1 //===- ValueHandle.h - Value Smart Pointer classes --------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file declares the ValueHandle class and its sub-classes.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_IR_VALUEHANDLE_H
15 #define LLVM_IR_VALUEHANDLE_H
17 #include "llvm/ADT/DenseMapInfo.h"
18 #include "llvm/ADT/PointerIntPair.h"
19 #include "llvm/IR/Value.h"
22 class ValueHandleBase;
23 template<typename From> struct simplify_type;
25 // ValueHandleBase** is only 4-byte aligned.
27 class PointerLikeTypeTraits<ValueHandleBase**> {
29 static inline void *getAsVoidPointer(ValueHandleBase** P) { return P; }
30 static inline ValueHandleBase **getFromVoidPointer(void *P) {
31 return static_cast<ValueHandleBase**>(P);
33 enum { NumLowBitsAvailable = 2 };
36 /// \brief This is the common base class of value handles.
38 /// ValueHandle's are smart pointers to Value's that have special behavior when
39 /// the value is deleted or ReplaceAllUsesWith'd. See the specific handles
40 /// below for details.
41 class ValueHandleBase {
44 /// \brief This indicates what sub class the handle actually is.
46 /// This is to avoid having a vtable for the light-weight handle pointers. The
47 /// fully general Callback version does have a vtable.
55 ValueHandleBase(const ValueHandleBase &RHS)
56 : ValueHandleBase(RHS.PrevPair.getInt(), RHS) {}
58 ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS)
59 : PrevPair(nullptr, Kind), Next(nullptr), V(RHS.V) {
61 AddToExistingUseList(RHS.getPrevPtr());
65 PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair;
66 ValueHandleBase *Next;
71 explicit ValueHandleBase(HandleBaseKind Kind)
72 : PrevPair(nullptr, Kind), Next(nullptr), V(nullptr) {}
73 ValueHandleBase(HandleBaseKind Kind, Value *V)
74 : PrevPair(nullptr, Kind), Next(nullptr), V(V) {
84 Value *operator=(Value *RHS) {
85 if (V == RHS) return RHS;
86 if (isValid(V)) RemoveFromUseList();
88 if (isValid(V)) AddToUseList();
92 Value *operator=(const ValueHandleBase &RHS) {
93 if (V == RHS.V) return RHS.V;
94 if (isValid(V)) RemoveFromUseList();
96 if (isValid(V)) AddToExistingUseList(RHS.getPrevPtr());
100 Value *operator->() const { return V; }
101 Value &operator*() const { return *V; }
104 Value *getValPtr() const { return V; }
106 static bool isValid(Value *V) {
108 V != DenseMapInfo<Value *>::getEmptyKey() &&
109 V != DenseMapInfo<Value *>::getTombstoneKey();
113 // Callbacks made from Value.
114 static void ValueIsDeleted(Value *V);
115 static void ValueIsRAUWd(Value *Old, Value *New);
118 // Internal implementation details.
119 ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
120 HandleBaseKind getKind() const { return PrevPair.getInt(); }
121 void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); }
123 /// \brief Add this ValueHandle to the use list for V.
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);
129 /// \brief Add this ValueHandle to the use list after Node.
130 void AddToExistingUseListAfter(ValueHandleBase *Node);
132 /// \brief Add this ValueHandle to the use list for V.
134 /// \brief Remove this ValueHandle from its current use list.
135 void RemoveFromUseList();
138 /// \brief Value handle that is nullable, but tries to track the Value.
140 /// This is a value handle that tries hard to point to a Value, even across
141 /// RAUW operations, but will null itself out if the value is destroyed. this
142 /// is useful for advisory sorts of information, but should not be used as the
143 /// key of a map (since the map would have to rearrange itself when the pointer
145 class WeakVH : public ValueHandleBase {
147 WeakVH() : ValueHandleBase(Weak) {}
148 WeakVH(Value *P) : ValueHandleBase(Weak, P) {}
149 WeakVH(const WeakVH &RHS)
150 : ValueHandleBase(Weak, RHS) {}
152 WeakVH &operator=(const WeakVH &RHS) = default;
154 Value *operator=(Value *RHS) {
155 return ValueHandleBase::operator=(RHS);
157 Value *operator=(const ValueHandleBase &RHS) {
158 return ValueHandleBase::operator=(RHS);
161 operator Value*() const {
166 // Specialize simplify_type to allow WeakVH to participate in
167 // dyn_cast, isa, etc.
168 template <> struct simplify_type<WeakVH> {
169 typedef Value *SimpleType;
170 static SimpleType getSimplifiedValue(WeakVH &WVH) { return WVH; }
172 template <> struct simplify_type<const WeakVH> {
173 typedef Value *SimpleType;
174 static SimpleType getSimplifiedValue(const WeakVH &WVH) { return WVH; }
177 /// \brief Value handle that asserts if the Value is deleted.
179 /// This is a Value Handle that points to a value and asserts out if the value
180 /// is destroyed while the handle is still live. This is very useful for
181 /// catching dangling pointer bugs and other things which can be non-obvious.
182 /// One particularly useful place to use this is as the Key of a map. Dangling
183 /// pointer bugs often lead to really subtle bugs that only occur if another
184 /// object happens to get allocated to the same address as the old one. Using
185 /// an AssertingVH ensures that an assert is triggered as soon as the bad
188 /// Note that an AssertingVH handle does *not* follow values across RAUW
189 /// operations. This means that RAUW's need to explicitly update the
190 /// AssertingVH's as it moves. This is required because in non-assert mode this
191 /// class turns into a trivial wrapper around a pointer.
192 template <typename ValueTy>
195 : public ValueHandleBase
198 friend struct DenseMapInfo<AssertingVH<ValueTy> >;
201 Value *getRawValPtr() const { return ValueHandleBase::getValPtr(); }
202 void setRawValPtr(Value *P) { ValueHandleBase::operator=(P); }
205 Value *getRawValPtr() const { return ThePtr; }
206 void setRawValPtr(Value *P) { ThePtr = P; }
208 // Convert a ValueTy*, which may be const, to the raw Value*.
209 static Value *GetAsValue(Value *V) { return V; }
210 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); }
212 ValueTy *getValPtr() const { return static_cast<ValueTy *>(getRawValPtr()); }
213 void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); }
217 AssertingVH() : ValueHandleBase(Assert) {}
218 AssertingVH(ValueTy *P) : ValueHandleBase(Assert, GetAsValue(P)) {}
219 AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {}
221 AssertingVH() : ThePtr(nullptr) {}
222 AssertingVH(ValueTy *P) : ThePtr(GetAsValue(P)) {}
225 operator ValueTy*() const {
229 ValueTy *operator=(ValueTy *RHS) {
233 ValueTy *operator=(const AssertingVH<ValueTy> &RHS) {
234 setValPtr(RHS.getValPtr());
238 ValueTy *operator->() const { return getValPtr(); }
239 ValueTy &operator*() const { return *getValPtr(); }
242 // Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap.
244 struct DenseMapInfo<AssertingVH<T> > {
245 static inline AssertingVH<T> getEmptyKey() {
247 Res.setRawValPtr(DenseMapInfo<Value *>::getEmptyKey());
250 static inline AssertingVH<T> getTombstoneKey() {
252 Res.setRawValPtr(DenseMapInfo<Value *>::getTombstoneKey());
255 static unsigned getHashValue(const AssertingVH<T> &Val) {
256 return DenseMapInfo<Value *>::getHashValue(Val.getRawValPtr());
258 static bool isEqual(const AssertingVH<T> &LHS, const AssertingVH<T> &RHS) {
259 return DenseMapInfo<Value *>::isEqual(LHS.getRawValPtr(),
264 template <typename T>
265 struct isPodLike<AssertingVH<T> > {
267 static const bool value = true;
269 static const bool value = false;
274 /// \brief Value handle that tracks a Value across RAUW.
276 /// TrackingVH is designed for situations where a client needs to hold a handle
277 /// to a Value (or subclass) across some operations which may move that value,
278 /// but should never destroy it or replace it with some unacceptable type.
280 /// It is an error to do anything with a TrackingVH whose value has been
281 /// destroyed, except to destruct it.
283 /// It is an error to attempt to replace a value with one of a type which is
284 /// incompatible with any of its outstanding TrackingVHs.
285 template<typename ValueTy>
286 class TrackingVH : public ValueHandleBase {
287 void CheckValidity() const {
288 Value *VP = ValueHandleBase::getValPtr();
290 // Null is always ok.
293 // Check that this value is valid (i.e., it hasn't been deleted). We
294 // explicitly delay this check until access to avoid requiring clients to be
295 // unnecessarily careful w.r.t. destruction.
296 assert(ValueHandleBase::isValid(VP) && "Tracked Value was deleted!");
298 // Check that the value is a member of the correct subclass. We would like
299 // to check this property on assignment for better debugging, but we don't
300 // want to require a virtual interface on this VH. Instead we allow RAUW to
301 // replace this value with a value of an invalid type, and check it here.
302 assert(isa<ValueTy>(VP) &&
303 "Tracked Value was replaced by one with an invalid type!");
306 ValueTy *getValPtr() const {
308 return (ValueTy*)ValueHandleBase::getValPtr();
310 void setValPtr(ValueTy *P) {
312 ValueHandleBase::operator=(GetAsValue(P));
315 // Convert a ValueTy*, which may be const, to the type the base
317 static Value *GetAsValue(Value *V) { return V; }
318 static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); }
321 TrackingVH() : ValueHandleBase(Tracking) {}
322 TrackingVH(ValueTy *P) : ValueHandleBase(Tracking, GetAsValue(P)) {}
324 operator ValueTy*() const {
328 ValueTy *operator=(ValueTy *RHS) {
333 ValueTy *operator->() const { return getValPtr(); }
334 ValueTy &operator*() const { return *getValPtr(); }
337 /// \brief Value handle with callbacks on RAUW and destruction.
339 /// This is a value handle that allows subclasses to define callbacks that run
340 /// when the underlying Value has RAUW called on it or is destroyed. This
341 /// class can be used as the key of a map, as long as the user takes it out of
342 /// the map before calling setValPtr() (since the map has to rearrange itself
343 /// when the pointer changes). Unlike ValueHandleBase, this class has a vtable.
344 class CallbackVH : public ValueHandleBase {
345 virtual void anchor();
347 ~CallbackVH() = default;
348 CallbackVH(const CallbackVH &) = default;
349 CallbackVH &operator=(const CallbackVH &) = default;
351 void setValPtr(Value *P) {
352 ValueHandleBase::operator=(P);
356 CallbackVH() : ValueHandleBase(Callback) {}
357 CallbackVH(Value *P) : ValueHandleBase(Callback, P) {}
359 operator Value*() const {
363 /// \brief Callback for Value destruction.
365 /// Called when this->getValPtr() is destroyed, inside ~Value(), so you
366 /// may call any non-virtual Value method on getValPtr(), but no subclass
367 /// methods. If WeakVH were implemented as a CallbackVH, it would use this
368 /// method to call setValPtr(NULL). AssertingVH would use this method to
369 /// cause an assertion failure.
371 /// All implementations must remove the reference from this object to the
372 /// Value that's being destroyed.
373 virtual void deleted() { setValPtr(nullptr); }
375 /// \brief Callback for Value RAUW.
377 /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called,
378 /// _before_ any of the uses have actually been replaced. If WeakVH were
379 /// implemented as a CallbackVH, it would use this method to call
380 /// setValPtr(new_value). AssertingVH would do nothing in this method.
381 virtual void allUsesReplacedWith(Value *) {}
384 } // End llvm namespace