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/Debug.h"
34 #include "llvm/Support/InstIterator.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/Transforms/ObjCARC.h"
37 #include "llvm/Transforms/Utils/Local.h"
42 /// \brief A handy option to enable/disable all ARC Optimizations.
43 extern bool EnableARCOpts;
45 /// \brief Test if the given module looks interesting to run ARC optimization
47 static inline bool ModuleHasARC(const Module &M) {
49 M.getNamedValue("objc_retain") ||
50 M.getNamedValue("objc_release") ||
51 M.getNamedValue("objc_autorelease") ||
52 M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
53 M.getNamedValue("objc_retainBlock") ||
54 M.getNamedValue("objc_autoreleaseReturnValue") ||
55 M.getNamedValue("objc_autoreleasePoolPush") ||
56 M.getNamedValue("objc_loadWeakRetained") ||
57 M.getNamedValue("objc_loadWeak") ||
58 M.getNamedValue("objc_destroyWeak") ||
59 M.getNamedValue("objc_storeWeak") ||
60 M.getNamedValue("objc_initWeak") ||
61 M.getNamedValue("objc_moveWeak") ||
62 M.getNamedValue("objc_copyWeak") ||
63 M.getNamedValue("objc_retainedObject") ||
64 M.getNamedValue("objc_unretainedObject") ||
65 M.getNamedValue("objc_unretainedPointer");
68 /// \enum InstructionClass
69 /// \brief A simple classification for instructions.
70 enum InstructionClass {
71 IC_Retain, ///< objc_retain
72 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
73 IC_RetainBlock, ///< objc_retainBlock
74 IC_Release, ///< objc_release
75 IC_Autorelease, ///< objc_autorelease
76 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
77 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
78 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
79 IC_NoopCast, ///< objc_retainedObject, etc.
80 IC_FusedRetainAutorelease, ///< objc_retainAutorelease
81 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
82 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
83 IC_StoreWeak, ///< objc_storeWeak (primitive)
84 IC_InitWeak, ///< objc_initWeak (derived)
85 IC_LoadWeak, ///< objc_loadWeak (derived)
86 IC_MoveWeak, ///< objc_moveWeak (derived)
87 IC_CopyWeak, ///< objc_copyWeak (derived)
88 IC_DestroyWeak, ///< objc_destroyWeak (derived)
89 IC_StoreStrong, ///< objc_storeStrong (derived)
90 IC_CallOrUser, ///< could call objc_release and/or "use" pointers
91 IC_Call, ///< could call objc_release
92 IC_User, ///< could "use" a pointer
93 IC_None ///< anything else
96 raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class);
98 /// \brief Test if the given class is objc_retain or equivalent.
99 static inline bool IsRetain(InstructionClass Class) {
100 return Class == IC_Retain ||
101 Class == IC_RetainRV;
104 /// \brief Test if the given class is objc_autorelease or equivalent.
105 static inline bool IsAutorelease(InstructionClass Class) {
106 return Class == IC_Autorelease ||
107 Class == IC_AutoreleaseRV;
110 /// \brief Test if the given class represents instructions which return their
111 /// argument verbatim.
112 static inline bool IsForwarding(InstructionClass Class) {
113 // objc_retainBlock technically doesn't always return its argument
114 // verbatim, but it doesn't matter for our purposes here.
115 return Class == IC_Retain ||
116 Class == IC_RetainRV ||
117 Class == IC_Autorelease ||
118 Class == IC_AutoreleaseRV ||
119 Class == IC_RetainBlock ||
120 Class == IC_NoopCast;
123 /// \brief Test if the given class represents instructions which do nothing if
124 /// passed a null pointer.
125 static inline bool IsNoopOnNull(InstructionClass Class) {
126 return Class == IC_Retain ||
127 Class == IC_RetainRV ||
128 Class == IC_Release ||
129 Class == IC_Autorelease ||
130 Class == IC_AutoreleaseRV ||
131 Class == IC_RetainBlock;
134 /// \brief Test if the given class represents instructions which are always safe
135 /// to mark with the "tail" keyword.
136 static inline bool IsAlwaysTail(InstructionClass Class) {
137 // IC_RetainBlock may be given a stack argument.
138 return Class == IC_Retain ||
139 Class == IC_RetainRV ||
140 Class == IC_AutoreleaseRV;
143 /// \brief Test if the given class represents instructions which are never safe
144 /// to mark with the "tail" keyword.
145 static inline bool IsNeverTail(InstructionClass Class) {
146 /// It is never safe to tail call objc_autorelease since by tail calling
147 /// objc_autorelease, we also tail call -[NSObject autorelease] which supports
148 /// fast autoreleasing causing our object to be potentially reclaimed from the
149 /// autorelease pool which violates the semantics of __autoreleasing types in
151 return Class == IC_Autorelease;
154 /// \brief Test if the given class represents instructions which are always safe
155 /// to mark with the nounwind attribute.
156 static inline bool IsNoThrow(InstructionClass Class) {
157 // objc_retainBlock is not nounwind because it calls user copy constructors
158 // which could theoretically throw.
159 return Class == IC_Retain ||
160 Class == IC_RetainRV ||
161 Class == IC_Release ||
162 Class == IC_Autorelease ||
163 Class == IC_AutoreleaseRV ||
164 Class == IC_AutoreleasepoolPush ||
165 Class == IC_AutoreleasepoolPop;
168 /// Test whether the given instruction can autorelease any pointer or cause an
169 /// autoreleasepool pop.
171 CanInterruptRV(InstructionClass Class) {
173 case IC_AutoreleasepoolPop:
177 case IC_AutoreleaseRV:
178 case IC_FusedRetainAutorelease:
179 case IC_FusedRetainAutoreleaseRV:
186 /// \brief Determine if F is one of the special known Functions. If it isn't,
187 /// return IC_CallOrUser.
188 InstructionClass GetFunctionClass(const Function *F);
190 /// \brief Determine which objc runtime call instruction class V belongs to.
192 /// This is similar to GetInstructionClass except that it only detects objc
193 /// runtime calls. This allows it to be faster.
195 static inline InstructionClass GetBasicInstructionClass(const Value *V) {
196 if (const CallInst *CI = dyn_cast<CallInst>(V)) {
197 if (const Function *F = CI->getCalledFunction())
198 return GetFunctionClass(F);
199 // Otherwise, be conservative.
200 return IC_CallOrUser;
203 // Otherwise, be conservative.
204 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
207 /// \brief Determine what kind of construct V is.
208 InstructionClass GetInstructionClass(const Value *V);
210 /// \brief This is a wrapper around getUnderlyingObject which also knows how to
211 /// look through objc_retain and objc_autorelease calls, which we know to return
212 /// their argument verbatim.
213 static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
215 V = GetUnderlyingObject(V);
216 if (!IsForwarding(GetBasicInstructionClass(V)))
218 V = cast<CallInst>(V)->getArgOperand(0);
224 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
225 /// how to look through objc_retain and objc_autorelease calls, which we know to
226 /// return their argument verbatim.
227 static inline const Value *StripPointerCastsAndObjCCalls(const Value *V) {
229 V = V->stripPointerCasts();
230 if (!IsForwarding(GetBasicInstructionClass(V)))
232 V = cast<CallInst>(V)->getArgOperand(0);
237 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
238 /// how to look through objc_retain and objc_autorelease calls, which we know to
239 /// return their argument verbatim.
240 static inline Value *StripPointerCastsAndObjCCalls(Value *V) {
242 V = V->stripPointerCasts();
243 if (!IsForwarding(GetBasicInstructionClass(V)))
245 V = cast<CallInst>(V)->getArgOperand(0);
250 /// \brief Assuming the given instruction is one of the special calls such as
251 /// objc_retain or objc_release, return the argument value, stripped of no-op
252 /// casts and forwarding calls.
253 static inline Value *GetObjCArg(Value *Inst) {
254 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
257 static inline bool isNullOrUndef(const Value *V) {
258 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
261 static inline bool isNoopInstruction(const Instruction *I) {
262 return isa<BitCastInst>(I) ||
263 (isa<GetElementPtrInst>(I) &&
264 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
268 /// \brief Erase the given instruction.
270 /// Many ObjC calls return their argument verbatim,
271 /// so if it's such a call and the return value has users, replace them with the
274 static inline void EraseInstruction(Instruction *CI) {
275 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
277 bool Unused = CI->use_empty();
280 // Replace the return value with the argument.
281 assert(IsForwarding(GetBasicInstructionClass(CI)) &&
282 "Can't delete non-forwarding instruction with users!");
283 CI->replaceAllUsesWith(OldArg);
286 CI->eraseFromParent();
289 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
292 /// \brief Test whether the given value is possible a retainable object pointer.
293 static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
294 // Pointers to static or stack storage are not valid retainable object pointers.
295 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
297 // Special arguments can not be a valid retainable object pointer.
298 if (const Argument *Arg = dyn_cast<Argument>(Op))
299 if (Arg->hasByValAttr() ||
300 Arg->hasNestAttr() ||
301 Arg->hasStructRetAttr())
303 // Only consider values with pointer types.
305 // It seemes intuitive to exclude function pointer types as well, since
306 // functions are never retainable object pointers, however clang occasionally
307 // bitcasts retainable object pointers to function-pointer type temporarily.
308 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
311 // Conservatively assume anything else is a potential retainable object pointer.
315 static inline bool IsPotentialRetainableObjPtr(const Value *Op,
317 // First make the rudimentary check.
318 if (!IsPotentialRetainableObjPtr(Op))
321 // Objects in constant memory are not reference-counted.
322 if (AA.pointsToConstantMemory(Op))
325 // Pointers in constant memory are not pointing to reference-counted objects.
326 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
327 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
330 // Otherwise assume the worst.
334 /// \brief Helper for GetInstructionClass. Determines what kind of construct CS
336 static inline InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
337 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
339 if (IsPotentialRetainableObjPtr(*I))
340 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
342 return CS.onlyReadsMemory() ? IC_None : IC_Call;
345 /// \brief Return true if this value refers to a distinct and identifiable
348 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
349 /// special knowledge of ObjC conventions.
350 static inline bool IsObjCIdentifiedObject(const Value *V) {
351 // Assume that call results and arguments have their own "provenance".
352 // Constants (including GlobalVariables) and Allocas are never
353 // reference-counted.
354 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
355 isa<Argument>(V) || isa<Constant>(V) ||
359 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
360 const Value *Pointer =
361 StripPointerCastsAndObjCCalls(LI->getPointerOperand());
362 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
363 // A constant pointer can't be pointing to an object on the heap. It may
364 // be reference-counted, but it won't be deleted.
365 if (GV->isConstant())
367 StringRef Name = GV->getName();
368 // These special variables are known to hold values which are not
369 // reference-counted pointers.
370 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
371 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
372 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
373 Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
374 Name.startswith("\01l_objc_msgSend_fixup_"))
382 } // end namespace objcarc
383 } // end namespace llvm
385 #endif // LLVM_TRANSFORMS_SCALAR_OBJCARC_H