1 //===- ObjCARCAnalysisUtils.h - ObjC ARC Analysis Utilities -----*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 /// \file 10 /// This file defines common analysis utilities used by the ObjC ARC Optimizer. 11 /// ARC stands for Automatic Reference Counting and is a system for managing 12 /// reference counts for objects in Objective C. 13 /// 14 /// WARNING: This file knows about certain library functions. It recognizes them 15 /// by name, and hardwires knowledge of their semantics. 16 /// 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. 20 /// 21 //===----------------------------------------------------------------------===// 22 23 #ifndef LLVM_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H 24 #define LLVM_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H 25 26 #include "llvm/ADT/Optional.h" 27 #include "llvm/ADT/StringSwitch.h" 28 #include "llvm/Analysis/AliasAnalysis.h" 29 #include "llvm/Analysis/ObjCARCInstKind.h" 30 #include "llvm/Analysis/Passes.h" 31 #include "llvm/Analysis/ValueTracking.h" 32 #include "llvm/IR/CallSite.h" 33 #include "llvm/IR/Constants.h" 34 #include "llvm/IR/InstIterator.h" 35 #include "llvm/IR/LLVMContext.h" 36 #include "llvm/IR/Module.h" 37 #include "llvm/Pass.h" 38 39 namespace llvm { 40 class raw_ostream; 41 } 42 43 namespace llvm { 44 namespace objcarc { 45 46 /// \brief A handy option to enable/disable all ARC Optimizations. 47 extern bool EnableARCOpts; 48 49 /// \brief Test if the given module looks interesting to run ARC optimization 50 /// on. 51 inline bool ModuleHasARC(const Module &M) { 52 return 53 M.getNamedValue("objc_retain") || 54 M.getNamedValue("objc_release") || 55 M.getNamedValue("objc_autorelease") || 56 M.getNamedValue("objc_retainAutoreleasedReturnValue") || 57 M.getNamedValue("objc_unsafeClaimAutoreleasedReturnValue") || 58 M.getNamedValue("objc_retainBlock") || 59 M.getNamedValue("objc_autoreleaseReturnValue") || 60 M.getNamedValue("objc_autoreleasePoolPush") || 61 M.getNamedValue("objc_loadWeakRetained") || 62 M.getNamedValue("objc_loadWeak") || 63 M.getNamedValue("objc_destroyWeak") || 64 M.getNamedValue("objc_storeWeak") || 65 M.getNamedValue("objc_initWeak") || 66 M.getNamedValue("objc_moveWeak") || 67 M.getNamedValue("objc_copyWeak") || 68 M.getNamedValue("objc_retainedObject") || 69 M.getNamedValue("objc_unretainedObject") || 70 M.getNamedValue("objc_unretainedPointer") || 71 M.getNamedValue("clang.arc.use"); 72 } 73 74 /// \brief This is a wrapper around getUnderlyingObject which also knows how to 75 /// look through objc_retain and objc_autorelease calls, which we know to return 76 /// their argument verbatim. 77 inline const Value *GetUnderlyingObjCPtr(const Value *V, 78 const DataLayout &DL) { 79 for (;;) { 80 V = GetUnderlyingObject(V, DL); 81 if (!IsForwarding(GetBasicARCInstKind(V))) 82 break; 83 V = cast<CallInst>(V)->getArgOperand(0); 84 } 85 86 return V; 87 } 88 89 /// The RCIdentity root of a value \p V is a dominating value U for which 90 /// retaining or releasing U is equivalent to retaining or releasing V. In other 91 /// words, ARC operations on \p V are equivalent to ARC operations on \p U. 92 /// 93 /// We use this in the ARC optimizer to make it easier to match up ARC 94 /// operations by always mapping ARC operations to RCIdentityRoots instead of 95 /// pointers themselves. 96 /// 97 /// The two ways that we see RCIdentical values in ObjC are via: 98 /// 99 /// 1. PointerCasts 100 /// 2. Forwarding Calls that return their argument verbatim. 101 /// 102 /// Thus this function strips off pointer casts and forwarding calls. *NOTE* 103 /// This implies that two RCIdentical values must alias. 104 inline const Value *GetRCIdentityRoot(const Value *V) { 105 for (;;) { 106 V = V->stripPointerCasts(); 107 if (!IsForwarding(GetBasicARCInstKind(V))) 108 break; 109 V = cast<CallInst>(V)->getArgOperand(0); 110 } 111 return V; 112 } 113 114 /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just 115 /// casts away the const of the result. For documentation about what an 116 /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that 117 /// function. 118 inline Value *GetRCIdentityRoot(Value *V) { 119 return const_cast<Value *>(GetRCIdentityRoot((const Value *)V)); 120 } 121 122 /// \brief Assuming the given instruction is one of the special calls such as 123 /// objc_retain or objc_release, return the RCIdentity root of the argument of 124 /// the call. 125 inline Value *GetArgRCIdentityRoot(Value *Inst) { 126 return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0)); 127 } 128 129 inline bool IsNullOrUndef(const Value *V) { 130 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V); 131 } 132 133 inline bool IsNoopInstruction(const Instruction *I) { 134 return isa<BitCastInst>(I) || 135 (isa<GetElementPtrInst>(I) && 136 cast<GetElementPtrInst>(I)->hasAllZeroIndices()); 137 } 138 139 /// \brief Test whether the given value is possible a retainable object pointer. 140 inline bool IsPotentialRetainableObjPtr(const Value *Op) { 141 // Pointers to static or stack storage are not valid retainable object 142 // pointers. 143 if (isa<Constant>(Op) || isa<AllocaInst>(Op)) 144 return false; 145 // Special arguments can not be a valid retainable object pointer. 146 if (const Argument *Arg = dyn_cast<Argument>(Op)) 147 if (Arg->hasByValAttr() || 148 Arg->hasInAllocaAttr() || 149 Arg->hasNestAttr() || 150 Arg->hasStructRetAttr()) 151 return false; 152 // Only consider values with pointer types. 153 // 154 // It seemes intuitive to exclude function pointer types as well, since 155 // functions are never retainable object pointers, however clang occasionally 156 // bitcasts retainable object pointers to function-pointer type temporarily. 157 PointerType *Ty = dyn_cast<PointerType>(Op->getType()); 158 if (!Ty) 159 return false; 160 // Conservatively assume anything else is a potential retainable object 161 // pointer. 162 return true; 163 } 164 165 inline bool IsPotentialRetainableObjPtr(const Value *Op, 166 AliasAnalysis &AA) { 167 // First make the rudimentary check. 168 if (!IsPotentialRetainableObjPtr(Op)) 169 return false; 170 171 // Objects in constant memory are not reference-counted. 172 if (AA.pointsToConstantMemory(Op)) 173 return false; 174 175 // Pointers in constant memory are not pointing to reference-counted objects. 176 if (const LoadInst *LI = dyn_cast<LoadInst>(Op)) 177 if (AA.pointsToConstantMemory(LI->getPointerOperand())) 178 return false; 179 180 // Otherwise assume the worst. 181 return true; 182 } 183 184 /// \brief Helper for GetARCInstKind. Determines what kind of construct CS 185 /// is. 186 inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) { 187 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 188 I != E; ++I) 189 if (IsPotentialRetainableObjPtr(*I)) 190 return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser; 191 192 return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call; 193 } 194 195 /// \brief Return true if this value refers to a distinct and identifiable 196 /// object. 197 /// 198 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses 199 /// special knowledge of ObjC conventions. 200 inline bool IsObjCIdentifiedObject(const Value *V) { 201 // Assume that call results and arguments have their own "provenance". 202 // Constants (including GlobalVariables) and Allocas are never 203 // reference-counted. 204 if (isa<CallInst>(V) || isa<InvokeInst>(V) || 205 isa<Argument>(V) || isa<Constant>(V) || 206 isa<AllocaInst>(V)) 207 return true; 208 209 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) { 210 const Value *Pointer = 211 GetRCIdentityRoot(LI->getPointerOperand()); 212 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) { 213 // A constant pointer can't be pointing to an object on the heap. It may 214 // be reference-counted, but it won't be deleted. 215 if (GV->isConstant()) 216 return true; 217 StringRef Name = GV->getName(); 218 // These special variables are known to hold values which are not 219 // reference-counted pointers. 220 if (Name.startswith("\01l_objc_msgSend_fixup_")) 221 return true; 222 223 StringRef Section = GV->getSection(); 224 if (Section.find("__message_refs") != StringRef::npos || 225 Section.find("__objc_classrefs") != StringRef::npos || 226 Section.find("__objc_superrefs") != StringRef::npos || 227 Section.find("__objc_methname") != StringRef::npos || 228 Section.find("__cstring") != StringRef::npos) 229 return true; 230 } 231 } 232 233 return false; 234 } 235 236 enum class ARCMDKindID { 237 ImpreciseRelease, 238 CopyOnEscape, 239 NoObjCARCExceptions, 240 }; 241 242 /// A cache of MDKinds used by various ARC optimizations. 243 class ARCMDKindCache { 244 Module *M; 245 246 /// The Metadata Kind for clang.imprecise_release metadata. 247 llvm::Optional<unsigned> ImpreciseReleaseMDKind; 248 249 /// The Metadata Kind for clang.arc.copy_on_escape metadata. 250 llvm::Optional<unsigned> CopyOnEscapeMDKind; 251 252 /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata. 253 llvm::Optional<unsigned> NoObjCARCExceptionsMDKind; 254 255 public: 256 void init(Module *Mod) { 257 M = Mod; 258 ImpreciseReleaseMDKind = NoneType::None; 259 CopyOnEscapeMDKind = NoneType::None; 260 NoObjCARCExceptionsMDKind = NoneType::None; 261 } 262 263 unsigned get(ARCMDKindID ID) { 264 switch (ID) { 265 case ARCMDKindID::ImpreciseRelease: 266 if (!ImpreciseReleaseMDKind) 267 ImpreciseReleaseMDKind = 268 M->getContext().getMDKindID("clang.imprecise_release"); 269 return *ImpreciseReleaseMDKind; 270 case ARCMDKindID::CopyOnEscape: 271 if (!CopyOnEscapeMDKind) 272 CopyOnEscapeMDKind = 273 M->getContext().getMDKindID("clang.arc.copy_on_escape"); 274 return *CopyOnEscapeMDKind; 275 case ARCMDKindID::NoObjCARCExceptions: 276 if (!NoObjCARCExceptionsMDKind) 277 NoObjCARCExceptionsMDKind = 278 M->getContext().getMDKindID("clang.arc.no_objc_arc_exceptions"); 279 return *NoObjCARCExceptionsMDKind; 280 } 281 llvm_unreachable("Covered switch isn't covered?!"); 282 } 283 }; 284 285 } // end namespace objcarc 286 } // end namespace llvm 287 288 #endif 289
