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");
310 /// \brief A sequence of states that a pointer may go through in which an
311 /// objc_retain and objc_release are actually needed.
314 S_Retain, ///< objc_retain(x).
315 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement.
316 S_Use, ///< any use of x.
317 S_Stop, ///< like S_Release, but code motion is stopped.
318 S_Release, ///< objc_release(x).
319 S_MovableRelease ///< objc_release(x), !clang.imprecise_release.
322 raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
323 LLVM_ATTRIBUTE_UNUSED;
324 raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
327 return OS << "S_None";
329 return OS << "S_Retain";
331 return OS << "S_CanRelease";
333 return OS << "S_Use";
335 return OS << "S_Release";
336 case S_MovableRelease:
337 return OS << "S_MovableRelease";
339 return OS << "S_Stop";
341 llvm_unreachable("Unknown sequence type.");
345 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
349 if (A == S_None || B == S_None)
352 if (A > B) std::swap(A, B);
354 // Choose the side which is further along in the sequence.
355 if ((A == S_Retain || A == S_CanRelease) &&
356 (B == S_CanRelease || B == S_Use))
359 // Choose the side which is further along in the sequence.
360 if ((A == S_Use || A == S_CanRelease) &&
361 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
363 // If both sides are releases, choose the more conservative one.
364 if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
366 if (A == S_Release && B == S_MovableRelease)
374 /// \brief Unidirectional information about either a
375 /// retain-decrement-use-release sequence or release-use-decrement-retain
376 /// reverse sequence.
378 /// After an objc_retain, the reference count of the referenced
379 /// object is known to be positive. Similarly, before an objc_release, the
380 /// reference count of the referenced object is known to be positive. If
381 /// there are retain-release pairs in code regions where the retain count
382 /// is known to be positive, they can be eliminated, regardless of any side
383 /// effects between them.
385 /// Also, a retain+release pair nested within another retain+release
386 /// pair all on the known same pointer value can be eliminated, regardless
387 /// of any intervening side effects.
389 /// KnownSafe is true when either of these conditions is satisfied.
392 /// True of the objc_release calls are all marked with the "tail" keyword.
393 bool IsTailCallRelease;
395 /// If the Calls are objc_release calls and they all have a
396 /// clang.imprecise_release tag, this is the metadata tag.
397 MDNode *ReleaseMetadata;
399 /// For a top-down sequence, the set of objc_retains or
400 /// objc_retainBlocks. For bottom-up, the set of objc_releases.
401 SmallPtrSet<Instruction *, 2> Calls;
403 /// The set of optimal insert positions for moving calls in the opposite
405 SmallPtrSet<Instruction *, 2> ReverseInsertPts;
408 KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(0) {}
412 bool IsTrackingImpreciseReleases() {
413 return ReleaseMetadata != 0;
418 void RRInfo::clear() {
420 IsTailCallRelease = false;
423 ReverseInsertPts.clear();
427 /// \brief This class summarizes several per-pointer runtime properties which
428 /// are propogated through the flow graph.
430 /// True if the reference count is known to be incremented.
431 bool KnownPositiveRefCount;
433 /// True if we've seen an opportunity for partial RR elimination, such as
434 /// pushing calls into a CFG triangle or into one side of a CFG diamond.
437 /// The current position in the sequence.
441 /// Unidirectional information about the current sequence.
443 /// TODO: Encapsulate this better.
446 PtrState() : KnownPositiveRefCount(false), Partial(false),
449 void SetKnownPositiveRefCount() {
450 KnownPositiveRefCount = true;
453 void ClearKnownPositiveRefCount() {
454 KnownPositiveRefCount = false;
457 bool HasKnownPositiveRefCount() const {
458 return KnownPositiveRefCount;
461 void SetSeq(Sequence NewSeq) {
462 DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
466 Sequence GetSeq() const {
470 void ClearSequenceProgress() {
471 ResetSequenceProgress(S_None);
474 void ResetSequenceProgress(Sequence NewSeq) {
480 void Merge(const PtrState &Other, bool TopDown);
485 PtrState::Merge(const PtrState &Other, bool TopDown) {
486 Seq = MergeSeqs(Seq, Other.Seq, TopDown);
487 KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
489 // If we're not in a sequence (anymore), drop all associated state.
493 } else if (Partial || Other.Partial) {
494 // If we're doing a merge on a path that's previously seen a partial
495 // merge, conservatively drop the sequence, to avoid doing partial
496 // RR elimination. If the branch predicates for the two merge differ,
497 // mixing them is unsafe.
498 ClearSequenceProgress();
500 // Conservatively merge the ReleaseMetadata information.
501 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
502 RRI.ReleaseMetadata = 0;
504 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
505 RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
506 Other.RRI.IsTailCallRelease;
507 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
509 // Merge the insert point sets. If there are any differences,
510 // that makes this a partial merge.
511 Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
512 for (SmallPtrSet<Instruction *, 2>::const_iterator
513 I = Other.RRI.ReverseInsertPts.begin(),
514 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
515 Partial |= RRI.ReverseInsertPts.insert(*I);
520 /// \brief Per-BasicBlock state.
522 /// The number of unique control paths from the entry which can reach this
524 unsigned TopDownPathCount;
526 /// The number of unique control paths to exits from this block.
527 unsigned BottomUpPathCount;
529 /// A type for PerPtrTopDown and PerPtrBottomUp.
530 typedef MapVector<const Value *, PtrState> MapTy;
532 /// The top-down traversal uses this to record information known about a
533 /// pointer at the bottom of each block.
536 /// The bottom-up traversal uses this to record information known about a
537 /// pointer at the top of each block.
538 MapTy PerPtrBottomUp;
540 /// Effective predecessors of the current block ignoring ignorable edges and
541 /// ignored backedges.
542 SmallVector<BasicBlock *, 2> Preds;
543 /// Effective successors of the current block ignoring ignorable edges and
544 /// ignored backedges.
545 SmallVector<BasicBlock *, 2> Succs;
548 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
550 typedef MapTy::iterator ptr_iterator;
551 typedef MapTy::const_iterator ptr_const_iterator;
553 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
554 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
555 ptr_const_iterator top_down_ptr_begin() const {
556 return PerPtrTopDown.begin();
558 ptr_const_iterator top_down_ptr_end() const {
559 return PerPtrTopDown.end();
562 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
563 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
564 ptr_const_iterator bottom_up_ptr_begin() const {
565 return PerPtrBottomUp.begin();
567 ptr_const_iterator bottom_up_ptr_end() const {
568 return PerPtrBottomUp.end();
571 /// Mark this block as being an entry block, which has one path from the
572 /// entry by definition.
573 void SetAsEntry() { TopDownPathCount = 1; }
575 /// Mark this block as being an exit block, which has one path to an exit by
577 void SetAsExit() { BottomUpPathCount = 1; }
579 PtrState &getPtrTopDownState(const Value *Arg) {
580 return PerPtrTopDown[Arg];
583 PtrState &getPtrBottomUpState(const Value *Arg) {
584 return PerPtrBottomUp[Arg];
587 void clearBottomUpPointers() {
588 PerPtrBottomUp.clear();
591 void clearTopDownPointers() {
592 PerPtrTopDown.clear();
595 void InitFromPred(const BBState &Other);
596 void InitFromSucc(const BBState &Other);
597 void MergePred(const BBState &Other);
598 void MergeSucc(const BBState &Other);
600 /// Return the number of possible unique paths from an entry to an exit
601 /// which pass through this block. This is only valid after both the
602 /// top-down and bottom-up traversals are complete.
603 unsigned GetAllPathCount() const {
604 assert(TopDownPathCount != 0);
605 assert(BottomUpPathCount != 0);
606 return TopDownPathCount * BottomUpPathCount;
609 // Specialized CFG utilities.
610 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
611 edge_iterator pred_begin() { return Preds.begin(); }
612 edge_iterator pred_end() { return Preds.end(); }
613 edge_iterator succ_begin() { return Succs.begin(); }
614 edge_iterator succ_end() { return Succs.end(); }
616 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
617 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
619 bool isExit() const { return Succs.empty(); }
623 void BBState::InitFromPred(const BBState &Other) {
624 PerPtrTopDown = Other.PerPtrTopDown;
625 TopDownPathCount = Other.TopDownPathCount;
628 void BBState::InitFromSucc(const BBState &Other) {
629 PerPtrBottomUp = Other.PerPtrBottomUp;
630 BottomUpPathCount = Other.BottomUpPathCount;
633 /// The top-down traversal uses this to merge information about predecessors to
634 /// form the initial state for a new block.
635 void BBState::MergePred(const BBState &Other) {
636 // Other.TopDownPathCount can be 0, in which case it is either dead or a
637 // loop backedge. Loop backedges are special.
638 TopDownPathCount += Other.TopDownPathCount;
640 // Check for overflow. If we have overflow, fall back to conservative
642 if (TopDownPathCount < Other.TopDownPathCount) {
643 clearTopDownPointers();
647 // For each entry in the other set, if our set has an entry with the same key,
648 // merge the entries. Otherwise, copy the entry and merge it with an empty
650 for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
651 ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
652 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
653 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
657 // For each entry in our set, if the other set doesn't have an entry with the
658 // same key, force it to merge with an empty entry.
659 for (ptr_iterator MI = top_down_ptr_begin(),
660 ME = top_down_ptr_end(); MI != ME; ++MI)
661 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
662 MI->second.Merge(PtrState(), /*TopDown=*/true);
665 /// The bottom-up traversal uses this to merge information about successors to
666 /// form the initial state for a new block.
667 void BBState::MergeSucc(const BBState &Other) {
668 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
669 // loop backedge. Loop backedges are special.
670 BottomUpPathCount += Other.BottomUpPathCount;
672 // Check for overflow. If we have overflow, fall back to conservative
674 if (BottomUpPathCount < Other.BottomUpPathCount) {
675 clearBottomUpPointers();
679 // For each entry in the other set, if our set has an entry with the
680 // same key, merge the entries. Otherwise, copy the entry and merge
681 // it with an empty entry.
682 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
683 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
684 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
685 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
689 // For each entry in our set, if the other set doesn't have an entry
690 // with the same key, force it to merge with an empty entry.
691 for (ptr_iterator MI = bottom_up_ptr_begin(),
692 ME = bottom_up_ptr_end(); MI != ME; ++MI)
693 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
694 MI->second.Merge(PtrState(), /*TopDown=*/false);
697 // Only enable ARC Annotations if we are building a debug version of
700 #define ARC_ANNOTATIONS
703 // Define some macros along the lines of DEBUG and some helper functions to make
704 // it cleaner to create annotations in the source code and to no-op when not
705 // building in debug mode.
706 #ifdef ARC_ANNOTATIONS
708 #include "llvm/Support/CommandLine.h"
710 /// Enable/disable ARC sequence annotations.
712 EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false),
713 cl::desc("Enable emission of arc data flow analysis "
716 DisableCheckForCFGHazards("disable-objc-arc-checkforcfghazards", cl::init(false),
717 cl::desc("Disable check for cfg hazards when "
720 /// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
721 /// instruction so that we can track backwards when post processing via the llvm
722 /// arc annotation processor tool. If the function is an
723 static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
727 // If pointer is a result of an instruction and it does not have a source
728 // MDNode it, attach a new MDNode onto it. If pointer is a result of
729 // an instruction and does have a source MDNode attached to it, return a
730 // reference to said Node. Otherwise just return 0.
731 if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
733 if (!(Node = Inst->getMetadata(NodeId))) {
734 // We do not have any node. Generate and attatch the hash MDString to the
737 // We just use an MDString to ensure that this metadata gets written out
738 // of line at the module level and to provide a very simple format
739 // encoding the information herein. Both of these makes it simpler to
740 // parse the annotations by a simple external program.
742 raw_string_ostream os(Str);
743 os << "(" << Inst->getParent()->getParent()->getName() << ",%"
744 << Inst->getName() << ")";
746 Hash = MDString::get(Inst->getContext(), os.str());
747 Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
749 // We have a node. Grab its hash and return it.
750 assert(Node->getNumOperands() == 1 &&
751 "An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
752 Hash = cast<MDString>(Node->getOperand(0));
754 } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
756 raw_string_ostream os(str);
757 os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
759 Hash = MDString::get(Arg->getContext(), os.str());
765 static std::string SequenceToString(Sequence A) {
767 raw_string_ostream os(str);
772 /// Helper function to change a Sequence into a String object using our overload
773 /// for raw_ostream so we only have printing code in one location.
774 static MDString *SequenceToMDString(LLVMContext &Context,
776 return MDString::get(Context, SequenceToString(A));
779 /// A simple function to generate a MDNode which describes the change in state
780 /// for Value *Ptr caused by Instruction *Inst.
781 static void AppendMDNodeToInstForPtr(unsigned NodeId,
784 MDString *PtrSourceMDNodeID,
788 Value *tmp[3] = {PtrSourceMDNodeID,
789 SequenceToMDString(Inst->getContext(),
791 SequenceToMDString(Inst->getContext(),
793 Node = MDNode::get(Inst->getContext(),
794 ArrayRef<Value*>(tmp, 3));
796 Inst->setMetadata(NodeId, Node);
799 /// Add to the beginning of the basic block llvm.ptr.annotations which show the
800 /// state of a pointer at the entrance to a basic block.
801 static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
802 Value *Ptr, Sequence Seq) {
803 Module *M = BB->getParent()->getParent();
804 LLVMContext &C = M->getContext();
805 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
806 Type *I8XX = PointerType::getUnqual(I8X);
807 Type *Params[] = {I8XX, I8XX};
808 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
809 ArrayRef<Type*>(Params, 2),
811 Constant *Callee = M->getOrInsertFunction(Name, FTy);
813 IRBuilder<> Builder(BB, BB->getFirstInsertionPt());
816 StringRef Tmp = Ptr->getName();
817 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
818 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
820 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
821 cast<Constant>(ActualPtrName), Tmp);
825 std::string SeqStr = SequenceToString(Seq);
826 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
827 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
829 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
830 cast<Constant>(ActualPtrName), SeqStr);
833 Builder.CreateCall2(Callee, PtrName, S);
836 /// Add to the end of the basic block llvm.ptr.annotations which show the state
837 /// of the pointer at the bottom of the basic block.
838 static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
839 Value *Ptr, Sequence Seq) {
840 Module *M = BB->getParent()->getParent();
841 LLVMContext &C = M->getContext();
842 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
843 Type *I8XX = PointerType::getUnqual(I8X);
844 Type *Params[] = {I8XX, I8XX};
845 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
846 ArrayRef<Type*>(Params, 2),
848 Constant *Callee = M->getOrInsertFunction(Name, FTy);
850 IRBuilder<> Builder(BB, llvm::prior(BB->end()));
853 StringRef Tmp = Ptr->getName();
854 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
855 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
857 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
858 cast<Constant>(ActualPtrName), Tmp);
862 std::string SeqStr = SequenceToString(Seq);
863 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
864 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
866 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
867 cast<Constant>(ActualPtrName), SeqStr);
869 Builder.CreateCall2(Callee, PtrName, S);
872 /// Adds a source annotation to pointer and a state change annotation to Inst
873 /// referencing the source annotation and the old/new state of pointer.
874 static void GenerateARCAnnotation(unsigned InstMDId,
880 if (EnableARCAnnotations) {
881 // First generate the source annotation on our pointer. This will return an
882 // MDString* if Ptr actually comes from an instruction implying we can put
883 // in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
884 // then we know that our pointer is from an Argument so we put a reference
885 // to the argument number.
887 // The point of this is to make it easy for the
888 // llvm-arc-annotation-processor tool to cross reference where the source
889 // pointer is in the LLVM IR since the LLVM IR parser does not submit such
890 // information via debug info for backends to use (since why would anyone
891 // need such a thing from LLVM IR besides in non standard cases
893 MDString *SourcePtrMDNode =
894 AppendMDNodeToSourcePtr(PtrMDId, Ptr);
895 AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
900 // The actual interface for accessing the above functionality is defined via
901 // some simple macros which are defined below. We do this so that the user does
902 // not need to pass in what metadata id is needed resulting in cleaner code and
903 // additionally since it provides an easy way to conditionally no-op all
904 // annotation support in a non-debug build.
906 /// Use this macro to annotate a sequence state change when processing
907 /// instructions bottom up,
908 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new) \
909 GenerateARCAnnotation(ARCAnnotationBottomUpMDKind, \
910 ARCAnnotationProvenanceSourceMDKind, (inst), \
911 const_cast<Value*>(ptr), (old), (new))
912 /// Use this macro to annotate a sequence state change when processing
913 /// instructions top down.
914 #define ANNOTATE_TOPDOWN(inst, ptr, old, new) \
915 GenerateARCAnnotation(ARCAnnotationTopDownMDKind, \
916 ARCAnnotationProvenanceSourceMDKind, (inst), \
917 const_cast<Value*>(ptr), (old), (new))
919 #define ANNOTATE_BB(_states, _bb, _name, _type, _direction) \
921 if (EnableARCAnnotations) { \
922 for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
923 E = (_states)._direction##_ptr_end(); I != E; ++I) { \
924 Value *Ptr = const_cast<Value*>(I->first); \
925 Sequence Seq = I->second.GetSeq(); \
926 GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq); \
931 #define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock) \
932 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
934 #define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock) \
935 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend", \
936 Terminator, bottom_up)
937 #define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock) \
938 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart", \
940 #define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock) \
941 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend", \
942 Terminator, top_down)
944 #else // !ARC_ANNOTATION
945 // If annotations are off, noop.
946 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
947 #define ANNOTATE_TOPDOWN(inst, ptr, old, new)
948 #define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
949 #define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
950 #define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
951 #define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
952 #endif // !ARC_ANNOTATION
955 /// \brief The main ARC optimization pass.
956 class ObjCARCOpt : public FunctionPass {
958 ProvenanceAnalysis PA;
960 /// A flag indicating whether this optimization pass should run.
963 /// Declarations for ObjC runtime functions, for use in creating calls to
964 /// them. These are initialized lazily to avoid cluttering up the Module
965 /// with unused declarations.
967 /// Declaration for ObjC runtime function
968 /// objc_retainAutoreleasedReturnValue.
969 Constant *RetainRVCallee;
970 /// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
971 Constant *AutoreleaseRVCallee;
972 /// Declaration for ObjC runtime function objc_release.
973 Constant *ReleaseCallee;
974 /// Declaration for ObjC runtime function objc_retain.
975 Constant *RetainCallee;
976 /// Declaration for ObjC runtime function objc_retainBlock.
977 Constant *RetainBlockCallee;
978 /// Declaration for ObjC runtime function objc_autorelease.
979 Constant *AutoreleaseCallee;
981 /// Flags which determine whether each of the interesting runtine functions
982 /// is in fact used in the current function.
983 unsigned UsedInThisFunction;
985 /// The Metadata Kind for clang.imprecise_release metadata.
986 unsigned ImpreciseReleaseMDKind;
988 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
989 unsigned CopyOnEscapeMDKind;
991 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
992 unsigned NoObjCARCExceptionsMDKind;
994 #ifdef ARC_ANNOTATIONS
995 /// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
996 unsigned ARCAnnotationBottomUpMDKind;
997 /// The Metadata Kind for llvm.arc.annotation.topdown metadata.
998 unsigned ARCAnnotationTopDownMDKind;
999 /// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
1000 unsigned ARCAnnotationProvenanceSourceMDKind;
1001 #endif // ARC_ANNOATIONS
1003 Constant *getRetainRVCallee(Module *M);
1004 Constant *getAutoreleaseRVCallee(Module *M);
1005 Constant *getReleaseCallee(Module *M);
1006 Constant *getRetainCallee(Module *M);
1007 Constant *getRetainBlockCallee(Module *M);
1008 Constant *getAutoreleaseCallee(Module *M);
1010 bool IsRetainBlockOptimizable(const Instruction *Inst);
1012 void OptimizeRetainCall(Function &F, Instruction *Retain);
1013 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
1014 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1015 InstructionClass &Class);
1016 bool OptimizeRetainBlockCall(Function &F, Instruction *RetainBlock,
1017 InstructionClass &Class);
1018 void OptimizeIndividualCalls(Function &F);
1020 void CheckForCFGHazards(const BasicBlock *BB,
1021 DenseMap<const BasicBlock *, BBState> &BBStates,
1022 BBState &MyStates) const;
1023 bool VisitInstructionBottomUp(Instruction *Inst,
1025 MapVector<Value *, RRInfo> &Retains,
1027 bool VisitBottomUp(BasicBlock *BB,
1028 DenseMap<const BasicBlock *, BBState> &BBStates,
1029 MapVector<Value *, RRInfo> &Retains);
1030 bool VisitInstructionTopDown(Instruction *Inst,
1031 DenseMap<Value *, RRInfo> &Releases,
1033 bool VisitTopDown(BasicBlock *BB,
1034 DenseMap<const BasicBlock *, BBState> &BBStates,
1035 DenseMap<Value *, RRInfo> &Releases);
1036 bool Visit(Function &F,
1037 DenseMap<const BasicBlock *, BBState> &BBStates,
1038 MapVector<Value *, RRInfo> &Retains,
1039 DenseMap<Value *, RRInfo> &Releases);
1041 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
1042 MapVector<Value *, RRInfo> &Retains,
1043 DenseMap<Value *, RRInfo> &Releases,
1044 SmallVectorImpl<Instruction *> &DeadInsts,
1047 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
1048 MapVector<Value *, RRInfo> &Retains,
1049 DenseMap<Value *, RRInfo> &Releases,
1051 SmallVector<Instruction *, 4> &NewRetains,
1052 SmallVector<Instruction *, 4> &NewReleases,
1053 SmallVector<Instruction *, 8> &DeadInsts,
1054 RRInfo &RetainsToMove,
1055 RRInfo &ReleasesToMove,
1058 bool &AnyPairsCompletelyEliminated);
1060 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
1061 MapVector<Value *, RRInfo> &Retains,
1062 DenseMap<Value *, RRInfo> &Releases,
1065 void OptimizeWeakCalls(Function &F);
1067 bool OptimizeSequences(Function &F);
1069 void OptimizeReturns(Function &F);
1071 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
1072 virtual bool doInitialization(Module &M);
1073 virtual bool runOnFunction(Function &F);
1074 virtual void releaseMemory();
1078 ObjCARCOpt() : FunctionPass(ID) {
1079 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
1084 char ObjCARCOpt::ID = 0;
1085 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
1086 "objc-arc", "ObjC ARC optimization", false, false)
1087 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
1088 INITIALIZE_PASS_END(ObjCARCOpt,
1089 "objc-arc", "ObjC ARC optimization", false, false)
1091 Pass *llvm::createObjCARCOptPass() {
1092 return new ObjCARCOpt();
1095 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
1096 AU.addRequired<ObjCARCAliasAnalysis>();
1097 AU.addRequired<AliasAnalysis>();
1098 // ARC optimization doesn't currently split critical edges.
1099 AU.setPreservesCFG();
1102 bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
1103 // Without the magic metadata tag, we have to assume this might be an
1104 // objc_retainBlock call inserted to convert a block pointer to an id,
1105 // in which case it really is needed.
1106 if (!Inst->getMetadata(CopyOnEscapeMDKind))
1109 // If the pointer "escapes" (not including being used in a call),
1110 // the copy may be needed.
1111 if (DoesRetainableObjPtrEscape(Inst))
1114 // Otherwise, it's not needed.
1118 Constant *ObjCARCOpt::getRetainRVCallee(Module *M) {
1119 if (!RetainRVCallee) {
1120 LLVMContext &C = M->getContext();
1121 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1122 Type *Params[] = { I8X };
1123 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1124 AttributeSet Attribute =
1125 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1126 Attribute::NoUnwind);
1128 M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy,
1131 return RetainRVCallee;
1134 Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
1135 if (!AutoreleaseRVCallee) {
1136 LLVMContext &C = M->getContext();
1137 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1138 Type *Params[] = { I8X };
1139 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1140 AttributeSet Attribute =
1141 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1142 Attribute::NoUnwind);
1143 AutoreleaseRVCallee =
1144 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
1147 return AutoreleaseRVCallee;
1150 Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
1151 if (!ReleaseCallee) {
1152 LLVMContext &C = M->getContext();
1153 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1154 AttributeSet Attribute =
1155 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1156 Attribute::NoUnwind);
1158 M->getOrInsertFunction(
1160 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
1163 return ReleaseCallee;
1166 Constant *ObjCARCOpt::getRetainCallee(Module *M) {
1167 if (!RetainCallee) {
1168 LLVMContext &C = M->getContext();
1169 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1170 AttributeSet Attribute =
1171 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1172 Attribute::NoUnwind);
1174 M->getOrInsertFunction(
1176 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1179 return RetainCallee;
1182 Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
1183 if (!RetainBlockCallee) {
1184 LLVMContext &C = M->getContext();
1185 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1186 // objc_retainBlock is not nounwind because it calls user copy constructors
1187 // which could theoretically throw.
1189 M->getOrInsertFunction(
1191 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1194 return RetainBlockCallee;
1197 Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
1198 if (!AutoreleaseCallee) {
1199 LLVMContext &C = M->getContext();
1200 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1201 AttributeSet Attribute =
1202 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1203 Attribute::NoUnwind);
1205 M->getOrInsertFunction(
1207 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1210 return AutoreleaseCallee;
1213 /// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
1216 ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) {
1217 ImmutableCallSite CS(GetObjCArg(Retain));
1218 const Instruction *Call = CS.getInstruction();
1220 if (Call->getParent() != Retain->getParent()) return;
1222 // Check that the call is next to the retain.
1223 BasicBlock::const_iterator I = Call;
1225 while (IsNoopInstruction(I)) ++I;
1229 // Turn it to an objc_retainAutoreleasedReturnValue..
1233 DEBUG(dbgs() << "Transforming objc_retain => "
1234 "objc_retainAutoreleasedReturnValue since the operand is a "
1235 "return value.\nOld: "<< *Retain << "\n");
1237 cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent()));
1239 DEBUG(dbgs() << "New: " << *Retain << "\n");
1242 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
1243 /// not a return value. Or, if it can be paired with an
1244 /// objc_autoreleaseReturnValue, delete the pair and return true.
1246 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
1247 // Check for the argument being from an immediately preceding call or invoke.
1248 const Value *Arg = GetObjCArg(RetainRV);
1249 ImmutableCallSite CS(Arg);
1250 if (const Instruction *Call = CS.getInstruction()) {
1251 if (Call->getParent() == RetainRV->getParent()) {
1252 BasicBlock::const_iterator I = Call;
1254 while (IsNoopInstruction(I)) ++I;
1255 if (&*I == RetainRV)
1257 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
1258 BasicBlock *RetainRVParent = RetainRV->getParent();
1259 if (II->getNormalDest() == RetainRVParent) {
1260 BasicBlock::const_iterator I = RetainRVParent->begin();
1261 while (IsNoopInstruction(I)) ++I;
1262 if (&*I == RetainRV)
1268 // Check for being preceded by an objc_autoreleaseReturnValue on the same
1269 // pointer. In this case, we can delete the pair.
1270 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
1272 do --I; while (I != Begin && IsNoopInstruction(I));
1273 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
1274 GetObjCArg(I) == Arg) {
1278 DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
1279 << "Erasing " << *RetainRV << "\n");
1281 EraseInstruction(I);
1282 EraseInstruction(RetainRV);
1287 // Turn it to a plain objc_retain.
1291 DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
1292 "objc_retain since the operand is not a return value.\n"
1293 "Old = " << *RetainRV << "\n");
1295 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));
1297 DEBUG(dbgs() << "New = " << *RetainRV << "\n");
1302 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
1303 /// used as a return value.
1305 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1306 InstructionClass &Class) {
1307 // Check for a return of the pointer value.
1308 const Value *Ptr = GetObjCArg(AutoreleaseRV);
1309 SmallVector<const Value *, 2> Users;
1310 Users.push_back(Ptr);
1312 Ptr = Users.pop_back_val();
1313 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
1315 const User *I = *UI;
1316 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
1318 if (isa<BitCastInst>(I))
1321 } while (!Users.empty());
1326 DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
1327 "objc_autorelease since its operand is not used as a return "
1329 "Old = " << *AutoreleaseRV << "\n");
1331 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
1333 setCalledFunction(getAutoreleaseCallee(F.getParent()));
1334 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
1335 Class = IC_Autorelease;
1337 DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
1341 // \brief Attempt to strength reduce objc_retainBlock calls to objc_retain
1344 // Specifically: If an objc_retainBlock call has the copy_on_escape metadata and
1345 // does not escape (following the rules of block escaping), strength reduce the
1346 // objc_retainBlock to an objc_retain.
1348 // TODO: If an objc_retainBlock call is dominated period by a previous
1349 // objc_retainBlock call, strength reduce the objc_retainBlock to an
1352 ObjCARCOpt::OptimizeRetainBlockCall(Function &F, Instruction *Inst,
1353 InstructionClass &Class) {
1354 assert(GetBasicInstructionClass(Inst) == Class);
1355 assert(IC_RetainBlock == Class);
1357 // If we can not optimize Inst, return false.
1358 if (!IsRetainBlockOptimizable(Inst))
1361 CallInst *RetainBlock = cast<CallInst>(Inst);
1362 RetainBlock->setCalledFunction(getRetainCallee(F.getParent()));
1363 // Remove copy_on_escape metadata.
1364 RetainBlock->setMetadata(CopyOnEscapeMDKind, 0);
1370 /// Visit each call, one at a time, and make simplifications without doing any
1371 /// additional analysis.
1372 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
1373 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
1374 // Reset all the flags in preparation for recomputing them.
1375 UsedInThisFunction = 0;
1377 // Visit all objc_* calls in F.
1378 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1379 Instruction *Inst = &*I++;
1381 InstructionClass Class = GetBasicInstructionClass(Inst);
1383 DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
1388 // Delete no-op casts. These function calls have special semantics, but
1389 // the semantics are entirely implemented via lowering in the front-end,
1390 // so by the time they reach the optimizer, they are just no-op calls
1391 // which return their argument.
1393 // There are gray areas here, as the ability to cast reference-counted
1394 // pointers to raw void* and back allows code to break ARC assumptions,
1395 // however these are currently considered to be unimportant.
1399 DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
1400 EraseInstruction(Inst);
1403 // If the pointer-to-weak-pointer is null, it's undefined behavior.
1406 case IC_LoadWeakRetained:
1408 case IC_DestroyWeak: {
1409 CallInst *CI = cast<CallInst>(Inst);
1410 if (IsNullOrUndef(CI->getArgOperand(0))) {
1412 Type *Ty = CI->getArgOperand(0)->getType();
1413 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1414 Constant::getNullValue(Ty),
1416 llvm::Value *NewValue = UndefValue::get(CI->getType());
1417 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1418 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1419 CI->replaceAllUsesWith(NewValue);
1420 CI->eraseFromParent();
1427 CallInst *CI = cast<CallInst>(Inst);
1428 if (IsNullOrUndef(CI->getArgOperand(0)) ||
1429 IsNullOrUndef(CI->getArgOperand(1))) {
1431 Type *Ty = CI->getArgOperand(0)->getType();
1432 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1433 Constant::getNullValue(Ty),
1436 llvm::Value *NewValue = UndefValue::get(CI->getType());
1437 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1438 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1440 CI->replaceAllUsesWith(NewValue);
1441 CI->eraseFromParent();
1446 case IC_RetainBlock:
1447 // If we strength reduce an objc_retainBlock to amn objc_retain, continue
1448 // onto the objc_retain peephole optimizations. Otherwise break.
1449 if (!OptimizeRetainBlockCall(F, Inst, Class))
1453 OptimizeRetainCall(F, Inst);
1456 if (OptimizeRetainRVCall(F, Inst))
1459 case IC_AutoreleaseRV:
1460 OptimizeAutoreleaseRVCall(F, Inst, Class);
1464 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
1465 if (IsAutorelease(Class) && Inst->use_empty()) {
1466 CallInst *Call = cast<CallInst>(Inst);
1467 const Value *Arg = Call->getArgOperand(0);
1468 Arg = FindSingleUseIdentifiedObject(Arg);
1473 // Create the declaration lazily.
1474 LLVMContext &C = Inst->getContext();
1476 CallInst::Create(getReleaseCallee(F.getParent()),
1477 Call->getArgOperand(0), "", Call);
1478 NewCall->setMetadata(ImpreciseReleaseMDKind,
1479 MDNode::get(C, ArrayRef<Value *>()));
1481 DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
1482 "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
1483 << *NewCall << "\n");
1485 EraseInstruction(Call);
1491 // For functions which can never be passed stack arguments, add
1493 if (IsAlwaysTail(Class)) {
1495 DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
1496 "passed stack args: " << *Inst << "\n");
1497 cast<CallInst>(Inst)->setTailCall();
1500 // Ensure that functions that can never have a "tail" keyword due to the
1501 // semantics of ARC truly do not do so.
1502 if (IsNeverTail(Class)) {
1504 DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
1506 cast<CallInst>(Inst)->setTailCall(false);
1509 // Set nounwind as needed.
1510 if (IsNoThrow(Class)) {
1512 DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
1514 cast<CallInst>(Inst)->setDoesNotThrow();
1517 if (!IsNoopOnNull(Class)) {
1518 UsedInThisFunction |= 1 << Class;
1522 const Value *Arg = GetObjCArg(Inst);
1524 // ARC calls with null are no-ops. Delete them.
1525 if (IsNullOrUndef(Arg)) {
1528 DEBUG(dbgs() << "ARC calls with null are no-ops. Erasing: " << *Inst
1530 EraseInstruction(Inst);
1534 // Keep track of which of retain, release, autorelease, and retain_block
1535 // are actually present in this function.
1536 UsedInThisFunction |= 1 << Class;
1538 // If Arg is a PHI, and one or more incoming values to the
1539 // PHI are null, and the call is control-equivalent to the PHI, and there
1540 // are no relevant side effects between the PHI and the call, the call
1541 // could be pushed up to just those paths with non-null incoming values.
1542 // For now, don't bother splitting critical edges for this.
1543 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
1544 Worklist.push_back(std::make_pair(Inst, Arg));
1546 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
1550 const PHINode *PN = dyn_cast<PHINode>(Arg);
1553 // Determine if the PHI has any null operands, or any incoming
1555 bool HasNull = false;
1556 bool HasCriticalEdges = false;
1557 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1559 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1560 if (IsNullOrUndef(Incoming))
1562 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
1563 .getNumSuccessors() != 1) {
1564 HasCriticalEdges = true;
1568 // If we have null operands and no critical edges, optimize.
1569 if (!HasCriticalEdges && HasNull) {
1570 SmallPtrSet<Instruction *, 4> DependingInstructions;
1571 SmallPtrSet<const BasicBlock *, 4> Visited;
1573 // Check that there is nothing that cares about the reference
1574 // count between the call and the phi.
1577 case IC_RetainBlock:
1578 // These can always be moved up.
1581 // These can't be moved across things that care about the retain
1583 FindDependencies(NeedsPositiveRetainCount, Arg,
1584 Inst->getParent(), Inst,
1585 DependingInstructions, Visited, PA);
1587 case IC_Autorelease:
1588 // These can't be moved across autorelease pool scope boundaries.
1589 FindDependencies(AutoreleasePoolBoundary, Arg,
1590 Inst->getParent(), Inst,
1591 DependingInstructions, Visited, PA);
1594 case IC_AutoreleaseRV:
1595 // Don't move these; the RV optimization depends on the autoreleaseRV
1596 // being tail called, and the retainRV being immediately after a call
1597 // (which might still happen if we get lucky with codegen layout, but
1598 // it's not worth taking the chance).
1601 llvm_unreachable("Invalid dependence flavor");
1604 if (DependingInstructions.size() == 1 &&
1605 *DependingInstructions.begin() == PN) {
1608 // Clone the call into each predecessor that has a non-null value.
1609 CallInst *CInst = cast<CallInst>(Inst);
1610 Type *ParamTy = CInst->getArgOperand(0)->getType();
1611 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1613 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1614 if (!IsNullOrUndef(Incoming)) {
1615 CallInst *Clone = cast<CallInst>(CInst->clone());
1616 Value *Op = PN->getIncomingValue(i);
1617 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
1618 if (Op->getType() != ParamTy)
1619 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
1620 Clone->setArgOperand(0, Op);
1621 Clone->insertBefore(InsertPos);
1623 DEBUG(dbgs() << "Cloning "
1625 "And inserting clone at " << *InsertPos << "\n");
1626 Worklist.push_back(std::make_pair(Clone, Incoming));
1629 // Erase the original call.
1630 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
1631 EraseInstruction(CInst);
1635 } while (!Worklist.empty());
1639 /// Check for critical edges, loop boundaries, irreducible control flow, or
1640 /// other CFG structures where moving code across the edge would result in it
1641 /// being executed more.
1643 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
1644 DenseMap<const BasicBlock *, BBState> &BBStates,
1645 BBState &MyStates) const {
1646 // If any top-down local-use or possible-dec has a succ which is earlier in
1647 // the sequence, forget it.
1648 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
1649 E = MyStates.top_down_ptr_end(); I != E; ++I)
1650 switch (I->second.GetSeq()) {
1653 const Value *Arg = I->first;
1654 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
1655 bool SomeSuccHasSame = false;
1656 bool AllSuccsHaveSame = true;
1657 PtrState &S = I->second;
1658 succ_const_iterator SI(TI), SE(TI, false);
1660 for (; SI != SE; ++SI) {
1661 Sequence SuccSSeq = S_None;
1662 bool SuccSRRIKnownSafe = false;
1663 // If VisitBottomUp has pointer information for this successor, take
1664 // what we know about it.
1665 DenseMap<const BasicBlock *, BBState>::iterator BBI =
1667 assert(BBI != BBStates.end());
1668 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
1669 SuccSSeq = SuccS.GetSeq();
1670 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
1673 case S_CanRelease: {
1674 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
1675 S.ClearSequenceProgress();
1681 SomeSuccHasSame = true;
1685 case S_MovableRelease:
1686 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1687 AllSuccsHaveSame = false;
1690 llvm_unreachable("bottom-up pointer in retain state!");
1693 // If the state at the other end of any of the successor edges
1694 // matches the current state, require all edges to match. This
1695 // guards against loops in the middle of a sequence.
1696 if (SomeSuccHasSame && !AllSuccsHaveSame)
1697 S.ClearSequenceProgress();
1700 case S_CanRelease: {
1701 const Value *Arg = I->first;
1702 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
1703 bool SomeSuccHasSame = false;
1704 bool AllSuccsHaveSame = true;
1705 PtrState &S = I->second;
1706 succ_const_iterator SI(TI), SE(TI, false);
1708 for (; SI != SE; ++SI) {
1709 Sequence SuccSSeq = S_None;
1710 bool SuccSRRIKnownSafe = false;
1711 // If VisitBottomUp has pointer information for this successor, take
1712 // what we know about it.
1713 DenseMap<const BasicBlock *, BBState>::iterator BBI =
1715 assert(BBI != BBStates.end());
1716 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
1717 SuccSSeq = SuccS.GetSeq();
1718 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
1721 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
1722 S.ClearSequenceProgress();
1728 SomeSuccHasSame = true;
1732 case S_MovableRelease:
1734 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1735 AllSuccsHaveSame = false;
1738 llvm_unreachable("bottom-up pointer in retain state!");
1741 // If the state at the other end of any of the successor edges
1742 // matches the current state, require all edges to match. This
1743 // guards against loops in the middle of a sequence.
1744 if (SomeSuccHasSame && !AllSuccsHaveSame)
1745 S.ClearSequenceProgress();
1752 ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
1754 MapVector<Value *, RRInfo> &Retains,
1755 BBState &MyStates) {
1756 bool NestingDetected = false;
1757 InstructionClass Class = GetInstructionClass(Inst);
1758 const Value *Arg = 0;
1760 DEBUG(dbgs() << "Class: " << Class << "\n");
1764 Arg = GetObjCArg(Inst);
1766 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1768 // If we see two releases in a row on the same pointer. If so, make
1769 // a note, and we'll cicle back to revisit it after we've
1770 // hopefully eliminated the second release, which may allow us to
1771 // eliminate the first release too.
1772 // Theoretically we could implement removal of nested retain+release
1773 // pairs by making PtrState hold a stack of states, but this is
1774 // simple and avoids adding overhead for the non-nested case.
1775 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
1776 DEBUG(dbgs() << "Found nested releases (i.e. a release pair)\n");
1777 NestingDetected = true;
1780 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
1781 Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
1782 ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
1783 S.ResetSequenceProgress(NewSeq);
1784 S.RRI.ReleaseMetadata = ReleaseMetadata;
1785 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
1786 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
1787 S.RRI.Calls.insert(Inst);
1788 S.SetKnownPositiveRefCount();
1791 case IC_RetainBlock:
1792 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1793 // objc_retainBlocks to objc_retains. Thus at this point any
1794 // objc_retainBlocks that we see are not optimizable.
1798 Arg = GetObjCArg(Inst);
1800 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1801 S.SetKnownPositiveRefCount();
1803 Sequence OldSeq = S.GetSeq();
1807 case S_MovableRelease:
1809 // If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
1810 // imprecise release, clear our reverse insertion points.
1811 if (OldSeq != S_Use || S.RRI.IsTrackingImpreciseReleases())
1812 S.RRI.ReverseInsertPts.clear();
1815 // Don't do retain+release tracking for IC_RetainRV, because it's
1816 // better to let it remain as the first instruction after a call.
1817 if (Class != IC_RetainRV)
1818 Retains[Inst] = S.RRI;
1819 S.ClearSequenceProgress();
1824 llvm_unreachable("bottom-up pointer in retain state!");
1826 ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
1827 // A retain moving bottom up can be a use.
1830 case IC_AutoreleasepoolPop:
1831 // Conservatively, clear MyStates for all known pointers.
1832 MyStates.clearBottomUpPointers();
1833 return NestingDetected;
1834 case IC_AutoreleasepoolPush:
1836 // These are irrelevant.
1837 return NestingDetected;
1842 // Consider any other possible effects of this instruction on each
1843 // pointer being tracked.
1844 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
1845 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
1846 const Value *Ptr = MI->first;
1848 continue; // Handled above.
1849 PtrState &S = MI->second;
1850 Sequence Seq = S.GetSeq();
1852 // Check for possible releases.
1853 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
1854 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
1856 S.ClearKnownPositiveRefCount();
1859 S.SetSeq(S_CanRelease);
1860 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
1864 case S_MovableRelease:
1869 llvm_unreachable("bottom-up pointer in retain state!");
1873 // Check for possible direct uses.
1876 case S_MovableRelease:
1877 if (CanUse(Inst, Ptr, PA, Class)) {
1878 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
1880 assert(S.RRI.ReverseInsertPts.empty());
1881 // If this is an invoke instruction, we're scanning it as part of
1882 // one of its successor blocks, since we can't insert code after it
1883 // in its own block, and we don't want to split critical edges.
1884 if (isa<InvokeInst>(Inst))
1885 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1887 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1889 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1890 } else if (Seq == S_Release && IsUser(Class)) {
1891 DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
1893 // Non-movable releases depend on any possible objc pointer use.
1895 ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
1896 assert(S.RRI.ReverseInsertPts.empty());
1897 // As above; handle invoke specially.
1898 if (isa<InvokeInst>(Inst))
1899 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1901 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1905 if (CanUse(Inst, Ptr, PA, Class)) {
1906 DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
1909 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1917 llvm_unreachable("bottom-up pointer in retain state!");
1921 return NestingDetected;
1925 ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
1926 DenseMap<const BasicBlock *, BBState> &BBStates,
1927 MapVector<Value *, RRInfo> &Retains) {
1929 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
1931 bool NestingDetected = false;
1932 BBState &MyStates = BBStates[BB];
1934 // Merge the states from each successor to compute the initial state
1935 // for the current block.
1936 BBState::edge_iterator SI(MyStates.succ_begin()),
1937 SE(MyStates.succ_end());
1939 const BasicBlock *Succ = *SI;
1940 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
1941 assert(I != BBStates.end());
1942 MyStates.InitFromSucc(I->second);
1944 for (; SI != SE; ++SI) {
1946 I = BBStates.find(Succ);
1947 assert(I != BBStates.end());
1948 MyStates.MergeSucc(I->second);
1952 // If ARC Annotations are enabled, output the current state of pointers at the
1953 // bottom of the basic block.
1954 ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);
1956 // Visit all the instructions, bottom-up.
1957 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
1958 Instruction *Inst = llvm::prior(I);
1960 // Invoke instructions are visited as part of their successors (below).
1961 if (isa<InvokeInst>(Inst))
1964 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1966 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
1969 // If there's a predecessor with an invoke, visit the invoke as if it were
1970 // part of this block, since we can't insert code after an invoke in its own
1971 // block, and we don't want to split critical edges.
1972 for (BBState::edge_iterator PI(MyStates.pred_begin()),
1973 PE(MyStates.pred_end()); PI != PE; ++PI) {
1974 BasicBlock *Pred = *PI;
1975 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
1976 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
1979 // If ARC Annotations are enabled, output the current state of pointers at the
1980 // top of the basic block.
1981 ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);
1983 return NestingDetected;
1987 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
1988 DenseMap<Value *, RRInfo> &Releases,
1989 BBState &MyStates) {
1990 bool NestingDetected = false;
1991 InstructionClass Class = GetInstructionClass(Inst);
1992 const Value *Arg = 0;
1995 case IC_RetainBlock:
1996 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1997 // objc_retainBlocks to objc_retains. Thus at this point any
1998 // objc_retainBlocks that we see are not optimizable.
2002 Arg = GetObjCArg(Inst);
2004 PtrState &S = MyStates.getPtrTopDownState(Arg);
2006 // Don't do retain+release tracking for IC_RetainRV, because it's
2007 // better to let it remain as the first instruction after a call.
2008 if (Class != IC_RetainRV) {
2009 // If we see two retains in a row on the same pointer. If so, make
2010 // a note, and we'll cicle back to revisit it after we've
2011 // hopefully eliminated the second retain, which may allow us to
2012 // eliminate the first retain too.
2013 // Theoretically we could implement removal of nested retain+release
2014 // pairs by making PtrState hold a stack of states, but this is
2015 // simple and avoids adding overhead for the non-nested case.
2016 if (S.GetSeq() == S_Retain)
2017 NestingDetected = true;
2019 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
2020 S.ResetSequenceProgress(S_Retain);
2021 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
2022 S.RRI.Calls.insert(Inst);
2025 S.SetKnownPositiveRefCount();
2027 // A retain can be a potential use; procede to the generic checking
2032 Arg = GetObjCArg(Inst);
2034 PtrState &S = MyStates.getPtrTopDownState(Arg);
2035 S.ClearKnownPositiveRefCount();
2037 Sequence OldSeq = S.GetSeq();
2039 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
2044 if (OldSeq == S_Retain || ReleaseMetadata != 0)
2045 S.RRI.ReverseInsertPts.clear();
2048 S.RRI.ReleaseMetadata = ReleaseMetadata;
2049 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
2050 Releases[Inst] = S.RRI;
2051 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
2052 S.ClearSequenceProgress();
2058 case S_MovableRelease:
2059 llvm_unreachable("top-down pointer in release state!");
2063 case IC_AutoreleasepoolPop:
2064 // Conservatively, clear MyStates for all known pointers.
2065 MyStates.clearTopDownPointers();
2066 return NestingDetected;
2067 case IC_AutoreleasepoolPush:
2069 // These are irrelevant.
2070 return NestingDetected;
2075 // Consider any other possible effects of this instruction on each
2076 // pointer being tracked.
2077 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
2078 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
2079 const Value *Ptr = MI->first;
2081 continue; // Handled above.
2082 PtrState &S = MI->second;
2083 Sequence Seq = S.GetSeq();
2085 // Check for possible releases.
2086 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
2087 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
2089 S.ClearKnownPositiveRefCount();
2092 S.SetSeq(S_CanRelease);
2093 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
2094 assert(S.RRI.ReverseInsertPts.empty());
2095 S.RRI.ReverseInsertPts.insert(Inst);
2097 // One call can't cause a transition from S_Retain to S_CanRelease
2098 // and S_CanRelease to S_Use. If we've made the first transition,
2107 case S_MovableRelease:
2108 llvm_unreachable("top-down pointer in release state!");
2112 // Check for possible direct uses.
2115 if (CanUse(Inst, Ptr, PA, Class)) {
2116 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
2119 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_Use);
2128 case S_MovableRelease:
2129 llvm_unreachable("top-down pointer in release state!");
2133 return NestingDetected;
2137 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
2138 DenseMap<const BasicBlock *, BBState> &BBStates,
2139 DenseMap<Value *, RRInfo> &Releases) {
2140 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
2141 bool NestingDetected = false;
2142 BBState &MyStates = BBStates[BB];
2144 // Merge the states from each predecessor to compute the initial state
2145 // for the current block.
2146 BBState::edge_iterator PI(MyStates.pred_begin()),
2147 PE(MyStates.pred_end());
2149 const BasicBlock *Pred = *PI;
2150 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
2151 assert(I != BBStates.end());
2152 MyStates.InitFromPred(I->second);
2154 for (; PI != PE; ++PI) {
2156 I = BBStates.find(Pred);
2157 assert(I != BBStates.end());
2158 MyStates.MergePred(I->second);
2162 // If ARC Annotations are enabled, output the current state of pointers at the
2163 // top of the basic block.
2164 ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);
2166 // Visit all the instructions, top-down.
2167 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
2168 Instruction *Inst = I;
2170 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
2172 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
2175 // If ARC Annotations are enabled, output the current state of pointers at the
2176 // bottom of the basic block.
2177 ANNOTATE_TOPDOWN_BBEND(MyStates, BB);
2179 #ifdef ARC_ANNOTATIONS
2180 if (!(EnableARCAnnotations && DisableCheckForCFGHazards))
2182 CheckForCFGHazards(BB, BBStates, MyStates);
2183 return NestingDetected;
2187 ComputePostOrders(Function &F,
2188 SmallVectorImpl<BasicBlock *> &PostOrder,
2189 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
2190 unsigned NoObjCARCExceptionsMDKind,
2191 DenseMap<const BasicBlock *, BBState> &BBStates) {
2192 /// The visited set, for doing DFS walks.
2193 SmallPtrSet<BasicBlock *, 16> Visited;
2195 // Do DFS, computing the PostOrder.
2196 SmallPtrSet<BasicBlock *, 16> OnStack;
2197 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
2199 // Functions always have exactly one entry block, and we don't have
2200 // any other block that we treat like an entry block.
2201 BasicBlock *EntryBB = &F.getEntryBlock();
2202 BBState &MyStates = BBStates[EntryBB];
2203 MyStates.SetAsEntry();
2204 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
2205 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
2206 Visited.insert(EntryBB);
2207 OnStack.insert(EntryBB);
2210 BasicBlock *CurrBB = SuccStack.back().first;
2211 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
2212 succ_iterator SE(TI, false);
2214 while (SuccStack.back().second != SE) {
2215 BasicBlock *SuccBB = *SuccStack.back().second++;
2216 if (Visited.insert(SuccBB)) {
2217 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
2218 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
2219 BBStates[CurrBB].addSucc(SuccBB);
2220 BBState &SuccStates = BBStates[SuccBB];
2221 SuccStates.addPred(CurrBB);
2222 OnStack.insert(SuccBB);
2226 if (!OnStack.count(SuccBB)) {
2227 BBStates[CurrBB].addSucc(SuccBB);
2228 BBStates[SuccBB].addPred(CurrBB);
2231 OnStack.erase(CurrBB);
2232 PostOrder.push_back(CurrBB);
2233 SuccStack.pop_back();
2234 } while (!SuccStack.empty());
2238 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
2239 // Functions may have many exits, and there also blocks which we treat
2240 // as exits due to ignored edges.
2241 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
2242 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
2243 BasicBlock *ExitBB = I;
2244 BBState &MyStates = BBStates[ExitBB];
2245 if (!MyStates.isExit())
2248 MyStates.SetAsExit();
2250 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
2251 Visited.insert(ExitBB);
2252 while (!PredStack.empty()) {
2253 reverse_dfs_next_succ:
2254 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
2255 while (PredStack.back().second != PE) {
2256 BasicBlock *BB = *PredStack.back().second++;
2257 if (Visited.insert(BB)) {
2258 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
2259 goto reverse_dfs_next_succ;
2262 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
2267 // Visit the function both top-down and bottom-up.
2269 ObjCARCOpt::Visit(Function &F,
2270 DenseMap<const BasicBlock *, BBState> &BBStates,
2271 MapVector<Value *, RRInfo> &Retains,
2272 DenseMap<Value *, RRInfo> &Releases) {
2274 // Use reverse-postorder traversals, because we magically know that loops
2275 // will be well behaved, i.e. they won't repeatedly call retain on a single
2276 // pointer without doing a release. We can't use the ReversePostOrderTraversal
2277 // class here because we want the reverse-CFG postorder to consider each
2278 // function exit point, and we want to ignore selected cycle edges.
2279 SmallVector<BasicBlock *, 16> PostOrder;
2280 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
2281 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
2282 NoObjCARCExceptionsMDKind,
2285 // Use reverse-postorder on the reverse CFG for bottom-up.
2286 bool BottomUpNestingDetected = false;
2287 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2288 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
2290 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
2292 // Use reverse-postorder for top-down.
2293 bool TopDownNestingDetected = false;
2294 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2295 PostOrder.rbegin(), E = PostOrder.rend();
2297 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
2299 return TopDownNestingDetected && BottomUpNestingDetected;
2302 /// Move the calls in RetainsToMove and ReleasesToMove.
2303 void ObjCARCOpt::MoveCalls(Value *Arg,
2304 RRInfo &RetainsToMove,
2305 RRInfo &ReleasesToMove,
2306 MapVector<Value *, RRInfo> &Retains,
2307 DenseMap<Value *, RRInfo> &Releases,
2308 SmallVectorImpl<Instruction *> &DeadInsts,
2310 Type *ArgTy = Arg->getType();
2311 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
2313 DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
2315 // Insert the new retain and release calls.
2316 for (SmallPtrSet<Instruction *, 2>::const_iterator
2317 PI = ReleasesToMove.ReverseInsertPts.begin(),
2318 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2319 Instruction *InsertPt = *PI;
2320 Value *MyArg = ArgTy == ParamTy ? Arg :
2321 new BitCastInst(Arg, ParamTy, "", InsertPt);
2323 CallInst::Create(getRetainCallee(M), MyArg, "", InsertPt);
2324 Call->setDoesNotThrow();
2325 Call->setTailCall();
2327 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
2328 "At insertion point: " << *InsertPt << "\n");
2330 for (SmallPtrSet<Instruction *, 2>::const_iterator
2331 PI = RetainsToMove.ReverseInsertPts.begin(),
2332 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2333 Instruction *InsertPt = *PI;
2334 Value *MyArg = ArgTy == ParamTy ? Arg :
2335 new BitCastInst(Arg, ParamTy, "", InsertPt);
2336 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
2338 // Attach a clang.imprecise_release metadata tag, if appropriate.
2339 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
2340 Call->setMetadata(ImpreciseReleaseMDKind, M);
2341 Call->setDoesNotThrow();
2342 if (ReleasesToMove.IsTailCallRelease)
2343 Call->setTailCall();
2345 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
2346 "At insertion point: " << *InsertPt << "\n");
2349 // Delete the original retain and release calls.
2350 for (SmallPtrSet<Instruction *, 2>::const_iterator
2351 AI = RetainsToMove.Calls.begin(),
2352 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
2353 Instruction *OrigRetain = *AI;
2354 Retains.blot(OrigRetain);
2355 DeadInsts.push_back(OrigRetain);
2356 DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
2358 for (SmallPtrSet<Instruction *, 2>::const_iterator
2359 AI = ReleasesToMove.Calls.begin(),
2360 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
2361 Instruction *OrigRelease = *AI;
2362 Releases.erase(OrigRelease);
2363 DeadInsts.push_back(OrigRelease);
2364 DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
2370 ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
2372 MapVector<Value *, RRInfo> &Retains,
2373 DenseMap<Value *, RRInfo> &Releases,
2375 SmallVector<Instruction *, 4> &NewRetains,
2376 SmallVector<Instruction *, 4> &NewReleases,
2377 SmallVector<Instruction *, 8> &DeadInsts,
2378 RRInfo &RetainsToMove,
2379 RRInfo &ReleasesToMove,
2382 bool &AnyPairsCompletelyEliminated) {
2383 // If a pair happens in a region where it is known that the reference count
2384 // is already incremented, we can similarly ignore possible decrements.
2385 bool KnownSafeTD = true, KnownSafeBU = true;
2387 // Connect the dots between the top-down-collected RetainsToMove and
2388 // bottom-up-collected ReleasesToMove to form sets of related calls.
2389 // This is an iterative process so that we connect multiple releases
2390 // to multiple retains if needed.
2391 unsigned OldDelta = 0;
2392 unsigned NewDelta = 0;
2393 unsigned OldCount = 0;
2394 unsigned NewCount = 0;
2395 bool FirstRelease = true;
2397 for (SmallVectorImpl<Instruction *>::const_iterator
2398 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
2399 Instruction *NewRetain = *NI;
2400 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
2401 assert(It != Retains.end());
2402 const RRInfo &NewRetainRRI = It->second;
2403 KnownSafeTD &= NewRetainRRI.KnownSafe;
2404 for (SmallPtrSet<Instruction *, 2>::const_iterator
2405 LI = NewRetainRRI.Calls.begin(),
2406 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
2407 Instruction *NewRetainRelease = *LI;
2408 DenseMap<Value *, RRInfo>::const_iterator Jt =
2409 Releases.find(NewRetainRelease);
2410 if (Jt == Releases.end())
2412 const RRInfo &NewRetainReleaseRRI = Jt->second;
2413 assert(NewRetainReleaseRRI.Calls.count(NewRetain));
2414 if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
2416 BBStates[NewRetainRelease->getParent()].GetAllPathCount();
2418 // Merge the ReleaseMetadata and IsTailCallRelease values.
2420 ReleasesToMove.ReleaseMetadata =
2421 NewRetainReleaseRRI.ReleaseMetadata;
2422 ReleasesToMove.IsTailCallRelease =
2423 NewRetainReleaseRRI.IsTailCallRelease;
2424 FirstRelease = false;
2426 if (ReleasesToMove.ReleaseMetadata !=
2427 NewRetainReleaseRRI.ReleaseMetadata)
2428 ReleasesToMove.ReleaseMetadata = 0;
2429 if (ReleasesToMove.IsTailCallRelease !=
2430 NewRetainReleaseRRI.IsTailCallRelease)
2431 ReleasesToMove.IsTailCallRelease = false;
2434 // Collect the optimal insertion points.
2436 for (SmallPtrSet<Instruction *, 2>::const_iterator
2437 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
2438 RE = NewRetainReleaseRRI.ReverseInsertPts.end();
2440 Instruction *RIP = *RI;
2441 if (ReleasesToMove.ReverseInsertPts.insert(RIP))
2442 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
2444 NewReleases.push_back(NewRetainRelease);
2449 if (NewReleases.empty()) break;
2451 // Back the other way.
2452 for (SmallVectorImpl<Instruction *>::const_iterator
2453 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
2454 Instruction *NewRelease = *NI;
2455 DenseMap<Value *, RRInfo>::const_iterator It =
2456 Releases.find(NewRelease);
2457 assert(It != Releases.end());
2458 const RRInfo &NewReleaseRRI = It->second;
2459 KnownSafeBU &= NewReleaseRRI.KnownSafe;
2460 for (SmallPtrSet<Instruction *, 2>::const_iterator
2461 LI = NewReleaseRRI.Calls.begin(),
2462 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
2463 Instruction *NewReleaseRetain = *LI;
2464 MapVector<Value *, RRInfo>::const_iterator Jt =
2465 Retains.find(NewReleaseRetain);
2466 if (Jt == Retains.end())
2468 const RRInfo &NewReleaseRetainRRI = Jt->second;
2469 assert(NewReleaseRetainRRI.Calls.count(NewRelease));
2470 if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
2471 unsigned PathCount =
2472 BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
2473 OldDelta += PathCount;
2474 OldCount += PathCount;
2476 // Collect the optimal insertion points.
2478 for (SmallPtrSet<Instruction *, 2>::const_iterator
2479 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
2480 RE = NewReleaseRetainRRI.ReverseInsertPts.end();
2482 Instruction *RIP = *RI;
2483 if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
2484 PathCount = BBStates[RIP->getParent()].GetAllPathCount();
2485 NewDelta += PathCount;
2486 NewCount += PathCount;
2489 NewRetains.push_back(NewReleaseRetain);
2493 NewReleases.clear();
2494 if (NewRetains.empty()) break;
2497 // If the pointer is known incremented or nested, we can safely delete the
2498 // pair regardless of what's between them.
2499 if (KnownSafeTD || KnownSafeBU) {
2500 RetainsToMove.ReverseInsertPts.clear();
2501 ReleasesToMove.ReverseInsertPts.clear();
2504 // Determine whether the new insertion points we computed preserve the
2505 // balance of retain and release calls through the program.
2506 // TODO: If the fully aggressive solution isn't valid, try to find a
2507 // less aggressive solution which is.
2512 // Determine whether the original call points are balanced in the retain and
2513 // release calls through the program. If not, conservatively don't touch
2515 // TODO: It's theoretically possible to do code motion in this case, as
2516 // long as the existing imbalances are maintained.
2521 assert(OldCount != 0 && "Unreachable code?");
2522 NumRRs += OldCount - NewCount;
2523 // Set to true if we completely removed any RR pairs.
2524 AnyPairsCompletelyEliminated = NewCount == 0;
2526 // We can move calls!
2530 /// Identify pairings between the retains and releases, and delete and/or move
2533 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
2535 MapVector<Value *, RRInfo> &Retains,
2536 DenseMap<Value *, RRInfo> &Releases,
2538 DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
2540 bool AnyPairsCompletelyEliminated = false;
2541 RRInfo RetainsToMove;
2542 RRInfo ReleasesToMove;
2543 SmallVector<Instruction *, 4> NewRetains;
2544 SmallVector<Instruction *, 4> NewReleases;
2545 SmallVector<Instruction *, 8> DeadInsts;
2547 // Visit each retain.
2548 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
2549 E = Retains.end(); I != E; ++I) {
2550 Value *V = I->first;
2551 if (!V) continue; // blotted
2553 Instruction *Retain = cast<Instruction>(V);
2555 DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
2557 Value *Arg = GetObjCArg(Retain);
2559 // If the object being released is in static or stack storage, we know it's
2560 // not being managed by ObjC reference counting, so we can delete pairs
2561 // regardless of what possible decrements or uses lie between them.
2562 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
2564 // A constant pointer can't be pointing to an object on the heap. It may
2565 // be reference-counted, but it won't be deleted.
2566 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
2567 if (const GlobalVariable *GV =
2568 dyn_cast<GlobalVariable>(
2569 StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
2570 if (GV->isConstant())
2573 // Connect the dots between the top-down-collected RetainsToMove and
2574 // bottom-up-collected ReleasesToMove to form sets of related calls.
2575 NewRetains.push_back(Retain);
2576 bool PerformMoveCalls =
2577 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
2578 NewReleases, DeadInsts, RetainsToMove,
2579 ReleasesToMove, Arg, KnownSafe,
2580 AnyPairsCompletelyEliminated);
2582 #ifdef ARC_ANNOTATIONS
2583 // Do not move calls if ARC annotations are requested. If we were to move
2584 // calls in this case, we would not be able
2585 PerformMoveCalls = PerformMoveCalls && !EnableARCAnnotations;
2586 #endif // ARC_ANNOTATIONS
2588 if (PerformMoveCalls) {
2589 // Ok, everything checks out and we're all set. Let's move/delete some
2591 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
2592 Retains, Releases, DeadInsts, M);
2595 // Clean up state for next retain.
2596 NewReleases.clear();
2598 RetainsToMove.clear();
2599 ReleasesToMove.clear();
2602 // Now that we're done moving everything, we can delete the newly dead
2603 // instructions, as we no longer need them as insert points.
2604 while (!DeadInsts.empty())
2605 EraseInstruction(DeadInsts.pop_back_val());
2607 return AnyPairsCompletelyEliminated;
2610 /// Weak pointer optimizations.
2611 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
2612 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
2614 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
2615 // itself because it uses AliasAnalysis and we need to do provenance
2617 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2618 Instruction *Inst = &*I++;
2620 DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
2622 InstructionClass Class = GetBasicInstructionClass(Inst);
2623 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
2626 // Delete objc_loadWeak calls with no users.
2627 if (Class == IC_LoadWeak && Inst->use_empty()) {
2628 Inst->eraseFromParent();
2632 // TODO: For now, just look for an earlier available version of this value
2633 // within the same block. Theoretically, we could do memdep-style non-local
2634 // analysis too, but that would want caching. A better approach would be to
2635 // use the technique that EarlyCSE uses.
2636 inst_iterator Current = llvm::prior(I);
2637 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
2638 for (BasicBlock::iterator B = CurrentBB->begin(),
2639 J = Current.getInstructionIterator();
2641 Instruction *EarlierInst = &*llvm::prior(J);
2642 InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
2643 switch (EarlierClass) {
2645 case IC_LoadWeakRetained: {
2646 // If this is loading from the same pointer, replace this load's value
2648 CallInst *Call = cast<CallInst>(Inst);
2649 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2650 Value *Arg = Call->getArgOperand(0);
2651 Value *EarlierArg = EarlierCall->getArgOperand(0);
2652 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2653 case AliasAnalysis::MustAlias:
2655 // If the load has a builtin retain, insert a plain retain for it.
2656 if (Class == IC_LoadWeakRetained) {
2658 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
2662 // Zap the fully redundant load.
2663 Call->replaceAllUsesWith(EarlierCall);
2664 Call->eraseFromParent();
2666 case AliasAnalysis::MayAlias:
2667 case AliasAnalysis::PartialAlias:
2669 case AliasAnalysis::NoAlias:
2676 // If this is storing to the same pointer and has the same size etc.
2677 // replace this load's value with the stored value.
2678 CallInst *Call = cast<CallInst>(Inst);
2679 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2680 Value *Arg = Call->getArgOperand(0);
2681 Value *EarlierArg = EarlierCall->getArgOperand(0);
2682 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2683 case AliasAnalysis::MustAlias:
2685 // If the load has a builtin retain, insert a plain retain for it.
2686 if (Class == IC_LoadWeakRetained) {
2688 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
2692 // Zap the fully redundant load.
2693 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
2694 Call->eraseFromParent();
2696 case AliasAnalysis::MayAlias:
2697 case AliasAnalysis::PartialAlias:
2699 case AliasAnalysis::NoAlias:
2706 // TOOD: Grab the copied value.
2708 case IC_AutoreleasepoolPush:
2710 case IC_IntrinsicUser:
2712 // Weak pointers are only modified through the weak entry points
2713 // (and arbitrary calls, which could call the weak entry points).
2716 // Anything else could modify the weak pointer.
2723 // Then, for each destroyWeak with an alloca operand, check to see if
2724 // the alloca and all its users can be zapped.
2725 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2726 Instruction *Inst = &*I++;
2727 InstructionClass Class = GetBasicInstructionClass(Inst);
2728 if (Class != IC_DestroyWeak)
2731 CallInst *Call = cast<CallInst>(Inst);
2732 Value *Arg = Call->getArgOperand(0);
2733 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
2734 for (Value::use_iterator UI = Alloca->use_begin(),
2735 UE = Alloca->use_end(); UI != UE; ++UI) {
2736 const Instruction *UserInst = cast<Instruction>(*UI);
2737 switch (GetBasicInstructionClass(UserInst)) {
2740 case IC_DestroyWeak:
2747 for (Value::use_iterator UI = Alloca->use_begin(),
2748 UE = Alloca->use_end(); UI != UE; ) {
2749 CallInst *UserInst = cast<CallInst>(*UI++);
2750 switch (GetBasicInstructionClass(UserInst)) {
2753 // These functions return their second argument.
2754 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
2756 case IC_DestroyWeak:
2760 llvm_unreachable("alloca really is used!");
2762 UserInst->eraseFromParent();
2764 Alloca->eraseFromParent();
2770 /// Identify program paths which execute sequences of retains and releases which
2771 /// can be eliminated.
2772 bool ObjCARCOpt::OptimizeSequences(Function &F) {
2773 /// Releases, Retains - These are used to store the results of the main flow
2774 /// analysis. These use Value* as the key instead of Instruction* so that the
2775 /// map stays valid when we get around to rewriting code and calls get
2776 /// replaced by arguments.
2777 DenseMap<Value *, RRInfo> Releases;
2778 MapVector<Value *, RRInfo> Retains;
2780 /// This is used during the traversal of the function to track the
2781 /// states for each identified object at each block.
2782 DenseMap<const BasicBlock *, BBState> BBStates;
2784 // Analyze the CFG of the function, and all instructions.
2785 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
2788 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
2792 /// Check if there is a dependent call earlier that does not have anything in
2793 /// between the Retain and the call that can affect the reference count of their
2794 /// shared pointer argument. Note that Retain need not be in BB.
2796 HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
2797 SmallPtrSet<Instruction *, 4> &DepInsts,
2798 SmallPtrSet<const BasicBlock *, 4> &Visited,
2799 ProvenanceAnalysis &PA) {
2800 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
2801 DepInsts, Visited, PA);
2802 if (DepInsts.size() != 1)
2806 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2808 // Check that the pointer is the return value of the call.
2809 if (!Call || Arg != Call)
2812 // Check that the call is a regular call.
2813 InstructionClass Class = GetBasicInstructionClass(Call);
2814 if (Class != IC_CallOrUser && Class != IC_Call)
2820 /// Find a dependent retain that precedes the given autorelease for which there
2821 /// is nothing in between the two instructions that can affect the ref count of
2824 FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
2825 Instruction *Autorelease,
2826 SmallPtrSet<Instruction *, 4> &DepInsts,
2827 SmallPtrSet<const BasicBlock *, 4> &Visited,
2828 ProvenanceAnalysis &PA) {
2829 FindDependencies(CanChangeRetainCount, Arg,
2830 BB, Autorelease, DepInsts, Visited, PA);
2831 if (DepInsts.size() != 1)
2835 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2837 // Check that we found a retain with the same argument.
2839 !IsRetain(GetBasicInstructionClass(Retain)) ||
2840 GetObjCArg(Retain) != Arg) {
2847 /// Look for an ``autorelease'' instruction dependent on Arg such that there are
2848 /// no instructions dependent on Arg that need a positive ref count in between
2849 /// the autorelease and the ret.
2851 FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
2853 SmallPtrSet<Instruction *, 4> &DepInsts,
2854 SmallPtrSet<const BasicBlock *, 4> &V,
2855 ProvenanceAnalysis &PA) {
2856 FindDependencies(NeedsPositiveRetainCount, Arg,
2857 BB, Ret, DepInsts, V, PA);
2858 if (DepInsts.size() != 1)
2861 CallInst *Autorelease =
2862 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2865 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
2866 if (!IsAutorelease(AutoreleaseClass))
2868 if (GetObjCArg(Autorelease) != Arg)
2874 /// Look for this pattern:
2876 /// %call = call i8* @something(...)
2877 /// %2 = call i8* @objc_retain(i8* %call)
2878 /// %3 = call i8* @objc_autorelease(i8* %2)
2881 /// And delete the retain and autorelease.
2882 void ObjCARCOpt::OptimizeReturns(Function &F) {
2883 if (!F.getReturnType()->isPointerTy())
2886 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
2888 SmallPtrSet<Instruction *, 4> DependingInstructions;
2889 SmallPtrSet<const BasicBlock *, 4> Visited;
2890 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
2891 BasicBlock *BB = FI;
2892 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
2894 DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
2899 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
2901 // Look for an ``autorelease'' instruction that is a predecssor of Ret and
2902 // dependent on Arg such that there are no instructions dependent on Arg
2903 // that need a positive ref count in between the autorelease and Ret.
2904 CallInst *Autorelease =
2905 FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
2906 DependingInstructions, Visited,
2909 DependingInstructions.clear();
2913 FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
2914 DependingInstructions, Visited, PA);
2916 DependingInstructions.clear();
2919 // Check that there is nothing that can affect the reference count
2920 // between the retain and the call. Note that Retain need not be in BB.
2921 if (HasSafePathToPredecessorCall(Arg, Retain, DependingInstructions,
2923 // If so, we can zap the retain and autorelease.
2926 DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
2927 << *Autorelease << "\n");
2928 EraseInstruction(Retain);
2929 EraseInstruction(Autorelease);
2934 DependingInstructions.clear();
2939 bool ObjCARCOpt::doInitialization(Module &M) {
2943 // If nothing in the Module uses ARC, don't do anything.
2944 Run = ModuleHasARC(M);
2948 // Identify the imprecise release metadata kind.
2949 ImpreciseReleaseMDKind =
2950 M.getContext().getMDKindID("clang.imprecise_release");
2951 CopyOnEscapeMDKind =
2952 M.getContext().getMDKindID("clang.arc.copy_on_escape");
2953 NoObjCARCExceptionsMDKind =
2954 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
2955 #ifdef ARC_ANNOTATIONS
2956 ARCAnnotationBottomUpMDKind =
2957 M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
2958 ARCAnnotationTopDownMDKind =
2959 M.getContext().getMDKindID("llvm.arc.annotation.topdown");
2960 ARCAnnotationProvenanceSourceMDKind =
2961 M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
2962 #endif // ARC_ANNOTATIONS
2964 // Intuitively, objc_retain and others are nocapture, however in practice
2965 // they are not, because they return their argument value. And objc_release
2966 // calls finalizers which can have arbitrary side effects.
2968 // These are initialized lazily.
2970 AutoreleaseRVCallee = 0;
2973 RetainBlockCallee = 0;
2974 AutoreleaseCallee = 0;
2979 bool ObjCARCOpt::runOnFunction(Function &F) {
2983 // If nothing in the Module uses ARC, don't do anything.
2989 DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
2992 PA.setAA(&getAnalysis<AliasAnalysis>());
2994 // This pass performs several distinct transformations. As a compile-time aid
2995 // when compiling code that isn't ObjC, skip these if the relevant ObjC
2996 // library functions aren't declared.
2998 // Preliminary optimizations. This also computs UsedInThisFunction.
2999 OptimizeIndividualCalls(F);
3001 // Optimizations for weak pointers.
3002 if (UsedInThisFunction & ((1 << IC_LoadWeak) |
3003 (1 << IC_LoadWeakRetained) |
3004 (1 << IC_StoreWeak) |
3005 (1 << IC_InitWeak) |
3006 (1 << IC_CopyWeak) |
3007 (1 << IC_MoveWeak) |
3008 (1 << IC_DestroyWeak)))
3009 OptimizeWeakCalls(F);
3011 // Optimizations for retain+release pairs.
3012 if (UsedInThisFunction & ((1 << IC_Retain) |
3013 (1 << IC_RetainRV) |
3014 (1 << IC_RetainBlock)))
3015 if (UsedInThisFunction & (1 << IC_Release))
3016 // Run OptimizeSequences until it either stops making changes or
3017 // no retain+release pair nesting is detected.
3018 while (OptimizeSequences(F)) {}
3020 // Optimizations if objc_autorelease is used.
3021 if (UsedInThisFunction & ((1 << IC_Autorelease) |
3022 (1 << IC_AutoreleaseRV)))
3025 DEBUG(dbgs() << "\n");
3030 void ObjCARCOpt::releaseMemory() {