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") ||
68 M.getNamedValue("clang.arc.use");
71 /// \enum InstructionClass
72 /// \brief A simple classification for instructions.
73 enum InstructionClass {
74 IC_Retain, ///< objc_retain
75 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
76 IC_RetainBlock, ///< objc_retainBlock
77 IC_Release, ///< objc_release
78 IC_Autorelease, ///< objc_autorelease
79 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
80 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
81 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
82 IC_NoopCast, ///< objc_retainedObject, etc.
83 IC_FusedRetainAutorelease, ///< objc_retainAutorelease
84 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
85 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
86 IC_StoreWeak, ///< objc_storeWeak (primitive)
87 IC_InitWeak, ///< objc_initWeak (derived)
88 IC_LoadWeak, ///< objc_loadWeak (derived)
89 IC_MoveWeak, ///< objc_moveWeak (derived)
90 IC_CopyWeak, ///< objc_copyWeak (derived)
91 IC_DestroyWeak, ///< objc_destroyWeak (derived)
92 IC_StoreStrong, ///< objc_storeStrong (derived)
93 IC_IntrinsicUser, ///< clang.arc.use
94 IC_CallOrUser, ///< could call objc_release and/or "use" pointers
95 IC_Call, ///< could call objc_release
96 IC_User, ///< could "use" a pointer
97 IC_None ///< anything else
100 raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class);
102 /// \brief Test if the given class is a kind of user.
103 inline static bool IsUser(InstructionClass Class) {
104 return Class == IC_User ||
105 Class == IC_CallOrUser ||
106 Class == IC_IntrinsicUser;
109 /// \brief Test if the given class is objc_retain or equivalent.
110 static inline bool IsRetain(InstructionClass Class) {
111 return Class == IC_Retain ||
112 Class == IC_RetainRV;
115 /// \brief Test if the given class is objc_autorelease or equivalent.
116 static inline bool IsAutorelease(InstructionClass Class) {
117 return Class == IC_Autorelease ||
118 Class == IC_AutoreleaseRV;
121 /// \brief Test if the given class represents instructions which return their
122 /// argument verbatim.
123 static inline bool IsForwarding(InstructionClass Class) {
124 return Class == IC_Retain ||
125 Class == IC_RetainRV ||
126 Class == IC_Autorelease ||
127 Class == IC_AutoreleaseRV ||
128 Class == IC_NoopCast;
131 /// \brief Test if the given class represents instructions which do nothing if
132 /// passed a null pointer.
133 static inline bool IsNoopOnNull(InstructionClass Class) {
134 return Class == IC_Retain ||
135 Class == IC_RetainRV ||
136 Class == IC_Release ||
137 Class == IC_Autorelease ||
138 Class == IC_AutoreleaseRV ||
139 Class == IC_RetainBlock;
142 /// \brief Test if the given class represents instructions which are always safe
143 /// to mark with the "tail" keyword.
144 static inline bool IsAlwaysTail(InstructionClass Class) {
145 // IC_RetainBlock may be given a stack argument.
146 return Class == IC_Retain ||
147 Class == IC_RetainRV ||
148 Class == IC_AutoreleaseRV;
151 /// \brief Test if the given class represents instructions which are never safe
152 /// to mark with the "tail" keyword.
153 static inline bool IsNeverTail(InstructionClass Class) {
154 /// It is never safe to tail call objc_autorelease since by tail calling
155 /// objc_autorelease, we also tail call -[NSObject autorelease] which supports
156 /// fast autoreleasing causing our object to be potentially reclaimed from the
157 /// autorelease pool which violates the semantics of __autoreleasing types in
159 return Class == IC_Autorelease;
162 /// \brief Test if the given class represents instructions which are always safe
163 /// to mark with the nounwind attribute.
164 static inline bool IsNoThrow(InstructionClass Class) {
165 // objc_retainBlock is not nounwind because it calls user copy constructors
166 // which could theoretically throw.
167 return Class == IC_Retain ||
168 Class == IC_RetainRV ||
169 Class == IC_Release ||
170 Class == IC_Autorelease ||
171 Class == IC_AutoreleaseRV ||
172 Class == IC_AutoreleasepoolPush ||
173 Class == IC_AutoreleasepoolPop;
176 /// Test whether the given instruction can autorelease any pointer or cause an
177 /// autoreleasepool pop.
179 CanInterruptRV(InstructionClass Class) {
181 case IC_AutoreleasepoolPop:
185 case IC_AutoreleaseRV:
186 case IC_FusedRetainAutorelease:
187 case IC_FusedRetainAutoreleaseRV:
194 /// \brief Determine if F is one of the special known Functions. If it isn't,
195 /// return IC_CallOrUser.
196 InstructionClass GetFunctionClass(const Function *F);
198 /// \brief Determine which objc runtime call instruction class V belongs to.
200 /// This is similar to GetInstructionClass except that it only detects objc
201 /// runtime calls. This allows it to be faster.
203 static inline InstructionClass GetBasicInstructionClass(const Value *V) {
204 if (const CallInst *CI = dyn_cast<CallInst>(V)) {
205 if (const Function *F = CI->getCalledFunction())
206 return GetFunctionClass(F);
207 // Otherwise, be conservative.
208 return IC_CallOrUser;
211 // Otherwise, be conservative.
212 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
215 /// \brief Determine what kind of construct V is.
216 InstructionClass GetInstructionClass(const Value *V);
218 /// \brief This is a wrapper around getUnderlyingObject which also knows how to
219 /// look through objc_retain and objc_autorelease calls, which we know to return
220 /// their argument verbatim.
221 static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
223 V = GetUnderlyingObject(V);
224 if (!IsForwarding(GetBasicInstructionClass(V)))
226 V = cast<CallInst>(V)->getArgOperand(0);
232 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
233 /// how to look through objc_retain and objc_autorelease calls, which we know to
234 /// return their argument verbatim.
235 static inline const Value *StripPointerCastsAndObjCCalls(const Value *V) {
237 V = V->stripPointerCasts();
238 if (!IsForwarding(GetBasicInstructionClass(V)))
240 V = cast<CallInst>(V)->getArgOperand(0);
245 /// \brief This is a wrapper around Value::stripPointerCasts which also knows
246 /// how to look through objc_retain and objc_autorelease calls, which we know to
247 /// return their argument verbatim.
248 static inline Value *StripPointerCastsAndObjCCalls(Value *V) {
250 V = V->stripPointerCasts();
251 if (!IsForwarding(GetBasicInstructionClass(V)))
253 V = cast<CallInst>(V)->getArgOperand(0);
258 /// \brief Assuming the given instruction is one of the special calls such as
259 /// objc_retain or objc_release, return the argument value, stripped of no-op
260 /// casts and forwarding calls.
261 static inline Value *GetObjCArg(Value *Inst) {
262 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
265 static inline bool IsNullOrUndef(const Value *V) {
266 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
269 static inline bool IsNoopInstruction(const Instruction *I) {
270 return isa<BitCastInst>(I) ||
271 (isa<GetElementPtrInst>(I) &&
272 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
276 /// \brief Erase the given instruction.
278 /// Many ObjC calls return their argument verbatim,
279 /// so if it's such a call and the return value has users, replace them with the
282 static inline void EraseInstruction(Instruction *CI) {
283 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
285 bool Unused = CI->use_empty();
288 // Replace the return value with the argument.
289 assert(IsForwarding(GetBasicInstructionClass(CI)) &&
290 "Can't delete non-forwarding instruction with users!");
291 CI->replaceAllUsesWith(OldArg);
294 CI->eraseFromParent();
297 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
300 /// \brief Test whether the given value is possible a retainable object pointer.
301 static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
302 // Pointers to static or stack storage are not valid retainable object
304 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
306 // Special arguments can not be a valid retainable object pointer.
307 if (const Argument *Arg = dyn_cast<Argument>(Op))
308 if (Arg->hasByValAttr() ||
309 Arg->hasNestAttr() ||
310 Arg->hasStructRetAttr())
312 // Only consider values with pointer types.
314 // It seemes intuitive to exclude function pointer types as well, since
315 // functions are never retainable object pointers, however clang occasionally
316 // bitcasts retainable object pointers to function-pointer type temporarily.
317 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
320 // Conservatively assume anything else is a potential retainable object
325 static inline bool IsPotentialRetainableObjPtr(const Value *Op,
327 // First make the rudimentary check.
328 if (!IsPotentialRetainableObjPtr(Op))
331 // Objects in constant memory are not reference-counted.
332 if (AA.pointsToConstantMemory(Op))
335 // Pointers in constant memory are not pointing to reference-counted objects.
336 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
337 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
340 // Otherwise assume the worst.
344 /// \brief Helper for GetInstructionClass. Determines what kind of construct CS
346 static inline InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
347 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
349 if (IsPotentialRetainableObjPtr(*I))
350 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
352 return CS.onlyReadsMemory() ? IC_None : IC_Call;
355 /// \brief Return true if this value refers to a distinct and identifiable
358 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
359 /// special knowledge of ObjC conventions.
360 static inline bool IsObjCIdentifiedObject(const Value *V) {
361 // Assume that call results and arguments have their own "provenance".
362 // Constants (including GlobalVariables) and Allocas are never
363 // reference-counted.
364 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
365 isa<Argument>(V) || isa<Constant>(V) ||
369 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
370 const Value *Pointer =
371 StripPointerCastsAndObjCCalls(LI->getPointerOperand());
372 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
373 // A constant pointer can't be pointing to an object on the heap. It may
374 // be reference-counted, but it won't be deleted.
375 if (GV->isConstant())
377 StringRef Name = GV->getName();
378 // These special variables are known to hold values which are not
379 // reference-counted pointers.
380 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
381 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
382 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
383 Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
384 Name.startswith("\01l_objc_msgSend_fixup_"))
392 } // end namespace objcarc
393 } // end namespace llvm
395 #endif // LLVM_TRANSFORMS_SCALAR_OBJCARC_H