1//===- ObjCARC.cpp - ObjC ARC Optimization --------------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file defines ObjC ARC optimizations. ARC stands for 11// Automatic Reference Counting and is a system for managing reference counts 12// for objects in Objective C. 13// 14// The optimizations performed include elimination of redundant, partially 15// redundant, and inconsequential reference count operations, elimination of 16// redundant weak pointer operations, pattern-matching and replacement of 17// low-level operations into higher-level operations, and numerous minor 18// simplifications. 19// 20// This file also defines a simple ARC-aware AliasAnalysis. 21// 22// WARNING: This file knows about certain library functions. It recognizes them 23// by name, and hardwires knowledge of their semantics. 24// 25// WARNING: This file knows about how certain Objective-C library functions are 26// used. Naive LLVM IR transformations which would otherwise be 27// behavior-preserving may break these assumptions. 28// 29//===----------------------------------------------------------------------===// 30 31#define DEBUG_TYPE "objc-arc" 32#include "llvm/Support/CommandLine.h" 33#include "llvm/ADT/DenseMap.h" 34using namespace llvm; 35 36// A handy option to enable/disable all optimizations in this file. 37static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true)); 38 39//===----------------------------------------------------------------------===// 40// Misc. Utilities 41//===----------------------------------------------------------------------===// 42 43namespace { 44 /// MapVector - An associative container with fast insertion-order 45 /// (deterministic) iteration over its elements. Plus the special 46 /// blot operation. 47 template<class KeyT, class ValueT> 48 class MapVector { 49 /// Map - Map keys to indices in Vector. 50 typedef DenseMap<KeyT, size_t> MapTy; 51 MapTy Map; 52 53 /// Vector - Keys and values. 54 typedef std::vector<std::pair<KeyT, ValueT> > VectorTy; 55 VectorTy Vector; 56 57 public: 58 typedef typename VectorTy::iterator iterator; 59 typedef typename VectorTy::const_iterator const_iterator; 60 iterator begin() { return Vector.begin(); } 61 iterator end() { return Vector.end(); } 62 const_iterator begin() const { return Vector.begin(); } 63 const_iterator end() const { return Vector.end(); } 64 65#ifdef XDEBUG 66 ~MapVector() { 67 assert(Vector.size() >= Map.size()); // May differ due to blotting. 68 for (typename MapTy::const_iterator I = Map.begin(), E = Map.end(); 69 I != E; ++I) { 70 assert(I->second < Vector.size()); 71 assert(Vector[I->second].first == I->first); 72 } 73 for (typename VectorTy::const_iterator I = Vector.begin(), 74 E = Vector.end(); I != E; ++I) 75 assert(!I->first || 76 (Map.count(I->first) && 77 Map[I->first] == size_t(I - Vector.begin()))); 78 } 79#endif 80 81 ValueT &operator[](const KeyT &Arg) { 82 std::pair<typename MapTy::iterator, bool> Pair = 83 Map.insert(std::make_pair(Arg, size_t(0))); 84 if (Pair.second) { 85 size_t Num = Vector.size(); 86 Pair.first->second = Num; 87 Vector.push_back(std::make_pair(Arg, ValueT())); 88 return Vector[Num].second; 89 } 90 return Vector[Pair.first->second].second; 91 } 92 93 std::pair<iterator, bool> 94 insert(const std::pair<KeyT, ValueT> &InsertPair) { 95 std::pair<typename MapTy::iterator, bool> Pair = 96 Map.insert(std::make_pair(InsertPair.first, size_t(0))); 97 if (Pair.second) { 98 size_t Num = Vector.size(); 99 Pair.first->second = Num; 100 Vector.push_back(InsertPair); 101 return std::make_pair(Vector.begin() + Num, true); 102 } 103 return std::make_pair(Vector.begin() + Pair.first->second, false); 104 } 105 106 const_iterator find(const KeyT &Key) const { 107 typename MapTy::const_iterator It = Map.find(Key); 108 if (It == Map.end()) return Vector.end(); 109 return Vector.begin() + It->second; 110 } 111 112 /// blot - This is similar to erase, but instead of removing the element 113 /// from the vector, it just zeros out the key in the vector. This leaves 114 /// iterators intact, but clients must be prepared for zeroed-out keys when 115 /// iterating. 116 void blot(const KeyT &Key) { 117 typename MapTy::iterator It = Map.find(Key); 118 if (It == Map.end()) return; 119 Vector[It->second].first = KeyT(); 120 Map.erase(It); 121 } 122 123 void clear() { 124 Map.clear(); 125 Vector.clear(); 126 } 127 }; 128} 129 130//===----------------------------------------------------------------------===// 131// ARC Utilities. 132//===----------------------------------------------------------------------===// 133 134#include "llvm/Intrinsics.h" 135#include "llvm/Module.h" 136#include "llvm/Analysis/ValueTracking.h" 137#include "llvm/Transforms/Utils/Local.h" 138#include "llvm/Support/CallSite.h" 139#include "llvm/ADT/StringSwitch.h" 140 141namespace { 142 /// InstructionClass - A simple classification for instructions. 143 enum InstructionClass { 144 IC_Retain, ///< objc_retain 145 IC_RetainRV, ///< objc_retainAutoreleasedReturnValue 146 IC_RetainBlock, ///< objc_retainBlock 147 IC_Release, ///< objc_release 148 IC_Autorelease, ///< objc_autorelease 149 IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue 150 IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush 151 IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop 152 IC_NoopCast, ///< objc_retainedObject, etc. 153 IC_FusedRetainAutorelease, ///< objc_retainAutorelease 154 IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue 155 IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive) 156 IC_StoreWeak, ///< objc_storeWeak (primitive) 157 IC_InitWeak, ///< objc_initWeak (derived) 158 IC_LoadWeak, ///< objc_loadWeak (derived) 159 IC_MoveWeak, ///< objc_moveWeak (derived) 160 IC_CopyWeak, ///< objc_copyWeak (derived) 161 IC_DestroyWeak, ///< objc_destroyWeak (derived) 162 IC_StoreStrong, ///< objc_storeStrong (derived) 163 IC_CallOrUser, ///< could call objc_release and/or "use" pointers 164 IC_Call, ///< could call objc_release 165 IC_User, ///< could "use" a pointer 166 IC_None ///< anything else 167 }; 168} 169 170/// IsPotentialUse - Test whether the given value is possible a 171/// reference-counted pointer. 172static bool IsPotentialUse(const Value *Op) { 173 // Pointers to static or stack storage are not reference-counted pointers. 174 if (isa<Constant>(Op) || isa<AllocaInst>(Op)) 175 return false; 176 // Special arguments are not reference-counted. 177 if (const Argument *Arg = dyn_cast<Argument>(Op)) 178 if (Arg->hasByValAttr() || 179 Arg->hasNestAttr() || 180 Arg->hasStructRetAttr()) 181 return false; 182 // Only consider values with pointer types. 183 // It seemes intuitive to exclude function pointer types as well, since 184 // functions are never reference-counted, however clang occasionally 185 // bitcasts reference-counted pointers to function-pointer type 186 // temporarily. 187 PointerType *Ty = dyn_cast<PointerType>(Op->getType()); 188 if (!Ty) 189 return false; 190 // Conservatively assume anything else is a potential use. 191 return true; 192} 193 194/// GetCallSiteClass - Helper for GetInstructionClass. Determines what kind 195/// of construct CS is. 196static InstructionClass GetCallSiteClass(ImmutableCallSite CS) { 197 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 198 I != E; ++I) 199 if (IsPotentialUse(*I)) 200 return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser; 201 202 return CS.onlyReadsMemory() ? IC_None : IC_Call; 203} 204 205/// GetFunctionClass - Determine if F is one of the special known Functions. 206/// If it isn't, return IC_CallOrUser. 207static InstructionClass GetFunctionClass(const Function *F) { 208 Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end(); 209 210 // No arguments. 211 if (AI == AE) 212 return StringSwitch<InstructionClass>(F->getName()) 213 .Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush) 214 .Default(IC_CallOrUser); 215 216 // One argument. 217 const Argument *A0 = AI++; 218 if (AI == AE) 219 // Argument is a pointer. 220 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) { 221 Type *ETy = PTy->getElementType(); 222 // Argument is i8*. 223 if (ETy->isIntegerTy(8)) 224 return StringSwitch<InstructionClass>(F->getName()) 225 .Case("objc_retain", IC_Retain) 226 .Case("objc_retainAutoreleasedReturnValue", IC_RetainRV) 227 .Case("objc_retainBlock", IC_RetainBlock) 228 .Case("objc_release", IC_Release) 229 .Case("objc_autorelease", IC_Autorelease) 230 .Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV) 231 .Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop) 232 .Case("objc_retainedObject", IC_NoopCast) 233 .Case("objc_unretainedObject", IC_NoopCast) 234 .Case("objc_unretainedPointer", IC_NoopCast) 235 .Case("objc_retain_autorelease", IC_FusedRetainAutorelease) 236 .Case("objc_retainAutorelease", IC_FusedRetainAutorelease) 237 .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV) 238 .Default(IC_CallOrUser); 239 240 // Argument is i8** 241 if (PointerType *Pte = dyn_cast<PointerType>(ETy)) 242 if (Pte->getElementType()->isIntegerTy(8)) 243 return StringSwitch<InstructionClass>(F->getName()) 244 .Case("objc_loadWeakRetained", IC_LoadWeakRetained) 245 .Case("objc_loadWeak", IC_LoadWeak) 246 .Case("objc_destroyWeak", IC_DestroyWeak) 247 .Default(IC_CallOrUser); 248 } 249 250 // Two arguments, first is i8**. 251 const Argument *A1 = AI++; 252 if (AI == AE) 253 if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) 254 if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType())) 255 if (Pte->getElementType()->isIntegerTy(8)) 256 if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) { 257 Type *ETy1 = PTy1->getElementType(); 258 // Second argument is i8* 259 if (ETy1->isIntegerTy(8)) 260 return StringSwitch<InstructionClass>(F->getName()) 261 .Case("objc_storeWeak", IC_StoreWeak) 262 .Case("objc_initWeak", IC_InitWeak) 263 .Case("objc_storeStrong", IC_StoreStrong) 264 .Default(IC_CallOrUser); 265 // Second argument is i8**. 266 if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1)) 267 if (Pte1->getElementType()->isIntegerTy(8)) 268 return StringSwitch<InstructionClass>(F->getName()) 269 .Case("objc_moveWeak", IC_MoveWeak) 270 .Case("objc_copyWeak", IC_CopyWeak) 271 .Default(IC_CallOrUser); 272 } 273 274 // Anything else. 275 return IC_CallOrUser; 276} 277 278/// GetInstructionClass - Determine what kind of construct V is. 279static InstructionClass GetInstructionClass(const Value *V) { 280 if (const Instruction *I = dyn_cast<Instruction>(V)) { 281 // Any instruction other than bitcast and gep with a pointer operand have a 282 // use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer 283 // to a subsequent use, rather than using it themselves, in this sense. 284 // As a short cut, several other opcodes are known to have no pointer 285 // operands of interest. And ret is never followed by a release, so it's 286 // not interesting to examine. 287 switch (I->getOpcode()) { 288 case Instruction::Call: { 289 const CallInst *CI = cast<CallInst>(I); 290 // Check for calls to special functions. 291 if (const Function *F = CI->getCalledFunction()) { 292 InstructionClass Class = GetFunctionClass(F); 293 if (Class != IC_CallOrUser) 294 return Class; 295 296 // None of the intrinsic functions do objc_release. For intrinsics, the 297 // only question is whether or not they may be users. 298 switch (F->getIntrinsicID()) { 299 case Intrinsic::returnaddress: case Intrinsic::frameaddress: 300 case Intrinsic::stacksave: case Intrinsic::stackrestore: 301 case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend: 302 case Intrinsic::objectsize: case Intrinsic::prefetch: 303 case Intrinsic::stackprotector: 304 case Intrinsic::eh_return_i32: case Intrinsic::eh_return_i64: 305 case Intrinsic::eh_typeid_for: case Intrinsic::eh_dwarf_cfa: 306 case Intrinsic::eh_sjlj_lsda: case Intrinsic::eh_sjlj_functioncontext: 307 case Intrinsic::init_trampoline: case Intrinsic::adjust_trampoline: 308 case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: 309 case Intrinsic::invariant_start: case Intrinsic::invariant_end: 310 // Don't let dbg info affect our results. 311 case Intrinsic::dbg_declare: case Intrinsic::dbg_value: 312 // Short cut: Some intrinsics obviously don't use ObjC pointers. 313 return IC_None; 314 default: 315 break; 316 } 317 } 318 return GetCallSiteClass(CI); 319 } 320 case Instruction::Invoke: 321 return GetCallSiteClass(cast<InvokeInst>(I)); 322 case Instruction::BitCast: 323 case Instruction::GetElementPtr: 324 case Instruction::Select: case Instruction::PHI: 325 case Instruction::Ret: case Instruction::Br: 326 case Instruction::Switch: case Instruction::IndirectBr: 327 case Instruction::Alloca: case Instruction::VAArg: 328 case Instruction::Add: case Instruction::FAdd: 329 case Instruction::Sub: case Instruction::FSub: 330 case Instruction::Mul: case Instruction::FMul: 331 case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv: 332 case Instruction::SRem: case Instruction::URem: case Instruction::FRem: 333 case Instruction::Shl: case Instruction::LShr: case Instruction::AShr: 334 case Instruction::And: case Instruction::Or: case Instruction::Xor: 335 case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc: 336 case Instruction::IntToPtr: case Instruction::FCmp: 337 case Instruction::FPTrunc: case Instruction::FPExt: 338 case Instruction::FPToUI: case Instruction::FPToSI: 339 case Instruction::UIToFP: case Instruction::SIToFP: 340 case Instruction::InsertElement: case Instruction::ExtractElement: 341 case Instruction::ShuffleVector: 342 case Instruction::ExtractValue: 343 break; 344 case Instruction::ICmp: 345 // Comparing a pointer with null, or any other constant, isn't an 346 // interesting use, because we don't care what the pointer points to, or 347 // about the values of any other dynamic reference-counted pointers. 348 if (IsPotentialUse(I->getOperand(1))) 349 return IC_User; 350 break; 351 default: 352 // For anything else, check all the operands. 353 // Note that this includes both operands of a Store: while the first 354 // operand isn't actually being dereferenced, it is being stored to 355 // memory where we can no longer track who might read it and dereference 356 // it, so we have to consider it potentially used. 357 for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end(); 358 OI != OE; ++OI) 359 if (IsPotentialUse(*OI)) 360 return IC_User; 361 } 362 } 363 364 // Otherwise, it's totally inert for ARC purposes. 365 return IC_None; 366} 367 368/// GetBasicInstructionClass - Determine what kind of construct V is. This is 369/// similar to GetInstructionClass except that it only detects objc runtine 370/// calls. This allows it to be faster. 371static InstructionClass GetBasicInstructionClass(const Value *V) { 372 if (const CallInst *CI = dyn_cast<CallInst>(V)) { 373 if (const Function *F = CI->getCalledFunction()) 374 return GetFunctionClass(F); 375 // Otherwise, be conservative. 376 return IC_CallOrUser; 377 } 378 379 // Otherwise, be conservative. 380 return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User; 381} 382 383/// IsRetain - Test if the given class is objc_retain or 384/// equivalent. 385static bool IsRetain(InstructionClass Class) { 386 return Class == IC_Retain || 387 Class == IC_RetainRV; 388} 389 390/// IsAutorelease - Test if the given class is objc_autorelease or 391/// equivalent. 392static bool IsAutorelease(InstructionClass Class) { 393 return Class == IC_Autorelease || 394 Class == IC_AutoreleaseRV; 395} 396 397/// IsForwarding - Test if the given class represents instructions which return 398/// their argument verbatim. 399static bool IsForwarding(InstructionClass Class) { 400 // objc_retainBlock technically doesn't always return its argument 401 // verbatim, but it doesn't matter for our purposes here. 402 return Class == IC_Retain || 403 Class == IC_RetainRV || 404 Class == IC_Autorelease || 405 Class == IC_AutoreleaseRV || 406 Class == IC_RetainBlock || 407 Class == IC_NoopCast; 408} 409 410/// IsNoopOnNull - Test if the given class represents instructions which do 411/// nothing if passed a null pointer. 412static bool IsNoopOnNull(InstructionClass Class) { 413 return Class == IC_Retain || 414 Class == IC_RetainRV || 415 Class == IC_Release || 416 Class == IC_Autorelease || 417 Class == IC_AutoreleaseRV || 418 Class == IC_RetainBlock; 419} 420 421/// IsAlwaysTail - Test if the given class represents instructions which are 422/// always safe to mark with the "tail" keyword. 423static bool IsAlwaysTail(InstructionClass Class) { 424 // IC_RetainBlock may be given a stack argument. 425 return Class == IC_Retain || 426 Class == IC_RetainRV || 427 Class == IC_Autorelease || 428 Class == IC_AutoreleaseRV; 429} 430 431/// IsNoThrow - Test if the given class represents instructions which are always 432/// safe to mark with the nounwind attribute.. 433static bool IsNoThrow(InstructionClass Class) { 434 // objc_retainBlock is not nounwind because it calls user copy constructors 435 // which could theoretically throw. 436 return Class == IC_Retain || 437 Class == IC_RetainRV || 438 Class == IC_Release || 439 Class == IC_Autorelease || 440 Class == IC_AutoreleaseRV || 441 Class == IC_AutoreleasepoolPush || 442 Class == IC_AutoreleasepoolPop; 443} 444 445/// EraseInstruction - Erase the given instruction. Many ObjC calls return their 446/// argument verbatim, so if it's such a call and the return value has users, 447/// replace them with the argument value. 448static void EraseInstruction(Instruction *CI) { 449 Value *OldArg = cast<CallInst>(CI)->getArgOperand(0); 450 451 bool Unused = CI->use_empty(); 452 453 if (!Unused) { 454 // Replace the return value with the argument. 455 assert(IsForwarding(GetBasicInstructionClass(CI)) && 456 "Can't delete non-forwarding instruction with users!"); 457 CI->replaceAllUsesWith(OldArg); 458 } 459 460 CI->eraseFromParent(); 461 462 if (Unused) 463 RecursivelyDeleteTriviallyDeadInstructions(OldArg); 464} 465 466/// GetUnderlyingObjCPtr - This is a wrapper around getUnderlyingObject which 467/// also knows how to look through objc_retain and objc_autorelease calls, which 468/// we know to return their argument verbatim. 469static const Value *GetUnderlyingObjCPtr(const Value *V) { 470 for (;;) { 471 V = GetUnderlyingObject(V); 472 if (!IsForwarding(GetBasicInstructionClass(V))) 473 break; 474 V = cast<CallInst>(V)->getArgOperand(0); 475 } 476 477 return V; 478} 479 480/// StripPointerCastsAndObjCCalls - This is a wrapper around 481/// Value::stripPointerCasts which also knows how to look through objc_retain 482/// and objc_autorelease calls, which we know to return their argument verbatim. 483static const Value *StripPointerCastsAndObjCCalls(const Value *V) { 484 for (;;) { 485 V = V->stripPointerCasts(); 486 if (!IsForwarding(GetBasicInstructionClass(V))) 487 break; 488 V = cast<CallInst>(V)->getArgOperand(0); 489 } 490 return V; 491} 492 493/// StripPointerCastsAndObjCCalls - This is a wrapper around 494/// Value::stripPointerCasts which also knows how to look through objc_retain 495/// and objc_autorelease calls, which we know to return their argument verbatim. 496static Value *StripPointerCastsAndObjCCalls(Value *V) { 497 for (;;) { 498 V = V->stripPointerCasts(); 499 if (!IsForwarding(GetBasicInstructionClass(V))) 500 break; 501 V = cast<CallInst>(V)->getArgOperand(0); 502 } 503 return V; 504} 505 506/// GetObjCArg - Assuming the given instruction is one of the special calls such 507/// as objc_retain or objc_release, return the argument value, stripped of no-op 508/// casts and forwarding calls. 509static Value *GetObjCArg(Value *Inst) { 510 return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0)); 511} 512 513/// IsObjCIdentifiedObject - This is similar to AliasAnalysis' 514/// isObjCIdentifiedObject, except that it uses special knowledge of 515/// ObjC conventions... 516static bool IsObjCIdentifiedObject(const Value *V) { 517 // Assume that call results and arguments have their own "provenance". 518 // Constants (including GlobalVariables) and Allocas are never 519 // reference-counted. 520 if (isa<CallInst>(V) || isa<InvokeInst>(V) || 521 isa<Argument>(V) || isa<Constant>(V) || 522 isa<AllocaInst>(V)) 523 return true; 524 525 if (const LoadInst *LI = dyn_cast<LoadInst>(V)) { 526 const Value *Pointer = 527 StripPointerCastsAndObjCCalls(LI->getPointerOperand()); 528 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) { 529 // A constant pointer can't be pointing to an object on the heap. It may 530 // be reference-counted, but it won't be deleted. 531 if (GV->isConstant()) 532 return true; 533 StringRef Name = GV->getName(); 534 // These special variables are known to hold values which are not 535 // reference-counted pointers. 536 if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") || 537 Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") || 538 Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") || 539 Name.startswith("\01L_OBJC_METH_VAR_NAME_") || 540 Name.startswith("\01l_objc_msgSend_fixup_")) 541 return true; 542 } 543 } 544 545 return false; 546} 547 548/// FindSingleUseIdentifiedObject - This is similar to 549/// StripPointerCastsAndObjCCalls but it stops as soon as it finds a value 550/// with multiple uses. 551static const Value *FindSingleUseIdentifiedObject(const Value *Arg) { 552 if (Arg->hasOneUse()) { 553 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg)) 554 return FindSingleUseIdentifiedObject(BC->getOperand(0)); 555 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg)) 556 if (GEP->hasAllZeroIndices()) 557 return FindSingleUseIdentifiedObject(GEP->getPointerOperand()); 558 if (IsForwarding(GetBasicInstructionClass(Arg))) 559 return FindSingleUseIdentifiedObject( 560 cast<CallInst>(Arg)->getArgOperand(0)); 561 if (!IsObjCIdentifiedObject(Arg)) 562 return 0; 563 return Arg; 564 } 565 566 // If we found an identifiable object but it has multiple uses, but they are 567 // trivial uses, we can still consider this to be a single-use value. 568 if (IsObjCIdentifiedObject(Arg)) { 569 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); 570 UI != UE; ++UI) { 571 const User *U = *UI; 572 if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg) 573 return 0; 574 } 575 576 return Arg; 577 } 578 579 return 0; 580} 581 582/// ModuleHasARC - Test if the given module looks interesting to run ARC 583/// optimization on. 584static bool ModuleHasARC(const Module &M) { 585 return 586 M.getNamedValue("objc_retain") || 587 M.getNamedValue("objc_release") || 588 M.getNamedValue("objc_autorelease") || 589 M.getNamedValue("objc_retainAutoreleasedReturnValue") || 590 M.getNamedValue("objc_retainBlock") || 591 M.getNamedValue("objc_autoreleaseReturnValue") || 592 M.getNamedValue("objc_autoreleasePoolPush") || 593 M.getNamedValue("objc_loadWeakRetained") || 594 M.getNamedValue("objc_loadWeak") || 595 M.getNamedValue("objc_destroyWeak") || 596 M.getNamedValue("objc_storeWeak") || 597 M.getNamedValue("objc_initWeak") || 598 M.getNamedValue("objc_moveWeak") || 599 M.getNamedValue("objc_copyWeak") || 600 M.getNamedValue("objc_retainedObject") || 601 M.getNamedValue("objc_unretainedObject") || 602 M.getNamedValue("objc_unretainedPointer"); 603} 604 605/// DoesObjCBlockEscape - Test whether the given pointer, which is an 606/// Objective C block pointer, does not "escape". This differs from regular 607/// escape analysis in that a use as an argument to a call is not considered 608/// an escape. 609static bool DoesObjCBlockEscape(const Value *BlockPtr) { 610 // Walk the def-use chains. 611 SmallVector<const Value *, 4> Worklist; 612 Worklist.push_back(BlockPtr); 613 do { 614 const Value *V = Worklist.pop_back_val(); 615 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end(); 616 UI != UE; ++UI) { 617 const User *UUser = *UI; 618 // Special - Use by a call (callee or argument) is not considered 619 // to be an escape. 620 switch (GetBasicInstructionClass(UUser)) { 621 case IC_StoreWeak: 622 case IC_InitWeak: 623 case IC_StoreStrong: 624 case IC_Autorelease: 625 case IC_AutoreleaseRV: 626 // These special functions make copies of their pointer arguments. 627 return true; 628 case IC_User: 629 case IC_None: 630 // Use by an instruction which copies the value is an escape if the 631 // result is an escape. 632 if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) || 633 isa<PHINode>(UUser) || isa<SelectInst>(UUser)) { 634 Worklist.push_back(UUser); 635 continue; 636 } 637 // Use by a load is not an escape. 638 if (isa<LoadInst>(UUser)) 639 continue; 640 // Use by a store is not an escape if the use is the address. 641 if (const StoreInst *SI = dyn_cast<StoreInst>(UUser)) 642 if (V != SI->getValueOperand()) 643 continue; 644 break; 645 default: 646 // Regular calls and other stuff are not considered escapes. 647 continue; 648 } 649 // Otherwise, conservatively assume an escape. 650 return true; 651 } 652 } while (!Worklist.empty()); 653 654 // No escapes found. 655 return false; 656} 657 658//===----------------------------------------------------------------------===// 659// ARC AliasAnalysis. 660//===----------------------------------------------------------------------===// 661 662#include "llvm/Pass.h" 663#include "llvm/Analysis/AliasAnalysis.h" 664#include "llvm/Analysis/Passes.h" 665 666namespace { 667 /// ObjCARCAliasAnalysis - This is a simple alias analysis 668 /// implementation that uses knowledge of ARC constructs to answer queries. 669 /// 670 /// TODO: This class could be generalized to know about other ObjC-specific 671 /// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing 672 /// even though their offsets are dynamic. 673 class ObjCARCAliasAnalysis : public ImmutablePass, 674 public AliasAnalysis { 675 public: 676 static char ID; // Class identification, replacement for typeinfo 677 ObjCARCAliasAnalysis() : ImmutablePass(ID) { 678 initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry()); 679 } 680 681 private: 682 virtual void initializePass() { 683 InitializeAliasAnalysis(this); 684 } 685 686 /// getAdjustedAnalysisPointer - This method is used when a pass implements 687 /// an analysis interface through multiple inheritance. If needed, it 688 /// should override this to adjust the this pointer as needed for the 689 /// specified pass info. 690 virtual void *getAdjustedAnalysisPointer(const void *PI) { 691 if (PI == &AliasAnalysis::ID) 692 return static_cast<AliasAnalysis *>(this); 693 return this; 694 } 695 696 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 697 virtual AliasResult alias(const Location &LocA, const Location &LocB); 698 virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); 699 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 700 virtual ModRefBehavior getModRefBehavior(const Function *F); 701 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 702 const Location &Loc); 703 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 704 ImmutableCallSite CS2); 705 }; 706} // End of anonymous namespace 707 708// Register this pass... 709char ObjCARCAliasAnalysis::ID = 0; 710INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa", 711 "ObjC-ARC-Based Alias Analysis", false, true, false) 712 713ImmutablePass *llvm::createObjCARCAliasAnalysisPass() { 714 return new ObjCARCAliasAnalysis(); 715} 716 717void 718ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 719 AU.setPreservesAll(); 720 AliasAnalysis::getAnalysisUsage(AU); 721} 722 723AliasAnalysis::AliasResult 724ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) { 725 if (!EnableARCOpts) 726 return AliasAnalysis::alias(LocA, LocB); 727 728 // First, strip off no-ops, including ObjC-specific no-ops, and try making a 729 // precise alias query. 730 const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr); 731 const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr); 732 AliasResult Result = 733 AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag), 734 Location(SB, LocB.Size, LocB.TBAATag)); 735 if (Result != MayAlias) 736 return Result; 737 738 // If that failed, climb to the underlying object, including climbing through 739 // ObjC-specific no-ops, and try making an imprecise alias query. 740 const Value *UA = GetUnderlyingObjCPtr(SA); 741 const Value *UB = GetUnderlyingObjCPtr(SB); 742 if (UA != SA || UB != SB) { 743 Result = AliasAnalysis::alias(Location(UA), Location(UB)); 744 // We can't use MustAlias or PartialAlias results here because 745 // GetUnderlyingObjCPtr may return an offsetted pointer value. 746 if (Result == NoAlias) 747 return NoAlias; 748 } 749 750 // If that failed, fail. We don't need to chain here, since that's covered 751 // by the earlier precise query. 752 return MayAlias; 753} 754 755bool 756ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc, 757 bool OrLocal) { 758 if (!EnableARCOpts) 759 return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); 760 761 // First, strip off no-ops, including ObjC-specific no-ops, and try making 762 // a precise alias query. 763 const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr); 764 if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag), 765 OrLocal)) 766 return true; 767 768 // If that failed, climb to the underlying object, including climbing through 769 // ObjC-specific no-ops, and try making an imprecise alias query. 770 const Value *U = GetUnderlyingObjCPtr(S); 771 if (U != S) 772 return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal); 773 774 // If that failed, fail. We don't need to chain here, since that's covered 775 // by the earlier precise query. 776 return false; 777} 778 779AliasAnalysis::ModRefBehavior 780ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { 781 // We have nothing to do. Just chain to the next AliasAnalysis. 782 return AliasAnalysis::getModRefBehavior(CS); 783} 784 785AliasAnalysis::ModRefBehavior 786ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) { 787 if (!EnableARCOpts) 788 return AliasAnalysis::getModRefBehavior(F); 789 790 switch (GetFunctionClass(F)) { 791 case IC_NoopCast: 792 return DoesNotAccessMemory; 793 default: 794 break; 795 } 796 797 return AliasAnalysis::getModRefBehavior(F); 798} 799 800AliasAnalysis::ModRefResult 801ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { 802 if (!EnableARCOpts) 803 return AliasAnalysis::getModRefInfo(CS, Loc); 804 805 switch (GetBasicInstructionClass(CS.getInstruction())) { 806 case IC_Retain: 807 case IC_RetainRV: 808 case IC_Autorelease: 809 case IC_AutoreleaseRV: 810 case IC_NoopCast: 811 case IC_AutoreleasepoolPush: 812 case IC_FusedRetainAutorelease: 813 case IC_FusedRetainAutoreleaseRV: 814 // These functions don't access any memory visible to the compiler. 815 // Note that this doesn't include objc_retainBlock, because it updates 816 // pointers when it copies block data. 817 return NoModRef; 818 default: 819 break; 820 } 821 822 return AliasAnalysis::getModRefInfo(CS, Loc); 823} 824 825AliasAnalysis::ModRefResult 826ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1, 827 ImmutableCallSite CS2) { 828 // TODO: Theoretically we could check for dependencies between objc_* calls 829 // and OnlyAccessesArgumentPointees calls or other well-behaved calls. 830 return AliasAnalysis::getModRefInfo(CS1, CS2); 831} 832 833//===----------------------------------------------------------------------===// 834// ARC expansion. 835//===----------------------------------------------------------------------===// 836 837#include "llvm/Support/InstIterator.h" 838#include "llvm/Transforms/Scalar.h" 839 840namespace { 841 /// ObjCARCExpand - Early ARC transformations. 842 class ObjCARCExpand : public FunctionPass { 843 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 844 virtual bool doInitialization(Module &M); 845 virtual bool runOnFunction(Function &F); 846 847 /// Run - A flag indicating whether this optimization pass should run. 848 bool Run; 849 850 public: 851 static char ID; 852 ObjCARCExpand() : FunctionPass(ID) { 853 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 854 } 855 }; 856} 857 858char ObjCARCExpand::ID = 0; 859INITIALIZE_PASS(ObjCARCExpand, 860 "objc-arc-expand", "ObjC ARC expansion", false, false) 861 862Pass *llvm::createObjCARCExpandPass() { 863 return new ObjCARCExpand(); 864} 865 866void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 867 AU.setPreservesCFG(); 868} 869 870bool ObjCARCExpand::doInitialization(Module &M) { 871 Run = ModuleHasARC(M); 872 return false; 873} 874 875bool ObjCARCExpand::runOnFunction(Function &F) { 876 if (!EnableARCOpts) 877 return false; 878 879 // If nothing in the Module uses ARC, don't do anything. 880 if (!Run) 881 return false; 882 883 bool Changed = false; 884 885 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 886 Instruction *Inst = &*I; 887 888 switch (GetBasicInstructionClass(Inst)) { 889 case IC_Retain: 890 case IC_RetainRV: 891 case IC_Autorelease: 892 case IC_AutoreleaseRV: 893 case IC_FusedRetainAutorelease: 894 case IC_FusedRetainAutoreleaseRV: 895 // These calls return their argument verbatim, as a low-level 896 // optimization. However, this makes high-level optimizations 897 // harder. Undo any uses of this optimization that the front-end 898 // emitted here. We'll redo them in the contract pass. 899 Changed = true; 900 Inst->replaceAllUsesWith(cast<CallInst>(Inst)->getArgOperand(0)); 901 break; 902 default: 903 break; 904 } 905 } 906 907 return Changed; 908} 909 910//===----------------------------------------------------------------------===// 911// ARC autorelease pool elimination. 912//===----------------------------------------------------------------------===// 913 914#include "llvm/Constants.h" 915#include "llvm/ADT/STLExtras.h" 916 917namespace { 918 /// ObjCARCAPElim - Autorelease pool elimination. 919 class ObjCARCAPElim : public ModulePass { 920 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 921 virtual bool runOnModule(Module &M); 922 923 static bool MayAutorelease(ImmutableCallSite CS, unsigned Depth = 0); 924 static bool OptimizeBB(BasicBlock *BB); 925 926 public: 927 static char ID; 928 ObjCARCAPElim() : ModulePass(ID) { 929 initializeObjCARCAPElimPass(*PassRegistry::getPassRegistry()); 930 } 931 }; 932} 933 934char ObjCARCAPElim::ID = 0; 935INITIALIZE_PASS(ObjCARCAPElim, 936 "objc-arc-apelim", 937 "ObjC ARC autorelease pool elimination", 938 false, false) 939 940Pass *llvm::createObjCARCAPElimPass() { 941 return new ObjCARCAPElim(); 942} 943 944void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const { 945 AU.setPreservesCFG(); 946} 947 948/// MayAutorelease - Interprocedurally determine if calls made by the 949/// given call site can possibly produce autoreleases. 950bool ObjCARCAPElim::MayAutorelease(ImmutableCallSite CS, unsigned Depth) { 951 if (const Function *Callee = CS.getCalledFunction()) { 952 if (Callee->isDeclaration() || Callee->mayBeOverridden()) 953 return true; 954 for (Function::const_iterator I = Callee->begin(), E = Callee->end(); 955 I != E; ++I) { 956 const BasicBlock *BB = I; 957 for (BasicBlock::const_iterator J = BB->begin(), F = BB->end(); 958 J != F; ++J) 959 if (ImmutableCallSite JCS = ImmutableCallSite(J)) 960 // This recursion depth limit is arbitrary. It's just great 961 // enough to cover known interesting testcases. 962 if (Depth < 3 && 963 !JCS.onlyReadsMemory() && 964 MayAutorelease(JCS, Depth + 1)) 965 return true; 966 } 967 return false; 968 } 969 970 return true; 971} 972 973bool ObjCARCAPElim::OptimizeBB(BasicBlock *BB) { 974 bool Changed = false; 975 976 Instruction *Push = 0; 977 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 978 Instruction *Inst = I++; 979 switch (GetBasicInstructionClass(Inst)) { 980 case IC_AutoreleasepoolPush: 981 Push = Inst; 982 break; 983 case IC_AutoreleasepoolPop: 984 // If this pop matches a push and nothing in between can autorelease, 985 // zap the pair. 986 if (Push && cast<CallInst>(Inst)->getArgOperand(0) == Push) { 987 Changed = true; 988 Inst->eraseFromParent(); 989 Push->eraseFromParent(); 990 } 991 Push = 0; 992 break; 993 case IC_CallOrUser: 994 if (MayAutorelease(ImmutableCallSite(Inst))) 995 Push = 0; 996 break; 997 default: 998 break; 999 } 1000 } 1001 1002 return Changed; 1003} 1004 1005bool ObjCARCAPElim::runOnModule(Module &M) { 1006 if (!EnableARCOpts) 1007 return false; 1008 1009 // If nothing in the Module uses ARC, don't do anything. 1010 if (!ModuleHasARC(M)) 1011 return false; 1012 1013 // Find the llvm.global_ctors variable, as the first step in 1014 // identifying the global constructors. In theory, unnecessary autorelease 1015 // pools could occur anywhere, but in practice it's pretty rare. Global 1016 // ctors are a place where autorelease pools get inserted automatically, 1017 // so it's pretty common for them to be unnecessary, and it's pretty 1018 // profitable to eliminate them. 1019 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors"); 1020 if (!GV) 1021 return false; 1022 1023 assert(GV->hasDefinitiveInitializer() && 1024 "llvm.global_ctors is uncooperative!"); 1025 1026 bool Changed = false; 1027 1028 // Dig the constructor functions out of GV's initializer. 1029 ConstantArray *Init = cast<ConstantArray>(GV->getInitializer()); 1030 for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end(); 1031 OI != OE; ++OI) { 1032 Value *Op = *OI; 1033 // llvm.global_ctors is an array of pairs where the second members 1034 // are constructor functions. 1035 Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1)); 1036 // If the user used a constructor function with the wrong signature and 1037 // it got bitcasted or whatever, look the other way. 1038 if (!F) 1039 continue; 1040 // Only look at function definitions. 1041 if (F->isDeclaration()) 1042 continue; 1043 // Only look at functions with one basic block. 1044 if (llvm::next(F->begin()) != F->end()) 1045 continue; 1046 // Ok, a single-block constructor function definition. Try to optimize it. 1047 Changed |= OptimizeBB(F->begin()); 1048 } 1049 1050 return Changed; 1051} 1052 1053//===----------------------------------------------------------------------===// 1054// ARC optimization. 1055//===----------------------------------------------------------------------===// 1056 1057// TODO: On code like this: 1058// 1059// objc_retain(%x) 1060// stuff_that_cannot_release() 1061// objc_autorelease(%x) 1062// stuff_that_cannot_release() 1063// objc_retain(%x) 1064// stuff_that_cannot_release() 1065// objc_autorelease(%x) 1066// 1067// The second retain and autorelease can be deleted. 1068 1069// TODO: It should be possible to delete 1070// objc_autoreleasePoolPush and objc_autoreleasePoolPop 1071// pairs if nothing is actually autoreleased between them. Also, autorelease 1072// calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code 1073// after inlining) can be turned into plain release calls. 1074 1075// TODO: Critical-edge splitting. If the optimial insertion point is 1076// a critical edge, the current algorithm has to fail, because it doesn't 1077// know how to split edges. It should be possible to make the optimizer 1078// think in terms of edges, rather than blocks, and then split critical 1079// edges on demand. 1080 1081// TODO: OptimizeSequences could generalized to be Interprocedural. 1082 1083// TODO: Recognize that a bunch of other objc runtime calls have 1084// non-escaping arguments and non-releasing arguments, and may be 1085// non-autoreleasing. 1086 1087// TODO: Sink autorelease calls as far as possible. Unfortunately we 1088// usually can't sink them past other calls, which would be the main 1089// case where it would be useful. 1090 1091// TODO: The pointer returned from objc_loadWeakRetained is retained. 1092 1093// TODO: Delete release+retain pairs (rare). 1094 1095#include "llvm/LLVMContext.h" 1096#include "llvm/Support/CFG.h" 1097#include "llvm/ADT/Statistic.h" 1098#include "llvm/ADT/SmallPtrSet.h" 1099 1100STATISTIC(NumNoops, "Number of no-op objc calls eliminated"); 1101STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated"); 1102STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases"); 1103STATISTIC(NumRets, "Number of return value forwarding " 1104 "retain+autoreleaes eliminated"); 1105STATISTIC(NumRRs, "Number of retain+release paths eliminated"); 1106STATISTIC(NumPeeps, "Number of calls peephole-optimized"); 1107 1108namespace { 1109 /// ProvenanceAnalysis - This is similar to BasicAliasAnalysis, and it 1110 /// uses many of the same techniques, except it uses special ObjC-specific 1111 /// reasoning about pointer relationships. 1112 class ProvenanceAnalysis { 1113 AliasAnalysis *AA; 1114 1115 typedef std::pair<const Value *, const Value *> ValuePairTy; 1116 typedef DenseMap<ValuePairTy, bool> CachedResultsTy; 1117 CachedResultsTy CachedResults; 1118 1119 bool relatedCheck(const Value *A, const Value *B); 1120 bool relatedSelect(const SelectInst *A, const Value *B); 1121 bool relatedPHI(const PHINode *A, const Value *B); 1122 1123 // Do not implement. 1124 void operator=(const ProvenanceAnalysis &); 1125 ProvenanceAnalysis(const ProvenanceAnalysis &); 1126 1127 public: 1128 ProvenanceAnalysis() {} 1129 1130 void setAA(AliasAnalysis *aa) { AA = aa; } 1131 1132 AliasAnalysis *getAA() const { return AA; } 1133 1134 bool related(const Value *A, const Value *B); 1135 1136 void clear() { 1137 CachedResults.clear(); 1138 } 1139 }; 1140} 1141 1142bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) { 1143 // If the values are Selects with the same condition, we can do a more precise 1144 // check: just check for relations between the values on corresponding arms. 1145 if (const SelectInst *SB = dyn_cast<SelectInst>(B)) 1146 if (A->getCondition() == SB->getCondition()) 1147 return related(A->getTrueValue(), SB->getTrueValue()) || 1148 related(A->getFalseValue(), SB->getFalseValue()); 1149 1150 // Check both arms of the Select node individually. 1151 return related(A->getTrueValue(), B) || 1152 related(A->getFalseValue(), B); 1153} 1154 1155bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) { 1156 // If the values are PHIs in the same block, we can do a more precise as well 1157 // as efficient check: just check for relations between the values on 1158 // corresponding edges. 1159 if (const PHINode *PNB = dyn_cast<PHINode>(B)) 1160 if (PNB->getParent() == A->getParent()) { 1161 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) 1162 if (related(A->getIncomingValue(i), 1163 PNB->getIncomingValueForBlock(A->getIncomingBlock(i)))) 1164 return true; 1165 return false; 1166 } 1167 1168 // Check each unique source of the PHI node against B. 1169 SmallPtrSet<const Value *, 4> UniqueSrc; 1170 for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) { 1171 const Value *PV1 = A->getIncomingValue(i); 1172 if (UniqueSrc.insert(PV1) && related(PV1, B)) 1173 return true; 1174 } 1175 1176 // All of the arms checked out. 1177 return false; 1178} 1179 1180/// isStoredObjCPointer - Test if the value of P, or any value covered by its 1181/// provenance, is ever stored within the function (not counting callees). 1182static bool isStoredObjCPointer(const Value *P) { 1183 SmallPtrSet<const Value *, 8> Visited; 1184 SmallVector<const Value *, 8> Worklist; 1185 Worklist.push_back(P); 1186 Visited.insert(P); 1187 do { 1188 P = Worklist.pop_back_val(); 1189 for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end(); 1190 UI != UE; ++UI) { 1191 const User *Ur = *UI; 1192 if (isa<StoreInst>(Ur)) { 1193 if (UI.getOperandNo() == 0) 1194 // The pointer is stored. 1195 return true; 1196 // The pointed is stored through. 1197 continue; 1198 } 1199 if (isa<CallInst>(Ur)) 1200 // The pointer is passed as an argument, ignore this. 1201 continue; 1202 if (isa<PtrToIntInst>(P)) 1203 // Assume the worst. 1204 return true; 1205 if (Visited.insert(Ur)) 1206 Worklist.push_back(Ur); 1207 } 1208 } while (!Worklist.empty()); 1209 1210 // Everything checked out. 1211 return false; 1212} 1213 1214bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) { 1215 // Skip past provenance pass-throughs. 1216 A = GetUnderlyingObjCPtr(A); 1217 B = GetUnderlyingObjCPtr(B); 1218 1219 // Quick check. 1220 if (A == B) 1221 return true; 1222 1223 // Ask regular AliasAnalysis, for a first approximation. 1224 switch (AA->alias(A, B)) { 1225 case AliasAnalysis::NoAlias: 1226 return false; 1227 case AliasAnalysis::MustAlias: 1228 case AliasAnalysis::PartialAlias: 1229 return true; 1230 case AliasAnalysis::MayAlias: 1231 break; 1232 } 1233 1234 bool AIsIdentified = IsObjCIdentifiedObject(A); 1235 bool BIsIdentified = IsObjCIdentifiedObject(B); 1236 1237 // An ObjC-Identified object can't alias a load if it is never locally stored. 1238 if (AIsIdentified) { 1239 // Check for an obvious escape. 1240 if (isa<LoadInst>(B)) 1241 return isStoredObjCPointer(A); 1242 if (BIsIdentified) { 1243 // Check for an obvious escape. 1244 if (isa<LoadInst>(A)) 1245 return isStoredObjCPointer(B); 1246 // Both pointers are identified and escapes aren't an evident problem. 1247 return false; 1248 } 1249 } else if (BIsIdentified) { 1250 // Check for an obvious escape. 1251 if (isa<LoadInst>(A)) 1252 return isStoredObjCPointer(B); 1253 } 1254 1255 // Special handling for PHI and Select. 1256 if (const PHINode *PN = dyn_cast<PHINode>(A)) 1257 return relatedPHI(PN, B); 1258 if (const PHINode *PN = dyn_cast<PHINode>(B)) 1259 return relatedPHI(PN, A); 1260 if (const SelectInst *S = dyn_cast<SelectInst>(A)) 1261 return relatedSelect(S, B); 1262 if (const SelectInst *S = dyn_cast<SelectInst>(B)) 1263 return relatedSelect(S, A); 1264 1265 // Conservative. 1266 return true; 1267} 1268 1269bool ProvenanceAnalysis::related(const Value *A, const Value *B) { 1270 // Begin by inserting a conservative value into the map. If the insertion 1271 // fails, we have the answer already. If it succeeds, leave it there until we 1272 // compute the real answer to guard against recursive queries. 1273 if (A > B) std::swap(A, B); 1274 std::pair<CachedResultsTy::iterator, bool> Pair = 1275 CachedResults.insert(std::make_pair(ValuePairTy(A, B), true)); 1276 if (!Pair.second) 1277 return Pair.first->second; 1278 1279 bool Result = relatedCheck(A, B); 1280 CachedResults[ValuePairTy(A, B)] = Result; 1281 return Result; 1282} 1283 1284namespace { 1285 // Sequence - A sequence of states that a pointer may go through in which an 1286 // objc_retain and objc_release are actually needed. 1287 enum Sequence { 1288 S_None, 1289 S_Retain, ///< objc_retain(x) 1290 S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement 1291 S_Use, ///< any use of x 1292 S_Stop, ///< like S_Release, but code motion is stopped 1293 S_Release, ///< objc_release(x) 1294 S_MovableRelease ///< objc_release(x), !clang.imprecise_release 1295 }; 1296} 1297 1298static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) { 1299 // The easy cases. 1300 if (A == B) 1301 return A; 1302 if (A == S_None || B == S_None) 1303 return S_None; 1304 1305 if (A > B) std::swap(A, B); 1306 if (TopDown) { 1307 // Choose the side which is further along in the sequence. 1308 if ((A == S_Retain || A == S_CanRelease) && 1309 (B == S_CanRelease || B == S_Use)) 1310 return B; 1311 } else { 1312 // Choose the side which is further along in the sequence. 1313 if ((A == S_Use || A == S_CanRelease) && 1314 (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease)) 1315 return A; 1316 // If both sides are releases, choose the more conservative one. 1317 if (A == S_Stop && (B == S_Release || B == S_MovableRelease)) 1318 return A; 1319 if (A == S_Release && B == S_MovableRelease) 1320 return A; 1321 } 1322 1323 return S_None; 1324} 1325 1326namespace { 1327 /// RRInfo - Unidirectional information about either a 1328 /// retain-decrement-use-release sequence or release-use-decrement-retain 1329 /// reverese sequence. 1330 struct RRInfo { 1331 /// KnownSafe - After an objc_retain, the reference count of the referenced 1332 /// object is known to be positive. Similarly, before an objc_release, the 1333 /// reference count of the referenced object is known to be positive. If 1334 /// there are retain-release pairs in code regions where the retain count 1335 /// is known to be positive, they can be eliminated, regardless of any side 1336 /// effects between them. 1337 /// 1338 /// Also, a retain+release pair nested within another retain+release 1339 /// pair all on the known same pointer value can be eliminated, regardless 1340 /// of any intervening side effects. 1341 /// 1342 /// KnownSafe is true when either of these conditions is satisfied. 1343 bool KnownSafe; 1344 1345 /// IsRetainBlock - True if the Calls are objc_retainBlock calls (as 1346 /// opposed to objc_retain calls). 1347 bool IsRetainBlock; 1348 1349 /// IsTailCallRelease - True of the objc_release calls are all marked 1350 /// with the "tail" keyword. 1351 bool IsTailCallRelease; 1352 1353 /// ReleaseMetadata - If the Calls are objc_release calls and they all have 1354 /// a clang.imprecise_release tag, this is the metadata tag. 1355 MDNode *ReleaseMetadata; 1356 1357 /// Calls - For a top-down sequence, the set of objc_retains or 1358 /// objc_retainBlocks. For bottom-up, the set of objc_releases. 1359 SmallPtrSet<Instruction *, 2> Calls; 1360 1361 /// ReverseInsertPts - The set of optimal insert positions for 1362 /// moving calls in the opposite sequence. 1363 SmallPtrSet<Instruction *, 2> ReverseInsertPts; 1364 1365 RRInfo() : 1366 KnownSafe(false), IsRetainBlock(false), 1367 IsTailCallRelease(false), 1368 ReleaseMetadata(0) {} 1369 1370 void clear(); 1371 }; 1372} 1373 1374void RRInfo::clear() { 1375 KnownSafe = false; 1376 IsRetainBlock = false; 1377 IsTailCallRelease = false; 1378 ReleaseMetadata = 0; 1379 Calls.clear(); 1380 ReverseInsertPts.clear(); 1381} 1382 1383namespace { 1384 /// PtrState - This class summarizes several per-pointer runtime properties 1385 /// which are propogated through the flow graph. 1386 class PtrState { 1387 /// KnownPositiveRefCount - True if the reference count is known to 1388 /// be incremented. 1389 bool KnownPositiveRefCount; 1390 1391 /// Partial - True of we've seen an opportunity for partial RR elimination, 1392 /// such as pushing calls into a CFG triangle or into one side of a 1393 /// CFG diamond. 1394 bool Partial; 1395 1396 /// Seq - The current position in the sequence. 1397 Sequence Seq : 8; 1398 1399 public: 1400 /// RRI - Unidirectional information about the current sequence. 1401 /// TODO: Encapsulate this better. 1402 RRInfo RRI; 1403 1404 PtrState() : KnownPositiveRefCount(false), Partial(false), 1405 Seq(S_None) {} 1406 1407 void SetKnownPositiveRefCount() { 1408 KnownPositiveRefCount = true; 1409 } 1410 1411 void ClearRefCount() { 1412 KnownPositiveRefCount = false; 1413 } 1414 1415 bool IsKnownIncremented() const { 1416 return KnownPositiveRefCount; 1417 } 1418 1419 void SetSeq(Sequence NewSeq) { 1420 Seq = NewSeq; 1421 } 1422 1423 Sequence GetSeq() const { 1424 return Seq; 1425 } 1426 1427 void ClearSequenceProgress() { 1428 ResetSequenceProgress(S_None); 1429 } 1430 1431 void ResetSequenceProgress(Sequence NewSeq) { 1432 Seq = NewSeq; 1433 Partial = false; 1434 RRI.clear(); 1435 } 1436 1437 void Merge(const PtrState &Other, bool TopDown); 1438 }; 1439} 1440 1441void 1442PtrState::Merge(const PtrState &Other, bool TopDown) { 1443 Seq = MergeSeqs(Seq, Other.Seq, TopDown); 1444 KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount; 1445 1446 // We can't merge a plain objc_retain with an objc_retainBlock. 1447 if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock) 1448 Seq = S_None; 1449 1450 // If we're not in a sequence (anymore), drop all associated state. 1451 if (Seq == S_None) { 1452 Partial = false; 1453 RRI.clear(); 1454 } else if (Partial || Other.Partial) { 1455 // If we're doing a merge on a path that's previously seen a partial 1456 // merge, conservatively drop the sequence, to avoid doing partial 1457 // RR elimination. If the branch predicates for the two merge differ, 1458 // mixing them is unsafe. 1459 ClearSequenceProgress(); 1460 } else { 1461 // Conservatively merge the ReleaseMetadata information. 1462 if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata) 1463 RRI.ReleaseMetadata = 0; 1464 1465 RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe; 1466 RRI.IsTailCallRelease = RRI.IsTailCallRelease && 1467 Other.RRI.IsTailCallRelease; 1468 RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end()); 1469 1470 // Merge the insert point sets. If there are any differences, 1471 // that makes this a partial merge. 1472 Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size(); 1473 for (SmallPtrSet<Instruction *, 2>::const_iterator 1474 I = Other.RRI.ReverseInsertPts.begin(), 1475 E = Other.RRI.ReverseInsertPts.end(); I != E; ++I) 1476 Partial |= RRI.ReverseInsertPts.insert(*I); 1477 } 1478} 1479 1480namespace { 1481 /// BBState - Per-BasicBlock state. 1482 class BBState { 1483 /// TopDownPathCount - The number of unique control paths from the entry 1484 /// which can reach this block. 1485 unsigned TopDownPathCount; 1486 1487 /// BottomUpPathCount - The number of unique control paths to exits 1488 /// from this block. 1489 unsigned BottomUpPathCount; 1490 1491 /// MapTy - A type for PerPtrTopDown and PerPtrBottomUp. 1492 typedef MapVector<const Value *, PtrState> MapTy; 1493 1494 /// PerPtrTopDown - The top-down traversal uses this to record information 1495 /// known about a pointer at the bottom of each block. 1496 MapTy PerPtrTopDown; 1497 1498 /// PerPtrBottomUp - The bottom-up traversal uses this to record information 1499 /// known about a pointer at the top of each block. 1500 MapTy PerPtrBottomUp; 1501 1502 /// Preds, Succs - Effective successors and predecessors of the current 1503 /// block (this ignores ignorable edges and ignored backedges). 1504 SmallVector<BasicBlock *, 2> Preds; 1505 SmallVector<BasicBlock *, 2> Succs; 1506 1507 public: 1508 BBState() : TopDownPathCount(0), BottomUpPathCount(0) {} 1509 1510 typedef MapTy::iterator ptr_iterator; 1511 typedef MapTy::const_iterator ptr_const_iterator; 1512 1513 ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); } 1514 ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); } 1515 ptr_const_iterator top_down_ptr_begin() const { 1516 return PerPtrTopDown.begin(); 1517 } 1518 ptr_const_iterator top_down_ptr_end() const { 1519 return PerPtrTopDown.end(); 1520 } 1521 1522 ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); } 1523 ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); } 1524 ptr_const_iterator bottom_up_ptr_begin() const { 1525 return PerPtrBottomUp.begin(); 1526 } 1527 ptr_const_iterator bottom_up_ptr_end() const { 1528 return PerPtrBottomUp.end(); 1529 } 1530 1531 /// SetAsEntry - Mark this block as being an entry block, which has one 1532 /// path from the entry by definition. 1533 void SetAsEntry() { TopDownPathCount = 1; } 1534 1535 /// SetAsExit - Mark this block as being an exit block, which has one 1536 /// path to an exit by definition. 1537 void SetAsExit() { BottomUpPathCount = 1; } 1538 1539 PtrState &getPtrTopDownState(const Value *Arg) { 1540 return PerPtrTopDown[Arg]; 1541 } 1542 1543 PtrState &getPtrBottomUpState(const Value *Arg) { 1544 return PerPtrBottomUp[Arg]; 1545 } 1546 1547 void clearBottomUpPointers() { 1548 PerPtrBottomUp.clear(); 1549 } 1550 1551 void clearTopDownPointers() { 1552 PerPtrTopDown.clear(); 1553 } 1554 1555 void InitFromPred(const BBState &Other); 1556 void InitFromSucc(const BBState &Other); 1557 void MergePred(const BBState &Other); 1558 void MergeSucc(const BBState &Other); 1559 1560 /// GetAllPathCount - Return the number of possible unique paths from an 1561 /// entry to an exit which pass through this block. This is only valid 1562 /// after both the top-down and bottom-up traversals are complete. 1563 unsigned GetAllPathCount() const { 1564 assert(TopDownPathCount != 0); 1565 assert(BottomUpPathCount != 0); 1566 return TopDownPathCount * BottomUpPathCount; 1567 } 1568 1569 // Specialized CFG utilities. 1570 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator; 1571 edge_iterator pred_begin() { return Preds.begin(); } 1572 edge_iterator pred_end() { return Preds.end(); } 1573 edge_iterator succ_begin() { return Succs.begin(); } 1574 edge_iterator succ_end() { return Succs.end(); } 1575 1576 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); } 1577 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); } 1578 1579 bool isExit() const { return Succs.empty(); } 1580 }; 1581} 1582 1583void BBState::InitFromPred(const BBState &Other) { 1584 PerPtrTopDown = Other.PerPtrTopDown; 1585 TopDownPathCount = Other.TopDownPathCount; 1586} 1587 1588void BBState::InitFromSucc(const BBState &Other) { 1589 PerPtrBottomUp = Other.PerPtrBottomUp; 1590 BottomUpPathCount = Other.BottomUpPathCount; 1591} 1592 1593/// MergePred - The top-down traversal uses this to merge information about 1594/// predecessors to form the initial state for a new block. 1595void BBState::MergePred(const BBState &Other) { 1596 // Other.TopDownPathCount can be 0, in which case it is either dead or a 1597 // loop backedge. Loop backedges are special. 1598 TopDownPathCount += Other.TopDownPathCount; 1599 1600 // For each entry in the other set, if our set has an entry with the same key, 1601 // merge the entries. Otherwise, copy the entry and merge it with an empty 1602 // entry. 1603 for (ptr_const_iterator MI = Other.top_down_ptr_begin(), 1604 ME = Other.top_down_ptr_end(); MI != ME; ++MI) { 1605 std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI); 1606 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, 1607 /*TopDown=*/true); 1608 } 1609 1610 // For each entry in our set, if the other set doesn't have an entry with the 1611 // same key, force it to merge with an empty entry. 1612 for (ptr_iterator MI = top_down_ptr_begin(), 1613 ME = top_down_ptr_end(); MI != ME; ++MI) 1614 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end()) 1615 MI->second.Merge(PtrState(), /*TopDown=*/true); 1616} 1617 1618/// MergeSucc - The bottom-up traversal uses this to merge information about 1619/// successors to form the initial state for a new block. 1620void BBState::MergeSucc(const BBState &Other) { 1621 // Other.BottomUpPathCount can be 0, in which case it is either dead or a 1622 // loop backedge. Loop backedges are special. 1623 BottomUpPathCount += Other.BottomUpPathCount; 1624 1625 // For each entry in the other set, if our set has an entry with the 1626 // same key, merge the entries. Otherwise, copy the entry and merge 1627 // it with an empty entry. 1628 for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(), 1629 ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) { 1630 std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI); 1631 Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, 1632 /*TopDown=*/false); 1633 } 1634 1635 // For each entry in our set, if the other set doesn't have an entry 1636 // with the same key, force it to merge with an empty entry. 1637 for (ptr_iterator MI = bottom_up_ptr_begin(), 1638 ME = bottom_up_ptr_end(); MI != ME; ++MI) 1639 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end()) 1640 MI->second.Merge(PtrState(), /*TopDown=*/false); 1641} 1642 1643namespace { 1644 /// ObjCARCOpt - The main ARC optimization pass. 1645 class ObjCARCOpt : public FunctionPass { 1646 bool Changed; 1647 ProvenanceAnalysis PA; 1648 1649 /// Run - A flag indicating whether this optimization pass should run. 1650 bool Run; 1651 1652 /// RetainRVCallee, etc. - Declarations for ObjC runtime 1653 /// functions, for use in creating calls to them. These are initialized 1654 /// lazily to avoid cluttering up the Module with unused declarations. 1655 Constant *RetainRVCallee, *AutoreleaseRVCallee, *ReleaseCallee, 1656 *RetainCallee, *RetainBlockCallee, *AutoreleaseCallee; 1657 1658 /// UsedInThisFunciton - Flags which determine whether each of the 1659 /// interesting runtine functions is in fact used in the current function. 1660 unsigned UsedInThisFunction; 1661 1662 /// ImpreciseReleaseMDKind - The Metadata Kind for clang.imprecise_release 1663 /// metadata. 1664 unsigned ImpreciseReleaseMDKind; 1665 1666 /// CopyOnEscapeMDKind - The Metadata Kind for clang.arc.copy_on_escape 1667 /// metadata. 1668 unsigned CopyOnEscapeMDKind; 1669 1670 /// NoObjCARCExceptionsMDKind - The Metadata Kind for 1671 /// clang.arc.no_objc_arc_exceptions metadata. 1672 unsigned NoObjCARCExceptionsMDKind; 1673 1674 Constant *getRetainRVCallee(Module *M); 1675 Constant *getAutoreleaseRVCallee(Module *M); 1676 Constant *getReleaseCallee(Module *M); 1677 Constant *getRetainCallee(Module *M); 1678 Constant *getRetainBlockCallee(Module *M); 1679 Constant *getAutoreleaseCallee(Module *M); 1680 1681 bool IsRetainBlockOptimizable(const Instruction *Inst); 1682 1683 void OptimizeRetainCall(Function &F, Instruction *Retain); 1684 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV); 1685 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV); 1686 void OptimizeIndividualCalls(Function &F); 1687 1688 void CheckForCFGHazards(const BasicBlock *BB, 1689 DenseMap<const BasicBlock *, BBState> &BBStates, 1690 BBState &MyStates) const; 1691 bool VisitInstructionBottomUp(Instruction *Inst, 1692 BasicBlock *BB, 1693 MapVector<Value *, RRInfo> &Retains, 1694 BBState &MyStates); 1695 bool VisitBottomUp(BasicBlock *BB, 1696 DenseMap<const BasicBlock *, BBState> &BBStates, 1697 MapVector<Value *, RRInfo> &Retains); 1698 bool VisitInstructionTopDown(Instruction *Inst, 1699 DenseMap<Value *, RRInfo> &Releases, 1700 BBState &MyStates); 1701 bool VisitTopDown(BasicBlock *BB, 1702 DenseMap<const BasicBlock *, BBState> &BBStates, 1703 DenseMap<Value *, RRInfo> &Releases); 1704 bool Visit(Function &F, 1705 DenseMap<const BasicBlock *, BBState> &BBStates, 1706 MapVector<Value *, RRInfo> &Retains, 1707 DenseMap<Value *, RRInfo> &Releases); 1708 1709 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove, 1710 MapVector<Value *, RRInfo> &Retains, 1711 DenseMap<Value *, RRInfo> &Releases, 1712 SmallVectorImpl<Instruction *> &DeadInsts, 1713 Module *M); 1714 1715 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates, 1716 MapVector<Value *, RRInfo> &Retains, 1717 DenseMap<Value *, RRInfo> &Releases, 1718 Module *M); 1719 1720 void OptimizeWeakCalls(Function &F); 1721 1722 bool OptimizeSequences(Function &F); 1723 1724 void OptimizeReturns(Function &F); 1725 1726 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 1727 virtual bool doInitialization(Module &M); 1728 virtual bool runOnFunction(Function &F); 1729 virtual void releaseMemory(); 1730 1731 public: 1732 static char ID; 1733 ObjCARCOpt() : FunctionPass(ID) { 1734 initializeObjCARCOptPass(*PassRegistry::getPassRegistry()); 1735 } 1736 }; 1737} 1738 1739char ObjCARCOpt::ID = 0; 1740INITIALIZE_PASS_BEGIN(ObjCARCOpt, 1741 "objc-arc", "ObjC ARC optimization", false, false) 1742INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis) 1743INITIALIZE_PASS_END(ObjCARCOpt, 1744 "objc-arc", "ObjC ARC optimization", false, false) 1745 1746Pass *llvm::createObjCARCOptPass() { 1747 return new ObjCARCOpt(); 1748} 1749 1750void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const { 1751 AU.addRequired<ObjCARCAliasAnalysis>(); 1752 AU.addRequired<AliasAnalysis>(); 1753 // ARC optimization doesn't currently split critical edges. 1754 AU.setPreservesCFG(); 1755} 1756 1757bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) { 1758 // Without the magic metadata tag, we have to assume this might be an 1759 // objc_retainBlock call inserted to convert a block pointer to an id, 1760 // in which case it really is needed. 1761 if (!Inst->getMetadata(CopyOnEscapeMDKind)) 1762 return false; 1763 1764 // If the pointer "escapes" (not including being used in a call), 1765 // the copy may be needed. 1766 if (DoesObjCBlockEscape(Inst)) 1767 return false; 1768 1769 // Otherwise, it's not needed. 1770 return true; 1771} 1772 1773Constant *ObjCARCOpt::getRetainRVCallee(Module *M) { 1774 if (!RetainRVCallee) { 1775 LLVMContext &C = M->getContext(); 1776 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 1777 Type *Params[] = { I8X }; 1778 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); 1779 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 1780 RetainRVCallee = 1781 M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy, 1782 Attributes); 1783 } 1784 return RetainRVCallee; 1785} 1786 1787Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) { 1788 if (!AutoreleaseRVCallee) { 1789 LLVMContext &C = M->getContext(); 1790 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 1791 Type *Params[] = { I8X }; 1792 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); 1793 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 1794 AutoreleaseRVCallee = 1795 M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy, 1796 Attributes); 1797 } 1798 return AutoreleaseRVCallee; 1799} 1800 1801Constant *ObjCARCOpt::getReleaseCallee(Module *M) { 1802 if (!ReleaseCallee) { 1803 LLVMContext &C = M->getContext(); 1804 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; 1805 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 1806 ReleaseCallee = 1807 M->getOrInsertFunction( 1808 "objc_release", 1809 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), 1810 Attributes); 1811 } 1812 return ReleaseCallee; 1813} 1814 1815Constant *ObjCARCOpt::getRetainCallee(Module *M) { 1816 if (!RetainCallee) { 1817 LLVMContext &C = M->getContext(); 1818 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; 1819 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 1820 RetainCallee = 1821 M->getOrInsertFunction( 1822 "objc_retain", 1823 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1824 Attributes); 1825 } 1826 return RetainCallee; 1827} 1828 1829Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) { 1830 if (!RetainBlockCallee) { 1831 LLVMContext &C = M->getContext(); 1832 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; 1833 // objc_retainBlock is not nounwind because it calls user copy constructors 1834 // which could theoretically throw. 1835 RetainBlockCallee = 1836 M->getOrInsertFunction( 1837 "objc_retainBlock", 1838 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1839 AttrListPtr()); 1840 } 1841 return RetainBlockCallee; 1842} 1843 1844Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) { 1845 if (!AutoreleaseCallee) { 1846 LLVMContext &C = M->getContext(); 1847 Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; 1848 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 1849 AutoreleaseCallee = 1850 M->getOrInsertFunction( 1851 "objc_autorelease", 1852 FunctionType::get(Params[0], Params, /*isVarArg=*/false), 1853 Attributes); 1854 } 1855 return AutoreleaseCallee; 1856} 1857 1858/// IsPotentialUse - Test whether the given value is possible a 1859/// reference-counted pointer, including tests which utilize AliasAnalysis. 1860static bool IsPotentialUse(const Value *Op, AliasAnalysis &AA) { 1861 // First make the rudimentary check. 1862 if (!IsPotentialUse(Op)) 1863 return false; 1864 1865 // Objects in constant memory are not reference-counted. 1866 if (AA.pointsToConstantMemory(Op)) 1867 return false; 1868 1869 // Pointers in constant memory are not pointing to reference-counted objects. 1870 if (const LoadInst *LI = dyn_cast<LoadInst>(Op)) 1871 if (AA.pointsToConstantMemory(LI->getPointerOperand())) 1872 return false; 1873 1874 // Otherwise assume the worst. 1875 return true; 1876} 1877 1878/// CanAlterRefCount - Test whether the given instruction can result in a 1879/// reference count modification (positive or negative) for the pointer's 1880/// object. 1881static bool 1882CanAlterRefCount(const Instruction *Inst, const Value *Ptr, 1883 ProvenanceAnalysis &PA, InstructionClass Class) { 1884 switch (Class) { 1885 case IC_Autorelease: 1886 case IC_AutoreleaseRV: 1887 case IC_User: 1888 // These operations never directly modify a reference count. 1889 return false; 1890 default: break; 1891 } 1892 1893 ImmutableCallSite CS = static_cast<const Value *>(Inst); 1894 assert(CS && "Only calls can alter reference counts!"); 1895 1896 // See if AliasAnalysis can help us with the call. 1897 AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS); 1898 if (AliasAnalysis::onlyReadsMemory(MRB)) 1899 return false; 1900 if (AliasAnalysis::onlyAccessesArgPointees(MRB)) { 1901 for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 1902 I != E; ++I) { 1903 const Value *Op = *I; 1904 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op)) 1905 return true; 1906 } 1907 return false; 1908 } 1909 1910 // Assume the worst. 1911 return true; 1912} 1913 1914/// CanUse - Test whether the given instruction can "use" the given pointer's 1915/// object in a way that requires the reference count to be positive. 1916static bool 1917CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA, 1918 InstructionClass Class) { 1919 // IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers. 1920 if (Class == IC_Call) 1921 return false; 1922 1923 // Consider various instructions which may have pointer arguments which are 1924 // not "uses". 1925 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) { 1926 // Comparing a pointer with null, or any other constant, isn't really a use, 1927 // because we don't care what the pointer points to, or about the values 1928 // of any other dynamic reference-counted pointers. 1929 if (!IsPotentialUse(ICI->getOperand(1), *PA.getAA())) 1930 return false; 1931 } else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) { 1932 // For calls, just check the arguments (and not the callee operand). 1933 for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(), 1934 OE = CS.arg_end(); OI != OE; ++OI) { 1935 const Value *Op = *OI; 1936 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op)) 1937 return true; 1938 } 1939 return false; 1940 } else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 1941 // Special-case stores, because we don't care about the stored value, just 1942 // the store address. 1943 const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand()); 1944 // If we can't tell what the underlying object was, assume there is a 1945 // dependence. 1946 return IsPotentialUse(Op, *PA.getAA()) && PA.related(Op, Ptr); 1947 } 1948 1949 // Check each operand for a match. 1950 for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end(); 1951 OI != OE; ++OI) { 1952 const Value *Op = *OI; 1953 if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op)) 1954 return true; 1955 } 1956 return false; 1957} 1958 1959/// CanInterruptRV - Test whether the given instruction can autorelease 1960/// any pointer or cause an autoreleasepool pop. 1961static bool 1962CanInterruptRV(InstructionClass Class) { 1963 switch (Class) { 1964 case IC_AutoreleasepoolPop: 1965 case IC_CallOrUser: 1966 case IC_Call: 1967 case IC_Autorelease: 1968 case IC_AutoreleaseRV: 1969 case IC_FusedRetainAutorelease: 1970 case IC_FusedRetainAutoreleaseRV: 1971 return true; 1972 default: 1973 return false; 1974 } 1975} 1976 1977namespace { 1978 /// DependenceKind - There are several kinds of dependence-like concepts in 1979 /// use here. 1980 enum DependenceKind { 1981 NeedsPositiveRetainCount, 1982 AutoreleasePoolBoundary, 1983 CanChangeRetainCount, 1984 RetainAutoreleaseDep, ///< Blocks objc_retainAutorelease. 1985 RetainAutoreleaseRVDep, ///< Blocks objc_retainAutoreleaseReturnValue. 1986 RetainRVDep ///< Blocks objc_retainAutoreleasedReturnValue. 1987 }; 1988} 1989 1990/// Depends - Test if there can be dependencies on Inst through Arg. This 1991/// function only tests dependencies relevant for removing pairs of calls. 1992static bool 1993Depends(DependenceKind Flavor, Instruction *Inst, const Value *Arg, 1994 ProvenanceAnalysis &PA) { 1995 // If we've reached the definition of Arg, stop. 1996 if (Inst == Arg) 1997 return true; 1998 1999 switch (Flavor) { 2000 case NeedsPositiveRetainCount: { 2001 InstructionClass Class = GetInstructionClass(Inst); 2002 switch (Class) { 2003 case IC_AutoreleasepoolPop: 2004 case IC_AutoreleasepoolPush: 2005 case IC_None: 2006 return false; 2007 default: 2008 return CanUse(Inst, Arg, PA, Class); 2009 } 2010 } 2011 2012 case AutoreleasePoolBoundary: { 2013 InstructionClass Class = GetInstructionClass(Inst); 2014 switch (Class) { 2015 case IC_AutoreleasepoolPop: 2016 case IC_AutoreleasepoolPush: 2017 // These mark the end and begin of an autorelease pool scope. 2018 return true; 2019 default: 2020 // Nothing else does this. 2021 return false; 2022 } 2023 } 2024 2025 case CanChangeRetainCount: { 2026 InstructionClass Class = GetInstructionClass(Inst); 2027 switch (Class) { 2028 case IC_AutoreleasepoolPop: 2029 // Conservatively assume this can decrement any count. 2030 return true; 2031 case IC_AutoreleasepoolPush: 2032 case IC_None: 2033 return false; 2034 default: 2035 return CanAlterRefCount(Inst, Arg, PA, Class); 2036 } 2037 } 2038 2039 case RetainAutoreleaseDep: 2040 switch (GetBasicInstructionClass(Inst)) { 2041 case IC_AutoreleasepoolPop: 2042 case IC_AutoreleasepoolPush: 2043 // Don't merge an objc_autorelease with an objc_retain inside a different 2044 // autoreleasepool scope. 2045 return true; 2046 case IC_Retain: 2047 case IC_RetainRV: 2048 // Check for a retain of the same pointer for merging. 2049 return GetObjCArg(Inst) == Arg; 2050 default: 2051 // Nothing else matters for objc_retainAutorelease formation. 2052 return false; 2053 } 2054 2055 case RetainAutoreleaseRVDep: { 2056 InstructionClass Class = GetBasicInstructionClass(Inst); 2057 switch (Class) { 2058 case IC_Retain: 2059 case IC_RetainRV: 2060 // Check for a retain of the same pointer for merging. 2061 return GetObjCArg(Inst) == Arg; 2062 default: 2063 // Anything that can autorelease interrupts 2064 // retainAutoreleaseReturnValue formation. 2065 return CanInterruptRV(Class); 2066 } 2067 } 2068 2069 case RetainRVDep: 2070 return CanInterruptRV(GetBasicInstructionClass(Inst)); 2071 } 2072 2073 llvm_unreachable("Invalid dependence flavor"); 2074} 2075 2076/// FindDependencies - Walk up the CFG from StartPos (which is in StartBB) and 2077/// find local and non-local dependencies on Arg. 2078/// TODO: Cache results? 2079static void 2080FindDependencies(DependenceKind Flavor, 2081 const Value *Arg, 2082 BasicBlock *StartBB, Instruction *StartInst, 2083 SmallPtrSet<Instruction *, 4> &DependingInstructions, 2084 SmallPtrSet<const BasicBlock *, 4> &Visited, 2085 ProvenanceAnalysis &PA) { 2086 BasicBlock::iterator StartPos = StartInst; 2087 2088 SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist; 2089 Worklist.push_back(std::make_pair(StartBB, StartPos)); 2090 do { 2091 std::pair<BasicBlock *, BasicBlock::iterator> Pair = 2092 Worklist.pop_back_val(); 2093 BasicBlock *LocalStartBB = Pair.first; 2094 BasicBlock::iterator LocalStartPos = Pair.second; 2095 BasicBlock::iterator StartBBBegin = LocalStartBB->begin(); 2096 for (;;) { 2097 if (LocalStartPos == StartBBBegin) { 2098 pred_iterator PI(LocalStartBB), PE(LocalStartBB, false); 2099 if (PI == PE) 2100 // If we've reached the function entry, produce a null dependence. 2101 DependingInstructions.insert(0); 2102 else 2103 // Add the predecessors to the worklist. 2104 do { 2105 BasicBlock *PredBB = *PI; 2106 if (Visited.insert(PredBB)) 2107 Worklist.push_back(std::make_pair(PredBB, PredBB->end())); 2108 } while (++PI != PE); 2109 break; 2110 } 2111 2112 Instruction *Inst = --LocalStartPos; 2113 if (Depends(Flavor, Inst, Arg, PA)) { 2114 DependingInstructions.insert(Inst); 2115 break; 2116 } 2117 } 2118 } while (!Worklist.empty()); 2119 2120 // Determine whether the original StartBB post-dominates all of the blocks we 2121 // visited. If not, insert a sentinal indicating that most optimizations are 2122 // not safe. 2123 for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(), 2124 E = Visited.end(); I != E; ++I) { 2125 const BasicBlock *BB = *I; 2126 if (BB == StartBB) 2127 continue; 2128 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2129 for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) { 2130 const BasicBlock *Succ = *SI; 2131 if (Succ != StartBB && !Visited.count(Succ)) { 2132 DependingInstructions.insert(reinterpret_cast<Instruction *>(-1)); 2133 return; 2134 } 2135 } 2136 } 2137} 2138 2139static bool isNullOrUndef(const Value *V) { 2140 return isa<ConstantPointerNull>(V) || isa<UndefValue>(V); 2141} 2142 2143static bool isNoopInstruction(const Instruction *I) { 2144 return isa<BitCastInst>(I) || 2145 (isa<GetElementPtrInst>(I) && 2146 cast<GetElementPtrInst>(I)->hasAllZeroIndices()); 2147} 2148 2149/// OptimizeRetainCall - Turn objc_retain into 2150/// objc_retainAutoreleasedReturnValue if the operand is a return value. 2151void 2152ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) { 2153 ImmutableCallSite CS(GetObjCArg(Retain)); 2154 const Instruction *Call = CS.getInstruction(); 2155 if (!Call) return; 2156 if (Call->getParent() != Retain->getParent()) return; 2157 2158 // Check that the call is next to the retain. 2159 BasicBlock::const_iterator I = Call; 2160 ++I; 2161 while (isNoopInstruction(I)) ++I; 2162 if (&*I != Retain) 2163 return; 2164 2165 // Turn it to an objc_retainAutoreleasedReturnValue.. 2166 Changed = true; 2167 ++NumPeeps; 2168 cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent())); 2169} 2170 2171/// OptimizeRetainRVCall - Turn objc_retainAutoreleasedReturnValue into 2172/// objc_retain if the operand is not a return value. Or, if it can be paired 2173/// with an objc_autoreleaseReturnValue, delete the pair and return true. 2174bool 2175ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) { 2176 // Check for the argument being from an immediately preceding call or invoke. 2177 const Value *Arg = GetObjCArg(RetainRV); 2178 ImmutableCallSite CS(Arg); 2179 if (const Instruction *Call = CS.getInstruction()) { 2180 if (Call->getParent() == RetainRV->getParent()) { 2181 BasicBlock::const_iterator I = Call; 2182 ++I; 2183 while (isNoopInstruction(I)) ++I; 2184 if (&*I == RetainRV) 2185 return false; 2186 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 2187 BasicBlock *RetainRVParent = RetainRV->getParent(); 2188 if (II->getNormalDest() == RetainRVParent) { 2189 BasicBlock::const_iterator I = RetainRVParent->begin(); 2190 while (isNoopInstruction(I)) ++I; 2191 if (&*I == RetainRV) 2192 return false; 2193 } 2194 } 2195 } 2196 2197 // Check for being preceded by an objc_autoreleaseReturnValue on the same 2198 // pointer. In this case, we can delete the pair. 2199 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin(); 2200 if (I != Begin) { 2201 do --I; while (I != Begin && isNoopInstruction(I)); 2202 if (GetBasicInstructionClass(I) == IC_AutoreleaseRV && 2203 GetObjCArg(I) == Arg) { 2204 Changed = true; 2205 ++NumPeeps; 2206 EraseInstruction(I); 2207 EraseInstruction(RetainRV); 2208 return true; 2209 } 2210 } 2211 2212 // Turn it to a plain objc_retain. 2213 Changed = true; 2214 ++NumPeeps; 2215 cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent())); 2216 return false; 2217} 2218 2219/// OptimizeAutoreleaseRVCall - Turn objc_autoreleaseReturnValue into 2220/// objc_autorelease if the result is not used as a return value. 2221void 2222ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV) { 2223 // Check for a return of the pointer value. 2224 const Value *Ptr = GetObjCArg(AutoreleaseRV); 2225 SmallVector<const Value *, 2> Users; 2226 Users.push_back(Ptr); 2227 do { 2228 Ptr = Users.pop_back_val(); 2229 for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end(); 2230 UI != UE; ++UI) { 2231 const User *I = *UI; 2232 if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV) 2233 return; 2234 if (isa<BitCastInst>(I)) 2235 Users.push_back(I); 2236 } 2237 } while (!Users.empty()); 2238 2239 Changed = true; 2240 ++NumPeeps; 2241 cast<CallInst>(AutoreleaseRV)-> 2242 setCalledFunction(getAutoreleaseCallee(F.getParent())); 2243} 2244 2245/// OptimizeIndividualCalls - Visit each call, one at a time, and make 2246/// simplifications without doing any additional analysis. 2247void ObjCARCOpt::OptimizeIndividualCalls(Function &F) { 2248 // Reset all the flags in preparation for recomputing them. 2249 UsedInThisFunction = 0; 2250 2251 // Visit all objc_* calls in F. 2252 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 2253 Instruction *Inst = &*I++; 2254 InstructionClass Class = GetBasicInstructionClass(Inst); 2255 2256 switch (Class) { 2257 default: break; 2258 2259 // Delete no-op casts. These function calls have special semantics, but 2260 // the semantics are entirely implemented via lowering in the front-end, 2261 // so by the time they reach the optimizer, they are just no-op calls 2262 // which return their argument. 2263 // 2264 // There are gray areas here, as the ability to cast reference-counted 2265 // pointers to raw void* and back allows code to break ARC assumptions, 2266 // however these are currently considered to be unimportant. 2267 case IC_NoopCast: 2268 Changed = true; 2269 ++NumNoops; 2270 EraseInstruction(Inst); 2271 continue; 2272 2273 // If the pointer-to-weak-pointer is null, it's undefined behavior. 2274 case IC_StoreWeak: 2275 case IC_LoadWeak: 2276 case IC_LoadWeakRetained: 2277 case IC_InitWeak: 2278 case IC_DestroyWeak: { 2279 CallInst *CI = cast<CallInst>(Inst); 2280 if (isNullOrUndef(CI->getArgOperand(0))) { 2281 Changed = true; 2282 Type *Ty = CI->getArgOperand(0)->getType(); 2283 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), 2284 Constant::getNullValue(Ty), 2285 CI); 2286 CI->replaceAllUsesWith(UndefValue::get(CI->getType())); 2287 CI->eraseFromParent(); 2288 continue; 2289 } 2290 break; 2291 } 2292 case IC_CopyWeak: 2293 case IC_MoveWeak: { 2294 CallInst *CI = cast<CallInst>(Inst); 2295 if (isNullOrUndef(CI->getArgOperand(0)) || 2296 isNullOrUndef(CI->getArgOperand(1))) { 2297 Changed = true; 2298 Type *Ty = CI->getArgOperand(0)->getType(); 2299 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), 2300 Constant::getNullValue(Ty), 2301 CI); 2302 CI->replaceAllUsesWith(UndefValue::get(CI->getType())); 2303 CI->eraseFromParent(); 2304 continue; 2305 } 2306 break; 2307 } 2308 case IC_Retain: 2309 OptimizeRetainCall(F, Inst); 2310 break; 2311 case IC_RetainRV: 2312 if (OptimizeRetainRVCall(F, Inst)) 2313 continue; 2314 break; 2315 case IC_AutoreleaseRV: 2316 OptimizeAutoreleaseRVCall(F, Inst); 2317 break; 2318 } 2319 2320 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused. 2321 if (IsAutorelease(Class) && Inst->use_empty()) { 2322 CallInst *Call = cast<CallInst>(Inst); 2323 const Value *Arg = Call->getArgOperand(0); 2324 Arg = FindSingleUseIdentifiedObject(Arg); 2325 if (Arg) { 2326 Changed = true; 2327 ++NumAutoreleases; 2328 2329 // Create the declaration lazily. 2330 LLVMContext &C = Inst->getContext(); 2331 CallInst *NewCall = 2332 CallInst::Create(getReleaseCallee(F.getParent()), 2333 Call->getArgOperand(0), "", Call); 2334 NewCall->setMetadata(ImpreciseReleaseMDKind, 2335 MDNode::get(C, ArrayRef<Value *>())); 2336 EraseInstruction(Call); 2337 Inst = NewCall; 2338 Class = IC_Release; 2339 } 2340 } 2341 2342 // For functions which can never be passed stack arguments, add 2343 // a tail keyword. 2344 if (IsAlwaysTail(Class)) { 2345 Changed = true; 2346 cast<CallInst>(Inst)->setTailCall(); 2347 } 2348 2349 // Set nounwind as needed. 2350 if (IsNoThrow(Class)) { 2351 Changed = true; 2352 cast<CallInst>(Inst)->setDoesNotThrow(); 2353 } 2354 2355 if (!IsNoopOnNull(Class)) { 2356 UsedInThisFunction |= 1 << Class; 2357 continue; 2358 } 2359 2360 const Value *Arg = GetObjCArg(Inst); 2361 2362 // ARC calls with null are no-ops. Delete them. 2363 if (isNullOrUndef(Arg)) { 2364 Changed = true; 2365 ++NumNoops; 2366 EraseInstruction(Inst); 2367 continue; 2368 } 2369 2370 // Keep track of which of retain, release, autorelease, and retain_block 2371 // are actually present in this function. 2372 UsedInThisFunction |= 1 << Class; 2373 2374 // If Arg is a PHI, and one or more incoming values to the 2375 // PHI are null, and the call is control-equivalent to the PHI, and there 2376 // are no relevant side effects between the PHI and the call, the call 2377 // could be pushed up to just those paths with non-null incoming values. 2378 // For now, don't bother splitting critical edges for this. 2379 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist; 2380 Worklist.push_back(std::make_pair(Inst, Arg)); 2381 do { 2382 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val(); 2383 Inst = Pair.first; 2384 Arg = Pair.second; 2385 2386 const PHINode *PN = dyn_cast<PHINode>(Arg); 2387 if (!PN) continue; 2388 2389 // Determine if the PHI has any null operands, or any incoming 2390 // critical edges. 2391 bool HasNull = false; 2392 bool HasCriticalEdges = false; 2393 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 2394 Value *Incoming = 2395 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); 2396 if (isNullOrUndef(Incoming)) 2397 HasNull = true; 2398 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back()) 2399 .getNumSuccessors() != 1) { 2400 HasCriticalEdges = true; 2401 break; 2402 } 2403 } 2404 // If we have null operands and no critical edges, optimize. 2405 if (!HasCriticalEdges && HasNull) { 2406 SmallPtrSet<Instruction *, 4> DependingInstructions; 2407 SmallPtrSet<const BasicBlock *, 4> Visited; 2408 2409 // Check that there is nothing that cares about the reference 2410 // count between the call and the phi. 2411 switch (Class) { 2412 case IC_Retain: 2413 case IC_RetainBlock: 2414 // These can always be moved up. 2415 break; 2416 case IC_Release: 2417 // These can't be moved across things that care about the retain 2418 // count. 2419 FindDependencies(NeedsPositiveRetainCount, Arg, 2420 Inst->getParent(), Inst, 2421 DependingInstructions, Visited, PA); 2422 break; 2423 case IC_Autorelease: 2424 // These can't be moved across autorelease pool scope boundaries. 2425 FindDependencies(AutoreleasePoolBoundary, Arg, 2426 Inst->getParent(), Inst, 2427 DependingInstructions, Visited, PA); 2428 break; 2429 case IC_RetainRV: 2430 case IC_AutoreleaseRV: 2431 // Don't move these; the RV optimization depends on the autoreleaseRV 2432 // being tail called, and the retainRV being immediately after a call 2433 // (which might still happen if we get lucky with codegen layout, but 2434 // it's not worth taking the chance). 2435 continue; 2436 default: 2437 llvm_unreachable("Invalid dependence flavor"); 2438 } 2439 2440 if (DependingInstructions.size() == 1 && 2441 *DependingInstructions.begin() == PN) { 2442 Changed = true; 2443 ++NumPartialNoops; 2444 // Clone the call into each predecessor that has a non-null value. 2445 CallInst *CInst = cast<CallInst>(Inst); 2446 Type *ParamTy = CInst->getArgOperand(0)->getType(); 2447 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 2448 Value *Incoming = 2449 StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); 2450 if (!isNullOrUndef(Incoming)) { 2451 CallInst *Clone = cast<CallInst>(CInst->clone()); 2452 Value *Op = PN->getIncomingValue(i); 2453 Instruction *InsertPos = &PN->getIncomingBlock(i)->back(); 2454 if (Op->getType() != ParamTy) 2455 Op = new BitCastInst(Op, ParamTy, "", InsertPos); 2456 Clone->setArgOperand(0, Op); 2457 Clone->insertBefore(InsertPos); 2458 Worklist.push_back(std::make_pair(Clone, Incoming)); 2459 } 2460 } 2461 // Erase the original call. 2462 EraseInstruction(CInst); 2463 continue; 2464 } 2465 } 2466 } while (!Worklist.empty()); 2467 } 2468} 2469 2470/// CheckForCFGHazards - Check for critical edges, loop boundaries, irreducible 2471/// control flow, or other CFG structures where moving code across the edge 2472/// would result in it being executed more. 2473void 2474ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB, 2475 DenseMap<const BasicBlock *, BBState> &BBStates, 2476 BBState &MyStates) const { 2477 // If any top-down local-use or possible-dec has a succ which is earlier in 2478 // the sequence, forget it. 2479 for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(), 2480 E = MyStates.top_down_ptr_end(); I != E; ++I) 2481 switch (I->second.GetSeq()) { 2482 default: break; 2483 case S_Use: { 2484 const Value *Arg = I->first; 2485 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2486 bool SomeSuccHasSame = false; 2487 bool AllSuccsHaveSame = true; 2488 PtrState &S = I->second; 2489 succ_const_iterator SI(TI), SE(TI, false); 2490 2491 // If the terminator is an invoke marked with the 2492 // clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be 2493 // ignored, for ARC purposes. 2494 if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) 2495 --SE; 2496 2497 for (; SI != SE; ++SI) { 2498 Sequence SuccSSeq = S_None; 2499 bool SuccSRRIKnownSafe = false; 2500 // If VisitBottomUp has pointer information for this successor, take 2501 // what we know about it. 2502 DenseMap<const BasicBlock *, BBState>::iterator BBI = 2503 BBStates.find(*SI); 2504 assert(BBI != BBStates.end()); 2505 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg); 2506 SuccSSeq = SuccS.GetSeq(); 2507 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe; 2508 switch (SuccSSeq) { 2509 case S_None: 2510 case S_CanRelease: { 2511 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) { 2512 S.ClearSequenceProgress(); 2513 break; 2514 } 2515 continue; 2516 } 2517 case S_Use: 2518 SomeSuccHasSame = true; 2519 break; 2520 case S_Stop: 2521 case S_Release: 2522 case S_MovableRelease: 2523 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) 2524 AllSuccsHaveSame = false; 2525 break; 2526 case S_Retain: 2527 llvm_unreachable("bottom-up pointer in retain state!"); 2528 } 2529 } 2530 // If the state at the other end of any of the successor edges 2531 // matches the current state, require all edges to match. This 2532 // guards against loops in the middle of a sequence. 2533 if (SomeSuccHasSame && !AllSuccsHaveSame) 2534 S.ClearSequenceProgress(); 2535 break; 2536 } 2537 case S_CanRelease: { 2538 const Value *Arg = I->first; 2539 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); 2540 bool SomeSuccHasSame = false; 2541 bool AllSuccsHaveSame = true; 2542 PtrState &S = I->second; 2543 succ_const_iterator SI(TI), SE(TI, false); 2544 2545 // If the terminator is an invoke marked with the 2546 // clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be 2547 // ignored, for ARC purposes. 2548 if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) 2549 --SE; 2550 2551 for (; SI != SE; ++SI) { 2552 Sequence SuccSSeq = S_None; 2553 bool SuccSRRIKnownSafe = false; 2554 // If VisitBottomUp has pointer information for this successor, take 2555 // what we know about it. 2556 DenseMap<const BasicBlock *, BBState>::iterator BBI = 2557 BBStates.find(*SI); 2558 assert(BBI != BBStates.end()); 2559 const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg); 2560 SuccSSeq = SuccS.GetSeq(); 2561 SuccSRRIKnownSafe = SuccS.RRI.KnownSafe; 2562 switch (SuccSSeq) { 2563 case S_None: { 2564 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) { 2565 S.ClearSequenceProgress(); 2566 break; 2567 } 2568 continue; 2569 } 2570 case S_CanRelease: 2571 SomeSuccHasSame = true; 2572 break; 2573 case S_Stop: 2574 case S_Release: 2575 case S_MovableRelease: 2576 case S_Use: 2577 if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) 2578 AllSuccsHaveSame = false; 2579 break; 2580 case S_Retain: 2581 llvm_unreachable("bottom-up pointer in retain state!"); 2582 } 2583 } 2584 // If the state at the other end of any of the successor edges 2585 // matches the current state, require all edges to match. This 2586 // guards against loops in the middle of a sequence. 2587 if (SomeSuccHasSame && !AllSuccsHaveSame) 2588 S.ClearSequenceProgress(); 2589 break; 2590 } 2591 } 2592} 2593 2594bool 2595ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst, 2596 BasicBlock *BB, 2597 MapVector<Value *, RRInfo> &Retains, 2598 BBState &MyStates) { 2599 bool NestingDetected = false; 2600 InstructionClass Class = GetInstructionClass(Inst); 2601 const Value *Arg = 0; 2602 2603 switch (Class) { 2604 case IC_Release: { 2605 Arg = GetObjCArg(Inst); 2606 2607 PtrState &S = MyStates.getPtrBottomUpState(Arg); 2608 2609 // If we see two releases in a row on the same pointer. If so, make 2610 // a note, and we'll cicle back to revisit it after we've 2611 // hopefully eliminated the second release, which may allow us to 2612 // eliminate the first release too. 2613 // Theoretically we could implement removal of nested retain+release 2614 // pairs by making PtrState hold a stack of states, but this is 2615 // simple and avoids adding overhead for the non-nested case. 2616 if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) 2617 NestingDetected = true; 2618 2619 MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind); 2620 S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release); 2621 S.RRI.ReleaseMetadata = ReleaseMetadata; 2622 S.RRI.KnownSafe = S.IsKnownIncremented(); 2623 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); 2624 S.RRI.Calls.insert(Inst); 2625 2626 S.SetKnownPositiveRefCount(); 2627 break; 2628 } 2629 case IC_RetainBlock: 2630 // An objc_retainBlock call with just a use may need to be kept, 2631 // because it may be copying a block from the stack to the heap. 2632 if (!IsRetainBlockOptimizable(Inst)) 2633 break; 2634 // FALLTHROUGH 2635 case IC_Retain: 2636 case IC_RetainRV: { 2637 Arg = GetObjCArg(Inst); 2638 2639 PtrState &S = MyStates.getPtrBottomUpState(Arg); 2640 S.SetKnownPositiveRefCount(); 2641 2642 switch (S.GetSeq()) { 2643 case S_Stop: 2644 case S_Release: 2645 case S_MovableRelease: 2646 case S_Use: 2647 S.RRI.ReverseInsertPts.clear(); 2648 // FALL THROUGH 2649 case S_CanRelease: 2650 // Don't do retain+release tracking for IC_RetainRV, because it's 2651 // better to let it remain as the first instruction after a call. 2652 if (Class != IC_RetainRV) { 2653 S.RRI.IsRetainBlock = Class == IC_RetainBlock; 2654 Retains[Inst] = S.RRI; 2655 } 2656 S.ClearSequenceProgress(); 2657 break; 2658 case S_None: 2659 break; 2660 case S_Retain: 2661 llvm_unreachable("bottom-up pointer in retain state!"); 2662 } 2663 return NestingDetected; 2664 } 2665 case IC_AutoreleasepoolPop: 2666 // Conservatively, clear MyStates for all known pointers. 2667 MyStates.clearBottomUpPointers(); 2668 return NestingDetected; 2669 case IC_AutoreleasepoolPush: 2670 case IC_None: 2671 // These are irrelevant. 2672 return NestingDetected; 2673 default: 2674 break; 2675 } 2676 2677 // Consider any other possible effects of this instruction on each 2678 // pointer being tracked. 2679 for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(), 2680 ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) { 2681 const Value *Ptr = MI->first; 2682 if (Ptr == Arg) 2683 continue; // Handled above. 2684 PtrState &S = MI->second; 2685 Sequence Seq = S.GetSeq(); 2686 2687 // Check for possible releases. 2688 if (CanAlterRefCount(Inst, Ptr, PA, Class)) { 2689 S.ClearRefCount(); 2690 switch (Seq) { 2691 case S_Use: 2692 S.SetSeq(S_CanRelease); 2693 continue; 2694 case S_CanRelease: 2695 case S_Release: 2696 case S_MovableRelease: 2697 case S_Stop: 2698 case S_None: 2699 break; 2700 case S_Retain: 2701 llvm_unreachable("bottom-up pointer in retain state!"); 2702 } 2703 } 2704 2705 // Check for possible direct uses. 2706 switch (Seq) { 2707 case S_Release: 2708 case S_MovableRelease: 2709 if (CanUse(Inst, Ptr, PA, Class)) { 2710 assert(S.RRI.ReverseInsertPts.empty()); 2711 // If this is an invoke instruction, we're scanning it as part of 2712 // one of its successor blocks, since we can't insert code after it 2713 // in its own block, and we don't want to split critical edges. 2714 if (isa<InvokeInst>(Inst)) 2715 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt()); 2716 else 2717 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst))); 2718 S.SetSeq(S_Use); 2719 } else if (Seq == S_Release && 2720 (Class == IC_User || Class == IC_CallOrUser)) { 2721 // Non-movable releases depend on any possible objc pointer use. 2722 S.SetSeq(S_Stop); 2723 assert(S.RRI.ReverseInsertPts.empty()); 2724 // As above; handle invoke specially. 2725 if (isa<InvokeInst>(Inst)) 2726 S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt()); 2727 else 2728 S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst))); 2729 } 2730 break; 2731 case S_Stop: 2732 if (CanUse(Inst, Ptr, PA, Class)) 2733 S.SetSeq(S_Use); 2734 break; 2735 case S_CanRelease: 2736 case S_Use: 2737 case S_None: 2738 break; 2739 case S_Retain: 2740 llvm_unreachable("bottom-up pointer in retain state!"); 2741 } 2742 } 2743 2744 return NestingDetected; 2745} 2746 2747bool 2748ObjCARCOpt::VisitBottomUp(BasicBlock *BB, 2749 DenseMap<const BasicBlock *, BBState> &BBStates, 2750 MapVector<Value *, RRInfo> &Retains) { 2751 bool NestingDetected = false; 2752 BBState &MyStates = BBStates[BB]; 2753 2754 // Merge the states from each successor to compute the initial state 2755 // for the current block. 2756 BBState::edge_iterator SI(MyStates.succ_begin()), 2757 SE(MyStates.succ_end()); 2758 if (SI != SE) { 2759 const BasicBlock *Succ = *SI; 2760 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ); 2761 assert(I != BBStates.end()); 2762 MyStates.InitFromSucc(I->second); 2763 ++SI; 2764 for (; SI != SE; ++SI) { 2765 Succ = *SI; 2766 I = BBStates.find(Succ); 2767 assert(I != BBStates.end()); 2768 MyStates.MergeSucc(I->second); 2769 } 2770 } 2771 2772 // Visit all the instructions, bottom-up. 2773 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) { 2774 Instruction *Inst = llvm::prior(I); 2775 2776 // Invoke instructions are visited as part of their successors (below). 2777 if (isa<InvokeInst>(Inst)) 2778 continue; 2779 2780 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates); 2781 } 2782 2783 // If there's a predecessor with an invoke, visit the invoke as if it were 2784 // part of this block, since we can't insert code after an invoke in its own 2785 // block, and we don't want to split critical edges. 2786 for (BBState::edge_iterator PI(MyStates.pred_begin()), 2787 PE(MyStates.pred_end()); PI != PE; ++PI) { 2788 BasicBlock *Pred = *PI; 2789 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back())) 2790 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates); 2791 } 2792 2793 return NestingDetected; 2794} 2795 2796bool 2797ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst, 2798 DenseMap<Value *, RRInfo> &Releases, 2799 BBState &MyStates) { 2800 bool NestingDetected = false; 2801 InstructionClass Class = GetInstructionClass(Inst); 2802 const Value *Arg = 0; 2803 2804 switch (Class) { 2805 case IC_RetainBlock: 2806 // An objc_retainBlock call with just a use may need to be kept, 2807 // because it may be copying a block from the stack to the heap. 2808 if (!IsRetainBlockOptimizable(Inst)) 2809 break; 2810 // FALLTHROUGH 2811 case IC_Retain: 2812 case IC_RetainRV: { 2813 Arg = GetObjCArg(Inst); 2814 2815 PtrState &S = MyStates.getPtrTopDownState(Arg); 2816 2817 // Don't do retain+release tracking for IC_RetainRV, because it's 2818 // better to let it remain as the first instruction after a call. 2819 if (Class != IC_RetainRV) { 2820 // If we see two retains in a row on the same pointer. If so, make 2821 // a note, and we'll cicle back to revisit it after we've 2822 // hopefully eliminated the second retain, which may allow us to 2823 // eliminate the first retain too. 2824 // Theoretically we could implement removal of nested retain+release 2825 // pairs by making PtrState hold a stack of states, but this is 2826 // simple and avoids adding overhead for the non-nested case. 2827 if (S.GetSeq() == S_Retain) 2828 NestingDetected = true; 2829 2830 S.ResetSequenceProgress(S_Retain); 2831 S.RRI.IsRetainBlock = Class == IC_RetainBlock; 2832 S.RRI.KnownSafe = S.IsKnownIncremented(); 2833 S.RRI.Calls.insert(Inst); 2834 } 2835 2836 S.SetKnownPositiveRefCount(); 2837 2838 // A retain can be a potential use; procede to the generic checking 2839 // code below. 2840 break; 2841 } 2842 case IC_Release: { 2843 Arg = GetObjCArg(Inst); 2844 2845 PtrState &S = MyStates.getPtrTopDownState(Arg); 2846 S.ClearRefCount(); 2847 2848 switch (S.GetSeq()) { 2849 case S_Retain: 2850 case S_CanRelease: 2851 S.RRI.ReverseInsertPts.clear(); 2852 // FALL THROUGH 2853 case S_Use: 2854 S.RRI.ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind); 2855 S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); 2856 Releases[Inst] = S.RRI; 2857 S.ClearSequenceProgress(); 2858 break; 2859 case S_None: 2860 break; 2861 case S_Stop: 2862 case S_Release: 2863 case S_MovableRelease: 2864 llvm_unreachable("top-down pointer in release state!"); 2865 } 2866 break; 2867 } 2868 case IC_AutoreleasepoolPop: 2869 // Conservatively, clear MyStates for all known pointers. 2870 MyStates.clearTopDownPointers(); 2871 return NestingDetected; 2872 case IC_AutoreleasepoolPush: 2873 case IC_None: 2874 // These are irrelevant. 2875 return NestingDetected; 2876 default: 2877 break; 2878 } 2879 2880 // Consider any other possible effects of this instruction on each 2881 // pointer being tracked. 2882 for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(), 2883 ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) { 2884 const Value *Ptr = MI->first; 2885 if (Ptr == Arg) 2886 continue; // Handled above. 2887 PtrState &S = MI->second; 2888 Sequence Seq = S.GetSeq(); 2889 2890 // Check for possible releases. 2891 if (CanAlterRefCount(Inst, Ptr, PA, Class)) { 2892 S.ClearRefCount(); 2893 switch (Seq) { 2894 case S_Retain: 2895 S.SetSeq(S_CanRelease); 2896 assert(S.RRI.ReverseInsertPts.empty()); 2897 S.RRI.ReverseInsertPts.insert(Inst); 2898 2899 // One call can't cause a transition from S_Retain to S_CanRelease 2900 // and S_CanRelease to S_Use. If we've made the first transition, 2901 // we're done. 2902 continue; 2903 case S_Use: 2904 case S_CanRelease: 2905 case S_None: 2906 break; 2907 case S_Stop: 2908 case S_Release: 2909 case S_MovableRelease: 2910 llvm_unreachable("top-down pointer in release state!"); 2911 } 2912 } 2913 2914 // Check for possible direct uses. 2915 switch (Seq) { 2916 case S_CanRelease: 2917 if (CanUse(Inst, Ptr, PA, Class)) 2918 S.SetSeq(S_Use); 2919 break; 2920 case S_Retain: 2921 case S_Use: 2922 case S_None: 2923 break; 2924 case S_Stop: 2925 case S_Release: 2926 case S_MovableRelease: 2927 llvm_unreachable("top-down pointer in release state!"); 2928 } 2929 } 2930 2931 return NestingDetected; 2932} 2933 2934bool 2935ObjCARCOpt::VisitTopDown(BasicBlock *BB, 2936 DenseMap<const BasicBlock *, BBState> &BBStates, 2937 DenseMap<Value *, RRInfo> &Releases) { 2938 bool NestingDetected = false; 2939 BBState &MyStates = BBStates[BB]; 2940 2941 // Merge the states from each predecessor to compute the initial state 2942 // for the current block. 2943 BBState::edge_iterator PI(MyStates.pred_begin()), 2944 PE(MyStates.pred_end()); 2945 if (PI != PE) { 2946 const BasicBlock *Pred = *PI; 2947 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred); 2948 assert(I != BBStates.end()); 2949 MyStates.InitFromPred(I->second); 2950 ++PI; 2951 for (; PI != PE; ++PI) { 2952 Pred = *PI; 2953 I = BBStates.find(Pred); 2954 assert(I != BBStates.end()); 2955 MyStates.MergePred(I->second); 2956 } 2957 } 2958 2959 // Visit all the instructions, top-down. 2960 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 2961 Instruction *Inst = I; 2962 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates); 2963 } 2964 2965 CheckForCFGHazards(BB, BBStates, MyStates); 2966 return NestingDetected; 2967} 2968 2969static void 2970ComputePostOrders(Function &F, 2971 SmallVectorImpl<BasicBlock *> &PostOrder, 2972 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder, 2973 unsigned NoObjCARCExceptionsMDKind, 2974 DenseMap<const BasicBlock *, BBState> &BBStates) { 2975 /// Visited - The visited set, for doing DFS walks. 2976 SmallPtrSet<BasicBlock *, 16> Visited; 2977 2978 // Do DFS, computing the PostOrder. 2979 SmallPtrSet<BasicBlock *, 16> OnStack; 2980 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack; 2981 2982 // Functions always have exactly one entry block, and we don't have 2983 // any other block that we treat like an entry block. 2984 BasicBlock *EntryBB = &F.getEntryBlock(); 2985 BBState &MyStates = BBStates[EntryBB]; 2986 MyStates.SetAsEntry(); 2987 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back()); 2988 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI))); 2989 Visited.insert(EntryBB); 2990 OnStack.insert(EntryBB); 2991 do { 2992 dfs_next_succ: 2993 BasicBlock *CurrBB = SuccStack.back().first; 2994 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back()); 2995 succ_iterator SE(TI, false); 2996 2997 // If the terminator is an invoke marked with the 2998 // clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be 2999 // ignored, for ARC purposes. 3000 if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) 3001 --SE; 3002 3003 while (SuccStack.back().second != SE) { 3004 BasicBlock *SuccBB = *SuccStack.back().second++; 3005 if (Visited.insert(SuccBB)) { 3006 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back()); 3007 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI))); 3008 BBStates[CurrBB].addSucc(SuccBB); 3009 BBState &SuccStates = BBStates[SuccBB]; 3010 SuccStates.addPred(CurrBB); 3011 OnStack.insert(SuccBB); 3012 goto dfs_next_succ; 3013 } 3014 3015 if (!OnStack.count(SuccBB)) { 3016 BBStates[CurrBB].addSucc(SuccBB); 3017 BBStates[SuccBB].addPred(CurrBB); 3018 } 3019 } 3020 OnStack.erase(CurrBB); 3021 PostOrder.push_back(CurrBB); 3022 SuccStack.pop_back(); 3023 } while (!SuccStack.empty()); 3024 3025 Visited.clear(); 3026 3027 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder. 3028 // Functions may have many exits, and there also blocks which we treat 3029 // as exits due to ignored edges. 3030 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack; 3031 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { 3032 BasicBlock *ExitBB = I; 3033 BBState &MyStates = BBStates[ExitBB]; 3034 if (!MyStates.isExit()) 3035 continue; 3036 3037 MyStates.SetAsExit(); 3038 3039 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin())); 3040 Visited.insert(ExitBB); 3041 while (!PredStack.empty()) { 3042 reverse_dfs_next_succ: 3043 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end(); 3044 while (PredStack.back().second != PE) { 3045 BasicBlock *BB = *PredStack.back().second++; 3046 if (Visited.insert(BB)) { 3047 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin())); 3048 goto reverse_dfs_next_succ; 3049 } 3050 } 3051 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first); 3052 } 3053 } 3054} 3055 3056// Visit - Visit the function both top-down and bottom-up. 3057bool 3058ObjCARCOpt::Visit(Function &F, 3059 DenseMap<const BasicBlock *, BBState> &BBStates, 3060 MapVector<Value *, RRInfo> &Retains, 3061 DenseMap<Value *, RRInfo> &Releases) { 3062 3063 // Use reverse-postorder traversals, because we magically know that loops 3064 // will be well behaved, i.e. they won't repeatedly call retain on a single 3065 // pointer without doing a release. We can't use the ReversePostOrderTraversal 3066 // class here because we want the reverse-CFG postorder to consider each 3067 // function exit point, and we want to ignore selected cycle edges. 3068 SmallVector<BasicBlock *, 16> PostOrder; 3069 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder; 3070 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder, 3071 NoObjCARCExceptionsMDKind, 3072 BBStates); 3073 3074 // Use reverse-postorder on the reverse CFG for bottom-up. 3075 bool BottomUpNestingDetected = false; 3076 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I = 3077 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend(); 3078 I != E; ++I) 3079 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains); 3080 3081 // Use reverse-postorder for top-down. 3082 bool TopDownNestingDetected = false; 3083 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I = 3084 PostOrder.rbegin(), E = PostOrder.rend(); 3085 I != E; ++I) 3086 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases); 3087 3088 return TopDownNestingDetected && BottomUpNestingDetected; 3089} 3090 3091/// MoveCalls - Move the calls in RetainsToMove and ReleasesToMove. 3092void ObjCARCOpt::MoveCalls(Value *Arg, 3093 RRInfo &RetainsToMove, 3094 RRInfo &ReleasesToMove, 3095 MapVector<Value *, RRInfo> &Retains, 3096 DenseMap<Value *, RRInfo> &Releases, 3097 SmallVectorImpl<Instruction *> &DeadInsts, 3098 Module *M) { 3099 Type *ArgTy = Arg->getType(); 3100 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext())); 3101 3102 // Insert the new retain and release calls. 3103 for (SmallPtrSet<Instruction *, 2>::const_iterator 3104 PI = ReleasesToMove.ReverseInsertPts.begin(), 3105 PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) { 3106 Instruction *InsertPt = *PI; 3107 Value *MyArg = ArgTy == ParamTy ? Arg : 3108 new BitCastInst(Arg, ParamTy, "", InsertPt); 3109 CallInst *Call = 3110 CallInst::Create(RetainsToMove.IsRetainBlock ? 3111 getRetainBlockCallee(M) : getRetainCallee(M), 3112 MyArg, "", InsertPt); 3113 Call->setDoesNotThrow(); 3114 if (RetainsToMove.IsRetainBlock) 3115 Call->setMetadata(CopyOnEscapeMDKind, 3116 MDNode::get(M->getContext(), ArrayRef<Value *>())); 3117 else 3118 Call->setTailCall(); 3119 } 3120 for (SmallPtrSet<Instruction *, 2>::const_iterator 3121 PI = RetainsToMove.ReverseInsertPts.begin(), 3122 PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) { 3123 Instruction *InsertPt = *PI; 3124 Value *MyArg = ArgTy == ParamTy ? Arg : 3125 new BitCastInst(Arg, ParamTy, "", InsertPt); 3126 CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg, 3127 "", InsertPt); 3128 // Attach a clang.imprecise_release metadata tag, if appropriate. 3129 if (MDNode *M = ReleasesToMove.ReleaseMetadata) 3130 Call->setMetadata(ImpreciseReleaseMDKind, M); 3131 Call->setDoesNotThrow(); 3132 if (ReleasesToMove.IsTailCallRelease) 3133 Call->setTailCall(); 3134 } 3135 3136 // Delete the original retain and release calls. 3137 for (SmallPtrSet<Instruction *, 2>::const_iterator 3138 AI = RetainsToMove.Calls.begin(), 3139 AE = RetainsToMove.Calls.end(); AI != AE; ++AI) { 3140 Instruction *OrigRetain = *AI; 3141 Retains.blot(OrigRetain); 3142 DeadInsts.push_back(OrigRetain); 3143 } 3144 for (SmallPtrSet<Instruction *, 2>::const_iterator 3145 AI = ReleasesToMove.Calls.begin(), 3146 AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) { 3147 Instruction *OrigRelease = *AI; 3148 Releases.erase(OrigRelease); 3149 DeadInsts.push_back(OrigRelease); 3150 } 3151} 3152 3153/// PerformCodePlacement - Identify pairings between the retains and releases, 3154/// and delete and/or move them. 3155bool 3156ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState> 3157 &BBStates, 3158 MapVector<Value *, RRInfo> &Retains, 3159 DenseMap<Value *, RRInfo> &Releases, 3160 Module *M) { 3161 bool AnyPairsCompletelyEliminated = false; 3162 RRInfo RetainsToMove; 3163 RRInfo ReleasesToMove; 3164 SmallVector<Instruction *, 4> NewRetains; 3165 SmallVector<Instruction *, 4> NewReleases; 3166 SmallVector<Instruction *, 8> DeadInsts; 3167 3168 // Visit each retain. 3169 for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(), 3170 E = Retains.end(); I != E; ++I) { 3171 Value *V = I->first; 3172 if (!V) continue; // blotted 3173 3174 Instruction *Retain = cast<Instruction>(V); 3175 Value *Arg = GetObjCArg(Retain); 3176 3177 // If the object being released is in static or stack storage, we know it's 3178 // not being managed by ObjC reference counting, so we can delete pairs 3179 // regardless of what possible decrements or uses lie between them. 3180 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg); 3181 3182 // A constant pointer can't be pointing to an object on the heap. It may 3183 // be reference-counted, but it won't be deleted. 3184 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg)) 3185 if (const GlobalVariable *GV = 3186 dyn_cast<GlobalVariable>( 3187 StripPointerCastsAndObjCCalls(LI->getPointerOperand()))) 3188 if (GV->isConstant()) 3189 KnownSafe = true; 3190 3191 // If a pair happens in a region where it is known that the reference count 3192 // is already incremented, we can similarly ignore possible decrements. 3193 bool KnownSafeTD = true, KnownSafeBU = true; 3194 3195 // Connect the dots between the top-down-collected RetainsToMove and 3196 // bottom-up-collected ReleasesToMove to form sets of related calls. 3197 // This is an iterative process so that we connect multiple releases 3198 // to multiple retains if needed. 3199 unsigned OldDelta = 0; 3200 unsigned NewDelta = 0; 3201 unsigned OldCount = 0; 3202 unsigned NewCount = 0; 3203 bool FirstRelease = true; 3204 bool FirstRetain = true; 3205 NewRetains.push_back(Retain); 3206 for (;;) { 3207 for (SmallVectorImpl<Instruction *>::const_iterator 3208 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) { 3209 Instruction *NewRetain = *NI; 3210 MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain); 3211 assert(It != Retains.end()); 3212 const RRInfo &NewRetainRRI = It->second; 3213 KnownSafeTD &= NewRetainRRI.KnownSafe; 3214 for (SmallPtrSet<Instruction *, 2>::const_iterator 3215 LI = NewRetainRRI.Calls.begin(), 3216 LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) { 3217 Instruction *NewRetainRelease = *LI; 3218 DenseMap<Value *, RRInfo>::const_iterator Jt = 3219 Releases.find(NewRetainRelease); 3220 if (Jt == Releases.end()) 3221 goto next_retain; 3222 const RRInfo &NewRetainReleaseRRI = Jt->second; 3223 assert(NewRetainReleaseRRI.Calls.count(NewRetain)); 3224 if (ReleasesToMove.Calls.insert(NewRetainRelease)) { 3225 OldDelta -= 3226 BBStates[NewRetainRelease->getParent()].GetAllPathCount(); 3227 3228 // Merge the ReleaseMetadata and IsTailCallRelease values. 3229 if (FirstRelease) { 3230 ReleasesToMove.ReleaseMetadata = 3231 NewRetainReleaseRRI.ReleaseMetadata; 3232 ReleasesToMove.IsTailCallRelease = 3233 NewRetainReleaseRRI.IsTailCallRelease; 3234 FirstRelease = false; 3235 } else { 3236 if (ReleasesToMove.ReleaseMetadata != 3237 NewRetainReleaseRRI.ReleaseMetadata) 3238 ReleasesToMove.ReleaseMetadata = 0; 3239 if (ReleasesToMove.IsTailCallRelease != 3240 NewRetainReleaseRRI.IsTailCallRelease) 3241 ReleasesToMove.IsTailCallRelease = false; 3242 } 3243 3244 // Collect the optimal insertion points. 3245 if (!KnownSafe) 3246 for (SmallPtrSet<Instruction *, 2>::const_iterator 3247 RI = NewRetainReleaseRRI.ReverseInsertPts.begin(), 3248 RE = NewRetainReleaseRRI.ReverseInsertPts.end(); 3249 RI != RE; ++RI) { 3250 Instruction *RIP = *RI; 3251 if (ReleasesToMove.ReverseInsertPts.insert(RIP)) 3252 NewDelta -= BBStates[RIP->getParent()].GetAllPathCount(); 3253 } 3254 NewReleases.push_back(NewRetainRelease); 3255 } 3256 } 3257 } 3258 NewRetains.clear(); 3259 if (NewReleases.empty()) break; 3260 3261 // Back the other way. 3262 for (SmallVectorImpl<Instruction *>::const_iterator 3263 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) { 3264 Instruction *NewRelease = *NI; 3265 DenseMap<Value *, RRInfo>::const_iterator It = 3266 Releases.find(NewRelease); 3267 assert(It != Releases.end()); 3268 const RRInfo &NewReleaseRRI = It->second; 3269 KnownSafeBU &= NewReleaseRRI.KnownSafe; 3270 for (SmallPtrSet<Instruction *, 2>::const_iterator 3271 LI = NewReleaseRRI.Calls.begin(), 3272 LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) { 3273 Instruction *NewReleaseRetain = *LI; 3274 MapVector<Value *, RRInfo>::const_iterator Jt = 3275 Retains.find(NewReleaseRetain); 3276 if (Jt == Retains.end()) 3277 goto next_retain; 3278 const RRInfo &NewReleaseRetainRRI = Jt->second; 3279 assert(NewReleaseRetainRRI.Calls.count(NewRelease)); 3280 if (RetainsToMove.Calls.insert(NewReleaseRetain)) { 3281 unsigned PathCount = 3282 BBStates[NewReleaseRetain->getParent()].GetAllPathCount(); 3283 OldDelta += PathCount; 3284 OldCount += PathCount; 3285 3286 // Merge the IsRetainBlock values. 3287 if (FirstRetain) { 3288 RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock; 3289 FirstRetain = false; 3290 } else if (ReleasesToMove.IsRetainBlock != 3291 NewReleaseRetainRRI.IsRetainBlock) 3292 // It's not possible to merge the sequences if one uses 3293 // objc_retain and the other uses objc_retainBlock. 3294 goto next_retain; 3295 3296 // Collect the optimal insertion points. 3297 if (!KnownSafe) 3298 for (SmallPtrSet<Instruction *, 2>::const_iterator 3299 RI = NewReleaseRetainRRI.ReverseInsertPts.begin(), 3300 RE = NewReleaseRetainRRI.ReverseInsertPts.end(); 3301 RI != RE; ++RI) { 3302 Instruction *RIP = *RI; 3303 if (RetainsToMove.ReverseInsertPts.insert(RIP)) { 3304 PathCount = BBStates[RIP->getParent()].GetAllPathCount(); 3305 NewDelta += PathCount; 3306 NewCount += PathCount; 3307 } 3308 } 3309 NewRetains.push_back(NewReleaseRetain); 3310 } 3311 } 3312 } 3313 NewReleases.clear(); 3314 if (NewRetains.empty()) break; 3315 } 3316 3317 // If the pointer is known incremented or nested, we can safely delete the 3318 // pair regardless of what's between them. 3319 if (KnownSafeTD || KnownSafeBU) { 3320 RetainsToMove.ReverseInsertPts.clear(); 3321 ReleasesToMove.ReverseInsertPts.clear(); 3322 NewCount = 0; 3323 } else { 3324 // Determine whether the new insertion points we computed preserve the 3325 // balance of retain and release calls through the program. 3326 // TODO: If the fully aggressive solution isn't valid, try to find a 3327 // less aggressive solution which is. 3328 if (NewDelta != 0) 3329 goto next_retain; 3330 } 3331 3332 // Determine whether the original call points are balanced in the retain and 3333 // release calls through the program. If not, conservatively don't touch 3334 // them. 3335 // TODO: It's theoretically possible to do code motion in this case, as 3336 // long as the existing imbalances are maintained. 3337 if (OldDelta != 0) 3338 goto next_retain; 3339 3340 // Ok, everything checks out and we're all set. Let's move some code! 3341 Changed = true; 3342 assert(OldCount != 0 && "Unreachable code?"); 3343 AnyPairsCompletelyEliminated = NewCount == 0; 3344 NumRRs += OldCount - NewCount; 3345 MoveCalls(Arg, RetainsToMove, ReleasesToMove, 3346 Retains, Releases, DeadInsts, M); 3347 3348 next_retain: 3349 NewReleases.clear(); 3350 NewRetains.clear(); 3351 RetainsToMove.clear(); 3352 ReleasesToMove.clear(); 3353 } 3354 3355 // Now that we're done moving everything, we can delete the newly dead 3356 // instructions, as we no longer need them as insert points. 3357 while (!DeadInsts.empty()) 3358 EraseInstruction(DeadInsts.pop_back_val()); 3359 3360 return AnyPairsCompletelyEliminated; 3361} 3362 3363/// OptimizeWeakCalls - Weak pointer optimizations. 3364void ObjCARCOpt::OptimizeWeakCalls(Function &F) { 3365 // First, do memdep-style RLE and S2L optimizations. We can't use memdep 3366 // itself because it uses AliasAnalysis and we need to do provenance 3367 // queries instead. 3368 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 3369 Instruction *Inst = &*I++; 3370 InstructionClass Class = GetBasicInstructionClass(Inst); 3371 if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained) 3372 continue; 3373 3374 // Delete objc_loadWeak calls with no users. 3375 if (Class == IC_LoadWeak && Inst->use_empty()) { 3376 Inst->eraseFromParent(); 3377 continue; 3378 } 3379 3380 // TODO: For now, just look for an earlier available version of this value 3381 // within the same block. Theoretically, we could do memdep-style non-local 3382 // analysis too, but that would want caching. A better approach would be to 3383 // use the technique that EarlyCSE uses. 3384 inst_iterator Current = llvm::prior(I); 3385 BasicBlock *CurrentBB = Current.getBasicBlockIterator(); 3386 for (BasicBlock::iterator B = CurrentBB->begin(), 3387 J = Current.getInstructionIterator(); 3388 J != B; --J) { 3389 Instruction *EarlierInst = &*llvm::prior(J); 3390 InstructionClass EarlierClass = GetInstructionClass(EarlierInst); 3391 switch (EarlierClass) { 3392 case IC_LoadWeak: 3393 case IC_LoadWeakRetained: { 3394 // If this is loading from the same pointer, replace this load's value 3395 // with that one. 3396 CallInst *Call = cast<CallInst>(Inst); 3397 CallInst *EarlierCall = cast<CallInst>(EarlierInst); 3398 Value *Arg = Call->getArgOperand(0); 3399 Value *EarlierArg = EarlierCall->getArgOperand(0); 3400 switch (PA.getAA()->alias(Arg, EarlierArg)) { 3401 case AliasAnalysis::MustAlias: 3402 Changed = true; 3403 // If the load has a builtin retain, insert a plain retain for it. 3404 if (Class == IC_LoadWeakRetained) { 3405 CallInst *CI = 3406 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, 3407 "", Call); 3408 CI->setTailCall(); 3409 } 3410 // Zap the fully redundant load. 3411 Call->replaceAllUsesWith(EarlierCall); 3412 Call->eraseFromParent(); 3413 goto clobbered; 3414 case AliasAnalysis::MayAlias: 3415 case AliasAnalysis::PartialAlias: 3416 goto clobbered; 3417 case AliasAnalysis::NoAlias: 3418 break; 3419 } 3420 break; 3421 } 3422 case IC_StoreWeak: 3423 case IC_InitWeak: { 3424 // If this is storing to the same pointer and has the same size etc. 3425 // replace this load's value with the stored value. 3426 CallInst *Call = cast<CallInst>(Inst); 3427 CallInst *EarlierCall = cast<CallInst>(EarlierInst); 3428 Value *Arg = Call->getArgOperand(0); 3429 Value *EarlierArg = EarlierCall->getArgOperand(0); 3430 switch (PA.getAA()->alias(Arg, EarlierArg)) { 3431 case AliasAnalysis::MustAlias: 3432 Changed = true; 3433 // If the load has a builtin retain, insert a plain retain for it. 3434 if (Class == IC_LoadWeakRetained) { 3435 CallInst *CI = 3436 CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, 3437 "", Call); 3438 CI->setTailCall(); 3439 } 3440 // Zap the fully redundant load. 3441 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1)); 3442 Call->eraseFromParent(); 3443 goto clobbered; 3444 case AliasAnalysis::MayAlias: 3445 case AliasAnalysis::PartialAlias: 3446 goto clobbered; 3447 case AliasAnalysis::NoAlias: 3448 break; 3449 } 3450 break; 3451 } 3452 case IC_MoveWeak: 3453 case IC_CopyWeak: 3454 // TOOD: Grab the copied value. 3455 goto clobbered; 3456 case IC_AutoreleasepoolPush: 3457 case IC_None: 3458 case IC_User: 3459 // Weak pointers are only modified through the weak entry points 3460 // (and arbitrary calls, which could call the weak entry points). 3461 break; 3462 default: 3463 // Anything else could modify the weak pointer. 3464 goto clobbered; 3465 } 3466 } 3467 clobbered:; 3468 } 3469 3470 // Then, for each destroyWeak with an alloca operand, check to see if 3471 // the alloca and all its users can be zapped. 3472 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 3473 Instruction *Inst = &*I++; 3474 InstructionClass Class = GetBasicInstructionClass(Inst); 3475 if (Class != IC_DestroyWeak) 3476 continue; 3477 3478 CallInst *Call = cast<CallInst>(Inst); 3479 Value *Arg = Call->getArgOperand(0); 3480 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) { 3481 for (Value::use_iterator UI = Alloca->use_begin(), 3482 UE = Alloca->use_end(); UI != UE; ++UI) { 3483 const Instruction *UserInst = cast<Instruction>(*UI); 3484 switch (GetBasicInstructionClass(UserInst)) { 3485 case IC_InitWeak: 3486 case IC_StoreWeak: 3487 case IC_DestroyWeak: 3488 continue; 3489 default: 3490 goto done; 3491 } 3492 } 3493 Changed = true; 3494 for (Value::use_iterator UI = Alloca->use_begin(), 3495 UE = Alloca->use_end(); UI != UE; ) { 3496 CallInst *UserInst = cast<CallInst>(*UI++); 3497 switch (GetBasicInstructionClass(UserInst)) { 3498 case IC_InitWeak: 3499 case IC_StoreWeak: 3500 // These functions return their second argument. 3501 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1)); 3502 break; 3503 case IC_DestroyWeak: 3504 // No return value. 3505 break; 3506 default: 3507 llvm_unreachable("alloca really is used!"); 3508 } 3509 UserInst->eraseFromParent(); 3510 } 3511 Alloca->eraseFromParent(); 3512 done:; 3513 } 3514 } 3515} 3516 3517/// OptimizeSequences - Identify program paths which execute sequences of 3518/// retains and releases which can be eliminated. 3519bool ObjCARCOpt::OptimizeSequences(Function &F) { 3520 /// Releases, Retains - These are used to store the results of the main flow 3521 /// analysis. These use Value* as the key instead of Instruction* so that the 3522 /// map stays valid when we get around to rewriting code and calls get 3523 /// replaced by arguments. 3524 DenseMap<Value *, RRInfo> Releases; 3525 MapVector<Value *, RRInfo> Retains; 3526 3527 /// BBStates, This is used during the traversal of the function to track the 3528 /// states for each identified object at each block. 3529 DenseMap<const BasicBlock *, BBState> BBStates; 3530 3531 // Analyze the CFG of the function, and all instructions. 3532 bool NestingDetected = Visit(F, BBStates, Retains, Releases); 3533 3534 // Transform. 3535 return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) && 3536 NestingDetected; 3537} 3538 3539/// OptimizeReturns - Look for this pattern: 3540/// 3541/// %call = call i8* @something(...) 3542/// %2 = call i8* @objc_retain(i8* %call) 3543/// %3 = call i8* @objc_autorelease(i8* %2) 3544/// ret i8* %3 3545/// 3546/// And delete the retain and autorelease. 3547/// 3548/// Otherwise if it's just this: 3549/// 3550/// %3 = call i8* @objc_autorelease(i8* %2) 3551/// ret i8* %3 3552/// 3553/// convert the autorelease to autoreleaseRV. 3554void ObjCARCOpt::OptimizeReturns(Function &F) { 3555 if (!F.getReturnType()->isPointerTy()) 3556 return; 3557 3558 SmallPtrSet<Instruction *, 4> DependingInstructions; 3559 SmallPtrSet<const BasicBlock *, 4> Visited; 3560 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { 3561 BasicBlock *BB = FI; 3562 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back()); 3563 if (!Ret) continue; 3564 3565 const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0)); 3566 FindDependencies(NeedsPositiveRetainCount, Arg, 3567 BB, Ret, DependingInstructions, Visited, PA); 3568 if (DependingInstructions.size() != 1) 3569 goto next_block; 3570 3571 { 3572 CallInst *Autorelease = 3573 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3574 if (!Autorelease) 3575 goto next_block; 3576 InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease); 3577 if (!IsAutorelease(AutoreleaseClass)) 3578 goto next_block; 3579 if (GetObjCArg(Autorelease) != Arg) 3580 goto next_block; 3581 3582 DependingInstructions.clear(); 3583 Visited.clear(); 3584 3585 // Check that there is nothing that can affect the reference 3586 // count between the autorelease and the retain. 3587 FindDependencies(CanChangeRetainCount, Arg, 3588 BB, Autorelease, DependingInstructions, Visited, PA); 3589 if (DependingInstructions.size() != 1) 3590 goto next_block; 3591 3592 { 3593 CallInst *Retain = 3594 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3595 3596 // Check that we found a retain with the same argument. 3597 if (!Retain || 3598 !IsRetain(GetBasicInstructionClass(Retain)) || 3599 GetObjCArg(Retain) != Arg) 3600 goto next_block; 3601 3602 DependingInstructions.clear(); 3603 Visited.clear(); 3604 3605 // Convert the autorelease to an autoreleaseRV, since it's 3606 // returning the value. 3607 if (AutoreleaseClass == IC_Autorelease) { 3608 Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent())); 3609 AutoreleaseClass = IC_AutoreleaseRV; 3610 } 3611 3612 // Check that there is nothing that can affect the reference 3613 // count between the retain and the call. 3614 // Note that Retain need not be in BB. 3615 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain, 3616 DependingInstructions, Visited, PA); 3617 if (DependingInstructions.size() != 1) 3618 goto next_block; 3619 3620 { 3621 CallInst *Call = 3622 dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3623 3624 // Check that the pointer is the return value of the call. 3625 if (!Call || Arg != Call) 3626 goto next_block; 3627 3628 // Check that the call is a regular call. 3629 InstructionClass Class = GetBasicInstructionClass(Call); 3630 if (Class != IC_CallOrUser && Class != IC_Call) 3631 goto next_block; 3632 3633 // If so, we can zap the retain and autorelease. 3634 Changed = true; 3635 ++NumRets; 3636 EraseInstruction(Retain); 3637 EraseInstruction(Autorelease); 3638 } 3639 } 3640 } 3641 3642 next_block: 3643 DependingInstructions.clear(); 3644 Visited.clear(); 3645 } 3646} 3647 3648bool ObjCARCOpt::doInitialization(Module &M) { 3649 if (!EnableARCOpts) 3650 return false; 3651 3652 // If nothing in the Module uses ARC, don't do anything. 3653 Run = ModuleHasARC(M); 3654 if (!Run) 3655 return false; 3656 3657 // Identify the imprecise release metadata kind. 3658 ImpreciseReleaseMDKind = 3659 M.getContext().getMDKindID("clang.imprecise_release"); 3660 CopyOnEscapeMDKind = 3661 M.getContext().getMDKindID("clang.arc.copy_on_escape"); 3662 NoObjCARCExceptionsMDKind = 3663 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions"); 3664 3665 // Intuitively, objc_retain and others are nocapture, however in practice 3666 // they are not, because they return their argument value. And objc_release 3667 // calls finalizers which can have arbitrary side effects. 3668 3669 // These are initialized lazily. 3670 RetainRVCallee = 0; 3671 AutoreleaseRVCallee = 0; 3672 ReleaseCallee = 0; 3673 RetainCallee = 0; 3674 RetainBlockCallee = 0; 3675 AutoreleaseCallee = 0; 3676 3677 return false; 3678} 3679 3680bool ObjCARCOpt::runOnFunction(Function &F) { 3681 if (!EnableARCOpts) 3682 return false; 3683 3684 // If nothing in the Module uses ARC, don't do anything. 3685 if (!Run) 3686 return false; 3687 3688 Changed = false; 3689 3690 PA.setAA(&getAnalysis<AliasAnalysis>()); 3691 3692 // This pass performs several distinct transformations. As a compile-time aid 3693 // when compiling code that isn't ObjC, skip these if the relevant ObjC 3694 // library functions aren't declared. 3695 3696 // Preliminary optimizations. This also computs UsedInThisFunction. 3697 OptimizeIndividualCalls(F); 3698 3699 // Optimizations for weak pointers. 3700 if (UsedInThisFunction & ((1 << IC_LoadWeak) | 3701 (1 << IC_LoadWeakRetained) | 3702 (1 << IC_StoreWeak) | 3703 (1 << IC_InitWeak) | 3704 (1 << IC_CopyWeak) | 3705 (1 << IC_MoveWeak) | 3706 (1 << IC_DestroyWeak))) 3707 OptimizeWeakCalls(F); 3708 3709 // Optimizations for retain+release pairs. 3710 if (UsedInThisFunction & ((1 << IC_Retain) | 3711 (1 << IC_RetainRV) | 3712 (1 << IC_RetainBlock))) 3713 if (UsedInThisFunction & (1 << IC_Release)) 3714 // Run OptimizeSequences until it either stops making changes or 3715 // no retain+release pair nesting is detected. 3716 while (OptimizeSequences(F)) {} 3717 3718 // Optimizations if objc_autorelease is used. 3719 if (UsedInThisFunction & ((1 << IC_Autorelease) | 3720 (1 << IC_AutoreleaseRV))) 3721 OptimizeReturns(F); 3722 3723 return Changed; 3724} 3725 3726void ObjCARCOpt::releaseMemory() { 3727 PA.clear(); 3728} 3729 3730//===----------------------------------------------------------------------===// 3731// ARC contraction. 3732//===----------------------------------------------------------------------===// 3733 3734// TODO: ObjCARCContract could insert PHI nodes when uses aren't 3735// dominated by single calls. 3736 3737#include "llvm/Operator.h" 3738#include "llvm/InlineAsm.h" 3739#include "llvm/Analysis/Dominators.h" 3740 3741STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed"); 3742 3743namespace { 3744 /// ObjCARCContract - Late ARC optimizations. These change the IR in a way 3745 /// that makes it difficult to be analyzed by ObjCARCOpt, so it's run late. 3746 class ObjCARCContract : public FunctionPass { 3747 bool Changed; 3748 AliasAnalysis *AA; 3749 DominatorTree *DT; 3750 ProvenanceAnalysis PA; 3751 3752 /// Run - A flag indicating whether this optimization pass should run. 3753 bool Run; 3754 3755 /// StoreStrongCallee, etc. - Declarations for ObjC runtime 3756 /// functions, for use in creating calls to them. These are initialized 3757 /// lazily to avoid cluttering up the Module with unused declarations. 3758 Constant *StoreStrongCallee, 3759 *RetainAutoreleaseCallee, *RetainAutoreleaseRVCallee; 3760 3761 /// RetainRVMarker - The inline asm string to insert between calls and 3762 /// RetainRV calls to make the optimization work on targets which need it. 3763 const MDString *RetainRVMarker; 3764 3765 /// StoreStrongCalls - The set of inserted objc_storeStrong calls. If 3766 /// at the end of walking the function we have found no alloca 3767 /// instructions, these calls can be marked "tail". 3768 SmallPtrSet<CallInst *, 8> StoreStrongCalls; 3769 3770 Constant *getStoreStrongCallee(Module *M); 3771 Constant *getRetainAutoreleaseCallee(Module *M); 3772 Constant *getRetainAutoreleaseRVCallee(Module *M); 3773 3774 bool ContractAutorelease(Function &F, Instruction *Autorelease, 3775 InstructionClass Class, 3776 SmallPtrSet<Instruction *, 4> 3777 &DependingInstructions, 3778 SmallPtrSet<const BasicBlock *, 4> 3779 &Visited); 3780 3781 void ContractRelease(Instruction *Release, 3782 inst_iterator &Iter); 3783 3784 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 3785 virtual bool doInitialization(Module &M); 3786 virtual bool runOnFunction(Function &F); 3787 3788 public: 3789 static char ID; 3790 ObjCARCContract() : FunctionPass(ID) { 3791 initializeObjCARCContractPass(*PassRegistry::getPassRegistry()); 3792 } 3793 }; 3794} 3795 3796char ObjCARCContract::ID = 0; 3797INITIALIZE_PASS_BEGIN(ObjCARCContract, 3798 "objc-arc-contract", "ObjC ARC contraction", false, false) 3799INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 3800INITIALIZE_PASS_DEPENDENCY(DominatorTree) 3801INITIALIZE_PASS_END(ObjCARCContract, 3802 "objc-arc-contract", "ObjC ARC contraction", false, false) 3803 3804Pass *llvm::createObjCARCContractPass() { 3805 return new ObjCARCContract(); 3806} 3807 3808void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const { 3809 AU.addRequired<AliasAnalysis>(); 3810 AU.addRequired<DominatorTree>(); 3811 AU.setPreservesCFG(); 3812} 3813 3814Constant *ObjCARCContract::getStoreStrongCallee(Module *M) { 3815 if (!StoreStrongCallee) { 3816 LLVMContext &C = M->getContext(); 3817 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3818 Type *I8XX = PointerType::getUnqual(I8X); 3819 Type *Params[] = { I8XX, I8X }; 3820 3821 AttrListPtr Attributes = AttrListPtr() 3822 .addAttr(~0u, Attribute::NoUnwind) 3823 .addAttr(1, Attribute::NoCapture); 3824 3825 StoreStrongCallee = 3826 M->getOrInsertFunction( 3827 "objc_storeStrong", 3828 FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), 3829 Attributes); 3830 } 3831 return StoreStrongCallee; 3832} 3833 3834Constant *ObjCARCContract::getRetainAutoreleaseCallee(Module *M) { 3835 if (!RetainAutoreleaseCallee) { 3836 LLVMContext &C = M->getContext(); 3837 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3838 Type *Params[] = { I8X }; 3839 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); 3840 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 3841 RetainAutoreleaseCallee = 3842 M->getOrInsertFunction("objc_retainAutorelease", FTy, Attributes); 3843 } 3844 return RetainAutoreleaseCallee; 3845} 3846 3847Constant *ObjCARCContract::getRetainAutoreleaseRVCallee(Module *M) { 3848 if (!RetainAutoreleaseRVCallee) { 3849 LLVMContext &C = M->getContext(); 3850 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3851 Type *Params[] = { I8X }; 3852 FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); 3853 AttrListPtr Attributes = AttrListPtr().addAttr(~0u, Attribute::NoUnwind); 3854 RetainAutoreleaseRVCallee = 3855 M->getOrInsertFunction("objc_retainAutoreleaseReturnValue", FTy, 3856 Attributes); 3857 } 3858 return RetainAutoreleaseRVCallee; 3859} 3860 3861/// ContractAutorelease - Merge an autorelease with a retain into a fused call. 3862bool 3863ObjCARCContract::ContractAutorelease(Function &F, Instruction *Autorelease, 3864 InstructionClass Class, 3865 SmallPtrSet<Instruction *, 4> 3866 &DependingInstructions, 3867 SmallPtrSet<const BasicBlock *, 4> 3868 &Visited) { 3869 const Value *Arg = GetObjCArg(Autorelease); 3870 3871 // Check that there are no instructions between the retain and the autorelease 3872 // (such as an autorelease_pop) which may change the count. 3873 CallInst *Retain = 0; 3874 if (Class == IC_AutoreleaseRV) 3875 FindDependencies(RetainAutoreleaseRVDep, Arg, 3876 Autorelease->getParent(), Autorelease, 3877 DependingInstructions, Visited, PA); 3878 else 3879 FindDependencies(RetainAutoreleaseDep, Arg, 3880 Autorelease->getParent(), Autorelease, 3881 DependingInstructions, Visited, PA); 3882 3883 Visited.clear(); 3884 if (DependingInstructions.size() != 1) { 3885 DependingInstructions.clear(); 3886 return false; 3887 } 3888 3889 Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); 3890 DependingInstructions.clear(); 3891 3892 if (!Retain || 3893 GetBasicInstructionClass(Retain) != IC_Retain || 3894 GetObjCArg(Retain) != Arg) 3895 return false; 3896 3897 Changed = true; 3898 ++NumPeeps; 3899 3900 if (Class == IC_AutoreleaseRV) 3901 Retain->setCalledFunction(getRetainAutoreleaseRVCallee(F.getParent())); 3902 else 3903 Retain->setCalledFunction(getRetainAutoreleaseCallee(F.getParent())); 3904 3905 EraseInstruction(Autorelease); 3906 return true; 3907} 3908 3909/// ContractRelease - Attempt to merge an objc_release with a store, load, and 3910/// objc_retain to form an objc_storeStrong. This can be a little tricky because 3911/// the instructions don't always appear in order, and there may be unrelated 3912/// intervening instructions. 3913void ObjCARCContract::ContractRelease(Instruction *Release, 3914 inst_iterator &Iter) { 3915 LoadInst *Load = dyn_cast<LoadInst>(GetObjCArg(Release)); 3916 if (!Load || !Load->isSimple()) return; 3917 3918 // For now, require everything to be in one basic block. 3919 BasicBlock *BB = Release->getParent(); 3920 if (Load->getParent() != BB) return; 3921 3922 // Walk down to find the store and the release, which may be in either order. 3923 BasicBlock::iterator I = Load, End = BB->end(); 3924 ++I; 3925 AliasAnalysis::Location Loc = AA->getLocation(Load); 3926 StoreInst *Store = 0; 3927 bool SawRelease = false; 3928 for (; !Store || !SawRelease; ++I) { 3929 if (I == End) 3930 return; 3931 3932 Instruction *Inst = I; 3933 if (Inst == Release) { 3934 SawRelease = true; 3935 continue; 3936 } 3937 3938 InstructionClass Class = GetBasicInstructionClass(Inst); 3939 3940 // Unrelated retains are harmless. 3941 if (IsRetain(Class)) 3942 continue; 3943 3944 if (Store) { 3945 // The store is the point where we're going to put the objc_storeStrong, 3946 // so make sure there are no uses after it. 3947 if (CanUse(Inst, Load, PA, Class)) 3948 return; 3949 } else if (AA->getModRefInfo(Inst, Loc) & AliasAnalysis::Mod) { 3950 // We are moving the load down to the store, so check for anything 3951 // else which writes to the memory between the load and the store. 3952 Store = dyn_cast<StoreInst>(Inst); 3953 if (!Store || !Store->isSimple()) return; 3954 if (Store->getPointerOperand() != Loc.Ptr) return; 3955 } 3956 } 3957 3958 Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand()); 3959 3960 // Walk up to find the retain. 3961 I = Store; 3962 BasicBlock::iterator Begin = BB->begin(); 3963 while (I != Begin && GetBasicInstructionClass(I) != IC_Retain) 3964 --I; 3965 Instruction *Retain = I; 3966 if (GetBasicInstructionClass(Retain) != IC_Retain) return; 3967 if (GetObjCArg(Retain) != New) return; 3968 3969 Changed = true; 3970 ++NumStoreStrongs; 3971 3972 LLVMContext &C = Release->getContext(); 3973 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); 3974 Type *I8XX = PointerType::getUnqual(I8X); 3975 3976 Value *Args[] = { Load->getPointerOperand(), New }; 3977 if (Args[0]->getType() != I8XX) 3978 Args[0] = new BitCastInst(Args[0], I8XX, "", Store); 3979 if (Args[1]->getType() != I8X) 3980 Args[1] = new BitCastInst(Args[1], I8X, "", Store); 3981 CallInst *StoreStrong = 3982 CallInst::Create(getStoreStrongCallee(BB->getParent()->getParent()), 3983 Args, "", Store); 3984 StoreStrong->setDoesNotThrow(); 3985 StoreStrong->setDebugLoc(Store->getDebugLoc()); 3986 3987 // We can't set the tail flag yet, because we haven't yet determined 3988 // whether there are any escaping allocas. Remember this call, so that 3989 // we can set the tail flag once we know it's safe. 3990 StoreStrongCalls.insert(StoreStrong); 3991 3992 if (&*Iter == Store) ++Iter; 3993 Store->eraseFromParent(); 3994 Release->eraseFromParent(); 3995 EraseInstruction(Retain); 3996 if (Load->use_empty()) 3997 Load->eraseFromParent(); 3998} 3999 4000bool ObjCARCContract::doInitialization(Module &M) { 4001 // If nothing in the Module uses ARC, don't do anything. 4002 Run = ModuleHasARC(M); 4003 if (!Run) 4004 return false; 4005 4006 // These are initialized lazily. 4007 StoreStrongCallee = 0; 4008 RetainAutoreleaseCallee = 0; 4009 RetainAutoreleaseRVCallee = 0; 4010 4011 // Initialize RetainRVMarker. 4012 RetainRVMarker = 0; 4013 if (NamedMDNode *NMD = 4014 M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker")) 4015 if (NMD->getNumOperands() == 1) { 4016 const MDNode *N = NMD->getOperand(0); 4017 if (N->getNumOperands() == 1) 4018 if (const MDString *S = dyn_cast<MDString>(N->getOperand(0))) 4019 RetainRVMarker = S; 4020 } 4021 4022 return false; 4023} 4024 4025bool ObjCARCContract::runOnFunction(Function &F) { 4026 if (!EnableARCOpts) 4027 return false; 4028 4029 // If nothing in the Module uses ARC, don't do anything. 4030 if (!Run) 4031 return false; 4032 4033 Changed = false; 4034 AA = &getAnalysis<AliasAnalysis>(); 4035 DT = &getAnalysis<DominatorTree>(); 4036 4037 PA.setAA(&getAnalysis<AliasAnalysis>()); 4038 4039 // Track whether it's ok to mark objc_storeStrong calls with the "tail" 4040 // keyword. Be conservative if the function has variadic arguments. 4041 // It seems that functions which "return twice" are also unsafe for the 4042 // "tail" argument, because they are setjmp, which could need to 4043 // return to an earlier stack state. 4044 bool TailOkForStoreStrongs = !F.isVarArg() && 4045 !F.callsFunctionThatReturnsTwice(); 4046 4047 // For ObjC library calls which return their argument, replace uses of the 4048 // argument with uses of the call return value, if it dominates the use. This 4049 // reduces register pressure. 4050 SmallPtrSet<Instruction *, 4> DependingInstructions; 4051 SmallPtrSet<const BasicBlock *, 4> Visited; 4052 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { 4053 Instruction *Inst = &*I++; 4054 4055 // Only these library routines return their argument. In particular, 4056 // objc_retainBlock does not necessarily return its argument. 4057 InstructionClass Class = GetBasicInstructionClass(Inst); 4058 switch (Class) { 4059 case IC_Retain: 4060 case IC_FusedRetainAutorelease: 4061 case IC_FusedRetainAutoreleaseRV: 4062 break; 4063 case IC_Autorelease: 4064 case IC_AutoreleaseRV: 4065 if (ContractAutorelease(F, Inst, Class, DependingInstructions, Visited)) 4066 continue; 4067 break; 4068 case IC_RetainRV: { 4069 // If we're compiling for a target which needs a special inline-asm 4070 // marker to do the retainAutoreleasedReturnValue optimization, 4071 // insert it now. 4072 if (!RetainRVMarker) 4073 break; 4074 BasicBlock::iterator BBI = Inst; 4075 BasicBlock *InstParent = Inst->getParent(); 4076 4077 // Step up to see if the call immediately precedes the RetainRV call. 4078 // If it's an invoke, we have to cross a block boundary. And we have 4079 // to carefully dodge no-op instructions. 4080 do { 4081 if (&*BBI == InstParent->begin()) { 4082 BasicBlock *Pred = InstParent->getSinglePredecessor(); 4083 if (!Pred) 4084 goto decline_rv_optimization; 4085 BBI = Pred->getTerminator(); 4086 break; 4087 } 4088 --BBI; 4089 } while (isNoopInstruction(BBI)); 4090 4091 if (&*BBI == GetObjCArg(Inst)) { 4092 Changed = true; 4093 InlineAsm *IA = 4094 InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()), 4095 /*isVarArg=*/false), 4096 RetainRVMarker->getString(), 4097 /*Constraints=*/"", /*hasSideEffects=*/true); 4098 CallInst::Create(IA, "", Inst); 4099 } 4100 decline_rv_optimization: 4101 break; 4102 } 4103 case IC_InitWeak: { 4104 // objc_initWeak(p, null) => *p = null 4105 CallInst *CI = cast<CallInst>(Inst); 4106 if (isNullOrUndef(CI->getArgOperand(1))) { 4107 Value *Null = 4108 ConstantPointerNull::get(cast<PointerType>(CI->getType())); 4109 Changed = true; 4110 new StoreInst(Null, CI->getArgOperand(0), CI); 4111 CI->replaceAllUsesWith(Null); 4112 CI->eraseFromParent(); 4113 } 4114 continue; 4115 } 4116 case IC_Release: 4117 ContractRelease(Inst, I); 4118 continue; 4119 case IC_User: 4120 // Be conservative if the function has any alloca instructions. 4121 // Technically we only care about escaping alloca instructions, 4122 // but this is sufficient to handle some interesting cases. 4123 if (isa<AllocaInst>(Inst)) 4124 TailOkForStoreStrongs = false; 4125 continue; 4126 default: 4127 continue; 4128 } 4129 4130 // Don't use GetObjCArg because we don't want to look through bitcasts 4131 // and such; to do the replacement, the argument must have type i8*. 4132 const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0); 4133 for (;;) { 4134 // If we're compiling bugpointed code, don't get in trouble. 4135 if (!isa<Instruction>(Arg) && !isa<Argument>(Arg)) 4136 break; 4137 // Look through the uses of the pointer. 4138 for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); 4139 UI != UE; ) { 4140 Use &U = UI.getUse(); 4141 unsigned OperandNo = UI.getOperandNo(); 4142 ++UI; // Increment UI now, because we may unlink its element. 4143 4144 // If the call's return value dominates a use of the call's argument 4145 // value, rewrite the use to use the return value. We check for 4146 // reachability here because an unreachable call is considered to 4147 // trivially dominate itself, which would lead us to rewriting its 4148 // argument in terms of its return value, which would lead to 4149 // infinite loops in GetObjCArg. 4150 if (DT->isReachableFromEntry(U) && DT->dominates(Inst, U)) { 4151 Changed = true; 4152 Instruction *Replacement = Inst; 4153 Type *UseTy = U.get()->getType(); 4154 if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) { 4155 // For PHI nodes, insert the bitcast in the predecessor block. 4156 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo); 4157 BasicBlock *BB = PHI->getIncomingBlock(ValNo); 4158 if (Replacement->getType() != UseTy) 4159 Replacement = new BitCastInst(Replacement, UseTy, "", 4160 &BB->back()); 4161 // While we're here, rewrite all edges for this PHI, rather 4162 // than just one use at a time, to minimize the number of 4163 // bitcasts we emit. 4164 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) 4165 if (PHI->getIncomingBlock(i) == BB) { 4166 // Keep the UI iterator valid. 4167 if (&PHI->getOperandUse( 4168 PHINode::getOperandNumForIncomingValue(i)) == 4169 &UI.getUse()) 4170 ++UI; 4171 PHI->setIncomingValue(i, Replacement); 4172 } 4173 } else { 4174 if (Replacement->getType() != UseTy) 4175 Replacement = new BitCastInst(Replacement, UseTy, "", 4176 cast<Instruction>(U.getUser())); 4177 U.set(Replacement); 4178 } 4179 } 4180 } 4181 4182 // If Arg is a no-op casted pointer, strip one level of casts and iterate. 4183 if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg)) 4184 Arg = BI->getOperand(0); 4185 else if (isa<GEPOperator>(Arg) && 4186 cast<GEPOperator>(Arg)->hasAllZeroIndices()) 4187 Arg = cast<GEPOperator>(Arg)->getPointerOperand(); 4188 else if (isa<GlobalAlias>(Arg) && 4189 !cast<GlobalAlias>(Arg)->mayBeOverridden()) 4190 Arg = cast<GlobalAlias>(Arg)->getAliasee(); 4191 else 4192 break; 4193 } 4194 } 4195 4196 // If this function has no escaping allocas or suspicious vararg usage, 4197 // objc_storeStrong calls can be marked with the "tail" keyword. 4198 if (TailOkForStoreStrongs) 4199 for (SmallPtrSet<CallInst *, 8>::iterator I = StoreStrongCalls.begin(), 4200 E = StoreStrongCalls.end(); I != E; ++I) 4201 (*I)->setTailCall(); 4202 StoreStrongCalls.clear(); 4203 4204 return Changed; 4205} 4206