1 //===- ObjCARC.h - ObjC ARC Optimization --------------*- mode: c++ -*-----===//
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 common definitions/declarations used by the ObjC ARC
11 /// Optimizer. ARC stands for Automatic Reference Counting and is a system for
12 /// managing reference counts for objects in Objective C.
14 /// WARNING: This file knows about certain library functions. It recognizes them
15 /// by name, and hardwires knowledge of their semantics.
17 /// WARNING: This file knows about how certain Objective-C library functions are
18 /// used. Naive LLVM IR transformations which would otherwise be
19 /// behavior-preserving may break these assumptions.
21 //===----------------------------------------------------------------------===//
23 #ifndef LLVM_TRANSFORMS_SCALAR_OBJCARC_H
24 #define LLVM_TRANSFORMS_SCALAR_OBJCARC_H
26 #include "llvm/ADT/StringSwitch.h"
27 #include "llvm/Analysis/AliasAnalysis.h"
28 #include "llvm/Analysis/Passes.h"
29 #include "llvm/Analysis/ValueTracking.h"
30 #include "llvm/IR/Module.h"
31 #include "llvm/Pass.h"
32 #include "llvm/Support/CallSite.h"
33 #include "llvm/Support/InstIterator.h"
34 #include "llvm/Transforms/ObjCARC.h"
35 #include "llvm/Transforms/Utils/Local.h"
44 /// \brief A handy option to enable/disable all ARC Optimizations.
45 extern bool EnableARCOpts;
47 /// \brief Test if the given module looks interesting to run ARC optimization
49 static inline bool ModuleHasARC(const Module &M) {
51 M.getNamedValue("objc_retain") ||
52 M.getNamedValue("objc_release") ||
53 M.getNamedValue("objc_autorelease") ||
54 M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
55 M.getNamedValue("objc_retainBlock") ||
56 M.getNamedValue("objc_autoreleaseReturnValue") ||
57 M.getNamedValue("objc_autoreleasePoolPush") ||
58 M.getNamedValue("objc_loadWeakRetained") ||
59 M.getNamedValue("objc_loadWeak") ||
60 M.getNamedValue("objc_destroyWeak") ||
61 M.getNamedValue("objc_storeWeak") ||
62 M.getNamedValue("objc_initWeak") ||
63 M.getNamedValue("objc_moveWeak") ||
64 M.getNamedValue("objc_copyWeak") ||
65 M.getNamedValue("objc_retainedObject") ||
66 M.getNamedValue("objc_unretainedObject") ||
67 M.getNamedValue("objc_unretainedPointer");
70 /// \enum InstructionClass
71 /// \brief A simple classification for instructions.
72 enum InstructionClass {
73 IC_Retain, ///< objc_retain
74 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
75 IC_RetainBlock, ///< objc_retainBlock
76 IC_Release, ///< objc_release
77 IC_Autorelease, ///< objc_autorelease
78 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
79 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
80 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
81 IC_NoopCast, ///< objc_retainedObject, etc.
82 IC_FusedRetainAutorelease, ///< objc_retainAutorelease
83 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
84 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
85 IC_StoreWeak, ///< objc_storeWeak (primitive)
86 IC_InitWeak, ///< objc_initWeak (derived)
87 IC_LoadWeak, ///< objc_loadWeak (derived)
88 IC_MoveWeak, ///< objc_moveWeak (derived)
89 IC_CopyWeak, ///< objc_copyWeak (derived)
90 IC_DestroyWeak, ///< objc_destroyWeak (derived)
91 IC_StoreStrong, ///< objc_storeStrong (derived)
92 IC_IntrinsicUser, ///< clang.arc.use
93 IC_CallOrUser, ///< could call objc_release and/or "use" pointers
94 IC_Call, ///< could call objc_release
95 IC_User, ///< could "use" a pointer
96 IC_None ///< anything else
99 raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class);
101 /// \brief Test if the given class is a kind of user.
102 inline static bool IsUser(InstructionClass Class) {
103 return Class == IC_User ||
104 Class == IC_CallOrUser ||
105 Class == IC_IntrinsicUser;
108 /// \brief Test if the given class is objc_retain or equivalent.
109 static inline bool IsRetain(InstructionClass Class) {
110 return Class == IC_Retain ||
111 Class == IC_RetainRV;
114 /// \brief Test if the given class is objc_autorelease or equivalent.
115 static inline bool IsAutorelease(InstructionClass Class) {
116 return Class == IC_Autorelease ||
117 Class == IC_AutoreleaseRV;
120 /// \brief Test if the given class represents instructions which return their
121 /// argument verbatim.
122 static inline bool IsForwarding(InstructionClass Class) {
123 // objc_retainBlock technically doesn't always return its argument
124 // verbatim, but it doesn't matter for our purposes here.
125 return Class == IC_Retain ||
126 Class == IC_RetainRV ||
127 Class == IC_Autorelease ||
128 Class == IC_AutoreleaseRV ||
129 Class == IC_RetainBlock ||
130 Class == IC_NoopCast;
133 /// \brief Test if the given class represents instructions which do nothing if
134 /// passed a null pointer.
135 static inline bool IsNoopOnNull(InstructionClass Class) {
136 return Class == IC_Retain ||
137 Class == IC_RetainRV ||
138 Class == IC_Release ||
139 Class == IC_Autorelease ||
140 Class == IC_AutoreleaseRV ||
141 Class == IC_RetainBlock;
144 /// \brief Test if the given class represents instructions which are always safe
145 /// to mark with the "tail" keyword.
146 static inline bool IsAlwaysTail(InstructionClass Class) {
147 // IC_RetainBlock may be given a stack argument.
148 return Class == IC_Retain ||
149 Class == IC_RetainRV ||
150 Class == IC_AutoreleaseRV;
153 /// \brief Test if the given class represents instructions which are never safe
154 /// to mark with the "tail" keyword.
155 static inline bool IsNeverTail(InstructionClass Class) {
156 /// It is never safe to tail call objc_autorelease since by tail calling
157 /// objc_autorelease, we also tail call -[NSObject autorelease] which supports
158 /// fast autoreleasing causing our object to be potentially reclaimed from the
159 /// autorelease pool which violates the semantics of __autoreleasing types in
161 return Class == IC_Autorelease;
164 /// \brief Test if the given class represents instructions which are always safe
165 /// to mark with the nounwind attribute.
166 static inline bool IsNoThrow(InstructionClass Class) {
167 // objc_retainBlock is not nounwind because it calls user copy constructors
168 // which could theoretically throw.
169 return Class == IC_Retain ||
170 Class == IC_RetainRV ||
171 Class == IC_Release ||
172 Class == IC_Autorelease ||
173 Class == IC_AutoreleaseRV ||
174 Class == IC_AutoreleasepoolPush ||
175 Class == IC_AutoreleasepoolPop;
178 /// Test whether the given instruction can autorelease any pointer or cause an
179 /// autoreleasepool pop.
181 CanInterruptRV(InstructionClass Class) {
183 case IC_AutoreleasepoolPop:
187 case IC_AutoreleaseRV:
188 case IC_FusedRetainAutorelease:
189 case IC_FusedRetainAutoreleaseRV:
196 /// \brief Determine if F is one of the special known Functions. If it isn't,
197 /// return IC_CallOrUser.
198 InstructionClass GetFunctionClass(const Function *F);
200 /// \brief Determine which objc runtime call instruction class V belongs to.
202 /// This is similar to GetInstructionClass except that it only detects objc
203 /// runtime calls. This allows it to be faster.
205 static inline InstructionClass GetBasicInstructionClass(const Value *V) {
206 if (const CallInst *CI = dyn_cast<CallInst>(V)) {
207 if (const Function *F = CI->getCalledFunction())
208 return GetFunctionClass(F);
209 // Otherwise, be conservative.
210 return IC_CallOrUser;
213 // Otherwise, be conservative.
214 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
217 /// \brief Determine what kind of construct V is.
218 InstructionClass GetInstructionClass(const Value *V);
220 /// \brief This is a wrapper around getUnderlyingObject which also knows how to
221 /// look through objc_retain and objc_autorelease calls, which we know to return
222 /// their argument verbatim.
223 static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
225 V = GetUnderlyingObject(V);
226 if (!IsForwarding(GetBasicInstructionClass(V)))
228 V = cast<CallInst>(V)->getArgOperand(0);
234 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
235 /// how to look through objc_retain and objc_autorelease calls, which we know to
236 /// return their argument verbatim.
237 static inline const Value *StripPointerCastsAndObjCCalls(const Value *V) {
239 V = V->stripPointerCasts();
240 if (!IsForwarding(GetBasicInstructionClass(V)))
242 V = cast<CallInst>(V)->getArgOperand(0);
247 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
248 /// how to look through objc_retain and objc_autorelease calls, which we know to
249 /// return their argument verbatim.
250 static inline Value *StripPointerCastsAndObjCCalls(Value *V) {
252 V = V->stripPointerCasts();
253 if (!IsForwarding(GetBasicInstructionClass(V)))
255 V = cast<CallInst>(V)->getArgOperand(0);
260 /// \brief Assuming the given instruction is one of the special calls such as
261 /// objc_retain or objc_release, return the argument value, stripped of no-op
262 /// casts and forwarding calls.
263 static inline Value *GetObjCArg(Value *Inst) {
264 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
267 static inline bool IsNullOrUndef(const Value *V) {
268 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
271 static inline bool IsNoopInstruction(const Instruction *I) {
272 return isa<BitCastInst>(I) ||
273 (isa<GetElementPtrInst>(I) &&
274 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
278 /// \brief Erase the given instruction.
280 /// Many ObjC calls return their argument verbatim,
281 /// so if it's such a call and the return value has users, replace them with the
284 static inline void EraseInstruction(Instruction *CI) {
285 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
287 bool Unused = CI->use_empty();
290 // Replace the return value with the argument.
291 assert(IsForwarding(GetBasicInstructionClass(CI)) &&
292 "Can't delete non-forwarding instruction with users!");
293 CI->replaceAllUsesWith(OldArg);
296 CI->eraseFromParent();
299 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
302 /// \brief Test whether the given value is possible a retainable object pointer.
303 static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
304 // Pointers to static or stack storage are not valid retainable object
306 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
308 // Special arguments can not be a valid retainable object pointer.
309 if (const Argument *Arg = dyn_cast<Argument>(Op))
310 if (Arg->hasByValAttr() ||
311 Arg->hasNestAttr() ||
312 Arg->hasStructRetAttr())
314 // Only consider values with pointer types.
316 // It seemes intuitive to exclude function pointer types as well, since
317 // functions are never retainable object pointers, however clang occasionally
318 // bitcasts retainable object pointers to function-pointer type temporarily.
319 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
322 // Conservatively assume anything else is a potential retainable object
327 static inline bool IsPotentialRetainableObjPtr(const Value *Op,
329 // First make the rudimentary check.
330 if (!IsPotentialRetainableObjPtr(Op))
333 // Objects in constant memory are not reference-counted.
334 if (AA.pointsToConstantMemory(Op))
337 // Pointers in constant memory are not pointing to reference-counted objects.
338 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
339 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
342 // Otherwise assume the worst.
346 /// \brief Helper for GetInstructionClass. Determines what kind of construct CS
348 static inline InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
349 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
351 if (IsPotentialRetainableObjPtr(*I))
352 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
354 return CS.onlyReadsMemory() ? IC_None : IC_Call;
357 /// \brief Return true if this value refers to a distinct and identifiable
360 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
361 /// special knowledge of ObjC conventions.
362 static inline bool IsObjCIdentifiedObject(const Value *V) {
363 // Assume that call results and arguments have their own "provenance".
364 // Constants (including GlobalVariables) and Allocas are never
365 // reference-counted.
366 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
367 isa<Argument>(V) || isa<Constant>(V) ||
371 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
372 const Value *Pointer =
373 StripPointerCastsAndObjCCalls(LI->getPointerOperand());
374 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
375 // A constant pointer can't be pointing to an object on the heap. It may
376 // be reference-counted, but it won't be deleted.
377 if (GV->isConstant())
379 StringRef Name = GV->getName();
380 // These special variables are known to hold values which are not
381 // reference-counted pointers.
382 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
383 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
384 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
385 Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
386 Name.startswith("\01l_objc_msgSend_fixup_"))
394 } // end namespace objcarc
395 } // end namespace llvm
397 #endif // LLVM_TRANSFORMS_SCALAR_OBJCARC_H