1 //===- llvm/Support/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_SUPPORT_VALUEHANDLE_H 15 #define LLVM_SUPPORT_VALUEHANDLE_H 16 17 #include "llvm/ADT/DenseMapInfo.h" 18 #include "llvm/ADT/PointerIntPair.h" 19 #include "llvm/Value.h" 20 21 namespace llvm { 22 class ValueHandleBase; 23 24 // ValueHandleBase** is only 4-byte aligned. 25 template<> 26 class PointerLikeTypeTraits<ValueHandleBase**> { 27 public: getAsVoidPointer(ValueHandleBase ** P)28 static inline void *getAsVoidPointer(ValueHandleBase** P) { return P; } getFromVoidPointer(void * P)29 static inline ValueHandleBase **getFromVoidPointer(void *P) { 30 return static_cast<ValueHandleBase**>(P); 31 } 32 enum { NumLowBitsAvailable = 2 }; 33 }; 34 35 /// ValueHandleBase - This is the common base class of value handles. 36 /// ValueHandle's are smart pointers to Value's that have special behavior when 37 /// the value is deleted or ReplaceAllUsesWith'd. See the specific handles 38 /// below for details. 39 /// 40 class ValueHandleBase { 41 friend class Value; 42 protected: 43 /// HandleBaseKind - This indicates what sub class the handle actually is. 44 /// This is to avoid having a vtable for the light-weight handle pointers. The 45 /// fully general Callback version does have a vtable. 46 enum HandleBaseKind { 47 Assert, 48 Callback, 49 Tracking, 50 Weak 51 }; 52 53 private: 54 PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair; 55 ValueHandleBase *Next; 56 57 // A subclass may want to store some information along with the value 58 // pointer. Allow them to do this by making the value pointer a pointer-int 59 // pair. The 'setValPtrInt' and 'getValPtrInt' methods below give them this 60 // access. 61 PointerIntPair<Value*, 2> VP; 62 63 explicit ValueHandleBase(const ValueHandleBase&); // DO NOT IMPLEMENT. 64 public: ValueHandleBase(HandleBaseKind Kind)65 explicit ValueHandleBase(HandleBaseKind Kind) 66 : PrevPair(0, Kind), Next(0), VP(0, 0) {} ValueHandleBase(HandleBaseKind Kind,Value * V)67 ValueHandleBase(HandleBaseKind Kind, Value *V) 68 : PrevPair(0, Kind), Next(0), VP(V, 0) { 69 if (isValid(VP.getPointer())) 70 AddToUseList(); 71 } ValueHandleBase(HandleBaseKind Kind,const ValueHandleBase & RHS)72 ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS) 73 : PrevPair(0, Kind), Next(0), VP(RHS.VP) { 74 if (isValid(VP.getPointer())) 75 AddToExistingUseList(RHS.getPrevPtr()); 76 } ~ValueHandleBase()77 ~ValueHandleBase() { 78 if (isValid(VP.getPointer())) 79 RemoveFromUseList(); 80 } 81 82 Value *operator=(Value *RHS) { 83 if (VP.getPointer() == RHS) return RHS; 84 if (isValid(VP.getPointer())) RemoveFromUseList(); 85 VP.setPointer(RHS); 86 if (isValid(VP.getPointer())) AddToUseList(); 87 return RHS; 88 } 89 90 Value *operator=(const ValueHandleBase &RHS) { 91 if (VP.getPointer() == RHS.VP.getPointer()) return RHS.VP.getPointer(); 92 if (isValid(VP.getPointer())) RemoveFromUseList(); 93 VP.setPointer(RHS.VP.getPointer()); 94 if (isValid(VP.getPointer())) AddToExistingUseList(RHS.getPrevPtr()); 95 return VP.getPointer(); 96 } 97 98 Value *operator->() const { return getValPtr(); } 99 Value &operator*() const { return *getValPtr(); } 100 101 protected: getValPtr()102 Value *getValPtr() const { return VP.getPointer(); } 103 setValPtrInt(unsigned K)104 void setValPtrInt(unsigned K) { VP.setInt(K); } getValPtrInt()105 unsigned getValPtrInt() const { return VP.getInt(); } 106 isValid(Value * V)107 static bool isValid(Value *V) { 108 return V && 109 V != DenseMapInfo<Value *>::getEmptyKey() && 110 V != DenseMapInfo<Value *>::getTombstoneKey(); 111 } 112 113 public: 114 // Callbacks made from Value. 115 static void ValueIsDeleted(Value *V); 116 static void ValueIsRAUWd(Value *Old, Value *New); 117 118 private: 119 // Internal implementation details. getPrevPtr()120 ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); } getKind()121 HandleBaseKind getKind() const { return PrevPair.getInt(); } setPrevPtr(ValueHandleBase ** Ptr)122 void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); } 123 124 /// AddToExistingUseList - Add this ValueHandle to the use list for VP, where 125 /// List is the address of either the head of the list or a Next node within 126 /// the existing use list. 127 void AddToExistingUseList(ValueHandleBase **List); 128 129 /// AddToExistingUseListAfter - Add this ValueHandle to the use list after 130 /// Node. 131 void AddToExistingUseListAfter(ValueHandleBase *Node); 132 133 /// AddToUseList - Add this ValueHandle to the use list for VP. 134 void AddToUseList(); 135 /// RemoveFromUseList - Remove this ValueHandle from its current use list. 136 void RemoveFromUseList(); 137 }; 138 139 /// WeakVH - This is a value handle that tries hard to point to a Value, even 140 /// across RAUW operations, but will null itself out if the value is destroyed. 141 /// this is useful for advisory sorts of information, but should not be used as 142 /// the key of a map (since the map would have to rearrange itself when the 143 /// pointer changes). 144 class WeakVH : public ValueHandleBase { 145 public: WeakVH()146 WeakVH() : ValueHandleBase(Weak) {} WeakVH(Value * P)147 WeakVH(Value *P) : ValueHandleBase(Weak, P) {} WeakVH(const WeakVH & RHS)148 WeakVH(const WeakVH &RHS) 149 : ValueHandleBase(Weak, RHS) {} 150 151 Value *operator=(Value *RHS) { 152 return ValueHandleBase::operator=(RHS); 153 } 154 Value *operator=(const ValueHandleBase &RHS) { 155 return ValueHandleBase::operator=(RHS); 156 } 157 158 operator Value*() const { 159 return getValPtr(); 160 } 161 }; 162 163 // Specialize simplify_type to allow WeakVH to participate in 164 // dyn_cast, isa, etc. 165 template<typename From> struct simplify_type; 166 template<> struct simplify_type<const WeakVH> { 167 typedef Value* SimpleType; 168 static SimpleType getSimplifiedValue(const WeakVH &WVH) { 169 return static_cast<Value *>(WVH); 170 } 171 }; 172 template<> struct simplify_type<WeakVH> : public simplify_type<const WeakVH> {}; 173 174 /// AssertingVH - This is a Value Handle that points to a value and asserts out 175 /// if the value is destroyed while the handle is still live. This is very 176 /// useful for catching dangling pointer bugs and other things which can be 177 /// non-obvious. One particularly useful place to use this is as the Key of a 178 /// map. Dangling pointer bugs often lead to really subtle bugs that only occur 179 /// if another object happens to get allocated to the same address as the old 180 /// one. Using an AssertingVH ensures that an assert is triggered as soon as 181 /// the bad delete occurs. 182 /// 183 /// Note that an AssertingVH handle does *not* follow values across RAUW 184 /// operations. This means that RAUW's need to explicitly update the 185 /// AssertingVH's as it moves. This is required because in non-assert mode this 186 /// class turns into a trivial wrapper around a pointer. 187 template <typename ValueTy> 188 class AssertingVH 189 #ifndef NDEBUG 190 : public ValueHandleBase 191 #endif 192 { 193 194 #ifndef NDEBUG 195 ValueTy *getValPtr() const { 196 return static_cast<ValueTy*>(ValueHandleBase::getValPtr()); 197 } 198 void setValPtr(ValueTy *P) { 199 ValueHandleBase::operator=(GetAsValue(P)); 200 } 201 #else 202 ValueTy *ThePtr; 203 ValueTy *getValPtr() const { return ThePtr; } 204 void setValPtr(ValueTy *P) { ThePtr = P; } 205 #endif 206 207 // Convert a ValueTy*, which may be const, to the type the base 208 // class expects. 209 static Value *GetAsValue(Value *V) { return V; } 210 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); } 211 212 public: 213 #ifndef NDEBUG 214 AssertingVH() : ValueHandleBase(Assert) {} 215 AssertingVH(ValueTy *P) : ValueHandleBase(Assert, GetAsValue(P)) {} 216 AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {} 217 #else 218 AssertingVH() : ThePtr(0) {} 219 AssertingVH(ValueTy *P) : ThePtr(P) {} 220 #endif 221 222 operator ValueTy*() const { 223 return getValPtr(); 224 } 225 226 ValueTy *operator=(ValueTy *RHS) { 227 setValPtr(RHS); 228 return getValPtr(); 229 } 230 ValueTy *operator=(const AssertingVH<ValueTy> &RHS) { 231 setValPtr(RHS.getValPtr()); 232 return getValPtr(); 233 } 234 235 ValueTy *operator->() const { return getValPtr(); } 236 ValueTy &operator*() const { return *getValPtr(); } 237 }; 238 239 // Specialize simplify_type to allow AssertingVH to participate in 240 // dyn_cast, isa, etc. 241 template<typename From> struct simplify_type; 242 template<> struct simplify_type<const AssertingVH<Value> > { 243 typedef Value* SimpleType; 244 static SimpleType getSimplifiedValue(const AssertingVH<Value> &AVH) { 245 return static_cast<Value *>(AVH); 246 } 247 }; 248 template<> struct simplify_type<AssertingVH<Value> > 249 : public simplify_type<const AssertingVH<Value> > {}; 250 251 // Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap. 252 template<typename T> 253 struct DenseMapInfo<AssertingVH<T> > { 254 typedef DenseMapInfo<T*> PointerInfo; 255 static inline AssertingVH<T> getEmptyKey() { 256 return AssertingVH<T>(PointerInfo::getEmptyKey()); 257 } 258 static inline T* getTombstoneKey() { 259 return AssertingVH<T>(PointerInfo::getTombstoneKey()); 260 } 261 static unsigned getHashValue(const AssertingVH<T> &Val) { 262 return PointerInfo::getHashValue(Val); 263 } 264 static bool isEqual(const AssertingVH<T> &LHS, const AssertingVH<T> &RHS) { 265 return LHS == RHS; 266 } 267 }; 268 269 template <typename T> 270 struct isPodLike<AssertingVH<T> > { 271 #ifdef NDEBUG 272 static const bool value = true; 273 #else 274 static const bool value = false; 275 #endif 276 }; 277 278 279 /// TrackingVH - This is a value handle that tracks a Value (or Value subclass), 280 /// even across RAUW operations. 281 /// 282 /// TrackingVH is designed for situations where a client needs to hold a handle 283 /// to a Value (or subclass) across some operations which may move that value, 284 /// but should never destroy it or replace it with some unacceptable type. 285 /// 286 /// It is an error to do anything with a TrackingVH whose value has been 287 /// destroyed, except to destruct it. 288 /// 289 /// It is an error to attempt to replace a value with one of a type which is 290 /// incompatible with any of its outstanding TrackingVHs. 291 template<typename ValueTy> 292 class TrackingVH : public ValueHandleBase { 293 void CheckValidity() const { 294 Value *VP = ValueHandleBase::getValPtr(); 295 296 // Null is always ok. 297 if (!VP) return; 298 299 // Check that this value is valid (i.e., it hasn't been deleted). We 300 // explicitly delay this check until access to avoid requiring clients to be 301 // unnecessarily careful w.r.t. destruction. 302 assert(ValueHandleBase::isValid(VP) && "Tracked Value was deleted!"); 303 304 // Check that the value is a member of the correct subclass. We would like 305 // to check this property on assignment for better debugging, but we don't 306 // want to require a virtual interface on this VH. Instead we allow RAUW to 307 // replace this value with a value of an invalid type, and check it here. 308 assert(isa<ValueTy>(VP) && 309 "Tracked Value was replaced by one with an invalid type!"); 310 } 311 312 ValueTy *getValPtr() const { 313 CheckValidity(); 314 return (ValueTy*)ValueHandleBase::getValPtr(); 315 } 316 void setValPtr(ValueTy *P) { 317 CheckValidity(); 318 ValueHandleBase::operator=(GetAsValue(P)); 319 } 320 321 // Convert a ValueTy*, which may be const, to the type the base 322 // class expects. 323 static Value *GetAsValue(Value *V) { return V; } 324 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); } 325 326 public: 327 TrackingVH() : ValueHandleBase(Tracking) {} 328 TrackingVH(ValueTy *P) : ValueHandleBase(Tracking, GetAsValue(P)) {} 329 TrackingVH(const TrackingVH &RHS) : ValueHandleBase(Tracking, RHS) {} 330 331 operator ValueTy*() const { 332 return getValPtr(); 333 } 334 335 ValueTy *operator=(ValueTy *RHS) { 336 setValPtr(RHS); 337 return getValPtr(); 338 } 339 ValueTy *operator=(const TrackingVH<ValueTy> &RHS) { 340 setValPtr(RHS.getValPtr()); 341 return getValPtr(); 342 } 343 344 ValueTy *operator->() const { return getValPtr(); } 345 ValueTy &operator*() const { return *getValPtr(); } 346 }; 347 348 // Specialize simplify_type to allow TrackingVH to participate in 349 // dyn_cast, isa, etc. 350 template<typename From> struct simplify_type; 351 template<> struct simplify_type<const TrackingVH<Value> > { 352 typedef Value* SimpleType; 353 static SimpleType getSimplifiedValue(const TrackingVH<Value> &AVH) { 354 return static_cast<Value *>(AVH); 355 } 356 }; 357 template<> struct simplify_type<TrackingVH<Value> > 358 : public simplify_type<const TrackingVH<Value> > {}; 359 360 /// CallbackVH - This is a value handle that allows subclasses to define 361 /// callbacks that run when the underlying Value has RAUW called on it or is 362 /// destroyed. This class can be used as the key of a map, as long as the user 363 /// takes it out of the map before calling setValPtr() (since the map has to 364 /// rearrange itself when the pointer changes). Unlike ValueHandleBase, this 365 /// class has a vtable and a virtual destructor. 366 class CallbackVH : public ValueHandleBase { 367 protected: 368 CallbackVH(const CallbackVH &RHS) 369 : ValueHandleBase(Callback, RHS) {} 370 371 virtual ~CallbackVH() {} 372 373 void setValPtr(Value *P) { 374 ValueHandleBase::operator=(P); 375 } 376 377 public: 378 CallbackVH() : ValueHandleBase(Callback) {} 379 CallbackVH(Value *P) : ValueHandleBase(Callback, P) {} 380 381 operator Value*() const { 382 return getValPtr(); 383 } 384 385 /// Called when this->getValPtr() is destroyed, inside ~Value(), so you may 386 /// call any non-virtual Value method on getValPtr(), but no subclass methods. 387 /// If WeakVH were implemented as a CallbackVH, it would use this method to 388 /// call setValPtr(NULL). AssertingVH would use this method to cause an 389 /// assertion failure. 390 /// 391 /// All implementations must remove the reference from this object to the 392 /// Value that's being destroyed. 393 virtual void deleted(); 394 395 /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called, 396 /// _before_ any of the uses have actually been replaced. If WeakVH were 397 /// implemented as a CallbackVH, it would use this method to call 398 /// setValPtr(new_value). AssertingVH would do nothing in this method. 399 virtual void allUsesReplacedWith(Value *); 400 }; 401 402 // Specialize simplify_type to allow CallbackVH to participate in 403 // dyn_cast, isa, etc. 404 template<typename From> struct simplify_type; 405 template<> struct simplify_type<const CallbackVH> { 406 typedef Value* SimpleType; 407 static SimpleType getSimplifiedValue(const CallbackVH &CVH) { 408 return static_cast<Value *>(CVH); 409 } 410 }; 411 template<> struct simplify_type<CallbackVH> 412 : public simplify_type<const CallbackVH> {}; 413 414 } // End llvm namespace 415 416 #endif 417