1 //===- ObjCARC.h - ObjC ARC Optimization --------------*- 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_LIB_TRANSFORMS_OBJCARC_OBJCARC_H
24 #define LLVM_LIB_TRANSFORMS_OBJCARC_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/CallSite.h"
31 #include "llvm/IR/InstIterator.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Transforms/ObjCARC.h"
35 #include "llvm/Transforms/Utils/Local.h"
36 #include "ARCInstKind.h"
45 /// \brief A handy option to enable/disable all ARC Optimizations.
46 extern bool EnableARCOpts;
48 /// \brief Test if the given module looks interesting to run ARC optimization
50 static inline bool ModuleHasARC(const Module &M) {
52 M.getNamedValue("objc_retain") ||
53 M.getNamedValue("objc_release") ||
54 M.getNamedValue("objc_autorelease") ||
55 M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
56 M.getNamedValue("objc_retainBlock") ||
57 M.getNamedValue("objc_autoreleaseReturnValue") ||
58 M.getNamedValue("objc_autoreleasePoolPush") ||
59 M.getNamedValue("objc_loadWeakRetained") ||
60 M.getNamedValue("objc_loadWeak") ||
61 M.getNamedValue("objc_destroyWeak") ||
62 M.getNamedValue("objc_storeWeak") ||
63 M.getNamedValue("objc_initWeak") ||
64 M.getNamedValue("objc_moveWeak") ||
65 M.getNamedValue("objc_copyWeak") ||
66 M.getNamedValue("objc_retainedObject") ||
67 M.getNamedValue("objc_unretainedObject") ||
68 M.getNamedValue("objc_unretainedPointer") ||
69 M.getNamedValue("clang.arc.use");
72 /// \brief This is a wrapper around getUnderlyingObject which also knows how to
73 /// look through objc_retain and objc_autorelease calls, which we know to return
74 /// their argument verbatim.
75 static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
77 V = GetUnderlyingObject(V);
78 if (!IsForwarding(GetBasicARCInstKind(V)))
80 V = cast<CallInst>(V)->getArgOperand(0);
86 /// The RCIdentity root of a value \p V is a dominating value U for which
87 /// retaining or releasing U is equivalent to retaining or releasing V. In other
88 /// words, ARC operations on \p V are equivalent to ARC operations on \p U.
90 /// We use this in the ARC optimizer to make it easier to match up ARC
91 /// operations by always mapping ARC operations to RCIdentityRoots instead of
92 /// pointers themselves.
94 /// The two ways that we see RCIdentical values in ObjC are via:
97 /// 2. Forwarding Calls that return their argument verbatim.
99 /// Thus this function strips off pointer casts and forwarding calls. *NOTE*
100 /// This implies that two RCIdentical values must alias.
101 static inline const Value *GetRCIdentityRoot(const Value *V) {
103 V = V->stripPointerCasts();
104 if (!IsForwarding(GetBasicARCInstKind(V)))
106 V = cast<CallInst>(V)->getArgOperand(0);
111 /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just
112 /// casts away the const of the result. For documentation about what an
113 /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that
115 static inline Value *GetRCIdentityRoot(Value *V) {
116 return const_cast<Value *>(GetRCIdentityRoot((const Value *)V));
119 /// \brief Assuming the given instruction is one of the special calls such as
120 /// objc_retain or objc_release, return the RCIdentity root of the argument of
122 static inline Value *GetArgRCIdentityRoot(Value *Inst) {
123 return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
126 static inline bool IsNullOrUndef(const Value *V) {
127 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
130 static inline bool IsNoopInstruction(const Instruction *I) {
131 return isa<BitCastInst>(I) ||
132 (isa<GetElementPtrInst>(I) &&
133 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
137 /// \brief Erase the given instruction.
139 /// Many ObjC calls return their argument verbatim,
140 /// so if it's such a call and the return value has users, replace them with the
143 static inline void EraseInstruction(Instruction *CI) {
144 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
146 bool Unused = CI->use_empty();
149 // Replace the return value with the argument.
150 assert((IsForwarding(GetBasicARCInstKind(CI)) ||
151 (IsNoopOnNull(GetBasicARCInstKind(CI)) &&
152 isa<ConstantPointerNull>(OldArg))) &&
153 "Can't delete non-forwarding instruction with users!");
154 CI->replaceAllUsesWith(OldArg);
157 CI->eraseFromParent();
160 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
163 /// \brief Test whether the given value is possible a retainable object pointer.
164 static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
165 // Pointers to static or stack storage are not valid retainable object
167 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
169 // Special arguments can not be a valid retainable object pointer.
170 if (const Argument *Arg = dyn_cast<Argument>(Op))
171 if (Arg->hasByValAttr() ||
172 Arg->hasInAllocaAttr() ||
173 Arg->hasNestAttr() ||
174 Arg->hasStructRetAttr())
176 // Only consider values with pointer types.
178 // It seemes intuitive to exclude function pointer types as well, since
179 // functions are never retainable object pointers, however clang occasionally
180 // bitcasts retainable object pointers to function-pointer type temporarily.
181 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
184 // Conservatively assume anything else is a potential retainable object
189 static inline bool IsPotentialRetainableObjPtr(const Value *Op,
191 // First make the rudimentary check.
192 if (!IsPotentialRetainableObjPtr(Op))
195 // Objects in constant memory are not reference-counted.
196 if (AA.pointsToConstantMemory(Op))
199 // Pointers in constant memory are not pointing to reference-counted objects.
200 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
201 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
204 // Otherwise assume the worst.
208 /// \brief Helper for GetARCInstKind. Determines what kind of construct CS
210 static inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) {
211 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
213 if (IsPotentialRetainableObjPtr(*I))
214 return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser;
216 return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call;
219 /// \brief Return true if this value refers to a distinct and identifiable
222 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
223 /// special knowledge of ObjC conventions.
224 static inline bool IsObjCIdentifiedObject(const Value *V) {
225 // Assume that call results and arguments have their own "provenance".
226 // Constants (including GlobalVariables) and Allocas are never
227 // reference-counted.
228 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
229 isa<Argument>(V) || isa<Constant>(V) ||
233 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
234 const Value *Pointer =
235 GetRCIdentityRoot(LI->getPointerOperand());
236 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
237 // A constant pointer can't be pointing to an object on the heap. It may
238 // be reference-counted, but it won't be deleted.
239 if (GV->isConstant())
241 StringRef Name = GV->getName();
242 // These special variables are known to hold values which are not
243 // reference-counted pointers.
244 if (Name.startswith("\01l_objc_msgSend_fixup_"))
247 StringRef Section = GV->getSection();
248 if (Section.find("__message_refs") != StringRef::npos ||
249 Section.find("__objc_classrefs") != StringRef::npos ||
250 Section.find("__objc_superrefs") != StringRef::npos ||
251 Section.find("__objc_methname") != StringRef::npos ||
252 Section.find("__cstring") != StringRef::npos)
260 } // end namespace objcarc
261 } // end namespace llvm