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,
76 const DataLayout &DL) {
78 V = GetUnderlyingObject(V, DL);
79 if (!IsForwarding(GetBasicARCInstKind(V)))
81 V = cast<CallInst>(V)->getArgOperand(0);
87 /// The RCIdentity root of a value \p V is a dominating value U for which
88 /// retaining or releasing U is equivalent to retaining or releasing V. In other
89 /// words, ARC operations on \p V are equivalent to ARC operations on \p U.
91 /// We use this in the ARC optimizer to make it easier to match up ARC
92 /// operations by always mapping ARC operations to RCIdentityRoots instead of
93 /// pointers themselves.
95 /// The two ways that we see RCIdentical values in ObjC are via:
98 /// 2. Forwarding Calls that return their argument verbatim.
100 /// Thus this function strips off pointer casts and forwarding calls. *NOTE*
101 /// This implies that two RCIdentical values must alias.
102 static inline const Value *GetRCIdentityRoot(const Value *V) {
104 V = V->stripPointerCasts();
105 if (!IsForwarding(GetBasicARCInstKind(V)))
107 V = cast<CallInst>(V)->getArgOperand(0);
112 /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just
113 /// casts away the const of the result. For documentation about what an
114 /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that
116 static inline Value *GetRCIdentityRoot(Value *V) {
117 return const_cast<Value *>(GetRCIdentityRoot((const Value *)V));
120 /// \brief Assuming the given instruction is one of the special calls such as
121 /// objc_retain or objc_release, return the RCIdentity root of the argument of
123 static inline Value *GetArgRCIdentityRoot(Value *Inst) {
124 return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
127 static inline bool IsNullOrUndef(const Value *V) {
128 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
131 static inline bool IsNoopInstruction(const Instruction *I) {
132 return isa<BitCastInst>(I) ||
133 (isa<GetElementPtrInst>(I) &&
134 cast<GetElementPtrInst>(I)->hasAllZeroIndices());
138 /// \brief Erase the given instruction.
140 /// Many ObjC calls return their argument verbatim,
141 /// so if it's such a call and the return value has users, replace them with the
144 static inline void EraseInstruction(Instruction *CI) {
145 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
147 bool Unused = CI->use_empty();
150 // Replace the return value with the argument.
151 assert((IsForwarding(GetBasicARCInstKind(CI)) ||
152 (IsNoopOnNull(GetBasicARCInstKind(CI)) &&
153 isa<ConstantPointerNull>(OldArg))) &&
154 "Can't delete non-forwarding instruction with users!");
155 CI->replaceAllUsesWith(OldArg);
158 CI->eraseFromParent();
161 RecursivelyDeleteTriviallyDeadInstructions(OldArg);
164 /// \brief Test whether the given value is possible a retainable object pointer.
165 static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
166 // Pointers to static or stack storage are not valid retainable object
168 if (isa<Constant>(Op) || isa<AllocaInst>(Op))
170 // Special arguments can not be a valid retainable object pointer.
171 if (const Argument *Arg = dyn_cast<Argument>(Op))
172 if (Arg->hasByValAttr() ||
173 Arg->hasInAllocaAttr() ||
174 Arg->hasNestAttr() ||
175 Arg->hasStructRetAttr())
177 // Only consider values with pointer types.
179 // It seemes intuitive to exclude function pointer types as well, since
180 // functions are never retainable object pointers, however clang occasionally
181 // bitcasts retainable object pointers to function-pointer type temporarily.
182 PointerType *Ty = dyn_cast<PointerType>(Op->getType());
185 // Conservatively assume anything else is a potential retainable object
190 static inline bool IsPotentialRetainableObjPtr(const Value *Op,
192 // First make the rudimentary check.
193 if (!IsPotentialRetainableObjPtr(Op))
196 // Objects in constant memory are not reference-counted.
197 if (AA.pointsToConstantMemory(Op))
200 // Pointers in constant memory are not pointing to reference-counted objects.
201 if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
202 if (AA.pointsToConstantMemory(LI->getPointerOperand()))
205 // Otherwise assume the worst.
209 /// \brief Helper for GetARCInstKind. Determines what kind of construct CS
211 static inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) {
212 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
214 if (IsPotentialRetainableObjPtr(*I))
215 return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser;
217 return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call;
220 /// \brief Return true if this value refers to a distinct and identifiable
223 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
224 /// special knowledge of ObjC conventions.
225 static inline bool IsObjCIdentifiedObject(const Value *V) {
226 // Assume that call results and arguments have their own "provenance".
227 // Constants (including GlobalVariables) and Allocas are never
228 // reference-counted.
229 if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
230 isa<Argument>(V) || isa<Constant>(V) ||
234 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
235 const Value *Pointer =
236 GetRCIdentityRoot(LI->getPointerOperand());
237 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
238 // A constant pointer can't be pointing to an object on the heap. It may
239 // be reference-counted, but it won't be deleted.
240 if (GV->isConstant())
242 StringRef Name = GV->getName();
243 // These special variables are known to hold values which are not
244 // reference-counted pointers.
245 if (Name.startswith("\01l_objc_msgSend_fixup_"))
248 StringRef Section = GV->getSection();
249 if (Section.find("__message_refs") != StringRef::npos ||
250 Section.find("__objc_classrefs") != StringRef::npos ||
251 Section.find("__objc_superrefs") != StringRef::npos ||
252 Section.find("__objc_methname") != StringRef::npos ||
253 Section.find("__cstring") != StringRef::npos)
261 /// A cache of MDKinds used by various ARC optimizations.
262 struct ARCMDKindCache {
263 /// The Metadata Kind for clang.imprecise_release metadata.
264 unsigned ImpreciseReleaseMDKind;
266 /// The Metadata Kind for clang.arc.copy_on_escape metadata.
267 unsigned CopyOnEscapeMDKind;
269 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
270 unsigned NoObjCARCExceptionsMDKind;
273 } // end namespace objcarc
274 } // end namespace llvm