ValueHandle.h revision f3014761c955345d6e05491608e73228d014afb7
1//===- ValueHandle.h - Value Smart Pointer classes --------------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file declares the ValueHandle class and its sub-classes. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_IR_VALUEHANDLE_H 15#define LLVM_IR_VALUEHANDLE_H 16 17#include "llvm/ADT/DenseMapInfo.h" 18#include "llvm/ADT/PointerIntPair.h" 19#include "llvm/IR/Value.h" 20#include "llvm/Support/Casting.h" 21#include <cassert> 22 23namespace llvm { 24 25/// \brief This is the common base class of value handles. 26/// 27/// ValueHandle's are smart pointers to Value's that have special behavior when 28/// the value is deleted or ReplaceAllUsesWith'd. See the specific handles 29/// below for details. 30class ValueHandleBase { 31 friend class Value; 32 33protected: 34 /// \brief This indicates what sub class the handle actually is. 35 /// 36 /// This is to avoid having a vtable for the light-weight handle pointers. The 37 /// fully general Callback version does have a vtable. 38 enum HandleBaseKind { Assert, Callback, Weak, WeakTracking }; 39 40 ValueHandleBase(const ValueHandleBase &RHS) 41 : ValueHandleBase(RHS.PrevPair.getInt(), RHS) {} 42 43 ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS) 44 : PrevPair(nullptr, Kind), Val(RHS.getValPtr()) { 45 if (isValid(getValPtr())) 46 AddToExistingUseList(RHS.getPrevPtr()); 47 } 48 49private: 50 PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair; 51 ValueHandleBase *Next = nullptr; 52 Value *Val = nullptr; 53 54 void setValPtr(Value *V) { Val = V; } 55 56public: 57 explicit ValueHandleBase(HandleBaseKind Kind) 58 : PrevPair(nullptr, Kind) {} 59 ValueHandleBase(HandleBaseKind Kind, Value *V) 60 : PrevPair(nullptr, Kind), Val(V) { 61 if (isValid(getValPtr())) 62 AddToUseList(); 63 } 64 65 ~ValueHandleBase() { 66 if (isValid(getValPtr())) 67 RemoveFromUseList(); 68 } 69 70 Value *operator=(Value *RHS) { 71 if (getValPtr() == RHS) 72 return RHS; 73 if (isValid(getValPtr())) 74 RemoveFromUseList(); 75 setValPtr(RHS); 76 if (isValid(getValPtr())) 77 AddToUseList(); 78 return RHS; 79 } 80 81 Value *operator=(const ValueHandleBase &RHS) { 82 if (getValPtr() == RHS.getValPtr()) 83 return RHS.getValPtr(); 84 if (isValid(getValPtr())) 85 RemoveFromUseList(); 86 setValPtr(RHS.getValPtr()); 87 if (isValid(getValPtr())) 88 AddToExistingUseList(RHS.getPrevPtr()); 89 return getValPtr(); 90 } 91 92 Value *operator->() const { return getValPtr(); } 93 Value &operator*() const { return *getValPtr(); } 94 95protected: 96 Value *getValPtr() const { return Val; } 97 98 static bool isValid(Value *V) { 99 return V && 100 V != DenseMapInfo<Value *>::getEmptyKey() && 101 V != DenseMapInfo<Value *>::getTombstoneKey(); 102 } 103 104 /// \brief Remove this ValueHandle from its current use list. 105 void RemoveFromUseList(); 106 107 /// \brief Clear the underlying pointer without clearing the use list. 108 /// 109 /// This should only be used if a derived class has manually removed the 110 /// handle from the use list. 111 void clearValPtr() { setValPtr(nullptr); } 112 113public: 114 // Callbacks made from Value. 115 static void ValueIsDeleted(Value *V); 116 static void ValueIsRAUWd(Value *Old, Value *New); 117 118private: 119 // Internal implementation details. 120 ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); } 121 HandleBaseKind getKind() const { return PrevPair.getInt(); } 122 void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); } 123 124 /// \brief Add this ValueHandle to the use list for V. 125 /// 126 /// List is the address of either the head of the list or a Next node within 127 /// the existing use list. 128 void AddToExistingUseList(ValueHandleBase **List); 129 130 /// \brief Add this ValueHandle to the use list after Node. 131 void AddToExistingUseListAfter(ValueHandleBase *Node); 132 133 /// \brief Add this ValueHandle to the use list for V. 134 void AddToUseList(); 135}; 136 137/// \brief A nullable Value handle that is nullable. 138/// 139/// This is a value handle that points to a value, and nulls itself 140/// out if that value is deleted. 141class WeakVH : public ValueHandleBase { 142public: 143 WeakVH() : ValueHandleBase(Weak) {} 144 WeakVH(Value *P) : ValueHandleBase(Weak, P) {} 145 WeakVH(const WeakVH &RHS) 146 : ValueHandleBase(Weak, RHS) {} 147 148 WeakVH &operator=(const WeakVH &RHS) = default; 149 150 Value *operator=(Value *RHS) { 151 return ValueHandleBase::operator=(RHS); 152 } 153 Value *operator=(const ValueHandleBase &RHS) { 154 return ValueHandleBase::operator=(RHS); 155 } 156 157 operator Value*() const { 158 return getValPtr(); 159 } 160}; 161 162// Specialize simplify_type to allow WeakVH to participate in 163// dyn_cast, isa, etc. 164template <> struct simplify_type<WeakVH> { 165 using SimpleType = Value *; 166 167 static SimpleType getSimplifiedValue(WeakVH &WVH) { return WVH; } 168}; 169template <> struct simplify_type<const WeakVH> { 170 using SimpleType = Value *; 171 172 static SimpleType getSimplifiedValue(const WeakVH &WVH) { return WVH; } 173}; 174 175/// \brief Value handle that is nullable, but tries to track the Value. 176/// 177/// This is a value handle that tries hard to point to a Value, even across 178/// RAUW operations, but will null itself out if the value is destroyed. this 179/// is useful for advisory sorts of information, but should not be used as the 180/// key of a map (since the map would have to rearrange itself when the pointer 181/// changes). 182class WeakTrackingVH : public ValueHandleBase { 183public: 184 WeakTrackingVH() : ValueHandleBase(WeakTracking) {} 185 WeakTrackingVH(Value *P) : ValueHandleBase(WeakTracking, P) {} 186 WeakTrackingVH(const WeakTrackingVH &RHS) 187 : ValueHandleBase(WeakTracking, RHS) {} 188 189 WeakTrackingVH &operator=(const WeakTrackingVH &RHS) = default; 190 191 Value *operator=(Value *RHS) { 192 return ValueHandleBase::operator=(RHS); 193 } 194 Value *operator=(const ValueHandleBase &RHS) { 195 return ValueHandleBase::operator=(RHS); 196 } 197 198 operator Value*() const { 199 return getValPtr(); 200 } 201 202 bool pointsToAliveValue() const { 203 return ValueHandleBase::isValid(getValPtr()); 204 } 205}; 206 207// Specialize simplify_type to allow WeakTrackingVH to participate in 208// dyn_cast, isa, etc. 209template <> struct simplify_type<WeakTrackingVH> { 210 using SimpleType = Value *; 211 212 static SimpleType getSimplifiedValue(WeakTrackingVH &WVH) { return WVH; } 213}; 214template <> struct simplify_type<const WeakTrackingVH> { 215 using SimpleType = Value *; 216 217 static SimpleType getSimplifiedValue(const WeakTrackingVH &WVH) { 218 return WVH; 219 } 220}; 221 222/// \brief Value handle that asserts if the Value is deleted. 223/// 224/// This is a Value Handle that points to a value and asserts out if the value 225/// is destroyed while the handle is still live. This is very useful for 226/// catching dangling pointer bugs and other things which can be non-obvious. 227/// One particularly useful place to use this is as the Key of a map. Dangling 228/// pointer bugs often lead to really subtle bugs that only occur if another 229/// object happens to get allocated to the same address as the old one. Using 230/// an AssertingVH ensures that an assert is triggered as soon as the bad 231/// delete occurs. 232/// 233/// Note that an AssertingVH handle does *not* follow values across RAUW 234/// operations. This means that RAUW's need to explicitly update the 235/// AssertingVH's as it moves. This is required because in non-assert mode this 236/// class turns into a trivial wrapper around a pointer. 237template <typename ValueTy> 238class AssertingVH 239#ifndef NDEBUG 240 : public ValueHandleBase 241#endif 242 { 243 friend struct DenseMapInfo<AssertingVH<ValueTy>>; 244 245#ifndef NDEBUG 246 Value *getRawValPtr() const { return ValueHandleBase::getValPtr(); } 247 void setRawValPtr(Value *P) { ValueHandleBase::operator=(P); } 248#else 249 Value *ThePtr; 250 Value *getRawValPtr() const { return ThePtr; } 251 void setRawValPtr(Value *P) { ThePtr = P; } 252#endif 253 // Convert a ValueTy*, which may be const, to the raw Value*. 254 static Value *GetAsValue(Value *V) { return V; } 255 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); } 256 257 ValueTy *getValPtr() const { return static_cast<ValueTy *>(getRawValPtr()); } 258 void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); } 259 260public: 261#ifndef NDEBUG 262 AssertingVH() : ValueHandleBase(Assert) {} 263 AssertingVH(ValueTy *P) : ValueHandleBase(Assert, GetAsValue(P)) {} 264 AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {} 265#else 266 AssertingVH() : ThePtr(nullptr) {} 267 AssertingVH(ValueTy *P) : ThePtr(GetAsValue(P)) {} 268#endif 269 270 operator ValueTy*() const { 271 return getValPtr(); 272 } 273 274 ValueTy *operator=(ValueTy *RHS) { 275 setValPtr(RHS); 276 return getValPtr(); 277 } 278 ValueTy *operator=(const AssertingVH<ValueTy> &RHS) { 279 setValPtr(RHS.getValPtr()); 280 return getValPtr(); 281 } 282 283 ValueTy *operator->() const { return getValPtr(); } 284 ValueTy &operator*() const { return *getValPtr(); } 285}; 286 287// Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap. 288template<typename T> 289struct DenseMapInfo<AssertingVH<T>> { 290 static inline AssertingVH<T> getEmptyKey() { 291 AssertingVH<T> Res; 292 Res.setRawValPtr(DenseMapInfo<Value *>::getEmptyKey()); 293 return Res; 294 } 295 296 static inline AssertingVH<T> getTombstoneKey() { 297 AssertingVH<T> Res; 298 Res.setRawValPtr(DenseMapInfo<Value *>::getTombstoneKey()); 299 return Res; 300 } 301 302 static unsigned getHashValue(const AssertingVH<T> &Val) { 303 return DenseMapInfo<Value *>::getHashValue(Val.getRawValPtr()); 304 } 305 306 static bool isEqual(const AssertingVH<T> &LHS, const AssertingVH<T> &RHS) { 307 return DenseMapInfo<Value *>::isEqual(LHS.getRawValPtr(), 308 RHS.getRawValPtr()); 309 } 310}; 311 312template <typename T> 313struct isPodLike<AssertingVH<T>> { 314#ifdef NDEBUG 315 static const bool value = true; 316#else 317 static const bool value = false; 318#endif 319}; 320 321/// \brief Value handle that tracks a Value across RAUW. 322/// 323/// TrackingVH is designed for situations where a client needs to hold a handle 324/// to a Value (or subclass) across some operations which may move that value, 325/// but should never destroy it or replace it with some unacceptable type. 326/// 327/// It is an error to attempt to replace a value with one of a type which is 328/// incompatible with any of its outstanding TrackingVHs. 329/// 330/// It is an error to read from a TrackingVH that does not point to a valid 331/// value. A TrackingVH is said to not point to a valid value if either it 332/// hasn't yet been assigned a value yet or because the value it was tracking 333/// has since been deleted. 334/// 335/// Assigning a value to a TrackingVH is always allowed, even if said TrackingVH 336/// no longer points to a valid value. 337template <typename ValueTy> class TrackingVH { 338 WeakTrackingVH InnerHandle; 339 340public: 341 ValueTy *getValPtr() const { 342 assert(InnerHandle.pointsToAliveValue() && 343 "TrackingVH must be non-null and valid on dereference!"); 344 345 // Check that the value is a member of the correct subclass. We would like 346 // to check this property on assignment for better debugging, but we don't 347 // want to require a virtual interface on this VH. Instead we allow RAUW to 348 // replace this value with a value of an invalid type, and check it here. 349 assert(isa<ValueTy>(InnerHandle) && 350 "Tracked Value was replaced by one with an invalid type!"); 351 return cast<ValueTy>(InnerHandle); 352 } 353 354 void setValPtr(ValueTy *P) { 355 // Assigning to non-valid TrackingVH's are fine so we just unconditionally 356 // assign here. 357 InnerHandle = GetAsValue(P); 358 } 359 360 // Convert a ValueTy*, which may be const, to the type the base 361 // class expects. 362 static Value *GetAsValue(Value *V) { return V; } 363 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); } 364 365public: 366 TrackingVH() = default; 367 TrackingVH(ValueTy *P) { setValPtr(P); } 368 369 operator ValueTy*() const { 370 return getValPtr(); 371 } 372 373 ValueTy *operator=(ValueTy *RHS) { 374 setValPtr(RHS); 375 return getValPtr(); 376 } 377 378 ValueTy *operator->() const { return getValPtr(); } 379 ValueTy &operator*() const { return *getValPtr(); } 380}; 381 382/// \brief Value handle with callbacks on RAUW and destruction. 383/// 384/// This is a value handle that allows subclasses to define callbacks that run 385/// when the underlying Value has RAUW called on it or is destroyed. This 386/// class can be used as the key of a map, as long as the user takes it out of 387/// the map before calling setValPtr() (since the map has to rearrange itself 388/// when the pointer changes). Unlike ValueHandleBase, this class has a vtable. 389class CallbackVH : public ValueHandleBase { 390 virtual void anchor(); 391protected: 392 ~CallbackVH() = default; 393 CallbackVH(const CallbackVH &) = default; 394 CallbackVH &operator=(const CallbackVH &) = default; 395 396 void setValPtr(Value *P) { 397 ValueHandleBase::operator=(P); 398 } 399 400public: 401 CallbackVH() : ValueHandleBase(Callback) {} 402 CallbackVH(Value *P) : ValueHandleBase(Callback, P) {} 403 404 operator Value*() const { 405 return getValPtr(); 406 } 407 408 /// \brief Callback for Value destruction. 409 /// 410 /// Called when this->getValPtr() is destroyed, inside ~Value(), so you 411 /// may call any non-virtual Value method on getValPtr(), but no subclass 412 /// methods. If WeakTrackingVH were implemented as a CallbackVH, it would use 413 /// this 414 /// method to call setValPtr(NULL). AssertingVH would use this method to 415 /// cause an assertion failure. 416 /// 417 /// All implementations must remove the reference from this object to the 418 /// Value that's being destroyed. 419 virtual void deleted() { setValPtr(nullptr); } 420 421 /// \brief Callback for Value RAUW. 422 /// 423 /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called, 424 /// _before_ any of the uses have actually been replaced. If WeakTrackingVH 425 /// were 426 /// implemented as a CallbackVH, it would use this method to call 427 /// setValPtr(new_value). AssertingVH would do nothing in this method. 428 virtual void allUsesReplacedWith(Value *) {} 429}; 430 431/// Value handle that poisons itself if the Value is deleted. 432/// 433/// This is a Value Handle that points to a value and poisons itself if the 434/// value is destroyed while the handle is still live. This is very useful for 435/// catching dangling pointer bugs where an \c AssertingVH cannot be used 436/// because the dangling handle needs to outlive the value without ever being 437/// used. 438/// 439/// One particularly useful place to use this is as the Key of a map. Dangling 440/// pointer bugs often lead to really subtle bugs that only occur if another 441/// object happens to get allocated to the same address as the old one. Using 442/// a PoisoningVH ensures that an assert is triggered if looking up a new value 443/// in the map finds a handle from the old value. 444/// 445/// Note that a PoisoningVH handle does *not* follow values across RAUW 446/// operations. This means that RAUW's need to explicitly update the 447/// PoisoningVH's as it moves. This is required because in non-assert mode this 448/// class turns into a trivial wrapper around a pointer. 449template <typename ValueTy> 450class PoisoningVH 451#ifndef NDEBUG 452 final : public CallbackVH 453#endif 454{ 455 friend struct DenseMapInfo<PoisoningVH<ValueTy>>; 456 457 // Convert a ValueTy*, which may be const, to the raw Value*. 458 static Value *GetAsValue(Value *V) { return V; } 459 static Value *GetAsValue(const Value *V) { return const_cast<Value *>(V); } 460 461#ifndef NDEBUG 462 /// A flag tracking whether this value has been poisoned. 463 /// 464 /// On delete and RAUW, we leave the value pointer alone so that as a raw 465 /// pointer it produces the same value (and we fit into the same key of 466 /// a hash table, etc), but we poison the handle so that any top-level usage 467 /// will fail. 468 bool Poisoned = false; 469 470 Value *getRawValPtr() const { return ValueHandleBase::getValPtr(); } 471 void setRawValPtr(Value *P) { ValueHandleBase::operator=(P); } 472 473 /// Handle deletion by poisoning the handle. 474 void deleted() override { 475 assert(!Poisoned && "Tried to delete an already poisoned handle!"); 476 Poisoned = true; 477 RemoveFromUseList(); 478 } 479 480 /// Handle RAUW by poisoning the handle. 481 void allUsesReplacedWith(Value *) override { 482 assert(!Poisoned && "Tried to RAUW an already poisoned handle!"); 483 Poisoned = true; 484 RemoveFromUseList(); 485 } 486#else // NDEBUG 487 Value *ThePtr = nullptr; 488 489 Value *getRawValPtr() const { return ThePtr; } 490 void setRawValPtr(Value *P) { ThePtr = P; } 491#endif 492 493 ValueTy *getValPtr() const { 494 assert(!Poisoned && "Accessed a poisoned value handle!"); 495 return static_cast<ValueTy *>(getRawValPtr()); 496 } 497 void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); } 498 499public: 500 PoisoningVH() = default; 501#ifndef NDEBUG 502 PoisoningVH(ValueTy *P) : CallbackVH(GetAsValue(P)) {} 503 PoisoningVH(const PoisoningVH &RHS) 504 : CallbackVH(RHS), Poisoned(RHS.Poisoned) {} 505 506 ~PoisoningVH() { 507 if (Poisoned) 508 clearValPtr(); 509 } 510 511 PoisoningVH &operator=(const PoisoningVH &RHS) { 512 if (Poisoned) 513 clearValPtr(); 514 CallbackVH::operator=(RHS); 515 Poisoned = RHS.Poisoned; 516 return *this; 517 } 518#else 519 PoisoningVH(ValueTy *P) : ThePtr(GetAsValue(P)) {} 520#endif 521 522 operator ValueTy *() const { return getValPtr(); } 523 524 ValueTy *operator->() const { return getValPtr(); } 525 ValueTy &operator*() const { return *getValPtr(); } 526}; 527 528// Specialize DenseMapInfo to allow PoisoningVH to participate in DenseMap. 529template <typename T> struct DenseMapInfo<PoisoningVH<T>> { 530 static inline PoisoningVH<T> getEmptyKey() { 531 PoisoningVH<T> Res; 532 Res.setRawValPtr(DenseMapInfo<Value *>::getEmptyKey()); 533 return Res; 534 } 535 536 static inline PoisoningVH<T> getTombstoneKey() { 537 PoisoningVH<T> Res; 538 Res.setRawValPtr(DenseMapInfo<Value *>::getTombstoneKey()); 539 return Res; 540 } 541 542 static unsigned getHashValue(const PoisoningVH<T> &Val) { 543 return DenseMapInfo<Value *>::getHashValue(Val.getRawValPtr()); 544 } 545 546 static bool isEqual(const PoisoningVH<T> &LHS, const PoisoningVH<T> &RHS) { 547 return DenseMapInfo<Value *>::isEqual(LHS.getRawValPtr(), 548 RHS.getRawValPtr()); 549 } 550}; 551 552template <typename T> struct isPodLike<PoisoningVH<T>> { 553#ifdef NDEBUG 554 static const bool value = true; 555#else 556 static const bool value = false; 557#endif 558}; 559 560} // end namespace llvm 561 562#endif // LLVM_IR_VALUEHANDLE_H 563