1 //===- ObjCARC.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, pattern-matching and replacement of
17 /// low-level operations into higher-level operations, and numerous minor
20 /// This file also defines a simple ARC-aware AliasAnalysis.
22 /// WARNING: This file knows about certain library functions. It recognizes them
23 /// by name, and hardwires knowledge of their semantics.
25 /// WARNING: This file knows about how certain Objective-C library functions are
26 /// used. Naive LLVM IR transformations which would otherwise be
27 /// behavior-preserving may break these assumptions.
29 //===----------------------------------------------------------------------===//
31 #define DEBUG_TYPE "objc-arc"
32 #include "llvm/ADT/DenseMap.h"
33 #include "llvm/ADT/SmallPtrSet.h"
34 #include "llvm/Support/CommandLine.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/raw_ostream.h"
39 /// \brief A handy option to enable/disable all optimizations in this file.
40 static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true));
42 /// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
46 /// \brief An associative container with fast insertion-order (deterministic)
47 /// iteration over its elements. Plus the special blot operation.
48 template<class KeyT, class ValueT>
50 /// Map keys to indices in Vector.
51 typedef DenseMap<KeyT, size_t> MapTy;
54 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
59 typedef typename VectorTy::iterator iterator;
60 typedef typename VectorTy::const_iterator const_iterator;
61 iterator begin() { return Vector.begin(); }
62 iterator end() { return Vector.end(); }
63 const_iterator begin() const { return Vector.begin(); }
64 const_iterator end() const { return Vector.end(); }
68 assert(Vector.size() >= Map.size()); // May differ due to blotting.
69 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
71 assert(I->second < Vector.size());
72 assert(Vector[I->second].first == I->first);
74 for (typename VectorTy::const_iterator I = Vector.begin(),
75 E = Vector.end(); I != E; ++I)
77 (Map.count(I->first) &&
78 Map[I->first] == size_t(I - Vector.begin())));
82 ValueT &operator[](const KeyT &Arg) {
83 std::pair<typename MapTy::iterator, bool> Pair =
84 Map.insert(std::make_pair(Arg, size_t(0)));
86 size_t Num = Vector.size();
87 Pair.first->second = Num;
88 Vector.push_back(std::make_pair(Arg, ValueT()));
89 return Vector[Num].second;
91 return Vector[Pair.first->second].second;
94 std::pair<iterator, bool>
95 insert(const std::pair<KeyT, ValueT> &InsertPair) {
96 std::pair<typename MapTy::iterator, bool> Pair =
97 Map.insert(std::make_pair(InsertPair.first, size_t(0)));
99 size_t Num = Vector.size();
100 Pair.first->second = Num;
101 Vector.push_back(InsertPair);
102 return std::make_pair(Vector.begin() + Num, true);
104 return std::make_pair(Vector.begin() + Pair.first->second, false);
107 const_iterator find(const KeyT &Key) const {
108 typename MapTy::const_iterator It = Map.find(Key);
109 if (It == Map.end()) return Vector.end();
110 return Vector.begin() + It->second;
113 /// This is similar to erase, but instead of removing the element from the
114 /// vector, it just zeros out the key in the vector. This leaves iterators
115 /// intact, but clients must be prepared for zeroed-out keys when iterating.
116 void blot(const KeyT &Key) {
117 typename MapTy::iterator It = Map.find(Key);
118 if (It == Map.end()) return;
119 Vector[It->second].first = KeyT();
132 /// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
135 #include "llvm/ADT/StringSwitch.h"
136 #include "llvm/Analysis/ValueTracking.h"
137 #include "llvm/IR/Intrinsics.h"
138 #include "llvm/IR/Module.h"
139 #include "llvm/Support/CallSite.h"
140 #include "llvm/Transforms/Utils/Local.h"
143 /// \enum InstructionClass
144 /// \brief A simple classification for instructions.
145 enum InstructionClass {
146 IC_Retain, ///< objc_retain
147 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
148 IC_RetainBlock, ///< objc_retainBlock
149 IC_Release, ///< objc_release
150 IC_Autorelease, ///< objc_autorelease
151 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
152 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
153 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
154 IC_NoopCast, ///< objc_retainedObject, etc.
155 IC_FusedRetainAutorelease, ///< objc_retainAutorelease
156 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
157 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
158 IC_StoreWeak, ///< objc_storeWeak (primitive)
159 IC_InitWeak, ///< objc_initWeak (derived)
160 IC_LoadWeak, ///< objc_loadWeak (derived)
161 IC_MoveWeak, ///< objc_moveWeak (derived)
162 IC_CopyWeak, ///< objc_copyWeak (derived)
163 IC_DestroyWeak, ///< objc_destroyWeak (derived)
164 IC_StoreStrong, ///< objc_storeStrong (derived)
165 IC_CallOrUser, ///< could call objc_release and/or "use" pointers
166 IC_Call, ///< could call objc_release
167 IC_User, ///< could "use" a pointer
168 IC_None ///< anything else
171 raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class)
173 raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class) {
176 return OS << "IC_Retain";
178 return OS << "IC_RetainRV";
180 return OS << "IC_RetainBlock";
182 return OS << "IC_Release";
184 return OS << "IC_Autorelease";
185 case IC_AutoreleaseRV:
186 return OS << "IC_AutoreleaseRV";
187 case IC_AutoreleasepoolPush:
188 return OS << "IC_AutoreleasepoolPush";
189 case IC_AutoreleasepoolPop:
190 return OS << "IC_AutoreleasepoolPop";
192 return OS << "IC_NoopCast";
193 case IC_FusedRetainAutorelease:
194 return OS << "IC_FusedRetainAutorelease";
195 case IC_FusedRetainAutoreleaseRV:
196 return OS << "IC_FusedRetainAutoreleaseRV";
197 case IC_LoadWeakRetained:
198 return OS << "IC_LoadWeakRetained";
200 return OS << "IC_StoreWeak";
202 return OS << "IC_InitWeak";
204 return OS << "IC_LoadWeak";
206 return OS << "IC_MoveWeak";
208 return OS << "IC_CopyWeak";
210 return OS << "IC_DestroyWeak";
212 return OS << "IC_StoreStrong";
214 return OS << "IC_CallOrUser";
216 return OS << "IC_Call";
218 return OS << "IC_User";
220 return OS << "IC_None";
222 llvm_unreachable("Unknown instruction class!");
226 /// \brief Test whether the given value is possible a reference-counted pointer.
227 static bool IsPotentialUse(const Value *Op) {
228 // Pointers to static or stack storage are not reference-counted pointers.
229 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
231 // Special arguments are not reference-counted.
232 if (const Argument *Arg = dyn_cast<Argument>(Op))
233 if (Arg->hasByValAttr() ||
234 Arg->hasNestAttr() ||
235 Arg->hasStructRetAttr())
237 // Only consider values with pointer types.
238 // It seemes intuitive to exclude function pointer types as well, since
239 // functions are never reference-counted, however clang occasionally
240 // bitcasts reference-counted pointers to function-pointer type
242 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
245 // Conservatively assume anything else is a potential use.
249 /// \brief Helper for GetInstructionClass. Determines what kind of construct CS
251 static InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
252 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
254 if (IsPotentialUse(*I))
255 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
257 return CS.onlyReadsMemory() ? IC_None : IC_Call;
260 /// \brief Determine if F is one of the special known Functions. If it isn't,
261 /// return IC_CallOrUser.
262 static InstructionClass GetFunctionClass(const Function *F) {
263 Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end();
267 return StringSwitch<InstructionClass>(F->getName())
268 .Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush)
269 .Default(IC_CallOrUser);
272 const Argument *A0 = AI++;
274 // Argument is a pointer.
275 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) {
276 Type *ETy = PTy->getElementType();
278 if (ETy->isIntegerTy(8))
279 return StringSwitch<InstructionClass>(F->getName())
280 .Case("objc_retain", IC_Retain)
281 .Case("objc_retainAutoreleasedReturnValue", IC_RetainRV)
282 .Case("objc_retainBlock", IC_RetainBlock)
283 .Case("objc_release", IC_Release)
284 .Case("objc_autorelease", IC_Autorelease)
285 .Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV)
286 .Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop)
287 .Case("objc_retainedObject", IC_NoopCast)
288 .Case("objc_unretainedObject", IC_NoopCast)
289 .Case("objc_unretainedPointer", IC_NoopCast)
290 .Case("objc_retain_autorelease", IC_FusedRetainAutorelease)
291 .Case("objc_retainAutorelease", IC_FusedRetainAutorelease)
292 .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV)
293 .Default(IC_CallOrUser);
296 if (PointerType *Pte = dyn_cast<PointerType>(ETy))
297 if (Pte->getElementType()->isIntegerTy(8))
298 return StringSwitch<InstructionClass>(F->getName())
299 .Case("objc_loadWeakRetained", IC_LoadWeakRetained)
300 .Case("objc_loadWeak", IC_LoadWeak)
301 .Case("objc_destroyWeak", IC_DestroyWeak)
302 .Default(IC_CallOrUser);
305 // Two arguments, first is i8**.
306 const Argument *A1 = AI++;
308 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType()))
309 if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType()))
310 if (Pte->getElementType()->isIntegerTy(8))
311 if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) {
312 Type *ETy1 = PTy1->getElementType();
313 // Second argument is i8*
314 if (ETy1->isIntegerTy(8))
315 return StringSwitch<InstructionClass>(F->getName())
316 .Case("objc_storeWeak", IC_StoreWeak)
317 .Case("objc_initWeak", IC_InitWeak)
318 .Case("objc_storeStrong", IC_StoreStrong)
319 .Default(IC_CallOrUser);
320 // Second argument is i8**.
321 if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1))
322 if (Pte1->getElementType()->isIntegerTy(8))
323 return StringSwitch<InstructionClass>(F->getName())
324 .Case("objc_moveWeak", IC_MoveWeak)
325 .Case("objc_copyWeak", IC_CopyWeak)
326 .Default(IC_CallOrUser);
330 return IC_CallOrUser;
333 /// \brief Determine what kind of construct V is.
334 static InstructionClass GetInstructionClass(const Value *V) {
335 if (const Instruction *I = dyn_cast<Instruction>(V)) {
336 // Any instruction other than bitcast and gep with a pointer operand have a
337 // use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer
338 // to a subsequent use, rather than using it themselves, in this sense.
339 // As a short cut, several other opcodes are known to have no pointer
340 // operands of interest. And ret is never followed by a release, so it's
341 // not interesting to examine.
342 switch (I->getOpcode()) {
343 case Instruction::Call: {
344 const CallInst *CI = cast<CallInst>(I);
345 // Check for calls to special functions.
346 if (const Function *F = CI->getCalledFunction()) {
347 InstructionClass Class = GetFunctionClass(F);
348 if (Class != IC_CallOrUser)
351 // None of the intrinsic functions do objc_release. For intrinsics, the
352 // only question is whether or not they may be users.
353 switch (F->getIntrinsicID()) {
354 case Intrinsic::returnaddress: case Intrinsic::frameaddress:
355 case Intrinsic::stacksave: case Intrinsic::stackrestore:
356 case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend:
357 case Intrinsic::objectsize: case Intrinsic::prefetch:
358 case Intrinsic::stackprotector:
359 case Intrinsic::eh_return_i32: case Intrinsic::eh_return_i64:
360 case Intrinsic::eh_typeid_for: case Intrinsic::eh_dwarf_cfa:
361 case Intrinsic::eh_sjlj_lsda: case Intrinsic::eh_sjlj_functioncontext:
362 case Intrinsic::init_trampoline: case Intrinsic::adjust_trampoline:
363 case Intrinsic::lifetime_start: case Intrinsic::lifetime_end:
364 case Intrinsic::invariant_start: case Intrinsic::invariant_end:
365 // Don't let dbg info affect our results.
366 case Intrinsic::dbg_declare: case Intrinsic::dbg_value:
367 // Short cut: Some intrinsics obviously don't use ObjC pointers.
373 return GetCallSiteClass(CI);
375 case Instruction::Invoke:
376 return GetCallSiteClass(cast<InvokeInst>(I));
377 case Instruction::BitCast:
378 case Instruction::GetElementPtr:
379 case Instruction::Select: case Instruction::PHI:
380 case Instruction::Ret: case Instruction::Br:
381 case Instruction::Switch: case Instruction::IndirectBr:
382 case Instruction::Alloca: case Instruction::VAArg:
383 case Instruction::Add: case Instruction::FAdd:
384 case Instruction::Sub: case Instruction::FSub:
385 case Instruction::Mul: case Instruction::FMul:
386 case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv:
387 case Instruction::SRem: case Instruction::URem: case Instruction::FRem:
388 case Instruction::Shl: case Instruction::LShr: case Instruction::AShr:
389 case Instruction::And: case Instruction::Or: case Instruction::Xor:
390 case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc:
391 case Instruction::IntToPtr: case Instruction::FCmp:
392 case Instruction::FPTrunc: case Instruction::FPExt:
393 case Instruction::FPToUI: case Instruction::FPToSI:
394 case Instruction::UIToFP: case Instruction::SIToFP:
395 case Instruction::InsertElement: case Instruction::ExtractElement:
396 case Instruction::ShuffleVector:
397 case Instruction::ExtractValue:
399 case Instruction::ICmp:
400 // Comparing a pointer with null, or any other constant, isn't an
401 // interesting use, because we don't care what the pointer points to, or
402 // about the values of any other dynamic reference-counted pointers.
403 if (IsPotentialUse(I->getOperand(1)))
407 // For anything else, check all the operands.
408 // Note that this includes both operands of a Store: while the first
409 // operand isn't actually being dereferenced, it is being stored to
410 // memory where we can no longer track who might read it and dereference
411 // it, so we have to consider it potentially used.
412 for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end();
414 if (IsPotentialUse(*OI))
419 // Otherwise, it's totally inert for ARC purposes.
423 /// \brief Determine which objc runtime call instruction class V belongs to.
425 /// This is similar to GetInstructionClass except that it only detects objc
426 /// runtime calls. This allows it to be faster.
428 static InstructionClass GetBasicInstructionClass(const Value *V) {
429 if (const CallInst *CI = dyn_cast<CallInst>(V)) {
430 if (const Function *F = CI->getCalledFunction())
431 return GetFunctionClass(F);
432 // Otherwise, be conservative.
433 return IC_CallOrUser;
436 // Otherwise, be conservative.
437 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
440 /// \brief Test if the given class is objc_retain or equivalent.
441 static bool IsRetain(InstructionClass Class) {
442 return Class == IC_Retain ||
443 Class == IC_RetainRV;
446 /// \brief Test if the given class is objc_autorelease or equivalent.
447 static bool IsAutorelease(InstructionClass Class) {
448 return Class == IC_Autorelease ||
449 Class == IC_AutoreleaseRV;
452 /// \brief Test if the given class represents instructions which return their
453 /// argument verbatim.
454 static bool IsForwarding(InstructionClass Class) {
455 // objc_retainBlock technically doesn't always return its argument
456 // verbatim, but it doesn't matter for our purposes here.
457 return Class == IC_Retain ||
458 Class == IC_RetainRV ||
459 Class == IC_Autorelease ||
460 Class == IC_AutoreleaseRV ||
461 Class == IC_RetainBlock ||
462 Class == IC_NoopCast;
465 /// \brief Test if the given class represents instructions which do nothing if
466 /// passed a null pointer.
467 static bool IsNoopOnNull(InstructionClass Class) {
468 return Class == IC_Retain ||
469 Class == IC_RetainRV ||
470 Class == IC_Release ||
471 Class == IC_Autorelease ||
472 Class == IC_AutoreleaseRV ||
473 Class == IC_RetainBlock;
476 /// \brief Test if the given class represents instructions which are always safe
477 /// to mark with the "tail" keyword.
478 static bool IsAlwaysTail(InstructionClass Class) {
479 // IC_RetainBlock may be given a stack argument.
480 return Class == IC_Retain ||
481 Class == IC_RetainRV ||
482 Class == IC_AutoreleaseRV;
485 /// \brief Test if the given class represents instructions which are never safe
486 /// to mark with the "tail" keyword.
487 static bool IsNeverTail(InstructionClass Class) {
488 /// It is never safe to tail call objc_autorelease since by tail calling
489 /// objc_autorelease, we also tail call -[NSObject autorelease] which supports
490 /// fast autoreleasing causing our object to be potentially reclaimed from the
491 /// autorelease pool which violates the semantics of __autoreleasing types in
493 return Class == IC_Autorelease;
496 /// \brief Test if the given class represents instructions which are always safe
497 /// to mark with the nounwind attribute.
498 static bool IsNoThrow(InstructionClass Class) {
499 // objc_retainBlock is not nounwind because it calls user copy constructors
500 // which could theoretically throw.
501 return Class == IC_Retain ||
502 Class == IC_RetainRV ||
503 Class == IC_Release ||
504 Class == IC_Autorelease ||
505 Class == IC_AutoreleaseRV ||
506 Class == IC_AutoreleasepoolPush ||
507 Class == IC_AutoreleasepoolPop;
510 /// \brief Erase the given instruction.
512 /// Many ObjC calls return their argument verbatim,
513 /// so if it's such a call and the return value has users, replace them with the
516 static void EraseInstruction(Instruction *CI) {
517 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
519 bool Unused = CI->use_empty();
522 // Replace the return value with the argument.
523 assert(IsForwarding(GetBasicInstructionClass(CI)) &&
524 "Can't delete non-forwarding instruction with users!");
525 CI->replaceAllUsesWith(OldArg);
528 CI->eraseFromParent();
531 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
534 /// \brief This is a wrapper around getUnderlyingObject which also knows how to
535 /// look through objc_retain and objc_autorelease calls, which we know to return
536 /// their argument verbatim.
537 static const Value *GetUnderlyingObjCPtr(const Value *V) {
539 V = GetUnderlyingObject(V);
540 if (!IsForwarding(GetBasicInstructionClass(V)))
542 V = cast<CallInst>(V)->getArgOperand(0);
548 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
549 /// how to look through objc_retain and objc_autorelease calls, which we know to
550 /// return their argument verbatim.
551 static const Value *StripPointerCastsAndObjCCalls(const Value *V) {
553 V = V->stripPointerCasts();
554 if (!IsForwarding(GetBasicInstructionClass(V)))
556 V = cast<CallInst>(V)->getArgOperand(0);
561 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
562 /// how to look through objc_retain and objc_autorelease calls, which we know to
563 /// return their argument verbatim.
564 static Value *StripPointerCastsAndObjCCalls(Value *V) {
566 V = V->stripPointerCasts();
567 if (!IsForwarding(GetBasicInstructionClass(V)))
569 V = cast<CallInst>(V)->getArgOperand(0);
574 /// \brief Assuming the given instruction is one of the special calls such as
575 /// objc_retain or objc_release, return the argument value, stripped of no-op
576 /// casts and forwarding calls.
577 static Value *GetObjCArg(Value *Inst) {
578 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
581 /// \brief Return true if this value refers to a distinct and identifiable
584 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
585 /// special knowledge of ObjC conventions.
586 static bool IsObjCIdentifiedObject(const Value *V) {
587 // Assume that call results and arguments have their own "provenance".
588 // Constants (including GlobalVariables) and Allocas are never
589 // reference-counted.
590 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
591 isa<Argument>(V) || isa<Constant>(V) ||
595 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
596 const Value *Pointer =
597 StripPointerCastsAndObjCCalls(LI->getPointerOperand());
598 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
599 // A constant pointer can't be pointing to an object on the heap. It may
600 // be reference-counted, but it won't be deleted.
601 if (GV->isConstant())
603 StringRef Name = GV->getName();
604 // These special variables are known to hold values which are not
605 // reference-counted pointers.
606 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
607 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
608 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
609 Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
610 Name.startswith("\01l_objc_msgSend_fixup_"))
618 /// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon
619 /// as it finds a value with multiple uses.
620 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
621 if (Arg->hasOneUse()) {
622 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
623 return FindSingleUseIdentifiedObject(BC->getOperand(0));
624 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
625 if (GEP->hasAllZeroIndices())
626 return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
627 if (IsForwarding(GetBasicInstructionClass(Arg)))
628 return FindSingleUseIdentifiedObject(
629 cast<CallInst>(Arg)->getArgOperand(0));
630 if (!IsObjCIdentifiedObject(Arg))
635 // If we found an identifiable object but it has multiple uses, but they are
636 // trivial uses, we can still consider this to be a single-use value.
637 if (IsObjCIdentifiedObject(Arg)) {
638 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
641 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
651 /// \brief Test if the given module looks interesting to run ARC optimization
653 static bool ModuleHasARC(const Module &M) {
655 M.getNamedValue("objc_retain") ||
656 M.getNamedValue("objc_release") ||
657 M.getNamedValue("objc_autorelease") ||
658 M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
659 M.getNamedValue("objc_retainBlock") ||
660 M.getNamedValue("objc_autoreleaseReturnValue") ||
661 M.getNamedValue("objc_autoreleasePoolPush") ||
662 M.getNamedValue("objc_loadWeakRetained") ||
663 M.getNamedValue("objc_loadWeak") ||
664 M.getNamedValue("objc_destroyWeak") ||
665 M.getNamedValue("objc_storeWeak") ||
666 M.getNamedValue("objc_initWeak") ||
667 M.getNamedValue("objc_moveWeak") ||
668 M.getNamedValue("objc_copyWeak") ||
669 M.getNamedValue("objc_retainedObject") ||
670 M.getNamedValue("objc_unretainedObject") ||
671 M.getNamedValue("objc_unretainedPointer");
674 /// \brief Test whether the given pointer, which is an Objective C block
675 /// pointer, does not "escape".
677 /// This differs from regular escape analysis in that a use as an
678 /// argument to a call is not considered an escape.
680 static bool DoesObjCBlockEscape(const Value *BlockPtr) {
682 DEBUG(dbgs() << "DoesObjCBlockEscape: Target: " << *BlockPtr << "\n");
684 // Walk the def-use chains.
685 SmallVector<const Value *, 4> Worklist;
686 Worklist.push_back(BlockPtr);
688 // Ensure we do not visit any value twice.
689 SmallPtrSet<const Value *, 4> VisitedSet;
692 const Value *V = Worklist.pop_back_val();
694 DEBUG(dbgs() << "DoesObjCBlockEscape: Visiting: " << *V << "\n");
696 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
698 const User *UUser = *UI;
700 DEBUG(dbgs() << "DoesObjCBlockEscape: User: " << *UUser << "\n");
702 // Special - Use by a call (callee or argument) is not considered
704 switch (GetBasicInstructionClass(UUser)) {
709 case IC_AutoreleaseRV: {
710 DEBUG(dbgs() << "DoesObjCBlockEscape: User copies pointer arguments. "
712 // These special functions make copies of their pointer arguments.
717 // Use by an instruction which copies the value is an escape if the
718 // result is an escape.
719 if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) ||
720 isa<PHINode>(UUser) || isa<SelectInst>(UUser)) {
722 if (!VisitedSet.insert(UUser)) {
723 DEBUG(dbgs() << "DoesObjCBlockEscape: User copies value. Escapes "
724 "if result escapes. Adding to list.\n");
725 Worklist.push_back(UUser);
727 DEBUG(dbgs() << "DoesObjCBlockEscape: Already visited node.\n");
731 // Use by a load is not an escape.
732 if (isa<LoadInst>(UUser))
734 // Use by a store is not an escape if the use is the address.
735 if (const StoreInst *SI = dyn_cast<StoreInst>(UUser))
736 if (V != SI->getValueOperand())
740 // Regular calls and other stuff are not considered escapes.
743 // Otherwise, conservatively assume an escape.
744 DEBUG(dbgs() << "DoesObjCBlockEscape: Assuming block escapes.\n");
747 } while (!Worklist.empty());
750 DEBUG(dbgs() << "DoesObjCBlockEscape: Block does not escape.\n");
756 /// \defgroup ARCAA Extends alias analysis using ObjC specific knowledge.
759 #include "llvm/Analysis/AliasAnalysis.h"
760 #include "llvm/Analysis/Passes.h"
761 #include "llvm/Pass.h"
764 /// \brief This is a simple alias analysis implementation that uses knowledge
765 /// of ARC constructs to answer queries.
767 /// TODO: This class could be generalized to know about other ObjC-specific
768 /// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing
769 /// even though their offsets are dynamic.
770 class ObjCARCAliasAnalysis : public ImmutablePass,
771 public AliasAnalysis {
773 static char ID; // Class identification, replacement for typeinfo
774 ObjCARCAliasAnalysis() : ImmutablePass(ID) {
775 initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry());
779 virtual void initializePass() {
780 InitializeAliasAnalysis(this);
783 /// This method is used when a pass implements an analysis interface through
784 /// multiple inheritance. If needed, it should override this to adjust the
785 /// this pointer as needed for the specified pass info.
786 virtual void *getAdjustedAnalysisPointer(const void *PI) {
787 if (PI == &AliasAnalysis::ID)
788 return static_cast<AliasAnalysis *>(this);
792 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
793 virtual AliasResult alias(const Location &LocA, const Location &LocB);
794 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
795 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
796 virtual ModRefBehavior getModRefBehavior(const Function *F);
797 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
798 const Location &Loc);
799 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
800 ImmutableCallSite CS2);
802 } // End of anonymous namespace
804 // Register this pass...
805 char ObjCARCAliasAnalysis::ID = 0;
806 INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
807 "ObjC-ARC-Based Alias Analysis", false, true, false)
809 ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
810 return new ObjCARCAliasAnalysis();
814 ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
815 AU.setPreservesAll();
816 AliasAnalysis::getAnalysisUsage(AU);
819 AliasAnalysis::AliasResult
820 ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) {
822 return AliasAnalysis::alias(LocA, LocB);
824 // First, strip off no-ops, including ObjC-specific no-ops, and try making a
825 // precise alias query.
826 const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr);
827 const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr);
829 AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag),
830 Location(SB, LocB.Size, LocB.TBAATag));
831 if (Result != MayAlias)
834 // If that failed, climb to the underlying object, including climbing through
835 // ObjC-specific no-ops, and try making an imprecise alias query.
836 const Value *UA = GetUnderlyingObjCPtr(SA);
837 const Value *UB = GetUnderlyingObjCPtr(SB);
838 if (UA != SA || UB != SB) {
839 Result = AliasAnalysis::alias(Location(UA), Location(UB));
840 // We can't use MustAlias or PartialAlias results here because
841 // GetUnderlyingObjCPtr may return an offsetted pointer value.
842 if (Result == NoAlias)
846 // If that failed, fail. We don't need to chain here, since that's covered
847 // by the earlier precise query.
852 ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc,
855 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
857 // First, strip off no-ops, including ObjC-specific no-ops, and try making
858 // a precise alias query.
859 const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr);
860 if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag),
864 // If that failed, climb to the underlying object, including climbing through
865 // ObjC-specific no-ops, and try making an imprecise alias query.
866 const Value *U = GetUnderlyingObjCPtr(S);
868 return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal);
870 // If that failed, fail. We don't need to chain here, since that's covered
871 // by the earlier precise query.
875 AliasAnalysis::ModRefBehavior
876 ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
877 // We have nothing to do. Just chain to the next AliasAnalysis.
878 return AliasAnalysis::getModRefBehavior(CS);
881 AliasAnalysis::ModRefBehavior
882 ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
884 return AliasAnalysis::getModRefBehavior(F);
886 switch (GetFunctionClass(F)) {
888 return DoesNotAccessMemory;
893 return AliasAnalysis::getModRefBehavior(F);
896 AliasAnalysis::ModRefResult
897 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
899 return AliasAnalysis::getModRefInfo(CS, Loc);
901 switch (GetBasicInstructionClass(CS.getInstruction())) {
905 case IC_AutoreleaseRV:
907 case IC_AutoreleasepoolPush:
908 case IC_FusedRetainAutorelease:
909 case IC_FusedRetainAutoreleaseRV:
910 // These functions don't access any memory visible to the compiler.
911 // Note that this doesn't include objc_retainBlock, because it updates
912 // pointers when it copies block data.
918 return AliasAnalysis::getModRefInfo(CS, Loc);
921 AliasAnalysis::ModRefResult
922 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
923 ImmutableCallSite CS2) {
924 // TODO: Theoretically we could check for dependencies between objc_* calls
925 // and OnlyAccessesArgumentPointees calls or other well-behaved calls.
926 return AliasAnalysis::getModRefInfo(CS1, CS2);
931 /// \defgroup ARCExpansion Early ARC Optimizations.
934 #include "llvm/Support/InstIterator.h"
935 #include "llvm/Transforms/Scalar.h"
938 /// \brief Early ARC transformations.
939 class ObjCARCExpand : public FunctionPass {
940 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
941 virtual bool doInitialization(Module &M);
942 virtual bool runOnFunction(Function &F);
944 /// A flag indicating whether this optimization pass should run.
949 ObjCARCExpand() : FunctionPass(ID) {
950 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
955 char ObjCARCExpand::ID = 0;
956 INITIALIZE_PASS(ObjCARCExpand,
957 "objc-arc-expand", "ObjC ARC expansion", false, false)
959 Pass *llvm::createObjCARCExpandPass() {
960 return new ObjCARCExpand();
963 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
964 AU.setPreservesCFG();
967 bool ObjCARCExpand::doInitialization(Module &M) {
968 Run = ModuleHasARC(M);
972 bool ObjCARCExpand::runOnFunction(Function &F) {
976 // If nothing in the Module uses ARC, don't do anything.
980 bool Changed = false;
982 DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() << "\n");
984 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) {
985 Instruction *Inst = &*I;
987 DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n");
989 switch (GetBasicInstructionClass(Inst)) {
993 case IC_AutoreleaseRV:
994 case IC_FusedRetainAutorelease:
995 case IC_FusedRetainAutoreleaseRV: {
996 // These calls return their argument verbatim, as a low-level
997 // optimization. However, this makes high-level optimizations
998 // harder. Undo any uses of this optimization that the front-end
999 // emitted here. We'll redo them in the contract pass.
1001 Value *Value = cast<CallInst>(Inst)->getArgOperand(0);
1002 DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst << "\n"
1003 " New = " << *Value << "\n");
1004 Inst->replaceAllUsesWith(Value);
1012 DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
1019 /// \defgroup ARCAPElim ARC Autorelease Pool Elimination.
1022 #include "llvm/ADT/STLExtras.h"
1023 #include "llvm/IR/Constants.h"
1026 /// \brief Autorelease pool elimination.
1027 class ObjCARCAPElim : public ModulePass {
1028 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
1029 virtual bool runOnModule(Module &M);
1031 static bool MayAutorelease(ImmutableCallSite CS, unsigned Depth = 0);
1032 static bool OptimizeBB(BasicBlock *BB);
1036 ObjCARCAPElim() : ModulePass(ID) {
1037 initializeObjCARCAPElimPass(*PassRegistry::getPassRegistry());
1042 char ObjCARCAPElim::ID = 0;
1043 INITIALIZE_PASS(ObjCARCAPElim,
1045 "ObjC ARC autorelease pool elimination",
1048 Pass *llvm::createObjCARCAPElimPass() {
1049 return new ObjCARCAPElim();
1052 void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const {
1053 AU.setPreservesCFG();
1056 /// Interprocedurally determine if calls made by the given call site can
1057 /// possibly produce autoreleases.
1058 bool ObjCARCAPElim::MayAutorelease(ImmutableCallSite CS, unsigned Depth) {
1059 if (const Function *Callee = CS.getCalledFunction()) {
1060 if (Callee->isDeclaration() || Callee->mayBeOverridden())
1062 for (Function::const_iterator I = Callee->begin(), E = Callee->end();
1064 const BasicBlock *BB = I;
1065 for (BasicBlock::const_iterator J = BB->begin(), F = BB->end();
1067 if (ImmutableCallSite JCS = ImmutableCallSite(J))
1068 // This recursion depth limit is arbitrary. It's just great
1069 // enough to cover known interesting testcases.
1071 !JCS.onlyReadsMemory() &&
1072 MayAutorelease(JCS, Depth + 1))
1081 bool ObjCARCAPElim::OptimizeBB(BasicBlock *BB) {
1082 bool Changed = false;
1084 Instruction *Push = 0;
1085 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
1086 Instruction *Inst = I++;
1087 switch (GetBasicInstructionClass(Inst)) {
1088 case IC_AutoreleasepoolPush:
1091 case IC_AutoreleasepoolPop:
1092 // If this pop matches a push and nothing in between can autorelease,
1094 if (Push && cast<CallInst>(Inst)->getArgOperand(0) == Push) {
1096 DEBUG(dbgs() << "ObjCARCAPElim::OptimizeBB: Zapping push pop "
1097 "autorelease pair:\n"
1098 " Pop: " << *Inst << "\n"
1099 << " Push: " << *Push << "\n");
1100 Inst->eraseFromParent();
1101 Push->eraseFromParent();
1106 if (MayAutorelease(ImmutableCallSite(Inst)))
1117 bool ObjCARCAPElim::runOnModule(Module &M) {
1121 // If nothing in the Module uses ARC, don't do anything.
1122 if (!ModuleHasARC(M))
1125 // Find the llvm.global_ctors variable, as the first step in
1126 // identifying the global constructors. In theory, unnecessary autorelease
1127 // pools could occur anywhere, but in practice it's pretty rare. Global
1128 // ctors are a place where autorelease pools get inserted automatically,
1129 // so it's pretty common for them to be unnecessary, and it's pretty
1130 // profitable to eliminate them.
1131 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
1135 assert(GV->hasDefinitiveInitializer() &&
1136 "llvm.global_ctors is uncooperative!");
1138 bool Changed = false;
1140 // Dig the constructor functions out of GV's initializer.
1141 ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
1142 for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end();
1145 // llvm.global_ctors is an array of pairs where the second members
1146 // are constructor functions.
1147 Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1));
1148 // If the user used a constructor function with the wrong signature and
1149 // it got bitcasted or whatever, look the other way.
1152 // Only look at function definitions.
1153 if (F->isDeclaration())
1155 // Only look at functions with one basic block.
1156 if (llvm::next(F->begin()) != F->end())
1158 // Ok, a single-block constructor function definition. Try to optimize it.
1159 Changed |= OptimizeBB(F->begin());
1167 /// \defgroup ARCOpt ARC Optimization.
1170 // TODO: On code like this:
1173 // stuff_that_cannot_release()
1174 // objc_autorelease(%x)
1175 // stuff_that_cannot_release()
1177 // stuff_that_cannot_release()
1178 // objc_autorelease(%x)
1180 // The second retain and autorelease can be deleted.
1182 // TODO: It should be possible to delete
1183 // objc_autoreleasePoolPush and objc_autoreleasePoolPop
1184 // pairs if nothing is actually autoreleased between them. Also, autorelease
1185 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
1186 // after inlining) can be turned into plain release calls.
1188 // TODO: Critical-edge splitting. If the optimial insertion point is
1189 // a critical edge, the current algorithm has to fail, because it doesn't
1190 // know how to split edges. It should be possible to make the optimizer
1191 // think in terms of edges, rather than blocks, and then split critical
1194 // TODO: OptimizeSequences could generalized to be Interprocedural.
1196 // TODO: Recognize that a bunch of other objc runtime calls have
1197 // non-escaping arguments and non-releasing arguments, and may be
1198 // non-autoreleasing.
1200 // TODO: Sink autorelease calls as far as possible. Unfortunately we
1201 // usually can't sink them past other calls, which would be the main
1202 // case where it would be useful.
1204 // TODO: The pointer returned from objc_loadWeakRetained is retained.
1206 // TODO: Delete release+retain pairs (rare).
1208 #include "llvm/ADT/SmallPtrSet.h"
1209 #include "llvm/ADT/Statistic.h"
1210 #include "llvm/IR/LLVMContext.h"
1211 #include "llvm/Support/CFG.h"
1213 STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
1214 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
1215 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
1216 STATISTIC(NumRets, "Number of return value forwarding "
1217 "retain+autoreleaes eliminated");
1218 STATISTIC(NumRRs, "Number of retain+release paths eliminated");
1219 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
1222 /// \brief This is similar to BasicAliasAnalysis, and it uses many of the same
1223 /// techniques, except it uses special ObjC-specific reasoning about pointer
1225 class ProvenanceAnalysis {
1228 typedef std::pair<const Value *, const Value *> ValuePairTy;
1229 typedef DenseMap<ValuePairTy, bool> CachedResultsTy;
1230 CachedResultsTy CachedResults;
1232 bool relatedCheck(const Value *A, const Value *B);
1233 bool relatedSelect(const SelectInst *A, const Value *B);
1234 bool relatedPHI(const PHINode *A, const Value *B);
1236 void operator=(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION;
1237 ProvenanceAnalysis(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION;
1240 ProvenanceAnalysis() {}
1242 void setAA(AliasAnalysis *aa) { AA = aa; }
1244 AliasAnalysis *getAA() const { return AA; }
1246 bool related(const Value *A, const Value *B);
1249 CachedResults.clear();
1254 bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) {
1255 // If the values are Selects with the same condition, we can do a more precise
1256 // check: just check for relations between the values on corresponding arms.
1257 if (const SelectInst *SB = dyn_cast<SelectInst>(B))
1258 if (A->getCondition() == SB->getCondition())
1259 return related(A->getTrueValue(), SB->getTrueValue()) ||
1260 related(A->getFalseValue(), SB->getFalseValue());
1262 // Check both arms of the Select node individually.
1263 return related(A->getTrueValue(), B) ||
1264 related(A->getFalseValue(), B);
1267 bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) {
1268 // If the values are PHIs in the same block, we can do a more precise as well
1269 // as efficient check: just check for relations between the values on
1270 // corresponding edges.
1271 if (const PHINode *PNB = dyn_cast<PHINode>(B))
1272 if (PNB->getParent() == A->getParent()) {
1273 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i)
1274 if (related(A->getIncomingValue(i),
1275 PNB->getIncomingValueForBlock(A->getIncomingBlock(i))))
1280 // Check each unique source of the PHI node against B.
1281 SmallPtrSet<const Value *, 4> UniqueSrc;
1282 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) {
1283 const Value *PV1 = A->getIncomingValue(i);
1284 if (UniqueSrc.insert(PV1) && related(PV1, B))
1288 // All of the arms checked out.
1292 /// Test if the value of P, or any value covered by its provenance, is ever
1293 /// stored within the function (not counting callees).
1294 static bool isStoredObjCPointer(const Value *P) {
1295 SmallPtrSet<const Value *, 8> Visited;
1296 SmallVector<const Value *, 8> Worklist;
1297 Worklist.push_back(P);
1300 P = Worklist.pop_back_val();
1301 for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end();
1303 const User *Ur = *UI;
1304 if (isa<StoreInst>(Ur)) {
1305 if (UI.getOperandNo() == 0)
1306 // The pointer is stored.
1308 // The pointed is stored through.
1311 if (isa<CallInst>(Ur))
1312 // The pointer is passed as an argument, ignore this.
1314 if (isa<PtrToIntInst>(P))
1315 // Assume the worst.
1317 if (Visited.insert(Ur))
1318 Worklist.push_back(Ur);
1320 } while (!Worklist.empty());
1322 // Everything checked out.
1326 bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) {
1327 // Skip past provenance pass-throughs.
1328 A = GetUnderlyingObjCPtr(A);
1329 B = GetUnderlyingObjCPtr(B);
1335 // Ask regular AliasAnalysis, for a first approximation.
1336 switch (AA->alias(A, B)) {
1337 case AliasAnalysis::NoAlias:
1339 case AliasAnalysis::MustAlias:
1340 case AliasAnalysis::PartialAlias:
1342 case AliasAnalysis::MayAlias:
1346 bool AIsIdentified = IsObjCIdentifiedObject(A);
1347 bool BIsIdentified = IsObjCIdentifiedObject(B);
1349 // An ObjC-Identified object can't alias a load if it is never locally stored.
1350 if (AIsIdentified) {
1351 // Check for an obvious escape.
1352 if (isa<LoadInst>(B))
1353 return isStoredObjCPointer(A);
1354 if (BIsIdentified) {
1355 // Check for an obvious escape.
1356 if (isa<LoadInst>(A))
1357 return isStoredObjCPointer(B);
1358 // Both pointers are identified and escapes aren't an evident problem.
1361 } else if (BIsIdentified) {
1362 // Check for an obvious escape.
1363 if (isa<LoadInst>(A))
1364 return isStoredObjCPointer(B);
1367 // Special handling for PHI and Select.
1368 if (const PHINode *PN = dyn_cast<PHINode>(A))
1369 return relatedPHI(PN, B);
1370 if (const PHINode *PN = dyn_cast<PHINode>(B))
1371 return relatedPHI(PN, A);
1372 if (const SelectInst *S = dyn_cast<SelectInst>(A))
1373 return relatedSelect(S, B);
1374 if (const SelectInst *S = dyn_cast<SelectInst>(B))
1375 return relatedSelect(S, A);
1381 bool ProvenanceAnalysis::related(const Value *A, const Value *B) {
1382 // Begin by inserting a conservative value into the map. If the insertion
1383 // fails, we have the answer already. If it succeeds, leave it there until we
1384 // compute the real answer to guard against recursive queries.
1385 if (A > B) std::swap(A, B);
1386 std::pair<CachedResultsTy::iterator, bool> Pair =
1387 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true));
1389 return Pair.first->second;
1391 bool Result = relatedCheck(A, B);
1392 CachedResults[ValuePairTy(A, B)] = Result;
1399 /// \brief A sequence of states that a pointer may go through in which an
1400 /// objc_retain and objc_release are actually needed.
1403 S_Retain, ///< objc_retain(x)
1404 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement
1405 S_Use, ///< any use of x
1406 S_Stop, ///< like S_Release, but code motion is stopped
1407 S_Release, ///< objc_release(x)
1408 S_MovableRelease ///< objc_release(x), !clang.imprecise_release
1412 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
1416 if (A == S_None || B == S_None)
1419 if (A > B) std::swap(A, B);
1421 // Choose the side which is further along in the sequence.
1422 if ((A == S_Retain || A == S_CanRelease) &&
1423 (B == S_CanRelease || B == S_Use))
1426 // Choose the side which is further along in the sequence.
1427 if ((A == S_Use || A == S_CanRelease) &&
1428 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
1430 // If both sides are releases, choose the more conservative one.
1431 if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
1433 if (A == S_Release && B == S_MovableRelease)
1441 /// \brief Unidirectional information about either a
1442 /// retain-decrement-use-release sequence or release-use-decrement-retain
1443 /// reverese sequence.
1445 /// After an objc_retain, the reference count of the referenced
1446 /// object is known to be positive. Similarly, before an objc_release, the
1447 /// reference count of the referenced object is known to be positive. If
1448 /// there are retain-release pairs in code regions where the retain count
1449 /// is known to be positive, they can be eliminated, regardless of any side
1450 /// effects between them.
1452 /// Also, a retain+release pair nested within another retain+release
1453 /// pair all on the known same pointer value can be eliminated, regardless
1454 /// of any intervening side effects.
1456 /// KnownSafe is true when either of these conditions is satisfied.
1459 /// True if the Calls are objc_retainBlock calls (as opposed to objc_retain
1463 /// True of the objc_release calls are all marked with the "tail" keyword.
1464 bool IsTailCallRelease;
1466 /// If the Calls are objc_release calls and they all have a
1467 /// clang.imprecise_release tag, this is the metadata tag.
1468 MDNode *ReleaseMetadata;
1470 /// For a top-down sequence, the set of objc_retains or
1471 /// objc_retainBlocks. For bottom-up, the set of objc_releases.
1472 SmallPtrSet<Instruction *, 2> Calls;
1474 /// The set of optimal insert positions for moving calls in the opposite
1476 SmallPtrSet<Instruction *, 2> ReverseInsertPts;
1479 KnownSafe(false), IsRetainBlock(false),
1480 IsTailCallRelease(false),
1481 ReleaseMetadata(0) {}
1487 void RRInfo::clear() {
1489 IsRetainBlock = false;
1490 IsTailCallRelease = false;
1491 ReleaseMetadata = 0;
1493 ReverseInsertPts.clear();
1497 /// \brief This class summarizes several per-pointer runtime properties which
1498 /// are propogated through the flow graph.
1500 /// True if the reference count is known to be incremented.
1501 bool KnownPositiveRefCount;
1503 /// True of we've seen an opportunity for partial RR elimination, such as
1504 /// pushing calls into a CFG triangle or into one side of a CFG diamond.
1507 /// The current position in the sequence.
1511 /// Unidirectional information about the current sequence.
1513 /// TODO: Encapsulate this better.
1516 PtrState() : KnownPositiveRefCount(false), Partial(false),
1519 void SetKnownPositiveRefCount() {
1520 KnownPositiveRefCount = true;
1523 void ClearRefCount() {
1524 KnownPositiveRefCount = false;
1527 bool IsKnownIncremented() const {
1528 return KnownPositiveRefCount;
1531 void SetSeq(Sequence NewSeq) {
1535 Sequence GetSeq() const {
1539 void ClearSequenceProgress() {
1540 ResetSequenceProgress(S_None);
1543 void ResetSequenceProgress(Sequence NewSeq) {
1549 void Merge(const PtrState &Other, bool TopDown);
1554 PtrState::Merge(const PtrState &Other, bool TopDown) {
1555 Seq = MergeSeqs(Seq, Other.Seq, TopDown);
1556 KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
1558 // We can't merge a plain objc_retain with an objc_retainBlock.
1559 if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
1562 // If we're not in a sequence (anymore), drop all associated state.
1563 if (Seq == S_None) {
1566 } else if (Partial || Other.Partial) {
1567 // If we're doing a merge on a path that's previously seen a partial
1568 // merge, conservatively drop the sequence, to avoid doing partial
1569 // RR elimination. If the branch predicates for the two merge differ,
1570 // mixing them is unsafe.
1571 ClearSequenceProgress();
1573 // Conservatively merge the ReleaseMetadata information.
1574 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
1575 RRI.ReleaseMetadata = 0;
1577 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
1578 RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
1579 Other.RRI.IsTailCallRelease;
1580 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
1582 // Merge the insert point sets. If there are any differences,
1583 // that makes this a partial merge.
1584 Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
1585 for (SmallPtrSet<Instruction *, 2>::const_iterator
1586 I = Other.RRI.ReverseInsertPts.begin(),
1587 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
1588 Partial |= RRI.ReverseInsertPts.insert(*I);
1593 /// \brief Per-BasicBlock state.
1595 /// The number of unique control paths from the entry which can reach this
1597 unsigned TopDownPathCount;
1599 /// The number of unique control paths to exits from this block.
1600 unsigned BottomUpPathCount;
1602 /// A type for PerPtrTopDown and PerPtrBottomUp.
1603 typedef MapVector<const Value *, PtrState> MapTy;
1605 /// The top-down traversal uses this to record information known about a
1606 /// pointer at the bottom of each block.
1607 MapTy PerPtrTopDown;
1609 /// The bottom-up traversal uses this to record information known about a
1610 /// pointer at the top of each block.
1611 MapTy PerPtrBottomUp;
1613 /// Effective predecessors of the current block ignoring ignorable edges and
1614 /// ignored backedges.
1615 SmallVector<BasicBlock *, 2> Preds;
1616 /// Effective successors of the current block ignoring ignorable edges and
1617 /// ignored backedges.
1618 SmallVector<BasicBlock *, 2> Succs;
1621 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
1623 typedef MapTy::iterator ptr_iterator;
1624 typedef MapTy::const_iterator ptr_const_iterator;
1626 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
1627 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
1628 ptr_const_iterator top_down_ptr_begin() const {
1629 return PerPtrTopDown.begin();
1631 ptr_const_iterator top_down_ptr_end() const {
1632 return PerPtrTopDown.end();
1635 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
1636 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
1637 ptr_const_iterator bottom_up_ptr_begin() const {
1638 return PerPtrBottomUp.begin();
1640 ptr_const_iterator bottom_up_ptr_end() const {
1641 return PerPtrBottomUp.end();
1644 /// Mark this block as being an entry block, which has one path from the
1645 /// entry by definition.
1646 void SetAsEntry() { TopDownPathCount = 1; }
1648 /// Mark this block as being an exit block, which has one path to an exit by
1650 void SetAsExit() { BottomUpPathCount = 1; }
1652 PtrState &getPtrTopDownState(const Value *Arg) {
1653 return PerPtrTopDown[Arg];
1656 PtrState &getPtrBottomUpState(const Value *Arg) {
1657 return PerPtrBottomUp[Arg];
1660 void clearBottomUpPointers() {
1661 PerPtrBottomUp.clear();
1664 void clearTopDownPointers() {
1665 PerPtrTopDown.clear();
1668 void InitFromPred(const BBState &Other);
1669 void InitFromSucc(const BBState &Other);
1670 void MergePred(const BBState &Other);
1671 void MergeSucc(const BBState &Other);
1673 /// Return the number of possible unique paths from an entry to an exit
1674 /// which pass through this block. This is only valid after both the
1675 /// top-down and bottom-up traversals are complete.
1676 unsigned GetAllPathCount() const {
1677 assert(TopDownPathCount != 0);
1678 assert(BottomUpPathCount != 0);
1679 return TopDownPathCount * BottomUpPathCount;
1682 // Specialized CFG utilities.
1683 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
1684 edge_iterator pred_begin() { return Preds.begin(); }
1685 edge_iterator pred_end() { return Preds.end(); }
1686 edge_iterator succ_begin() { return Succs.begin(); }
1687 edge_iterator succ_end() { return Succs.end(); }
1689 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
1690 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
1692 bool isExit() const { return Succs.empty(); }
1696 void BBState::InitFromPred(const BBState &Other) {
1697 PerPtrTopDown = Other.PerPtrTopDown;
1698 TopDownPathCount = Other.TopDownPathCount;
1701 void BBState::InitFromSucc(const BBState &Other) {
1702 PerPtrBottomUp = Other.PerPtrBottomUp;
1703 BottomUpPathCount = Other.BottomUpPathCount;
1706 /// The top-down traversal uses this to merge information about predecessors to
1707 /// form the initial state for a new block.
1708 void BBState::MergePred(const BBState &Other) {
1709 // Other.TopDownPathCount can be 0, in which case it is either dead or a
1710 // loop backedge. Loop backedges are special.
1711 TopDownPathCount += Other.TopDownPathCount;
1713 // Check for overflow. If we have overflow, fall back to conservative
1715 if (TopDownPathCount < Other.TopDownPathCount) {
1716 clearTopDownPointers();
1720 // For each entry in the other set, if our set has an entry with the same key,
1721 // merge the entries. Otherwise, copy the entry and merge it with an empty
1723 for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
1724 ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
1725 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
1726 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
1730 // For each entry in our set, if the other set doesn't have an entry with the
1731 // same key, force it to merge with an empty entry.
1732 for (ptr_iterator MI = top_down_ptr_begin(),
1733 ME = top_down_ptr_end(); MI != ME; ++MI)
1734 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
1735 MI->second.Merge(PtrState(), /*TopDown=*/true);
1738 /// The bottom-up traversal uses this to merge information about successors to
1739 /// form the initial state for a new block.
1740 void BBState::MergeSucc(const BBState &Other) {
1741 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
1742 // loop backedge. Loop backedges are special.
1743 BottomUpPathCount += Other.BottomUpPathCount;
1745 // Check for overflow. If we have overflow, fall back to conservative
1747 if (BottomUpPathCount < Other.BottomUpPathCount) {
1748 clearBottomUpPointers();
1752 // For each entry in the other set, if our set has an entry with the
1753 // same key, merge the entries. Otherwise, copy the entry and merge
1754 // it with an empty entry.
1755 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
1756 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
1757 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
1758 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
1762 // For each entry in our set, if the other set doesn't have an entry
1763 // with the same key, force it to merge with an empty entry.
1764 for (ptr_iterator MI = bottom_up_ptr_begin(),
1765 ME = bottom_up_ptr_end(); MI != ME; ++MI)
1766 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
1767 MI->second.Merge(PtrState(), /*TopDown=*/false);
1771 /// \brief The main ARC optimization pass.
1772 class ObjCARCOpt : public FunctionPass {
1774 ProvenanceAnalysis PA;
1776 /// A flag indicating whether this optimization pass should run.
1779 /// Declarations for ObjC runtime functions, for use in creating calls to
1780 /// them. These are initialized lazily to avoid cluttering up the Module
1781 /// with unused declarations.
1783 /// Declaration for ObjC runtime function
1784 /// objc_retainAutoreleasedReturnValue.
1785 Constant *RetainRVCallee;
1786 /// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
1787 Constant *AutoreleaseRVCallee;
1788 /// Declaration for ObjC runtime function objc_release.
1789 Constant *ReleaseCallee;
1790 /// Declaration for ObjC runtime function objc_retain.
1791 Constant *RetainCallee;
1792 /// Declaration for ObjC runtime function objc_retainBlock.
1793 Constant *RetainBlockCallee;
1794 /// Declaration for ObjC runtime function objc_autorelease.
1795 Constant *AutoreleaseCallee;
1797 /// Flags which determine whether each of the interesting runtine functions
1798 /// is in fact used in the current function.
1799 unsigned UsedInThisFunction;
1801 /// The Metadata Kind for clang.imprecise_release metadata.
1802 unsigned ImpreciseReleaseMDKind;
1804 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
1805 unsigned CopyOnEscapeMDKind;
1807 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
1808 unsigned NoObjCARCExceptionsMDKind;
1810 Constant *getRetainRVCallee(Module *M);
1811 Constant *getAutoreleaseRVCallee(Module *M);
1812 Constant *getReleaseCallee(Module *M);
1813 Constant *getRetainCallee(Module *M);
1814 Constant *getRetainBlockCallee(Module *M);
1815 Constant *getAutoreleaseCallee(Module *M);
1817 bool IsRetainBlockOptimizable(const Instruction *Inst);
1819 void OptimizeRetainCall(Function &F, Instruction *Retain);
1820 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
1821 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
1822 InstructionClass &Class);
1823 void OptimizeIndividualCalls(Function &F);
1825 void CheckForCFGHazards(const BasicBlock *BB,
1826 DenseMap<const BasicBlock *, BBState> &BBStates,
1827 BBState &MyStates) const;
1828 bool VisitInstructionBottomUp(Instruction *Inst,
1830 MapVector<Value *, RRInfo> &Retains,
1832 bool VisitBottomUp(BasicBlock *BB,
1833 DenseMap<const BasicBlock *, BBState> &BBStates,
1834 MapVector<Value *, RRInfo> &Retains);
1835 bool VisitInstructionTopDown(Instruction *Inst,
1836 DenseMap<Value *, RRInfo> &Releases,
1838 bool VisitTopDown(BasicBlock *BB,
1839 DenseMap<const BasicBlock *, BBState> &BBStates,
1840 DenseMap<Value *, RRInfo> &Releases);
1841 bool Visit(Function &F,
1842 DenseMap<const BasicBlock *, BBState> &BBStates,
1843 MapVector<Value *, RRInfo> &Retains,
1844 DenseMap<Value *, RRInfo> &Releases);
1846 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
1847 MapVector<Value *, RRInfo> &Retains,
1848 DenseMap<Value *, RRInfo> &Releases,
1849 SmallVectorImpl<Instruction *> &DeadInsts,
1852 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
1853 MapVector<Value *, RRInfo> &Retains,
1854 DenseMap<Value *, RRInfo> &Releases,
1856 SmallVector<Instruction *, 4> &NewRetains,
1857 SmallVector<Instruction *, 4> &NewReleases,
1858 SmallVector<Instruction *, 8> &DeadInsts,
1859 RRInfo &RetainsToMove,
1860 RRInfo &ReleasesToMove,
1863 bool &AnyPairsCompletelyEliminated);
1865 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
1866 MapVector<Value *, RRInfo> &Retains,
1867 DenseMap<Value *, RRInfo> &Releases,
1870 void OptimizeWeakCalls(Function &F);
1872 bool OptimizeSequences(Function &F);
1874 void OptimizeReturns(Function &F);
1876 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
1877 virtual bool doInitialization(Module &M);
1878 virtual bool runOnFunction(Function &F);
1879 virtual void releaseMemory();
1883 ObjCARCOpt() : FunctionPass(ID) {
1884 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
1889 char ObjCARCOpt::ID = 0;
1890 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
1891 "objc-arc", "ObjC ARC optimization", false, false)
1892 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
1893 INITIALIZE_PASS_END(ObjCARCOpt,
1894 "objc-arc", "ObjC ARC optimization", false, false)
1896 Pass *llvm::createObjCARCOptPass() {
1897 return new ObjCARCOpt();
1900 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
1901 AU.addRequired<ObjCARCAliasAnalysis>();
1902 AU.addRequired<AliasAnalysis>();
1903 // ARC optimization doesn't currently split critical edges.
1904 AU.setPreservesCFG();
1907 bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
1908 // Without the magic metadata tag, we have to assume this might be an
1909 // objc_retainBlock call inserted to convert a block pointer to an id,
1910 // in which case it really is needed.
1911 if (!Inst->getMetadata(CopyOnEscapeMDKind))
1914 // If the pointer "escapes" (not including being used in a call),
1915 // the copy may be needed.
1916 if (DoesObjCBlockEscape(Inst))
1919 // Otherwise, it's not needed.
1923 Constant *ObjCARCOpt::getRetainRVCallee(Module *M) {
1924 if (!RetainRVCallee) {
1925 LLVMContext &C = M->getContext();
1926 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1927 Type *Params[] = { I8X };
1928 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1929 AttributeSet Attribute =
1930 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1931 Attribute::NoUnwind);
1933 M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy,
1936 return RetainRVCallee;
1939 Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
1940 if (!AutoreleaseRVCallee) {
1941 LLVMContext &C = M->getContext();
1942 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
1943 Type *Params[] = { I8X };
1944 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
1945 AttributeSet Attribute =
1946 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1947 Attribute::NoUnwind);
1948 AutoreleaseRVCallee =
1949 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
1952 return AutoreleaseRVCallee;
1955 Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
1956 if (!ReleaseCallee) {
1957 LLVMContext &C = M->getContext();
1958 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1959 AttributeSet Attribute =
1960 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1961 Attribute::NoUnwind);
1963 M->getOrInsertFunction(
1965 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
1968 return ReleaseCallee;
1971 Constant *ObjCARCOpt::getRetainCallee(Module *M) {
1972 if (!RetainCallee) {
1973 LLVMContext &C = M->getContext();
1974 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1975 AttributeSet Attribute =
1976 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
1977 Attribute::NoUnwind);
1979 M->getOrInsertFunction(
1981 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1984 return RetainCallee;
1987 Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
1988 if (!RetainBlockCallee) {
1989 LLVMContext &C = M->getContext();
1990 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
1991 // objc_retainBlock is not nounwind because it calls user copy constructors
1992 // which could theoretically throw.
1994 M->getOrInsertFunction(
1996 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
1999 return RetainBlockCallee;
2002 Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
2003 if (!AutoreleaseCallee) {
2004 LLVMContext &C = M->getContext();
2005 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
2006 AttributeSet Attribute =
2007 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
2008 Attribute::NoUnwind);
2010 M->getOrInsertFunction(
2012 FunctionType::get(Params[0], Params, /*isVarArg=*/false),
2015 return AutoreleaseCallee;
2018 /// Test whether the given value is possible a reference-counted pointer,
2019 /// including tests which utilize AliasAnalysis.
2020 static bool IsPotentialUse(const Value *Op, AliasAnalysis &AA) {
2021 // First make the rudimentary check.
2022 if (!IsPotentialUse(Op))
2025 // Objects in constant memory are not reference-counted.
2026 if (AA.pointsToConstantMemory(Op))
2029 // Pointers in constant memory are not pointing to reference-counted objects.
2030 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
2031 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
2034 // Otherwise assume the worst.
2038 /// Test whether the given instruction can result in a reference count
2039 /// modification (positive or negative) for the pointer's object.
2041 CanAlterRefCount(const Instruction *Inst, const Value *Ptr,
2042 ProvenanceAnalysis &PA, InstructionClass Class) {
2044 case IC_Autorelease:
2045 case IC_AutoreleaseRV:
2047 // These operations never directly modify a reference count.
2052 ImmutableCallSite CS = static_cast<const Value *>(Inst);
2053 assert(CS && "Only calls can alter reference counts!");
2055 // See if AliasAnalysis can help us with the call.
2056 AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS);
2057 if (AliasAnalysis::onlyReadsMemory(MRB))
2059 if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
2060 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
2062 const Value *Op = *I;
2063 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
2069 // Assume the worst.
2073 /// Test whether the given instruction can "use" the given pointer's object in a
2074 /// way that requires the reference count to be positive.
2076 CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA,
2077 InstructionClass Class) {
2078 // IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers.
2079 if (Class == IC_Call)
2082 // Consider various instructions which may have pointer arguments which are
2084 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) {
2085 // Comparing a pointer with null, or any other constant, isn't really a use,
2086 // because we don't care what the pointer points to, or about the values
2087 // of any other dynamic reference-counted pointers.
2088 if (!IsPotentialUse(ICI->getOperand(1), *PA.getAA()))
2090 } else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) {
2091 // For calls, just check the arguments (and not the callee operand).
2092 for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(),
2093 OE = CS.arg_end(); OI != OE; ++OI) {
2094 const Value *Op = *OI;
2095 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
2099 } else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
2100 // Special-case stores, because we don't care about the stored value, just
2101 // the store address.
2102 const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand());
2103 // If we can't tell what the underlying object was, assume there is a
2105 return IsPotentialUse(Op, *PA.getAA()) && PA.related(Op, Ptr);
2108 // Check each operand for a match.
2109 for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
2111 const Value *Op = *OI;
2112 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
2118 /// Test whether the given instruction can autorelease any pointer or cause an
2119 /// autoreleasepool pop.
2121 CanInterruptRV(InstructionClass Class) {
2123 case IC_AutoreleasepoolPop:
2126 case IC_Autorelease:
2127 case IC_AutoreleaseRV:
2128 case IC_FusedRetainAutorelease:
2129 case IC_FusedRetainAutoreleaseRV:
2137 /// \enum DependenceKind
2138 /// \brief Defines different dependence kinds among various ARC constructs.
2140 /// There are several kinds of dependence-like concepts in use here.
2142 enum DependenceKind {
2143 NeedsPositiveRetainCount,
2144 AutoreleasePoolBoundary,
2145 CanChangeRetainCount,
2146 RetainAutoreleaseDep, ///< Blocks objc_retainAutorelease.
2147 RetainAutoreleaseRVDep, ///< Blocks objc_retainAutoreleaseReturnValue.
2148 RetainRVDep ///< Blocks objc_retainAutoreleasedReturnValue.
2152 /// Test if there can be dependencies on Inst through Arg. This function only
2153 /// tests dependencies relevant for removing pairs of calls.
2155 Depends(DependenceKind Flavor, Instruction *Inst, const Value *Arg,
2156 ProvenanceAnalysis &PA) {
2157 // If we've reached the definition of Arg, stop.
2162 case NeedsPositiveRetainCount: {
2163 InstructionClass Class = GetInstructionClass(Inst);
2165 case IC_AutoreleasepoolPop:
2166 case IC_AutoreleasepoolPush:
2170 return CanUse(Inst, Arg, PA, Class);
2174 case AutoreleasePoolBoundary: {
2175 InstructionClass Class = GetInstructionClass(Inst);
2177 case IC_AutoreleasepoolPop:
2178 case IC_AutoreleasepoolPush:
2179 // These mark the end and begin of an autorelease pool scope.
2182 // Nothing else does this.
2187 case CanChangeRetainCount: {
2188 InstructionClass Class = GetInstructionClass(Inst);
2190 case IC_AutoreleasepoolPop:
2191 // Conservatively assume this can decrement any count.
2193 case IC_AutoreleasepoolPush:
2197 return CanAlterRefCount(Inst, Arg, PA, Class);
2201 case RetainAutoreleaseDep:
2202 switch (GetBasicInstructionClass(Inst)) {
2203 case IC_AutoreleasepoolPop:
2204 case IC_AutoreleasepoolPush:
2205 // Don't merge an objc_autorelease with an objc_retain inside a different
2206 // autoreleasepool scope.
2210 // Check for a retain of the same pointer for merging.
2211 return GetObjCArg(Inst) == Arg;
2213 // Nothing else matters for objc_retainAutorelease formation.
2217 case RetainAutoreleaseRVDep: {
2218 InstructionClass Class = GetBasicInstructionClass(Inst);
2222 // Check for a retain of the same pointer for merging.
2223 return GetObjCArg(Inst) == Arg;
2225 // Anything that can autorelease interrupts
2226 // retainAutoreleaseReturnValue formation.
2227 return CanInterruptRV(Class);
2232 return CanInterruptRV(GetBasicInstructionClass(Inst));
2235 llvm_unreachable("Invalid dependence flavor");
2238 /// Walk up the CFG from StartPos (which is in StartBB) and find local and
2239 /// non-local dependencies on Arg.
2241 /// TODO: Cache results?
2243 FindDependencies(DependenceKind Flavor,
2245 BasicBlock *StartBB, Instruction *StartInst,
2246 SmallPtrSet<Instruction *, 4> &DependingInstructions,
2247 SmallPtrSet<const BasicBlock *, 4> &Visited,
2248 ProvenanceAnalysis &PA) {
2249 BasicBlock::iterator StartPos = StartInst;
2251 SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist;
2252 Worklist.push_back(std::make_pair(StartBB, StartPos));
2254 std::pair<BasicBlock *, BasicBlock::iterator> Pair =
2255 Worklist.pop_back_val();
2256 BasicBlock *LocalStartBB = Pair.first;
2257 BasicBlock::iterator LocalStartPos = Pair.second;
2258 BasicBlock::iterator StartBBBegin = LocalStartBB->begin();
2260 if (LocalStartPos == StartBBBegin) {
2261 pred_iterator PI(LocalStartBB), PE(LocalStartBB, false);
2263 // If we've reached the function entry, produce a null dependence.
2264 DependingInstructions.insert(0);
2266 // Add the predecessors to the worklist.
2268 BasicBlock *PredBB = *PI;
2269 if (Visited.insert(PredBB))
2270 Worklist.push_back(std::make_pair(PredBB, PredBB->end()));
2271 } while (++PI != PE);
2275 Instruction *Inst = --LocalStartPos;
2276 if (Depends(Flavor, Inst, Arg, PA)) {
2277 DependingInstructions.insert(Inst);
2281 } while (!Worklist.empty());
2283 // Determine whether the original StartBB post-dominates all of the blocks we
2284 // visited. If not, insert a sentinal indicating that most optimizations are
2286 for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(),
2287 E = Visited.end(); I != E; ++I) {
2288 const BasicBlock *BB = *I;
2291 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
2292 for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) {
2293 const BasicBlock *Succ = *SI;
2294 if (Succ != StartBB && !Visited.count(Succ)) {
2295 DependingInstructions.insert(reinterpret_cast<Instruction *>(-1));
2302 static bool isNullOrUndef(const Value *V) {
2303 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
2306 static bool isNoopInstruction(const Instruction *I) {
2307 return isa<BitCastInst>(I) ||
2308 (isa<GetElementPtrInst>(I) &&
2309 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
2312 /// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
2315 ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) {
2316 ImmutableCallSite CS(GetObjCArg(Retain));
2317 const Instruction *Call = CS.getInstruction();
2319 if (Call->getParent() != Retain->getParent()) return;
2321 // Check that the call is next to the retain.
2322 BasicBlock::const_iterator I = Call;
2324 while (isNoopInstruction(I)) ++I;
2328 // Turn it to an objc_retainAutoreleasedReturnValue..
2332 DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainCall: Transforming "
2333 "objc_retain => objc_retainAutoreleasedReturnValue"
2334 " since the operand is a return value.\n"
2336 << *Retain << "\n");
2338 cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent()));
2340 DEBUG(dbgs() << " New: "
2341 << *Retain << "\n");
2344 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
2345 /// not a return value. Or, if it can be paired with an
2346 /// objc_autoreleaseReturnValue, delete the pair and return true.
2348 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
2349 // Check for the argument being from an immediately preceding call or invoke.
2350 const Value *Arg = GetObjCArg(RetainRV);
2351 ImmutableCallSite CS(Arg);
2352 if (const Instruction *Call = CS.getInstruction()) {
2353 if (Call->getParent() == RetainRV->getParent()) {
2354 BasicBlock::const_iterator I = Call;
2356 while (isNoopInstruction(I)) ++I;
2357 if (&*I == RetainRV)
2359 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
2360 BasicBlock *RetainRVParent = RetainRV->getParent();
2361 if (II->getNormalDest() == RetainRVParent) {
2362 BasicBlock::const_iterator I = RetainRVParent->begin();
2363 while (isNoopInstruction(I)) ++I;
2364 if (&*I == RetainRV)
2370 // Check for being preceded by an objc_autoreleaseReturnValue on the same
2371 // pointer. In this case, we can delete the pair.
2372 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
2374 do --I; while (I != Begin && isNoopInstruction(I));
2375 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
2376 GetObjCArg(I) == Arg) {
2380 DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Erasing " << *I << "\n"
2381 << " Erasing " << *RetainRV
2384 EraseInstruction(I);
2385 EraseInstruction(RetainRV);
2390 // Turn it to a plain objc_retain.
2394 DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Transforming "
2395 "objc_retainAutoreleasedReturnValue => "
2396 "objc_retain since the operand is not a return value.\n"
2398 << *RetainRV << "\n");
2400 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));
2402 DEBUG(dbgs() << " New: "
2403 << *RetainRV << "\n");
2408 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
2409 /// used as a return value.
2411 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
2412 InstructionClass &Class) {
2413 // Check for a return of the pointer value.
2414 const Value *Ptr = GetObjCArg(AutoreleaseRV);
2415 SmallVector<const Value *, 2> Users;
2416 Users.push_back(Ptr);
2418 Ptr = Users.pop_back_val();
2419 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
2421 const User *I = *UI;
2422 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
2424 if (isa<BitCastInst>(I))
2427 } while (!Users.empty());
2432 DEBUG(dbgs() << "ObjCARCOpt::OptimizeAutoreleaseRVCall: Transforming "
2433 "objc_autoreleaseReturnValue => "
2434 "objc_autorelease since its operand is not used as a return "
2437 << *AutoreleaseRV << "\n");
2439 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
2441 setCalledFunction(getAutoreleaseCallee(F.getParent()));
2442 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
2443 Class = IC_Autorelease;
2445 DEBUG(dbgs() << " New: "
2446 << *AutoreleaseRV << "\n");
2450 /// Visit each call, one at a time, and make simplifications without doing any
2451 /// additional analysis.
2452 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
2453 // Reset all the flags in preparation for recomputing them.
2454 UsedInThisFunction = 0;
2456 // Visit all objc_* calls in F.
2457 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2458 Instruction *Inst = &*I++;
2460 InstructionClass Class = GetBasicInstructionClass(Inst);
2462 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Visiting: Class: "
2463 << Class << "; " << *Inst << "\n");
2468 // Delete no-op casts. These function calls have special semantics, but
2469 // the semantics are entirely implemented via lowering in the front-end,
2470 // so by the time they reach the optimizer, they are just no-op calls
2471 // which return their argument.
2473 // There are gray areas here, as the ability to cast reference-counted
2474 // pointers to raw void* and back allows code to break ARC assumptions,
2475 // however these are currently considered to be unimportant.
2479 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Erasing no-op cast:"
2480 " " << *Inst << "\n");
2481 EraseInstruction(Inst);
2484 // If the pointer-to-weak-pointer is null, it's undefined behavior.
2487 case IC_LoadWeakRetained:
2489 case IC_DestroyWeak: {
2490 CallInst *CI = cast<CallInst>(Inst);
2491 if (isNullOrUndef(CI->getArgOperand(0))) {
2493 Type *Ty = CI->getArgOperand(0)->getType();
2494 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
2495 Constant::getNullValue(Ty),
2497 llvm::Value *NewValue = UndefValue::get(CI->getType());
2498 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null "
2499 "pointer-to-weak-pointer is undefined behavior.\n"
2503 CI->replaceAllUsesWith(NewValue);
2504 CI->eraseFromParent();
2511 CallInst *CI = cast<CallInst>(Inst);
2512 if (isNullOrUndef(CI->getArgOperand(0)) ||
2513 isNullOrUndef(CI->getArgOperand(1))) {
2515 Type *Ty = CI->getArgOperand(0)->getType();
2516 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
2517 Constant::getNullValue(Ty),
2520 llvm::Value *NewValue = UndefValue::get(CI->getType());
2521 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null "
2522 "pointer-to-weak-pointer is undefined behavior.\n"
2527 CI->replaceAllUsesWith(NewValue);
2528 CI->eraseFromParent();
2534 OptimizeRetainCall(F, Inst);
2537 if (OptimizeRetainRVCall(F, Inst))
2540 case IC_AutoreleaseRV:
2541 OptimizeAutoreleaseRVCall(F, Inst, Class);
2545 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
2546 if (IsAutorelease(Class) && Inst->use_empty()) {
2547 CallInst *Call = cast<CallInst>(Inst);
2548 const Value *Arg = Call->getArgOperand(0);
2549 Arg = FindSingleUseIdentifiedObject(Arg);
2554 // Create the declaration lazily.
2555 LLVMContext &C = Inst->getContext();
2557 CallInst::Create(getReleaseCallee(F.getParent()),
2558 Call->getArgOperand(0), "", Call);
2559 NewCall->setMetadata(ImpreciseReleaseMDKind,
2560 MDNode::get(C, ArrayRef<Value *>()));
2562 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Replacing "
2563 "objc_autorelease(x) with objc_release(x) since x is "
2564 "otherwise unused.\n"
2565 " Old: " << *Call <<
2569 EraseInstruction(Call);
2575 // For functions which can never be passed stack arguments, add
2577 if (IsAlwaysTail(Class)) {
2579 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Adding tail keyword"
2580 " to function since it can never be passed stack args: " << *Inst <<
2582 cast<CallInst>(Inst)->setTailCall();
2585 // Ensure that functions that can never have a "tail" keyword due to the
2586 // semantics of ARC truly do not do so.
2587 if (IsNeverTail(Class)) {
2589 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Removing tail "
2590 "keyword from function: " << *Inst <<
2592 cast<CallInst>(Inst)->setTailCall(false);
2595 // Set nounwind as needed.
2596 if (IsNoThrow(Class)) {
2598 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Found no throw"
2599 " class. Setting nounwind on: " << *Inst << "\n");
2600 cast<CallInst>(Inst)->setDoesNotThrow();
2603 if (!IsNoopOnNull(Class)) {
2604 UsedInThisFunction |= 1 << Class;
2608 const Value *Arg = GetObjCArg(Inst);
2610 // ARC calls with null are no-ops. Delete them.
2611 if (isNullOrUndef(Arg)) {
2614 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: ARC calls with "
2615 " null are no-ops. Erasing: " << *Inst << "\n");
2616 EraseInstruction(Inst);
2620 // Keep track of which of retain, release, autorelease, and retain_block
2621 // are actually present in this function.
2622 UsedInThisFunction |= 1 << Class;
2624 // If Arg is a PHI, and one or more incoming values to the
2625 // PHI are null, and the call is control-equivalent to the PHI, and there
2626 // are no relevant side effects between the PHI and the call, the call
2627 // could be pushed up to just those paths with non-null incoming values.
2628 // For now, don't bother splitting critical edges for this.
2629 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
2630 Worklist.push_back(std::make_pair(Inst, Arg));
2632 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
2636 const PHINode *PN = dyn_cast<PHINode>(Arg);
2639 // Determine if the PHI has any null operands, or any incoming
2641 bool HasNull = false;
2642 bool HasCriticalEdges = false;
2643 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2645 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
2646 if (isNullOrUndef(Incoming))
2648 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
2649 .getNumSuccessors() != 1) {
2650 HasCriticalEdges = true;
2654 // If we have null operands and no critical edges, optimize.
2655 if (!HasCriticalEdges && HasNull) {
2656 SmallPtrSet<Instruction *, 4> DependingInstructions;
2657 SmallPtrSet<const BasicBlock *, 4> Visited;
2659 // Check that there is nothing that cares about the reference
2660 // count between the call and the phi.
2663 case IC_RetainBlock:
2664 // These can always be moved up.
2667 // These can't be moved across things that care about the retain
2669 FindDependencies(NeedsPositiveRetainCount, Arg,
2670 Inst->getParent(), Inst,
2671 DependingInstructions, Visited, PA);
2673 case IC_Autorelease:
2674 // These can't be moved across autorelease pool scope boundaries.
2675 FindDependencies(AutoreleasePoolBoundary, Arg,
2676 Inst->getParent(), Inst,
2677 DependingInstructions, Visited, PA);
2680 case IC_AutoreleaseRV:
2681 // Don't move these; the RV optimization depends on the autoreleaseRV
2682 // being tail called, and the retainRV being immediately after a call
2683 // (which might still happen if we get lucky with codegen layout, but
2684 // it's not worth taking the chance).
2687 llvm_unreachable("Invalid dependence flavor");
2690 if (DependingInstructions.size() == 1 &&
2691 *DependingInstructions.begin() == PN) {
2694 // Clone the call into each predecessor that has a non-null value.
2695 CallInst *CInst = cast<CallInst>(Inst);
2696 Type *ParamTy = CInst->getArgOperand(0)->getType();
2697 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2699 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
2700 if (!isNullOrUndef(Incoming)) {
2701 CallInst *Clone = cast<CallInst>(CInst->clone());
2702 Value *Op = PN->getIncomingValue(i);
2703 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
2704 if (Op->getType() != ParamTy)
2705 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
2706 Clone->setArgOperand(0, Op);
2707 Clone->insertBefore(InsertPos);
2709 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Cloning "
2712 "clone at " << *InsertPos << "\n");
2713 Worklist.push_back(std::make_pair(Clone, Incoming));
2716 // Erase the original call.
2717 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
2718 EraseInstruction(CInst);
2722 } while (!Worklist.empty());
2724 DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Finished List.\n");
2727 /// Check for critical edges, loop boundaries, irreducible control flow, or
2728 /// other CFG structures where moving code across the edge would result in it
2729 /// being executed more.
2731 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
2732 DenseMap<const BasicBlock *, BBState> &BBStates,
2733 BBState &MyStates) const {
2734 // If any top-down local-use or possible-dec has a succ which is earlier in
2735 // the sequence, forget it.
2736 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
2737 E = MyStates.top_down_ptr_end(); I != E; ++I)
2738 switch (I->second.GetSeq()) {
2741 const Value *Arg = I->first;
2742 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
2743 bool SomeSuccHasSame = false;
2744 bool AllSuccsHaveSame = true;
2745 PtrState &S = I->second;
2746 succ_const_iterator SI(TI), SE(TI, false);
2748 for (; SI != SE; ++SI) {
2749 Sequence SuccSSeq = S_None;
2750 bool SuccSRRIKnownSafe = false;
2751 // If VisitBottomUp has pointer information for this successor, take
2752 // what we know about it.
2753 DenseMap<const BasicBlock *, BBState>::iterator BBI =
2755 assert(BBI != BBStates.end());
2756 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
2757 SuccSSeq = SuccS.GetSeq();
2758 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
2761 case S_CanRelease: {
2762 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
2763 S.ClearSequenceProgress();
2769 SomeSuccHasSame = true;
2773 case S_MovableRelease:
2774 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
2775 AllSuccsHaveSame = false;
2778 llvm_unreachable("bottom-up pointer in retain state!");
2781 // If the state at the other end of any of the successor edges
2782 // matches the current state, require all edges to match. This
2783 // guards against loops in the middle of a sequence.
2784 if (SomeSuccHasSame && !AllSuccsHaveSame)
2785 S.ClearSequenceProgress();
2788 case S_CanRelease: {
2789 const Value *Arg = I->first;
2790 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
2791 bool SomeSuccHasSame = false;
2792 bool AllSuccsHaveSame = true;
2793 PtrState &S = I->second;
2794 succ_const_iterator SI(TI), SE(TI, false);
2796 for (; SI != SE; ++SI) {
2797 Sequence SuccSSeq = S_None;
2798 bool SuccSRRIKnownSafe = false;
2799 // If VisitBottomUp has pointer information for this successor, take
2800 // what we know about it.
2801 DenseMap<const BasicBlock *, BBState>::iterator BBI =
2803 assert(BBI != BBStates.end());
2804 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
2805 SuccSSeq = SuccS.GetSeq();
2806 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
2809 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
2810 S.ClearSequenceProgress();
2816 SomeSuccHasSame = true;
2820 case S_MovableRelease:
2822 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
2823 AllSuccsHaveSame = false;
2826 llvm_unreachable("bottom-up pointer in retain state!");
2829 // If the state at the other end of any of the successor edges
2830 // matches the current state, require all edges to match. This
2831 // guards against loops in the middle of a sequence.
2832 if (SomeSuccHasSame && !AllSuccsHaveSame)
2833 S.ClearSequenceProgress();
2840 ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
2842 MapVector<Value *, RRInfo> &Retains,
2843 BBState &MyStates) {
2844 bool NestingDetected = false;
2845 InstructionClass Class = GetInstructionClass(Inst);
2846 const Value *Arg = 0;
2850 Arg = GetObjCArg(Inst);
2852 PtrState &S = MyStates.getPtrBottomUpState(Arg);
2854 // If we see two releases in a row on the same pointer. If so, make
2855 // a note, and we'll cicle back to revisit it after we've
2856 // hopefully eliminated the second release, which may allow us to
2857 // eliminate the first release too.
2858 // Theoretically we could implement removal of nested retain+release
2859 // pairs by making PtrState hold a stack of states, but this is
2860 // simple and avoids adding overhead for the non-nested case.
2861 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
2862 DEBUG(dbgs() << "ObjCARCOpt::VisitInstructionBottomUp: Found nested "
2863 "releases (i.e. a release pair)\n");
2864 NestingDetected = true;
2867 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
2868 S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release);
2869 S.RRI.ReleaseMetadata = ReleaseMetadata;
2870 S.RRI.KnownSafe = S.IsKnownIncremented();
2871 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
2872 S.RRI.Calls.insert(Inst);
2874 S.SetKnownPositiveRefCount();
2877 case IC_RetainBlock:
2878 // An objc_retainBlock call with just a use may need to be kept,
2879 // because it may be copying a block from the stack to the heap.
2880 if (!IsRetainBlockOptimizable(Inst))
2885 Arg = GetObjCArg(Inst);
2887 PtrState &S = MyStates.getPtrBottomUpState(Arg);
2888 S.SetKnownPositiveRefCount();
2890 switch (S.GetSeq()) {
2893 case S_MovableRelease:
2895 S.RRI.ReverseInsertPts.clear();
2898 // Don't do retain+release tracking for IC_RetainRV, because it's
2899 // better to let it remain as the first instruction after a call.
2900 if (Class != IC_RetainRV) {
2901 S.RRI.IsRetainBlock = Class == IC_RetainBlock;
2902 Retains[Inst] = S.RRI;
2904 S.ClearSequenceProgress();
2909 llvm_unreachable("bottom-up pointer in retain state!");
2911 return NestingDetected;
2913 case IC_AutoreleasepoolPop:
2914 // Conservatively, clear MyStates for all known pointers.
2915 MyStates.clearBottomUpPointers();
2916 return NestingDetected;
2917 case IC_AutoreleasepoolPush:
2919 // These are irrelevant.
2920 return NestingDetected;
2925 // Consider any other possible effects of this instruction on each
2926 // pointer being tracked.
2927 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
2928 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
2929 const Value *Ptr = MI->first;
2931 continue; // Handled above.
2932 PtrState &S = MI->second;
2933 Sequence Seq = S.GetSeq();
2935 // Check for possible releases.
2936 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
2940 S.SetSeq(S_CanRelease);
2944 case S_MovableRelease:
2949 llvm_unreachable("bottom-up pointer in retain state!");
2953 // Check for possible direct uses.
2956 case S_MovableRelease:
2957 if (CanUse(Inst, Ptr, PA, Class)) {
2958 assert(S.RRI.ReverseInsertPts.empty());
2959 // If this is an invoke instruction, we're scanning it as part of
2960 // one of its successor blocks, since we can't insert code after it
2961 // in its own block, and we don't want to split critical edges.
2962 if (isa<InvokeInst>(Inst))
2963 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
2965 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
2967 } else if (Seq == S_Release &&
2968 (Class == IC_User || Class == IC_CallOrUser)) {
2969 // Non-movable releases depend on any possible objc pointer use.
2971 assert(S.RRI.ReverseInsertPts.empty());
2972 // As above; handle invoke specially.
2973 if (isa<InvokeInst>(Inst))
2974 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
2976 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
2980 if (CanUse(Inst, Ptr, PA, Class))
2988 llvm_unreachable("bottom-up pointer in retain state!");
2992 return NestingDetected;
2996 ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
2997 DenseMap<const BasicBlock *, BBState> &BBStates,
2998 MapVector<Value *, RRInfo> &Retains) {
2999 bool NestingDetected = false;
3000 BBState &MyStates = BBStates[BB];
3002 // Merge the states from each successor to compute the initial state
3003 // for the current block.
3004 BBState::edge_iterator SI(MyStates.succ_begin()),
3005 SE(MyStates.succ_end());
3007 const BasicBlock *Succ = *SI;
3008 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
3009 assert(I != BBStates.end());
3010 MyStates.InitFromSucc(I->second);
3012 for (; SI != SE; ++SI) {
3014 I = BBStates.find(Succ);
3015 assert(I != BBStates.end());
3016 MyStates.MergeSucc(I->second);
3020 // Visit all the instructions, bottom-up.
3021 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
3022 Instruction *Inst = llvm::prior(I);
3024 // Invoke instructions are visited as part of their successors (below).
3025 if (isa<InvokeInst>(Inst))
3028 DEBUG(dbgs() << "ObjCARCOpt::VisitButtonUp: Visiting " << *Inst << "\n");
3030 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
3033 // If there's a predecessor with an invoke, visit the invoke as if it were
3034 // part of this block, since we can't insert code after an invoke in its own
3035 // block, and we don't want to split critical edges.
3036 for (BBState::edge_iterator PI(MyStates.pred_begin()),
3037 PE(MyStates.pred_end()); PI != PE; ++PI) {
3038 BasicBlock *Pred = *PI;
3039 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
3040 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
3043 return NestingDetected;
3047 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
3048 DenseMap<Value *, RRInfo> &Releases,
3049 BBState &MyStates) {
3050 bool NestingDetected = false;
3051 InstructionClass Class = GetInstructionClass(Inst);
3052 const Value *Arg = 0;
3055 case IC_RetainBlock:
3056 // An objc_retainBlock call with just a use may need to be kept,
3057 // because it may be copying a block from the stack to the heap.
3058 if (!IsRetainBlockOptimizable(Inst))
3063 Arg = GetObjCArg(Inst);
3065 PtrState &S = MyStates.getPtrTopDownState(Arg);
3067 // Don't do retain+release tracking for IC_RetainRV, because it's
3068 // better to let it remain as the first instruction after a call.
3069 if (Class != IC_RetainRV) {
3070 // If we see two retains in a row on the same pointer. If so, make
3071 // a note, and we'll cicle back to revisit it after we've
3072 // hopefully eliminated the second retain, which may allow us to
3073 // eliminate the first retain too.
3074 // Theoretically we could implement removal of nested retain+release
3075 // pairs by making PtrState hold a stack of states, but this is
3076 // simple and avoids adding overhead for the non-nested case.
3077 if (S.GetSeq() == S_Retain)
3078 NestingDetected = true;
3080 S.ResetSequenceProgress(S_Retain);
3081 S.RRI.IsRetainBlock = Class == IC_RetainBlock;
3082 S.RRI.KnownSafe = S.IsKnownIncremented();
3083 S.RRI.Calls.insert(Inst);
3086 S.SetKnownPositiveRefCount();
3088 // A retain can be a potential use; procede to the generic checking
3093 Arg = GetObjCArg(Inst);
3095 PtrState &S = MyStates.getPtrTopDownState(Arg);
3098 switch (S.GetSeq()) {
3101 S.RRI.ReverseInsertPts.clear();
3104 S.RRI.ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
3105 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
3106 Releases[Inst] = S.RRI;
3107 S.ClearSequenceProgress();
3113 case S_MovableRelease:
3114 llvm_unreachable("top-down pointer in release state!");
3118 case IC_AutoreleasepoolPop:
3119 // Conservatively, clear MyStates for all known pointers.
3120 MyStates.clearTopDownPointers();
3121 return NestingDetected;
3122 case IC_AutoreleasepoolPush:
3124 // These are irrelevant.
3125 return NestingDetected;
3130 // Consider any other possible effects of this instruction on each
3131 // pointer being tracked.
3132 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
3133 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
3134 const Value *Ptr = MI->first;
3136 continue; // Handled above.
3137 PtrState &S = MI->second;
3138 Sequence Seq = S.GetSeq();
3140 // Check for possible releases.
3141 if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
3145 S.SetSeq(S_CanRelease);
3146 assert(S.RRI.ReverseInsertPts.empty());
3147 S.RRI.ReverseInsertPts.insert(Inst);
3149 // One call can't cause a transition from S_Retain to S_CanRelease
3150 // and S_CanRelease to S_Use. If we've made the first transition,
3159 case S_MovableRelease:
3160 llvm_unreachable("top-down pointer in release state!");
3164 // Check for possible direct uses.
3167 if (CanUse(Inst, Ptr, PA, Class))
3176 case S_MovableRelease:
3177 llvm_unreachable("top-down pointer in release state!");
3181 return NestingDetected;
3185 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
3186 DenseMap<const BasicBlock *, BBState> &BBStates,
3187 DenseMap<Value *, RRInfo> &Releases) {
3188 bool NestingDetected = false;
3189 BBState &MyStates = BBStates[BB];
3191 // Merge the states from each predecessor to compute the initial state
3192 // for the current block.
3193 BBState::edge_iterator PI(MyStates.pred_begin()),
3194 PE(MyStates.pred_end());
3196 const BasicBlock *Pred = *PI;
3197 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
3198 assert(I != BBStates.end());
3199 MyStates.InitFromPred(I->second);
3201 for (; PI != PE; ++PI) {
3203 I = BBStates.find(Pred);
3204 assert(I != BBStates.end());
3205 MyStates.MergePred(I->second);
3209 // Visit all the instructions, top-down.
3210 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
3211 Instruction *Inst = I;
3213 DEBUG(dbgs() << "ObjCARCOpt::VisitTopDown: Visiting " << *Inst << "\n");
3215 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
3218 CheckForCFGHazards(BB, BBStates, MyStates);
3219 return NestingDetected;
3223 ComputePostOrders(Function &F,
3224 SmallVectorImpl<BasicBlock *> &PostOrder,
3225 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
3226 unsigned NoObjCARCExceptionsMDKind,
3227 DenseMap<const BasicBlock *, BBState> &BBStates) {
3228 /// The visited set, for doing DFS walks.
3229 SmallPtrSet<BasicBlock *, 16> Visited;
3231 // Do DFS, computing the PostOrder.
3232 SmallPtrSet<BasicBlock *, 16> OnStack;
3233 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
3235 // Functions always have exactly one entry block, and we don't have
3236 // any other block that we treat like an entry block.
3237 BasicBlock *EntryBB = &F.getEntryBlock();
3238 BBState &MyStates = BBStates[EntryBB];
3239 MyStates.SetAsEntry();
3240 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
3241 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
3242 Visited.insert(EntryBB);
3243 OnStack.insert(EntryBB);
3246 BasicBlock *CurrBB = SuccStack.back().first;
3247 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
3248 succ_iterator SE(TI, false);
3250 while (SuccStack.back().second != SE) {
3251 BasicBlock *SuccBB = *SuccStack.back().second++;
3252 if (Visited.insert(SuccBB)) {
3253 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
3254 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
3255 BBStates[CurrBB].addSucc(SuccBB);
3256 BBState &SuccStates = BBStates[SuccBB];
3257 SuccStates.addPred(CurrBB);
3258 OnStack.insert(SuccBB);
3262 if (!OnStack.count(SuccBB)) {
3263 BBStates[CurrBB].addSucc(SuccBB);
3264 BBStates[SuccBB].addPred(CurrBB);
3267 OnStack.erase(CurrBB);
3268 PostOrder.push_back(CurrBB);
3269 SuccStack.pop_back();
3270 } while (!SuccStack.empty());
3274 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
3275 // Functions may have many exits, and there also blocks which we treat
3276 // as exits due to ignored edges.
3277 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
3278 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
3279 BasicBlock *ExitBB = I;
3280 BBState &MyStates = BBStates[ExitBB];
3281 if (!MyStates.isExit())
3284 MyStates.SetAsExit();
3286 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
3287 Visited.insert(ExitBB);
3288 while (!PredStack.empty()) {
3289 reverse_dfs_next_succ:
3290 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
3291 while (PredStack.back().second != PE) {
3292 BasicBlock *BB = *PredStack.back().second++;
3293 if (Visited.insert(BB)) {
3294 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
3295 goto reverse_dfs_next_succ;
3298 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
3303 // Visit the function both top-down and bottom-up.
3305 ObjCARCOpt::Visit(Function &F,
3306 DenseMap<const BasicBlock *, BBState> &BBStates,
3307 MapVector<Value *, RRInfo> &Retains,
3308 DenseMap<Value *, RRInfo> &Releases) {
3310 // Use reverse-postorder traversals, because we magically know that loops
3311 // will be well behaved, i.e. they won't repeatedly call retain on a single
3312 // pointer without doing a release. We can't use the ReversePostOrderTraversal
3313 // class here because we want the reverse-CFG postorder to consider each
3314 // function exit point, and we want to ignore selected cycle edges.
3315 SmallVector<BasicBlock *, 16> PostOrder;
3316 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
3317 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
3318 NoObjCARCExceptionsMDKind,
3321 // Use reverse-postorder on the reverse CFG for bottom-up.
3322 bool BottomUpNestingDetected = false;
3323 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
3324 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
3326 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
3328 // Use reverse-postorder for top-down.
3329 bool TopDownNestingDetected = false;
3330 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
3331 PostOrder.rbegin(), E = PostOrder.rend();
3333 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
3335 return TopDownNestingDetected && BottomUpNestingDetected;
3338 /// Move the calls in RetainsToMove and ReleasesToMove.
3339 void ObjCARCOpt::MoveCalls(Value *Arg,
3340 RRInfo &RetainsToMove,
3341 RRInfo &ReleasesToMove,
3342 MapVector<Value *, RRInfo> &Retains,
3343 DenseMap<Value *, RRInfo> &Releases,
3344 SmallVectorImpl<Instruction *> &DeadInsts,
3346 Type *ArgTy = Arg->getType();
3347 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
3349 // Insert the new retain and release calls.
3350 for (SmallPtrSet<Instruction *, 2>::const_iterator
3351 PI = ReleasesToMove.ReverseInsertPts.begin(),
3352 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
3353 Instruction *InsertPt = *PI;
3354 Value *MyArg = ArgTy == ParamTy ? Arg :
3355 new BitCastInst(Arg, ParamTy, "", InsertPt);
3357 CallInst::Create(RetainsToMove.IsRetainBlock ?
3358 getRetainBlockCallee(M) : getRetainCallee(M),
3359 MyArg, "", InsertPt);
3360 Call->setDoesNotThrow();
3361 if (RetainsToMove.IsRetainBlock)
3362 Call->setMetadata(CopyOnEscapeMDKind,
3363 MDNode::get(M->getContext(), ArrayRef<Value *>()));
3365 Call->setTailCall();
3367 DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Release: " << *Call
3369 " At insertion point: " << *InsertPt
3372 for (SmallPtrSet<Instruction *, 2>::const_iterator
3373 PI = RetainsToMove.ReverseInsertPts.begin(),
3374 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
3375 Instruction *InsertPt = *PI;
3376 Value *MyArg = ArgTy == ParamTy ? Arg :
3377 new BitCastInst(Arg, ParamTy, "", InsertPt);
3378 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
3380 // Attach a clang.imprecise_release metadata tag, if appropriate.
3381 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
3382 Call->setMetadata(ImpreciseReleaseMDKind, M);
3383 Call->setDoesNotThrow();
3384 if (ReleasesToMove.IsTailCallRelease)
3385 Call->setTailCall();
3387 DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Retain: " << *Call
3389 " At insertion point: " << *InsertPt
3393 // Delete the original retain and release calls.
3394 for (SmallPtrSet<Instruction *, 2>::const_iterator
3395 AI = RetainsToMove.Calls.begin(),
3396 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
3397 Instruction *OrigRetain = *AI;
3398 Retains.blot(OrigRetain);
3399 DeadInsts.push_back(OrigRetain);
3400 DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting retain: " << *OrigRetain <<
3403 for (SmallPtrSet<Instruction *, 2>::const_iterator
3404 AI = ReleasesToMove.Calls.begin(),
3405 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
3406 Instruction *OrigRelease = *AI;
3407 Releases.erase(OrigRelease);
3408 DeadInsts.push_back(OrigRelease);
3409 DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting release: " << *OrigRelease
3415 ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
3417 MapVector<Value *, RRInfo> &Retains,
3418 DenseMap<Value *, RRInfo> &Releases,
3420 SmallVector<Instruction *, 4> &NewRetains,
3421 SmallVector<Instruction *, 4> &NewReleases,
3422 SmallVector<Instruction *, 8> &DeadInsts,
3423 RRInfo &RetainsToMove,
3424 RRInfo &ReleasesToMove,
3427 bool &AnyPairsCompletelyEliminated) {
3428 // If a pair happens in a region where it is known that the reference count
3429 // is already incremented, we can similarly ignore possible decrements.
3430 bool KnownSafeTD = true, KnownSafeBU = true;
3432 // Connect the dots between the top-down-collected RetainsToMove and
3433 // bottom-up-collected ReleasesToMove to form sets of related calls.
3434 // This is an iterative process so that we connect multiple releases
3435 // to multiple retains if needed.
3436 unsigned OldDelta = 0;
3437 unsigned NewDelta = 0;
3438 unsigned OldCount = 0;
3439 unsigned NewCount = 0;
3440 bool FirstRelease = true;
3441 bool FirstRetain = true;
3443 for (SmallVectorImpl<Instruction *>::const_iterator
3444 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
3445 Instruction *NewRetain = *NI;
3446 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
3447 assert(It != Retains.end());
3448 const RRInfo &NewRetainRRI = It->second;
3449 KnownSafeTD &= NewRetainRRI.KnownSafe;
3450 for (SmallPtrSet<Instruction *, 2>::const_iterator
3451 LI = NewRetainRRI.Calls.begin(),
3452 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
3453 Instruction *NewRetainRelease = *LI;
3454 DenseMap<Value *, RRInfo>::const_iterator Jt =
3455 Releases.find(NewRetainRelease);
3456 if (Jt == Releases.end())
3458 const RRInfo &NewRetainReleaseRRI = Jt->second;
3459 assert(NewRetainReleaseRRI.Calls.count(NewRetain));
3460 if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
3462 BBStates[NewRetainRelease->getParent()].GetAllPathCount();
3464 // Merge the ReleaseMetadata and IsTailCallRelease values.
3466 ReleasesToMove.ReleaseMetadata =
3467 NewRetainReleaseRRI.ReleaseMetadata;
3468 ReleasesToMove.IsTailCallRelease =
3469 NewRetainReleaseRRI.IsTailCallRelease;
3470 FirstRelease = false;
3472 if (ReleasesToMove.ReleaseMetadata !=
3473 NewRetainReleaseRRI.ReleaseMetadata)
3474 ReleasesToMove.ReleaseMetadata = 0;
3475 if (ReleasesToMove.IsTailCallRelease !=
3476 NewRetainReleaseRRI.IsTailCallRelease)
3477 ReleasesToMove.IsTailCallRelease = false;
3480 // Collect the optimal insertion points.
3482 for (SmallPtrSet<Instruction *, 2>::const_iterator
3483 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
3484 RE = NewRetainReleaseRRI.ReverseInsertPts.end();
3486 Instruction *RIP = *RI;
3487 if (ReleasesToMove.ReverseInsertPts.insert(RIP))
3488 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
3490 NewReleases.push_back(NewRetainRelease);
3495 if (NewReleases.empty()) break;
3497 // Back the other way.
3498 for (SmallVectorImpl<Instruction *>::const_iterator
3499 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
3500 Instruction *NewRelease = *NI;
3501 DenseMap<Value *, RRInfo>::const_iterator It =
3502 Releases.find(NewRelease);
3503 assert(It != Releases.end());
3504 const RRInfo &NewReleaseRRI = It->second;
3505 KnownSafeBU &= NewReleaseRRI.KnownSafe;
3506 for (SmallPtrSet<Instruction *, 2>::const_iterator
3507 LI = NewReleaseRRI.Calls.begin(),
3508 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
3509 Instruction *NewReleaseRetain = *LI;
3510 MapVector<Value *, RRInfo>::const_iterator Jt =
3511 Retains.find(NewReleaseRetain);
3512 if (Jt == Retains.end())
3514 const RRInfo &NewReleaseRetainRRI = Jt->second;
3515 assert(NewReleaseRetainRRI.Calls.count(NewRelease));
3516 if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
3517 unsigned PathCount =
3518 BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
3519 OldDelta += PathCount;
3520 OldCount += PathCount;
3522 // Merge the IsRetainBlock values.
3524 RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock;
3525 FirstRetain = false;
3526 } else if (ReleasesToMove.IsRetainBlock !=
3527 NewReleaseRetainRRI.IsRetainBlock)
3528 // It's not possible to merge the sequences if one uses
3529 // objc_retain and the other uses objc_retainBlock.
3532 // Collect the optimal insertion points.
3534 for (SmallPtrSet<Instruction *, 2>::const_iterator
3535 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
3536 RE = NewReleaseRetainRRI.ReverseInsertPts.end();
3538 Instruction *RIP = *RI;
3539 if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
3540 PathCount = BBStates[RIP->getParent()].GetAllPathCount();
3541 NewDelta += PathCount;
3542 NewCount += PathCount;
3545 NewRetains.push_back(NewReleaseRetain);
3549 NewReleases.clear();
3550 if (NewRetains.empty()) break;
3553 // If the pointer is known incremented or nested, we can safely delete the
3554 // pair regardless of what's between them.
3555 if (KnownSafeTD || KnownSafeBU) {
3556 RetainsToMove.ReverseInsertPts.clear();
3557 ReleasesToMove.ReverseInsertPts.clear();
3560 // Determine whether the new insertion points we computed preserve the
3561 // balance of retain and release calls through the program.
3562 // TODO: If the fully aggressive solution isn't valid, try to find a
3563 // less aggressive solution which is.
3568 // Determine whether the original call points are balanced in the retain and
3569 // release calls through the program. If not, conservatively don't touch
3571 // TODO: It's theoretically possible to do code motion in this case, as
3572 // long as the existing imbalances are maintained.
3577 assert(OldCount != 0 && "Unreachable code?");
3578 NumRRs += OldCount - NewCount;
3580 // Set to true if we completely removed any RR pairs.
3581 AnyPairsCompletelyEliminated |= NewCount == 0;
3583 // We can move calls!
3587 /// Identify pairings between the retains and releases, and delete and/or move
3590 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
3592 MapVector<Value *, RRInfo> &Retains,
3593 DenseMap<Value *, RRInfo> &Releases,
3595 bool AnyPairsCompletelyEliminated = false;
3596 RRInfo RetainsToMove;
3597 RRInfo ReleasesToMove;
3598 SmallVector<Instruction *, 4> NewRetains;
3599 SmallVector<Instruction *, 4> NewReleases;
3600 SmallVector<Instruction *, 8> DeadInsts;
3602 // Visit each retain.
3603 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
3604 E = Retains.end(); I != E; ++I) {
3605 Value *V = I->first;
3606 if (!V) continue; // blotted
3608 Instruction *Retain = cast<Instruction>(V);
3610 DEBUG(dbgs() << "ObjCARCOpt::PerformCodePlacement: Visiting: " << *Retain
3613 Value *Arg = GetObjCArg(Retain);
3615 // If the object being released is in static or stack storage, we know it's
3616 // not being managed by ObjC reference counting, so we can delete pairs
3617 // regardless of what possible decrements or uses lie between them.
3618 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
3620 // A constant pointer can't be pointing to an object on the heap. It may
3621 // be reference-counted, but it won't be deleted.
3622 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
3623 if (const GlobalVariable *GV =
3624 dyn_cast<GlobalVariable>(
3625 StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
3626 if (GV->isConstant())
3629 // Connect the dots between the top-down-collected RetainsToMove and
3630 // bottom-up-collected ReleasesToMove to form sets of related calls.
3631 NewRetains.push_back(Retain);
3632 bool PerformMoveCalls =
3633 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
3634 NewReleases, DeadInsts, RetainsToMove,
3635 ReleasesToMove, Arg, KnownSafe,
3636 AnyPairsCompletelyEliminated);
3638 if (PerformMoveCalls) {
3639 // Ok, everything checks out and we're all set. Let's move/delete some
3641 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
3642 Retains, Releases, DeadInsts, M);
3645 // Clean up state for next retain.
3646 NewReleases.clear();
3648 RetainsToMove.clear();
3649 ReleasesToMove.clear();
3652 // Now that we're done moving everything, we can delete the newly dead
3653 // instructions, as we no longer need them as insert points.
3654 while (!DeadInsts.empty())
3655 EraseInstruction(DeadInsts.pop_back_val());
3657 return AnyPairsCompletelyEliminated;
3660 /// Weak pointer optimizations.
3661 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
3662 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
3663 // itself because it uses AliasAnalysis and we need to do provenance
3665 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
3666 Instruction *Inst = &*I++;
3668 DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Visiting: " << *Inst <<
3671 InstructionClass Class = GetBasicInstructionClass(Inst);
3672 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
3675 // Delete objc_loadWeak calls with no users.
3676 if (Class == IC_LoadWeak && Inst->use_empty()) {
3677 Inst->eraseFromParent();
3681 // TODO: For now, just look for an earlier available version of this value
3682 // within the same block. Theoretically, we could do memdep-style non-local
3683 // analysis too, but that would want caching. A better approach would be to
3684 // use the technique that EarlyCSE uses.
3685 inst_iterator Current = llvm::prior(I);
3686 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
3687 for (BasicBlock::iterator B = CurrentBB->begin(),
3688 J = Current.getInstructionIterator();
3690 Instruction *EarlierInst = &*llvm::prior(J);
3691 InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
3692 switch (EarlierClass) {
3694 case IC_LoadWeakRetained: {
3695 // If this is loading from the same pointer, replace this load's value
3697 CallInst *Call = cast<CallInst>(Inst);
3698 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
3699 Value *Arg = Call->getArgOperand(0);
3700 Value *EarlierArg = EarlierCall->getArgOperand(0);
3701 switch (PA.getAA()->alias(Arg, EarlierArg)) {
3702 case AliasAnalysis::MustAlias:
3704 // If the load has a builtin retain, insert a plain retain for it.
3705 if (Class == IC_LoadWeakRetained) {
3707 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
3711 // Zap the fully redundant load.
3712 Call->replaceAllUsesWith(EarlierCall);
3713 Call->eraseFromParent();
3715 case AliasAnalysis::MayAlias:
3716 case AliasAnalysis::PartialAlias:
3718 case AliasAnalysis::NoAlias:
3725 // If this is storing to the same pointer and has the same size etc.
3726 // replace this load's value with the stored value.
3727 CallInst *Call = cast<CallInst>(Inst);
3728 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
3729 Value *Arg = Call->getArgOperand(0);
3730 Value *EarlierArg = EarlierCall->getArgOperand(0);
3731 switch (PA.getAA()->alias(Arg, EarlierArg)) {
3732 case AliasAnalysis::MustAlias:
3734 // If the load has a builtin retain, insert a plain retain for it.
3735 if (Class == IC_LoadWeakRetained) {
3737 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
3741 // Zap the fully redundant load.
3742 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
3743 Call->eraseFromParent();
3745 case AliasAnalysis::MayAlias:
3746 case AliasAnalysis::PartialAlias:
3748 case AliasAnalysis::NoAlias:
3755 // TOOD: Grab the copied value.
3757 case IC_AutoreleasepoolPush:
3760 // Weak pointers are only modified through the weak entry points
3761 // (and arbitrary calls, which could call the weak entry points).
3764 // Anything else could modify the weak pointer.
3771 // Then, for each destroyWeak with an alloca operand, check to see if
3772 // the alloca and all its users can be zapped.
3773 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
3774 Instruction *Inst = &*I++;
3775 InstructionClass Class = GetBasicInstructionClass(Inst);
3776 if (Class != IC_DestroyWeak)
3779 CallInst *Call = cast<CallInst>(Inst);
3780 Value *Arg = Call->getArgOperand(0);
3781 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
3782 for (Value::use_iterator UI = Alloca->use_begin(),
3783 UE = Alloca->use_end(); UI != UE; ++UI) {
3784 const Instruction *UserInst = cast<Instruction>(*UI);
3785 switch (GetBasicInstructionClass(UserInst)) {
3788 case IC_DestroyWeak:
3795 for (Value::use_iterator UI = Alloca->use_begin(),
3796 UE = Alloca->use_end(); UI != UE; ) {
3797 CallInst *UserInst = cast<CallInst>(*UI++);
3798 switch (GetBasicInstructionClass(UserInst)) {
3801 // These functions return their second argument.
3802 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
3804 case IC_DestroyWeak:
3808 llvm_unreachable("alloca really is used!");
3810 UserInst->eraseFromParent();
3812 Alloca->eraseFromParent();
3817 DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Finished List.\n\n");
3821 /// Identify program paths which execute sequences of retains and releases which
3822 /// can be eliminated.
3823 bool ObjCARCOpt::OptimizeSequences(Function &F) {
3824 /// Releases, Retains - These are used to store the results of the main flow
3825 /// analysis. These use Value* as the key instead of Instruction* so that the
3826 /// map stays valid when we get around to rewriting code and calls get
3827 /// replaced by arguments.
3828 DenseMap<Value *, RRInfo> Releases;
3829 MapVector<Value *, RRInfo> Retains;
3831 /// This is used during the traversal of the function to track the
3832 /// states for each identified object at each block.
3833 DenseMap<const BasicBlock *, BBState> BBStates;
3835 // Analyze the CFG of the function, and all instructions.
3836 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
3839 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
3843 /// Look for this pattern:
3845 /// %call = call i8* @something(...)
3846 /// %2 = call i8* @objc_retain(i8* %call)
3847 /// %3 = call i8* @objc_autorelease(i8* %2)
3850 /// And delete the retain and autorelease.
3852 /// Otherwise if it's just this:
3854 /// %3 = call i8* @objc_autorelease(i8* %2)
3857 /// convert the autorelease to autoreleaseRV.
3858 void ObjCARCOpt::OptimizeReturns(Function &F) {
3859 if (!F.getReturnType()->isPointerTy())
3862 SmallPtrSet<Instruction *, 4> DependingInstructions;
3863 SmallPtrSet<const BasicBlock *, 4> Visited;
3864 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
3865 BasicBlock *BB = FI;
3866 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
3868 DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Visiting: " << *Ret << "\n");
3872 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
3873 FindDependencies(NeedsPositiveRetainCount, Arg,
3874 BB, Ret, DependingInstructions, Visited, PA);
3875 if (DependingInstructions.size() != 1)
3879 CallInst *Autorelease =
3880 dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
3883 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
3884 if (!IsAutorelease(AutoreleaseClass))
3886 if (GetObjCArg(Autorelease) != Arg)
3889 DependingInstructions.clear();
3892 // Check that there is nothing that can affect the reference
3893 // count between the autorelease and the retain.
3894 FindDependencies(CanChangeRetainCount, Arg,
3895 BB, Autorelease, DependingInstructions, Visited, PA);
3896 if (DependingInstructions.size() != 1)
3901 dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
3903 // Check that we found a retain with the same argument.
3905 !IsRetain(GetBasicInstructionClass(Retain)) ||
3906 GetObjCArg(Retain) != Arg)
3909 DependingInstructions.clear();
3912 // Convert the autorelease to an autoreleaseRV, since it's
3913 // returning the value.
3914 if (AutoreleaseClass == IC_Autorelease) {
3915 DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Converting autorelease "
3916 "=> autoreleaseRV since it's returning a value.\n"
3917 " In: " << *Autorelease
3919 Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent()));
3920 DEBUG(dbgs() << " Out: " << *Autorelease
3922 Autorelease->setTailCall(); // Always tail call autoreleaseRV.
3923 AutoreleaseClass = IC_AutoreleaseRV;
3926 // Check that there is nothing that can affect the reference
3927 // count between the retain and the call.
3928 // Note that Retain need not be in BB.
3929 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
3930 DependingInstructions, Visited, PA);
3931 if (DependingInstructions.size() != 1)
3936 dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
3938 // Check that the pointer is the return value of the call.
3939 if (!Call || Arg != Call)
3942 // Check that the call is a regular call.
3943 InstructionClass Class = GetBasicInstructionClass(Call);
3944 if (Class != IC_CallOrUser && Class != IC_Call)
3947 // If so, we can zap the retain and autorelease.
3950 DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Erasing: " << *Retain
3952 << *Autorelease << "\n");
3953 EraseInstruction(Retain);
3954 EraseInstruction(Autorelease);
3960 DependingInstructions.clear();
3964 DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Finished List.\n\n");
3968 bool ObjCARCOpt::doInitialization(Module &M) {
3972 // If nothing in the Module uses ARC, don't do anything.
3973 Run = ModuleHasARC(M);
3977 // Identify the imprecise release metadata kind.
3978 ImpreciseReleaseMDKind =
3979 M.getContext().getMDKindID("clang.imprecise_release");
3980 CopyOnEscapeMDKind =
3981 M.getContext().getMDKindID("clang.arc.copy_on_escape");
3982 NoObjCARCExceptionsMDKind =
3983 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
3985 // Intuitively, objc_retain and others are nocapture, however in practice
3986 // they are not, because they return their argument value. And objc_release
3987 // calls finalizers which can have arbitrary side effects.
3989 // These are initialized lazily.
3991 AutoreleaseRVCallee = 0;
3994 RetainBlockCallee = 0;
3995 AutoreleaseCallee = 0;
4000 bool ObjCARCOpt::runOnFunction(Function &F) {
4004 // If nothing in the Module uses ARC, don't do anything.
4010 DEBUG(dbgs() << "ObjCARCOpt: Visiting Function: " << F.getName() << "\n");
4012 PA.setAA(&getAnalysis<AliasAnalysis>());
4014 // This pass performs several distinct transformations. As a compile-time aid
4015 // when compiling code that isn't ObjC, skip these if the relevant ObjC
4016 // library functions aren't declared.
4018 // Preliminary optimizations. This also computs UsedInThisFunction.
4019 OptimizeIndividualCalls(F);
4021 // Optimizations for weak pointers.
4022 if (UsedInThisFunction & ((1 << IC_LoadWeak) |
4023 (1 << IC_LoadWeakRetained) |
4024 (1 << IC_StoreWeak) |
4025 (1 << IC_InitWeak) |
4026 (1 << IC_CopyWeak) |
4027 (1 << IC_MoveWeak) |
4028 (1 << IC_DestroyWeak)))
4029 OptimizeWeakCalls(F);
4031 // Optimizations for retain+release pairs.
4032 if (UsedInThisFunction & ((1 << IC_Retain) |
4033 (1 << IC_RetainRV) |
4034 (1 << IC_RetainBlock)))
4035 if (UsedInThisFunction & (1 << IC_Release))
4036 // Run OptimizeSequences until it either stops making changes or
4037 // no retain+release pair nesting is detected.
4038 while (OptimizeSequences(F)) {}
4040 // Optimizations if objc_autorelease is used.
4041 if (UsedInThisFunction & ((1 << IC_Autorelease) |
4042 (1 << IC_AutoreleaseRV)))
4045 DEBUG(dbgs() << "\n");
4050 void ObjCARCOpt::releaseMemory() {
4056 /// \defgroup ARCContract ARC Contraction.
4059 // TODO: ObjCARCContract could insert PHI nodes when uses aren't
4060 // dominated by single calls.
4062 #include "llvm/Analysis/Dominators.h"
4063 #include "llvm/IR/InlineAsm.h"
4064 #include "llvm/IR/Operator.h"
4066 STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed");
4069 /// \brief Late ARC optimizations
4071 /// These change the IR in a way that makes it difficult to be analyzed by
4072 /// ObjCARCOpt, so it's run late.
4073 class ObjCARCContract : public FunctionPass {
4077 ProvenanceAnalysis PA;
4079 /// A flag indicating whether this optimization pass should run.
4082 /// Declarations for ObjC runtime functions, for use in creating calls to
4083 /// them. These are initialized lazily to avoid cluttering up the Module
4084 /// with unused declarations.
4086 /// Declaration for objc_storeStrong().
4087 Constant *StoreStrongCallee;
4088 /// Declaration for objc_retainAutorelease().
4089 Constant *RetainAutoreleaseCallee;
4090 /// Declaration for objc_retainAutoreleaseReturnValue().
4091 Constant *RetainAutoreleaseRVCallee;
4093 /// The inline asm string to insert between calls and RetainRV calls to make
4094 /// the optimization work on targets which need it.
4095 const MDString *RetainRVMarker;
4097 /// The set of inserted objc_storeStrong calls. If at the end of walking the
4098 /// function we have found no alloca instructions, these calls can be marked
4100 SmallPtrSet<CallInst *, 8> StoreStrongCalls;
4102 Constant *getStoreStrongCallee(Module *M);
4103 Constant *getRetainAutoreleaseCallee(Module *M);
4104 Constant *getRetainAutoreleaseRVCallee(Module *M);
4106 bool ContractAutorelease(Function &F, Instruction *Autorelease,
4107 InstructionClass Class,
4108 SmallPtrSet<Instruction *, 4>
4109 &DependingInstructions,
4110 SmallPtrSet<const BasicBlock *, 4>
4113 void ContractRelease(Instruction *Release,
4114 inst_iterator &Iter);
4116 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
4117 virtual bool doInitialization(Module &M);
4118 virtual bool runOnFunction(Function &F);
4122 ObjCARCContract() : FunctionPass(ID) {
4123 initializeObjCARCContractPass(*PassRegistry::getPassRegistry());
4128 char ObjCARCContract::ID = 0;
4129 INITIALIZE_PASS_BEGIN(ObjCARCContract,
4130 "objc-arc-contract", "ObjC ARC contraction", false, false)
4131 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
4132 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
4133 INITIALIZE_PASS_END(ObjCARCContract,
4134 "objc-arc-contract", "ObjC ARC contraction", false, false)
4136 Pass *llvm::createObjCARCContractPass() {
4137 return new ObjCARCContract();
4140 void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const {
4141 AU.addRequired<AliasAnalysis>();
4142 AU.addRequired<DominatorTree>();
4143 AU.setPreservesCFG();
4146 Constant *ObjCARCContract::getStoreStrongCallee(Module *M) {
4147 if (!StoreStrongCallee) {
4148 LLVMContext &C = M->getContext();
4149 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
4150 Type *I8XX = PointerType::getUnqual(I8X);
4151 Type *Params[] = { I8XX, I8X };
4153 AttributeSet Attr = AttributeSet()
4154 .addAttribute(M->getContext(), AttributeSet::FunctionIndex,
4155 Attribute::NoUnwind)
4156 .addAttribute(M->getContext(), 1, Attribute::NoCapture);
4159 M->getOrInsertFunction(
4161 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
4164 return StoreStrongCallee;
4167 Constant *ObjCARCContract::getRetainAutoreleaseCallee(Module *M) {
4168 if (!RetainAutoreleaseCallee) {
4169 LLVMContext &C = M->getContext();
4170 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
4171 Type *Params[] = { I8X };
4172 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
4173 AttributeSet Attribute =
4174 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
4175 Attribute::NoUnwind);
4176 RetainAutoreleaseCallee =
4177 M->getOrInsertFunction("objc_retainAutorelease", FTy, Attribute);
4179 return RetainAutoreleaseCallee;
4182 Constant *ObjCARCContract::getRetainAutoreleaseRVCallee(Module *M) {
4183 if (!RetainAutoreleaseRVCallee) {
4184 LLVMContext &C = M->getContext();
4185 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
4186 Type *Params[] = { I8X };
4187 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
4188 AttributeSet Attribute =
4189 AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
4190 Attribute::NoUnwind);
4191 RetainAutoreleaseRVCallee =
4192 M->getOrInsertFunction("objc_retainAutoreleaseReturnValue", FTy,
4195 return RetainAutoreleaseRVCallee;
4198 /// Merge an autorelease with a retain into a fused call.
4200 ObjCARCContract::ContractAutorelease(Function &F, Instruction *Autorelease,
4201 InstructionClass Class,
4202 SmallPtrSet<Instruction *, 4>
4203 &DependingInstructions,
4204 SmallPtrSet<const BasicBlock *, 4>
4206 const Value *Arg = GetObjCArg(Autorelease);
4208 // Check that there are no instructions between the retain and the autorelease
4209 // (such as an autorelease_pop) which may change the count.
4210 CallInst *Retain = 0;
4211 if (Class == IC_AutoreleaseRV)
4212 FindDependencies(RetainAutoreleaseRVDep, Arg,
4213 Autorelease->getParent(), Autorelease,
4214 DependingInstructions, Visited, PA);
4216 FindDependencies(RetainAutoreleaseDep, Arg,
4217 Autorelease->getParent(), Autorelease,
4218 DependingInstructions, Visited, PA);
4221 if (DependingInstructions.size() != 1) {
4222 DependingInstructions.clear();
4226 Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
4227 DependingInstructions.clear();
4230 GetBasicInstructionClass(Retain) != IC_Retain ||
4231 GetObjCArg(Retain) != Arg)
4237 DEBUG(dbgs() << "ObjCARCContract::ContractAutorelease: Fusing "
4238 "retain/autorelease. Erasing: " << *Autorelease << "\n"
4240 << *Retain << "\n");
4242 if (Class == IC_AutoreleaseRV)
4243 Retain->setCalledFunction(getRetainAutoreleaseRVCallee(F.getParent()));
4245 Retain->setCalledFunction(getRetainAutoreleaseCallee(F.getParent()));
4247 DEBUG(dbgs() << " New Retain: "
4248 << *Retain << "\n");
4250 EraseInstruction(Autorelease);
4254 /// Attempt to merge an objc_release with a store, load, and objc_retain to form
4255 /// an objc_storeStrong. This can be a little tricky because the instructions
4256 /// don't always appear in order, and there may be unrelated intervening
4258 void ObjCARCContract::ContractRelease(Instruction *Release,
4259 inst_iterator &Iter) {
4260 LoadInst *Load = dyn_cast<LoadInst>(GetObjCArg(Release));
4261 if (!Load || !Load->isSimple()) return;
4263 // For now, require everything to be in one basic block.
4264 BasicBlock *BB = Release->getParent();
4265 if (Load->getParent() != BB) return;
4267 // Walk down to find the store and the release, which may be in either order.
4268 BasicBlock::iterator I = Load, End = BB->end();
4270 AliasAnalysis::Location Loc = AA->getLocation(Load);
4271 StoreInst *Store = 0;
4272 bool SawRelease = false;
4273 for (; !Store || !SawRelease; ++I) {
4277 Instruction *Inst = I;
4278 if (Inst == Release) {
4283 InstructionClass Class = GetBasicInstructionClass(Inst);
4285 // Unrelated retains are harmless.
4286 if (IsRetain(Class))
4290 // The store is the point where we're going to put the objc_storeStrong,
4291 // so make sure there are no uses after it.
4292 if (CanUse(Inst, Load, PA, Class))
4294 } else if (AA->getModRefInfo(Inst, Loc) & AliasAnalysis::Mod) {
4295 // We are moving the load down to the store, so check for anything
4296 // else which writes to the memory between the load and the store.
4297 Store = dyn_cast<StoreInst>(Inst);
4298 if (!Store || !Store->isSimple()) return;
4299 if (Store->getPointerOperand() != Loc.Ptr) return;
4303 Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand());
4305 // Walk up to find the retain.
4307 BasicBlock::iterator Begin = BB->begin();
4308 while (I != Begin && GetBasicInstructionClass(I) != IC_Retain)
4310 Instruction *Retain = I;
4311 if (GetBasicInstructionClass(Retain) != IC_Retain) return;
4312 if (GetObjCArg(Retain) != New) return;
4317 LLVMContext &C = Release->getContext();
4318 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
4319 Type *I8XX = PointerType::getUnqual(I8X);
4321 Value *Args[] = { Load->getPointerOperand(), New };
4322 if (Args[0]->getType() != I8XX)
4323 Args[0] = new BitCastInst(Args[0], I8XX, "", Store);
4324 if (Args[1]->getType() != I8X)
4325 Args[1] = new BitCastInst(Args[1], I8X, "", Store);
4326 CallInst *StoreStrong =
4327 CallInst::Create(getStoreStrongCallee(BB->getParent()->getParent()),
4329 StoreStrong->setDoesNotThrow();
4330 StoreStrong->setDebugLoc(Store->getDebugLoc());
4332 // We can't set the tail flag yet, because we haven't yet determined
4333 // whether there are any escaping allocas. Remember this call, so that
4334 // we can set the tail flag once we know it's safe.
4335 StoreStrongCalls.insert(StoreStrong);
4337 if (&*Iter == Store) ++Iter;
4338 Store->eraseFromParent();
4339 Release->eraseFromParent();
4340 EraseInstruction(Retain);
4341 if (Load->use_empty())
4342 Load->eraseFromParent();
4345 bool ObjCARCContract::doInitialization(Module &M) {
4346 // If nothing in the Module uses ARC, don't do anything.
4347 Run = ModuleHasARC(M);
4351 // These are initialized lazily.
4352 StoreStrongCallee = 0;
4353 RetainAutoreleaseCallee = 0;
4354 RetainAutoreleaseRVCallee = 0;
4356 // Initialize RetainRVMarker.
4358 if (NamedMDNode *NMD =
4359 M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker"))
4360 if (NMD->getNumOperands() == 1) {
4361 const MDNode *N = NMD->getOperand(0);
4362 if (N->getNumOperands() == 1)
4363 if (const MDString *S = dyn_cast<MDString>(N->getOperand(0)))
4370 bool ObjCARCContract::runOnFunction(Function &F) {
4374 // If nothing in the Module uses ARC, don't do anything.
4379 AA = &getAnalysis<AliasAnalysis>();
4380 DT = &getAnalysis<DominatorTree>();
4382 PA.setAA(&getAnalysis<AliasAnalysis>());
4384 // Track whether it's ok to mark objc_storeStrong calls with the "tail"
4385 // keyword. Be conservative if the function has variadic arguments.
4386 // It seems that functions which "return twice" are also unsafe for the
4387 // "tail" argument, because they are setjmp, which could need to
4388 // return to an earlier stack state.
4389 bool TailOkForStoreStrongs = !F.isVarArg() &&
4390 !F.callsFunctionThatReturnsTwice();
4392 // For ObjC library calls which return their argument, replace uses of the
4393 // argument with uses of the call return value, if it dominates the use. This
4394 // reduces register pressure.
4395 SmallPtrSet<Instruction *, 4> DependingInstructions;
4396 SmallPtrSet<const BasicBlock *, 4> Visited;
4397 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
4398 Instruction *Inst = &*I++;
4400 DEBUG(dbgs() << "ObjCARCContract: Visiting: " << *Inst << "\n");
4402 // Only these library routines return their argument. In particular,
4403 // objc_retainBlock does not necessarily return its argument.
4404 InstructionClass Class = GetBasicInstructionClass(Inst);
4407 case IC_FusedRetainAutorelease:
4408 case IC_FusedRetainAutoreleaseRV:
4410 case IC_Autorelease:
4411 case IC_AutoreleaseRV:
4412 if (ContractAutorelease(F, Inst, Class, DependingInstructions, Visited))
4416 // If we're compiling for a target which needs a special inline-asm
4417 // marker to do the retainAutoreleasedReturnValue optimization,
4419 if (!RetainRVMarker)
4421 BasicBlock::iterator BBI = Inst;
4422 BasicBlock *InstParent = Inst->getParent();
4424 // Step up to see if the call immediately precedes the RetainRV call.
4425 // If it's an invoke, we have to cross a block boundary. And we have
4426 // to carefully dodge no-op instructions.
4428 if (&*BBI == InstParent->begin()) {
4429 BasicBlock *Pred = InstParent->getSinglePredecessor();
4431 goto decline_rv_optimization;
4432 BBI = Pred->getTerminator();
4436 } while (isNoopInstruction(BBI));
4438 if (&*BBI == GetObjCArg(Inst)) {
4439 DEBUG(dbgs() << "ObjCARCContract: Adding inline asm marker for "
4440 "retainAutoreleasedReturnValue optimization.\n");
4443 InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()),
4444 /*isVarArg=*/false),
4445 RetainRVMarker->getString(),
4446 /*Constraints=*/"", /*hasSideEffects=*/true);
4447 CallInst::Create(IA, "", Inst);
4449 decline_rv_optimization:
4453 // objc_initWeak(p, null) => *p = null
4454 CallInst *CI = cast<CallInst>(Inst);
4455 if (isNullOrUndef(CI->getArgOperand(1))) {
4457 ConstantPointerNull::get(cast<PointerType>(CI->getType()));
4459 new StoreInst(Null, CI->getArgOperand(0), CI);
4461 DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n"
4462 << " New = " << *Null << "\n");
4464 CI->replaceAllUsesWith(Null);
4465 CI->eraseFromParent();
4470 ContractRelease(Inst, I);
4473 // Be conservative if the function has any alloca instructions.
4474 // Technically we only care about escaping alloca instructions,
4475 // but this is sufficient to handle some interesting cases.
4476 if (isa<AllocaInst>(Inst))
4477 TailOkForStoreStrongs = false;
4483 DEBUG(dbgs() << "ObjCARCContract: Finished List.\n\n");
4485 // Don't use GetObjCArg because we don't want to look through bitcasts
4486 // and such; to do the replacement, the argument must have type i8*.
4487 const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
4489 // If we're compiling bugpointed code, don't get in trouble.
4490 if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
4492 // Look through the uses of the pointer.
4493 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
4495 Use &U = UI.getUse();
4496 unsigned OperandNo = UI.getOperandNo();
4497 ++UI; // Increment UI now, because we may unlink its element.
4499 // If the call's return value dominates a use of the call's argument
4500 // value, rewrite the use to use the return value. We check for
4501 // reachability here because an unreachable call is considered to
4502 // trivially dominate itself, which would lead us to rewriting its
4503 // argument in terms of its return value, which would lead to
4504 // infinite loops in GetObjCArg.
4505 if (DT->isReachableFromEntry(U) && DT->dominates(Inst, U)) {
4507 Instruction *Replacement = Inst;
4508 Type *UseTy = U.get()->getType();
4509 if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) {
4510 // For PHI nodes, insert the bitcast in the predecessor block.
4511 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
4512 BasicBlock *BB = PHI->getIncomingBlock(ValNo);
4513 if (Replacement->getType() != UseTy)
4514 Replacement = new BitCastInst(Replacement, UseTy, "",
4516 // While we're here, rewrite all edges for this PHI, rather
4517 // than just one use at a time, to minimize the number of
4518 // bitcasts we emit.
4519 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
4520 if (PHI->getIncomingBlock(i) == BB) {
4521 // Keep the UI iterator valid.
4522 if (&PHI->getOperandUse(
4523 PHINode::getOperandNumForIncomingValue(i)) ==
4526 PHI->setIncomingValue(i, Replacement);
4529 if (Replacement->getType() != UseTy)
4530 Replacement = new BitCastInst(Replacement, UseTy, "",
4531 cast<Instruction>(U.getUser()));
4537 // If Arg is a no-op casted pointer, strip one level of casts and iterate.
4538 if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg))
4539 Arg = BI->getOperand(0);
4540 else if (isa<GEPOperator>(Arg) &&
4541 cast<GEPOperator>(Arg)->hasAllZeroIndices())
4542 Arg = cast<GEPOperator>(Arg)->getPointerOperand();
4543 else if (isa<GlobalAlias>(Arg) &&
4544 !cast<GlobalAlias>(Arg)->mayBeOverridden())
4545 Arg = cast<GlobalAlias>(Arg)->getAliasee();
4551 // If this function has no escaping allocas or suspicious vararg usage,
4552 // objc_storeStrong calls can be marked with the "tail" keyword.
4553 if (TailOkForStoreStrongs)
4554 for (SmallPtrSet<CallInst *, 8>::iterator I = StoreStrongCalls.begin(),
4555 E = StoreStrongCalls.end(); I != E; ++I)
4556 (*I)->setTailCall();
4557 StoreStrongCalls.clear();