/3rd_party/llvm/lib/Transforms/Scalar/ObjCARC.cpp
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1//===- ObjCARC.cpp - ObjC ARC Optimization --------------------------------===// 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// 10// This file defines ObjC ARC optimizations. ARC stands for 11// Automatic Reference Counting and is a system for managing reference counts 12// for objects in Objective C. 13// 14// The optimizations performed include elimination of redundant, partially 15// redundant, and inconsequential reference count operations, elimination of 16// redundant weak pointer operations, pattern-matching and replacement of 17// low-level operations into higher-level operations, and numerous minor 18// simplifications. 19// 20// This file also defines a simple ARC-aware AliasAnalysis. 21// 22// WARNING: This file knows about certain library functions. It recognizes them 23// by name, and hardwires knowledge of their semantics. 24// 25// WARNING: This file knows about how certain Objective-C library functions are 26// used. Naive LLVM IR transformations which would otherwise be 27// behavior-preserving may break these assumptions. 28// 29//===----------------------------------------------------------------------===// 30 31#define DEBUG_TYPE "objc-arc" 32#include "llvm/Support/CommandLine.h" 33#include "llvm/ADT/DenseMap.h" 34using namespace llvm; 35 36// A handy option to enable/disable all optimizations in this file. 37static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true)); 38 39//===----------------------------------------------------------------------===// 40// Misc. Utilities 41//===----------------------------------------------------------------------===// 42 43namespace { 44 /// MapVector - An associative container with fast insertion-order 45 /// (deterministic) iteration over its elements. Plus the special 46 /// blot operation. 47 template<class KeyT, class ValueT> 48 class MapVector { 49 /// Map - Map keys to indices in Vector. 50 typedef DenseMap<KeyT, size_t> MapTy; 51 MapTy Map; 52 53 /// Vector - Keys and values. 54 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy; 55 VectorTy Vector; 56 57 public: 58 typedef typename VectorTy::iterator iterator; 59 typedef typename VectorTy::const_iterator const_iterator; 60 iterator begin() { return Vector.begin(); } 61 iterator end() { return Vector.end(); } 62 const_iterator begin() const { return Vector.begin(); } 63 const_iterator end() const { return Vector.end(); } 64 65#ifdef XDEBUG 66 ~MapVector() { 67 assert(Vector.size() >= Map.size()); // May differ due to blotting. 68 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end(); 69 I != E; ++I) { 70 assert(I->second < Vector.size()); 71 assert(Vector[I->second].first == I->first); 72 } 73 for (typename VectorTy::const_iterator I = Vector.begin(), 74 E = Vector.end(); I != E; ++I) 75 assert(!I->first || 76 (Map.count(I->first) && 77 Map[I->first] == size_t(I - Vector.begin()))); 78 } 79#endif 80 81 ValueT &operator[](const KeyT &Arg) { 82 std::pair<typename MapTy::iterator, bool> Pair = 83 Map.insert(std::make_pair(Arg, size_t(0))); 84 if (Pair.second) { 85 size_t Num = Vector.size(); 86 Pair.first->second = Num; 87 Vector.push_back(std::make_pair(Arg, ValueT())); 88 return Vector[Num].second; 89 } 90 return Vector[Pair.first->second].second; 91 } 92 93 std::pair<iterator, bool> 94 insert(const std::pair<KeyT, ValueT> &InsertPair) { 95 std::pair<typename MapTy::iterator, bool> Pair = 96 Map.insert(std::make_pair(InsertPair.first, size_t(0))); 97 if (Pair.second) { 98 size_t Num = Vector.size(); 99 Pair.first->second = Num; 100 Vector.push_back(InsertPair); 101 return std::make_pair(Vector.begin() + Num, true); 102 } 103 return std::make_pair(Vector.begin() + Pair.first->second, false); 104 } 105 106 const_iterator find(const KeyT &Key) const { 107 typename MapTy::const_iterator It = Map.find(Key); 108 if (It == Map.end()) return Vector.end(); 109 return Vector.begin() + It->second; 110 } 111 112 /// blot - This is similar to erase, but instead of removing the element 113 /// from the vector, it just zeros out the key in the vector. This leaves 114 /// iterators intact, but clients must be prepared for zeroed-out keys when 115 /// iterating. 116 void blot(const KeyT &Key) { 117 typename MapTy::iterator It = Map.find(Key); 118 if (It == Map.end()) return; 119 Vector[It->second].first = KeyT(); 120 Map.erase(It); 121 } 122 123 void clear() { 124 Map.clear(); 125 Vector.clear(); 126 } 127 }; 128} 129 130//===----------------------------------------------------------------------===// 131// ARC Utilities. 132//===----------------------------------------------------------------------===// 133 134#include "llvm/Intrinsics.h" 135#include "llvm/Module.h" 136#include "llvm/Analysis/ValueTracking.h" 137#include "llvm/Transforms/Utils/Local.h" 138#include "llvm/Support/CallSite.h" 139#include "llvm/ADT/StringSwitch.h" 140 141namespace { 142 /// InstructionClass - A simple classification for instructions. 143 enum InstructionClass { 144 IC_Retain, ///< objc_retain 145 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue 146 IC_RetainBlock, ///< objc_retainBlock 147 IC_Release, ///< objc_release 148 IC_Autorelease, ///< objc_autorelease 149 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue 150 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush 151 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop 152 IC_NoopCast, ///< objc_retainedObject, etc. 153 IC_FusedRetainAutorelease, ///< objc_retainAutorelease 154 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue 155 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive) 156 IC_StoreWeak, ///< objc_storeWeak (primitive) 157 IC_InitWeak, ///< objc_initWeak (derived) 158 IC_LoadWeak, ///< objc_loadWeak (derived) 159 IC_MoveWeak, ///< objc_moveWeak (derived) 160 IC_CopyWeak, ///< objc_copyWeak (derived) 161 IC_DestroyWeak, ///< objc_destroyWeak (derived) 162 IC_StoreStrong, ///< objc_storeStrong (derived) 163 IC_CallOrUser, ///< could call objc_release and/or "use" pointers 164 IC_Call, ///< could call objc_release 165 IC_User, ///< could "use" a pointer 166 IC_None ///< anything else 167 }; 168} 169 170/// IsPotentialUse - Test whether the given value is possible a 171/// reference-counted pointer. 172static bool IsPotentialUse(const Value *Op) { 173 // Pointers to static or stack storage are not reference-counted pointers. 174 if (isa<Constant>(Op) || isa<AllocaInst>(Op)) 175 return false; 176 // Special arguments are not reference-counted. 177 if (const Argument *Arg = dyn_cast<Argument>(Op)) 178 if (Arg->hasByValAttr() || 179 Arg->hasNestAttr() || 180 Arg->hasStructRetAttr()) 181 return false; 182 // Only consider values with pointer types. 183 // It seemes intuitive to exclude function pointer types as well, since 184 // functions are never reference-counted, however clang occasionally 185 // bitcasts reference-counted pointers to function-pointer type 186 // temporarily. 187 PointerType *Ty = dyn_cast<PointerType>(Op->getType()); 188 if (!Ty) 189 return false; 190 // Conservatively assume anything else is a potential use. 191 return true; 192} 193 194/// GetCallSiteClass - Helper for GetInstructionClass. Determines what kind 195/// of construct CS is. 196static InstructionClass GetCallSiteClass(ImmutableCallSite CS) { 197 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 198 I != E; ++I) 199 if (IsPotentialUse(*I)) 200 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser; 201 202 return CS.onlyReadsMemory() ? IC_None : IC_Call; 203} 204 205/// GetFunctionClass - Determine if F is one of the special known Functions. 206/// If it isn't, return IC_CallOrUser. 207static InstructionClass GetFunctionClass(const Function *F) { 208 Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end(); 209 210 // No arguments. 211 if (AI == AE) 212 return StringSwitch<InstructionClass>(F->getName()) 213 .Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush) 214 .Default(IC_CallOrUser); 215 216 // One argument. 217 const Argument *A0 = AI++; 218 if (AI == AE) 219 // Argument is a pointer. 220 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) { 221 Type *ETy = PTy->getElementType(); 222 // Argument is i8*. 223 if (ETy->isIntegerTy(8)) 224 return StringSwitch<InstructionClass>(F->getName()) 225 .Case("objc_retain", IC_Retain) 226 .Case("objc_retainAutoreleasedReturnValue", IC_RetainRV) 227 .Case("objc_retainBlock", IC_RetainBlock) 228 .Case("objc_release", IC_Release) 229 .Case("objc_autorelease", IC_Autorelease) 230 .Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV) 231 .Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop) 232 .Case("objc_retainedObject", IC_NoopCast) 233 .Case("objc_unretainedObject", IC_NoopCast) 234 .Case("objc_unretainedPointer", IC_NoopCast) 235 .Case("objc_retain_autorelease", IC_FusedRetainAutorelease) 236 .Case("objc_retainAutorelease", IC_FusedRetainAutorelease) 237 .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV) 238 .Default(IC_CallOrUser); 239 240 // Argument is i8** 241 if (PointerType *Pte = dyn_cast<PointerType>(ETy)) 242 if (Pte->getElementType()->isIntegerTy(8)) 243 return StringSwitch<InstructionClass>(F->getName()) 244 .Case("objc_loadWeakRetained", IC_LoadWeakRetained) 245 .Case("objc_loadWeak", IC_LoadWeak) 246 .Case("objc_destroyWeak", IC_DestroyWeak) 247 .Default(IC_CallOrUser); 248 } 249 250 // Two arguments, first is i8**. 251 const Argument *A1 = AI++; 252 if (AI == AE) 253 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) 254 if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType())) 255 if (Pte->getElementType()->isIntegerTy(8)) 256 if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) { 257 Type *ETy1 = PTy1->getElementType(); 258 // Second argument is i8* 259 if (ETy1->isIntegerTy(8)) 260 return StringSwitch<InstructionClass>(F->getName()) 261 .Case("objc_storeWeak", IC_StoreWeak) 262 .Case("objc_initWeak", IC_InitWeak) 263 .Case("objc_storeStrong", IC_StoreStrong) 264 .Default(IC_CallOrUser); 265 // Second argument is i8**. 266 if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1)) 267 if (Pte1->getElementType()->isIntegerTy(8)) 268 return StringSwitch<InstructionClass>(F->getName()) 269 .Case("objc_moveWeak", IC_MoveWeak) 270 .Case("objc_copyWeak", IC_CopyWeak) 271 .Default(IC_CallOrUser); 272 } 273 274 // Anything else. 275 return IC_CallOrUser; 276} 277 278/// GetInstructionClass - Determine what kind of construct V is. 279static InstructionClass GetInstructionClass(const Value *V) { 280 if (const Instruction *I = dyn_cast<Instruction>(V)) { 281 // Any instruction other than bitcast and gep with a pointer operand have a 282 // use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer 283 // to a subsequent use, rather than using it themselves, in this sense. 284 // As a short cut, several other opcodes are known to have no pointer 285 // operands of interest. And ret is never followed by a release, so it's 286 // not interesting to examine. 287 switch (I->getOpcode()) { 288 case Instruction::Call: { 289 const CallInst *CI = cast<CallInst>(I); 290 // Check for calls to special functions. 291 if (const Function *F = CI->getCalledFunction()) { 292 InstructionClass Class = GetFunctionClass(F); 293 if (Class != IC_CallOrUser) 294 return Class; 295 296 // None of the intrinsic functions do objc_release. For intrinsics, the 297 // only question is whether or not they may be users. 298 switch (F->getIntrinsicID()) { 299 case Intrinsic::returnaddress: case Intrinsic::frameaddress: 300 case Intrinsic::stacksave: case Intrinsic::stackrestore: 301 case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend: 302 case Intrinsic::objectsize: case Intrinsic::prefetch: 303 case Intrinsic::stackprotector: 304 case Intrinsic::eh_return_i32: case Intrinsic::eh_return_i64: 305 case Intrinsic::eh_typeid_for: case Intrinsic::eh_dwarf_cfa: 306 case Intrinsic::eh_sjlj_lsda: case Intrinsic::eh_sjlj_functioncontext: 307 case Intrinsic::init_trampoline: case Intrinsic::adjust_trampoline: 308 case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: 309 case Intrinsic::invariant_start: case Intrinsic::invariant_end: 310 // Don't let dbg info affect our results. 311 case Intrinsic::dbg_declare: case Intrinsic::dbg_value: 312 // Short cut: Some intrinsics obviously don't use ObjC pointers. 313 return IC_None; 314 default: 315 break; 316 } 317 } 318 return GetCallSiteClass(CI); 319 } 320 case Instruction::Invoke: 321 return GetCallSiteClass(cast<InvokeInst>(I)); 322 case Instruction::BitCast: 323 case Instruction::GetElementPtr: 324 case Instruction::Select: case Instruction::PHI: 325 case Instruction::Ret: case Instruction::Br: 326 case Instruction::Switch: case Instruction::IndirectBr: 327 case Instruction::Alloca: case Instruction::VAArg: 328 case Instruction::Add: case Instruction::FAdd: 329 case Instruction::Sub: case Instruction::FSub: 330 case Instruction::Mul: case Instruction::FMul: 331 case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv: 332 case Instruction::SRem: case Instruction::URem: case Instruction::FRem: 333 case Instruction::Shl: case Instruction::LShr: case Instruction::AShr: 334 case Instruction::And: case Instruction::Or: case Instruction::Xor: 335 case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc: 336 case Instruction::IntToPtr: case Instruction::FCmp: 337 case Instruction::FPTrunc: case Instruction::FPExt: 338 case Instruction::FPToUI: case Instruction::FPToSI: 339 case Instruction::UIToFP: case Instruction::SIToFP: 340 case Instruction::InsertElement: case Instruction::ExtractElement: 341 case Instruction::ShuffleVector: 342 case Instruction::ExtractValue: 343 break; 344 case Instruction::ICmp: 345 // Comparing a pointer with null, or any other constant, isn't an 346 // interesting use, because we don't care what the pointer points to, or 347 // about the values of any other dynamic reference-counted pointers. 348 if (IsPotentialUse(I->getOperand(1))) 349 return IC_User; 350 break; 351 default: 352 // For anything else, check all the operands. 353 // Note that this includes both operands of a Store: while the first 354 // operand isn't actually being dereferenced, it is being stored to 355 // memory where we can no longer track who might read it and dereference 356 // it, so we have to consider it potentially used. 357 for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end(); 358 OI != OE; ++OI) 359 if (IsPotentialUse(*OI)) 360 return IC_User; 361 } 362 } 363 364 // Otherwise, it's totally inert for ARC purposes. 365 return IC_None; 366} 367 368/// GetBasicInstructionClass - Determine what kind of construct V is. This is 369/// similar to GetInstructionClass except that it only detects objc runtine 370/// calls. This allows it to be faster. 371static InstructionClass GetBasicInstructionClass(const Value *V) { 372 if (const CallInst *CI = dyn_cast<CallInst>(V)) { 373 if (const Function *F = CI->getCalledFunction()) 374 return GetFunctionClass(F); 375 // Otherwise, be conservative. 376 return IC_CallOrUser; 377 } 378 379 // Otherwise, be conservative. 380 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User; 381} 382 383/// IsRetain - Test if the given class is objc_retain or 384/// equivalent. 385static bool IsRetain(InstructionClass Class) { 386 return Class == IC_Retain || 387 Class == IC_RetainRV; 388} 389 390/// IsAutorelease - Test if the given class is objc_autorelease or 391/// equivalent. 392static bool IsAutorelease(InstructionClass Class) { 393 return Class == IC_Autorelease || 394 Class == IC_AutoreleaseRV; 395} 396 397/// IsForwarding - Test if the given class represents instructions which return 398/// their argument verbatim. 399static bool IsForwarding(InstructionClass Class) { 400 // objc_retainBlock technically doesn't always return its argument 401 // verbatim, but it doesn't matter for our purposes here. 402 return Class == IC_Retain || 403 Class == IC_RetainRV || 404 Class == IC_Autorelease || 405 Class == IC_AutoreleaseRV || 406 Class == IC_RetainBlock || 407 Class == IC_NoopCast; 408} 409 410/// IsNoopOnNull - Test if the given class represents instructions which do 411/// nothing if passed a null pointer. 412static bool IsNoopOnNull(InstructionClass Class) { 413 return Class == IC_Retain || 414 Class == IC_RetainRV || 415 Class == IC_Release || 416 Class == IC_Autorelease || 417 Class == IC_AutoreleaseRV || 418 Class == IC_RetainBlock; 419} 420 421/// IsAlwaysTail - Test if the given class represents instructions which are 422/// always safe to mark with the "tail" keyword. 423static bool IsAlwaysTail(InstructionClass Class) { 424 // IC_RetainBlock may be given a stack argument. 425 return Class == IC_Retain || 426 Class == IC_RetainRV || 427 Class == IC_Autorelease || 428 Class == IC_AutoreleaseRV; 429} 430 431/// IsNoThrow - Test if the given class represents instructions which are always 432/// safe to mark with the nounwind attribute.. 433static bool IsNoThrow(InstructionClass Class) { 434 // objc_retainBlock is not nounwind because it calls user copy constructors 435 // which could theoretically throw. 436 return Class == IC_Retain || 437 Class == IC_RetainRV || 438 Class == IC_Release || 439 Class == IC_Autorelease || 440 Class == IC_AutoreleaseRV || 441 Class == IC_AutoreleasepoolPush || 442 Class == IC_AutoreleasepoolPop; 443} 444 445/// EraseInstruction - Erase the given instruction. Many ObjC calls return their 446/// argument verbatim, so if it's such a call and the return value has users, 447/// replace them with the argument value. 448static void EraseInstruction(Instruction *CI) { 449 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0); 450 451 bool Unused = CI->use_empty(); 452 453 if (!Unused) { 454 // Replace the return value with the argument. 455 assert(IsForwarding(GetBasicInstructionClass(CI)) && 456 "Can't delete non-forwarding instruction with users!"); 457 CI->replaceAllUsesWith(OldArg); 458 } 459 460 CI->eraseFromParent(); 461 462 if (Unused) 463 RecursivelyDeleteTriviallyDeadInstructions(OldArg); 464} 465 466/// GetUnderlyingObjCPtr - This is a wrapper around getUnderlyingObject which 467/// also knows how to look through objc_retain and objc_autorelease calls, which 468/// we know to return their argument verbatim. 469static const Value *GetUnderlyingObjCPtr(const Value *V) { 470 for (;;) { 471 V = GetUnderlyingObject(V); 472 if (!IsForwarding(GetBasicInstructionClass(V))) 473 break; 474 V = cast<CallInst>(V)->getArgOperand(0); 475 } 476 477 return V; 478} 479 480/// StripPointerCastsAndObjCCalls - This is a wrapper around 481/// Value::stripPointerCasts which also knows how to look through objc_retain 482/// and objc_autorelease calls, which we know to return their argument verbatim. 483static const Value *StripPointerCastsAndObjCCalls(const Value *V) { 484 for (;;) { 485 V = V->stripPointerCasts(); 486 if (!IsForwarding(GetBasicInstructionClass(V))) 487 break; 488 V = cast<CallInst>(V)->getArgOperand(0); 489 } 490 return V; 491} 492 493/// StripPointerCastsAndObjCCalls - This is a wrapper around 494/// Value::stripPointerCasts which also knows how to look through objc_retain 495/// and objc_autorelease calls, which we know to return their argument verbatim. 496static Value *StripPointerCastsAndObjCCalls(Value *V) { 497 for (;;) { 498 V = V->stripPointerCasts(); 499 if (!IsForwarding(GetBasicInstructionClass(V))) 500 break; 501 V = cast<CallInst>(V)->getArgOperand(0); 502 } 503 return V; 504} 505 506/// GetObjCArg - Assuming the given instruction is one of the special calls such 507/// as objc_retain or objc_release, return the argument value, stripped of no-op 508/// casts and forwarding calls. 509static Value *GetObjCArg(Value *Inst) { 510 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0)); 511} 512 513/// IsObjCIdentifiedObject - This is similar to AliasAnalysis' 514/// isObjCIdentifiedObject, except that it uses special knowledge of 515/// ObjC conventions... 516static bool IsObjCIdentifiedObject(const Value *V) { 517 // Assume that call results and arguments have their own "provenance". 518 // Constants (including GlobalVariables) and Allocas are never 519 // reference-counted. 520 if (isa<CallInst>(V) || isa<InvokeInst>(V) || 521 isa<Argument>(V) || isa<Constant>(V) || 522 isa<AllocaInst>(V)) 523 return true; 524 525 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) { 526 const Value *Pointer = 527 StripPointerCastsAndObjCCalls(LI->getPointerOperand()); 528 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) { 529 // A constant pointer can't be pointing to an object on the heap. It may 530 // be reference-counted, but it won't be deleted. 531 if (GV->isConstant()) 532 return true; 533 StringRef Name = GV->getName(); 534 // These special variables are known to hold values which are not 535 // reference-counted pointers. 536 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") || 537 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") || 538 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") || 539 Name.startswith("\01L_OBJC_METH_VAR_NAME_") || 540 Name.startswith("\01l_objc_msgSend_fixup_")) 541 return true; 542 } 543 } 544 545 return false; 546} 547 548/// FindSingleUseIdentifiedObject - This is similar to 549/// StripPointerCastsAndObjCCalls but it stops as soon as it finds a value 550/// with multiple uses. 551static const Value *FindSingleUseIdentifiedObject(const Value *Arg) { 552 if (Arg->hasOneUse()) { 553 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg)) 554 return FindSingleUseIdentifiedObject(BC->getOperand(0)); 555 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg)) 556 if (GEP->hasAllZeroIndices()) 557 return FindSingleUseIdentifiedObject(GEP->getPointerOperand()); 558 if (IsForwarding(GetBasicInstructionClass(Arg))) 559 return FindSingleUseIdentifiedObject( 560 cast<CallInst>(Arg)->getArgOperand(0)); 561 if (!IsObjCIdentifiedObject(Arg)) 562 return 0; 563 return Arg; 564 } 565 566 // If we found an identifiable object but it has multiple uses, but they are 567 // trivial uses, we can still consider this to be a single-use value. 568 if (IsObjCIdentifiedObject(Arg)) { 569 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); 570 UI != UE; ++UI) { 571 const User *U = *UI; 572 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg) 573 return 0; 574 } 575 576 return Arg; 577 } 578 579 return 0; 580} 581 582/// ModuleHasARC - Test if the given module looks interesting to run ARC 583/// optimization on. 584static bool ModuleHasARC(const Module &M) { 585 return 586 M.getNamedValue("objc_retain") || 587 M.getNamedValue("objc_release") || 588 M.getNamedValue("objc_autorelease") || 589 M.getNamedValue("objc_retainAutoreleasedReturnValue") || 590 M.getNamedValue("objc_retainBlock") || 591 M.getNamedValue("objc_autoreleaseReturnValue") || 592 M.getNamedValue("objc_autoreleasePoolPush") || 593 M.getNamedValue("objc_loadWeakRetained") || 594 M.getNamedValue("objc_loadWeak") || 595 M.getNamedValue("objc_destroyWeak") || 596 M.getNamedValue("objc_storeWeak") || 597 M.getNamedValue("objc_initWeak") || 598 M.getNamedValue("objc_moveWeak") || 599 M.getNamedValue("objc_copyWeak") || 600 M.getNamedValue("objc_retainedObject") || 601 M.getNamedValue("objc_unretainedObject") || 602 M.getNamedValue("objc_unretainedPointer"); 603} 604 605/// DoesObjCBlockEscape - Test whether the given pointer, which is an 606/// Objective C block pointer, does not "escape". This differs from regular 607/// escape analysis in that a use as an argument to a call is not considered 608/// an escape. 609static bool DoesObjCBlockEscape(const Value *BlockPtr) { 610 // Walk the def-use chains. 611 SmallVector<const Value *, 4> Worklist; 612 Worklist.push_back(BlockPtr); 613 do { 614 const Value *V = Worklist.pop_back_val(); 615 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end(); 616 UI != UE; ++UI) { 617 const User *UUser = *UI; 618 // Special - Use by a call (callee or argument) is not considered 619 // to be an escape. 620 switch (GetBasicInstructionClass(UUser)) { 621 case IC_StoreWeak: 622 case IC_InitWeak: 623 case IC_StoreStrong: 624 case IC_Autorelease: 625 case IC_AutoreleaseRV: 626 // These special functions make copies of their pointer arguments. 627 return true; 628 case IC_User: 629 case IC_None: 630 // Use by an instruction which copies the value is an escape if the 631 // result is an escape. 632 if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) || 633 isa<PHINode>(UUser) || isa<SelectInst>(UUser)) { 634 Worklist.push_back(UUser); 635 continue; 636 } 637 // Use by a load is not an escape. 638 if (isa<LoadInst>(UUser)) 639 continue; 640 // Use by a store is not an escape if the use is the address. 641 if (const StoreInst *SI = dyn_cast<StoreInst>(UUser)) 642 if (V != SI->getValueOperand()) 643 continue; 644 break; 645 default: 646 // Regular calls and other stuff are not considered escapes. 647 continue; 648 } 649 // Otherwise, conservatively assume an escape. 650 return true; 651 } 652 } while (!Worklist.empty()); 653 654 // No escapes found. 655 return false; 656} 657 658//===----------------------------------------------------------------------===// 659// ARC AliasAnalysis. 660//===----------------------------------------------------------------------===// 661 662#include "llvm/Pass.h" 663#include "llvm/Analysis/AliasAnalysis.h" 664#include "llvm/Analysis/Passes.h" 665 666namespace { 667 /// ObjCARCAliasAnalysis - This is a simple alias analysis 668 /// implementation that uses knowledge of ARC constructs to answer queries. 669 /// 670 /// TODO: This class could be generalized to know about other ObjC-specific 671 /// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing 672 /// even though their offsets are dynamic. 673 class ObjCARCAliasAnalysis : public ImmutablePass, 674 public AliasAnalysis { 675 public: 676 static char ID; // Class identification, replacement for typeinfo 677 ObjCARCAliasAnalysis() : ImmutablePass(ID) { 678 initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry()); 679 } 680 681 private: 682 virtual void initializePass() { 683 InitializeAliasAnalysis(this); 684 } 685 686 /// getAdjustedAnalysisPointer - This method is used when a pass implements 687 /// an analysis interface through multiple inheritance. If needed, it 688 /// should override this to adjust the this pointer as needed for the 689 /// specified pass info. 690 virtual void *getAdjustedAnalysisPointer(const void *PI) { 691 if (PI == &AliasAnalysis::ID) 692 return static_cast<AliasAnalysis *>(this); 693 return this; 694 } 695 696 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 697 virtual AliasResult alias(const Location &LocA, const Location &LocB); 698 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); 699 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 700 virtual ModRefBehavior getModRefBehavior(const Function *F); 701 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 702 const Location &Loc); 703 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 704 ImmutableCallSite CS2); 705 }; 706} // End of anonymous namespace 707 708// Register this pass... 709char ObjCARCAliasAnalysis::ID = 0; 710INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa", 711 "ObjC-ARC-Based Alias Analysis", false, true, false) 712 713ImmutablePass *llvm::createObjCARCAliasAnalysisPass() { 714 return new ObjCARCAliasAnalysis(); 715} 716 717void 718ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 719 AU.setPreservesAll(); 720 AliasAnalysis::getAnalysisUsage(AU); 721} 722 723AliasAnalysis::AliasResult 724ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) { 725 if (!EnableARCOpts) 726 return AliasAnalysis::alias(LocA, LocB); 727 728 // First, strip off no-ops, including ObjC-specific no-ops, and try making a 729 // precise alias query. 730 const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr); 731 const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr); 732 AliasResult Result = 733 AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag), 734 Location(SB, LocB.Size, LocB.TBAATag)); 735 if (Result != MayAlias) 736 return Result; 737 738 // If that failed, climb to the underlying object, including climbing through 739 // ObjC-specific no-ops, and try making an imprecise alias query. 740 const Value *UA = GetUnderlyingObjCPtr(SA); 741 const Value *UB = GetUnderlyingObjCPtr(SB); 742 if (UA != SA || UB != SB) { 743 Result = AliasAnalysis::alias(Location(UA), Location(UB)); 744 // We can't use MustAlias or PartialAlias results here because 745 // GetUnderlyingObjCPtr may return an offsetted pointer value. 746 if (Result == NoAlias) 747 return NoAlias; 748 } 749 750 // If that failed, fail. We don't need to chain here, since that's covered 751 // by the earlier precise query. 752 return MayAlias; 753} 754 755bool 756ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc, 757 bool OrLocal) { 758 if (!EnableARCOpts) 759 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 760 761 // First, strip off no-ops, including ObjC-specific no-ops, and try making 762 // a precise alias query. 763 const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr); 764 if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag), 765 OrLocal)) 766 return true; 767 768 // If that failed, climb to the underlying object, including climbing through 769 // ObjC-specific no-ops, and try making an imprecise alias query. 770 const Value *U = GetUnderlyingObjCPtr(S); 771 if (U != S) 772 return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal); 773 774 // If that failed, fail. We don't need to chain here, since that's covered 775 // by the earlier precise query. 776 return false; 777} 778 779AliasAnalysis::ModRefBehavior 780ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { 781 // We have nothing to do. Just chain to the next AliasAnalysis. 782 return AliasAnalysis::getModRefBehavior(CS); 783} 784 785AliasAnalysis::ModRefBehavior 786ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) { 787 if (!EnableARCOpts) 788 return AliasAnalysis::getModRefBehavior(F); 789 790 switch (GetFunctionClass(F)) { 791 case IC_NoopCast: 792 return DoesNotAccessMemory; 793 default: 794 break; 795 } 796 797 return AliasAnalysis::getModRefBehavior(F); 798} 799 800AliasAnalysis::ModRefResult 801ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { 802 if (!EnableARCOpts) 803 return AliasAnalysis::getModRefInfo(CS, Loc); 804 805 switch (GetBasicInstructionClass(CS.getInstruction())) { 806 case IC_Retain: 807 case IC_RetainRV: 808 case IC_Autorelease: 809 case IC_AutoreleaseRV: 810 case IC_NoopCast: 811 case IC_AutoreleasepoolPush: 812 case IC_FusedRetainAutorelease: 813 case IC_FusedRetainAutoreleaseRV: 814 // These functions don't access any memory visible to the compiler. 815 // Note that this doesn't include objc_retainBlock, because it updates 816 // pointers when it copies block data. 817 return NoModRef; 818 default: 819 break; 820 } 821 822 return AliasAnalysis::getModRefInfo(CS, Loc); 823} 824 825AliasAnalysis::ModRefResult 826ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1, 827 ImmutableCallSite CS2) { 828 // TODO: Theoretically we could check for dependencies between objc_* calls 829 // and OnlyAccessesArgumentPointees calls or other well-behaved calls. 830 return AliasAnalysis::getModRefInfo(CS1, CS2); 831} 832 833//===----------------------------------------------------------------------===// 834// ARC expansion. 835//===----------------------------------------------------------------------===// 836 837#include "llvm/Support/InstIterator.h" 838#include "llvm/Transforms/Scalar.h" 839 840namespace { 841 /// ObjCARCExpand - Early ARC transformations. 842 class ObjCARCExpand : public FunctionPass { 843 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 844 virtual bool doInitialization(Module &M); 845 virtual bool runOnFunction(Function &F); 846 847 /// Run - A flag indicating whether this optimization pass should run. 848 bool Run; 849 850 public: 851 static char ID; 852 ObjCARCExpand() : FunctionPass(ID) { 853 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 854 } 855 }; 856} 857 858char ObjCARCExpand::ID = 0; 859INITIALIZE_PASS(ObjCARCExpand, 860 "objc-arc-expand", "ObjC ARC expansion", false, false) 861 862Pass *llvm::createObjCARCExpandPass() { 863 return new ObjCARCExpand(); 864} 865 866void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 867 AU.setPreservesCFG(); 868} 869 870bool ObjCARCExpand::doInitialization(Module &M) { 871 Run = ModuleHasARC(M); 872 return false; 873} 874 875bool ObjCARCExpand::runOnFunction(Function &F) { 876 if (!EnableARCOpts) 877 return false; 878 879 // If nothing in the Module uses ARC, don't do anything. 880 if (!Run) 881 return false; 882 883 bool Changed = false; 884 885 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 886 Instruction *Inst = &*I; 887 888 switch (GetBasicInstructionClass(Inst)) { 889 case IC_Retain: 890 case IC_RetainRV: 891 case IC_Autorelease: 892 case IC_AutoreleaseRV: 893 case IC_FusedRetainAutorelease: 894 case IC_FusedRetainAutoreleaseRV: 895 // These calls return their argument verbatim, as a low-level 896 // optimization. However, this makes high-level optimizations 897 // harder. Undo any uses of this optimization that the front-end 898 // emitted here. We'll redo them in the contract pass. 899 Changed = true; 900 Inst->replaceAllUsesWith(cast<CallInst>(Inst)->getArgOperand(0)); 901 break; 902 default: 903 break; 904 } 905 } 906 907 return Changed; 908} 909 910//===----------------------------------------------------------------------===// 911// ARC autorelease pool elimination. 912//===----------------------------------------------------------------------===// 913 914#include "llvm/Constants.h" 915#include "llvm/ADT/STLExtras.h" 916 917namespace { 918 /// ObjCARCAPElim - Autorelease pool elimination. 919 class ObjCARCAPElim : public ModulePass { 920 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 921 virtual bool runOnModule(Module &M); 922 923 static bool MayAutorelease(ImmutableCallSite CS, unsigned Depth = 0); 924 static bool OptimizeBB(BasicBlock *BB); 925 926 public: 927 static char ID; 928 ObjCARCAPElim() : ModulePass(ID) { 929 initializeObjCARCAPElimPass(*PassRegistry::getPassRegistry()); 930 } 931 }; 932} 933 934char ObjCARCAPElim::ID = 0; 935INITIALIZE_PASS(ObjCARCAPElim, 936 "objc-arc-apelim", 937 "ObjC ARC autorelease pool elimination", 938 false, false) 939 940Pass *llvm::createObjCARCAPElimPass() { 941 return new ObjCARCAPElim(); 942} 943 944void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const { 945 AU.setPreservesCFG(); 946} 947 948/// MayAutorelease - Interprocedurally determine if calls made by the 949/// given call site can possibly produce autoreleases. 950bool ObjCARCAPElim::MayAutorelease(ImmutableCallSite CS, unsigned Depth) { 951 if (const Function *Callee = CS.getCalledFunction()) { 952 if (Callee->isDeclaration() || Callee->mayBeOverridden()) 953 return true; 954 for (Function::const_iterator I = Callee->begin(), E = Callee->end(); 955 I != E; ++I) { 956 const BasicBlock *BB = I; 957 for (BasicBlock::const_iterator J = BB->begin(), F = BB->end(); 958 J != F; ++J) 959 if (ImmutableCallSite JCS = ImmutableCallSite(J)) 960 // This recursion depth limit is arbitrary. It's just great 961 // enough to cover known interesting testcases. 962 if (Depth < 3 && 963 !JCS.onlyReadsMemory() && 964 MayAutorelease(JCS, Depth + 1)) 965 return true; 966 } 967 return false; 968 } 969 970 return true; 971} 972 973bool ObjCARCAPElim::OptimizeBB(BasicBlock *BB) { 974 bool Changed = false; 975 976 Instruction *Push = 0; 977 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 978 Instruction *Inst = I++; 979 switch (GetBasicInstructionClass(Inst)) { 980 case IC_AutoreleasepoolPush: 981 Push = Inst; 982 break; 983 case IC_AutoreleasepoolPop: 984 // If this pop matches a push and nothing in between can autorelease, 985 // zap the pair. 986 if (Push && cast<CallInst>(Inst)->getArgOperand(0) == Push) { 987 Changed = true; 988 Inst->eraseFromParent(); 989 Push->eraseFromParent(); 990 } 991 Push = 0; 992 break; 993 case IC_CallOrUser: 994 if (MayAutorelease(ImmutableCallSite(Inst))) 995 Push = 0; 996 break; 997 default: 998 break; 999 } 1000 } 1001 1002 return Changed; 1003} 1004 1005bool ObjCARCAPElim::runOnModule(Module &M) { 1006 if (!EnableARCOpts) 1007 return false; 1008 1009 // If nothing in the Module uses ARC, don't do anything. 1010 if (!ModuleHasARC(M)) 1011 return false; 1012 1013 // Find the llvm.global_ctors variable, as the first step in 1014 // identifying the global constructors. In theory, unnecessary autorelease 1015 // pools could occur anywhere, but in practice it's pretty rare. Global 1016 // ctors are a place where autorelease pools get inserted automatically, 1017 // so it's pretty common for them to be unnecessary, and it's pretty 1018 // profitable to eliminate them. 1019 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors"); 1020 if (!GV) 1021 return false; 1022 1023 assert(GV->hasDefinitiveInitializer() && 1024 "llvm.global_ctors is uncooperative!"); 1025 1026 bool Changed = false; 1027 1028 // Dig the constructor functions out of GV's initializer. 1029 ConstantArray *Init = cast<ConstantArray>(GV->getInitializer()); 1030 for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end(); 1031 OI != OE; ++OI) { 1032 Value *Op = *OI; 1033 // llvm.global_ctors is an array of pairs where the second members 1034 // are constructor functions. 1035 Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1)); 1036 // If the user used a constructor function with the wrong signature and 1037 // it got bitcasted or whatever, look the other way. 1038 if (!F) 1039 continue; 1040 // Only look at function definitions. 1041 if (F->isDeclaration()) 1042 continue; 1043 // Only look at functions with one basic block. 1044 if (llvm::next(F->begin()) != F->end()) 1045 continue; 1046 // Ok, a single-block constructor function definition. Try to optimize it. 1047 Changed |= OptimizeBB(F->begin()); 1048 } 1049 1050 return Changed; 1051} 1052 1053//===----------------------------------------------------------------------===// 1054// ARC optimization. 1055//===----------------------------------------------------------------------===// 1056 1057// TODO: On code like this: 1058// 1059// objc_retain(%x) 1060// stuff_that_cannot_release() 1061// objc_autorelease(%x) 1062// stuff_that_cannot_release() 1063// objc_retain(%x) 1064// stuff_that_cannot_release() 1065// objc_autorelease(%x) 1066// 1067// The second retain and autorelease can be deleted. 1068 1069// TODO: It should be possible to delete 1070// objc_autoreleasePoolPush and objc_autoreleasePoolPop 1071// pairs if nothing is actually autoreleased between them. Also, autorelease 1072// calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code 1073// after inlining) can be turned into plain release calls. 1074 1075// TODO: Critical-edge splitting. If the optimial insertion point is 1076// a critical edge, the current algorithm has to fail, because it doesn't 1077// know how to split edges. It should be possible to make the optimizer 1078// think in terms of edges, rather than blocks, and then split critical 1079// edges on demand. 1080 1081// TODO: OptimizeSequences could generalized to be Interprocedural. 1082 1083// TODO: Recognize that a bunch of other objc runtime calls have 1084// non-escaping arguments and non-releasing arguments, and may be 1085// non-autoreleasing. 1086 1087// TODO: Sink autorelease calls as far as possible. Unfortunately we 1088// usually can't sink them past other calls, which would be the main 1089// case where it would be useful. 1090 1091// TODO: The pointer returned from objc_loadWeakRetained is retained. 1092 1093// TODO: Delete release+retain pairs (rare). 1094 1095#include "llvm/LLVMContext.h" 1096#include "llvm/Support/CFG.h" 1097#include "llvm/ADT/Statistic.h" 1098#include "llvm/ADT/SmallPtrSet.h" 1099 1100STATISTIC(NumNoops, "Number of no-op objc calls eliminated"); 1101STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated"); 1102STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases"); 1103STATISTIC(NumRets, "Number of return value forwarding " 1104 "retain+autoreleaes eliminated"); 1105STATISTIC(NumRRs, "Number of retain+release paths eliminated"); 1106STATISTIC(NumPeeps, "Number of calls peephole-optimized"); 1107 1108namespace { 1109 /// ProvenanceAnalysis - This is similar to BasicAliasAnalysis, and it 1110 /// uses many of the same techniques, except it uses special ObjC-specific 1111 /// reasoning about pointer relationships. 1112 class ProvenanceAnalysis { 1113 AliasAnalysis *AA; 1114 1115 typedef std::pair<const Value *, const Value *> ValuePairTy; 1116 typedef DenseMap<ValuePairTy, bool> CachedResultsTy; 1117 CachedResultsTy CachedResults; 1118 1119 bool relatedCheck(const Value *A, const Value *B); 1120 bool relatedSelect(const SelectInst *A, const Value *B); 1121 bool relatedPHI(const PHINode *A, const Value *B); 1122 1123 // Do not implement. 1124 void operator=(const ProvenanceAnalysis &); 1125 ProvenanceAnalysis(const ProvenanceAnalysis &); 1126 1127 public: 1128 ProvenanceAnalysis() {} 1129 1130 void setAA(AliasAnalysis *aa) { AA = aa; } 1131 1132 AliasAnalysis *getAA() const { return AA; } 1133 1134 bool related(const Value *A, const Value *B); 1135 1136 void clear() { 1137 CachedResults.clear(); 1138 } 1139 }; 1140} 1141 1142bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) { 1143 // If the values are Selects with the same condition, we can do a more precise 1144 // check: just check for relations between the values on corresponding arms. 1145 if (const SelectInst *SB = dyn_cast<SelectInst>(B)) 1146 if (A->getCondition() == SB->getCondition()) 1147 return related(A->getTrueValue(), SB->getTrueValue()) || 1148 related(A->getFalseValue(), SB->getFalseValue()); 1149 1150 // Check both arms of the Select node individually. 1151 return related(A->getTrueValue(), B) || 1152 related(A->getFalseValue(), B); 1153} 1154 1155bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) { 1156 // If the values are PHIs in the same block, we can do a more precise as well 1157 // as efficient check: just check for relations between the values on 1158 // corresponding edges. 1159 if (const PHINode *PNB = dyn_cast<PHINode>(B)) 1160 if (PNB->getParent() == A->getParent()) { 1161 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) 1162 if (related(A->getIncomingValue(i), 1163 PNB->getIncomingValueForBlock(A->getIncomingBlock(i)))) 1164 return true; 1165 return false; 1166 } 1167 1168 // Check each unique source of the PHI node against B. 1169 SmallPtrSet<const Value *, 4> UniqueSrc; 1170 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) { 1171 const Value *PV1 = A->getIncomingValue(i); 1172 if (UniqueSrc.insert(PV1) && related(PV1, B)) 1173 return true; 1174 } 1175 1176 // All of the arms checked out. 1177 return false; 1178} 1179 1180/// isStoredObjCPointer - Test if the value of P, or any value covered by its 1181/// provenance, is ever stored within the function (not counting callees). 1182static bool isStoredObjCPointer(const Value *P) { 1183 SmallPtrSet<const Value *, 8> Visited; 1184 SmallVector<const Value *, 8> Worklist; 1185 Worklist.push_back(P); 1186 Visited.insert(P); 1187 do { 1188 P = Worklist.pop_back_val(); 1189 for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end(); 1190 UI != UE; ++UI) { 1191 const User *Ur = *UI; 1192 if (isa<StoreInst>(Ur)) { 1193 if (UI.getOperandNo() == 0) 1194 // The pointer is stored. 1195 return true; 1196 // The pointed is stored through. 1197 continue; 1198 } 1199 if (isa<CallInst>(Ur)) 1200 // The pointer is passed as an argument, ignore this. 1201 continue; 1202 if (isa<PtrToIntInst>(P)) 1203 // Assume the worst. 1204 return true; 1205 if (Visited.insert(Ur)) 1206 Worklist.push_back(Ur); 1207 } 1208 } while (!Worklist.empty()); 1209 1210 // Everything checked out. 1211 return false; 1212} 1213 1214bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) { 1215 // Skip past provenance pass-throughs. 1216 A = GetUnderlyingObjCPtr(A); 1217 B = GetUnderlyingObjCPtr(B); 1218 1219 // Quick check. 1220 if (A == B) 1221 return true; 1222 1223 // Ask regular AliasAnalysis, for a first approximation. 1224 switch (AA->alias(A, B)) { 1225 case AliasAnalysis::NoAlias: 1226 return false; 1227 case AliasAnalysis::MustAlias: 1228 case AliasAnalysis::PartialAlias: 1229 return true; 1230 case AliasAnalysis::MayAlias: 1231 break; 1232 } 1233 1234 bool AIsIdentified = IsObjCIdentifiedObject(A); 1235 bool BIsIdentified = IsObjCIdentifiedObject(B); 1236 1237 // An ObjC-Identified object can't alias a load if it is never locally stored. 1238 if (AIsIdentified) { 1239 if (BIsIdentified) { 1240 // If both pointers have provenance, they can be directly compared. 1241 if (A != B) 1242 return false; 1243 } else { 1244 if (isa<LoadInst>(B)) 1245 return isStoredObjCPointer(A); 1246 } 1247 } else { 1248 if (BIsIdentified && isa<LoadInst>(A)) 1249 return isStoredObjCPointer(B); 1250 } 1251 1252 // Special handling for PHI and Select. 1253 if (const PHINode *PN = dyn_cast<PHINode>(A)) 1254 return relatedPHI(PN, B); 1255 if (const PHINode *PN = dyn_cast<PHINode>(B)) 1256 return relatedPHI(PN, A); 1257 if (const SelectInst *S = dyn_cast<SelectInst>(A)) 1258 return relatedSelect(S, B); 1259 if (const SelectInst *S = dyn_cast<SelectInst>(B)) 1260 return relatedSelect(S, A); 1261 1262 // Conservative. 1263 return true; 1264} 1265 1266bool ProvenanceAnalysis::related(const Value *A, const Value *B) { 1267 // Begin by inserting a conservative value into the map. If the insertion 1268 // fails, we have the answer already. If it succeeds, leave it there until we 1269 // compute the real answer to guard against recursive queries. 1270 if (A > B) std::swap(A, B); 1271 std::pair<CachedResultsTy::iterator, bool> Pair = 1272 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true)); 1273 if (!Pair.second) 1274 return Pair.first->second; 1275 1276 bool Result = relatedCheck(A, B); 1277 CachedResults[ValuePairTy(A, B)] = Result; 1278 return Result; 1279} 1280 1281namespace { 1282 // Sequence - A sequence of states that a pointer may go through in which an 1283 // objc_retain and objc_release are actually needed. 1284 enum Sequence { 1285 S_None, 1286 S_Retain, ///< objc_retain(x) 1287 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement 1288 S_Use, ///< any use of x 1289 S_Stop, ///< like S_Release, but code motion is stopped 1290 S_Release, ///< objc_release(x) 1291 S_MovableRelease ///< objc_release(x), !clang.imprecise_release 1292 }; 1293} 1294 1295static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) { 1296 // The easy cases. 1297 if (A == B) 1298 return A; 1299 if (A == S_None || B == S_None) 1300 return S_None; 1301 1302 if (A > B) std::swap(A, B); 1303 if (TopDown) { 1304 // Choose the side which is further along in the sequence. 1305 if ((A == S_Retain || A == S_CanRelease) && 1306 (B == S_CanRelease || B == S_Use)) 1307 return B; 1308 } else { 1309 // Choose the side which is further along in the sequence. 1310 if ((A == S_Use || A == S_CanRelease) && 1311 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease)) 1312 return A; 1313 // If both sides are releases, choose the more conservative one. 1314 if (A == S_Stop && (B == S_Release || B == S_MovableRelease)) 1315 return A; 1316 if (A == S_Release && B == S_MovableRelease) 1317 return A; 1318 } 1319 1320 return S_None; 1321} 1322 1323namespace { 1324 /// RRInfo - Unidirectional information about either a 1325 /// retain-decrement-use-release sequence or release-use-decrement-retain 1326 /// reverese sequence. 1327 struct RRInfo { 1328 /// KnownSafe - After an objc_retain, the reference count of the referenced 1329 /// object is known to be positive. Similarly, before an objc_release, the 1330 /// reference count of the referenced object is known to be positive. If 1331 /// there are retain-release pairs in code regions where the retain count 1332 /// is known to be positive, they can be eliminated, regardless of any side 1333 /// effects between them. 1334 /// 1335 /// Also, a retain+release pair nested within another retain+release 1336 /// pair all on the known same pointer value can be eliminated, regardless 1337 /// of any intervening side effects. 1338 /// 1339 /// KnownSafe is true when either of these conditions is satisfied. 1340 bool KnownSafe; 1341 1342 /// IsRetainBlock - True if the Calls are objc_retainBlock calls (as 1343 /// opposed to objc_retain calls). 1344 bool IsRetainBlock; 1345 1346 /// IsTailCallRelease - True of the objc_release calls are all marked 1347 /// with the "tail" keyword. 1348 bool IsTailCallRelease; 1349 1350 /// ReleaseMetadata - If the Calls are objc_release calls and they all have 1351 /// a clang.imprecise_release tag, this is the metadata tag. 1352 MDNode *ReleaseMetadata; 1353 1354 /// Calls - For a top-down sequence, the set of objc_retains or 1355 /// objc_retainBlocks. For bottom-up, the set of objc_releases. 1356 SmallPtrSet<Instruction *, 2> Calls; 1357 1358 /// ReverseInsertPts - The set of optimal insert positions for 1359 /// moving calls in the opposite sequence. 1360 SmallPtrSet<Instruction *, 2> ReverseInsertPts; 1361 1362 RRInfo() …
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