CanRelease) &&
371 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
373 // If both sides are releases, choose the more conservative one.
374 if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
376 if (A == S_Release && B == S_MovableRelease)
384 /// \brief Unidirectional information about either a
385 /// retain-decrement-use-release sequence or release-use-decrement-retain
386 /// reverse sequence.
388 /// After an objc_retain, the reference count of the referenced
389 /// object is known to be positive. Similarly, before an objc_release, the
390 /// reference count of the referenced object is known to be positive. If
391 /// there are retain-release pairs in code regions where the retain count
392 /// is known to be positive, they can be eliminated, regardless of any side
393 /// effects between them.
395 /// Also, a retain+release pair nested within another retain+release
396 /// pair all on the known same pointer value can be eliminated, regardless
397 /// of any intervening side effects.
399 /// KnownSafe is true when either of these conditions is satisfied.
402 /// True of the objc_release calls are all marked with the "tail" keyword.
403 bool IsTailCallRelease;
405 /// If the Calls are objc_release calls and they all have a
406 /// clang.imprecise_release tag, this is the metadata tag.
407 MDNode *ReleaseMetadata;
409 /// For a top-down sequence, the set of objc_retains or
410 /// objc_retainBlocks. For bottom-up, the set of objc_releases.
411 SmallPtrSet<Instruction *, 2> Calls;
413 /// The set of optimal insert positions for moving calls in the opposite
415 SmallPtrSet<Instruction *, 2> ReverseInsertPts;
418 KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(0) {}
422 bool IsTrackingImpreciseReleases() {
423 return ReleaseMetadata != 0;
428 void RRInfo::clear() {
430 IsTailCallRelease = false;
433 ReverseInsertPts.clear();
437 /// \brief This class summarizes several per-pointer runtime properties which
438 /// are propogated through the flow graph.
440 /// True if the reference count is known to be incremented.
441 bool KnownPositiveRefCount;
443 /// True if we've seen an opportunity for partial RR elimination, such as
444 /// pushing calls into a CFG triangle or into one side of a CFG diamond.
447 /// The current position in the sequence.
451 /// Unidirectional information about the current sequence.
453 /// TODO: Encapsulate this better.
456 PtrState() : KnownPositiveRefCount(false), Partial(false),
459 void SetKnownPositiveRefCount() {
460 KnownPositiveRefCount = true;
463 void ClearKnownPositiveRefCount() {
464 KnownPositiveRefCount = false;
467 bool HasKnownPositiveRefCount() const {
468 return KnownPositiveRefCount;
471 void SetSeq(Sequence NewSeq) {
472 DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
476 Sequence GetSeq() const {
480 void ClearSequenceProgress() {
481 ResetSequenceProgress(S_None);
484 void ResetSequenceProgress(Sequence NewSeq) {
485 DEBUG(dbgs() << "Resetting sequence progress.\n");
491 void Merge(const PtrState &Other, bool TopDown);
496 PtrState::Merge(const PtrState &Other, bool TopDown) {
497 Seq = MergeSeqs(Seq, Other.Seq, TopDown);
498 KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
500 // If we're not in a sequence (anymore), drop all associated state.
504 } else if (Partial || Other.Partial) {
505 // If we're doing a merge on a path that's previously seen a partial
506 // merge, conservatively drop the sequence, to avoid doing partial
507 // RR elimination. If the branch predicates for the two merge differ,
508 // mixing them is unsafe.
509 ClearSequenceProgress();
511 // Conservatively merge the ReleaseMetadata information.
512 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
513 RRI.ReleaseMetadata = 0;
515 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
516 RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
517 Other.RRI.IsTailCallRelease;
518 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
520 // Merge the insert point sets. If there are any differences,
521 // that makes this a partial merge.
522 Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
523 for (SmallPtrSet<Instruction *, 2>::const_iterator
524 I = Other.RRI.ReverseInsertPts.begin(),
525 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
526 Partial |= RRI.ReverseInsertPts.insert(*I);
531 /// \brief Per-BasicBlock state.
533 /// The number of unique control paths from the entry which can reach this
535 unsigned TopDownPathCount;
537 /// The number of unique control paths to exits from this block.
538 unsigned BottomUpPathCount;
540 /// A type for PerPtrTopDown and PerPtrBottomUp.
541 typedef MapVector<const Value *, PtrState> MapTy;
543 /// The top-down traversal uses this to record information known about a
544 /// pointer at the bottom of each block.
547 /// The bottom-up traversal uses this to record information known about a
548 /// pointer at the top of each block.
549 MapTy PerPtrBottomUp;
551 /// Effective predecessors of the current block ignoring ignorable edges and
552 /// ignored backedges.
553 SmallVector<BasicBlock *, 2> Preds;
554 /// Effective successors of the current block ignoring ignorable edges and
555 /// ignored backedges.
556 SmallVector<BasicBlock *, 2> Succs;
559 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
561 typedef MapTy::iterator ptr_iterator;
562 typedef MapTy::const_iterator ptr_const_iterator;
564 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
565 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
566 ptr_const_iterator top_down_ptr_begin() const {
567 return PerPtrTopDown.begin();
569 ptr_const_iterator top_down_ptr_end() const {
570 return PerPtrTopDown.end();
573 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
574 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
575 ptr_const_iterator bottom_up_ptr_begin() const {
576 return PerPtrBottomUp.begin();
578 ptr_const_iterator bottom_up_ptr_end() const {
579 return PerPtrBottomUp.end();
582 /// Mark this block as being an entry block, which has one path from the
583 /// entry by definition.
584 void SetAsEntry() { TopDownPathCount = 1; }
586 /// Mark this block as being an exit block, which has one path to an exit by
588 void SetAsExit() { BottomUpPathCount = 1; }
590 PtrState &getPtrTopDownState(const Value *Arg) {
591 return PerPtrTopDown[Arg];
594 PtrState &getPtrBottomUpState(const Value *Arg) {
595 return PerPtrBottomUp[Arg];
598 void clearBottomUpPointers() {
599 PerPtrBottomUp.clear();
602 void clearTopDownPointers() {
603 PerPtrTopDown.clear();
606 void InitFromPred(const BBState &Other);
607 void InitFromSucc(const BBState &Other);
608 void MergePred(const BBState &Other);
609 void MergeSucc(const BBState &Other);
611 /// Return the number of possible unique paths from an entry to an exit
612 /// which pass through this block. This is only valid after both the
613 /// top-down and bottom-up traversals are complete.
614 unsigned GetAllPathCount() const {
615 assert(TopDownPathCount != 0);
616 assert(BottomUpPathCount != 0);
617 return TopDownPathCount * BottomUpPathCount;
620 // Specialized CFG utilities.
621 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
622 edge_iterator pred_begin() { return Preds.begin(); }
623 edge_iterator pred_end() { return Preds.end(); }
624 edge_iterator succ_begin() { return Succs.begin(); }
625 edge_iterator succ_end() { return Succs.end(); }
627 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
628 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
630 bool isExit() const { return Succs.empty(); }
634 void BBState::InitFromPred(const BBState &Other) {
635 PerPtrTopDown = Other.PerPtrTopDown;
636 TopDownPathCount = Other.TopDownPathCount;
639 void BBState::InitFromSucc(const BBState &Other) {
640 PerPtrBottomUp = Other.PerPtrBottomUp;
641 BottomUpPathCount = Other.BottomUpPathCount;
644 /// The top-down traversal uses this to merge information about predecessors to
645 /// form the initial state for a new block.
646 void BBState::MergePred(const BBState &Other) {
647 // Other.TopDownPathCount can be 0, in which case it is either dead or a
648 // loop backedge. Loop backedges are special.
649 TopDownPathCount += Other.TopDownPathCount;
651 // Check for overflow. If we have overflow, fall back to conservative
653 if (TopDownPathCount < Other.TopDownPathCount) {
654 clearTopDownPointers();
658 // For each entry in the other set, if our set has an entry with the same key,
659 // merge the entries. Otherwise, copy the entry and merge it with an empty
661 for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
662 ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
663 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
664 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
668 // For each entry in our set, if the other set doesn't have an entry with the
669 // same key, force it to merge with an empty entry.
670 for (ptr_iterator MI = top_down_ptr_begin(),
671 ME = top_down_ptr_end(); MI != ME; ++MI)
672 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
673 MI->second.Merge(PtrState(), /*TopDown=*/true);
676 /// The bottom-up traversal uses this to merge information about successors to
677 /// form the initial state for a new block.
678 void BBState::MergeSucc(const BBState &Other) {
679 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
680 // loop backedge. Loop backedges are special.
681 BottomUpPathCount += Other.BottomUpPathCount;
683 // Check for overflow. If we have overflow, fall back to conservative
685 if (BottomUpPathCount < Other.BottomUpPathCount) {
686 clearBottomUpPointers();
690 // For each entry in the other set, if our set has an entry with the
691 // same key, merge the entries. Otherwise, copy the entry and merge
692 // it with an empty entry.
693 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
694 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
695 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
696 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
700 // For each entry in our set, if the other set doesn't have an entry
701 // with the same key, force it to merge with an empty entry.
702 for (ptr_iterator MI = bottom_up_ptr_begin(),
703 ME = bottom_up_ptr_end(); MI != ME; ++MI)
704 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
705 MI->second.Merge(PtrState(), /*TopDown=*/false);
708 // Only enable ARC Annotations if we are building a debug version of
711 #define ARC_ANNOTATIONS
714 // Define some macros along the lines of DEBUG and some helper functions to make
715 // it cleaner to create annotations in the source code and to no-op when not
716 // building in debug mode.
717 #ifdef ARC_ANNOTATIONS
719 #include "llvm/Support/CommandLine.h"
721 /// Enable/disable ARC sequence annotations.
723 EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false),
724 cl::desc("Enable emission of arc data flow analysis "
727 DisableCheckForCFGHazards("disable-objc-arc-checkforcfghazards", cl::init(false),
728 cl::desc("Disable check for cfg hazards when "
730 static cl::opt<std::string>
731 ARCAnnotationTargetIdentifier("objc-arc-annotation-target-identifier",
733 cl::desc("filter out all data flow annotations "
734 "but those that apply to the given "
735 "target llvm identifier."));
737 /// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
738 /// instruction so that we can track backwards when post processing via the llvm
739 /// arc annotation processor tool. If the function is an
740 static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
744 // If pointer is a result of an instruction and it does not have a source
745 // MDNode it, attach a new MDNode onto it. If pointer is a result of
746 // an instruction and does have a source MDNode attached to it, return a
747 // reference to said Node. Otherwise just return 0.
748 if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
750 if (!(Node = Inst->getMetadata(NodeId))) {
751 // We do not have any node. Generate and attatch the hash MDString to the
754 // We just use an MDString to ensure that this metadata gets written out
755 // of line at the module level and to provide a very simple format
756 // encoding the information herein. Both of these makes it simpler to
757 // parse the annotations by a simple external program.
759 raw_string_ostream os(Str);
760 os << "(" << Inst->getParent()->getParent()->getName() << ",%"
761 << Inst->getName() << ")";
763 Hash = MDString::get(Inst->getContext(), os.str());
764 Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
766 // We have a node. Grab its hash and return it.
767 assert(Node->getNumOperands() == 1 &&
768 "An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
769 Hash = cast<MDString>(Node->getOperand(0));
771 } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
773 raw_string_ostream os(str);
774 os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
776 Hash = MDString::get(Arg->getContext(), os.str());
782 static std::string SequenceToString(Sequence A) {
784 raw_string_ostream os(str);
789 /// Helper function to change a Sequence into a String object using our overload
790 /// for raw_ostream so we only have printing code in one location.
791 static MDString *SequenceToMDString(LLVMContext &Context,
793 return MDString::get(Context, SequenceToString(A));
796 /// A simple function to generate a MDNode which describes the change in state
797 /// for Value *Ptr caused by Instruction *Inst.
798 static void AppendMDNodeToInstForPtr(unsigned NodeId,
801 MDString *PtrSourceMDNodeID,
805 Value *tmp[3] = {PtrSourceMDNodeID,
806 SequenceToMDString(Inst->getContext(),
808 SequenceToMDString(Inst->getContext(),
810 Node = MDNode::get(Inst->getContext(),
811 ArrayRef<Value*>(tmp, 3));
813 Inst->setMetadata(NodeId, Node);
816 /// Add to the beginning of the basic block llvm.ptr.annotations which show the
817 /// state of a pointer at the entrance to a basic block.
818 static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
819 Value *Ptr, Sequence Seq) {
820 // If we have a target identifier, make sure that we match it before
822 if(!ARCAnnotationTargetIdentifier.empty() &&
823 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
826 Module *M = BB->getParent()->getParent();
827 LLVMContext &C = M->getContext();
828 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
829 Type *I8XX = PointerType::getUnqual(I8X);
830 Type *Params[] = {I8XX, I8XX};
831 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
832 ArrayRef<Type*>(Params, 2),
834 Constant *Callee = M->getOrInsertFunction(Name, FTy);
836 IRBuilder<> Builder(BB, BB->getFirstInsertionPt());
839 StringRef Tmp = Ptr->getName();
840 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
841 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
843 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
844 cast<Constant>(ActualPtrName), Tmp);
848 std::string SeqStr = SequenceToString(Seq);
849 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
850 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
852 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
853 cast<Constant>(ActualPtrName), SeqStr);
856 Builder.CreateCall2(Callee, PtrName, S);
859 /// Add to the end of the basic block llvm.ptr.annotations which show the state
860 /// of the pointer at the bottom of the basic block.
861 static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
862 Value *Ptr, Sequence Seq) {
863 // If we have a target identifier, make sure that we match it before emitting
865 if(!ARCAnnotationTargetIdentifier.empty() &&
866 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
869 Module *M = BB->getParent()->getParent();
870 LLVMContext &C = M->getContext();
871 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
872 Type *I8XX = PointerType::getUnqual(I8X);
873 Type *Params[] = {I8XX, I8XX};
874 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
875 ArrayRef<Type*>(Params, 2),
877 Constant *Callee = M->getOrInsertFunction(Name, FTy);
879 IRBuilder<> Builder(BB, llvm::prior(BB->end()));
882 StringRef Tmp = Ptr->getName();
883 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
884 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
886 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
887 cast<Constant>(ActualPtrName), Tmp);
891 std::string SeqStr = SequenceToString(Seq);
892 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
893 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
895 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
896 cast<Constant>(ActualPtrName), SeqStr);
898 Builder.CreateCall2(Callee, PtrName, S);
901 /// Adds a source annotation to pointer and a state change annotation to Inst
902 /// referencing the source annotation and the old/new state of pointer.
903 static void GenerateARCAnnotation(unsigned InstMDId,
909 if (EnableARCAnnotations) {
910 // If we have a target identifier, make sure that we match it before
911 // emitting an annotation.
912 if(!ARCAnnotationTargetIdentifier.empty() &&
913 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
916 // First generate the source annotation on our pointer. This will return an
917 // MDString* if Ptr actually comes from an instruction implying we can put
918 // in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
919 // then we know that our pointer is from an Argument so we put a reference
920 // to the argument number.
922 // The point of this is to make it easy for the
923 // llvm-arc-annotation-processor tool to cross reference where the source
924 // pointer is in the LLVM IR since the LLVM IR parser does not submit such
925 // information via debug info for backends to use (since why would anyone
926 // need such a thing from LLVM IR besides in non standard cases
928 MDString *SourcePtrMDNode =
929 AppendMDNodeToSourcePtr(PtrMDId, Ptr);
930 AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
935 // The actual interface for accessing the above functionality is defined via
936 // some simple macros which are defined below. We do this so that the user does
937 // not need to pass in what metadata id is needed resulting in cleaner code and
938 // additionally since it provides an easy way to conditionally no-op all
939 // annotation support in a non-debug build.
941 /// Use this macro to annotate a sequence state change when processing
942 /// instructions bottom up,
943 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new) \
944 GenerateARCAnnotation(ARCAnnotationBottomUpMDKind, \
945 ARCAnnotationProvenanceSourceMDKind, (inst), \
946 const_cast<Value*>(ptr), (old), (new))
947 /// Use this macro to annotate a sequence state change when processing
948 /// instructions top down.
949 #define ANNOTATE_TOPDOWN(inst, ptr, old, new) \
950 GenerateARCAnnotation(ARCAnnotationTopDownMDKind, \
951 ARCAnnotationProvenanceSourceMDKind, (inst), \
952 const_cast<Value*>(ptr), (old), (new))
954 #define ANNOTATE_BB(_states, _bb, _name, _type, _direction) \
956 if (EnableARCAnnotations) { \
957 for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
958 E = (_states)._direction##_ptr_end(); I != E; ++I) { \
959 Value *Ptr = const_cast<Value*>(I->first); \
960 Sequence Seq = I->second.GetSeq(); \
961 GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq); \
966 #define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock) \
967 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
969 #define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock) \
970 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend", \
971 Terminator, bottom_up)
972 #define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock) \
973 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart", \
975 #define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock) \
976 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend", \
977 Terminator, top_down)
979 #else // !ARC_ANNOTATION
980 // If annotations are off, noop.
981 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
982 #define ANNOTATE_TOPDOWN(inst, ptr, old, new)
983 #define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
984 #define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
985 #define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
986 #define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
987 #endif // !ARC_ANNOTATION
990 /// \brief The main ARC optimization pass.
991 class ObjCARCOpt : public FunctionPass {
993 ProvenanceAnalysis PA;
995 /// A flag indicating whether this optimization pass should run.
998 /// Declarations for ObjC runtime functions, for use in creating calls to
999 /// them. These are initialized lazily to avoid cluttering up the Module
1000 /// with unused declarations.
1002 /// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
1003 Constant *AutoreleaseRVCallee;
1004 /// Declaration for ObjC runtime function objc_release.
1005 Constant *ReleaseCallee;
1006 /// Declaration for ObjC runtime function objc_retain.
1007 Constant *RetainCallee;
1008 /// Declaration for ObjC runtime function objc_retainBlock.
1009 Constant *RetainBlockCallee;
1010 /// Declaration for ObjC runtime function objc_autorelease.
1011 Constant *AutoreleaseCallee;
1013 /// Flags which determine whether each of the interesting runtine functions
1014 /// is in fact used in the current function.
1015 unsigned UsedInThisFunction;
1017 /// The Metadata Kind for clang.imprecise_release metadata.
1018 unsigned ImpreciseReleaseMDKind;
1020 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
1021 unsigned CopyOnEscapeMDKind;
1023 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
1024 unsigned NoObjCARCExceptionsMDKind;
1026 #ifdef ARC_ANNOTATIONS
1027 /// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
1028 unsigned ARCAnnotationBottomUpMDKind;
1029 /// The Metadata Kind for llvm.arc.annotation.topdown metadata.
1030 unsigned ARCAnnotationTopDownMDKind;
1031 /// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
1032 unsigned ARCAnnotationProvenanceSourceMDKind;
1033 #endif // ARC_ANNOATIONS
1035 Constant *getAutoreleaseRVCallee(Module *M);
1036 Constant *getReleaseCallee(Module *M);
1037 Constant *getRetainCallee(Module *M);
1038 Constant *getRetainBlockCallee(Module *M);
1039 Constant *getAutoreleaseCallee(Module *M);
1041 bool IsRetainBlockOptimizable(const Instruction *Inst);
1043 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
1044 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1045 InstructionClass &Class);
1046 bool OptimizeRetainBlockCall(Function &F, Instruction *RetainBlock,
1047 InstructionClass &Class);
1048 void OptimizeIndividualCalls(Function &F);
1050 void CheckForCFGHazards(const BasicBlock *BB,
1051 DenseMap<const BasicBlock *, BBState> &BBStates,
1052 BBState &MyStates) const;
1053 bool VisitInstructionBottomUp(Instruction *Inst,
1055 MapVector<Value *, RRInfo> &Retains,
1057 bool VisitBottomUp(BasicBlock *BB,
1058 DenseMap<const BasicBlock *, BBState> &BBStates,
1059 MapVector<Value *, RRInfo> &Retains);
1060 bool VisitInstructionTopDown(Instruction *Inst,
1061 DenseMap<Value *, RRInfo> &Releases,
1063 bool VisitTopDown(BasicBlock *BB,
1064 DenseMap<const BasicBlock *, BBState> &BBStates,
1065 DenseMap<Value *, RRInfo> &Releases);
1066 bool Visit(Function &F,
1067 DenseMap<const BasicBlock *, BBState> &BBStates,
1068 MapVector<Value *, RRInfo> &Retains,
1069 DenseMap<Value *, RRInfo> &Releases);
1071 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
1072 MapVector<Value *, RRInfo> &Retains,
1073 DenseMap<Value *, RRInfo> &Releases,
1074 SmallVectorImpl<Instruction *> &DeadInsts,
1077 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
1078 MapVector<Value *, RRInfo> &Retains,
1079 DenseMap<Value *, RRInfo> &Releases,
1081 SmallVector<Instruction *, 4> &NewRetains,
1082 SmallVector<Instruction *, 4> &NewReleases,
1083 SmallVector<Instruction *, 8> &DeadInsts,
1084 RRInfo &RetainsToMove,
1085 RRInfo &ReleasesToMove,
1088 bool &AnyPairsCompletelyEliminated);
1090 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
1091 MapVector<Value *, RRInfo> &Retains,
1092 DenseMap<Value *, RRInfo> &Releases,
1095 void OptimizeWeakCalls(Function &F);
1097 bool OptimizeSequences(Function &F);
1099 void OptimizeReturns(Function &F);
1102 void GatherStatistics(Function &F, bool AfterOptimization = false);
1105 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
1106 virtual bool doInitialization(Module &M);
1107 virtual bool runOnFunction(Function &F);
1108 virtual void releaseMemory();
1112 ObjCARCOpt() : FunctionPass(ID) {
1113 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
1118 char ObjCARCOpt::ID = 0;
1119 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
1120 "objc-arc", "ObjC ARC optimization", false, false)
1121 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
1122 INITIALIZE_PASS_END(ObjCARCOpt,
1123 "objc-arc", "ObjC ARC optimization", false, false)
1125 Pass *llvm::createObjCARCOptPass() {
1126 return new ObjCARCOpt();
1129 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
1130 AU.addRequired<ObjCARCAliasAnalysis>();
1131 AU.addRequired<AliasAnalysis>();
1132 // ARC optimization doesn't currently split critical edges.
1133 AU.setPreservesCFG();
1136 bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
1137 // Without the magic metadata tag, we have to assume this might be an
1138 // objc_retainBlock call inserted to convert a block pointer to an id,
1139 // in which case it really is needed.
1140 if (!Inst->getMetadata(CopyOnEscapeMDKind))
1143 // If the pointer "escapes" (not including being used in a call),
1144 // the copy may be needed.
1145 if (DoesRetainableObjPtrEscape(Inst))
1148 // Otherwise, it's not needed.
1152 Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
1153 if (!AutoreleaseRVCallee) {
1154 LLVMContext &C = M->getContext();
1155 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1156 Type *Params[] = { I8X };
1157 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1158 AttributeSet Attribute =
1159 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1160 Attribute::NoUnwind);
1161 AutoreleaseRVCallee =
1162 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
1165 return AutoreleaseRVCallee;
1168 Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
1169 if (!ReleaseCallee) {
1170 LLVMContext &C = M->getContext();
1171 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1172 AttributeSet Attribute =
1173 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1174 Attribute::NoUnwind);
1176 M->getOrInsertFunction(
1178 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
1181 return ReleaseCallee;
1184 Constant *ObjCARCOpt::getRetainCallee(Module *M) {
1185 if (!RetainCallee) {
1186 LLVMContext &C = M->getContext();
1187 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1188 AttributeSet Attribute =
1189 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1190 Attribute::NoUnwind);
1192 M->getOrInsertFunction(
1194 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1197 return RetainCallee;
1200 Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
1201 if (!RetainBlockCallee) {
1202 LLVMContext &C = M->getContext();
1203 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1204 // objc_retainBlock is not nounwind because it calls user copy constructors
1205 // which could theoretically throw.
1207 M->getOrInsertFunction(
1209 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1212 return RetainBlockCallee;
1215 Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
1216 if (!AutoreleaseCallee) {
1217 LLVMContext &C = M->getContext();
1218 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1219 AttributeSet Attribute =
1220 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1221 Attribute::NoUnwind);
1223 M->getOrInsertFunction(
1225 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1228 return AutoreleaseCallee;
1231 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
1232 /// not a return value. Or, if it can be paired with an
1233 /// objc_autoreleaseReturnValue, delete the pair and return true.
1235 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
1236 // Check for the argument being from an immediately preceding call or invoke.
1237 const Value *Arg = GetObjCArg(RetainRV);
1238 ImmutableCallSite CS(Arg);
1239 if (const Instruction *Call = CS.getInstruction()) {
1240 if (Call->getParent() == RetainRV->getParent()) {
1241 BasicBlock::const_iterator I = Call;
1243 while (IsNoopInstruction(I)) ++I;
1244 if (&*I == RetainRV)
1246 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
1247 BasicBlock *RetainRVParent = RetainRV->getParent();
1248 if (II->getNormalDest() == RetainRVParent) {
1249 BasicBlock::const_iterator I = RetainRVParent->begin();
1250 while (IsNoopInstruction(I)) ++I;
1251 if (&*I == RetainRV)
1257 // Check for being preceded by an objc_autoreleaseReturnValue on the same
1258 // pointer. In this case, we can delete the pair.
1259 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
1261 do --I; while (I != Begin && IsNoopInstruction(I));
1262 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
1263 GetObjCArg(I) == Arg) {
1267 DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
1268 << "Erasing " << *RetainRV << "\n");
1270 EraseInstruction(I);
1271 EraseInstruction(RetainRV);
1276 // Turn it to a plain objc_retain.
1280 DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
1281 "objc_retain since the operand is not a return value.\n"
1282 "Old = " << *RetainRV << "\n");
1284 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));
1286 DEBUG(dbgs() << "New = " << *RetainRV << "\n");
1291 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
1292 /// used as a return value.
1294 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1295 InstructionClass &Class) {
1296 // Check for a return of the pointer value.
1297 const Value *Ptr = GetObjCArg(AutoreleaseRV);
1298 SmallVector<const Value *, 2> Users;
1299 Users.push_back(Ptr);
1301 Ptr = Users.pop_back_val();
1302 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
1304 const User *I = *UI;
1305 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
1307 if (isa<BitCastInst>(I))
1310 } while (!Users.empty());
1315 DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
1316 "objc_autorelease since its operand is not used as a return "
1318 "Old = " << *AutoreleaseRV << "\n");
1320 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
1322 setCalledFunction(getAutoreleaseCallee(F.getParent()));
1323 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
1324 Class = IC_Autorelease;
1326 DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
1330 // \brief Attempt to strength reduce objc_retainBlock calls to objc_retain
1333 // Specifically: If an objc_retainBlock call has the copy_on_escape metadata and
1334 // does not escape (following the rules of block escaping), strength reduce the
1335 // objc_retainBlock to an objc_retain.
1337 // TODO: If an objc_retainBlock call is dominated period by a previous
1338 // objc_retainBlock call, strength reduce the objc_retainBlock to an
1341 ObjCARCOpt::OptimizeRetainBlockCall(Function &F, Instruction *Inst,
1342 InstructionClass &Class) {
1343 assert(GetBasicInstructionClass(Inst) == Class);
1344 assert(IC_RetainBlock == Class);
1346 // If we can not optimize Inst, return false.
1347 if (!IsRetainBlockOptimizable(Inst))
1353 DEBUG(dbgs() << "Strength reduced retainBlock => retain.\n");
1354 DEBUG(dbgs() << "Old: " << *Inst << "\n");
1355 CallInst *RetainBlock = cast<CallInst>(Inst);
1356 RetainBlock->setCalledFunction(getRetainCallee(F.getParent()));
1357 // Remove copy_on_escape metadata.
1358 RetainBlock->setMetadata(CopyOnEscapeMDKind, 0);
1360 DEBUG(dbgs() << "New: " << *Inst << "\n");
1364 /// Visit each call, one at a time, and make simplifications without doing any
1365 /// additional analysis.
1366 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
1367 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
1368 // Reset all the flags in preparation for recomputing them.
1369 UsedInThisFunction = 0;
1371 // Visit all objc_* calls in F.
1372 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1373 Instruction *Inst = &*I++;
1375 InstructionClass Class = GetBasicInstructionClass(Inst);
1377 DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
1382 // Delete no-op casts. These function calls have special semantics, but
1383 // the semantics are entirely implemented via lowering in the front-end,
1384 // so by the time they reach the optimizer, they are just no-op calls
1385 // which return their argument.
1387 // There are gray areas here, as the ability to cast reference-counted
1388 // pointers to raw void* and back allows code to break ARC assumptions,
1389 // however these are currently considered to be unimportant.
1393 DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
1394 EraseInstruction(Inst);
1397 // If the pointer-to-weak-pointer is null, it's undefined behavior.
1400 case IC_LoadWeakRetained:
1402 case IC_DestroyWeak: {
1403 CallInst *CI = cast<CallInst>(Inst);
1404 if (IsNullOrUndef(CI->getArgOperand(0))) {
1406 Type *Ty = CI->getArgOperand(0)->getType();
1407 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1408 Constant::getNullValue(Ty),
1410 llvm::Value *NewValue = UndefValue::get(CI->getType());
1411 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1412 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1413 CI->replaceAllUsesWith(NewValue);
1414 CI->eraseFromParent();
1421 CallInst *CI = cast<CallInst>(Inst);
1422 if (IsNullOrUndef(CI->getArgOperand(0)) ||
1423 IsNullOrUndef(CI->getArgOperand(1))) {
1425 Type *Ty = CI->getArgOperand(0)->getType();
1426 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1427 Constant::getNullValue(Ty),
1430 llvm::Value *NewValue = UndefValue::get(CI->getType());
1431 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1432 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1434 CI->replaceAllUsesWith(NewValue);
1435 CI->eraseFromParent();
1440 case IC_RetainBlock:
1441 // If we strength reduce an objc_retainBlock to an objc_retain, continue
1442 // onto the objc_retain peephole optimizations. Otherwise break.
1443 if (!OptimizeRetainBlockCall(F, Inst, Class))
1447 ++NumRetainsBeforeOpt;
1450 if (OptimizeRetainRVCall(F, Inst))
1453 case IC_AutoreleaseRV:
1454 OptimizeAutoreleaseRVCall(F, Inst, Class);
1457 ++NumReleasesBeforeOpt;
1461 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
1462 if (IsAutorelease(Class) && Inst->use_empty()) {
1463 CallInst *Call = cast<CallInst>(Inst);
1464 const Value *Arg = Call->getArgOperand(0);
1465 Arg = FindSingleUseIdentifiedObject(Arg);
1470 // Create the declaration lazily.
1471 LLVMContext &C = Inst->getContext();
1473 CallInst::Create(getReleaseCallee(F.getParent()),
1474 Call->getArgOperand(0), "", Call);
1475 NewCall->setMetadata(ImpreciseReleaseMDKind,
1476 MDNode::get(C, ArrayRef<Value *>()));
1478 DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
1479 "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
1480 << *NewCall << "\n");
1482 EraseInstruction(Call);
1488 // For functions which can never be passed stack arguments, add
1490 if (IsAlwaysTail(Class)) {
1492 DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
1493 "passed stack args: " << *Inst << "\n");
1494 cast<CallInst>(Inst)->setTailCall();
1497 // Ensure that functions that can never have a "tail" keyword due to the
1498 // semantics of ARC truly do not do so.
1499 if (IsNeverTail(Class)) {
1501 DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
1503 cast<CallInst>(Inst)->setTailCall(false);
1506 // Set nounwind as needed.
1507 if (IsNoThrow(Class)) {
1509 DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
1511 cast<CallInst>(Inst)->setDoesNotThrow();
1514 if (!IsNoopOnNull(Class)) {
1515 UsedInThisFunction |= 1 << Class;
1519 const Value *Arg = GetObjCArg(Inst);
1521 // ARC calls with null are no-ops. Delete them.
1522 if (IsNullOrUndef(Arg)) {
1525 DEBUG(dbgs() << "ARC calls with null are no-ops. Erasing: " << *Inst
1527 EraseInstruction(Inst);
1531 // Keep track of which of retain, release, autorelease, and retain_block
1532 // are actually present in this function.
1533 UsedInThisFunction |= 1 << Class;
1535 // If Arg is a PHI, and one or more incoming values to the
1536 // PHI are null, and the call is control-equivalent to the PHI, and there
1537 // are no relevant side effects between the PHI and the call, the call
1538 // could be pushed up to just those paths with non-null incoming values.
1539 // For now, don't bother splitting critical edges for this.
1540 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
1541 Worklist.push_back(std::make_pair(Inst, Arg));
1543 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
1547 const PHINode *PN = dyn_cast<PHINode>(Arg);
1550 // Determine if the PHI has any null operands, or any incoming
1552 bool HasNull = false;
1553 bool HasCriticalEdges = false;
1554 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1556 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1557 if (IsNullOrUndef(Incoming))
1559 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
1560 .getNumSuccessors() != 1) {
1561 HasCriticalEdges = true;
1565 // If we have null operands and no critical edges, optimize.
1566 if (!HasCriticalEdges && HasNull) {
1567 SmallPtrSet<Instruction *, 4> DependingInstructions;
1568 SmallPtrSet<const BasicBlock *, 4> Visited;
1570 // Check that there is nothing that cares about the reference
1571 // count between the call and the phi.
1574 case IC_RetainBlock:
1575 // These can always be moved up.
1578 // These can't be moved across things that care about the retain
1580 FindDependencies(NeedsPositiveRetainCount, Arg,
1581 Inst->getParent(), Inst,
1582 DependingInstructions, Visited, PA);
1584 case IC_Autorelease:
1585 // These can't be moved across autorelease pool scope boundaries.
1586 FindDependencies(AutoreleasePoolBoundary, Arg,
1587 Inst->getParent(), Inst,
1588 DependingInstructions, Visited, PA);
1591 case IC_AutoreleaseRV:
1592 // Don't move these; the RV optimization depends on the autoreleaseRV
1593 // being tail called, and the retainRV being immediately after a call
1594 // (which might still happen if we get lucky with codegen layout, but
1595 // it's not worth taking the chance).
1598 llvm_unreachable("Invalid dependence flavor");
1601 if (DependingInstructions.size() == 1 &&
1602 *DependingInstructions.begin() == PN) {
1605 // Clone the call into each predecessor that has a non-null value.
1606 CallInst *CInst = cast<CallInst>(Inst);
1607 Type *ParamTy = CInst->getArgOperand(0)->getType();
1608 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1610 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1611 if (!IsNullOrUndef(Incoming)) {
1612 CallInst *Clone = cast<CallInst>(CInst->clone());
1613 Value *Op = PN->getIncomingValue(i);
1614 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
1615 if (Op->getType() != ParamTy)
1616 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
1617 Clone->setArgOperand(0, Op);
1618 Clone->insertBefore(InsertPos);
1620 DEBUG(dbgs() << "Cloning "
1622 "And inserting clone at " << *InsertPos << "\n");
1623 Worklist.push_back(std::make_pair(Clone, Incoming));
1626 // Erase the original call.
1627 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
1628 EraseInstruction(CInst);
1632 } while (!Worklist.empty());
1636 /// If we have a top down pointer in the S_Use state, make sure that there are
1637 /// no CFG hazards by checking the states of various bottom up pointers.
1638 static void CheckForUseCFGHazard(const Sequence SuccSSeq,
1639 const bool SuccSRRIKnownSafe,
1641 bool &SomeSuccHasSame,
1642 bool &AllSuccsHaveSame,
1643 bool &ShouldContinue) {
1645 case S_CanRelease: {
1646 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
1647 S.ClearSequenceProgress();
1650 ShouldContinue = true;
1654 SomeSuccHasSame = true;
1658 case S_MovableRelease:
1659 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1660 AllSuccsHaveSame = false;
1663 llvm_unreachable("bottom-up pointer in retain state!");
1665 llvm_unreachable("This should have been handled earlier.");
1669 /// If we have a Top Down pointer in the S_CanRelease state, make sure that
1670 /// there are no CFG hazards by checking the states of various bottom up
1672 static void CheckForCanReleaseCFGHazard(const Sequence SuccSSeq,
1673 const bool SuccSRRIKnownSafe,
1675 bool &SomeSuccHasSame,
1676 bool &AllSuccsHaveSame) {
1679 SomeSuccHasSame = true;
1683 case S_MovableRelease:
1685 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1686 AllSuccsHaveSame = false;
1689 llvm_unreachable("bottom-up pointer in retain state!");
1691 llvm_unreachable("This should have been handled earlier.");
1695 /// Check for critical edges, loop boundaries, irreducible control flow, or
1696 /// other CFG structures where moving code across the edge would result in it
1697 /// being executed more.
1699 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
1700 DenseMap<const BasicBlock *, BBState> &BBStates,
1701 BBState &MyStates) const {
1702 // If any top-down local-use or possible-dec has a succ which is earlier in
1703 // the sequence, forget it.
1704 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
1705 E = MyStates.top_down_ptr_end(); I != E; ++I) {
1706 PtrState &S = I->second;
1707 const Sequence Seq = I->second.GetSeq();
1709 // We only care about S_Retain, S_CanRelease, and S_Use.
1713 // Make sure that if extra top down states are added in the future that this
1714 // code is updated to handle it.
1715 assert((Seq == S_Retain || Seq == S_CanRelease || Seq == S_Use) &&
1716 "Unknown top down sequence state.");
1718 const Value *Arg = I->first;
1719 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
1720 bool SomeSuccHasSame = false;
1721 bool AllSuccsHaveSame = true;
1723 succ_const_iterator SI(TI), SE(TI, false);
1725 for (; SI != SE; ++SI) {
1726 // If VisitBottomUp has pointer information for this successor, take
1727 // what we know about it.
1728 const DenseMap<const BasicBlock *, BBState>::iterator BBI =
1730 assert(BBI != BBStates.end());
1731 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
1732 const Sequence SuccSSeq = SuccS.GetSeq();
1734 // If bottom up, the pointer is in an S_None state, clear the sequence
1735 // progress since the sequence in the bottom up state finished
1736 // suggesting a mismatch in between retains/releases. This is true for
1737 // all three cases that we are handling here: S_Retain, S_Use, and
1739 if (SuccSSeq == S_None) {
1740 S.ClearSequenceProgress();
1744 // If we have S_Use or S_CanRelease, perform our check for cfg hazard
1746 const bool SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
1748 // *NOTE* We do not use Seq from above here since we are allowing for
1749 // S.GetSeq() to change while we are visiting basic blocks.
1750 switch(S.GetSeq()) {
1752 bool ShouldContinue = false;
1753 CheckForUseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S,
1754 SomeSuccHasSame, AllSuccsHaveSame,
1760 case S_CanRelease: {
1761 CheckForCanReleaseCFGHazard(SuccSSeq, SuccSRRIKnownSafe,
1770 case S_MovableRelease:
1775 // If the state at the other end of any of the successor edges
1776 // matches the current state, require all edges to match. This
1777 // guards against loops in the middle of a sequence.
1778 if (SomeSuccHasSame && !AllSuccsHaveSame)
1779 S.ClearSequenceProgress();
1784 ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
1786 MapVector<Value *, RRInfo> &Retains,
1787 BBState &MyStates) {
1788 bool NestingDetected = false;
1789 InstructionClass Class = GetInstructionClass(Inst);
1790 const Value *Arg = 0;
1792 DEBUG(dbgs() << "Class: " << Class << "\n");
1796 Arg = GetObjCArg(Inst);
1798 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1800 // If we see two releases in a row on the same pointer. If so, make
1801 // a note, and we'll cicle back to revisit it after we've
1802 // hopefully eliminated the second release, which may allow us to
1803 // eliminate the first release too.
1804 // Theoretically we could implement removal of nested retain+release
1805 // pairs by making PtrState hold a stack of states, but this is
1806 // simple and avoids adding overhead for the non-nested case.
1807 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
1808 DEBUG(dbgs() << "Found nested releases (i.e. a release pair)\n");
1809 NestingDetected = true;
1812 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
1813 Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
1814 ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
1815 S.ResetSequenceProgress(NewSeq);
1816 S.RRI.ReleaseMetadata = ReleaseMetadata;
1817 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
1818 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
1819 S.RRI.Calls.insert(Inst);
1820 S.SetKnownPositiveRefCount();
1823 case IC_RetainBlock:
1824 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1825 // objc_retainBlocks to objc_retains. Thus at this point any
1826 // objc_retainBlocks that we see are not optimizable.
1830 Arg = GetObjCArg(Inst);
1832 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1833 S.SetKnownPositiveRefCount();
1835 Sequence OldSeq = S.GetSeq();
1839 case S_MovableRelease:
1841 // If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
1842 // imprecise release, clear our reverse insertion points.
1843 if (OldSeq != S_Use || S.RRI.IsTrackingImpreciseReleases())
1844 S.RRI.ReverseInsertPts.clear();
1847 // Don't do retain+release tracking for IC_RetainRV, because it's
1848 // better to let it remain as the first instruction after a call.
1849 if (Class != IC_RetainRV)
1850 Retains[Inst] = S.RRI;
1851 S.ClearSequenceProgress();
1856 llvm_unreachable("bottom-up pointer in retain state!");
1858 ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
1859 // A retain moving bottom up can be a use.
1862 case IC_AutoreleasepoolPop:
1863 // Conservatively, clear MyStates for all known pointers.
1864 MyStates.clearBottomUpPointers();
1865 return NestingDetected;
1866 case IC_AutoreleasepoolPush:
1868 // These are irrelevant.
1869 return NestingDetected;
1874 // Consider any other possible effects of this instruction on each
1875 // pointer being tracked.
1876 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
1877 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
1878 const Value *Ptr = MI->first;
1880 continue; // Handled above.
1881 PtrState &S = MI->second;
1882 Sequence Seq = S.GetSeq();
1884 // Check for possible releases.
1885 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
1886 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
1888 S.ClearKnownPositiveRefCount();
1891 S.SetSeq(S_CanRelease);
1892 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
1896 case S_MovableRelease:
1901 llvm_unreachable("bottom-up pointer in retain state!");
1905 // Check for possible direct uses.
1908 case S_MovableRelease:
1909 if (CanUse(Inst, Ptr, PA, Class)) {
1910 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
1912 assert(S.RRI.ReverseInsertPts.empty());
1913 // If this is an invoke instruction, we're scanning it as part of
1914 // one of its successor blocks, since we can't insert code after it
1915 // in its own block, and we don't want to split critical edges.
1916 if (isa<InvokeInst>(Inst))
1917 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1919 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1921 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1922 } else if (Seq == S_Release && IsUser(Class)) {
1923 DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
1925 // Non-movable releases depend on any possible objc pointer use.
1927 ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
1928 assert(S.RRI.ReverseInsertPts.empty());
1929 // As above; handle invoke specially.
1930 if (isa<InvokeInst>(Inst))
1931 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1933 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1937 if (CanUse(Inst, Ptr, PA, Class)) {
1938 DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
1941 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1949 llvm_unreachable("bottom-up pointer in retain state!");
1953 return NestingDetected;
1957 ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
1958 DenseMap<const BasicBlock *, BBState> &BBStates,
1959 MapVector<Value *, RRInfo> &Retains) {
1961 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
1963 bool NestingDetected = false;
1964 BBState &MyStates = BBStates[BB];
1966 // Merge the states from each successor to compute the initial state
1967 // for the current block.
1968 BBState::edge_iterator SI(MyStates.succ_begin()),
1969 SE(MyStates.succ_end());
1971 const BasicBlock *Succ = *SI;
1972 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
1973 assert(I != BBStates.end());
1974 MyStates.InitFromSucc(I->second);
1976 for (; SI != SE; ++SI) {
1978 I = BBStates.find(Succ);
1979 assert(I != BBStates.end());
1980 MyStates.MergeSucc(I->second);
1984 // If ARC Annotations are enabled, output the current state of pointers at the
1985 // bottom of the basic block.
1986 ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);
1988 // Visit all the instructions, bottom-up.
1989 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
1990 Instruction *Inst = llvm::prior(I);
1992 // Invoke instructions are visited as part of their successors (below).
1993 if (isa<InvokeInst>(Inst))
1996 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1998 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
2001 // If there's a predecessor with an invoke, visit the invoke as if it were
2002 // part of this block, since we can't insert code after an invoke in its own
2003 // block, and we don't want to split critical edges.
2004 for (BBState::edge_iterator PI(MyStates.pred_begin()),
2005 PE(MyStates.pred_end()); PI != PE; ++PI) {
2006 BasicBlock *Pred = *PI;
2007 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
2008 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
2011 // If ARC Annotations are enabled, output the current state of pointers at the
2012 // top of the basic block.
2013 ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);
2015 return NestingDetected;
2019 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
2020 DenseMap<Value *, RRInfo> &Releases,
2021 BBState &MyStates) {
2022 bool NestingDetected = false;
2023 InstructionClass Class = GetInstructionClass(Inst);
2024 const Value *Arg = 0;
2027 case IC_RetainBlock:
2028 // In OptimizeIndividualCalls, we have strength reduced all optimizable
2029 // objc_retainBlocks to objc_retains. Thus at this point any
2030 // objc_retainBlocks that we see are not optimizable.
2034 Arg = GetObjCArg(Inst);
2036 PtrState &S = MyStates.getPtrTopDownState(Arg);
2038 // Don't do retain+release tracking for IC_RetainRV, because it's
2039 // better to let it remain as the first instruction after a call.
2040 if (Class != IC_RetainRV) {
2041 // If we see two retains in a row on the same pointer. If so, make
2042 // a note, and we'll cicle back to revisit it after we've
2043 // hopefully eliminated the second retain, which may allow us to
2044 // eliminate the first retain too.
2045 // Theoretically we could implement removal of nested retain+release
2046 // pairs by making PtrState hold a stack of states, but this is
2047 // simple and avoids adding overhead for the non-nested case.
2048 if (S.GetSeq() == S_Retain)
2049 NestingDetected = true;
2051 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
2052 S.ResetSequenceProgress(S_Retain);
2053 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
2054 S.RRI.Calls.insert(Inst);
2057 S.SetKnownPositiveRefCount();
2059 // A retain can be a potential use; procede to the generic checking
2064 Arg = GetObjCArg(Inst);
2066 PtrState &S = MyStates.getPtrTopDownState(Arg);
2067 S.ClearKnownPositiveRefCount();
2069 Sequence OldSeq = S.GetSeq();
2071 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
2076 if (OldSeq == S_Retain || ReleaseMetadata != 0)
2077 S.RRI.ReverseInsertPts.clear();
2080 S.RRI.ReleaseMetadata = ReleaseMetadata;
2081 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
2082 Releases[Inst] = S.RRI;
2083 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
2084 S.ClearSequenceProgress();
2090 case S_MovableRelease:
2091 llvm_unreachable("top-down pointer in release state!");
2095 case IC_AutoreleasepoolPop:
2096 // Conservatively, clear MyStates for all known pointers.
2097 MyStates.clearTopDownPointers();
2098 return NestingDetected;
2099 case IC_AutoreleasepoolPush:
2101 // These are irrelevant.
2102 return NestingDetected;
2107 // Consider any other possible effects of this instruction on each
2108 // pointer being tracked.
2109 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
2110 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
2111 const Value *Ptr = MI->first;
2113 continue; // Handled above.
2114 PtrState &S = MI->second;
2115 Sequence Seq = S.GetSeq();
2117 // Check for possible releases.
2118 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
2119 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
2121 S.ClearKnownPositiveRefCount();
2124 S.SetSeq(S_CanRelease);
2125 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
2126 assert(S.RRI.ReverseInsertPts.empty());
2127 S.RRI.ReverseInsertPts.insert(Inst);
2129 // One call can't cause a transition from S_Retain to S_CanRelease
2130 // and S_CanRelease to S_Use. If we've made the first transition,
2139 case S_MovableRelease:
2140 llvm_unreachable("top-down pointer in release state!");
2144 // Check for possible direct uses.
2147 if (CanUse(Inst, Ptr, PA, Class)) {
2148 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
2151 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_Use);
2160 case S_MovableRelease:
2161 llvm_unreachable("top-down pointer in release state!");
2165 return NestingDetected;
2169 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
2170 DenseMap<const BasicBlock *, BBState> &BBStates,
2171 DenseMap<Value *, RRInfo> &Releases) {
2172 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
2173 bool NestingDetected = false;
2174 BBState &MyStates = BBStates[BB];
2176 // Merge the states from each predecessor to compute the initial state
2177 // for the current block.
2178 BBState::edge_iterator PI(MyStates.pred_begin()),
2179 PE(MyStates.pred_end());
2181 const BasicBlock *Pred = *PI;
2182 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
2183 assert(I != BBStates.end());
2184 MyStates.InitFromPred(I->second);
2186 for (; PI != PE; ++PI) {
2188 I = BBStates.find(Pred);
2189 assert(I != BBStates.end());
2190 MyStates.MergePred(I->second);
2194 // If ARC Annotations are enabled, output the current state of pointers at the
2195 // top of the basic block.
2196 ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);
2198 // Visit all the instructions, top-down.
2199 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
2200 Instruction *Inst = I;
2202 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
2204 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
2207 // If ARC Annotations are enabled, output the current state of pointers at the
2208 // bottom of the basic block.
2209 ANNOTATE_TOPDOWN_BBEND(MyStates, BB);
2211 #ifdef ARC_ANNOTATIONS
2212 if (!(EnableARCAnnotations && DisableCheckForCFGHazards))
2214 CheckForCFGHazards(BB, BBStates, MyStates);
2215 return NestingDetected;
2219 ComputePostOrders(Function &F,
2220 SmallVectorImpl<BasicBlock *> &PostOrder,
2221 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
2222 unsigned NoObjCARCExceptionsMDKind,
2223 DenseMap<const BasicBlock *, BBState> &BBStates) {
2224 /// The visited set, for doing DFS walks.
2225 SmallPtrSet<BasicBlock *, 16> Visited;
2227 // Do DFS, computing the PostOrder.
2228 SmallPtrSet<BasicBlock *, 16> OnStack;
2229 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
2231 // Functions always have exactly one entry block, and we don't have
2232 // any other block that we treat like an entry block.
2233 BasicBlock *EntryBB = &F.getEntryBlock();
2234 BBState &MyStates = BBStates[EntryBB];
2235 MyStates.SetAsEntry();
2236 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
2237 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
2238 Visited.insert(EntryBB);
2239 OnStack.insert(EntryBB);
2242 BasicBlock *CurrBB = SuccStack.back().first;
2243 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
2244 succ_iterator SE(TI, false);
2246 while (SuccStack.back().second != SE) {
2247 BasicBlock *SuccBB = *SuccStack.back().second++;
2248 if (Visited.insert(SuccBB)) {
2249 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
2250 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
2251 BBStates[CurrBB].addSucc(SuccBB);
2252 BBState &SuccStates = BBStates[SuccBB];
2253 SuccStates.addPred(CurrBB);
2254 OnStack.insert(SuccBB);
2258 if (!OnStack.count(SuccBB)) {
2259 BBStates[CurrBB].addSucc(SuccBB);
2260 BBStates[SuccBB].addPred(CurrBB);
2263 OnStack.erase(CurrBB);
2264 PostOrder.push_back(CurrBB);
2265 SuccStack.pop_back();
2266 } while (!SuccStack.empty());
2270 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
2271 // Functions may have many exits, and there also blocks which we treat
2272 // as exits due to ignored edges.
2273 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
2274 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
2275 BasicBlock *ExitBB = I;
2276 BBState &MyStates = BBStates[ExitBB];
2277 if (!MyStates.isExit())
2280 MyStates.SetAsExit();
2282 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
2283 Visited.insert(ExitBB);
2284 while (!PredStack.empty()) {
2285 reverse_dfs_next_succ:
2286 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
2287 while (PredStack.back().second != PE) {
2288 BasicBlock *BB = *PredStack.back().second++;
2289 if (Visited.insert(BB)) {
2290 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
2291 goto reverse_dfs_next_succ;
2294 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
2299 // Visit the function both top-down and bottom-up.
2301 ObjCARCOpt::Visit(Function &F,
2302 DenseMap<const BasicBlock *, BBState> &BBStates,
2303 MapVector<Value *, RRInfo> &Retains,
2304 DenseMap<Value *, RRInfo> &Releases) {
2306 // Use reverse-postorder traversals, because we magically know that loops
2307 // will be well behaved, i.e. they won't repeatedly call retain on a single
2308 // pointer without doing a release. We can't use the ReversePostOrderTraversal
2309 // class here because we want the reverse-CFG postorder to consider each
2310 // function exit point, and we want to ignore selected cycle edges.
2311 SmallVector<BasicBlock *, 16> PostOrder;
2312 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
2313 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
2314 NoObjCARCExceptionsMDKind,
2317 // Use reverse-postorder on the reverse CFG for bottom-up.
2318 bool BottomUpNestingDetected = false;
2319 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2320 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
2322 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
2324 // Use reverse-postorder for top-down.
2325 bool TopDownNestingDetected = false;
2326 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2327 PostOrder.rbegin(), E = PostOrder.rend();
2329 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
2331 return TopDownNestingDetected && BottomUpNestingDetected;
2334 /// Move the calls in RetainsToMove and ReleasesToMove.
2335 void ObjCARCOpt::MoveCalls(Value *Arg,
2336 RRInfo &RetainsToMove,
2337 RRInfo &ReleasesToMove,
2338 MapVector<Value *, RRInfo> &Retains,
2339 DenseMap<Value *, RRInfo> &Releases,
2340 SmallVectorImpl<Instruction *> &DeadInsts,
2342 Type *ArgTy = Arg->getType();
2343 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
2345 DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
2347 // Insert the new retain and release calls.
2348 for (SmallPtrSet<Instruction *, 2>::const_iterator
2349 PI = ReleasesToMove.ReverseInsertPts.begin(),
2350 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2351 Instruction *InsertPt = *PI;
2352 Value *MyArg = ArgTy == ParamTy ? Arg :
2353 new BitCastInst(Arg, ParamTy, "", InsertPt);
2355 CallInst::Create(getRetainCallee(M), MyArg, "", InsertPt);
2356 Call->setDoesNotThrow();
2357 Call->setTailCall();
2359 DEBUG(dbgs() << "Inserting new Retain: " << *Call << "\n"
2360 "At insertion point: " << *InsertPt << "\n");
2362 for (SmallPtrSet<Instruction *, 2>::const_iterator
2363 PI = RetainsToMove.ReverseInsertPts.begin(),
2364 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2365 Instruction *InsertPt = *PI;
2366 Value *MyArg = ArgTy == ParamTy ? Arg :
2367 new BitCastInst(Arg, ParamTy, "", InsertPt);
2368 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
2370 // Attach a clang.imprecise_release metadata tag, if appropriate.
2371 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
2372 Call->setMetadata(ImpreciseReleaseMDKind, M);
2373 Call->setDoesNotThrow();
2374 if (ReleasesToMove.IsTailCallRelease)
2375 Call->setTailCall();
2377 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
2378 "At insertion point: " << *InsertPt << "\n");
2381 // Delete the original retain and release calls.
2382 for (SmallPtrSet<Instruction *, 2>::const_iterator
2383 AI = RetainsToMove.Calls.begin(),
2384 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
2385 Instruction *OrigRetain = *AI;
2386 Retains.blot(OrigRetain);
2387 DeadInsts.push_back(OrigRetain);
2388 DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
2390 for (SmallPtrSet<Instruction *, 2>::const_iterator
2391 AI = ReleasesToMove.Calls.begin(),
2392 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
2393 Instruction *OrigRelease = *AI;
2394 Releases.erase(OrigRelease);
2395 DeadInsts.push_back(OrigRelease);
2396 DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
2402 ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
2404 MapVector<Value *, RRInfo> &Retains,
2405 DenseMap<Value *, RRInfo> &Releases,
2407 SmallVector<Instruction *, 4> &NewRetains,
2408 SmallVector<Instruction *, 4> &NewReleases,
2409 SmallVector<Instruction *, 8> &DeadInsts,
2410 RRInfo &RetainsToMove,
2411 RRInfo &ReleasesToMove,
2414 bool &AnyPairsCompletelyEliminated) {
2415 // If a pair happens in a region where it is known that the reference count
2416 // is already incremented, we can similarly ignore possible decrements.
2417 bool KnownSafeTD = true, KnownSafeBU = true;
2419 // Connect the dots between the top-down-collected RetainsToMove and
2420 // bottom-up-collected ReleasesToMove to form sets of related calls.
2421 // This is an iterative process so that we connect multiple releases
2422 // to multiple retains if needed.
2423 unsigned OldDelta = 0;
2424 unsigned NewDelta = 0;
2425 unsigned OldCount = 0;
2426 unsigned NewCount = 0;
2427 bool FirstRelease = true;
2429 for (SmallVectorImpl<Instruction *>::const_iterator
2430 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
2431 Instruction *NewRetain = *NI;
2432 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
2433 assert(It != Retains.end());
2434 const RRInfo &NewRetainRRI = It->second;
2435 KnownSafeTD &= NewRetainRRI.KnownSafe;
2436 for (SmallPtrSet<Instruction *, 2>::const_iterator
2437 LI = NewRetainRRI.Calls.begin(),
2438 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
2439 Instruction *NewRetainRelease = *LI;
2440 DenseMap<Value *, RRInfo>::const_iterator Jt =
2441 Releases.find(NewRetainRelease);
2442 if (Jt == Releases.end())
2444 const RRInfo &NewRetainReleaseRRI = Jt->second;
2445 assert(NewRetainReleaseRRI.Calls.count(NewRetain));
2446 if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
2448 BBStates[NewRetainRelease->getParent()].GetAllPathCount();
2450 // Merge the ReleaseMetadata and IsTailCallRelease values.
2452 ReleasesToMove.ReleaseMetadata =
2453 NewRetainReleaseRRI.ReleaseMetadata;
2454 ReleasesToMove.IsTailCallRelease =
2455 NewRetainReleaseRRI.IsTailCallRelease;
2456 FirstRelease = false;
2458 if (ReleasesToMove.ReleaseMetadata !=
2459 NewRetainReleaseRRI.ReleaseMetadata)
2460 ReleasesToMove.ReleaseMetadata = 0;
2461 if (ReleasesToMove.IsTailCallRelease !=
2462 NewRetainReleaseRRI.IsTailCallRelease)
2463 ReleasesToMove.IsTailCallRelease = false;
2466 // Collect the optimal insertion points.
2468 for (SmallPtrSet<Instruction *, 2>::const_iterator
2469 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
2470 RE = NewRetainReleaseRRI.ReverseInsertPts.end();
2472 Instruction *RIP = *RI;
2473 if (ReleasesToMove.ReverseInsertPts.insert(RIP))
2474 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
2476 NewReleases.push_back(NewRetainRelease);
2481 if (NewReleases.empty()) break;
2483 // Back the other way.
2484 for (SmallVectorImpl<Instruction *>::const_iterator
2485 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
2486 Instruction *NewRelease = *NI;
2487 DenseMap<Value *, RRInfo>::const_iterator It =
2488 Releases.find(NewRelease);
2489 assert(It != Releases.end());
2490 const RRInfo &NewReleaseRRI = It->second;
2491 KnownSafeBU &= NewReleaseRRI.KnownSafe;
2492 for (SmallPtrSet<Instruction *, 2>::const_iterator
2493 LI = NewReleaseRRI.Calls.begin(),
2494 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
2495 Instruction *NewReleaseRetain = *LI;
2496 MapVector<Value *, RRInfo>::const_iterator Jt =
2497 Retains.find(NewReleaseRetain);
2498 if (Jt == Retains.end())
2500 const RRInfo &NewReleaseRetainRRI = Jt->second;
2501 assert(NewReleaseRetainRRI.Calls.count(NewRelease));
2502 if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
2503 unsigned PathCount =
2504 BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
2505 OldDelta += PathCount;
2506 OldCount += PathCount;
2508 // Collect the optimal insertion points.
2510 for (SmallPtrSet<Instruction *, 2>::const_iterator
2511 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
2512 RE = NewReleaseRetainRRI.ReverseInsertPts.end();
2514 Instruction *RIP = *RI;
2515 if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
2516 PathCount = BBStates[RIP->getParent()].GetAllPathCount();
2517 NewDelta += PathCount;
2518 NewCount += PathCount;
2521 NewRetains.push_back(NewReleaseRetain);
2525 NewReleases.clear();
2526 if (NewRetains.empty()) break;
2529 // If the pointer is known incremented or nested, we can safely delete the
2530 // pair regardless of what's between them.
2531 if (KnownSafeTD || KnownSafeBU) {
2532 RetainsToMove.ReverseInsertPts.clear();
2533 ReleasesToMove.ReverseInsertPts.clear();
2536 // Determine whether the new insertion points we computed preserve the
2537 // balance of retain and release calls through the program.
2538 // TODO: If the fully aggressive solution isn't valid, try to find a
2539 // less aggressive solution which is.
2544 // Determine whether the original call points are balanced in the retain and
2545 // release calls through the program. If not, conservatively don't touch
2547 // TODO: It's theoretically possible to do code motion in this case, as
2548 // long as the existing imbalances are maintained.
2552 #ifdef ARC_ANNOTATIONS
2553 // Do not move calls if ARC annotations are requested.
2554 if (EnableARCAnnotations)
2556 #endif // ARC_ANNOTATIONS
2559 assert(OldCount != 0 && "Unreachable code?");
2560 NumRRs += OldCount - NewCount;
2561 // Set to true if we completely removed any RR pairs.
2562 AnyPairsCompletelyEliminated = NewCount == 0;
2564 // We can move calls!
2568 /// Identify pairings between the retains and releases, and delete and/or move
2571 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
2573 MapVector<Value *, RRInfo> &Retains,
2574 DenseMap<Value *, RRInfo> &Releases,
2576 DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
2578 bool AnyPairsCompletelyEliminated = false;
2579 RRInfo RetainsToMove;
2580 RRInfo ReleasesToMove;
2581 SmallVector<Instruction *, 4> NewRetains;
2582 SmallVector<Instruction *, 4> NewReleases;
2583 SmallVector<Instruction *, 8> DeadInsts;
2585 // Visit each retain.
2586 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
2587 E = Retains.end(); I != E; ++I) {
2588 Value *V = I->first;
2589 if (!V) continue; // blotted
2591 Instruction *Retain = cast<Instruction>(V);
2593 DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
2595 Value *Arg = GetObjCArg(Retain);
2597 // If the object being released is in static or stack storage, we know it's
2598 // not being managed by ObjC reference counting, so we can delete pairs
2599 // regardless of what possible decrements or uses lie between them.
2600 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
2602 // A constant pointer can't be pointing to an object on the heap. It may
2603 // be reference-counted, but it won't be deleted.
2604 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
2605 if (const GlobalVariable *GV =
2606 dyn_cast<GlobalVariable>(
2607 StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
2608 if (GV->isConstant())
2611 // Connect the dots between the top-down-collected RetainsToMove and
2612 // bottom-up-collected ReleasesToMove to form sets of related calls.
2613 NewRetains.push_back(Retain);
2614 bool PerformMoveCalls =
2615 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
2616 NewReleases, DeadInsts, RetainsToMove,
2617 ReleasesToMove, Arg, KnownSafe,
2618 AnyPairsCompletelyEliminated);
2620 if (PerformMoveCalls) {
2621 // Ok, everything checks out and we're all set. Let's move/delete some
2623 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
2624 Retains, Releases, DeadInsts, M);
2627 // Clean up state for next retain.
2628 NewReleases.clear();
2630 RetainsToMove.clear();
2631 ReleasesToMove.clear();
2634 // Now that we're done moving everything, we can delete the newly dead
2635 // instructions, as we no longer need them as insert points.
2636 while (!DeadInsts.empty())
2637 EraseInstruction(DeadInsts.pop_back_val());
2639 return AnyPairsCompletelyEliminated;
2642 /// Weak pointer optimizations.
2643 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
2644 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
2646 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
2647 // itself because it uses AliasAnalysis and we need to do provenance
2649 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2650 Instruction *Inst = &*I++;
2652 DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
2654 InstructionClass Class = GetBasicInstructionClass(Inst);
2655 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
2658 // Delete objc_loadWeak calls with no users.
2659 if (Class == IC_LoadWeak && Inst->use_empty()) {
2660 Inst->eraseFromParent();
2664 // TODO: For now, just look for an earlier available version of this value
2665 // within the same block. Theoretically, we could do memdep-style non-local
2666 // analysis too, but that would want caching. A better approach would be to
2667 // use the technique that EarlyCSE uses.
2668 inst_iterator Current = llvm::prior(I);
2669 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
2670 for (BasicBlock::iterator B = CurrentBB->begin(),
2671 J = Current.getInstructionIterator();
2673 Instruction *EarlierInst = &*llvm::prior(J);
2674 InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
2675 switch (EarlierClass) {
2677 case IC_LoadWeakRetained: {
2678 // If this is loading from the same pointer, replace this load's value
2680 CallInst *Call = cast<CallInst>(Inst);
2681 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2682 Value *Arg = Call->getArgOperand(0);
2683 Value *EarlierArg = EarlierCall->getArgOperand(0);
2684 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2685 case AliasAnalysis::MustAlias:
2687 // If the load has a builtin retain, insert a plain retain for it.
2688 if (Class == IC_LoadWeakRetained) {
2690 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
2694 // Zap the fully redundant load.
2695 Call->replaceAllUsesWith(EarlierCall);
2696 Call->eraseFromParent();
2698 case AliasAnalysis::MayAlias:
2699 case AliasAnalysis::PartialAlias:
2701 case AliasAnalysis::NoAlias:
2708 // If this is storing to the same pointer and has the same size etc.
2709 // replace this load's value with the stored value.
2710 CallInst *Call = cast<CallInst>(Inst);
2711 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2712 Value *Arg = Call->getArgOperand(0);
2713 Value *EarlierArg = EarlierCall->getArgOperand(0);
2714 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2715 case AliasAnalysis::MustAlias:
2717 // If the load has a builtin retain, insert a plain retain for it.
2718 if (Class == IC_LoadWeakRetained) {
2720 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
2724 // Zap the fully redundant load.
2725 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
2726 Call->eraseFromParent();
2728 case AliasAnalysis::MayAlias:
2729 case AliasAnalysis::PartialAlias:
2731 case AliasAnalysis::NoAlias:
2738 // TOOD: Grab the copied value.
2740 case IC_AutoreleasepoolPush:
2742 case IC_IntrinsicUser:
2744 // Weak pointers are only modified through the weak entry points
2745 // (and arbitrary calls, which could call the weak entry points).
2748 // Anything else could modify the weak pointer.
2755 // Then, for each destroyWeak with an alloca operand, check to see if
2756 // the alloca and all its users can be zapped.
2757 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2758 Instruction *Inst = &*I++;
2759 InstructionClass Class = GetBasicInstructionClass(Inst);
2760 if (Class != IC_DestroyWeak)
2763 CallInst *Call = cast<CallInst>(Inst);
2764 Value *Arg = Call->getArgOperand(0);
2765 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
2766 for (Value::use_iterator UI = Alloca->use_begin(),
2767 UE = Alloca->use_end(); UI != UE; ++UI) {
2768 const Instruction *UserInst = cast<Instruction>(*UI);
2769 switch (GetBasicInstructionClass(UserInst)) {
2772 case IC_DestroyWeak:
2779 for (Value::use_iterator UI = Alloca->use_begin(),
2780 UE = Alloca->use_end(); UI != UE; ) {
2781 CallInst *UserInst = cast<CallInst>(*UI++);
2782 switch (GetBasicInstructionClass(UserInst)) {
2785 // These functions return their second argument.
2786 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
2788 case IC_DestroyWeak:
2792 llvm_unreachable("alloca really is used!");
2794 UserInst->eraseFromParent();
2796 Alloca->eraseFromParent();
2802 /// Identify program paths which execute sequences of retains and releases which
2803 /// can be eliminated.
2804 bool ObjCARCOpt::OptimizeSequences(Function &F) {
2805 /// Releases, Retains - These are used to store the results of the main flow
2806 /// analysis. These use Value* as the key instead of Instruction* so that the
2807 /// map stays valid when we get around to rewriting code and calls get
2808 /// replaced by arguments.
2809 DenseMap<Value *, RRInfo> Releases;
2810 MapVector<Value *, RRInfo> Retains;
2812 /// This is used during the traversal of the function to track the
2813 /// states for each identified object at each block.
2814 DenseMap<const BasicBlock *, BBState> BBStates;
2816 // Analyze the CFG of the function, and all instructions.
2817 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
2820 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
2824 /// Check if there is a dependent call earlier that does not have anything in
2825 /// between the Retain and the call that can affect the reference count of their
2826 /// shared pointer argument. Note that Retain need not be in BB.
2828 HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
2829 SmallPtrSet<Instruction *, 4> &DepInsts,
2830 SmallPtrSet<const BasicBlock *, 4> &Visited,
2831 ProvenanceAnalysis &PA) {
2832 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
2833 DepInsts, Visited, PA);
2834 if (DepInsts.size() != 1)
2838 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2840 // Check that the pointer is the return value of the call.
2841 if (!Call || Arg != Call)
2844 // Check that the call is a regular call.
2845 InstructionClass Class = GetBasicInstructionClass(Call);
2846 if (Class != IC_CallOrUser && Class != IC_Call)
2852 /// Find a dependent retain that precedes the given autorelease for which there
2853 /// is nothing in between the two instructions that can affect the ref count of
2856 FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
2857 Instruction *Autorelease,
2858 SmallPtrSet<Instruction *, 4> &DepInsts,
2859 SmallPtrSet<const BasicBlock *, 4> &Visited,
2860 ProvenanceAnalysis &PA) {
2861 FindDependencies(CanChangeRetainCount, Arg,
2862 BB, Autorelease, DepInsts, Visited, PA);
2863 if (DepInsts.size() != 1)
2867 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2869 // Check that we found a retain with the same argument.
2871 !IsRetain(GetBasicInstructionClass(Retain)) ||
2872 GetObjCArg(Retain) != Arg) {
2879 /// Look for an ``autorelease'' instruction dependent on Arg such that there are
2880 /// no instructions dependent on Arg that need a positive ref count in between
2881 /// the autorelease and the ret.
2883 FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
2885 SmallPtrSet<Instruction *, 4> &DepInsts,
2886 SmallPtrSet<const BasicBlock *, 4> &V,
2887 ProvenanceAnalysis &PA) {
2888 FindDependencies(NeedsPositiveRetainCount, Arg,
2889 BB, Ret, DepInsts, V, PA);
2890 if (DepInsts.size() != 1)
2893 CallInst *Autorelease =
2894 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2897 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
2898 if (!IsAutorelease(AutoreleaseClass))
2900 if (GetObjCArg(Autorelease) != Arg)
2906 /// Look for this pattern:
2908 /// %call = call i8* @something(...)
2909 /// %2 = call i8* @objc_retain(i8* %call)
2910 /// %3 = call i8* @objc_autorelease(i8* %2)
2913 /// And delete the retain and autorelease.
2914 void ObjCARCOpt::OptimizeReturns(Function &F) {
2915 if (!F.getReturnType()->isPointerTy())
2918 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
2920 SmallPtrSet<Instruction *, 4> DependingInstructions;
2921 SmallPtrSet<const BasicBlock *, 4> Visited;
2922 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
2923 BasicBlock *BB = FI;
2924 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
2926 DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
2931 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
2933 // Look for an ``autorelease'' instruction that is a predecessor of Ret and
2934 // dependent on Arg such that there are no instructions dependent on Arg
2935 // that need a positive ref count in between the autorelease and Ret.
2936 CallInst *Autorelease =
2937 FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
2938 DependingInstructions, Visited,
2940 DependingInstructions.clear();
2947 FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
2948 DependingInstructions, Visited, PA);
2949 DependingInstructions.clear();
2955 // Check that there is nothing that can affect the reference count
2956 // between the retain and the call. Note that Retain need not be in BB.
2957 bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
2958 DependingInstructions,
2960 DependingInstructions.clear();
2963 if (!HasSafePathToCall)
2966 // If so, we can zap the retain and autorelease.
2969 DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
2970 << *Autorelease << "\n");
2971 EraseInstruction(Retain);
2972 EraseInstruction(Autorelease);
2978 ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
2979 llvm::Statistic &NumRetains =
2980 AfterOptimization? NumRetainsAfterOpt : NumRetainsBeforeOpt;
2981 llvm::Statistic &NumReleases =
2982 AfterOptimization? NumReleasesAfterOpt : NumReleasesBeforeOpt;
2984 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2985 Instruction *Inst = &*I++;
2986 switch (GetBasicInstructionClass(Inst)) {
3000 bool ObjCARCOpt::doInitialization(Module &M) {
3004 // If nothing in the Module uses ARC, don't do anything.
3005 Run = ModuleHasARC(M);
3009 // Identify the imprecise release metadata kind.
3010 ImpreciseReleaseMDKind =
3011 M.getContext().getMDKindID("clang.imprecise_release");
3012 CopyOnEscapeMDKind =
3013 M.getContext().getMDKindID("clang.arc.copy_on_escape");
3014 NoObjCARCExceptionsMDKind =
3015 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
3016 #ifdef ARC_ANNOTATIONS
3017 ARCAnnotationBottomUpMDKind =
3018 M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
3019 ARCAnnotationTopDownMDKind =
3020 M.getContext().getMDKindID("llvm.arc.annotation.topdown");
3021 ARCAnnotationProvenanceSourceMDKind =
3022 M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
3023 #endif // ARC_ANNOTATIONS
3025 // Intuitively, objc_retain and others are nocapture, however in practice
3026 // they are not, because they return their argument value. And objc_release
3027 // calls finalizers which can have arbitrary side effects.
3029 // These are initialized lazily.
3030 AutoreleaseRVCallee = 0;
3033 RetainBlockCallee = 0;
3034 AutoreleaseCallee = 0;
3039 bool ObjCARCOpt::runOnFunction(Function &F) {
3043 // If nothing in the Module uses ARC, don't do anything.
3049 DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
3052 PA.setAA(&getAnalysis<AliasAnalysis>());
3054 // This pass performs several distinct transformations. As a compile-time aid
3055 // when compiling code that isn't ObjC, skip these if the relevant ObjC
3056 // library functions aren't declared.
3058 // Preliminary optimizations. This also computes UsedInThisFunction.
3059 OptimizeIndividualCalls(F);
3061 // Optimizations for weak pointers.
3062 if (UsedInThisFunction & ((1 << IC_LoadWeak) |
3063 (1 << IC_LoadWeakRetained) |
3064 (1 << IC_StoreWeak) |
3065 (1 << IC_InitWeak) |
3066 (1 << IC_CopyWeak) |
3067 (1 << IC_MoveWeak) |
3068 (1 << IC_DestroyWeak)))
3069 OptimizeWeakCalls(F);
3071 // Optimizations for retain+release pairs.
3072 if (UsedInThisFunction & ((1 << IC_Retain) |
3073 (1 << IC_RetainRV) |
3074 (1 << IC_RetainBlock)))
3075 if (UsedInThisFunction & (1 << IC_Release))
3076 // Run OptimizeSequences until it either stops making changes or
3077 // no retain+release pair nesting is detected.
3078 while (OptimizeSequences(F)) {}
3080 // Optimizations if objc_autorelease is used.
3081 if (UsedInThisFunction & ((1 << IC_Autorelease) |
3082 (1 << IC_AutoreleaseRV)))
3085 // Gather statistics after optimization.
3087 if (AreStatisticsEnabled()) {
3088 GatherStatistics(F, true);
3092 DEBUG(dbgs() << "\n");
3097 void ObjCARCOpt::releaseMemory() {