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 knowedge 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/Function.h" 33 #include "llvm/Intrinsics.h" 34 #include "llvm/GlobalVariable.h" 35 #include "llvm/DerivedTypes.h" 36 #include "llvm/Module.h" 37 #include "llvm/Analysis/ValueTracking.h" 38 #include "llvm/Transforms/Utils/Local.h" 39 #include "llvm/Support/CallSite.h" 40 #include "llvm/Support/CommandLine.h" 41 #include "llvm/ADT/StringSwitch.h" 42 #include "llvm/ADT/DenseMap.h" 43 #include "llvm/ADT/STLExtras.h" 44 using namespace llvm; 45 46 // A handy option to enable/disable all optimizations in this file. 47 static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true)); 48 49 //===----------------------------------------------------------------------===// 50 // Misc. Utilities 51 //===----------------------------------------------------------------------===// 52 53 namespace { 54 /// MapVector - An associative container with fast insertion-order 55 /// (deterministic) iteration over its elements. Plus the special 56 /// blot operation. 57 template<class KeyT, class ValueT> 58 class MapVector { 59 /// Map - Map keys to indices in Vector. 60 typedef DenseMap<KeyT, size_t> MapTy; 61 MapTy Map; 62 63 /// Vector - Keys and values. 64 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy; 65 VectorTy Vector; 66 67 public: 68 typedef typename VectorTy::iterator iterator; 69 typedef typename VectorTy::const_iterator const_iterator; 70 iterator begin() { return Vector.begin(); } 71 iterator end() { return Vector.end(); } 72 const_iterator begin() const { return Vector.begin(); } 73 const_iterator end() const { return Vector.end(); } 74 75 #ifdef XDEBUG 76 ~MapVector() { 77 assert(Vector.size() >= Map.size()); // May differ due to blotting. 78 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end(); 79 I != E; ++I) { 80 assert(I->second < Vector.size()); 81 assert(Vector[I->second].first == I->first); 82 } 83 for (typename VectorTy::const_iterator I = Vector.begin(), 84 E = Vector.end(); I != E; ++I) 85 assert(!I->first || 86 (Map.count(I->first) && 87 Map[I->first] == size_t(I - Vector.begin()))); 88 } 89 #endif 90 91 ValueT &operator[](KeyT Arg) { 92 std::pair<typename MapTy::iterator, bool> Pair = 93 Map.insert(std::make_pair(Arg, size_t(0))); 94 if (Pair.second) { 95 Pair.first->second = Vector.size(); 96 Vector.push_back(std::make_pair(Arg, ValueT())); 97 return Vector.back().second; 98 } 99 return Vector[Pair.first->second].second; 100 } 101 102 std::pair<iterator, bool> 103 insert(const std::pair<KeyT, ValueT> &InsertPair) { 104 std::pair<typename MapTy::iterator, bool> Pair = 105 Map.insert(std::make_pair(InsertPair.first, size_t(0))); 106 if (Pair.second) { 107 Pair.first->second = Vector.size(); 108 Vector.push_back(InsertPair); 109 return std::make_pair(llvm::prior(Vector.end()), true); 110 } 111 return std::make_pair(Vector.begin() + Pair.first->second, false); 112 } 113 114 const_iterator find(KeyT Key) const { 115 typename MapTy::const_iterator It = Map.find(Key); 116 if (It == Map.end()) return Vector.end(); 117 return Vector.begin() + It->second; 118 } 119 120 /// blot - This is similar to erase, but instead of removing the element 121 /// from the vector, it just zeros out the key in the vector. This leaves 122 /// iterators intact, but clients must be prepared for zeroed-out keys when 123 /// iterating. 124 void blot(KeyT Key) { 125 typename MapTy::iterator It = Map.find(Key); 126 if (It == Map.end()) return; 127 Vector[It->second].first = KeyT(); 128 Map.erase(It); 129 } 130 131 void clear() { 132 Map.clear(); 133 Vector.clear(); 134 } 135 }; 136 } 137 138 //===----------------------------------------------------------------------===// 139 // ARC Utilities. 140 //===----------------------------------------------------------------------===// 141 142 namespace { 143 /// InstructionClass - A simple classification for instructions. 144 enum InstructionClass { 145 IC_Retain, ///< objc_retain 146 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue 147 IC_RetainBlock, ///< objc_retainBlock 148 IC_Release, ///< objc_release 149 IC_Autorelease, ///< objc_autorelease 150 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue 151 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush 152 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop 153 IC_NoopCast, ///< objc_retainedObject, etc. 154 IC_FusedRetainAutorelease, ///< objc_retainAutorelease 155 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue 156 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive) 157 IC_StoreWeak, ///< objc_storeWeak (primitive) 158 IC_InitWeak, ///< objc_initWeak (derived) 159 IC_LoadWeak, ///< objc_loadWeak (derived) 160 IC_MoveWeak, ///< objc_moveWeak (derived) 161 IC_CopyWeak, ///< objc_copyWeak (derived) 162 IC_DestroyWeak, ///< objc_destroyWeak (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. 172 static 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, and not function pointers. 183 PointerType *Ty = dyn_cast<PointerType>(Op->getType()); 184 if (!Ty || isa<FunctionType>(Ty->getElementType())) 185 return false; 186 // Conservatively assume anything else is a potential use. 187 return true; 188 } 189 190 /// GetCallSiteClass - Helper for GetInstructionClass. Determines what kind 191 /// of construct CS is. 192 static InstructionClass GetCallSiteClass(ImmutableCallSite CS) { 193 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 194 I != E; ++I) 195 if (IsPotentialUse(*I)) 196 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser; 197 198 return CS.onlyReadsMemory() ? IC_None : IC_Call; 199 } 200 201 /// GetFunctionClass - Determine if F is one of the special known Functions. 202 /// If it isn't, return IC_CallOrUser. 203 static InstructionClass GetFunctionClass(const Function *F) { 204 Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end(); 205 206 // No arguments. 207 if (AI == AE) 208 return StringSwitch<InstructionClass>(F->getName()) 209 .Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush) 210 .Default(IC_CallOrUser); 211 212 // One argument. 213 const Argument *A0 = AI++; 214 if (AI == AE) 215 // Argument is a pointer. 216 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) { 217 Type *ETy = PTy->getElementType(); 218 // Argument is i8*. 219 if (ETy->isIntegerTy(8)) 220 return StringSwitch<InstructionClass>(F->getName()) 221 .Case("objc_retain", IC_Retain) 222 .Case("objc_retainAutoreleasedReturnValue", IC_RetainRV) 223 .Case("objc_retainBlock", IC_RetainBlock) 224 .Case("objc_release", IC_Release) 225 .Case("objc_autorelease", IC_Autorelease) 226 .Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV) 227 .Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop) 228 .Case("objc_retainedObject", IC_NoopCast) 229 .Case("objc_unretainedObject", IC_NoopCast) 230 .Case("objc_unretainedPointer", IC_NoopCast) 231 .Case("objc_retain_autorelease", IC_FusedRetainAutorelease) 232 .Case("objc_retainAutorelease", IC_FusedRetainAutorelease) 233 .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV) 234 .Default(IC_CallOrUser); 235 236 // Argument is i8** 237 if (PointerType *Pte = dyn_cast<PointerType>(ETy)) 238 if (Pte->getElementType()->isIntegerTy(8)) 239 return StringSwitch<InstructionClass>(F->getName()) 240 .Case("objc_loadWeakRetained", IC_LoadWeakRetained) 241 .Case("objc_loadWeak", IC_LoadWeak) 242 .Case("objc_destroyWeak", IC_DestroyWeak) 243 .Default(IC_CallOrUser); 244 } 245 246 // Two arguments, first is i8**. 247 const Argument *A1 = AI++; 248 if (AI == AE) 249 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) 250 if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType())) 251 if (Pte->getElementType()->isIntegerTy(8)) 252 if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) { 253 Type *ETy1 = PTy1->getElementType(); 254 // Second argument is i8* 255 if (ETy1->isIntegerTy(8)) 256 return StringSwitch<InstructionClass>(F->getName()) 257 .Case("objc_storeWeak", IC_StoreWeak) 258 .Case("objc_initWeak", IC_InitWeak) 259 .Default(IC_CallOrUser); 260 // Second argument is i8**. 261 if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1)) 262 if (Pte1->getElementType()->isIntegerTy(8)) 263 return StringSwitch<InstructionClass>(F->getName()) 264 .Case("objc_moveWeak", IC_MoveWeak) 265 .Case("objc_copyWeak", IC_CopyWeak) 266 .Default(IC_CallOrUser); 267 } 268 269 // Anything else. 270 return IC_CallOrUser; 271 } 272 273 /// GetInstructionClass - Determine what kind of construct V is. 274 static InstructionClass GetInstructionClass(const Value *V) { 275 if (const Instruction *I = dyn_cast<Instruction>(V)) { 276 // Any instruction other than bitcast and gep with a pointer operand have a 277 // use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer 278 // to a subsequent use, rather than using it themselves, in this sense. 279 // As a short cut, several other opcodes are known to have no pointer 280 // operands of interest. And ret is never followed by a release, so it's 281 // not interesting to examine. 282 switch (I->getOpcode()) { 283 case Instruction::Call: { 284 const CallInst *CI = cast<CallInst>(I); 285 // Check for calls to special functions. 286 if (const Function *F = CI->getCalledFunction()) { 287 InstructionClass Class = GetFunctionClass(F); 288 if (Class != IC_CallOrUser) 289 return Class; 290 291 // None of the intrinsic functions do objc_release. For intrinsics, the 292 // only question is whether or not they may be users. 293 switch (F->getIntrinsicID()) { 294 case 0: break; 295 case Intrinsic::bswap: case Intrinsic::ctpop: 296 case Intrinsic::ctlz: case Intrinsic::cttz: 297 case Intrinsic::returnaddress: case Intrinsic::frameaddress: 298 case Intrinsic::stacksave: case Intrinsic::stackrestore: 299 case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend: 300 // Don't let dbg info affect our results. 301 case Intrinsic::dbg_declare: case Intrinsic::dbg_value: 302 // Short cut: Some intrinsics obviously don't use ObjC pointers. 303 return IC_None; 304 default: 305 for (Function::const_arg_iterator AI = F->arg_begin(), 306 AE = F->arg_end(); AI != AE; ++AI) 307 if (IsPotentialUse(AI)) 308 return IC_User; 309 return IC_None; 310 } 311 } 312 return GetCallSiteClass(CI); 313 } 314 case Instruction::Invoke: 315 return GetCallSiteClass(cast<InvokeInst>(I)); 316 case Instruction::BitCast: 317 case Instruction::GetElementPtr: 318 case Instruction::Select: case Instruction::PHI: 319 case Instruction::Ret: case Instruction::Br: 320 case Instruction::Switch: case Instruction::IndirectBr: 321 case Instruction::Alloca: case Instruction::VAArg: 322 case Instruction::Add: case Instruction::FAdd: 323 case Instruction::Sub: case Instruction::FSub: 324 case Instruction::Mul: case Instruction::FMul: 325 case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv: 326 case Instruction::SRem: case Instruction::URem: case Instruction::FRem: 327 case Instruction::Shl: case Instruction::LShr: case Instruction::AShr: 328 case Instruction::And: case Instruction::Or: case Instruction::Xor: 329 case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc: 330 case Instruction::IntToPtr: case Instruction::FCmp: 331 case Instruction::FPTrunc: case Instruction::FPExt: 332 case Instruction::FPToUI: case Instruction::FPToSI: 333 case Instruction::UIToFP: case Instruction::SIToFP: 334 case Instruction::InsertElement: case Instruction::ExtractElement: 335 case Instruction::ShuffleVector: 336 case Instruction::ExtractValue: 337 break; 338 case Instruction::ICmp: 339 // Comparing a pointer with null, or any other constant, isn't an 340 // interesting use, because we don't care what the pointer points to, or 341 // about the values of any other dynamic reference-counted pointers. 342 if (IsPotentialUse(I->getOperand(1))) 343 return IC_User; 344 break; 345 default: 346 // For anything else, check all the operands. 347 // Note that this includes both operands of a Store: while the first 348 // operand isn't actually being dereferenced, it is being stored to 349 // memory where we can no longer track who might read it and dereference 350 // it, so we have to consider it potentially used. 351 for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end(); 352 OI != OE; ++OI) 353 if (IsPotentialUse(*OI)) 354 return IC_User; 355 } 356 } 357 358 // Otherwise, it's totally inert for ARC purposes. 359 return IC_None; 360 } 361 362 /// GetBasicInstructionClass - Determine what kind of construct V is. This is 363 /// similar to GetInstructionClass except that it only detects objc runtine 364 /// calls. This allows it to be faster. 365 static InstructionClass GetBasicInstructionClass(const Value *V) { 366 if (const CallInst *CI = dyn_cast<CallInst>(V)) { 367 if (const Function *F = CI->getCalledFunction()) 368 return GetFunctionClass(F); 369 // Otherwise, be conservative. 370 return IC_CallOrUser; 371 } 372 373 // Otherwise, be conservative. 374 return IC_User; 375 } 376 377 /// IsRetain - Test if the the given class is objc_retain or 378 /// equivalent. 379 static bool IsRetain(InstructionClass Class) { 380 return Class == IC_Retain || 381 Class == IC_RetainRV; 382 } 383 384 /// IsAutorelease - Test if the the given class is objc_autorelease or 385 /// equivalent. 386 static bool IsAutorelease(InstructionClass Class) { 387 return Class == IC_Autorelease || 388 Class == IC_AutoreleaseRV; 389 } 390 391 /// IsForwarding - Test if the given class represents instructions which return 392 /// their argument verbatim. 393 static bool IsForwarding(InstructionClass Class) { 394 // objc_retainBlock technically doesn't always return its argument 395 // verbatim, but it doesn't matter for our purposes here. 396 return Class == IC_Retain || 397 Class == IC_RetainRV || 398 Class == IC_Autorelease || 399 Class == IC_AutoreleaseRV || 400 Class == IC_RetainBlock || 401 Class == IC_NoopCast; 402 } 403 404 /// IsNoopOnNull - Test if the given class represents instructions which do 405 /// nothing if passed a null pointer. 406 static bool IsNoopOnNull(InstructionClass Class) { 407 return Class == IC_Retain || 408 Class == IC_RetainRV || 409 Class == IC_Release || 410 Class == IC_Autorelease || 411 Class == IC_AutoreleaseRV || 412 Class == IC_RetainBlock; 413 } 414 415 /// IsAlwaysTail - Test if the given class represents instructions which are 416 /// always safe to mark with the "tail" keyword. 417 static bool IsAlwaysTail(InstructionClass Class) { 418 // IC_RetainBlock may be given a stack argument. 419 return Class == IC_Retain || 420 Class == IC_RetainRV || 421 Class == IC_Autorelease || 422 Class == IC_AutoreleaseRV; 423 } 424 425 /// IsNoThrow - Test if the given class represents instructions which are always 426 /// safe to mark with the nounwind attribute.. 427 static bool IsNoThrow(InstructionClass Class) { 428 // objc_retainBlock is not nounwind because it calls user copy constructors 429 // which could theoretically throw. 430 return Class == IC_Retain || 431 Class == IC_RetainRV || 432 Class == IC_Release || 433 Class == IC_Autorelease || 434 Class == IC_AutoreleaseRV || 435 Class == IC_AutoreleasepoolPush || 436 Class == IC_AutoreleasepoolPop; 437 } 438 439 /// EraseInstruction - Erase the given instruction. ObjC calls return their 440 /// argument verbatim, so if it's such a call and the return value has users, 441 /// replace them with the argument value. 442 static void EraseInstruction(Instruction *CI) { 443 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0); 444 445 bool Unused = CI->use_empty(); 446 447 if (!Unused) { 448 // Replace the return value with the argument. 449 assert(IsForwarding(GetBasicInstructionClass(CI)) && 450 "Can't delete non-forwarding instruction with users!"); 451 CI->replaceAllUsesWith(OldArg); 452 } 453 454 CI->eraseFromParent(); 455 456 if (Unused) 457 RecursivelyDeleteTriviallyDeadInstructions(OldArg); 458 } 459 460 /// GetUnderlyingObjCPtr - This is a wrapper around getUnderlyingObject which 461 /// also knows how to look through objc_retain and objc_autorelease calls, which 462 /// we know to return their argument verbatim. 463 static const Value *GetUnderlyingObjCPtr(const Value *V) { 464 for (;;) { 465 V = GetUnderlyingObject(V); 466 if (!IsForwarding(GetBasicInstructionClass(V))) 467 break; 468 V = cast<CallInst>(V)->getArgOperand(0); 469 } 470 471 return V; 472 } 473 474 /// StripPointerCastsAndObjCCalls - This is a wrapper around 475 /// Value::stripPointerCasts which also knows how to look through objc_retain 476 /// and objc_autorelease calls, which we know to return their argument verbatim. 477 static const Value *StripPointerCastsAndObjCCalls(const Value *V) { 478 for (;;) { 479 V = V->stripPointerCasts(); 480 if (!IsForwarding(GetBasicInstructionClass(V))) 481 break; 482 V = cast<CallInst>(V)->getArgOperand(0); 483 } 484 return V; 485 } 486 487 /// StripPointerCastsAndObjCCalls - This is a wrapper around 488 /// Value::stripPointerCasts which also knows how to look through objc_retain 489 /// and objc_autorelease calls, which we know to return their argument verbatim. 490 static Value *StripPointerCastsAndObjCCalls(Value *V) { 491 for (;;) { 492 V = V->stripPointerCasts(); 493 if (!IsForwarding(GetBasicInstructionClass(V))) 494 break; 495 V = cast<CallInst>(V)->getArgOperand(0); 496 } 497 return V; 498 } 499 500 /// GetObjCArg - Assuming the given instruction is one of the special calls such 501 /// as objc_retain or objc_release, return the argument value, stripped of no-op 502 /// casts and forwarding calls. 503 static Value *GetObjCArg(Value *Inst) { 504 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0)); 505 } 506 507 /// IsObjCIdentifiedObject - This is similar to AliasAnalysis' 508 /// isObjCIdentifiedObject, except that it uses special knowledge of 509 /// ObjC conventions... 510 static bool IsObjCIdentifiedObject(const Value *V) { 511 // Assume that call results and arguments have their own "provenance". 512 // Constants (including GlobalVariables) and Allocas are never 513 // reference-counted. 514 if (isa<CallInst>(V) || isa<InvokeInst>(V) || 515 isa<Argument>(V) || isa<Constant>(V) || 516 isa<AllocaInst>(V)) 517 return true; 518 519 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) { 520 const Value *Pointer = 521 StripPointerCastsAndObjCCalls(LI->getPointerOperand()); 522 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) { 523 // A constant pointer can't be pointing to an object on the heap. It may 524 // be reference-counted, but it won't be deleted. 525 if (GV->isConstant()) 526 return true; 527 StringRef Name = GV->getName(); 528 // These special variables are known to hold values which are not 529 // reference-counted pointers. 530 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") || 531 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") || 532 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") || 533 Name.startswith("\01L_OBJC_METH_VAR_NAME_") || 534 Name.startswith("\01l_objc_msgSend_fixup_")) 535 return true; 536 } 537 } 538 539 return false; 540 } 541 542 /// FindSingleUseIdentifiedObject - This is similar to 543 /// StripPointerCastsAndObjCCalls but it stops as soon as it finds a value 544 /// with multiple uses. 545 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) { 546 if (Arg->hasOneUse()) { 547 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg)) 548 return FindSingleUseIdentifiedObject(BC->getOperand(0)); 549 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg)) 550 if (GEP->hasAllZeroIndices()) 551 return FindSingleUseIdentifiedObject(GEP->getPointerOperand()); 552 if (IsForwarding(GetBasicInstructionClass(Arg))) 553 return FindSingleUseIdentifiedObject( 554 cast<CallInst>(Arg)->getArgOperand(0)); 555 if (!IsObjCIdentifiedObject(Arg)) 556 return 0; 557 return Arg; 558 } 559 560 // If we found an identifiable object but it has multiple uses, but they 561 // are trivial uses, we can still consider this to be a single-use 562 // value. 563 if (IsObjCIdentifiedObject(Arg)) { 564 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); 565 UI != UE; ++UI) { 566 const User *U = *UI; 567 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg) 568 return 0; 569 } 570 571 return Arg; 572 } 573 574 return 0; 575 } 576 577 /// ModuleHasARC - Test if the given module looks interesting to run ARC 578 /// optimization on. 579 static bool ModuleHasARC(const Module &M) { 580 return 581 M.getNamedValue("objc_retain") || 582 M.getNamedValue("objc_release") || 583 M.getNamedValue("objc_autorelease") || 584 M.getNamedValue("objc_retainAutoreleasedReturnValue") || 585 M.getNamedValue("objc_retainBlock") || 586 M.getNamedValue("objc_autoreleaseReturnValue") || 587 M.getNamedValue("objc_autoreleasePoolPush") || 588 M.getNamedValue("objc_loadWeakRetained") || 589 M.getNamedValue("objc_loadWeak") || 590 M.getNamedValue("objc_destroyWeak") || 591 M.getNamedValue("objc_storeWeak") || 592 M.getNamedValue("objc_initWeak") || 593 M.getNamedValue("objc_moveWeak") || 594 M.getNamedValue("objc_copyWeak") || 595 M.getNamedValue("objc_retainedObject") || 596 M.getNamedValue("objc_unretainedObject") || 597 M.getNamedValue("objc_unretainedPointer"); 598 } 599 600 //===----------------------------------------------------------------------===// 601 // ARC AliasAnalysis. 602 //===----------------------------------------------------------------------===// 603 604 #include "llvm/Pass.h" 605 #include "llvm/Analysis/AliasAnalysis.h" 606 #include "llvm/Analysis/Passes.h" 607 608 namespace { 609 /// ObjCARCAliasAnalysis - This is a simple alias analysis 610 /// implementation that uses knowledge of ARC constructs to answer queries. 611 /// 612 /// TODO: This class could be generalized to know about other ObjC-specific 613 /// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing 614 /// even though their offsets are dynamic. 615 class ObjCARCAliasAnalysis : public ImmutablePass, 616 public AliasAnalysis { 617 public: 618 static char ID; // Class identification, replacement for typeinfo 619 ObjCARCAliasAnalysis() : ImmutablePass(ID) { 620 initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry()); 621 } 622 623 private: 624 virtual void initializePass() { 625 InitializeAliasAnalysis(this); 626 } 627 628 /// getAdjustedAnalysisPointer - This method is used when a pass implements 629 /// an analysis interface through multiple inheritance. If needed, it 630 /// should override this to adjust the this pointer as needed for the 631 /// specified pass info. 632 virtual void *getAdjustedAnalysisPointer(const void *PI) { 633 if (PI == &AliasAnalysis::ID) 634 return (AliasAnalysis*)this; 635 return this; 636 } 637 638 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 639 virtual AliasResult alias(const Location &LocA, const Location &LocB); 640 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); 641 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 642 virtual ModRefBehavior getModRefBehavior(const Function *F); 643 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 644 const Location &Loc); 645 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 646 ImmutableCallSite CS2); 647 }; 648 } // End of anonymous namespace 649 650 // Register this pass... 651 char ObjCARCAliasAnalysis::ID = 0; 652 INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa", 653 "ObjC-ARC-Based Alias Analysis", false, true, false) 654 655 ImmutablePass *llvm::createObjCARCAliasAnalysisPass() { 656 return new ObjCARCAliasAnalysis(); 657 } 658 659 void 660 ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 661 AU.setPreservesAll(); 662 AliasAnalysis::getAnalysisUsage(AU); 663 } 664 665 AliasAnalysis::AliasResult 666 ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) { 667 if (!EnableARCOpts) 668 return AliasAnalysis::alias(LocA, LocB); 669 670 // First, strip off no-ops, including ObjC-specific no-ops, and try making a 671 // precise alias query. 672 const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr); 673 const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr); 674 AliasResult Result = 675 AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag), 676 Location(SB, LocB.Size, LocB.TBAATag)); 677 if (Result != MayAlias) 678 return Result; 679 680 // If that failed, climb to the underlying object, including climbing through 681 // ObjC-specific no-ops, and try making an imprecise alias query. 682 const Value *UA = GetUnderlyingObjCPtr(SA); 683 const Value *UB = GetUnderlyingObjCPtr(SB); 684 if (UA != SA || UB != SB) { 685 Result = AliasAnalysis::alias(Location(UA), Location(UB)); 686 // We can't use MustAlias or PartialAlias results here because 687 // GetUnderlyingObjCPtr may return an offsetted pointer value. 688 if (Result == NoAlias) 689 return NoAlias; 690 } 691 692 // If that failed, fail. We don't need to chain here, since that's covered 693 // by the earlier precise query. 694 return MayAlias; 695 } 696 697 bool 698 ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc, 699 bool OrLocal) { 700 if (!EnableARCOpts) 701 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 702 703 // First, strip off no-ops, including ObjC-specific no-ops, and try making 704 // a precise alias query. 705 const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr); 706 if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag), 707 OrLocal)) 708 return true; 709 710 // If that failed, climb to the underlying object, including climbing through 711 // ObjC-specific no-ops, and try making an imprecise alias query. 712 const Value *U = GetUnderlyingObjCPtr(S); 713 if (U != S) 714 return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal); 715 716 // If that failed, fail. We don't need to chain here, since that's covered 717 // by the earlier precise query. 718 return false; 719 } 720 721 AliasAnalysis::ModRefBehavior 722 ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { 723 // We have nothing to do. Just chain to the next AliasAnalysis. 724 return AliasAnalysis::getModRefBehavior(CS); 725 } 726 727 AliasAnalysis::ModRefBehavior 728 ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) { 729 if (!EnableARCOpts) 730 return AliasAnalysis::getModRefBehavior(F); 731 732 switch (GetFunctionClass(F)) { 733 case IC_NoopCast: 734 return DoesNotAccessMemory; 735 default: 736 break; 737 } 738 739 return AliasAnalysis::getModRefBehavior(F); 740 } 741 742 AliasAnalysis::ModRefResult 743 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { 744 if (!EnableARCOpts) 745 return AliasAnalysis::getModRefInfo(CS, Loc); 746 747 switch (GetBasicInstructionClass(CS.getInstruction())) { 748 case IC_Retain: 749 case IC_RetainRV: 750 case IC_Autorelease: 751 case IC_AutoreleaseRV: 752 case IC_NoopCast: 753 case IC_AutoreleasepoolPush: 754 case IC_FusedRetainAutorelease: 755 case IC_FusedRetainAutoreleaseRV: 756 // These functions don't access any memory visible to the compiler. 757 // Note that this doesn't include objc_retainBlock, becuase it updates 758 // pointers when it copies block data. 759 return NoModRef; 760 default: 761 break; 762 } 763 764 return AliasAnalysis::getModRefInfo(CS, Loc); 765 } 766 767 AliasAnalysis::ModRefResult 768 ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1, 769 ImmutableCallSite CS2) { 770 // TODO: Theoretically we could check for dependencies between objc_* calls 771 // and OnlyAccessesArgumentPointees calls or other well-behaved calls. 772 return AliasAnalysis::getModRefInfo(CS1, CS2); 773 } 774 775 //===----------------------------------------------------------------------===// 776 // ARC expansion. 777 //===----------------------------------------------------------------------===// 778 779 #include "llvm/Support/InstIterator.h" 780 #include "llvm/Transforms/Scalar.h" 781 782 namespace { 783 /// ObjCARCExpand - Early ARC transformations. 784 class ObjCARCExpand : public FunctionPass { 785 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 786 virtual bool doInitialization(Module &M); 787 virtual bool runOnFunction(Function &F); 788 789 /// Run - A flag indicating whether this optimization pass should run. 790 bool Run; 791 792 public: 793 static char ID; 794 ObjCARCExpand() : FunctionPass(ID) { 795 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 796 } 797 }; 798 } 799 800 char ObjCARCExpand::ID = 0; 801 INITIALIZE_PASS(ObjCARCExpand, 802 "objc-arc-expand", "ObjC ARC expansion", false, false) 803 804 Pass *llvm::createObjCARCExpandPass() { 805 return new ObjCARCExpand(); 806 } 807 808 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 809 AU.setPreservesCFG(); 810 } 811 812 bool ObjCARCExpand::doInitialization(Module &M) { 813 Run = ModuleHasARC(M); 814 return false; 815 } 816 817 bool ObjCARCExpand::runOnFunction(Function &F) { 818 if (!EnableARCOpts) 819 return false; 820 821 // If nothing in the Module uses ARC, don't do anything. 822 if (!Run) 823 return false; 824 825 bool Changed = false; 826 827 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 828 Instruction *Inst = &*I; 829 830 switch (GetBasicInstructionClass(Inst)) { 831 case IC_Retain: 832 case IC_RetainRV: 833 case IC_Autorelease: 834 case IC_AutoreleaseRV: 835 case IC_FusedRetainAutorelease: 836 case IC_FusedRetainAutoreleaseRV: 837 // These calls return their argument verbatim, as a low-level 838 // optimization. However, this makes high-level optimizations 839 // harder. Undo any uses of this optimization that the front-end 840 // emitted here. We'll redo them in a later pass. 841 Changed = true; 842 Inst->replaceAllUsesWith(cast<CallInst>(Inst)->getArgOperand(0)); 843 break; 844 default: 845 break; 846 } 847 } 848 849 return Changed; 850 } 851 852 //===----------------------------------------------------------------------===// 853 // ARC optimization. 854 //===----------------------------------------------------------------------===// 855 856 // TODO: On code like this: 857 // 858 // objc_retain(%x) 859 // stuff_that_cannot_release() 860 // objc_autorelease(%x) 861 // stuff_that_cannot_release() 862 // objc_retain(%x) 863 // stuff_that_cannot_release() 864 // objc_autorelease(%x) 865 // 866 // The second retain and autorelease can be deleted. 867 868 // TODO: It should be possible to delete 869 // objc_autoreleasePoolPush and objc_autoreleasePoolPop 870 // pairs if nothing is actually autoreleased between them. Also, autorelease 871 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code 872 // after inlining) can be turned into plain release calls. 873 874 // TODO: Critical-edge splitting. If the optimial insertion point is 875 // a critical edge, the current algorithm has to fail, because it doesn't 876 // know how to split edges. It should be possible to make the optimizer 877 // think in terms of edges, rather than blocks, and then split critical 878 // edges on demand. 879 880 // TODO: OptimizeSequences could generalized to be Interprocedural. 881 882 // TODO: Recognize that a bunch of other objc runtime calls have 883 // non-escaping arguments and non-releasing arguments, and may be 884 // non-autoreleasing. 885 886 // TODO: Sink autorelease calls as far as possible. Unfortunately we 887 // usually can't sink them past other calls, which would be the main 888 // case where it would be useful. 889 890 // TODO: The pointer returned from objc_loadWeakRetained is retained. 891 892 // TODO: Delete release+retain pairs (rare). 893 894 #include "llvm/GlobalAlias.h" 895 #include "llvm/Constants.h" 896 #include "llvm/LLVMContext.h" 897 #include "llvm/Support/ErrorHandling.h" 898 #include "llvm/Support/CFG.h" 899 #include "llvm/ADT/PostOrderIterator.h" 900 #include "llvm/ADT/Statistic.h" 901 902 STATISTIC(NumNoops, "Number of no-op objc calls eliminated"); 903 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated"); 904 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases"); 905 STATISTIC(NumRets, "Number of return value forwarding " 906 "retain+autoreleaes eliminated"); 907 STATISTIC(NumRRs, "Number of retain+release paths eliminated"); 908 STATISTIC(NumPeeps, "Number of calls peephole-optimized"); 909 910 namespace { 911 /// ProvenanceAnalysis - This is similar to BasicAliasAnalysis, and it 912 /// uses many of the same techniques, except it uses special ObjC-specific 913 /// reasoning about pointer relationships. 914 class ProvenanceAnalysis { 915 AliasAnalysis *AA; 916 917 typedef std::pair<const Value *, const Value *> ValuePairTy; 918 typedef DenseMap<ValuePairTy, bool> CachedResultsTy; 919 CachedResultsTy CachedResults; 920 921 bool relatedCheck(const Value *A, const Value *B); 922 bool relatedSelect(const SelectInst *A, const Value *B); 923 bool relatedPHI(const PHINode *A, const Value *B); 924 925 // Do not implement. 926 void operator=(const ProvenanceAnalysis &); 927 ProvenanceAnalysis(const ProvenanceAnalysis &); 928 929 public: 930 ProvenanceAnalysis() {} 931 932 void setAA(AliasAnalysis *aa) { AA = aa; } 933 934 AliasAnalysis *getAA() const { return AA; } 935 936 bool related(const Value *A, const Value *B); 937 938 void clear() { 939 CachedResults.clear(); 940 } 941 }; 942 } 943 944 bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) { 945 // If the values are Selects with the same condition, we can do a more precise 946 // check: just check for relations between the values on corresponding arms. 947 if (const SelectInst *SB = dyn_cast<SelectInst>(B)) 948 if (A->getCondition() == SB->getCondition()) { 949 if (related(A->getTrueValue(), SB->getTrueValue())) 950 return true; 951 if (related(A->getFalseValue(), SB->getFalseValue())) 952 return true; 953 return false; 954 } 955 956 // Check both arms of the Select node individually. 957 if (related(A->getTrueValue(), B)) 958 return true; 959 if (related(A->getFalseValue(), B)) 960 return true; 961 962 // The arms both checked out. 963 return false; 964 } 965 966 bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) { 967 // If the values are PHIs in the same block, we can do a more precise as well 968 // as efficient check: just check for relations between the values on 969 // corresponding edges. 970 if (const PHINode *PNB = dyn_cast<PHINode>(B)) 971 if (PNB->getParent() == A->getParent()) { 972 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) 973 if (related(A->getIncomingValue(i), 974 PNB->getIncomingValueForBlock(A->getIncomingBlock(i)))) 975 return true; 976 return false; 977 } 978 979 // Check each unique source of the PHI node against B. 980 SmallPtrSet<const Value *, 4> UniqueSrc; 981 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) { 982 const Value *PV1 = A->getIncomingValue(i); 983 if (UniqueSrc.insert(PV1) && related(PV1, B)) 984 return true; 985 } 986 987 // All of the arms checked out. 988 return false; 989 } 990 991 /// isStoredObjCPointer - Test if the value of P, or any value covered by its 992 /// provenance, is ever stored within the function (not counting callees). 993 static bool isStoredObjCPointer(const Value *P) { 994 SmallPtrSet<const Value *, 8> Visited; 995 SmallVector<const Value *, 8> Worklist; 996 Worklist.push_back(P); 997 Visited.insert(P); 998 do { 999 P = Worklist.pop_back_val(); 1000 for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end(); 1001 UI != UE; ++UI) { 1002 const User *Ur = *UI; 1003 if (isa<StoreInst>(Ur)) { 1004 if (UI.getOperandNo() == 0) 1005 // The pointer is stored. 1006 return true; 1007 // The pointed is stored through. 1008 continue; 1009 } 1010 if (isa<CallInst>(Ur)) 1011 // The pointer is passed as an argument, ignore this. 1012 continue; 1013 if (isa<PtrToIntInst>(P)) 1014 // Assume the worst. 1015 return true; 1016 if (Visited.insert(Ur)) 1017 Worklist.push_back(Ur); 1018 } 1019 } while (!Worklist.empty()); 1020 1021 // Everything checked out. 1022 return false; 1023 } 1024 1025 bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) { 1026 // Skip past provenance pass-throughs. 1027 A = GetUnderlyingObjCPtr(A); 1028 B = GetUnderlyingObjCPtr(B); 1029 1030 // Quick check. 1031 if (A == B) 1032 return true; 1033 1034 // Ask regular AliasAnalysis, for a first approximation. 1035 switch (AA->alias(A, B)) { 1036 case AliasAnalysis::NoAlias: 1037 return false; 1038 case AliasAnalysis::MustAlias: 1039 case AliasAnalysis::PartialAlias: 1040 return true; 1041 case AliasAnalysis::MayAlias: 1042 break; 1043 } 1044 1045 bool AIsIdentified = IsObjCIdentifiedObject(A); 1046 bool BIsIdentified = IsObjCIdentifiedObject(B); 1047 1048 // An ObjC-Identified object can't alias a load if it is never locally stored. 1049 if (AIsIdentified) { 1050 if (BIsIdentified) { 1051 // If both pointers have provenance, they can be directly compared. 1052 if (A != B) 1053 return false; 1054 } else { 1055 if (isa<LoadInst>(B)) 1056 return isStoredObjCPointer(A); 1057 } 1058 } else { 1059 if (BIsIdentified && isa<LoadInst>(A)) 1060 return isStoredObjCPointer(B); 1061 } 1062 1063 // Special handling for PHI and Select. 1064 if (const PHINode *PN = dyn_cast<PHINode>(A)) 1065 return relatedPHI(PN, B); 1066 if (const PHINode *PN = dyn_cast<PHINode>(B)) 1067 return relatedPHI(PN, A); 1068 if (const SelectInst *S = dyn_cast<SelectInst>(A)) 1069 return relatedSelect(S, B); 1070 if (const SelectInst *S = dyn_cast<SelectInst>(B)) 1071 return relatedSelect(S, A); 1072 1073 // Conservative. 1074 return true; 1075 } 1076 1077 bool ProvenanceAnalysis::related(const Value *A, const Value *B) { 1078 // Begin by inserting a conservative value into the map. If the insertion 1079 // fails, we have the answer already. If it succeeds, leave it there until we 1080 // compute the real answer to guard against recursive queries. 1081 if (A > B) std::swap(A, B); 1082 std::pair<CachedResultsTy::iterator, bool> Pair = 1083 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true)); 1084 if (!Pair.second) 1085 return Pair.first->second; 1086 1087 bool Result = relatedCheck(A, B); 1088 CachedResults[ValuePairTy(A, B)] = Result; 1089 return Result; 1090 } 1091 1092 namespace { 1093 // Sequence - A sequence of states that a pointer may go through in which an 1094 // objc_retain and objc_release are actually needed. 1095 enum Sequence { 1096 S_None, 1097 S_Retain, ///< objc_retain(x) 1098 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement 1099 S_Use, ///< any use of x 1100 S_Stop, ///< like S_Release, but code motion is stopped 1101 S_Release, ///< objc_release(x) 1102 S_MovableRelease ///< objc_release(x), !clang.imprecise_release 1103 }; 1104 } 1105 1106 static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) { 1107 // The easy cases. 1108 if (A == B) 1109 return A; 1110 if (A == S_None || B == S_None) 1111 return S_None; 1112 1113 if (A > B) std::swap(A, B); 1114 if (TopDown) { 1115 // Choose the side which is further along in the sequence. 1116 if ((A == S_Retain || A == S_CanRelease) && 1117 (B == S_CanRelease || B == S_Use)) 1118 return B; 1119 } else { 1120 // Choose the side which is further along in the sequence. 1121 if ((A == S_Use || A == S_CanRelease) && 1122 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease)) 1123 return A; 1124 // If both sides are releases, choose the more conservative one. 1125 if (A == S_Stop && (B == S_Release || B == S_MovableRelease)) 1126 return A; 1127 if (A == S_Release && B == S_MovableRelease) 1128 return A; 1129 } 1130 1131 return S_None; 1132 } 1133 1134 namespace { 1135 /// RRInfo - Unidirectional information about either a 1136 /// retain-decrement-use-release sequence or release-use-decrement-retain 1137 /// reverese sequence. 1138 struct RRInfo { 1139 /// KnownSafe - After an objc_retain, the reference count of the referenced 1140 /// object is known to be positive. Similarly, before an objc_release, the 1141 /// reference count of the referenced object is known to be positive. If 1142 /// there are retain-release pairs in code regions where the retain count 1143 /// is known to be positive, they can be eliminated, regardless of any side 1144 /// effects between them. 1145 /// 1146 /// Also, a retain+release pair nested within another retain+release 1147 /// pair all on the known same pointer value can be eliminated, regardless 1148 /// of any intervening side effects. 1149 /// 1150 /// KnownSafe is true when either of these conditions is satisfied. 1151 bool KnownSafe; 1152 1153 /// IsRetainBlock - True if the Calls are objc_retainBlock calls (as 1154 /// opposed to objc_retain calls). 1155 bool IsRetainBlock; 1156 1157 /// CopyOnEscape - True if this the Calls are objc_retainBlock calls 1158 /// which all have the !clang.arc.copy_on_escape metadata. 1159 bool CopyOnEscape; 1160 1161 /// IsTailCallRelease - True of the objc_release calls are all marked 1162 /// with the "tail" keyword. 1163 bool IsTailCallRelease; 1164 1165 /// Partial - True of we've seen an opportunity for partial RR elimination, 1166 /// such as pushing calls into a CFG triangle or into one side of a 1167 /// CFG diamond. 1168 bool Partial; 1169 1170 /// ReleaseMetadata - If the Calls are objc_release calls and they all have 1171 /// a clang.imprecise_release tag, this is the metadata tag. 1172 MDNode *ReleaseMetadata; 1173 1174 /// Calls - For a top-down sequence, the set of objc_retains or 1175 /// objc_retainBlocks. For bottom-up, the set of objc_releases. 1176 SmallPtrSet<Instruction *, 2> Calls; 1177 1178 /// ReverseInsertPts - The set of optimal insert positions for 1179 /// moving calls in the opposite sequence. 1180 SmallPtrSet<Instruction *, 2> ReverseInsertPts; 1181 1182 RRInfo() : 1183 KnownSafe(false), IsRetainBlock(false), CopyOnEscape(false), 1184 IsTailCallRelease(false), Partial(false), 1185 ReleaseMetadata(0) {} 1186 1187 void clear(); 1188 }; 1189 } 1190 1191 void RRInfo::clear() { 1192 KnownSafe = false; 1193 IsRetainBlock = false; 1194 CopyOnEscape = false; 1195 IsTailCallRelease = false; 1196 Partial = false; 1197 ReleaseMetadata = 0; 1198 Calls.clear(); 1199 ReverseInsertPts.clear(); 1200 } 1201 1202 namespace { 1203 /// PtrState - This class summarizes several per-pointer runtime properties 1204 /// which are propogated through the flow graph. 1205 class PtrState { 1206 /// RefCount - The known minimum number of reference count increments. 1207 unsigned RefCount; 1208 1209 /// NestCount - The known minimum level of retain+release nesting. 1210 unsigned NestCount; 1211 1212 /// Seq - The current position in the sequence. 1213 Sequence Seq; 1214 1215 public: 1216 /// RRI - Unidirectional information about the current sequence. 1217 /// TODO: Encapsulate this better. 1218 RRInfo RRI; 1219 1220 PtrState() : RefCount(0), NestCount(0), Seq(S_None) {} 1221 1222 void SetAtLeastOneRefCount() { 1223 if (RefCount == 0) RefCount = 1; 1224 } 1225 1226 void IncrementRefCount() { 1227 if (RefCount != UINT_MAX) ++RefCount; 1228 } 1229 1230 void DecrementRefCount() { 1231 if (RefCount != 0) --RefCount; 1232 } 1233 1234 bool IsKnownIncremented() const { 1235 return RefCount > 0; 1236 } 1237 1238 void IncrementNestCount() { 1239 if (NestCount != UINT_MAX) ++NestCount; 1240 } 1241 1242 void DecrementNestCount() { 1243 if (NestCount != 0) --NestCount; 1244 } 1245 1246 bool IsKnownNested() const { 1247 return NestCount > 0; 1248 } 1249 1250 void SetSeq(Sequence NewSeq) { 1251 Seq = NewSeq; 1252 } 1253 1254 void SetSeqToRelease(MDNode *M) { 1255 if (Seq == S_None || Seq == S_Use) { 1256 Seq = M ? S_MovableRelease : S_Release; 1257 RRI.ReleaseMetadata = M; 1258 } else if (Seq != S_MovableRelease || RRI.ReleaseMetadata != M) { 1259 Seq = S_Release; 1260 RRI.ReleaseMetadata = 0; 1261 } 1262 } 1263 1264 Sequence GetSeq() const { 1265 return Seq; 1266 } 1267 1268 void ClearSequenceProgress() { 1269 Seq = S_None; 1270 RRI.clear(); 1271 } 1272 1273 void Merge(const PtrState &Other, bool TopDown); 1274 }; 1275 } 1276 1277 void 1278 PtrState::Merge(const PtrState &Other, bool TopDown) { 1279 Seq = MergeSeqs(Seq, Other.Seq, TopDown); 1280 RefCount = std::min(RefCount, Other.RefCount); 1281 NestCount = std::min(NestCount, Other.NestCount); 1282 1283 // We can't merge a plain objc_retain with an objc_retainBlock. 1284 if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock) 1285 Seq = S_None; 1286 1287 // If we're not in a sequence (anymore), drop all associated state. 1288 if (Seq == S_None) { 1289 RRI.clear(); 1290 } else if (RRI.Partial || Other.RRI.Partial) { 1291 // If we're doing a merge on a path that's previously seen a partial 1292 // merge, conservatively drop the sequence, to avoid doing partial 1293 // RR elimination. If the branch predicates for the two merge differ, 1294 // mixing them is unsafe. 1295 Seq = S_None; 1296 RRI.clear(); 1297 } else { 1298 // Conservatively merge the ReleaseMetadata information. 1299 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata) 1300 RRI.ReleaseMetadata = 0; 1301 1302 RRI.CopyOnEscape = RRI.CopyOnEscape && Other.RRI.CopyOnEscape; 1303 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe; 1304 RRI.IsTailCallRelease = RRI.IsTailCallRelease && Other.RRI.IsTailCallRelease; 1305 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end()); 1306 1307 // Merge the insert point sets. If there are any differences, 1308 // that makes this a partial merge. 1309 RRI.Partial = RRI.ReverseInsertPts.size() != 1310 Other.RRI.ReverseInsertPts.size(); 1311 for (SmallPtrSet<Instruction *, 2>::const_iterator 1312 I = Other.RRI.ReverseInsertPts.begin(), 1313 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I) 1314 RRI.Partial |= RRI.ReverseInsertPts.insert(*I); 1315 } 1316 } 1317 1318 namespace { 1319 /// BBState - Per-BasicBlock state. 1320 class BBState { 1321 /// TopDownPathCount - The number of unique control paths from the entry 1322 /// which can reach this block. 1323 unsigned TopDownPathCount; 1324 1325 /// BottomUpPathCount - The number of unique control paths to exits 1326 /// from this block. 1327 unsigned BottomUpPathCount; 1328 1329 /// MapTy - A type for PerPtrTopDown and PerPtrBottomUp. 1330 typedef MapVector<const Value *, PtrState> MapTy; 1331 1332 /// PerPtrTopDown - The top-down traversal uses this to record information 1333 /// known about a pointer at the bottom of each block. 1334 MapTy PerPtrTopDown; 1335 1336 /// PerPtrBottomUp - The bottom-up traversal uses this to record information 1337 /// known about a pointer at the top of each block. 1338 MapTy PerPtrBottomUp; 1339 1340 public: 1341 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {} 1342 1343 typedef MapTy::iterator ptr_iterator; 1344 typedef MapTy::const_iterator ptr_const_iterator; 1345 1346 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); } 1347 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); } 1348 ptr_const_iterator top_down_ptr_begin() const { 1349 return PerPtrTopDown.begin(); 1350 } 1351 ptr_const_iterator top_down_ptr_end() const { 1352 return PerPtrTopDown.end(); 1353 } 1354 1355 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); } 1356 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); } 1357 ptr_const_iterator bottom_up_ptr_begin() const { 1358 return PerPtrBottomUp.begin(); 1359 } 1360 ptr_const_iterator bottom_up_ptr_end() const { 1361 return PerPtrBottomUp.end(); 1362 } 1363 1364 /// SetAsEntry - Mark this block as being an entry block, which has one 1365 /// path from the entry by definition. 1366 void SetAsEntry() { TopDownPathCount = 1; } 1367 1368 /// SetAsExit - Mark this block as being an exit block, which has one 1369 /// path to an exit by definition. 1370 void SetAsExit() { BottomUpPathCount = 1; } 1371 1372 PtrState &getPtrTopDownState(const Value *Arg) { 1373 return PerPtrTopDown[Arg]; 1374 } 1375 1376 PtrState &getPtrBottomUpState(const Value *Arg) { 1377 return PerPtrBottomUp[Arg]; 1378 } 1379 1380 void clearBottomUpPointers() { 1381 PerPtrBottomUp.clear(); 1382 } 1383 1384 void clearTopDownPointers() { 1385 PerPtrTopDown.clear(); 1386 } 1387 1388 void InitFromPred(const BBState &Other); 1389 void InitFromSucc(const BBState &Other); 1390 void MergePred(const BBState &Other); 1391 void MergeSucc(const BBState &Other); 1392 1393 /// GetAllPathCount - Return the number of possible unique paths from an 1394 /// entry to an exit which pass through this block. This is only valid 1395 /// after both the top-down and bottom-up traversals are complete. 1396 unsigned GetAllPathCount() const { 1397 return TopDownPathCount * BottomUpPathCount; 1398 } 1399 1400 /// IsVisitedTopDown - Test whether the block for this BBState has been 1401 /// visited by the top-down portion of the algorithm. 1402 bool isVisitedTopDown() const { 1403 return TopDownPathCount != 0; 1404 } 1405 }; 1406 } 1407 1408 void BBState::InitFromPred(const BBState &Other) { 1409 PerPtrTopDown = Other.PerPtrTopDown; 1410 TopDownPathCount = Other.TopDownPathCount; 1411 } 1412 1413 void BBState::InitFromSucc(const BBState &Other) { 1414 PerPtrBottomUp = Other.PerPtrBottomUp; 1415 BottomUpPathCount = Other.BottomUpPathCount; 1416 } 1417 1418 /// MergePred - The top-down traversal uses this to merge information about 1419 /// predecessors to form the initial state for a new block. 1420 void BBState::MergePred(const BBState &Other) { 1421 // Other.TopDownPathCount can be 0, in which case it is either dead or a 1422 // loop backedge. Loop backedges are special. 1423 TopDownPathCount += Other.TopDownPathCount; 1424 1425 // For each entry in the other set, if our set has an entry with the same key, 1426 // merge the entries. Otherwise, copy the entry and merge it with an empty 1427 // entry. 1428 for (ptr_const_iterator MI = Other.top_down_ptr_begin(), 1429 ME = Other.top_down_ptr_end(); MI != ME; ++MI) { 1430 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI); 1431 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, 1432 /*TopDown=*/true); 1433 } 1434 1435 // For each entry in our set, if the other set doesn't have an entry with the 1436 // same key, force it to merge with an empty entry. 1437 for (ptr_iterator MI = top_down_ptr_begin(), 1438 ME = top_down_ptr_end(); MI != ME; ++MI) 1439 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end()) 1440 MI->second.Merge(PtrState(), /*TopDown=*/true); 1441 } 1442 1443 /// MergeSucc - The bottom-up traversal uses this to merge information about 1444 /// successors to form the initial state for a new block. 1445 void BBState::MergeSucc(const BBState &Other) { 1446 // Other.BottomUpPathCount can be 0, in which case it is either dead or a 1447 // loop backedge. Loop backedges are special. 1448 BottomUpPathCount += Other.BottomUpPathCount; 1449 1450 // For each entry in the other set, if our set has an entry with the 1451 // same key, merge the entries. Otherwise, copy the entry and merge 1452 // it with an empty entry. 1453 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(), 1454 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) { 1455 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI); 1456 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, 1457 /*TopDown=*/false); 1458 } 1459 1460 // For each entry in our set, if the other set doesn't have an entry 1461 // with the same key, force it to merge with an empty entry. 1462 for (ptr_iterator MI = bottom_up_ptr_begin(), 1463 ME = bottom_up_ptr_end(); MI != ME; ++MI) 1464 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end()) 1465 MI->second.Merge(PtrState(), /*TopDown=*/false); 1466 } 1467 1468 namespace { 1469 /// ObjCARCOpt - The main ARC optimization pass. 1470 class ObjCARCOpt : public FunctionPass { 1471 bool Changed; 1472 ProvenanceAnalysis PA; 1473 1474 /// Run - A flag indicating whether this optimization pass should run. 1475 bool Run; 1476 1477 /// RetainRVCallee, etc. - Declarations for ObjC runtime 1478 /// functions, for use in creating calls to them. These are initialized 1479 /// lazily to avoid cluttering up the Module with unused declarations. 1480 Constant *RetainRVCallee, *AutoreleaseRVCallee, *ReleaseCallee, 1481 *RetainCallee, *RetainBlockCallee, *AutoreleaseCallee; 1482 1483 /// UsedInThisFunciton - Flags which determine whether each of the 1484 /// interesting runtine functions is in fact used in the current function. 1485 unsigned UsedInThisFunction; 1486 1487 /// ImpreciseReleaseMDKind - The Metadata Kind for clang.imprecise_release 1488 /// metadata. 1489 unsigned ImpreciseReleaseMDKind; 1490 1491 /// CopyOnEscape - The Metadata Kind for clang.arc.copy_on_escape 1492 /// metadata. 1493 unsigned CopyOnEscapeMDKind; 1494 1495 Constant *getRetainRVCallee(Module *M); 1496 Constant *getAutoreleaseRVCallee(Module *M); 1497 Constant *getReleaseCallee(Module *M); 1498 Constant *getRetainCallee(Module *M); 1499 Constant *getRetainBlockCallee(Module *M); 1500 Constant *getAutoreleaseCallee(Module *M); 1501 1502 void OptimizeRetainCall(Function &F, Instruction *Retain); 1503 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV); 1504 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV); 1505 void OptimizeIndividualCalls(Function &F); 1506 1507 void CheckForCFGHazards(const BasicBlock *BB, 1508 DenseMap<const BasicBlock *, BBState> &BBStates, 1509 BBState &MyStates) const; 1510 bool VisitBottomUp(BasicBlock *BB, 1511 DenseMap<const BasicBlock *, BBState> &BBStates, 1512 MapVector<Value *, RRInfo> &Retains); 1513 bool VisitTopDown(BasicBlock *BB, 1514 DenseMap<const BasicBlock *, BBState> &BBStates, 1515 DenseMap<Value *, RRInfo> &Releases); 1516 bool Visit(Function &F, 1517 DenseMap<const BasicBlock *, BBState> &BBStates, 1518 MapVector<Value *, RRInfo> &Retains, 1519 DenseMap<Value *, RRInfo> &Releases); 1520 1521 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove, 1522 MapVector<Value *, RRInfo> &Retains, 1523 DenseMap<Value *, RRInfo> &Releases, 1524 SmallVectorImpl<Instruction *> &DeadInsts, 1525 Module *M); 1526 1527 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates, 1528 MapVector<Value *, RRInfo> &Retains, 1529 DenseMap<Value *, RRInfo> &Releases, 1530 Module *M); 1531 1532 void OptimizeWeakCalls(Function &F); 1533 1534 bool OptimizeSequences(Function &F); 1535 1536 void OptimizeReturns(Function &F); 1537 1538 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 1539 virtual bool doInitialization(Module &M); 1540 virtual bool runOnFunction(Function &F); 1541 virtual void releaseMemory(); 1542 1543 public: 1544 static char ID; 1545 ObjCARCOpt() : FunctionPass(ID) { 1546 initializeObjCARCOptPass(*PassRegistry::getPassRegistry()); 1547 } 1548 }; 1549 } 1550 1551 char ObjCARCOpt::ID = 0; 1552 INITIALIZE_PASS_BEGIN(ObjCARCOpt, 1553 "objc-arc", "ObjC ARC optimization", false, false) 1554 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis) 1555 INITIALIZE_PASS_END(ObjCARCOpt, 1556 "objc-arc", "ObjC ARC optimization", false, false) 1557 1558 Pass *llvm::createObjCARCOptPass() { 1559 return new ObjCARCOpt(); 1560 } 1561 1562 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const { 1563 AU.addRequired<ObjCARCAliasAnalysis>(); 1564 AU.addRequired<AliasAnalysis>(); 1565 // ARC optimization doesn't currently split critical edges. 1566 AU.setPreservesCFG(); 1567 } 1568 1569 Constant *ObjCARCOpt::getRetainRVCallee(Module *M) { 1570 if (!RetainRVCallee) { 1571 LLVMContext &C = M->getContext(); 1572 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 1573 std::vector<Type *> Params; 1574 Params.push_back(I8X); 1575 FunctionType *FTy = 1576 FunctionType::get(I8X, Params, /*isVarArg=*/false); 1577 AttrListPtr Attributes; 1578 Attributes.addAttr(~0u, Attribute::NoUnwind); 1579 RetainRVCallee = 1580 M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy, 1581 Attributes); 1582 } 1583 return RetainRVCallee; 1584 } 1585 1586 Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) { 1587 if (!AutoreleaseRVCallee) { 1588 LLVMContext &C = M->getContext(); 1589 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 1590 std::vector<Type *> Params; 1591 Params.push_back(I8X); 1592 FunctionType *FTy = 1593 FunctionType::get(I8X, Params, /*isVarArg=*/false); 1594 AttrListPtr Attributes; 1595 Attributes.addAttr(~0u, Attribute::NoUnwind); 1596 AutoreleaseRVCallee = 1597 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy, 1598 Attributes); 1599 } 1600 return AutoreleaseRVCallee; 1601 } 1602 1603 Constant *ObjCARCOpt::getReleaseCallee(Module *M) { 1604 if (!ReleaseCallee) { 1605 LLVMContext &C = M->getContext(); 1606 std::vector<Type *> Params; 1607 Params.push_back(PointerType::getUnqual(Type::getInt8Ty(C))); 1608 AttrListPtr Attributes; 1609 Attributes.addAttr(~0u, Attribute::NoUnwind); 1610 ReleaseCallee = 1611 M->getOrInsertFunction( 1612 "objc_release", 1613 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), 1614 Attributes); 1615 } 1616 return ReleaseCallee; 1617 } 1618 1619 Constant *ObjCARCOpt::getRetainCallee(Module *M) { 1620 if (!RetainCallee) { 1621 LLVMContext &C = M->getContext(); 1622 std::vector<Type *> Params; 1623 Params.push_back(PointerType::getUnqual(Type::getInt8Ty(C))); 1624 AttrListPtr Attributes; 1625 Attributes.addAttr(~0u, Attribute::NoUnwind); 1626 RetainCallee = 1627 M->getOrInsertFunction( 1628 "objc_retain", 1629 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1630 Attributes); 1631 } 1632 return RetainCallee; 1633 } 1634 1635 Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) { 1636 if (!RetainBlockCallee) { 1637 LLVMContext &C = M->getContext(); 1638 std::vector<Type *> Params; 1639 Params.push_back(PointerType::getUnqual(Type::getInt8Ty(C))); 1640 AttrListPtr Attributes; 1641 // objc_retainBlock is not nounwind because it calls user copy constructors 1642 // which could theoretically throw. 1643 RetainBlockCallee = 1644 M->getOrInsertFunction( 1645 "objc_retainBlock", 1646 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1647 Attributes); 1648 } 1649 return RetainBlockCallee; 1650 } 1651 1652 Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) { 1653 if (!AutoreleaseCallee) { 1654 LLVMContext &C = M->getContext(); 1655 std::vector<Type *> Params; 1656 Params.push_back(PointerType::getUnqual(Type::getInt8Ty(C))); 1657 AttrListPtr Attributes; 1658 Attributes.addAttr(~0u, Attribute::NoUnwind); 1659 AutoreleaseCallee = 1660 M->getOrInsertFunction( 1661 "objc_autorelease", 1662 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1663 Attributes); 1664 } 1665 return AutoreleaseCallee; 1666 } 1667 1668 /// CanAlterRefCount - Test whether the given instruction can result in a 1669 /// reference count modification (positive or negative) for the pointer's 1670 /// object. 1671 static bool 1672 CanAlterRefCount(const Instruction *Inst, const Value *Ptr, 1673 ProvenanceAnalysis &PA, InstructionClass Class) { 1674 switch (Class) { 1675 case IC_Autorelease: 1676 case IC_AutoreleaseRV: 1677 case IC_User: 1678 // These operations never directly modify a reference count. 1679 return false; 1680 default: break; 1681 } 1682 1683 ImmutableCallSite CS = static_cast<const Value *>(Inst); 1684 assert(CS && "Only calls can alter reference counts!"); 1685 1686 // See if AliasAnalysis can help us with the call. 1687 AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS); 1688 if (AliasAnalysis::onlyReadsMemory(MRB)) 1689 return false; 1690 if (AliasAnalysis::onlyAccessesArgPointees(MRB)) { 1691 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 1692 I != E; ++I) { 1693 const Value *Op = *I; 1694 if (IsPotentialUse(Op) && PA.related(Ptr, Op)) 1695 return true; 1696 } 1697 return false; 1698 } 1699 1700 // Assume the worst. 1701 return true; 1702 } 1703 1704 /// CanUse - Test whether the given instruction can "use" the given pointer's 1705 /// object in a way that requires the reference count to be positive. 1706 static bool 1707 CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA, 1708 InstructionClass Class) { 1709 // IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers. 1710 if (Class == IC_Call) 1711 return false; 1712 1713 // Consider various instructions which may have pointer arguments which are 1714 // not "uses". 1715 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) { 1716 // Comparing a pointer with null, or any other constant, isn't really a use, 1717 // because we don't care what the pointer points to, or about the values 1718 // of any other dynamic reference-counted pointers. 1719 if (!IsPotentialUse(ICI->getOperand(1))) 1720 return false; 1721 } else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) { 1722 // For calls, just check the arguments (and not the callee operand). 1723 for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(), 1724 OE = CS.arg_end(); OI != OE; ++OI) { 1725 const Value *Op = *OI; 1726 if (IsPotentialUse(Op) && PA.related(Ptr, Op)) 1727 return true; 1728 } 1729 return false; 1730 } else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 1731 // Special-case stores, because we don't care about the stored value, just 1732 // the store address. 1733 const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand()); 1734 // If we can't tell what the underlying object was, assume there is a 1735 // dependence. 1736 return IsPotentialUse(Op) && PA.related(Op, Ptr); 1737 } 1738 1739 // Check each operand for a match. 1740 for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end(); 1741 OI != OE; ++OI) { 1742 const Value *Op = *OI; 1743 if (IsPotentialUse(Op) && PA.related(Ptr, Op)) 1744 return true; 1745 } 1746 return false; 1747 } 1748 1749 /// CanInterruptRV - Test whether the given instruction can autorelease 1750 /// any pointer or cause an autoreleasepool pop. 1751 static bool 1752 CanInterruptRV(InstructionClass Class) { 1753 switch (Class) { 1754 case IC_AutoreleasepoolPop: 1755 case IC_CallOrUser: 1756 case IC_Call: 1757 case IC_Autorelease: 1758 case IC_AutoreleaseRV: 1759 case IC_FusedRetainAutorelease: 1760 case IC_FusedRetainAutoreleaseRV: 1761 return true; 1762 default: 1763 return false; 1764 } 1765 } 1766 1767 namespace { 1768 /// DependenceKind - There are several kinds of dependence-like concepts in 1769 /// use here. 1770 enum DependenceKind { 1771 NeedsPositiveRetainCount, 1772 CanChangeRetainCount, 1773 RetainAutoreleaseDep, ///< Blocks objc_retainAutorelease. 1774 RetainAutoreleaseRVDep, ///< Blocks objc_retainAutoreleaseReturnValue. 1775 RetainRVDep ///< Blocks objc_retainAutoreleasedReturnValue. 1776 }; 1777 } 1778 1779 /// Depends - Test if there can be dependencies on Inst through Arg. This 1780 /// function only tests dependencies relevant for removing pairs of calls. 1781 static bool 1782 Depends(DependenceKind Flavor, Instruction *Inst, const Value *Arg, 1783 ProvenanceAnalysis &PA) { 1784 // If we've reached the definition of Arg, stop. 1785 if (Inst == Arg) 1786 return true; 1787 1788 switch (Flavor) { 1789 case NeedsPositiveRetainCount: { 1790 InstructionClass Class = GetInstructionClass(Inst); 1791 switch (Class) { 1792 case IC_AutoreleasepoolPop: 1793 case IC_AutoreleasepoolPush: 1794 case IC_None: 1795 return false; 1796 default: 1797 return CanUse(Inst, Arg, PA, Class); 1798 } 1799 } 1800 1801 case CanChangeRetainCount: { 1802 InstructionClass Class = GetInstructionClass(Inst); 1803 switch (Class) { 1804 case IC_AutoreleasepoolPop: 1805 // Conservatively assume this can decrement any count. 1806 return true; 1807 case IC_AutoreleasepoolPush: 1808 case IC_None: 1809 return false; 1810 default: 1811 return CanAlterRefCount(Inst, Arg, PA, Class); 1812 } 1813 } 1814 1815 case RetainAutoreleaseDep: 1816 switch (GetBasicInstructionClass(Inst)) { 1817 case IC_AutoreleasepoolPop: 1818 // Don't merge an objc_autorelease with an objc_retain inside a different 1819 // autoreleasepool scope. 1820 return true; 1821 case IC_Retain: 1822 case IC_RetainRV: 1823 // Check for a retain of the same pointer for merging. 1824 return GetObjCArg(Inst) == Arg; 1825 default: 1826 // Nothing else matters for objc_retainAutorelease formation. 1827 return false; 1828 } 1829 break; 1830 1831 case RetainAutoreleaseRVDep: { 1832 InstructionClass Class = GetBasicInstructionClass(Inst); 1833 switch (Class) { 1834 case IC_Retain: 1835 case IC_RetainRV: 1836 // Check for a retain of the same pointer for merging. 1837 return GetObjCArg(Inst) == Arg; 1838 default: 1839 // Anything that can autorelease interrupts 1840 // retainAutoreleaseReturnValue formation. 1841 return CanInterruptRV(Class); 1842 } 1843 break; 1844 } 1845 1846 case RetainRVDep: 1847 return CanInterruptRV(GetBasicInstructionClass(Inst)); 1848 } 1849 1850 llvm_unreachable("Invalid dependence flavor"); 1851 return true; 1852 } 1853 1854 /// FindDependencies - Walk up the CFG from StartPos (which is in StartBB) and 1855 /// find local and non-local dependencies on Arg. 1856 /// TODO: Cache results? 1857 static void 1858 FindDependencies(DependenceKind Flavor, 1859 const Value *Arg, 1860 BasicBlock *StartBB, Instruction *StartInst, 1861 SmallPtrSet<Instruction *, 4> &DependingInstructions, 1862 SmallPtrSet<const BasicBlock *, 4> &Visited, 1863 ProvenanceAnalysis &PA) { 1864 BasicBlock::iterator StartPos = StartInst; 1865 1866 SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist; 1867 Worklist.push_back(std::make_pair(StartBB, StartPos)); 1868 do { 1869 std::pair<BasicBlock *, BasicBlock::iterator> Pair = 1870 Worklist.pop_back_val(); 1871 BasicBlock *LocalStartBB = Pair.first; 1872 BasicBlock::iterator LocalStartPos = Pair.second; 1873 BasicBlock::iterator StartBBBegin = LocalStartBB->begin(); 1874 for (;;) { 1875 if (LocalStartPos == StartBBBegin) { 1876 pred_iterator PI(LocalStartBB), PE(LocalStartBB, false); 1877 if (PI == PE) 1878 // If we've reached the function entry, produce a null dependence. 1879 DependingInstructions.insert(0); 1880 else 1881 // Add the predecessors to the worklist. 1882 do { 1883 BasicBlock *PredBB = *PI; 1884 if (Visited.insert(PredBB)) 1885 Worklist.push_back(std::make_pair(PredBB, PredBB->end())); 1886 } while (++PI != PE); 1887 break; 1888 } 1889 1890 Instruction *Inst = --LocalStartPos; 1891 if (Depends(Flavor, Inst, Arg, PA)) { 1892 DependingInstructions.insert(Inst); 1893 break; 1894 } 1895 } 1896 } while (!Worklist.empty()); 1897 1898 // Determine whether the original StartBB post-dominates all of the blocks we 1899 // visited. If not, insert a sentinal indicating that most optimizations are 1900 // not safe. 1901 for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(), 1902 E = Visited.end(); I != E; ++I) { 1903 const BasicBlock *BB = *I; 1904 if (BB == StartBB) 1905 continue; 1906 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 1907 for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) { 1908 const BasicBlock *Succ = *SI; 1909 if (Succ != StartBB && !Visited.count(Succ)) { 1910 DependingInstructions.insert(reinterpret_cast<Instruction *>(-1)); 1911 return; 1912 } 1913 } 1914 } 1915 } 1916 1917 static bool isNullOrUndef(const Value *V) { 1918 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V); 1919 } 1920 1921 static bool isNoopInstruction(const Instruction *I) { 1922 return isa<BitCastInst>(I) || 1923 (isa<GetElementPtrInst>(I) && 1924 cast<GetElementPtrInst>(I)->hasAllZeroIndices()); 1925 } 1926 1927 /// OptimizeRetainCall - Turn objc_retain into 1928 /// objc_retainAutoreleasedReturnValue if the operand is a return value. 1929 void 1930 ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) { 1931 CallSite CS(GetObjCArg(Retain)); 1932 Instruction *Call = CS.getInstruction(); 1933 if (!Call) return; 1934 if (Call->getParent() != Retain->getParent()) return; 1935 1936 // Check that the call is next to the retain. 1937 BasicBlock::iterator I = Call; 1938 ++I; 1939 while (isNoopInstruction(I)) ++I; 1940 if (&*I != Retain) 1941 return; 1942 1943 // Turn it to an objc_retainAutoreleasedReturnValue.. 1944 Changed = true; 1945 ++NumPeeps; 1946 cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent())); 1947 } 1948 1949 /// OptimizeRetainRVCall - Turn objc_retainAutoreleasedReturnValue into 1950 /// objc_retain if the operand is not a return value. Or, if it can be 1951 /// paired with an objc_autoreleaseReturnValue, delete the pair and 1952 /// return true. 1953 bool 1954 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) { 1955 // Check for the argument being from an immediately preceding call. 1956 Value *Arg = GetObjCArg(RetainRV); 1957 CallSite CS(Arg); 1958 if (Instruction *Call = CS.getInstruction()) 1959 if (Call->getParent() == RetainRV->getParent()) { 1960 BasicBlock::iterator I = Call; 1961 ++I; 1962 while (isNoopInstruction(I)) ++I; 1963 if (&*I == RetainRV) 1964 return false; 1965 } 1966 1967 // Check for being preceded by an objc_autoreleaseReturnValue on the same 1968 // pointer. In this case, we can delete the pair. 1969 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin(); 1970 if (I != Begin) { 1971 do --I; while (I != Begin && isNoopInstruction(I)); 1972 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV && 1973 GetObjCArg(I) == Arg) { 1974 Changed = true; 1975 ++NumPeeps; 1976 EraseInstruction(I); 1977 EraseInstruction(RetainRV); 1978 return true; 1979 } 1980 } 1981 1982 // Turn it to a plain objc_retain. 1983 Changed = true; 1984 ++NumPeeps; 1985 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent())); 1986 return false; 1987 } 1988 1989 /// OptimizeAutoreleaseRVCall - Turn objc_autoreleaseReturnValue into 1990 /// objc_autorelease if the result is not used as a return value. 1991 void 1992 ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV) { 1993 // Check for a return of the pointer value. 1994 const Value *Ptr = GetObjCArg(AutoreleaseRV); 1995 SmallVector<const Value *, 2> Users; 1996 Users.push_back(Ptr); 1997 do { 1998 Ptr = Users.pop_back_val(); 1999 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end(); 2000 UI != UE; ++UI) { 2001 const User *I = *UI; 2002 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV) 2003 return; 2004 if (isa<BitCastInst>(I)) 2005 Users.push_back(I); 2006 } 2007 } while (!Users.empty()); 2008 2009 Changed = true; 2010 ++NumPeeps; 2011 cast<CallInst>(AutoreleaseRV)-> 2012 setCalledFunction(getAutoreleaseCallee(F.getParent())); 2013 } 2014 2015 /// OptimizeIndividualCalls - Visit each call, one at a time, and make 2016 /// simplifications without doing any additional analysis. 2017 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) { 2018 // Reset all the flags in preparation for recomputing them. 2019 UsedInThisFunction = 0; 2020 2021 // Visit all objc_* calls in F. 2022 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 2023 Instruction *Inst = &*I++; 2024 InstructionClass Class = GetBasicInstructionClass(Inst); 2025 2026 switch (Class) { 2027 default: break; 2028 2029 // Delete no-op casts. These function calls have special semantics, but 2030 // the semantics are entirely implemented via lowering in the front-end, 2031 // so by the time they reach the optimizer, they are just no-op calls 2032 // which return their argument. 2033 // 2034 // There are gray areas here, as the ability to cast reference-counted 2035 // pointers to raw void* and back allows code to break ARC assumptions, 2036 // however these are currently considered to be unimportant. 2037 case IC_NoopCast: 2038 Changed = true; 2039 ++NumNoops; 2040 EraseInstruction(Inst); 2041 continue; 2042 2043 // If the pointer-to-weak-pointer is null, it's undefined behavior. 2044 case IC_StoreWeak: 2045 case IC_LoadWeak: 2046 case IC_LoadWeakRetained: 2047 case IC_InitWeak: 2048 case IC_DestroyWeak: { 2049 CallInst *CI = cast<CallInst>(Inst); 2050 if (isNullOrUndef(CI->getArgOperand(0))) { 2051 Type *Ty = CI->getArgOperand(0)->getType(); 2052 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), 2053 Constant::getNullValue(Ty), 2054 CI); 2055 CI->replaceAllUsesWith(UndefValue::get(CI->getType())); 2056 CI->eraseFromParent(); 2057 continue; 2058 } 2059 break; 2060 } 2061 case IC_CopyWeak: 2062 case IC_MoveWeak: { 2063 CallInst *CI = cast<CallInst>(Inst); 2064 if (isNullOrUndef(CI->getArgOperand(0)) || 2065 isNullOrUndef(CI->getArgOperand(1))) { 2066 Type *Ty = CI->getArgOperand(0)->getType(); 2067 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), 2068 Constant::getNullValue(Ty), 2069 CI); 2070 CI->replaceAllUsesWith(UndefValue::get(CI->getType())); 2071 CI->eraseFromParent(); 2072 continue; 2073 } 2074 break; 2075 } 2076 case IC_Retain: 2077 OptimizeRetainCall(F, Inst); 2078 break; 2079 case IC_RetainRV: 2080 if (OptimizeRetainRVCall(F, Inst)) 2081 continue; 2082 break; 2083 case IC_AutoreleaseRV: 2084 OptimizeAutoreleaseRVCall(F, Inst); 2085 break; 2086 } 2087 2088 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused. 2089 if (IsAutorelease(Class) && Inst->use_empty()) { 2090 CallInst *Call = cast<CallInst>(Inst); 2091 const Value *Arg = Call->getArgOperand(0); 2092 Arg = FindSingleUseIdentifiedObject(Arg); 2093 if (Arg) { 2094 Changed = true; 2095 ++NumAutoreleases; 2096 2097 // Create the declaration lazily. 2098 LLVMContext &C = Inst->getContext(); 2099 CallInst *NewCall = 2100 CallInst::Create(getReleaseCallee(F.getParent()), 2101 Call->getArgOperand(0), "", Call); 2102 NewCall->setMetadata(ImpreciseReleaseMDKind, 2103 MDNode::get(C, ArrayRef<Value *>())); 2104 EraseInstruction(Call); 2105 Inst = NewCall; 2106 Class = IC_Release; 2107 } 2108 } 2109 2110 // For functions which can never be passed stack arguments, add 2111 // a tail keyword. 2112 if (IsAlwaysTail(Class)) { 2113 Changed = true; 2114 cast<CallInst>(Inst)->setTailCall(); 2115 } 2116 2117 // Set nounwind as needed. 2118 if (IsNoThrow(Class)) { 2119 Changed = true; 2120 cast<CallInst>(Inst)->setDoesNotThrow(); 2121 } 2122 2123 if (!IsNoopOnNull(Class)) { 2124 UsedInThisFunction |= 1 << Class; 2125 continue; 2126 } 2127 2128 const Value *Arg = GetObjCArg(Inst); 2129 2130 // ARC calls with null are no-ops. Delete them. 2131 if (isNullOrUndef(Arg)) { 2132 Changed = true; 2133 ++NumNoops; 2134 EraseInstruction(Inst); 2135 continue; 2136 } 2137 2138 // Keep track of which of retain, release, autorelease, and retain_block 2139 // are actually present in this function. 2140 UsedInThisFunction |= 1 << Class; 2141 2142 // If Arg is a PHI, and one or more incoming values to the 2143 // PHI are null, and the call is control-equivalent to the PHI, and there 2144 // are no relevant side effects between the PHI and the call, the call 2145 // could be pushed up to just those paths with non-null incoming values. 2146 // For now, don't bother splitting critical edges for this. 2147 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist; 2148 Worklist.push_back(std::make_pair(Inst, Arg)); 2149 do { 2150 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val(); 2151 Inst = Pair.first; 2152 Arg = Pair.second; 2153 2154 const PHINode *PN = dyn_cast<PHINode>(Arg); 2155 if (!PN) continue; 2156 2157 // Determine if the PHI has any null operands, or any incoming 2158 // critical edges. 2159 bool HasNull = false; 2160 bool HasCriticalEdges = false; 2161 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 2162 Value *Incoming = 2163 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); 2164 if (isNullOrUndef(Incoming)) 2165 HasNull = true; 2166 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back()) 2167 .getNumSuccessors() != 1) { 2168 HasCriticalEdges = true; 2169 break; 2170 } 2171 } 2172 // If we have null operands and no critical edges, optimize. 2173 if (!HasCriticalEdges && HasNull) { 2174 SmallPtrSet<Instruction *, 4> DependingInstructions; 2175 SmallPtrSet<const BasicBlock *, 4> Visited; 2176 2177 // Check that there is nothing that cares about the reference 2178 // count between the call and the phi. 2179 FindDependencies(NeedsPositiveRetainCount, Arg, 2180 Inst->getParent(), Inst, 2181 DependingInstructions, Visited, PA); 2182 if (DependingInstructions.size() == 1 && 2183 *DependingInstructions.begin() == PN) { 2184 Changed = true; 2185 ++NumPartialNoops; 2186 // Clone the call into each predecessor that has a non-null value. 2187 CallInst *CInst = cast<CallInst>(Inst); 2188 Type *ParamTy = CInst->getArgOperand(0)->getType(); 2189 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 2190 Value *Incoming = 2191 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); 2192 if (!isNullOrUndef(Incoming)) { 2193 CallInst *Clone = cast<CallInst>(CInst->clone()); 2194 Value *Op = PN->getIncomingValue(i); 2195 Instruction *InsertPos = &PN->getIncomingBlock(i)->back(); 2196 if (Op->getType() != ParamTy) 2197 Op = new BitCastInst(Op, ParamTy, "", InsertPos); 2198 Clone->setArgOperand(0, Op); 2199 Clone->insertBefore(InsertPos); 2200 Worklist.push_back(std::make_pair(Clone, Incoming)); 2201 } 2202 } 2203 // Erase the original call. 2204 EraseInstruction(CInst); 2205 continue; 2206 } 2207 } 2208 } while (!Worklist.empty()); 2209 } 2210 } 2211 2212 /// CheckForCFGHazards - Check for critical edges, loop boundaries, irreducible 2213 /// control flow, or other CFG structures where moving code across the edge 2214 /// would result in it being executed more. 2215 void 2216 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB, 2217 DenseMap<const BasicBlock *, BBState> &BBStates, 2218 BBState &MyStates) const { 2219 // If any top-down local-use or possible-dec has a succ which is earlier in 2220 // the sequence, forget it. 2221 for (BBState::ptr_const_iterator I = MyStates.top_down_ptr_begin(), 2222 E = MyStates.top_down_ptr_end(); I != E; ++I) 2223 switch (I->second.GetSeq()) { 2224 default: break; 2225 case S_Use: { 2226 const Value *Arg = I->first; 2227 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2228 bool SomeSuccHasSame = false; 2229 bool AllSuccsHaveSame = true; 2230 PtrState &S = MyStates.getPtrTopDownState(Arg); 2231 for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) { 2232 PtrState &SuccS = BBStates[*SI].getPtrBottomUpState(Arg); 2233 switch (SuccS.GetSeq()) { 2234 case S_None: 2235 case S_CanRelease: { 2236 if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe) 2237 S.ClearSequenceProgress(); 2238 continue; 2239 } 2240 case S_Use: 2241 SomeSuccHasSame = true; 2242 break; 2243 case S_Stop: 2244 case S_Release: 2245 case S_MovableRelease: 2246 if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe) 2247 AllSuccsHaveSame = false; 2248 break; 2249 case S_Retain: 2250 llvm_unreachable("bottom-up pointer in retain state!"); 2251 } 2252 } 2253 // If the state at the other end of any of the successor edges 2254 // matches the current state, require all edges to match. This 2255 // guards against loops in the middle of a sequence. 2256 if (SomeSuccHasSame && !AllSuccsHaveSame) 2257 S.ClearSequenceProgress(); 2258 } 2259 case S_CanRelease: { 2260 const Value *Arg = I->first; 2261 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2262 bool SomeSuccHasSame = false; 2263 bool AllSuccsHaveSame = true; 2264 PtrState &S = MyStates.getPtrTopDownState(Arg); 2265 for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) { 2266 PtrState &SuccS = BBStates[*SI].getPtrBottomUpState(Arg); 2267 switch (SuccS.GetSeq()) { 2268 case S_None: { 2269 if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe) 2270 S.ClearSequenceProgress(); 2271 continue; 2272 } 2273 case S_CanRelease: 2274 SomeSuccHasSame = true; 2275 break; 2276 case S_Stop: 2277 case S_Release: 2278 case S_MovableRelease: 2279 case S_Use: 2280 if (!S.RRI.KnownSafe && !SuccS.RRI.KnownSafe) 2281 AllSuccsHaveSame = false; 2282 break; 2283 case S_Retain: 2284 llvm_unreachable("bottom-up pointer in retain state!"); 2285 } 2286 } 2287 // If the state at the other end of any of the successor edges 2288 // matches the current state, require all edges to match. This 2289 // guards against loops in the middle of a sequence. 2290 if (SomeSuccHasSame && !AllSuccsHaveSame) 2291 S.ClearSequenceProgress(); 2292 } 2293 } 2294 } 2295 2296 bool 2297 ObjCARCOpt::VisitBottomUp(BasicBlock *BB, 2298 DenseMap<const BasicBlock *, BBState> &BBStates, 2299 MapVector<Value *, RRInfo> &Retains) { 2300 bool NestingDetected = false; 2301 BBState &MyStates = BBStates[BB]; 2302 2303 // Merge the states from each successor to compute the initial state 2304 // for the current block. 2305 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2306 succ_const_iterator SI(TI), SE(TI, false); 2307 if (SI == SE) 2308 MyStates.SetAsExit(); 2309 else 2310 do { 2311 const BasicBlock *Succ = *SI++; 2312 if (Succ == BB) 2313 continue; 2314 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ); 2315 // If we haven't seen this node yet, then we've found a CFG cycle. 2316 // Be optimistic here; it's CheckForCFGHazards' job detect trouble. 2317 if (I == BBStates.end()) 2318 continue; 2319 MyStates.InitFromSucc(I->second); 2320 while (SI != SE) { 2321 Succ = *SI++; 2322 if (Succ != BB) { 2323 I = BBStates.find(Succ); 2324 if (I != BBStates.end()) 2325 MyStates.MergeSucc(I->second); 2326 } 2327 } 2328 break; 2329 } while (SI != SE); 2330 2331 // Visit all the instructions, bottom-up. 2332 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) { 2333 Instruction *Inst = llvm::prior(I); 2334 InstructionClass Class = GetInstructionClass(Inst); 2335 const Value *Arg = 0; 2336 2337 switch (Class) { 2338 case IC_Release: { 2339 Arg = GetObjCArg(Inst); 2340 2341 PtrState &S = MyStates.getPtrBottomUpState(Arg); 2342 2343 // If we see two releases in a row on the same pointer. If so, make 2344 // a note, and we'll cicle back to revisit it after we've 2345 // hopefully eliminated the second release, which may allow us to 2346 // eliminate the first release too. 2347 // Theoretically we could implement removal of nested retain+release 2348 // pairs by making PtrState hold a stack of states, but this is 2349 // simple and avoids adding overhead for the non-nested case. 2350 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) 2351 NestingDetected = true; 2352 2353 S.SetSeqToRelease(Inst->getMetadata(ImpreciseReleaseMDKind)); 2354 S.RRI.clear(); 2355 S.RRI.KnownSafe = S.IsKnownNested() || S.IsKnownIncremented(); 2356 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); 2357 S.RRI.Calls.insert(Inst); 2358 2359 S.IncrementRefCount(); 2360 S.IncrementNestCount(); 2361 break; 2362 } 2363 case IC_RetainBlock: 2364 case IC_Retain: 2365 case IC_RetainRV: { 2366 Arg = GetObjCArg(Inst); 2367 2368 PtrState &S = MyStates.getPtrBottomUpState(Arg); 2369 S.DecrementRefCount(); 2370 S.SetAtLeastOneRefCount(); 2371 S.DecrementNestCount(); 2372 2373 // An non-copy-on-escape objc_retainBlock call with just a use still 2374 // needs to be kept, because it may be copying a block from the stack 2375 // to the heap. 2376 if (Class == IC_RetainBlock && 2377 !Inst->getMetadata(CopyOnEscapeMDKind) && 2378 S.GetSeq() == S_Use) 2379 S.SetSeq(S_CanRelease); 2380 2381 switch (S.GetSeq()) { 2382 case S_Stop: 2383 case S_Release: 2384 case S_MovableRelease: 2385 case S_Use: 2386 S.RRI.ReverseInsertPts.clear(); 2387 // FALL THROUGH 2388 case S_CanRelease: 2389 // Don't do retain+release tracking for IC_RetainRV, because it's 2390 // better to let it remain as the first instruction after a call. 2391 if (Class != IC_RetainRV) { 2392 S.RRI.IsRetainBlock = Class == IC_RetainBlock; 2393 if (S.RRI.IsRetainBlock) 2394 S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind); 2395 Retains[Inst] = S.RRI; 2396 } 2397 S.ClearSequenceProgress(); 2398 break; 2399 case S_None: 2400 break; 2401 case S_Retain: 2402 llvm_unreachable("bottom-up pointer in retain state!"); 2403 } 2404 continue; 2405 } 2406 case IC_AutoreleasepoolPop: 2407 // Conservatively, clear MyStates for all known pointers. 2408 MyStates.clearBottomUpPointers(); 2409 continue; 2410 case IC_AutoreleasepoolPush: 2411 case IC_None: 2412 // These are irrelevant. 2413 continue; 2414 default: 2415 break; 2416 } 2417 2418 // Consider any other possible effects of this instruction on each 2419 // pointer being tracked. 2420 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(), 2421 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) { 2422 const Value *Ptr = MI->first; 2423 if (Ptr == Arg) 2424 continue; // Handled above. 2425 PtrState &S = MI->second; 2426 Sequence Seq = S.GetSeq(); 2427 2428 // Check for possible releases. 2429 if (CanAlterRefCount(Inst, Ptr, PA, Class)) { 2430 S.DecrementRefCount(); 2431 switch (Seq) { 2432 case S_Use: 2433 S.SetSeq(S_CanRelease); 2434 continue; 2435 case S_CanRelease: 2436 case S_Release: 2437 case S_MovableRelease: 2438 case S_Stop: 2439 case S_None: 2440 break; 2441 case S_Retain: 2442 llvm_unreachable("bottom-up pointer in retain state!"); 2443 } 2444 } 2445 2446 // Check for possible direct uses. 2447 switch (Seq) { 2448 case S_Release: 2449 case S_MovableRelease: 2450 if (CanUse(Inst, Ptr, PA, Class)) { 2451 assert(S.RRI.ReverseInsertPts.empty()); 2452 S.RRI.ReverseInsertPts.insert(Inst); 2453 S.SetSeq(S_Use); 2454 } else if (Seq == S_Release && 2455 (Class == IC_User || Class == IC_CallOrUser)) { 2456 // Non-movable releases depend on any possible objc pointer use. 2457 S.SetSeq(S_Stop); 2458 assert(S.RRI.ReverseInsertPts.empty()); 2459 S.RRI.ReverseInsertPts.insert(Inst); 2460 } 2461 break; 2462 case S_Stop: 2463 if (CanUse(Inst, Ptr, PA, Class)) 2464 S.SetSeq(S_Use); 2465 break; 2466 case S_CanRelease: 2467 case S_Use: 2468 case S_None: 2469 break; 2470 case S_Retain: 2471 llvm_unreachable("bottom-up pointer in retain state!"); 2472 } 2473 } 2474 } 2475 2476 return NestingDetected; 2477 } 2478 2479 bool 2480 ObjCARCOpt::VisitTopDown(BasicBlock *BB, 2481 DenseMap<const BasicBlock *, BBState> &BBStates, 2482 DenseMap<Value *, RRInfo> &Releases) { 2483 bool NestingDetected = false; 2484 BBState &MyStates = BBStates[BB]; 2485 2486 // Merge the states from each predecessor to compute the initial state 2487 // for the current block. 2488 const_pred_iterator PI(BB), PE(BB, false); 2489 if (PI == PE) 2490 MyStates.SetAsEntry(); 2491 else 2492 do { 2493 const BasicBlock *Pred = *PI++; 2494 if (Pred == BB) 2495 continue; 2496 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred); 2497 assert(I != BBStates.end()); 2498 // If we haven't seen this node yet, then we've found a CFG cycle. 2499 // Be optimistic here; it's CheckForCFGHazards' job detect trouble. 2500 if (!I->second.isVisitedTopDown()) 2501 continue; 2502 MyStates.InitFromPred(I->second); 2503 while (PI != PE) { 2504 Pred = *PI++; 2505 if (Pred != BB) { 2506 I = BBStates.find(Pred); 2507 assert(I != BBStates.end()); 2508 if (I->second.isVisitedTopDown()) 2509 MyStates.MergePred(I->second); 2510 } 2511 } 2512 break; 2513 } while (PI != PE); 2514 2515 // Visit all the instructions, top-down. 2516 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 2517 Instruction *Inst = I; 2518 InstructionClass Class = GetInstructionClass(Inst); 2519 const Value *Arg = 0; 2520 2521 switch (Class) { 2522 case IC_RetainBlock: 2523 case IC_Retain: 2524 case IC_RetainRV: { 2525 Arg = GetObjCArg(Inst); 2526 2527 PtrState &S = MyStates.getPtrTopDownState(Arg); 2528 2529 // Don't do retain+release tracking for IC_RetainRV, because it's 2530 // better to let it remain as the first instruction after a call. 2531 if (Class != IC_RetainRV) { 2532 // If we see two retains in a row on the same pointer. If so, make 2533 // a note, and we'll cicle back to revisit it after we've 2534 // hopefully eliminated the second retain, which may allow us to 2535 // eliminate the first retain too. 2536 // Theoretically we could implement removal of nested retain+release 2537 // pairs by making PtrState hold a stack of states, but this is 2538 // simple and avoids adding overhead for the non-nested case. 2539 if (S.GetSeq() == S_Retain) 2540 NestingDetected = true; 2541 2542 S.SetSeq(S_Retain); 2543 S.RRI.clear(); 2544 S.RRI.IsRetainBlock = Class == IC_RetainBlock; 2545 if (S.RRI.IsRetainBlock) 2546 S.RRI.CopyOnEscape = !!Inst->getMetadata(CopyOnEscapeMDKind); 2547 // Don't check S.IsKnownIncremented() here because it's not 2548 // sufficient. 2549 S.RRI.KnownSafe = S.IsKnownNested(); 2550 S.RRI.Calls.insert(Inst); 2551 } 2552 2553 S.SetAtLeastOneRefCount(); 2554 S.IncrementRefCount(); 2555 S.IncrementNestCount(); 2556 continue; 2557 } 2558 case IC_Release: { 2559 Arg = GetObjCArg(Inst); 2560 2561 PtrState &S = MyStates.getPtrTopDownState(Arg); 2562 S.DecrementRefCount(); 2563 S.DecrementNestCount(); 2564 2565 switch (S.GetSeq()) { 2566 case S_Retain: 2567 case S_CanRelease: 2568 S.RRI.ReverseInsertPts.clear(); 2569 // FALL THROUGH 2570 case S_Use: 2571 S.RRI.ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind); 2572 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); 2573 Releases[Inst] = S.RRI; 2574 S.ClearSequenceProgress(); 2575 break; 2576 case S_None: 2577 break; 2578 case S_Stop: 2579 case S_Release: 2580 case S_MovableRelease: 2581 llvm_unreachable("top-down pointer in release state!"); 2582 } 2583 break; 2584 } 2585 case IC_AutoreleasepoolPop: 2586 // Conservatively, clear MyStates for all known pointers. 2587 MyStates.clearTopDownPointers(); 2588 continue; 2589 case IC_AutoreleasepoolPush: 2590 case IC_None: 2591 // These are irrelevant. 2592 continue; 2593 default: 2594 break; 2595 } 2596 2597 // Consider any other possible effects of this instruction on each 2598 // pointer being tracked. 2599 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(), 2600 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) { 2601 const Value *Ptr = MI->first; 2602 if (Ptr == Arg) 2603 continue; // Handled above. 2604 PtrState &S = MI->second; 2605 Sequence Seq = S.GetSeq(); 2606 2607 // Check for possible releases. 2608 if (CanAlterRefCount(Inst, Ptr, PA, Class)) { 2609 S.DecrementRefCount(); 2610 switch (Seq) { 2611 case S_Retain: 2612 S.SetSeq(S_CanRelease); 2613 assert(S.RRI.ReverseInsertPts.empty()); 2614 S.RRI.ReverseInsertPts.insert(Inst); 2615 2616 // One call can't cause a transition from S_Retain to S_CanRelease 2617 // and S_CanRelease to S_Use. If we've made the first transition, 2618 // we're done. 2619 continue; 2620 case S_Use: 2621 case S_CanRelease: 2622 case S_None: 2623 break; 2624 case S_Stop: 2625 case S_Release: 2626 case S_MovableRelease: 2627 llvm_unreachable("top-down pointer in release state!"); 2628 } 2629 } 2630 2631 // Check for possible direct uses. 2632 switch (Seq) { 2633 case S_CanRelease: 2634 if (CanUse(Inst, Ptr, PA, Class)) 2635 S.SetSeq(S_Use); 2636 break; 2637 case S_Retain: 2638 // A non-copy-on-scape objc_retainBlock call may be responsible for 2639 // copying the block data from the stack to the heap. Model this by 2640 // moving it straight from S_Retain to S_Use. 2641 if (S.RRI.IsRetainBlock && 2642 !S.RRI.CopyOnEscape && 2643 CanUse(Inst, Ptr, PA, Class)) { 2644 assert(S.RRI.ReverseInsertPts.empty()); 2645 S.RRI.ReverseInsertPts.insert(Inst); 2646 S.SetSeq(S_Use); 2647 } 2648 break; 2649 case S_Use: 2650 case S_None: 2651 break; 2652 case S_Stop: 2653 case S_Release: 2654 case S_MovableRelease: 2655 llvm_unreachable("top-down pointer in release state!"); 2656 } 2657 } 2658 } 2659 2660 CheckForCFGHazards(BB, BBStates, MyStates); 2661 return NestingDetected; 2662 } 2663 2664 // Visit - Visit the function both top-down and bottom-up. 2665 bool 2666 ObjCARCOpt::Visit(Function &F, 2667 DenseMap<const BasicBlock *, BBState> &BBStates, 2668 MapVector<Value *, RRInfo> &Retains, 2669 DenseMap<Value *, RRInfo> &Releases) { 2670 // Use reverse-postorder on the reverse CFG for bottom-up, because we 2671 // magically know that loops will be well behaved, i.e. they won't repeatedly 2672 // call retain on a single pointer without doing a release. We can't use 2673 // ReversePostOrderTraversal here because we want to walk up from each 2674 // function exit point. 2675 SmallPtrSet<BasicBlock *, 16> Visited; 2676 SmallVector<std::pair<BasicBlock *, pred_iterator>, 16> Stack; 2677 SmallVector<BasicBlock *, 16> Order; 2678 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { 2679 BasicBlock *BB = I; 2680 if (BB->getTerminator()->getNumSuccessors() == 0) 2681 Stack.push_back(std::make_pair(BB, pred_begin(BB))); 2682 } 2683 while (!Stack.empty()) { 2684 pred_iterator End = pred_end(Stack.back().first); 2685 while (Stack.back().second != End) { 2686 BasicBlock *BB = *Stack.back().second++; 2687 if (Visited.insert(BB)) 2688 Stack.push_back(std::make_pair(BB, pred_begin(BB))); 2689 } 2690 Order.push_back(Stack.pop_back_val().first); 2691 } 2692 bool BottomUpNestingDetected = false; 2693 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I = 2694 Order.rbegin(), E = Order.rend(); I != E; ++I) { 2695 BasicBlock *BB = *I; 2696 BottomUpNestingDetected |= VisitBottomUp(BB, BBStates, Retains); 2697 } 2698 2699 // Use regular reverse-postorder for top-down. 2700 bool TopDownNestingDetected = false; 2701 typedef ReversePostOrderTraversal<Function *> RPOTType; 2702 RPOTType RPOT(&F); 2703 for (RPOTType::rpo_iterator I = RPOT.begin(), E = RPOT.end(); I != E; ++I) { 2704 BasicBlock *BB = *I; 2705 TopDownNestingDetected |= VisitTopDown(BB, BBStates, Releases); 2706 } 2707 2708 return TopDownNestingDetected && BottomUpNestingDetected; 2709 } 2710 2711 /// MoveCalls - Move the calls in RetainsToMove and ReleasesToMove. 2712 void ObjCARCOpt::MoveCalls(Value *Arg, 2713 RRInfo &RetainsToMove, 2714 RRInfo &ReleasesToMove, 2715 MapVector<Value *, RRInfo> &Retains, 2716 DenseMap<Value *, RRInfo> &Releases, 2717 SmallVectorImpl<Instruction *> &DeadInsts, 2718 Module *M) { 2719 Type *ArgTy = Arg->getType(); 2720 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext())); 2721 2722 // Insert the new retain and release calls. 2723 for (SmallPtrSet<Instruction *, 2>::const_iterator 2724 PI = ReleasesToMove.ReverseInsertPts.begin(), 2725 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) { 2726 Instruction *InsertPt = *PI; 2727 Value *MyArg = ArgTy == ParamTy ? Arg : 2728 new BitCastInst(Arg, ParamTy, "", InsertPt); 2729 CallInst *Call = 2730 CallInst::Create(RetainsToMove.IsRetainBlock ? 2731 getRetainBlockCallee(M) : getRetainCallee(M), 2732 MyArg, "", InsertPt); 2733 Call->setDoesNotThrow(); 2734 if (RetainsToMove.CopyOnEscape) 2735 Call->setMetadata(CopyOnEscapeMDKind, 2736 MDNode::get(M->getContext(), ArrayRef<Value *>())); 2737 if (!RetainsToMove.IsRetainBlock) 2738 Call->setTailCall(); 2739 } 2740 for (SmallPtrSet<Instruction *, 2>::const_iterator 2741 PI = RetainsToMove.ReverseInsertPts.begin(), 2742 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) { 2743 Instruction *LastUse = *PI; 2744 Instruction *InsertPts[] = { 0, 0, 0 }; 2745 if (InvokeInst *II = dyn_cast<InvokeInst>(LastUse)) { 2746 // We can't insert code immediately after an invoke instruction, so 2747 // insert code at the beginning of both successor blocks instead. 2748 // The invoke's return value isn't available in the unwind block, 2749 // but our releases will never depend on it, because they must be 2750 // paired with retains from before the invoke. 2751 InsertPts[0] = II->getNormalDest()->getFirstInsertionPt(); 2752 InsertPts[1] = II->getUnwindDest()->getFirstInsertionPt(); 2753 } else { 2754 // Insert code immediately after the last use. 2755 InsertPts[0] = llvm::next(BasicBlock::iterator(LastUse)); 2756 } 2757 2758 for (Instruction **I = InsertPts; *I; ++I) { 2759 Instruction *InsertPt = *I; 2760 Value *MyArg = ArgTy == ParamTy ? Arg : 2761 new BitCastInst(Arg, ParamTy, "", InsertPt); 2762 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg, 2763 "", InsertPt); 2764 // Attach a clang.imprecise_release metadata tag, if appropriate. 2765 if (MDNode *M = ReleasesToMove.ReleaseMetadata) 2766 Call->setMetadata(ImpreciseReleaseMDKind, M); 2767 Call->setDoesNotThrow(); 2768 if (ReleasesToMove.IsTailCallRelease) 2769 Call->setTailCall(); 2770 } 2771 } 2772 2773 // Delete the original retain and release calls. 2774 for (SmallPtrSet<Instruction *, 2>::const_iterator 2775 AI = RetainsToMove.Calls.begin(), 2776 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) { 2777 Instruction *OrigRetain = *AI; 2778 Retains.blot(OrigRetain); 2779 DeadInsts.push_back(OrigRetain); 2780 } 2781 for (SmallPtrSet<Instruction *, 2>::const_iterator 2782 AI = ReleasesToMove.Calls.begin(), 2783 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) { 2784 Instruction *OrigRelease = *AI; 2785 Releases.erase(OrigRelease); 2786 DeadInsts.push_back(OrigRelease); 2787 } 2788 } 2789 2790 bool 2791 ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState> 2792 &BBStates, 2793 MapVector<Value *, RRInfo> &Retains, 2794 DenseMap<Value *, RRInfo> &Releases, 2795 Module *M) { 2796 bool AnyPairsCompletelyEliminated = false; 2797 RRInfo RetainsToMove; 2798 RRInfo ReleasesToMove; 2799 SmallVector<Instruction *, 4> NewRetains; 2800 SmallVector<Instruction *, 4> NewReleases; 2801 SmallVector<Instruction *, 8> DeadInsts; 2802 2803 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(), 2804 E = Retains.end(); I != E; ++I) { 2805 Value *V = I->first; 2806 if (!V) continue; // blotted 2807 2808 Instruction *Retain = cast<Instruction>(V); 2809 Value *Arg = GetObjCArg(Retain); 2810 2811 // If the object being released is in static storage, we know it's 2812 // not being managed by ObjC reference counting, so we can delete pairs 2813 // regardless of what possible decrements or uses lie between them. 2814 bool KnownSafe = isa<Constant>(Arg); 2815 2816 // Same for stack storage, unless this is a non-copy-on-escape 2817 // objc_retainBlock call, which is responsible for copying the block data 2818 // from the stack to the heap. 2819 if ((!I->second.IsRetainBlock || I->second.CopyOnEscape) && 2820 isa<AllocaInst>(Arg)) 2821 KnownSafe = true; 2822 2823 // A constant pointer can't be pointing to an object on the heap. It may 2824 // be reference-counted, but it won't be deleted. 2825 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg)) 2826 if (const GlobalVariable *GV = 2827 dyn_cast<GlobalVariable>( 2828 StripPointerCastsAndObjCCalls(LI->getPointerOperand()))) 2829 if (GV->isConstant()) 2830 KnownSafe = true; 2831 2832 // If a pair happens in a region where it is known that the reference count 2833 // is already incremented, we can similarly ignore possible decrements. 2834 bool KnownSafeTD = true, KnownSafeBU = true; 2835 2836 // Connect the dots between the top-down-collected RetainsToMove and 2837 // bottom-up-collected ReleasesToMove to form sets of related calls. 2838 // This is an iterative process so that we connect multiple releases 2839 // to multiple retains if needed. 2840 unsigned OldDelta = 0; 2841 unsigned NewDelta = 0; 2842 unsigned OldCount = 0; 2843 unsigned NewCount = 0; 2844 bool FirstRelease = true; 2845 bool FirstRetain = true; 2846 NewRetains.push_back(Retain); 2847 for (;;) { 2848 for (SmallVectorImpl<Instruction *>::const_iterator 2849 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) { 2850 Instruction *NewRetain = *NI; 2851 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain); 2852 assert(It != Retains.end()); 2853 const RRInfo &NewRetainRRI = It->second; 2854 KnownSafeTD &= NewRetainRRI.KnownSafe; 2855 for (SmallPtrSet<Instruction *, 2>::const_iterator 2856 LI = NewRetainRRI.Calls.begin(), 2857 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) { 2858 Instruction *NewRetainRelease = *LI; 2859 DenseMap<Value *, RRInfo>::const_iterator Jt = 2860 Releases.find(NewRetainRelease); 2861 if (Jt == Releases.end()) 2862 goto next_retain; 2863 const RRInfo &NewRetainReleaseRRI = Jt->second; 2864 assert(NewRetainReleaseRRI.Calls.count(NewRetain)); 2865 if (ReleasesToMove.Calls.insert(NewRetainRelease)) { 2866 OldDelta -= 2867 BBStates[NewRetainRelease->getParent()].GetAllPathCount(); 2868 2869 // Merge the ReleaseMetadata and IsTailCallRelease values. 2870 if (FirstRelease) { 2871 ReleasesToMove.ReleaseMetadata = 2872 NewRetainReleaseRRI.ReleaseMetadata; 2873 ReleasesToMove.IsTailCallRelease = 2874 NewRetainReleaseRRI.IsTailCallRelease; 2875 FirstRelease = false; 2876 } else { 2877 if (ReleasesToMove.ReleaseMetadata != 2878 NewRetainReleaseRRI.ReleaseMetadata) 2879 ReleasesToMove.ReleaseMetadata = 0; 2880 if (ReleasesToMove.IsTailCallRelease != 2881 NewRetainReleaseRRI.IsTailCallRelease) 2882 ReleasesToMove.IsTailCallRelease = false; 2883 } 2884 2885 // Collect the optimal insertion points. 2886 if (!KnownSafe) 2887 for (SmallPtrSet<Instruction *, 2>::const_iterator 2888 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(), 2889 RE = NewRetainReleaseRRI.ReverseInsertPts.end(); 2890 RI != RE; ++RI) { 2891 Instruction *RIP = *RI; 2892 if (ReleasesToMove.ReverseInsertPts.insert(RIP)) 2893 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount(); 2894 } 2895 NewReleases.push_back(NewRetainRelease); 2896 } 2897 } 2898 } 2899 NewRetains.clear(); 2900 if (NewReleases.empty()) break; 2901 2902 // Back the other way. 2903 for (SmallVectorImpl<Instruction *>::const_iterator 2904 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) { 2905 Instruction *NewRelease = *NI; 2906 DenseMap<Value *, RRInfo>::const_iterator It = 2907 Releases.find(NewRelease); 2908 assert(It != Releases.end()); 2909 const RRInfo &NewReleaseRRI = It->second; 2910 KnownSafeBU &= NewReleaseRRI.KnownSafe; 2911 for (SmallPtrSet<Instruction *, 2>::const_iterator 2912 LI = NewReleaseRRI.Calls.begin(), 2913 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) { 2914 Instruction *NewReleaseRetain = *LI; 2915 MapVector<Value *, RRInfo>::const_iterator Jt = 2916 Retains.find(NewReleaseRetain); 2917 if (Jt == Retains.end()) 2918 goto next_retain; 2919 const RRInfo &NewReleaseRetainRRI = Jt->second; 2920 assert(NewReleaseRetainRRI.Calls.count(NewRelease)); 2921 if (RetainsToMove.Calls.insert(NewReleaseRetain)) { 2922 unsigned PathCount = 2923 BBStates[NewReleaseRetain->getParent()].GetAllPathCount(); 2924 OldDelta += PathCount; 2925 OldCount += PathCount; 2926 2927 // Merge the IsRetainBlock values. 2928 if (FirstRetain) { 2929 RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock; 2930 RetainsToMove.CopyOnEscape = NewReleaseRetainRRI.CopyOnEscape; 2931 FirstRetain = false; 2932 } else if (ReleasesToMove.IsRetainBlock != 2933 NewReleaseRetainRRI.IsRetainBlock) 2934 // It's not possible to merge the sequences if one uses 2935 // objc_retain and the other uses objc_retainBlock. 2936 goto next_retain; 2937 2938 // Merge the CopyOnEscape values. 2939 RetainsToMove.CopyOnEscape &= NewReleaseRetainRRI.CopyOnEscape; 2940 2941 // Collect the optimal insertion points. 2942 if (!KnownSafe) 2943 for (SmallPtrSet<Instruction *, 2>::const_iterator 2944 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(), 2945 RE = NewReleaseRetainRRI.ReverseInsertPts.end(); 2946 RI != RE; ++RI) { 2947 Instruction *RIP = *RI; 2948 if (RetainsToMove.ReverseInsertPts.insert(RIP)) { 2949 PathCount = BBStates[RIP->getParent()].GetAllPathCount(); 2950 NewDelta += PathCount; 2951 NewCount += PathCount; 2952 } 2953 } 2954 NewRetains.push_back(NewReleaseRetain); 2955 } 2956 } 2957 } 2958 NewReleases.clear(); 2959 if (NewRetains.empty()) break; 2960 } 2961 2962 // If the pointer is known incremented or nested, we can safely delete the 2963 // pair regardless of what's between them. 2964 if (KnownSafeTD || KnownSafeBU) { 2965 RetainsToMove.ReverseInsertPts.clear(); 2966 ReleasesToMove.ReverseInsertPts.clear(); 2967 NewCount = 0; 2968 } else { 2969 // Determine whether the new insertion points we computed preserve the 2970 // balance of retain and release calls through the program. 2971 // TODO: If the fully aggressive solution isn't valid, try to find a 2972 // less aggressive solution which is. 2973 if (NewDelta != 0) 2974 goto next_retain; 2975 } 2976 2977 // Determine whether the original call points are balanced in the retain and 2978 // release calls through the program. If not, conservatively don't touch 2979 // them. 2980 // TODO: It's theoretically possible to do code motion in this case, as 2981 // long as the existing imbalances are maintained. 2982 if (OldDelta != 0) 2983 goto next_retain; 2984 2985 // Ok, everything checks out and we're all set. Let's move some code! 2986 Changed = true; 2987 AnyPairsCompletelyEliminated = NewCount == 0; 2988 NumRRs += OldCount - NewCount; 2989 MoveCalls(Arg, RetainsToMove, ReleasesToMove, 2990 Retains, Releases, DeadInsts, M); 2991 2992 next_retain: 2993 NewReleases.clear(); 2994 NewRetains.clear(); 2995 RetainsToMove.clear(); 2996 ReleasesToMove.clear(); 2997 } 2998 2999 // Now that we're done moving everything, we can delete the newly dead 3000 // instructions, as we no longer need them as insert points. 3001 while (!DeadInsts.empty()) 3002 EraseInstruction(DeadInsts.pop_back_val()); 3003 3004 return AnyPairsCompletelyEliminated; 3005 } 3006 3007 /// OptimizeWeakCalls - Weak pointer optimizations. 3008 void ObjCARCOpt::OptimizeWeakCalls(Function &F) { 3009 // First, do memdep-style RLE and S2L optimizations. We can't use memdep 3010 // itself because it uses AliasAnalysis and we need to do provenance 3011 // queries instead. 3012 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 3013 Instruction *Inst = &*I++; 3014 InstructionClass Class = GetBasicInstructionClass(Inst); 3015 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained) 3016 continue; 3017 3018 // Delete objc_loadWeak calls with no users. 3019 if (Class == IC_LoadWeak && Inst->use_empty()) { 3020 Inst->eraseFromParent(); 3021 continue; 3022 } 3023 3024 // TODO: For now, just look for an earlier available version of this value 3025 // within the same block. Theoretically, we could do memdep-style non-local 3026 // analysis too, but that would want caching. A better approach would be to 3027 // use the technique that EarlyCSE uses. 3028 inst_iterator Current = llvm::prior(I); 3029 BasicBlock *CurrentBB = Current.getBasicBlockIterator(); 3030 for (BasicBlock::iterator B = CurrentBB->begin(), 3031 J = Current.getInstructionIterator(); 3032 J != B; --J) { 3033 Instruction *EarlierInst = &*llvm::prior(J); 3034 InstructionClass EarlierClass = GetInstructionClass(EarlierInst); 3035 switch (EarlierClass) { 3036 case IC_LoadWeak: 3037 case IC_LoadWeakRetained: { 3038 // If this is loading from the same pointer, replace this load's value 3039 // with that one. 3040 CallInst *Call = cast<CallInst>(Inst); 3041 CallInst *EarlierCall = cast<CallInst>(EarlierInst); 3042 Value *Arg = Call->getArgOperand(0); 3043 Value *EarlierArg = EarlierCall->getArgOperand(0); 3044 switch (PA.getAA()->alias(Arg, EarlierArg)) { 3045 case AliasAnalysis::MustAlias: 3046 Changed = true; 3047 // If the load has a builtin retain, insert a plain retain for it. 3048 if (Class == IC_LoadWeakRetained) { 3049 CallInst *CI = 3050 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, 3051 "", Call); 3052 CI->setTailCall(); 3053 } 3054 // Zap the fully redundant load. 3055 Call->replaceAllUsesWith(EarlierCall); 3056 Call->eraseFromParent(); 3057 goto clobbered; 3058 case AliasAnalysis::MayAlias: 3059 case AliasAnalysis::PartialAlias: 3060 goto clobbered; 3061 case AliasAnalysis::NoAlias: 3062 break; 3063 } 3064 break; 3065 } 3066 case IC_StoreWeak: 3067 case IC_InitWeak: { 3068 // If this is storing to the same pointer and has the same size etc. 3069 // replace this load's value with the stored value. 3070 CallInst *Call = cast<CallInst>(Inst); 3071 CallInst *EarlierCall = cast<CallInst>(EarlierInst); 3072 Value *Arg = Call->getArgOperand(0); 3073 Value *EarlierArg = EarlierCall->getArgOperand(0); 3074 switch (PA.getAA()->alias(Arg, EarlierArg)) { 3075 case AliasAnalysis::MustAlias: 3076 Changed = true; 3077 // If the load has a builtin retain, insert a plain retain for it. 3078 if (Class == IC_LoadWeakRetained) { 3079 CallInst *CI = 3080 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, 3081 "", Call); 3082 CI->setTailCall(); 3083 } 3084 // Zap the fully redundant load. 3085 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1)); 3086 Call->eraseFromParent(); 3087 goto clobbered; 3088 case AliasAnalysis::MayAlias: 3089 case AliasAnalysis::PartialAlias: 3090 goto clobbered; 3091 case AliasAnalysis::NoAlias: 3092 break; 3093 } 3094 break; 3095 } 3096 case IC_MoveWeak: 3097 case IC_CopyWeak: 3098 // TOOD: Grab the copied value. 3099 goto clobbered; 3100 case IC_AutoreleasepoolPush: 3101 case IC_None: 3102 case IC_User: 3103 // Weak pointers are only modified through the weak entry points 3104 // (and arbitrary calls, which could call the weak entry points). 3105 break; 3106 default: 3107 // Anything else could modify the weak pointer. 3108 goto clobbered; 3109 } 3110 } 3111 clobbered:; 3112 } 3113 3114 // Then, for each destroyWeak with an alloca operand, check to see if 3115 // the alloca and all its users can be zapped. 3116 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 3117 Instruction *Inst = &*I++; 3118 InstructionClass Class = GetBasicInstructionClass(Inst); 3119 if (Class != IC_DestroyWeak) 3120 continue; 3121 3122 CallInst *Call = cast<CallInst>(Inst); 3123 Value *Arg = Call->getArgOperand(0); 3124 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) { 3125 for (Value::use_iterator UI = Alloca->use_begin(), 3126 UE = Alloca->use_end(); UI != UE; ++UI) { 3127 Instruction *UserInst = cast<Instruction>(*UI); 3128 switch (GetBasicInstructionClass(UserInst)) { 3129 case IC_InitWeak: 3130 case IC_StoreWeak: 3131 case IC_DestroyWeak: 3132 continue; 3133 default: 3134 goto done; 3135 } 3136 } 3137 Changed = true; 3138 for (Value::use_iterator UI = Alloca->use_begin(), 3139 UE = Alloca->use_end(); UI != UE; ) { 3140 CallInst *UserInst = cast<CallInst>(*UI++); 3141 if (!UserInst->use_empty()) 3142 UserInst->replaceAllUsesWith(UserInst->getOperand(1)); 3143 UserInst->eraseFromParent(); 3144 } 3145 Alloca->eraseFromParent(); 3146 done:; 3147 } 3148 } 3149 } 3150 3151 /// OptimizeSequences - Identify program paths which execute sequences of 3152 /// retains and releases which can be eliminated. 3153 bool ObjCARCOpt::OptimizeSequences(Function &F) { 3154 /// Releases, Retains - These are used to store the results of the main flow 3155 /// analysis. These use Value* as the key instead of Instruction* so that the 3156 /// map stays valid when we get around to rewriting code and calls get 3157 /// replaced by arguments. 3158 DenseMap<Value *, RRInfo> Releases; 3159 MapVector<Value *, RRInfo> Retains; 3160 3161 /// BBStates, This is used during the traversal of the function to track the 3162 /// states for each identified object at each block. 3163 DenseMap<const BasicBlock *, BBState> BBStates; 3164 3165 // Analyze the CFG of the function, and all instructions. 3166 bool NestingDetected = Visit(F, BBStates, Retains, Releases); 3167 3168 // Transform. 3169 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) && 3170 NestingDetected; 3171 } 3172 3173 /// OptimizeReturns - Look for this pattern: 3174 /// 3175 /// %call = call i8* @something(...) 3176 /// %2 = call i8* @objc_retain(i8* %call) 3177 /// %3 = call i8* @objc_autorelease(i8* %2) 3178 /// ret i8* %3 3179 /// 3180 /// And delete the retain and autorelease. 3181 /// 3182 /// Otherwise if it's just this: 3183 /// 3184 /// %3 = call i8* @objc_autorelease(i8* %2) 3185 /// ret i8* %3 3186 /// 3187 /// convert the autorelease to autoreleaseRV. 3188 void ObjCARCOpt::OptimizeReturns(Function &F) { 3189 if (!F.getReturnType()->isPointerTy()) 3190 return; 3191 3192 SmallPtrSet<Instruction *, 4> DependingInstructions; 3193 SmallPtrSet<const BasicBlock *, 4> Visited; 3194 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { 3195 BasicBlock *BB = FI; 3196 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back()); 3197 if (!Ret) continue; 3198 3199 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0)); 3200 FindDependencies(NeedsPositiveRetainCount, Arg, 3201 BB, Ret, DependingInstructions, Visited, PA); 3202 if (DependingInstructions.size() != 1) 3203 goto next_block; 3204 3205 { 3206 CallInst *Autorelease = 3207 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3208 if (!Autorelease) 3209 goto next_block; 3210 InstructionClass AutoreleaseClass = 3211 GetBasicInstructionClass(Autorelease); 3212 if (!IsAutorelease(AutoreleaseClass)) 3213 goto next_block; 3214 if (GetObjCArg(Autorelease) != Arg) 3215 goto next_block; 3216 3217 DependingInstructions.clear(); 3218 Visited.clear(); 3219 3220 // Check that there is nothing that can affect the reference 3221 // count between the autorelease and the retain. 3222 FindDependencies(CanChangeRetainCount, Arg, 3223 BB, Autorelease, DependingInstructions, Visited, PA); 3224 if (DependingInstructions.size() != 1) 3225 goto next_block; 3226 3227 { 3228 CallInst *Retain = 3229 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3230 3231 // Check that we found a retain with the same argument. 3232 if (!Retain || 3233 !IsRetain(GetBasicInstructionClass(Retain)) || 3234 GetObjCArg(Retain) != Arg) 3235 goto next_block; 3236 3237 DependingInstructions.clear(); 3238 Visited.clear(); 3239 3240 // Convert the autorelease to an autoreleaseRV, since it's 3241 // returning the value. 3242 if (AutoreleaseClass == IC_Autorelease) { 3243 Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent())); 3244 AutoreleaseClass = IC_AutoreleaseRV; 3245 } 3246 3247 // Check that there is nothing that can affect the reference 3248 // count between the retain and the call. 3249 // Note that Retain need not be in BB. 3250 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain, 3251 DependingInstructions, Visited, PA); 3252 if (DependingInstructions.size() != 1) 3253 goto next_block; 3254 3255 { 3256 CallInst *Call = 3257 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3258 3259 // Check that the pointer is the return value of the call. 3260 if (!Call || Arg != Call) 3261 goto next_block; 3262 3263 // Check that the call is a regular call. 3264 InstructionClass Class = GetBasicInstructionClass(Call); 3265 if (Class != IC_CallOrUser && Class != IC_Call) 3266 goto next_block; 3267 3268 // If so, we can zap the retain and autorelease. 3269 Changed = true; 3270 ++NumRets; 3271 EraseInstruction(Retain); 3272 EraseInstruction(Autorelease); 3273 } 3274 } 3275 } 3276 3277 next_block: 3278 DependingInstructions.clear(); 3279 Visited.clear(); 3280 } 3281 } 3282 3283 bool ObjCARCOpt::doInitialization(Module &M) { 3284 if (!EnableARCOpts) 3285 return false; 3286 3287 Run = ModuleHasARC(M); 3288 if (!Run) 3289 return false; 3290 3291 // Identify the imprecise release metadata kind. 3292 ImpreciseReleaseMDKind = 3293 M.getContext().getMDKindID("clang.imprecise_release"); 3294 CopyOnEscapeMDKind = 3295 M.getContext().getMDKindID("clang.arc.copy_on_escape"); 3296 3297 // Intuitively, objc_retain and others are nocapture, however in practice 3298 // they are not, because they return their argument value. And objc_release 3299 // calls finalizers. 3300 3301 // These are initialized lazily. 3302 RetainRVCallee = 0; 3303 AutoreleaseRVCallee = 0; 3304 ReleaseCallee = 0; 3305 RetainCallee = 0; 3306 RetainBlockCallee = 0; 3307 AutoreleaseCallee = 0; 3308 3309 return false; 3310 } 3311 3312 bool ObjCARCOpt::runOnFunction(Function &F) { 3313 if (!EnableARCOpts) 3314 return false; 3315 3316 // If nothing in the Module uses ARC, don't do anything. 3317 if (!Run) 3318 return false; 3319 3320 Changed = false; 3321 3322 PA.setAA(&getAnalysis<AliasAnalysis>()); 3323 3324 // This pass performs several distinct transformations. As a compile-time aid 3325 // when compiling code that isn't ObjC, skip these if the relevant ObjC 3326 // library functions aren't declared. 3327 3328 // Preliminary optimizations. This also computs UsedInThisFunction. 3329 OptimizeIndividualCalls(F); 3330 3331 // Optimizations for weak pointers. 3332 if (UsedInThisFunction & ((1 << IC_LoadWeak) | 3333 (1 << IC_LoadWeakRetained) | 3334 (1 << IC_StoreWeak) | 3335 (1 << IC_InitWeak) | 3336 (1 << IC_CopyWeak) | 3337 (1 << IC_MoveWeak) | 3338 (1 << IC_DestroyWeak))) 3339 OptimizeWeakCalls(F); 3340 3341 // Optimizations for retain+release pairs. 3342 if (UsedInThisFunction & ((1 << IC_Retain) | 3343 (1 << IC_RetainRV) | 3344 (1 << IC_RetainBlock))) 3345 if (UsedInThisFunction & (1 << IC_Release)) 3346 // Run OptimizeSequences until it either stops making changes or 3347 // no retain+release pair nesting is detected. 3348 while (OptimizeSequences(F)) {} 3349 3350 // Optimizations if objc_autorelease is used. 3351 if (UsedInThisFunction & 3352 ((1 << IC_Autorelease) | (1 << IC_AutoreleaseRV))) 3353 OptimizeReturns(F); 3354 3355 return Changed; 3356 } 3357 3358 void ObjCARCOpt::releaseMemory() { 3359 PA.clear(); 3360 } 3361 3362 //===----------------------------------------------------------------------===// 3363 // ARC contraction. 3364 //===----------------------------------------------------------------------===// 3365 3366 // TODO: ObjCARCContract could insert PHI nodes when uses aren't 3367 // dominated by single calls. 3368 3369 #include "llvm/Operator.h" 3370 #include "llvm/InlineAsm.h" 3371 #include "llvm/Analysis/Dominators.h" 3372 3373 STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed"); 3374 3375 namespace { 3376 /// ObjCARCContract - Late ARC optimizations. These change the IR in a way 3377 /// that makes it difficult to be analyzed by ObjCARCOpt, so it's run late. 3378 class ObjCARCContract : public FunctionPass { 3379 bool Changed; 3380 AliasAnalysis *AA; 3381 DominatorTree *DT; 3382 ProvenanceAnalysis PA; 3383 3384 /// Run - A flag indicating whether this optimization pass should run. 3385 bool Run; 3386 3387 /// StoreStrongCallee, etc. - Declarations for ObjC runtime 3388 /// functions, for use in creating calls to them. These are initialized 3389 /// lazily to avoid cluttering up the Module with unused declarations. 3390 Constant *StoreStrongCallee, 3391 *RetainAutoreleaseCallee, *RetainAutoreleaseRVCallee; 3392 3393 /// RetainRVMarker - The inline asm string to insert between calls and 3394 /// RetainRV calls to make the optimization work on targets which need it. 3395 const MDString *RetainRVMarker; 3396 3397 Constant *getStoreStrongCallee(Module *M); 3398 Constant *getRetainAutoreleaseCallee(Module *M); 3399 Constant *getRetainAutoreleaseRVCallee(Module *M); 3400 3401 bool ContractAutorelease(Function &F, Instruction *Autorelease, 3402 InstructionClass Class, 3403 SmallPtrSet<Instruction *, 4> 3404 &DependingInstructions, 3405 SmallPtrSet<const BasicBlock *, 4> 3406 &Visited); 3407 3408 void ContractRelease(Instruction *Release, 3409 inst_iterator &Iter); 3410 3411 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 3412 virtual bool doInitialization(Module &M); 3413 virtual bool runOnFunction(Function &F); 3414 3415 public: 3416 static char ID; 3417 ObjCARCContract() : FunctionPass(ID) { 3418 initializeObjCARCContractPass(*PassRegistry::getPassRegistry()); 3419 } 3420 }; 3421 } 3422 3423 char ObjCARCContract::ID = 0; 3424 INITIALIZE_PASS_BEGIN(ObjCARCContract, 3425 "objc-arc-contract", "ObjC ARC contraction", false, false) 3426 INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 3427 INITIALIZE_PASS_DEPENDENCY(DominatorTree) 3428 INITIALIZE_PASS_END(ObjCARCContract, 3429 "objc-arc-contract", "ObjC ARC contraction", false, false) 3430 3431 Pass *llvm::createObjCARCContractPass() { 3432 return new ObjCARCContract(); 3433 } 3434 3435 void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const { 3436 AU.addRequired<AliasAnalysis>(); 3437 AU.addRequired<DominatorTree>(); 3438 AU.setPreservesCFG(); 3439 } 3440 3441 Constant *ObjCARCContract::getStoreStrongCallee(Module *M) { 3442 if (!StoreStrongCallee) { 3443 LLVMContext &C = M->getContext(); 3444 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3445 Type *I8XX = PointerType::getUnqual(I8X); 3446 std::vector<Type *> Params; 3447 Params.push_back(I8XX); 3448 Params.push_back(I8X); 3449 3450 AttrListPtr Attributes; 3451 Attributes.addAttr(~0u, Attribute::NoUnwind); 3452 Attributes.addAttr(1, Attribute::NoCapture); 3453 3454 StoreStrongCallee = 3455 M->getOrInsertFunction( 3456 "objc_storeStrong", 3457 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), 3458 Attributes); 3459 } 3460 return StoreStrongCallee; 3461 } 3462 3463 Constant *ObjCARCContract::getRetainAutoreleaseCallee(Module *M) { 3464 if (!RetainAutoreleaseCallee) { 3465 LLVMContext &C = M->getContext(); 3466 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3467 std::vector<Type *> Params; 3468 Params.push_back(I8X); 3469 FunctionType *FTy = 3470 FunctionType::get(I8X, Params, /*isVarArg=*/false); 3471 AttrListPtr Attributes; 3472 Attributes.addAttr(~0u, Attribute::NoUnwind); 3473 RetainAutoreleaseCallee = 3474 M->getOrInsertFunction("objc_retainAutorelease", FTy, Attributes); 3475 } 3476 return RetainAutoreleaseCallee; 3477 } 3478 3479 Constant *ObjCARCContract::getRetainAutoreleaseRVCallee(Module *M) { 3480 if (!RetainAutoreleaseRVCallee) { 3481 LLVMContext &C = M->getContext(); 3482 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3483 std::vector<Type *> Params; 3484 Params.push_back(I8X); 3485 FunctionType *FTy = 3486 FunctionType::get(I8X, Params, /*isVarArg=*/false); 3487 AttrListPtr Attributes; 3488 Attributes.addAttr(~0u, Attribute::NoUnwind); 3489 RetainAutoreleaseRVCallee = 3490 M->getOrInsertFunction("objc_retainAutoreleaseReturnValue", FTy, 3491 Attributes); 3492 } 3493 return RetainAutoreleaseRVCallee; 3494 } 3495 3496 /// ContractAutorelease - Merge an autorelease with a retain into a fused 3497 /// call. 3498 bool 3499 ObjCARCContract::ContractAutorelease(Function &F, Instruction *Autorelease, 3500 InstructionClass Class, 3501 SmallPtrSet<Instruction *, 4> 3502 &DependingInstructions, 3503 SmallPtrSet<const BasicBlock *, 4> 3504 &Visited) { 3505 const Value *Arg = GetObjCArg(Autorelease); 3506 3507 // Check that there are no instructions between the retain and the autorelease 3508 // (such as an autorelease_pop) which may change the count. 3509 CallInst *Retain = 0; 3510 if (Class == IC_AutoreleaseRV) 3511 FindDependencies(RetainAutoreleaseRVDep, Arg, 3512 Autorelease->getParent(), Autorelease, 3513 DependingInstructions, Visited, PA); 3514 else 3515 FindDependencies(RetainAutoreleaseDep, Arg, 3516 Autorelease->getParent(), Autorelease, 3517 DependingInstructions, Visited, PA); 3518 3519 Visited.clear(); 3520 if (DependingInstructions.size() != 1) { 3521 DependingInstructions.clear(); 3522 return false; 3523 } 3524 3525 Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3526 DependingInstructions.clear(); 3527 3528 if (!Retain || 3529 GetBasicInstructionClass(Retain) != IC_Retain || 3530 GetObjCArg(Retain) != Arg) 3531 return false; 3532 3533 Changed = true; 3534 ++NumPeeps; 3535 3536 if (Class == IC_AutoreleaseRV) 3537 Retain->setCalledFunction(getRetainAutoreleaseRVCallee(F.getParent())); 3538 else 3539 Retain->setCalledFunction(getRetainAutoreleaseCallee(F.getParent())); 3540 3541 EraseInstruction(Autorelease); 3542 return true; 3543 } 3544 3545 /// ContractRelease - Attempt to merge an objc_release with a store, load, and 3546 /// objc_retain to form an objc_storeStrong. This can be a little tricky because 3547 /// the instructions don't always appear in order, and there may be unrelated 3548 /// intervening instructions. 3549 void ObjCARCContract::ContractRelease(Instruction *Release, 3550 inst_iterator &Iter) { 3551 LoadInst *Load = dyn_cast<LoadInst>(GetObjCArg(Release)); 3552 if (!Load || !Load->isSimple()) return; 3553 3554 // For now, require everything to be in one basic block. 3555 BasicBlock *BB = Release->getParent(); 3556 if (Load->getParent() != BB) return; 3557 3558 // Walk down to find the store. 3559 BasicBlock::iterator I = Load, End = BB->end(); 3560 ++I; 3561 AliasAnalysis::Location Loc = AA->getLocation(Load); 3562 while (I != End && 3563 (&*I == Release || 3564 IsRetain(GetBasicInstructionClass(I)) || 3565 !(AA->getModRefInfo(I, Loc) & AliasAnalysis::Mod))) 3566 ++I; 3567 StoreInst *Store = dyn_cast<StoreInst>(I); 3568 if (!Store || !Store->isSimple()) return; 3569 if (Store->getPointerOperand() != Loc.Ptr) return; 3570 3571 Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand()); 3572 3573 // Walk up to find the retain. 3574 I = Store; 3575 BasicBlock::iterator Begin = BB->begin(); 3576 while (I != Begin && GetBasicInstructionClass(I) != IC_Retain) 3577 --I; 3578 Instruction *Retain = I; 3579 if (GetBasicInstructionClass(Retain) != IC_Retain) return; 3580 if (GetObjCArg(Retain) != New) return; 3581 3582 Changed = true; 3583 ++NumStoreStrongs; 3584 3585 LLVMContext &C = Release->getContext(); 3586 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3587 Type *I8XX = PointerType::getUnqual(I8X); 3588 3589 Value *Args[] = { Load->getPointerOperand(), New }; 3590 if (Args[0]->getType() != I8XX) 3591 Args[0] = new BitCastInst(Args[0], I8XX, "", Store); 3592 if (Args[1]->getType() != I8X) 3593 Args[1] = new BitCastInst(Args[1], I8X, "", Store); 3594 CallInst *StoreStrong = 3595 CallInst::Create(getStoreStrongCallee(BB->getParent()->getParent()), 3596 Args, "", Store); 3597 StoreStrong->setDoesNotThrow(); 3598 StoreStrong->setDebugLoc(Store->getDebugLoc()); 3599 3600 if (&*Iter == Store) ++Iter; 3601 Store->eraseFromParent(); 3602 Release->eraseFromParent(); 3603 EraseInstruction(Retain); 3604 if (Load->use_empty()) 3605 Load->eraseFromParent(); 3606 } 3607 3608 bool ObjCARCContract::doInitialization(Module &M) { 3609 Run = ModuleHasARC(M); 3610 if (!Run) 3611 return false; 3612 3613 // These are initialized lazily. 3614 StoreStrongCallee = 0; 3615 RetainAutoreleaseCallee = 0; 3616 RetainAutoreleaseRVCallee = 0; 3617 3618 // Initialize RetainRVMarker. 3619 RetainRVMarker = 0; 3620 if (NamedMDNode *NMD = 3621 M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker")) 3622 if (NMD->getNumOperands() == 1) { 3623 const MDNode *N = NMD->getOperand(0); 3624 if (N->getNumOperands() == 1) 3625 if (const MDString *S = dyn_cast<MDString>(N->getOperand(0))) 3626 RetainRVMarker = S; 3627 } 3628 3629 return false; 3630 } 3631 3632 bool ObjCARCContract::runOnFunction(Function &F) { 3633 if (!EnableARCOpts) 3634 return false; 3635 3636 // If nothing in the Module uses ARC, don't do anything. 3637 if (!Run) 3638 return false; 3639 3640 Changed = false; 3641 AA = &getAnalysis<AliasAnalysis>(); 3642 DT = &getAnalysis<DominatorTree>(); 3643 3644 PA.setAA(&getAnalysis<AliasAnalysis>()); 3645 3646 // For ObjC library calls which return their argument, replace uses of the 3647 // argument with uses of the call return value, if it dominates the use. This 3648 // reduces register pressure. 3649 SmallPtrSet<Instruction *, 4> DependingInstructions; 3650 SmallPtrSet<const BasicBlock *, 4> Visited; 3651 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 3652 Instruction *Inst = &*I++; 3653 3654 // Only these library routines return their argument. In particular, 3655 // objc_retainBlock does not necessarily return its argument. 3656 InstructionClass Class = GetBasicInstructionClass(Inst); 3657 switch (Class) { 3658 case IC_Retain: 3659 case IC_FusedRetainAutorelease: 3660 case IC_FusedRetainAutoreleaseRV: 3661 break; 3662 case IC_Autorelease: 3663 case IC_AutoreleaseRV: 3664 if (ContractAutorelease(F, Inst, Class, DependingInstructions, Visited)) 3665 continue; 3666 break; 3667 case IC_RetainRV: { 3668 // If we're compiling for a target which needs a special inline-asm 3669 // marker to do the retainAutoreleasedReturnValue optimization, 3670 // insert it now. 3671 if (!RetainRVMarker) 3672 break; 3673 BasicBlock::iterator BBI = Inst; 3674 --BBI; 3675 while (isNoopInstruction(BBI)) --BBI; 3676 if (&*BBI == GetObjCArg(Inst)) { 3677 InlineAsm *IA = 3678 InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()), 3679 /*isVarArg=*/false), 3680 RetainRVMarker->getString(), 3681 /*Constraints=*/"", /*hasSideEffects=*/true); 3682 CallInst::Create(IA, "", Inst); 3683 } 3684 break; 3685 } 3686 case IC_InitWeak: { 3687 // objc_initWeak(p, null) => *p = null 3688 CallInst *CI = cast<CallInst>(Inst); 3689 if (isNullOrUndef(CI->getArgOperand(1))) { 3690 Value *Null = 3691 ConstantPointerNull::get(cast<PointerType>(CI->getType())); 3692 Changed = true; 3693 new StoreInst(Null, CI->getArgOperand(0), CI); 3694 CI->replaceAllUsesWith(Null); 3695 CI->eraseFromParent(); 3696 } 3697 continue; 3698 } 3699 case IC_Release: 3700 ContractRelease(Inst, I); 3701 continue; 3702 default: 3703 continue; 3704 } 3705 3706 // Don't use GetObjCArg because we don't want to look through bitcasts 3707 // and such; to do the replacement, the argument must have type i8*. 3708 const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0); 3709 for (;;) { 3710 // If we're compiling bugpointed code, don't get in trouble. 3711 if (!isa<Instruction>(Arg) && !isa<Argument>(Arg)) 3712 break; 3713 // Look through the uses of the pointer. 3714 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); 3715 UI != UE; ) { 3716 Use &U = UI.getUse(); 3717 unsigned OperandNo = UI.getOperandNo(); 3718 ++UI; // Increment UI now, because we may unlink its element. 3719 if (Instruction *UserInst = dyn_cast<Instruction>(U.getUser())) 3720 if (Inst != UserInst && DT->dominates(Inst, UserInst)) { 3721 Changed = true; 3722 Instruction *Replacement = Inst; 3723 Type *UseTy = U.get()->getType(); 3724 if (PHINode *PHI = dyn_cast<PHINode>(UserInst)) { 3725 // For PHI nodes, insert the bitcast in the predecessor block. 3726 unsigned ValNo = 3727 PHINode::getIncomingValueNumForOperand(OperandNo); 3728 BasicBlock *BB = 3729 PHI->getIncomingBlock(ValNo); 3730 if (Replacement->getType() != UseTy) 3731 Replacement = new BitCastInst(Replacement, UseTy, "", 3732 &BB->back()); 3733 for (unsigned i = 0, e = PHI->getNumIncomingValues(); 3734 i != e; ++i) 3735 if (PHI->getIncomingBlock(i) == BB) { 3736 // Keep the UI iterator valid. 3737 if (&PHI->getOperandUse( 3738 PHINode::getOperandNumForIncomingValue(i)) == 3739 &UI.getUse()) 3740 ++UI; 3741 PHI->setIncomingValue(i, Replacement); 3742 } 3743 } else { 3744 if (Replacement->getType() != UseTy) 3745 Replacement = new BitCastInst(Replacement, UseTy, "", UserInst); 3746 U.set(Replacement); 3747 } 3748 } 3749 } 3750 3751 // If Arg is a no-op casted pointer, strip one level of casts and 3752 // iterate. 3753 if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg)) 3754 Arg = BI->getOperand(0); 3755 else if (isa<GEPOperator>(Arg) && 3756 cast<GEPOperator>(Arg)->hasAllZeroIndices()) 3757 Arg = cast<GEPOperator>(Arg)->getPointerOperand(); 3758 else if (isa<GlobalAlias>(Arg) && 3759 !cast<GlobalAlias>(Arg)->mayBeOverridden()) 3760 Arg = cast<GlobalAlias>(Arg)->getAliasee(); 3761 else 3762 break; 3763 } 3764 } 3765 3766 return Changed; 3767 } 3768