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/// 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 /// 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 /// Remove this ValueHandle from its current use list.
105 void RemoveFromUseList();
106
107 /// 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 /// 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 /// Add this ValueHandle to the use list after Node.
131 void AddToExistingUseListAfter(ValueHandleBase *Node);
132
133 /// Add this ValueHandle to the use list for V.
134 void AddToUseList();
135};
136
137/// 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/// 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/// 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/// 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/// 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 /// 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 /// 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