1 //===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// This file defines ObjC ARC optimizations. ARC stands for Automatic
11 /// Reference Counting and is a system for managing reference counts for objects
14 /// The optimizations performed include elimination of redundant, partially
15 /// redundant, and inconsequential reference count operations, elimination of
16 /// redundant weak pointer operations, and numerous minor simplifications.
18 /// WARNING: This file knows about certain library functions. It recognizes them
19 /// by name, and hardwires knowledge of their semantics.
21 /// WARNING: This file knows about how certain Objective-C library functions are
22 /// used. Naive LLVM IR transformations which would otherwise be
23 /// behavior-preserving may break these assumptions.
25 //===----------------------------------------------------------------------===//
27 #define DEBUG_TYPE "objc-arc-opts"
29 #include "DependencyAnalysis.h"
30 #include "ObjCARCAliasAnalysis.h"
31 #include "ProvenanceAnalysis.h"
32 #include "llvm/ADT/DenseMap.h"
33 #include "llvm/ADT/STLExtras.h"
34 #include "llvm/ADT/SmallPtrSet.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/IR/IRBuilder.h"
37 #include "llvm/IR/LLVMContext.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/raw_ostream.h"
43 using namespace llvm::objcarc;
45 /// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
49 /// \brief An associative container with fast insertion-order (deterministic)
50 /// iteration over its elements. Plus the special blot operation.
51 template<class KeyT, class ValueT>
53 /// Map keys to indices in Vector.
54 typedef DenseMap<KeyT, size_t> MapTy;
57 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
62 typedef typename VectorTy::iterator iterator;
63 typedef typename VectorTy::const_iterator const_iterator;
64 iterator begin() { return Vector.begin(); }
65 iterator end() { return Vector.end(); }
66 const_iterator begin() const { return Vector.begin(); }
67 const_iterator end() const { return Vector.end(); }
71 assert(Vector.size() >= Map.size()); // May differ due to blotting.
72 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
74 assert(I->second < Vector.size());
75 assert(Vector[I->second].first == I->first);
77 for (typename VectorTy::const_iterator I = Vector.begin(),
78 E = Vector.end(); I != E; ++I)
80 (Map.count(I->first) &&
81 Map[I->first] == size_t(I - Vector.begin())));
85 ValueT &operator[](const KeyT &Arg) {
86 std::pair<typename MapTy::iterator, bool> Pair =
87 Map.insert(std::make_pair(Arg, size_t(0)));
89 size_t Num = Vector.size();
90 Pair.first->second = Num;
91 Vector.push_back(std::make_pair(Arg, ValueT()));
92 return Vector[Num].second;
94 return Vector[Pair.first->second].second;
97 std::pair<iterator, bool>
98 insert(const std::pair<KeyT, ValueT> &InsertPair) {
99 std::pair<typename MapTy::iterator, bool> Pair =
100 Map.insert(std::make_pair(InsertPair.first, size_t(0)));
102 size_t Num = Vector.size();
103 Pair.first->second = Num;
104 Vector.push_back(InsertPair);
105 return std::make_pair(Vector.begin() + Num, true);
107 return std::make_pair(Vector.begin() + Pair.first->second, false);
110 const_iterator find(const KeyT &Key) const {
111 typename MapTy::const_iterator It = Map.find(Key);
112 if (It == Map.end()) return Vector.end();
113 return Vector.begin() + It->second;
116 /// This is similar to erase, but instead of removing the element from the
117 /// vector, it just zeros out the key in the vector. This leaves iterators
118 /// intact, but clients must be prepared for zeroed-out keys when iterating.
119 void blot(const KeyT &Key) {
120 typename MapTy::iterator It = Map.find(Key);
121 if (It == Map.end()) return;
122 Vector[It->second].first = KeyT();
135 /// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
138 /// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon
139 /// as it finds a value with multiple uses.
140 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
141 if (Arg->hasOneUse()) {
142 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
143 return FindSingleUseIdentifiedObject(BC->getOperand(0));
144 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
145 if (GEP->hasAllZeroIndices())
146 return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
147 if (IsForwarding(GetBasicInstructionClass(Arg)))
148 return FindSingleUseIdentifiedObject(
149 cast<CallInst>(Arg)->getArgOperand(0));
150 if (!IsObjCIdentifiedObject(Arg))
155 // If we found an identifiable object but it has multiple uses, but they are
156 // trivial uses, we can still consider this to be a single-use value.
157 if (IsObjCIdentifiedObject(Arg)) {
158 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
161 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
171 /// \brief Test whether the given retainable object pointer escapes.
173 /// This differs from regular escape analysis in that a use as an
174 /// argument to a call is not considered an escape.
176 static bool DoesRetainableObjPtrEscape(const User *Ptr) {
177 DEBUG(dbgs() << "DoesRetainableObjPtrEscape: Target: " << *Ptr << "\n");
179 // Walk the def-use chains.
180 SmallVector<const Value *, 4> Worklist;
181 Worklist.push_back(Ptr);
182 // If Ptr has any operands add them as well.
183 for (User::const_op_iterator I = Ptr->op_begin(), E = Ptr->op_end(); I != E;
185 Worklist.push_back(*I);
188 // Ensure we do not visit any value twice.
189 SmallPtrSet<const Value *, 8> VisitedSet;
192 const Value *V = Worklist.pop_back_val();
194 DEBUG(dbgs() << "Visiting: " << *V << "\n");
196 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
198 const User *UUser = *UI;
200 DEBUG(dbgs() << "User: " << *UUser << "\n");
202 // Special - Use by a call (callee or argument) is not considered
204 switch (GetBasicInstructionClass(UUser)) {
209 case IC_AutoreleaseRV: {
210 DEBUG(dbgs() << "User copies pointer arguments. Pointer Escapes!\n");
211 // These special functions make copies of their pointer arguments.
214 case IC_IntrinsicUser:
215 // Use by the use intrinsic is not an escape.
219 // Use by an instruction which copies the value is an escape if the
220 // result is an escape.
221 if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) ||
222 isa<PHINode>(UUser) || isa<SelectInst>(UUser)) {
224 if (VisitedSet.insert(UUser)) {
225 DEBUG(dbgs() << "User copies value. Ptr escapes if result escapes."
226 " Adding to list.\n");
227 Worklist.push_back(UUser);
229 DEBUG(dbgs() << "Already visited node.\n");
233 // Use by a load is not an escape.
234 if (isa<LoadInst>(UUser))
236 // Use by a store is not an escape if the use is the address.
237 if (const StoreInst *SI = dyn_cast<StoreInst>(UUser))
238 if (V != SI->getValueOperand())
242 // Regular calls and other stuff are not considered escapes.
245 // Otherwise, conservatively assume an escape.
246 DEBUG(dbgs() << "Assuming ptr escapes.\n");
249 } while (!Worklist.empty());
252 DEBUG(dbgs() << "Ptr does not escape.\n");
258 /// \defgroup ARCOpt ARC Optimization.
261 // TODO: On code like this:
264 // stuff_that_cannot_release()
265 // objc_autorelease(%x)
266 // stuff_that_cannot_release()
268 // stuff_that_cannot_release()
269 // objc_autorelease(%x)
271 // The second retain and autorelease can be deleted.
273 // TODO: It should be possible to delete
274 // objc_autoreleasePoolPush and objc_autoreleasePoolPop
275 // pairs if nothing is actually autoreleased between them. Also, autorelease
276 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
277 // after inlining) can be turned into plain release calls.
279 // TODO: Critical-edge splitting. If the optimial insertion point is
280 // a critical edge, the current algorithm has to fail, because it doesn't
281 // know how to split edges. It should be possible to make the optimizer
282 // think in terms of edges, rather than blocks, and then split critical
285 // TODO: OptimizeSequences could generalized to be Interprocedural.
287 // TODO: Recognize that a bunch of other objc runtime calls have
288 // non-escaping arguments and non-releasing arguments, and may be
289 // non-autoreleasing.
291 // TODO: Sink autorelease calls as far as possible. Unfortunately we
292 // usually can't sink them past other calls, which would be the main
293 // case where it would be useful.
295 // TODO: The pointer returned from objc_loadWeakRetained is retained.
297 // TODO: Delete release+retain pairs (rare).
299 STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
300 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
301 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
302 STATISTIC(NumRets, "Number of return value forwarding "
303 "retain+autoreleaes eliminated");
304 STATISTIC(NumRRs, "Number of retain+release paths eliminated");
305 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
306 STATISTIC(NumRetainsBeforeOpt,
307 "Number of retains before optimization.");
308 STATISTIC(NumReleasesBeforeOpt,
309 "Number of releases before optimization.");
310 STATISTIC(NumRetainsAfterOpt,
311 "Number of retains after optimization.");
312 STATISTIC(NumReleasesAfterOpt,
313 "Number of releases after optimization.");
318 /// \brief A sequence of states that a pointer may go through in which an
319 /// objc_retain and objc_release are actually needed.
322 S_Retain, ///< objc_retain(x).
323 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement.
324 S_Use, ///< any use of x.
325 S_Stop, ///< like S_Release, but code motion is stopped.
326 S_Release, ///< objc_release(x).
327 S_MovableRelease ///< objc_release(x), !clang.imprecise_release.
330 raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
331 LLVM_ATTRIBUTE_UNUSED;
332 raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
335 return OS << "S_None";
337 return OS << "S_Retain";
339 return OS << "S_CanRelease";
341 return OS << "S_Use";
343 return OS << "S_Release";
344 case S_MovableRelease:
345 return OS << "S_MovableRelease";
347 return OS << "S_Stop";
349 llvm_unreachable("Unknown sequence type.");
353 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
357 if (A == S_None || B == S_None)
360 if (A > B) std::swap(A, B);
362 // Choose the side which is further along in the sequence.
363 if ((A == S_Retain || A == S_CanRelease) &&
364 (B == S_CanRelease || B == S_Use))
367 // Choose the side which is further along in the sequence.
368 if ((A == S_Use || A == S_CanRelease) &&
369 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
371 // If both sides are releases, choose the more conservative one.
372 if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
374 if (A == S_Release && B == S_MovableRelease)
382 /// \brief Unidirectional information about either a
383 /// retain-decrement-use-release sequence or release-use-decrement-retain
384 /// reverse sequence.
386 /// After an objc_retain, the reference count of the referenced
387 /// object is known to be positive. Similarly, before an objc_release, the
388 /// reference count of the referenced object is known to be positive. If
389 /// there are retain-release pairs in code regions where the retain count
390 /// is known to be positive, they can be eliminated, regardless of any side
391 /// effects between them.
393 /// Also, a retain+release pair nested within another retain+release
394 /// pair all on the known same pointer value can be eliminated, regardless
395 /// of any intervening side effects.
397 /// KnownSafe is true when either of these conditions is satisfied.
400 /// True of the objc_release calls are all marked with the "tail" keyword.
401 bool IsTailCallRelease;
403 /// If the Calls are objc_release calls and they all have a
404 /// clang.imprecise_release tag, this is the metadata tag.
405 MDNode *ReleaseMetadata;
407 /// For a top-down sequence, the set of objc_retains or
408 /// objc_retainBlocks. For bottom-up, the set of objc_releases.
409 SmallPtrSet<Instruction *, 2> Calls;
411 /// The set of optimal insert positions for moving calls in the opposite
413 SmallPtrSet<Instruction *, 2> ReverseInsertPts;
416 KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(0) {}
420 bool IsTrackingImpreciseReleases() {
421 return ReleaseMetadata != 0;
426 void RRInfo::clear() {
428 IsTailCallRelease = false;
431 ReverseInsertPts.clear();
435 /// \brief This class summarizes several per-pointer runtime properties which
436 /// are propogated through the flow graph.
438 /// True if the reference count is known to be incremented.
439 bool KnownPositiveRefCount;
441 /// True if we've seen an opportunity for partial RR elimination, such as
442 /// pushing calls into a CFG triangle or into one side of a CFG diamond.
445 /// The current position in the sequence.
449 /// Unidirectional information about the current sequence.
451 /// TODO: Encapsulate this better.
454 PtrState() : KnownPositiveRefCount(false), Partial(false),
457 void SetKnownPositiveRefCount() {
458 KnownPositiveRefCount = true;
461 void ClearKnownPositiveRefCount() {
462 KnownPositiveRefCount = false;
465 bool HasKnownPositiveRefCount() const {
466 return KnownPositiveRefCount;
469 void SetSeq(Sequence NewSeq) {
470 DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
474 Sequence GetSeq() const {
478 void ClearSequenceProgress() {
479 ResetSequenceProgress(S_None);
482 void ResetSequenceProgress(Sequence NewSeq) {
483 DEBUG(dbgs() << "Resetting sequence progress.\n");
489 void Merge(const PtrState &Other, bool TopDown);
494 PtrState::Merge(const PtrState &Other, bool TopDown) {
495 Seq = MergeSeqs(Seq, Other.Seq, TopDown);
496 KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
498 // If we're not in a sequence (anymore), drop all associated state.
502 } else if (Partial || Other.Partial) {
503 // If we're doing a merge on a path that's previously seen a partial
504 // merge, conservatively drop the sequence, to avoid doing partial
505 // RR elimination. If the branch predicates for the two merge differ,
506 // mixing them is unsafe.
507 ClearSequenceProgress();
509 // Conservatively merge the ReleaseMetadata information.
510 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
511 RRI.ReleaseMetadata = 0;
513 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
514 RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
515 Other.RRI.IsTailCallRelease;
516 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
518 // Merge the insert point sets. If there are any differences,
519 // that makes this a partial merge.
520 Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
521 for (SmallPtrSet<Instruction *, 2>::const_iterator
522 I = Other.RRI.ReverseInsertPts.begin(),
523 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
524 Partial |= RRI.ReverseInsertPts.insert(*I);
529 /// \brief Per-BasicBlock state.
531 /// The number of unique control paths from the entry which can reach this
533 unsigned TopDownPathCount;
535 /// The number of unique control paths to exits from this block.
536 unsigned BottomUpPathCount;
538 /// A type for PerPtrTopDown and PerPtrBottomUp.
539 typedef MapVector<const Value *, PtrState> MapTy;
541 /// The top-down traversal uses this to record information known about a
542 /// pointer at the bottom of each block.
545 /// The bottom-up traversal uses this to record information known about a
546 /// pointer at the top of each block.
547 MapTy PerPtrBottomUp;
549 /// Effective predecessors of the current block ignoring ignorable edges and
550 /// ignored backedges.
551 SmallVector<BasicBlock *, 2> Preds;
552 /// Effective successors of the current block ignoring ignorable edges and
553 /// ignored backedges.
554 SmallVector<BasicBlock *, 2> Succs;
557 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
559 typedef MapTy::iterator ptr_iterator;
560 typedef MapTy::const_iterator ptr_const_iterator;
562 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
563 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
564 ptr_const_iterator top_down_ptr_begin() const {
565 return PerPtrTopDown.begin();
567 ptr_const_iterator top_down_ptr_end() const {
568 return PerPtrTopDown.end();
571 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
572 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
573 ptr_const_iterator bottom_up_ptr_begin() const {
574 return PerPtrBottomUp.begin();
576 ptr_const_iterator bottom_up_ptr_end() const {
577 return PerPtrBottomUp.end();
580 /// Mark this block as being an entry block, which has one path from the
581 /// entry by definition.
582 void SetAsEntry() { TopDownPathCount = 1; }
584 /// Mark this block as being an exit block, which has one path to an exit by
586 void SetAsExit() { BottomUpPathCount = 1; }
588 PtrState &getPtrTopDownState(const Value *Arg) {
589 return PerPtrTopDown[Arg];
592 PtrState &getPtrBottomUpState(const Value *Arg) {
593 return PerPtrBottomUp[Arg];
596 void clearBottomUpPointers() {
597 PerPtrBottomUp.clear();
600 void clearTopDownPointers() {
601 PerPtrTopDown.clear();
604 void InitFromPred(const BBState &Other);
605 void InitFromSucc(const BBState &Other);
606 void MergePred(const BBState &Other);
607 void MergeSucc(const BBState &Other);
609 /// Return the number of possible unique paths from an entry to an exit
610 /// which pass through this block. This is only valid after both the
611 /// top-down and bottom-up traversals are complete.
612 unsigned GetAllPathCount() const {
613 assert(TopDownPathCount != 0);
614 assert(BottomUpPathCount != 0);
615 return TopDownPathCount * BottomUpPathCount;
618 // Specialized CFG utilities.
619 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
620 edge_iterator pred_begin() { return Preds.begin(); }
621 edge_iterator pred_end() { return Preds.end(); }
622 edge_iterator succ_begin() { return Succs.begin(); }
623 edge_iterator succ_end() { return Succs.end(); }
625 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
626 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
628 bool isExit() const { return Succs.empty(); }
632 void BBState::InitFromPred(const BBState &Other) {
633 PerPtrTopDown = Other.PerPtrTopDown;
634 TopDownPathCount = Other.TopDownPathCount;
637 void BBState::InitFromSucc(const BBState &Other) {
638 PerPtrBottomUp = Other.PerPtrBottomUp;
639 BottomUpPathCount = Other.BottomUpPathCount;
642 /// The top-down traversal uses this to merge information about predecessors to
643 /// form the initial state for a new block.
644 void BBState::MergePred(const BBState &Other) {
645 // Other.TopDownPathCount can be 0, in which case it is either dead or a
646 // loop backedge. Loop backedges are special.
647 TopDownPathCount += Other.TopDownPathCount;
649 // Check for overflow. If we have overflow, fall back to conservative
651 if (TopDownPathCount < Other.TopDownPathCount) {
652 clearTopDownPointers();
656 // For each entry in the other set, if our set has an entry with the same key,
657 // merge the entries. Otherwise, copy the entry and merge it with an empty
659 for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
660 ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
661 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
662 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
666 // For each entry in our set, if the other set doesn't have an entry with the
667 // same key, force it to merge with an empty entry.
668 for (ptr_iterator MI = top_down_ptr_begin(),
669 ME = top_down_ptr_end(); MI != ME; ++MI)
670 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
671 MI->second.Merge(PtrState(), /*TopDown=*/true);
674 /// The bottom-up traversal uses this to merge information about successors to
675 /// form the initial state for a new block.
676 void BBState::MergeSucc(const BBState &Other) {
677 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
678 // loop backedge. Loop backedges are special.
679 BottomUpPathCount += Other.BottomUpPathCount;
681 // Check for overflow. If we have overflow, fall back to conservative
683 if (BottomUpPathCount < Other.BottomUpPathCount) {
684 clearBottomUpPointers();
688 // For each entry in the other set, if our set has an entry with the
689 // same key, merge the entries. Otherwise, copy the entry and merge
690 // it with an empty entry.
691 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
692 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
693 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
694 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
698 // For each entry in our set, if the other set doesn't have an entry
699 // with the same key, force it to merge with an empty entry.
700 for (ptr_iterator MI = bottom_up_ptr_begin(),
701 ME = bottom_up_ptr_end(); MI != ME; ++MI)
702 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
703 MI->second.Merge(PtrState(), /*TopDown=*/false);
706 // Only enable ARC Annotations if we are building a debug version of
709 #define ARC_ANNOTATIONS
712 // Define some macros along the lines of DEBUG and some helper functions to make
713 // it cleaner to create annotations in the source code and to no-op when not
714 // building in debug mode.
715 #ifdef ARC_ANNOTATIONS
717 #include "llvm/Support/CommandLine.h"
719 /// Enable/disable ARC sequence annotations.
721 EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false),
722 cl::desc("Enable emission of arc data flow analysis "
725 DisableCheckForCFGHazards("disable-objc-arc-checkforcfghazards", cl::init(false),
726 cl::desc("Disable check for cfg hazards when "
728 static cl::opt<std::string>
729 ARCAnnotationTargetIdentifier("objc-arc-annotation-target-identifier",
731 cl::desc("filter out all data flow annotations "
732 "but those that apply to the given "
733 "target llvm identifier."));
735 /// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
736 /// instruction so that we can track backwards when post processing via the llvm
737 /// arc annotation processor tool. If the function is an
738 static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
742 // If pointer is a result of an instruction and it does not have a source
743 // MDNode it, attach a new MDNode onto it. If pointer is a result of
744 // an instruction and does have a source MDNode attached to it, return a
745 // reference to said Node. Otherwise just return 0.
746 if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
748 if (!(Node = Inst->getMetadata(NodeId))) {
749 // We do not have any node. Generate and attatch the hash MDString to the
752 // We just use an MDString to ensure that this metadata gets written out
753 // of line at the module level and to provide a very simple format
754 // encoding the information herein. Both of these makes it simpler to
755 // parse the annotations by a simple external program.
757 raw_string_ostream os(Str);
758 os << "(" << Inst->getParent()->getParent()->getName() << ",%"
759 << Inst->getName() << ")";
761 Hash = MDString::get(Inst->getContext(), os.str());
762 Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
764 // We have a node. Grab its hash and return it.
765 assert(Node->getNumOperands() == 1 &&
766 "An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
767 Hash = cast<MDString>(Node->getOperand(0));
769 } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
771 raw_string_ostream os(str);
772 os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
774 Hash = MDString::get(Arg->getContext(), os.str());
780 static std::string SequenceToString(Sequence A) {
782 raw_string_ostream os(str);
787 /// Helper function to change a Sequence into a String object using our overload
788 /// for raw_ostream so we only have printing code in one location.
789 static MDString *SequenceToMDString(LLVMContext &Context,
791 return MDString::get(Context, SequenceToString(A));
794 /// A simple function to generate a MDNode which describes the change in state
795 /// for Value *Ptr caused by Instruction *Inst.
796 static void AppendMDNodeToInstForPtr(unsigned NodeId,
799 MDString *PtrSourceMDNodeID,
803 Value *tmp[3] = {PtrSourceMDNodeID,
804 SequenceToMDString(Inst->getContext(),
806 SequenceToMDString(Inst->getContext(),
808 Node = MDNode::get(Inst->getContext(),
809 ArrayRef<Value*>(tmp, 3));
811 Inst->setMetadata(NodeId, Node);
814 /// Add to the beginning of the basic block llvm.ptr.annotations which show the
815 /// state of a pointer at the entrance to a basic block.
816 static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
817 Value *Ptr, Sequence Seq) {
818 // If we have a target identifier, make sure that we match it before
820 if(!ARCAnnotationTargetIdentifier.empty() &&
821 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
824 Module *M = BB->getParent()->getParent();
825 LLVMContext &C = M->getContext();
826 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
827 Type *I8XX = PointerType::getUnqual(I8X);
828 Type *Params[] = {I8XX, I8XX};
829 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
830 ArrayRef<Type*>(Params, 2),
832 Constant *Callee = M->getOrInsertFunction(Name, FTy);
834 IRBuilder<> Builder(BB, BB->getFirstInsertionPt());
837 StringRef Tmp = Ptr->getName();
838 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
839 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
841 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
842 cast<Constant>(ActualPtrName), Tmp);
846 std::string SeqStr = SequenceToString(Seq);
847 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
848 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
850 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
851 cast<Constant>(ActualPtrName), SeqStr);
854 Builder.CreateCall2(Callee, PtrName, S);
857 /// Add to the end of the basic block llvm.ptr.annotations which show the state
858 /// of the pointer at the bottom of the basic block.
859 static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
860 Value *Ptr, Sequence Seq) {
861 // If we have a target identifier, make sure that we match it before emitting
863 if(!ARCAnnotationTargetIdentifier.empty() &&
864 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
867 Module *M = BB->getParent()->getParent();
868 LLVMContext &C = M->getContext();
869 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
870 Type *I8XX = PointerType::getUnqual(I8X);
871 Type *Params[] = {I8XX, I8XX};
872 FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
873 ArrayRef<Type*>(Params, 2),
875 Constant *Callee = M->getOrInsertFunction(Name, FTy);
877 IRBuilder<> Builder(BB, llvm::prior(BB->end()));
880 StringRef Tmp = Ptr->getName();
881 if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
882 Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
884 PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
885 cast<Constant>(ActualPtrName), Tmp);
889 std::string SeqStr = SequenceToString(Seq);
890 if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
891 Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
893 S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
894 cast<Constant>(ActualPtrName), SeqStr);
896 Builder.CreateCall2(Callee, PtrName, S);
899 /// Adds a source annotation to pointer and a state change annotation to Inst
900 /// referencing the source annotation and the old/new state of pointer.
901 static void GenerateARCAnnotation(unsigned InstMDId,
907 if (EnableARCAnnotations) {
908 // If we have a target identifier, make sure that we match it before
909 // emitting an annotation.
910 if(!ARCAnnotationTargetIdentifier.empty() &&
911 !Ptr->getName().equals(ARCAnnotationTargetIdentifier))
914 // First generate the source annotation on our pointer. This will return an
915 // MDString* if Ptr actually comes from an instruction implying we can put
916 // in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
917 // then we know that our pointer is from an Argument so we put a reference
918 // to the argument number.
920 // The point of this is to make it easy for the
921 // llvm-arc-annotation-processor tool to cross reference where the source
922 // pointer is in the LLVM IR since the LLVM IR parser does not submit such
923 // information via debug info for backends to use (since why would anyone
924 // need such a thing from LLVM IR besides in non standard cases
926 MDString *SourcePtrMDNode =
927 AppendMDNodeToSourcePtr(PtrMDId, Ptr);
928 AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
933 // The actual interface for accessing the above functionality is defined via
934 // some simple macros which are defined below. We do this so that the user does
935 // not need to pass in what metadata id is needed resulting in cleaner code and
936 // additionally since it provides an easy way to conditionally no-op all
937 // annotation support in a non-debug build.
939 /// Use this macro to annotate a sequence state change when processing
940 /// instructions bottom up,
941 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new) \
942 GenerateARCAnnotation(ARCAnnotationBottomUpMDKind, \
943 ARCAnnotationProvenanceSourceMDKind, (inst), \
944 const_cast<Value*>(ptr), (old), (new))
945 /// Use this macro to annotate a sequence state change when processing
946 /// instructions top down.
947 #define ANNOTATE_TOPDOWN(inst, ptr, old, new) \
948 GenerateARCAnnotation(ARCAnnotationTopDownMDKind, \
949 ARCAnnotationProvenanceSourceMDKind, (inst), \
950 const_cast<Value*>(ptr), (old), (new))
952 #define ANNOTATE_BB(_states, _bb, _name, _type, _direction) \
954 if (EnableARCAnnotations) { \
955 for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
956 E = (_states)._direction##_ptr_end(); I != E; ++I) { \
957 Value *Ptr = const_cast<Value*>(I->first); \
958 Sequence Seq = I->second.GetSeq(); \
959 GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq); \
964 #define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock) \
965 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
967 #define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock) \
968 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend", \
969 Terminator, bottom_up)
970 #define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock) \
971 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart", \
973 #define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock) \
974 ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend", \
975 Terminator, top_down)
977 #else // !ARC_ANNOTATION
978 // If annotations are off, noop.
979 #define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
980 #define ANNOTATE_TOPDOWN(inst, ptr, old, new)
981 #define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
982 #define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
983 #define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
984 #define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
985 #endif // !ARC_ANNOTATION
988 /// \brief The main ARC optimization pass.
989 class ObjCARCOpt : public FunctionPass {
991 ProvenanceAnalysis PA;
993 /// A flag indicating whether this optimization pass should run.
996 /// Declarations for ObjC runtime functions, for use in creating calls to
997 /// them. These are initialized lazily to avoid cluttering up the Module
998 /// with unused declarations.
1000 /// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
1001 Constant *AutoreleaseRVCallee;
1002 /// Declaration for ObjC runtime function objc_release.
1003 Constant *ReleaseCallee;
1004 /// Declaration for ObjC runtime function objc_retain.
1005 Constant *RetainCallee;
1006 /// Declaration for ObjC runtime function objc_retainBlock.
1007 Constant *RetainBlockCallee;
1008 /// Declaration for ObjC runtime function objc_autorelease.
1009 Constant *AutoreleaseCallee;
1011 /// Flags which determine whether each of the interesting runtine functions
1012 /// is in fact used in the current function.
1013 unsigned UsedInThisFunction;
1015 /// The Metadata Kind for clang.imprecise_release metadata.
1016 unsigned ImpreciseReleaseMDKind;
1018 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
1019 unsigned CopyOnEscapeMDKind;
1021 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
1022 unsigned NoObjCARCExceptionsMDKind;
1024 #ifdef ARC_ANNOTATIONS
1025 /// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
1026 unsigned ARCAnnotationBottomUpMDKind;
1027 /// The Metadata Kind for llvm.arc.annotation.topdown metadata.
1028 unsigned ARCAnnotationTopDownMDKind;
1029 /// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
1030 unsigned ARCAnnotationProvenanceSourceMDKind;
1031 #endif // ARC_ANNOATIONS
1033 Constant *getAutoreleaseRVCallee(Module *M);
1034 Constant *getReleaseCallee(Module *M);
1035 Constant *getRetainCallee(Module *M);
1036 Constant *getRetainBlockCallee(Module *M);
1037 Constant *getAutoreleaseCallee(Module *M);
1039 bool IsRetainBlockOptimizable(const Instruction *Inst);
1041 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
1042 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1043 InstructionClass &Class);
1044 bool OptimizeRetainBlockCall(Function &F, Instruction *RetainBlock,
1045 InstructionClass &Class);
1046 void OptimizeIndividualCalls(Function &F);
1048 void CheckForCFGHazards(const BasicBlock *BB,
1049 DenseMap<const BasicBlock *, BBState> &BBStates,
1050 BBState &MyStates) const;
1051 bool VisitInstructionBottomUp(Instruction *Inst,
1053 MapVector<Value *, RRInfo> &Retains,
1055 bool VisitBottomUp(BasicBlock *BB,
1056 DenseMap<const BasicBlock *, BBState> &BBStates,
1057 MapVector<Value *, RRInfo> &Retains);
1058 bool VisitInstructionTopDown(Instruction *Inst,
1059 DenseMap<Value *, RRInfo> &Releases,
1061 bool VisitTopDown(BasicBlock *BB,
1062 DenseMap<const BasicBlock *, BBState> &BBStates,
1063 DenseMap<Value *, RRInfo> &Releases);
1064 bool Visit(Function &F,
1065 DenseMap<const BasicBlock *, BBState> &BBStates,
1066 MapVector<Value *, RRInfo> &Retains,
1067 DenseMap<Value *, RRInfo> &Releases);
1069 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
1070 MapVector<Value *, RRInfo> &Retains,
1071 DenseMap<Value *, RRInfo> &Releases,
1072 SmallVectorImpl<Instruction *> &DeadInsts,
1075 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
1076 MapVector<Value *, RRInfo> &Retains,
1077 DenseMap<Value *, RRInfo> &Releases,
1079 SmallVector<Instruction *, 4> &NewRetains,
1080 SmallVector<Instruction *, 4> &NewReleases,
1081 SmallVector<Instruction *, 8> &DeadInsts,
1082 RRInfo &RetainsToMove,
1083 RRInfo &ReleasesToMove,
1086 bool &AnyPairsCompletelyEliminated);
1088 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
1089 MapVector<Value *, RRInfo> &Retains,
1090 DenseMap<Value *, RRInfo> &Releases,
1093 void OptimizeWeakCalls(Function &F);
1095 bool OptimizeSequences(Function &F);
1097 void OptimizeReturns(Function &F);
1100 void GatherStatistics(Function &F, bool AfterOptimization = false);
1103 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
1104 virtual bool doInitialization(Module &M);
1105 virtual bool runOnFunction(Function &F);
1106 virtual void releaseMemory();
1110 ObjCARCOpt() : FunctionPass(ID) {
1111 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
1116 char ObjCARCOpt::ID = 0;
1117 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
1118 "objc-arc", "ObjC ARC optimization", false, false)
1119 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
1120 INITIALIZE_PASS_END(ObjCARCOpt,
1121 "objc-arc", "ObjC ARC optimization", false, false)
1123 Pass *llvm::createObjCARCOptPass() {
1124 return new ObjCARCOpt();
1127 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
1128 AU.addRequired<ObjCARCAliasAnalysis>();
1129 AU.addRequired<AliasAnalysis>();
1130 // ARC optimization doesn't currently split critical edges.
1131 AU.setPreservesCFG();
1134 bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
1135 // Without the magic metadata tag, we have to assume this might be an
1136 // objc_retainBlock call inserted to convert a block pointer to an id,
1137 // in which case it really is needed.
1138 if (!Inst->getMetadata(CopyOnEscapeMDKind))
1141 // If the pointer "escapes" (not including being used in a call),
1142 // the copy may be needed.
1143 if (DoesRetainableObjPtrEscape(Inst))
1146 // Otherwise, it's not needed.
1150 Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
1151 if (!AutoreleaseRVCallee) {
1152 LLVMContext &C = M->getContext();
1153 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1154 Type *Params[] = { I8X };
1155 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1156 AttributeSet Attribute =
1157 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1158 Attribute::NoUnwind);
1159 AutoreleaseRVCallee =
1160 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
1163 return AutoreleaseRVCallee;
1166 Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
1167 if (!ReleaseCallee) {
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(Type::getVoidTy(C), Params, /*isVarArg=*/false),
1179 return ReleaseCallee;
1182 Constant *ObjCARCOpt::getRetainCallee(Module *M) {
1183 if (!RetainCallee) {
1184 LLVMContext &C = M->getContext();
1185 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1186 AttributeSet Attribute =
1187 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1188 Attribute::NoUnwind);
1190 M->getOrInsertFunction(
1192 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1195 return RetainCallee;
1198 Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
1199 if (!RetainBlockCallee) {
1200 LLVMContext &C = M->getContext();
1201 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1202 // objc_retainBlock is not nounwind because it calls user copy constructors
1203 // which could theoretically throw.
1205 M->getOrInsertFunction(
1207 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1210 return RetainBlockCallee;
1213 Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
1214 if (!AutoreleaseCallee) {
1215 LLVMContext &C = M->getContext();
1216 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1217 AttributeSet Attribute =
1218 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1219 Attribute::NoUnwind);
1221 M->getOrInsertFunction(
1223 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1226 return AutoreleaseCallee;
1229 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
1230 /// not a return value. Or, if it can be paired with an
1231 /// objc_autoreleaseReturnValue, delete the pair and return true.
1233 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
1234 // Check for the argument being from an immediately preceding call or invoke.
1235 const Value *Arg = GetObjCArg(RetainRV);
1236 ImmutableCallSite CS(Arg);
1237 if (const Instruction *Call = CS.getInstruction()) {
1238 if (Call->getParent() == RetainRV->getParent()) {
1239 BasicBlock::const_iterator I = Call;
1241 while (IsNoopInstruction(I)) ++I;
1242 if (&*I == RetainRV)
1244 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
1245 BasicBlock *RetainRVParent = RetainRV->getParent();
1246 if (II->getNormalDest() == RetainRVParent) {
1247 BasicBlock::const_iterator I = RetainRVParent->begin();
1248 while (IsNoopInstruction(I)) ++I;
1249 if (&*I == RetainRV)
1255 // Check for being preceded by an objc_autoreleaseReturnValue on the same
1256 // pointer. In this case, we can delete the pair.
1257 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
1259 do --I; while (I != Begin && IsNoopInstruction(I));
1260 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
1261 GetObjCArg(I) == Arg) {
1265 DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
1266 << "Erasing " << *RetainRV << "\n");
1268 EraseInstruction(I);
1269 EraseInstruction(RetainRV);
1274 // Turn it to a plain objc_retain.
1278 DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
1279 "objc_retain since the operand is not a return value.\n"
1280 "Old = " << *RetainRV << "\n");
1282 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));
1284 DEBUG(dbgs() << "New = " << *RetainRV << "\n");
1289 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
1290 /// used as a return value.
1292 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1293 InstructionClass &Class) {
1294 // Check for a return of the pointer value.
1295 const Value *Ptr = GetObjCArg(AutoreleaseRV);
1296 SmallVector<const Value *, 2> Users;
1297 Users.push_back(Ptr);
1299 Ptr = Users.pop_back_val();
1300 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
1302 const User *I = *UI;
1303 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
1305 if (isa<BitCastInst>(I))
1308 } while (!Users.empty());
1313 DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
1314 "objc_autorelease since its operand is not used as a return "
1316 "Old = " << *AutoreleaseRV << "\n");
1318 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
1320 setCalledFunction(getAutoreleaseCallee(F.getParent()));
1321 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
1322 Class = IC_Autorelease;
1324 DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
1328 // \brief Attempt to strength reduce objc_retainBlock calls to objc_retain
1331 // Specifically: If an objc_retainBlock call has the copy_on_escape metadata and
1332 // does not escape (following the rules of block escaping), strength reduce the
1333 // objc_retainBlock to an objc_retain.
1335 // TODO: If an objc_retainBlock call is dominated period by a previous
1336 // objc_retainBlock call, strength reduce the objc_retainBlock to an
1339 ObjCARCOpt::OptimizeRetainBlockCall(Function &F, Instruction *Inst,
1340 InstructionClass &Class) {
1341 assert(GetBasicInstructionClass(Inst) == Class);
1342 assert(IC_RetainBlock == Class);
1344 // If we can not optimize Inst, return false.
1345 if (!IsRetainBlockOptimizable(Inst))
1351 DEBUG(dbgs() << "Strength reduced retainBlock => retain.\n");
1352 DEBUG(dbgs() << "Old: " << *Inst << "\n");
1353 CallInst *RetainBlock = cast<CallInst>(Inst);
1354 RetainBlock->setCalledFunction(getRetainCallee(F.getParent()));
1355 // Remove copy_on_escape metadata.
1356 RetainBlock->setMetadata(CopyOnEscapeMDKind, 0);
1358 DEBUG(dbgs() << "New: " << *Inst << "\n");
1362 /// Visit each call, one at a time, and make simplifications without doing any
1363 /// additional analysis.
1364 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
1365 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
1366 // Reset all the flags in preparation for recomputing them.
1367 UsedInThisFunction = 0;
1369 // Visit all objc_* calls in F.
1370 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1371 Instruction *Inst = &*I++;
1373 InstructionClass Class = GetBasicInstructionClass(Inst);
1375 DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
1380 // Delete no-op casts. These function calls have special semantics, but
1381 // the semantics are entirely implemented via lowering in the front-end,
1382 // so by the time they reach the optimizer, they are just no-op calls
1383 // which return their argument.
1385 // There are gray areas here, as the ability to cast reference-counted
1386 // pointers to raw void* and back allows code to break ARC assumptions,
1387 // however these are currently considered to be unimportant.
1391 DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
1392 EraseInstruction(Inst);
1395 // If the pointer-to-weak-pointer is null, it's undefined behavior.
1398 case IC_LoadWeakRetained:
1400 case IC_DestroyWeak: {
1401 CallInst *CI = cast<CallInst>(Inst);
1402 if (IsNullOrUndef(CI->getArgOperand(0))) {
1404 Type *Ty = CI->getArgOperand(0)->getType();
1405 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1406 Constant::getNullValue(Ty),
1408 llvm::Value *NewValue = UndefValue::get(CI->getType());
1409 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1410 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1411 CI->replaceAllUsesWith(NewValue);
1412 CI->eraseFromParent();
1419 CallInst *CI = cast<CallInst>(Inst);
1420 if (IsNullOrUndef(CI->getArgOperand(0)) ||
1421 IsNullOrUndef(CI->getArgOperand(1))) {
1423 Type *Ty = CI->getArgOperand(0)->getType();
1424 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
1425 Constant::getNullValue(Ty),
1428 llvm::Value *NewValue = UndefValue::get(CI->getType());
1429 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
1430 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
1432 CI->replaceAllUsesWith(NewValue);
1433 CI->eraseFromParent();
1438 case IC_RetainBlock:
1439 // If we strength reduce an objc_retainBlock to an objc_retain, continue
1440 // onto the objc_retain peephole optimizations. Otherwise break.
1441 if (!OptimizeRetainBlockCall(F, Inst, Class))
1445 ++NumRetainsBeforeOpt;
1448 if (OptimizeRetainRVCall(F, Inst))
1451 case IC_AutoreleaseRV:
1452 OptimizeAutoreleaseRVCall(F, Inst, Class);
1455 ++NumReleasesBeforeOpt;
1459 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
1460 if (IsAutorelease(Class) && Inst->use_empty()) {
1461 CallInst *Call = cast<CallInst>(Inst);
1462 const Value *Arg = Call->getArgOperand(0);
1463 Arg = FindSingleUseIdentifiedObject(Arg);
1468 // Create the declaration lazily.
1469 LLVMContext &C = Inst->getContext();
1471 CallInst::Create(getReleaseCallee(F.getParent()),
1472 Call->getArgOperand(0), "", Call);
1473 NewCall->setMetadata(ImpreciseReleaseMDKind,
1474 MDNode::get(C, ArrayRef<Value *>()));
1476 DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
1477 "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
1478 << *NewCall << "\n");
1480 EraseInstruction(Call);
1486 // For functions which can never be passed stack arguments, add
1488 if (IsAlwaysTail(Class)) {
1490 DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
1491 "passed stack args: " << *Inst << "\n");
1492 cast<CallInst>(Inst)->setTailCall();
1495 // Ensure that functions that can never have a "tail" keyword due to the
1496 // semantics of ARC truly do not do so.
1497 if (IsNeverTail(Class)) {
1499 DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
1501 cast<CallInst>(Inst)->setTailCall(false);
1504 // Set nounwind as needed.
1505 if (IsNoThrow(Class)) {
1507 DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
1509 cast<CallInst>(Inst)->setDoesNotThrow();
1512 if (!IsNoopOnNull(Class)) {
1513 UsedInThisFunction |= 1 << Class;
1517 const Value *Arg = GetObjCArg(Inst);
1519 // ARC calls with null are no-ops. Delete them.
1520 if (IsNullOrUndef(Arg)) {
1523 DEBUG(dbgs() << "ARC calls with null are no-ops. Erasing: " << *Inst
1525 EraseInstruction(Inst);
1529 // Keep track of which of retain, release, autorelease, and retain_block
1530 // are actually present in this function.
1531 UsedInThisFunction |= 1 << Class;
1533 // If Arg is a PHI, and one or more incoming values to the
1534 // PHI are null, and the call is control-equivalent to the PHI, and there
1535 // are no relevant side effects between the PHI and the call, the call
1536 // could be pushed up to just those paths with non-null incoming values.
1537 // For now, don't bother splitting critical edges for this.
1538 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
1539 Worklist.push_back(std::make_pair(Inst, Arg));
1541 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
1545 const PHINode *PN = dyn_cast<PHINode>(Arg);
1548 // Determine if the PHI has any null operands, or any incoming
1550 bool HasNull = false;
1551 bool HasCriticalEdges = false;
1552 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1554 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1555 if (IsNullOrUndef(Incoming))
1557 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
1558 .getNumSuccessors() != 1) {
1559 HasCriticalEdges = true;
1563 // If we have null operands and no critical edges, optimize.
1564 if (!HasCriticalEdges && HasNull) {
1565 SmallPtrSet<Instruction *, 4> DependingInstructions;
1566 SmallPtrSet<const BasicBlock *, 4> Visited;
1568 // Check that there is nothing that cares about the reference
1569 // count between the call and the phi.
1572 case IC_RetainBlock:
1573 // These can always be moved up.
1576 // These can't be moved across things that care about the retain
1578 FindDependencies(NeedsPositiveRetainCount, Arg,
1579 Inst->getParent(), Inst,
1580 DependingInstructions, Visited, PA);
1582 case IC_Autorelease:
1583 // These can't be moved across autorelease pool scope boundaries.
1584 FindDependencies(AutoreleasePoolBoundary, Arg,
1585 Inst->getParent(), Inst,
1586 DependingInstructions, Visited, PA);
1589 case IC_AutoreleaseRV:
1590 // Don't move these; the RV optimization depends on the autoreleaseRV
1591 // being tail called, and the retainRV being immediately after a call
1592 // (which might still happen if we get lucky with codegen layout, but
1593 // it's not worth taking the chance).
1596 llvm_unreachable("Invalid dependence flavor");
1599 if (DependingInstructions.size() == 1 &&
1600 *DependingInstructions.begin() == PN) {
1603 // Clone the call into each predecessor that has a non-null value.
1604 CallInst *CInst = cast<CallInst>(Inst);
1605 Type *ParamTy = CInst->getArgOperand(0)->getType();
1606 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1608 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
1609 if (!IsNullOrUndef(Incoming)) {
1610 CallInst *Clone = cast<CallInst>(CInst->clone());
1611 Value *Op = PN->getIncomingValue(i);
1612 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
1613 if (Op->getType() != ParamTy)
1614 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
1615 Clone->setArgOperand(0, Op);
1616 Clone->insertBefore(InsertPos);
1618 DEBUG(dbgs() << "Cloning "
1620 "And inserting clone at " << *InsertPos << "\n");
1621 Worklist.push_back(std::make_pair(Clone, Incoming));
1624 // Erase the original call.
1625 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
1626 EraseInstruction(CInst);
1630 } while (!Worklist.empty());
1634 /// If we have a top down pointer in the S_Use state, make sure that there are
1635 /// no CFG hazards by checking the states of various bottom up pointers.
1636 static void CheckForUseCFGHazard(const Sequence SuccSSeq,
1637 const bool SuccSRRIKnownSafe,
1639 bool &SomeSuccHasSame,
1640 bool &AllSuccsHaveSame,
1641 bool &ShouldContinue) {
1643 case S_CanRelease: {
1644 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
1645 S.ClearSequenceProgress();
1648 ShouldContinue = true;
1652 SomeSuccHasSame = true;
1656 case S_MovableRelease:
1657 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1658 AllSuccsHaveSame = false;
1661 llvm_unreachable("bottom-up pointer in retain state!");
1663 llvm_unreachable("This should have been handled earlier.");
1667 /// If we have a Top Down pointer in the S_CanRelease state, make sure that
1668 /// there are no CFG hazards by checking the states of various bottom up
1670 static void CheckForCanReleaseCFGHazard(const Sequence SuccSSeq,
1671 const bool SuccSRRIKnownSafe,
1673 bool &SomeSuccHasSame,
1674 bool &AllSuccsHaveSame) {
1677 SomeSuccHasSame = true;
1681 case S_MovableRelease:
1683 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
1684 AllSuccsHaveSame = false;
1687 llvm_unreachable("bottom-up pointer in retain state!");
1689 llvm_unreachable("This should have been handled earlier.");
1693 /// Check for critical edges, loop boundaries, irreducible control flow, or
1694 /// other CFG structures where moving code across the edge would result in it
1695 /// being executed more.
1697 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
1698 DenseMap<const BasicBlock *, BBState> &BBStates,
1699 BBState &MyStates) const {
1700 // If any top-down local-use or possible-dec has a succ which is earlier in
1701 // the sequence, forget it.
1702 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
1703 E = MyStates.top_down_ptr_end(); I != E; ++I) {
1704 PtrState &S = I->second;
1705 const Sequence Seq = I->second.GetSeq();
1707 // We only care about S_Retain, S_CanRelease, and S_Use.
1711 // Make sure that if extra top down states are added in the future that this
1712 // code is updated to handle it.
1713 assert((Seq == S_Retain || Seq == S_CanRelease || Seq == S_Use) &&
1714 "Unknown top down sequence state.");
1716 const Value *Arg = I->first;
1717 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
1718 bool SomeSuccHasSame = false;
1719 bool AllSuccsHaveSame = true;
1721 succ_const_iterator SI(TI), SE(TI, false);
1723 for (; SI != SE; ++SI) {
1724 // If VisitBottomUp has pointer information for this successor, take
1725 // what we know about it.
1726 const DenseMap<const BasicBlock *, BBState>::iterator BBI =
1728 assert(BBI != BBStates.end());
1729 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
1730 const Sequence SuccSSeq = SuccS.GetSeq();
1732 // If bottom up, the pointer is in an S_None state, clear the sequence
1733 // progress since the sequence in the bottom up state finished
1734 // suggesting a mismatch in between retains/releases. This is true for
1735 // all three cases that we are handling here: S_Retain, S_Use, and
1737 if (SuccSSeq == S_None) {
1738 S.ClearSequenceProgress();
1742 // If we have S_Use or S_CanRelease, perform our check for cfg hazard
1744 const bool SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
1746 // *NOTE* We do not use Seq from above here since we are allowing for
1747 // S.GetSeq() to change while we are visiting basic blocks.
1748 switch(S.GetSeq()) {
1750 bool ShouldContinue = false;
1751 CheckForUseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S,
1752 SomeSuccHasSame, AllSuccsHaveSame,
1758 case S_CanRelease: {
1759 CheckForCanReleaseCFGHazard(SuccSSeq, SuccSRRIKnownSafe,
1768 case S_MovableRelease:
1773 // If the state at the other end of any of the successor edges
1774 // matches the current state, require all edges to match. This
1775 // guards against loops in the middle of a sequence.
1776 if (SomeSuccHasSame && !AllSuccsHaveSame)
1777 S.ClearSequenceProgress();
1782 ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
1784 MapVector<Value *, RRInfo> &Retains,
1785 BBState &MyStates) {
1786 bool NestingDetected = false;
1787 InstructionClass Class = GetInstructionClass(Inst);
1788 const Value *Arg = 0;
1790 DEBUG(dbgs() << "Class: " << Class << "\n");
1794 Arg = GetObjCArg(Inst);
1796 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1798 // If we see two releases in a row on the same pointer. If so, make
1799 // a note, and we'll cicle back to revisit it after we've
1800 // hopefully eliminated the second release, which may allow us to
1801 // eliminate the first release too.
1802 // Theoretically we could implement removal of nested retain+release
1803 // pairs by making PtrState hold a stack of states, but this is
1804 // simple and avoids adding overhead for the non-nested case.
1805 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
1806 DEBUG(dbgs() << "Found nested releases (i.e. a release pair)\n");
1807 NestingDetected = true;
1810 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
1811 Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
1812 ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
1813 S.ResetSequenceProgress(NewSeq);
1814 S.RRI.ReleaseMetadata = ReleaseMetadata;
1815 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
1816 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
1817 S.RRI.Calls.insert(Inst);
1818 S.SetKnownPositiveRefCount();
1821 case IC_RetainBlock:
1822 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1823 // objc_retainBlocks to objc_retains. Thus at this point any
1824 // objc_retainBlocks that we see are not optimizable.
1828 Arg = GetObjCArg(Inst);
1830 PtrState &S = MyStates.getPtrBottomUpState(Arg);
1831 S.SetKnownPositiveRefCount();
1833 Sequence OldSeq = S.GetSeq();
1837 case S_MovableRelease:
1839 // If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
1840 // imprecise release, clear our reverse insertion points.
1841 if (OldSeq != S_Use || S.RRI.IsTrackingImpreciseReleases())
1842 S.RRI.ReverseInsertPts.clear();
1845 // Don't do retain+release tracking for IC_RetainRV, because it's
1846 // better to let it remain as the first instruction after a call.
1847 if (Class != IC_RetainRV)
1848 Retains[Inst] = S.RRI;
1849 S.ClearSequenceProgress();
1854 llvm_unreachable("bottom-up pointer in retain state!");
1856 ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
1857 // A retain moving bottom up can be a use.
1860 case IC_AutoreleasepoolPop:
1861 // Conservatively, clear MyStates for all known pointers.
1862 MyStates.clearBottomUpPointers();
1863 return NestingDetected;
1864 case IC_AutoreleasepoolPush:
1866 // These are irrelevant.
1867 return NestingDetected;
1872 // Consider any other possible effects of this instruction on each
1873 // pointer being tracked.
1874 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
1875 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
1876 const Value *Ptr = MI->first;
1878 continue; // Handled above.
1879 PtrState &S = MI->second;
1880 Sequence Seq = S.GetSeq();
1882 // Check for possible releases.
1883 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
1884 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
1886 S.ClearKnownPositiveRefCount();
1889 S.SetSeq(S_CanRelease);
1890 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
1894 case S_MovableRelease:
1899 llvm_unreachable("bottom-up pointer in retain state!");
1903 // Check for possible direct uses.
1906 case S_MovableRelease:
1907 if (CanUse(Inst, Ptr, PA, Class)) {
1908 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
1910 assert(S.RRI.ReverseInsertPts.empty());
1911 // If this is an invoke instruction, we're scanning it as part of
1912 // one of its successor blocks, since we can't insert code after it
1913 // in its own block, and we don't want to split critical edges.
1914 if (isa<InvokeInst>(Inst))
1915 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1917 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1919 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1920 } else if (Seq == S_Release && IsUser(Class)) {
1921 DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
1923 // Non-movable releases depend on any possible objc pointer use.
1925 ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
1926 assert(S.RRI.ReverseInsertPts.empty());
1927 // As above; handle invoke specially.
1928 if (isa<InvokeInst>(Inst))
1929 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
1931 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
1935 if (CanUse(Inst, Ptr, PA, Class)) {
1936 DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
1939 ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
1947 llvm_unreachable("bottom-up pointer in retain state!");
1951 return NestingDetected;
1955 ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
1956 DenseMap<const BasicBlock *, BBState> &BBStates,
1957 MapVector<Value *, RRInfo> &Retains) {
1959 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
1961 bool NestingDetected = false;
1962 BBState &MyStates = BBStates[BB];
1964 // Merge the states from each successor to compute the initial state
1965 // for the current block.
1966 BBState::edge_iterator SI(MyStates.succ_begin()),
1967 SE(MyStates.succ_end());
1969 const BasicBlock *Succ = *SI;
1970 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
1971 assert(I != BBStates.end());
1972 MyStates.InitFromSucc(I->second);
1974 for (; SI != SE; ++SI) {
1976 I = BBStates.find(Succ);
1977 assert(I != BBStates.end());
1978 MyStates.MergeSucc(I->second);
1982 // If ARC Annotations are enabled, output the current state of pointers at the
1983 // bottom of the basic block.
1984 ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);
1986 // Visit all the instructions, bottom-up.
1987 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
1988 Instruction *Inst = llvm::prior(I);
1990 // Invoke instructions are visited as part of their successors (below).
1991 if (isa<InvokeInst>(Inst))
1994 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1996 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
1999 // If there's a predecessor with an invoke, visit the invoke as if it were
2000 // part of this block, since we can't insert code after an invoke in its own
2001 // block, and we don't want to split critical edges.
2002 for (BBState::edge_iterator PI(MyStates.pred_begin()),
2003 PE(MyStates.pred_end()); PI != PE; ++PI) {
2004 BasicBlock *Pred = *PI;
2005 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
2006 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
2009 // If ARC Annotations are enabled, output the current state of pointers at the
2010 // top of the basic block.
2011 ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);
2013 return NestingDetected;
2017 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
2018 DenseMap<Value *, RRInfo> &Releases,
2019 BBState &MyStates) {
2020 bool NestingDetected = false;
2021 InstructionClass Class = GetInstructionClass(Inst);
2022 const Value *Arg = 0;
2025 case IC_RetainBlock:
2026 // In OptimizeIndividualCalls, we have strength reduced all optimizable
2027 // objc_retainBlocks to objc_retains. Thus at this point any
2028 // objc_retainBlocks that we see are not optimizable.
2032 Arg = GetObjCArg(Inst);
2034 PtrState &S = MyStates.getPtrTopDownState(Arg);
2036 // Don't do retain+release tracking for IC_RetainRV, because it's
2037 // better to let it remain as the first instruction after a call.
2038 if (Class != IC_RetainRV) {
2039 // If we see two retains in a row on the same pointer. If so, make
2040 // a note, and we'll cicle back to revisit it after we've
2041 // hopefully eliminated the second retain, which may allow us to
2042 // eliminate the first retain too.
2043 // Theoretically we could implement removal of nested retain+release
2044 // pairs by making PtrState hold a stack of states, but this is
2045 // simple and avoids adding overhead for the non-nested case.
2046 if (S.GetSeq() == S_Retain)
2047 NestingDetected = true;
2049 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
2050 S.ResetSequenceProgress(S_Retain);
2051 S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
2052 S.RRI.Calls.insert(Inst);
2055 S.SetKnownPositiveRefCount();
2057 // A retain can be a potential use; procede to the generic checking
2062 Arg = GetObjCArg(Inst);
2064 PtrState &S = MyStates.getPtrTopDownState(Arg);
2065 S.ClearKnownPositiveRefCount();
2067 Sequence OldSeq = S.GetSeq();
2069 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
2074 if (OldSeq == S_Retain || ReleaseMetadata != 0)
2075 S.RRI.ReverseInsertPts.clear();
2078 S.RRI.ReleaseMetadata = ReleaseMetadata;
2079 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
2080 Releases[Inst] = S.RRI;
2081 ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
2082 S.ClearSequenceProgress();
2088 case S_MovableRelease:
2089 llvm_unreachable("top-down pointer in release state!");
2093 case IC_AutoreleasepoolPop:
2094 // Conservatively, clear MyStates for all known pointers.
2095 MyStates.clearTopDownPointers();
2096 return NestingDetected;
2097 case IC_AutoreleasepoolPush:
2099 // These are irrelevant.
2100 return NestingDetected;
2105 // Consider any other possible effects of this instruction on each
2106 // pointer being tracked.
2107 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
2108 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
2109 const Value *Ptr = MI->first;
2111 continue; // Handled above.
2112 PtrState &S = MI->second;
2113 Sequence Seq = S.GetSeq();
2115 // Check for possible releases.
2116 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
2117 DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
2119 S.ClearKnownPositiveRefCount();
2122 S.SetSeq(S_CanRelease);
2123 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
2124 assert(S.RRI.ReverseInsertPts.empty());
2125 S.RRI.ReverseInsertPts.insert(Inst);
2127 // One call can't cause a transition from S_Retain to S_CanRelease
2128 // and S_CanRelease to S_Use. If we've made the first transition,
2137 case S_MovableRelease:
2138 llvm_unreachable("top-down pointer in release state!");
2142 // Check for possible direct uses.
2145 if (CanUse(Inst, Ptr, PA, Class)) {
2146 DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
2149 ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_Use);
2158 case S_MovableRelease:
2159 llvm_unreachable("top-down pointer in release state!");
2163 return NestingDetected;
2167 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
2168 DenseMap<const BasicBlock *, BBState> &BBStates,
2169 DenseMap<Value *, RRInfo> &Releases) {
2170 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
2171 bool NestingDetected = false;
2172 BBState &MyStates = BBStates[BB];
2174 // Merge the states from each predecessor to compute the initial state
2175 // for the current block.
2176 BBState::edge_iterator PI(MyStates.pred_begin()),
2177 PE(MyStates.pred_end());
2179 const BasicBlock *Pred = *PI;
2180 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
2181 assert(I != BBStates.end());
2182 MyStates.InitFromPred(I->second);
2184 for (; PI != PE; ++PI) {
2186 I = BBStates.find(Pred);
2187 assert(I != BBStates.end());
2188 MyStates.MergePred(I->second);
2192 // If ARC Annotations are enabled, output the current state of pointers at the
2193 // top of the basic block.
2194 ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);
2196 // Visit all the instructions, top-down.
2197 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
2198 Instruction *Inst = I;
2200 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
2202 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
2205 // If ARC Annotations are enabled, output the current state of pointers at the
2206 // bottom of the basic block.
2207 ANNOTATE_TOPDOWN_BBEND(MyStates, BB);
2209 #ifdef ARC_ANNOTATIONS
2210 if (!(EnableARCAnnotations && DisableCheckForCFGHazards))
2212 CheckForCFGHazards(BB, BBStates, MyStates);
2213 return NestingDetected;
2217 ComputePostOrders(Function &F,
2218 SmallVectorImpl<BasicBlock *> &PostOrder,
2219 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
2220 unsigned NoObjCARCExceptionsMDKind,
2221 DenseMap<const BasicBlock *, BBState> &BBStates) {
2222 /// The visited set, for doing DFS walks.
2223 SmallPtrSet<BasicBlock *, 16> Visited;
2225 // Do DFS, computing the PostOrder.
2226 SmallPtrSet<BasicBlock *, 16> OnStack;
2227 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
2229 // Functions always have exactly one entry block, and we don't have
2230 // any other block that we treat like an entry block.
2231 BasicBlock *EntryBB = &F.getEntryBlock();
2232 BBState &MyStates = BBStates[EntryBB];
2233 MyStates.SetAsEntry();
2234 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
2235 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
2236 Visited.insert(EntryBB);
2237 OnStack.insert(EntryBB);
2240 BasicBlock *CurrBB = SuccStack.back().first;
2241 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
2242 succ_iterator SE(TI, false);
2244 while (SuccStack.back().second != SE) {
2245 BasicBlock *SuccBB = *SuccStack.back().second++;
2246 if (Visited.insert(SuccBB)) {
2247 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
2248 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
2249 BBStates[CurrBB].addSucc(SuccBB);
2250 BBState &SuccStates = BBStates[SuccBB];
2251 SuccStates.addPred(CurrBB);
2252 OnStack.insert(SuccBB);
2256 if (!OnStack.count(SuccBB)) {
2257 BBStates[CurrBB].addSucc(SuccBB);
2258 BBStates[SuccBB].addPred(CurrBB);
2261 OnStack.erase(CurrBB);
2262 PostOrder.push_back(CurrBB);
2263 SuccStack.pop_back();
2264 } while (!SuccStack.empty());
2268 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
2269 // Functions may have many exits, and there also blocks which we treat
2270 // as exits due to ignored edges.
2271 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
2272 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
2273 BasicBlock *ExitBB = I;
2274 BBState &MyStates = BBStates[ExitBB];
2275 if (!MyStates.isExit())
2278 MyStates.SetAsExit();
2280 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
2281 Visited.insert(ExitBB);
2282 while (!PredStack.empty()) {
2283 reverse_dfs_next_succ:
2284 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
2285 while (PredStack.back().second != PE) {
2286 BasicBlock *BB = *PredStack.back().second++;
2287 if (Visited.insert(BB)) {
2288 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
2289 goto reverse_dfs_next_succ;
2292 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
2297 // Visit the function both top-down and bottom-up.
2299 ObjCARCOpt::Visit(Function &F,
2300 DenseMap<const BasicBlock *, BBState> &BBStates,
2301 MapVector<Value *, RRInfo> &Retains,
2302 DenseMap<Value *, RRInfo> &Releases) {
2304 // Use reverse-postorder traversals, because we magically know that loops
2305 // will be well behaved, i.e. they won't repeatedly call retain on a single
2306 // pointer without doing a release. We can't use the ReversePostOrderTraversal
2307 // class here because we want the reverse-CFG postorder to consider each
2308 // function exit point, and we want to ignore selected cycle edges.
2309 SmallVector<BasicBlock *, 16> PostOrder;
2310 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
2311 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
2312 NoObjCARCExceptionsMDKind,
2315 // Use reverse-postorder on the reverse CFG for bottom-up.
2316 bool BottomUpNestingDetected = false;
2317 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2318 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
2320 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
2322 // Use reverse-postorder for top-down.
2323 bool TopDownNestingDetected = false;
2324 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
2325 PostOrder.rbegin(), E = PostOrder.rend();
2327 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
2329 return TopDownNestingDetected && BottomUpNestingDetected;
2332 /// Move the calls in RetainsToMove and ReleasesToMove.
2333 void ObjCARCOpt::MoveCalls(Value *Arg,
2334 RRInfo &RetainsToMove,
2335 RRInfo &ReleasesToMove,
2336 MapVector<Value *, RRInfo> &Retains,
2337 DenseMap<Value *, RRInfo> &Releases,
2338 SmallVectorImpl<Instruction *> &DeadInsts,
2340 Type *ArgTy = Arg->getType();
2341 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
2343 DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
2345 // Insert the new retain and release calls.
2346 for (SmallPtrSet<Instruction *, 2>::const_iterator
2347 PI = ReleasesToMove.ReverseInsertPts.begin(),
2348 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2349 Instruction *InsertPt = *PI;
2350 Value *MyArg = ArgTy == ParamTy ? Arg :
2351 new BitCastInst(Arg, ParamTy, "", InsertPt);
2353 CallInst::Create(getRetainCallee(M), MyArg, "", InsertPt);
2354 Call->setDoesNotThrow();
2355 Call->setTailCall();
2357 DEBUG(dbgs() << "Inserting new Retain: " << *Call << "\n"
2358 "At insertion point: " << *InsertPt << "\n");
2360 for (SmallPtrSet<Instruction *, 2>::const_iterator
2361 PI = RetainsToMove.ReverseInsertPts.begin(),
2362 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
2363 Instruction *InsertPt = *PI;
2364 Value *MyArg = ArgTy == ParamTy ? Arg :
2365 new BitCastInst(Arg, ParamTy, "", InsertPt);
2366 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
2368 // Attach a clang.imprecise_release metadata tag, if appropriate.
2369 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
2370 Call->setMetadata(ImpreciseReleaseMDKind, M);
2371 Call->setDoesNotThrow();
2372 if (ReleasesToMove.IsTailCallRelease)
2373 Call->setTailCall();
2375 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
2376 "At insertion point: " << *InsertPt << "\n");
2379 // Delete the original retain and release calls.
2380 for (SmallPtrSet<Instruction *, 2>::const_iterator
2381 AI = RetainsToMove.Calls.begin(),
2382 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
2383 Instruction *OrigRetain = *AI;
2384 Retains.blot(OrigRetain);
2385 DeadInsts.push_back(OrigRetain);
2386 DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
2388 for (SmallPtrSet<Instruction *, 2>::const_iterator
2389 AI = ReleasesToMove.Calls.begin(),
2390 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
2391 Instruction *OrigRelease = *AI;
2392 Releases.erase(OrigRelease);
2393 DeadInsts.push_back(OrigRelease);
2394 DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
2400 ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
2402 MapVector<Value *, RRInfo> &Retains,
2403 DenseMap<Value *, RRInfo> &Releases,
2405 SmallVector<Instruction *, 4> &NewRetains,
2406 SmallVector<Instruction *, 4> &NewReleases,
2407 SmallVector<Instruction *, 8> &DeadInsts,
2408 RRInfo &RetainsToMove,
2409 RRInfo &ReleasesToMove,
2412 bool &AnyPairsCompletelyEliminated) {
2413 // If a pair happens in a region where it is known that the reference count
2414 // is already incremented, we can similarly ignore possible decrements.
2415 bool KnownSafeTD = true, KnownSafeBU = true;
2417 // Connect the dots between the top-down-collected RetainsToMove and
2418 // bottom-up-collected ReleasesToMove to form sets of related calls.
2419 // This is an iterative process so that we connect multiple releases
2420 // to multiple retains if needed.
2421 unsigned OldDelta = 0;
2422 unsigned NewDelta = 0;
2423 unsigned OldCount = 0;
2424 unsigned NewCount = 0;
2425 bool FirstRelease = true;
2427 for (SmallVectorImpl<Instruction *>::const_iterator
2428 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
2429 Instruction *NewRetain = *NI;
2430 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
2431 assert(It != Retains.end());
2432 const RRInfo &NewRetainRRI = It->second;
2433 KnownSafeTD &= NewRetainRRI.KnownSafe;
2434 for (SmallPtrSet<Instruction *, 2>::const_iterator
2435 LI = NewRetainRRI.Calls.begin(),
2436 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
2437 Instruction *NewRetainRelease = *LI;
2438 DenseMap<Value *, RRInfo>::const_iterator Jt =
2439 Releases.find(NewRetainRelease);
2440 if (Jt == Releases.end())
2442 const RRInfo &NewRetainReleaseRRI = Jt->second;
2443 assert(NewRetainReleaseRRI.Calls.count(NewRetain));
2444 if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
2446 BBStates[NewRetainRelease->getParent()].GetAllPathCount();
2448 // Merge the ReleaseMetadata and IsTailCallRelease values.
2450 ReleasesToMove.ReleaseMetadata =
2451 NewRetainReleaseRRI.ReleaseMetadata;
2452 ReleasesToMove.IsTailCallRelease =
2453 NewRetainReleaseRRI.IsTailCallRelease;
2454 FirstRelease = false;
2456 if (ReleasesToMove.ReleaseMetadata !=
2457 NewRetainReleaseRRI.ReleaseMetadata)
2458 ReleasesToMove.ReleaseMetadata = 0;
2459 if (ReleasesToMove.IsTailCallRelease !=
2460 NewRetainReleaseRRI.IsTailCallRelease)
2461 ReleasesToMove.IsTailCallRelease = false;
2464 // Collect the optimal insertion points.
2466 for (SmallPtrSet<Instruction *, 2>::const_iterator
2467 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
2468 RE = NewRetainReleaseRRI.ReverseInsertPts.end();
2470 Instruction *RIP = *RI;
2471 if (ReleasesToMove.ReverseInsertPts.insert(RIP))
2472 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
2474 NewReleases.push_back(NewRetainRelease);
2479 if (NewReleases.empty()) break;
2481 // Back the other way.
2482 for (SmallVectorImpl<Instruction *>::const_iterator
2483 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
2484 Instruction *NewRelease = *NI;
2485 DenseMap<Value *, RRInfo>::const_iterator It =
2486 Releases.find(NewRelease);
2487 assert(It != Releases.end());
2488 const RRInfo &NewReleaseRRI = It->second;
2489 KnownSafeBU &= NewReleaseRRI.KnownSafe;
2490 for (SmallPtrSet<Instruction *, 2>::const_iterator
2491 LI = NewReleaseRRI.Calls.begin(),
2492 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
2493 Instruction *NewReleaseRetain = *LI;
2494 MapVector<Value *, RRInfo>::const_iterator Jt =
2495 Retains.find(NewReleaseRetain);
2496 if (Jt == Retains.end())
2498 const RRInfo &NewReleaseRetainRRI = Jt->second;
2499 assert(NewReleaseRetainRRI.Calls.count(NewRelease));
2500 if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
2501 unsigned PathCount =
2502 BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
2503 OldDelta += PathCount;
2504 OldCount += PathCount;
2506 // Collect the optimal insertion points.
2508 for (SmallPtrSet<Instruction *, 2>::const_iterator
2509 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
2510 RE = NewReleaseRetainRRI.ReverseInsertPts.end();
2512 Instruction *RIP = *RI;
2513 if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
2514 PathCount = BBStates[RIP->getParent()].GetAllPathCount();
2515 NewDelta += PathCount;
2516 NewCount += PathCount;
2519 NewRetains.push_back(NewReleaseRetain);
2523 NewReleases.clear();
2524 if (NewRetains.empty()) break;
2527 // If the pointer is known incremented or nested, we can safely delete the
2528 // pair regardless of what's between them.
2529 if (KnownSafeTD || KnownSafeBU) {
2530 RetainsToMove.ReverseInsertPts.clear();
2531 ReleasesToMove.ReverseInsertPts.clear();
2534 // Determine whether the new insertion points we computed preserve the
2535 // balance of retain and release calls through the program.
2536 // TODO: If the fully aggressive solution isn't valid, try to find a
2537 // less aggressive solution which is.
2542 // Determine whether the original call points are balanced in the retain and
2543 // release calls through the program. If not, conservatively don't touch
2545 // TODO: It's theoretically possible to do code motion in this case, as
2546 // long as the existing imbalances are maintained.
2550 #ifdef ARC_ANNOTATIONS
2551 // Do not move calls if ARC annotations are requested.
2552 if (EnableARCAnnotations)
2554 #endif // ARC_ANNOTATIONS
2557 assert(OldCount != 0 && "Unreachable code?");
2558 NumRRs += OldCount - NewCount;
2559 // Set to true if we completely removed any RR pairs.
2560 AnyPairsCompletelyEliminated = NewCount == 0;
2562 // We can move calls!
2566 /// Identify pairings between the retains and releases, and delete and/or move
2569 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
2571 MapVector<Value *, RRInfo> &Retains,
2572 DenseMap<Value *, RRInfo> &Releases,
2574 DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
2576 bool AnyPairsCompletelyEliminated = false;
2577 RRInfo RetainsToMove;
2578 RRInfo ReleasesToMove;
2579 SmallVector<Instruction *, 4> NewRetains;
2580 SmallVector<Instruction *, 4> NewReleases;
2581 SmallVector<Instruction *, 8> DeadInsts;
2583 // Visit each retain.
2584 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
2585 E = Retains.end(); I != E; ++I) {
2586 Value *V = I->first;
2587 if (!V) continue; // blotted
2589 Instruction *Retain = cast<Instruction>(V);
2591 DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
2593 Value *Arg = GetObjCArg(Retain);
2595 // If the object being released is in static or stack storage, we know it's
2596 // not being managed by ObjC reference counting, so we can delete pairs
2597 // regardless of what possible decrements or uses lie between them.
2598 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
2600 // A constant pointer can't be pointing to an object on the heap. It may
2601 // be reference-counted, but it won't be deleted.
2602 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
2603 if (const GlobalVariable *GV =
2604 dyn_cast<GlobalVariable>(
2605 StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
2606 if (GV->isConstant())
2609 // Connect the dots between the top-down-collected RetainsToMove and
2610 // bottom-up-collected ReleasesToMove to form sets of related calls.
2611 NewRetains.push_back(Retain);
2612 bool PerformMoveCalls =
2613 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
2614 NewReleases, DeadInsts, RetainsToMove,
2615 ReleasesToMove, Arg, KnownSafe,
2616 AnyPairsCompletelyEliminated);
2618 if (PerformMoveCalls) {
2619 // Ok, everything checks out and we're all set. Let's move/delete some
2621 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
2622 Retains, Releases, DeadInsts, M);
2625 // Clean up state for next retain.
2626 NewReleases.clear();
2628 RetainsToMove.clear();
2629 ReleasesToMove.clear();
2632 // Now that we're done moving everything, we can delete the newly dead
2633 // instructions, as we no longer need them as insert points.
2634 while (!DeadInsts.empty())
2635 EraseInstruction(DeadInsts.pop_back_val());
2637 return AnyPairsCompletelyEliminated;
2640 /// Weak pointer optimizations.
2641 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
2642 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
2644 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
2645 // itself because it uses AliasAnalysis and we need to do provenance
2647 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2648 Instruction *Inst = &*I++;
2650 DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
2652 InstructionClass Class = GetBasicInstructionClass(Inst);
2653 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
2656 // Delete objc_loadWeak calls with no users.
2657 if (Class == IC_LoadWeak && Inst->use_empty()) {
2658 Inst->eraseFromParent();
2662 // TODO: For now, just look for an earlier available version of this value
2663 // within the same block. Theoretically, we could do memdep-style non-local
2664 // analysis too, but that would want caching. A better approach would be to
2665 // use the technique that EarlyCSE uses.
2666 inst_iterator Current = llvm::prior(I);
2667 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
2668 for (BasicBlock::iterator B = CurrentBB->begin(),
2669 J = Current.getInstructionIterator();
2671 Instruction *EarlierInst = &*llvm::prior(J);
2672 InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
2673 switch (EarlierClass) {
2675 case IC_LoadWeakRetained: {
2676 // If this is loading from the same pointer, replace this load's 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);
2694 Call->eraseFromParent();
2696 case AliasAnalysis::MayAlias:
2697 case AliasAnalysis::PartialAlias:
2699 case AliasAnalysis::NoAlias:
2706 // If this is storing to the same pointer and has the same size etc.
2707 // replace this load's value with the stored value.
2708 CallInst *Call = cast<CallInst>(Inst);
2709 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
2710 Value *Arg = Call->getArgOperand(0);
2711 Value *EarlierArg = EarlierCall->getArgOperand(0);
2712 switch (PA.getAA()->alias(Arg, EarlierArg)) {
2713 case AliasAnalysis::MustAlias:
2715 // If the load has a builtin retain, insert a plain retain for it.
2716 if (Class == IC_LoadWeakRetained) {
2718 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
2722 // Zap the fully redundant load.
2723 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
2724 Call->eraseFromParent();
2726 case AliasAnalysis::MayAlias:
2727 case AliasAnalysis::PartialAlias:
2729 case AliasAnalysis::NoAlias:
2736 // TOOD: Grab the copied value.
2738 case IC_AutoreleasepoolPush:
2740 case IC_IntrinsicUser:
2742 // Weak pointers are only modified through the weak entry points
2743 // (and arbitrary calls, which could call the weak entry points).
2746 // Anything else could modify the weak pointer.
2753 // Then, for each destroyWeak with an alloca operand, check to see if
2754 // the alloca and all its users can be zapped.
2755 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2756 Instruction *Inst = &*I++;
2757 InstructionClass Class = GetBasicInstructionClass(Inst);
2758 if (Class != IC_DestroyWeak)
2761 CallInst *Call = cast<CallInst>(Inst);
2762 Value *Arg = Call->getArgOperand(0);
2763 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
2764 for (Value::use_iterator UI = Alloca->use_begin(),
2765 UE = Alloca->use_end(); UI != UE; ++UI) {
2766 const Instruction *UserInst = cast<Instruction>(*UI);
2767 switch (GetBasicInstructionClass(UserInst)) {
2770 case IC_DestroyWeak:
2777 for (Value::use_iterator UI = Alloca->use_begin(),
2778 UE = Alloca->use_end(); UI != UE; ) {
2779 CallInst *UserInst = cast<CallInst>(*UI++);
2780 switch (GetBasicInstructionClass(UserInst)) {
2783 // These functions return their second argument.
2784 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
2786 case IC_DestroyWeak:
2790 llvm_unreachable("alloca really is used!");
2792 UserInst->eraseFromParent();
2794 Alloca->eraseFromParent();
2800 /// Identify program paths which execute sequences of retains and releases which
2801 /// can be eliminated.
2802 bool ObjCARCOpt::OptimizeSequences(Function &F) {
2803 /// Releases, Retains - These are used to store the results of the main flow
2804 /// analysis. These use Value* as the key instead of Instruction* so that the
2805 /// map stays valid when we get around to rewriting code and calls get
2806 /// replaced by arguments.
2807 DenseMap<Value *, RRInfo> Releases;
2808 MapVector<Value *, RRInfo> Retains;
2810 /// This is used during the traversal of the function to track the
2811 /// states for each identified object at each block.
2812 DenseMap<const BasicBlock *, BBState> BBStates;
2814 // Analyze the CFG of the function, and all instructions.
2815 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
2818 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
2822 /// Check if there is a dependent call earlier that does not have anything in
2823 /// between the Retain and the call that can affect the reference count of their
2824 /// shared pointer argument. Note that Retain need not be in BB.
2826 HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
2827 SmallPtrSet<Instruction *, 4> &DepInsts,
2828 SmallPtrSet<const BasicBlock *, 4> &Visited,
2829 ProvenanceAnalysis &PA) {
2830 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
2831 DepInsts, Visited, PA);
2832 if (DepInsts.size() != 1)
2836 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2838 // Check that the pointer is the return value of the call.
2839 if (!Call || Arg != Call)
2842 // Check that the call is a regular call.
2843 InstructionClass Class = GetBasicInstructionClass(Call);
2844 if (Class != IC_CallOrUser && Class != IC_Call)
2850 /// Find a dependent retain that precedes the given autorelease for which there
2851 /// is nothing in between the two instructions that can affect the ref count of
2854 FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
2855 Instruction *Autorelease,
2856 SmallPtrSet<Instruction *, 4> &DepInsts,
2857 SmallPtrSet<const BasicBlock *, 4> &Visited,
2858 ProvenanceAnalysis &PA) {
2859 FindDependencies(CanChangeRetainCount, Arg,
2860 BB, Autorelease, DepInsts, Visited, PA);
2861 if (DepInsts.size() != 1)
2865 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2867 // Check that we found a retain with the same argument.
2869 !IsRetain(GetBasicInstructionClass(Retain)) ||
2870 GetObjCArg(Retain) != Arg) {
2877 /// Look for an ``autorelease'' instruction dependent on Arg such that there are
2878 /// no instructions dependent on Arg that need a positive ref count in between
2879 /// the autorelease and the ret.
2881 FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
2883 SmallPtrSet<Instruction *, 4> &DepInsts,
2884 SmallPtrSet<const BasicBlock *, 4> &V,
2885 ProvenanceAnalysis &PA) {
2886 FindDependencies(NeedsPositiveRetainCount, Arg,
2887 BB, Ret, DepInsts, V, PA);
2888 if (DepInsts.size() != 1)
2891 CallInst *Autorelease =
2892 dyn_cast_or_null<CallInst>(*DepInsts.begin());
2895 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
2896 if (!IsAutorelease(AutoreleaseClass))
2898 if (GetObjCArg(Autorelease) != Arg)
2904 /// Look for this pattern:
2906 /// %call = call i8* @something(...)
2907 /// %2 = call i8* @objc_retain(i8* %call)
2908 /// %3 = call i8* @objc_autorelease(i8* %2)
2911 /// And delete the retain and autorelease.
2912 void ObjCARCOpt::OptimizeReturns(Function &F) {
2913 if (!F.getReturnType()->isPointerTy())
2916 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
2918 SmallPtrSet<Instruction *, 4> DependingInstructions;
2919 SmallPtrSet<const BasicBlock *, 4> Visited;
2920 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
2921 BasicBlock *BB = FI;
2922 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
2924 DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
2929 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
2931 // Look for an ``autorelease'' instruction that is a predecessor of Ret and
2932 // dependent on Arg such that there are no instructions dependent on Arg
2933 // that need a positive ref count in between the autorelease and Ret.
2934 CallInst *Autorelease =
2935 FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
2936 DependingInstructions, Visited,
2938 DependingInstructions.clear();
2945 FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
2946 DependingInstructions, Visited, PA);
2947 DependingInstructions.clear();
2953 // Check that there is nothing that can affect the reference count
2954 // between the retain and the call. Note that Retain need not be in BB.
2955 bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
2956 DependingInstructions,
2958 DependingInstructions.clear();
2961 if (!HasSafePathToCall)
2964 // If so, we can zap the retain and autorelease.
2967 DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
2968 << *Autorelease << "\n");
2969 EraseInstruction(Retain);
2970 EraseInstruction(Autorelease);
2976 ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
2977 llvm::Statistic &NumRetains =
2978 AfterOptimization? NumRetainsAfterOpt : NumRetainsBeforeOpt;
2979 llvm::Statistic &NumReleases =
2980 AfterOptimization? NumReleasesAfterOpt : NumReleasesBeforeOpt;
2982 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2983 Instruction *Inst = &*I++;
2984 switch (GetBasicInstructionClass(Inst)) {
2998 bool ObjCARCOpt::doInitialization(Module &M) {
3002 // If nothing in the Module uses ARC, don't do anything.
3003 Run = ModuleHasARC(M);
3007 // Identify the imprecise release metadata kind.
3008 ImpreciseReleaseMDKind =
3009 M.getContext().getMDKindID("clang.imprecise_release");
3010 CopyOnEscapeMDKind =
3011 M.getContext().getMDKindID("clang.arc.copy_on_escape");
3012 NoObjCARCExceptionsMDKind =
3013 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
3014 #ifdef ARC_ANNOTATIONS
3015 ARCAnnotationBottomUpMDKind =
3016 M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
3017 ARCAnnotationTopDownMDKind =
3018 M.getContext().getMDKindID("llvm.arc.annotation.topdown");
3019 ARCAnnotationProvenanceSourceMDKind =
3020 M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
3021 #endif // ARC_ANNOTATIONS
3023 // Intuitively, objc_retain and others are nocapture, however in practice
3024 // they are not, because they return their argument value. And objc_release
3025 // calls finalizers which can have arbitrary side effects.
3027 // These are initialized lazily.
3028 AutoreleaseRVCallee = 0;
3031 RetainBlockCallee = 0;
3032 AutoreleaseCallee = 0;
3037 bool ObjCARCOpt::runOnFunction(Function &F) {
3041 // If nothing in the Module uses ARC, don't do anything.
3047 DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
3050 PA.setAA(&getAnalysis<AliasAnalysis>());
3052 // This pass performs several distinct transformations. As a compile-time aid
3053 // when compiling code that isn't ObjC, skip these if the relevant ObjC
3054 // library functions aren't declared.
3056 // Preliminary optimizations. This also computes UsedInThisFunction.
3057 OptimizeIndividualCalls(F);
3059 // Optimizations for weak pointers.
3060 if (UsedInThisFunction & ((1 << IC_LoadWeak) |
3061 (1 << IC_LoadWeakRetained) |
3062 (1 << IC_StoreWeak) |
3063 (1 << IC_InitWeak) |
3064 (1 << IC_CopyWeak) |
3065 (1 << IC_MoveWeak) |
3066 (1 << IC_DestroyWeak)))
3067 OptimizeWeakCalls(F);
3069 // Optimizations for retain+release pairs.
3070 if (UsedInThisFunction & ((1 << IC_Retain) |
3071 (1 << IC_RetainRV) |
3072 (1 << IC_RetainBlock)))
3073 if (UsedInThisFunction & (1 << IC_Release))
3074 // Run OptimizeSequences until it either stops making changes or
3075 // no retain+release pair nesting is detected.
3076 while (OptimizeSequences(F)) {}
3078 // Optimizations if objc_autorelease is used.
3079 if (UsedInThisFunction & ((1 << IC_Autorelease) |
3080 (1 << IC_AutoreleaseRV)))
3083 // Gather statistics after optimization.
3085 if (AreStatisticsEnabled()) {
3086 GatherStatistics(F, true);
3090 DEBUG(dbgs() << "\n");
3095 void ObjCARCOpt::releaseMemory() {