1 //===- ValueHandle.h - Value Smart Pointer classes --------------*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This file declares the ValueHandle class and its sub-classes.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_IR_VALUEHANDLE_H
14 #define LLVM_IR_VALUEHANDLE_H
16 #include "llvm/ADT/DenseMapInfo.h"
17 #include "llvm/ADT/PointerIntPair.h"
18 #include "llvm/IR/Value.h"
19 #include "llvm/Support/Casting.h"
24 /// This is the common base class of value handles.
26 /// ValueHandle's are smart pointers to Value's that have special behavior when
27 /// the value is deleted or ReplaceAllUsesWith'd. See the specific handles
28 /// below for details.
29 class ValueHandleBase
{
33 /// This indicates what sub class the handle actually is.
35 /// This is to avoid having a vtable for the light-weight handle pointers. The
36 /// fully general Callback version does have a vtable.
37 enum HandleBaseKind
{ Assert
, Callback
, Weak
, WeakTracking
};
39 ValueHandleBase(const ValueHandleBase
&RHS
)
40 : ValueHandleBase(RHS
.PrevPair
.getInt(), RHS
) {}
42 ValueHandleBase(HandleBaseKind Kind
, const ValueHandleBase
&RHS
)
43 : PrevPair(nullptr, Kind
), Val(RHS
.getValPtr()) {
44 if (isValid(getValPtr()))
45 AddToExistingUseList(RHS
.getPrevPtr());
49 PointerIntPair
<ValueHandleBase
**, 2, HandleBaseKind
> PrevPair
;
50 ValueHandleBase
*Next
= nullptr;
53 void setValPtr(Value
*V
) { Val
= V
; }
56 explicit ValueHandleBase(HandleBaseKind Kind
)
57 : PrevPair(nullptr, Kind
) {}
58 ValueHandleBase(HandleBaseKind Kind
, Value
*V
)
59 : PrevPair(nullptr, Kind
), Val(V
) {
60 if (isValid(getValPtr()))
65 if (isValid(getValPtr()))
69 Value
*operator=(Value
*RHS
) {
70 if (getValPtr() == RHS
)
72 if (isValid(getValPtr()))
75 if (isValid(getValPtr()))
80 Value
*operator=(const ValueHandleBase
&RHS
) {
81 if (getValPtr() == RHS
.getValPtr())
82 return RHS
.getValPtr();
83 if (isValid(getValPtr()))
85 setValPtr(RHS
.getValPtr());
86 if (isValid(getValPtr()))
87 AddToExistingUseList(RHS
.getPrevPtr());
91 Value
*operator->() const { return getValPtr(); }
92 Value
&operator*() const { return *getValPtr(); }
95 Value
*getValPtr() const { return Val
; }
97 static bool isValid(Value
*V
) {
99 V
!= DenseMapInfo
<Value
*>::getEmptyKey() &&
100 V
!= DenseMapInfo
<Value
*>::getTombstoneKey();
103 /// Remove this ValueHandle from its current use list.
104 void RemoveFromUseList();
106 /// Clear the underlying pointer without clearing the use list.
108 /// This should only be used if a derived class has manually removed the
109 /// handle from the use list.
110 void clearValPtr() { setValPtr(nullptr); }
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 /// 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 /// Add this ValueHandle to the use list after Node.
130 void AddToExistingUseListAfter(ValueHandleBase
*Node
);
132 /// Add this ValueHandle to the use list for V.
136 /// A nullable Value handle that is nullable.
138 /// This is a value handle that points to a value, and nulls itself
139 /// out if that value is deleted.
140 class WeakVH
: public ValueHandleBase
{
142 WeakVH() : ValueHandleBase(Weak
) {}
143 WeakVH(Value
*P
) : ValueHandleBase(Weak
, P
) {}
144 WeakVH(const WeakVH
&RHS
)
145 : ValueHandleBase(Weak
, RHS
) {}
147 WeakVH
&operator=(const WeakVH
&RHS
) = default;
149 Value
*operator=(Value
*RHS
) {
150 return ValueHandleBase::operator=(RHS
);
152 Value
*operator=(const ValueHandleBase
&RHS
) {
153 return ValueHandleBase::operator=(RHS
);
156 operator Value
*() const {
161 // Specialize simplify_type to allow WeakVH to participate in
162 // dyn_cast, isa, etc.
163 template <> struct simplify_type
<WeakVH
> {
164 using SimpleType
= Value
*;
166 static SimpleType
getSimplifiedValue(WeakVH
&WVH
) { return WVH
; }
168 template <> struct simplify_type
<const WeakVH
> {
169 using SimpleType
= Value
*;
171 static SimpleType
getSimplifiedValue(const WeakVH
&WVH
) { return WVH
; }
174 /// Value handle that is nullable, but tries to track the Value.
176 /// This is a value handle that tries hard to point to a Value, even across
177 /// RAUW operations, but will null itself out if the value is destroyed. this
178 /// is useful for advisory sorts of information, but should not be used as the
179 /// key of a map (since the map would have to rearrange itself when the pointer
181 class WeakTrackingVH
: public ValueHandleBase
{
183 WeakTrackingVH() : ValueHandleBase(WeakTracking
) {}
184 WeakTrackingVH(Value
*P
) : ValueHandleBase(WeakTracking
, P
) {}
185 WeakTrackingVH(const WeakTrackingVH
&RHS
)
186 : ValueHandleBase(WeakTracking
, RHS
) {}
188 WeakTrackingVH
&operator=(const WeakTrackingVH
&RHS
) = default;
190 Value
*operator=(Value
*RHS
) {
191 return ValueHandleBase::operator=(RHS
);
193 Value
*operator=(const ValueHandleBase
&RHS
) {
194 return ValueHandleBase::operator=(RHS
);
197 operator Value
*() const {
201 bool pointsToAliveValue() const {
202 return ValueHandleBase::isValid(getValPtr());
206 // Specialize simplify_type to allow WeakTrackingVH to participate in
207 // dyn_cast, isa, etc.
208 template <> struct simplify_type
<WeakTrackingVH
> {
209 using SimpleType
= Value
*;
211 static SimpleType
getSimplifiedValue(WeakTrackingVH
&WVH
) { return WVH
; }
213 template <> struct simplify_type
<const WeakTrackingVH
> {
214 using SimpleType
= Value
*;
216 static SimpleType
getSimplifiedValue(const WeakTrackingVH
&WVH
) {
221 /// Value handle that asserts if the Value is deleted.
223 /// This is a Value Handle that points to a value and asserts out if the value
224 /// is destroyed while the handle is still live. This is very useful for
225 /// catching dangling pointer bugs and other things which can be non-obvious.
226 /// One particularly useful place to use this is as the Key of a map. Dangling
227 /// pointer bugs often lead to really subtle bugs that only occur if another
228 /// object happens to get allocated to the same address as the old one. Using
229 /// an AssertingVH ensures that an assert is triggered as soon as the bad
232 /// Note that an AssertingVH handle does *not* follow values across RAUW
233 /// operations. This means that RAUW's need to explicitly update the
234 /// AssertingVH's as it moves. This is required because in non-assert mode this
235 /// class turns into a trivial wrapper around a pointer.
236 template <typename ValueTy
>
239 : public ValueHandleBase
242 friend struct DenseMapInfo
<AssertingVH
<ValueTy
>>;
245 Value
*getRawValPtr() const { return ValueHandleBase::getValPtr(); }
246 void setRawValPtr(Value
*P
) { ValueHandleBase::operator=(P
); }
249 Value
*getRawValPtr() const { return ThePtr
; }
250 void setRawValPtr(Value
*P
) { ThePtr
= P
; }
252 // Convert a ValueTy*, which may be const, to the raw Value*.
253 static Value
*GetAsValue(Value
*V
) { return V
; }
254 static Value
*GetAsValue(const Value
*V
) { return const_cast<Value
*>(V
); }
256 ValueTy
*getValPtr() const { return static_cast<ValueTy
*>(getRawValPtr()); }
257 void setValPtr(ValueTy
*P
) { setRawValPtr(GetAsValue(P
)); }
261 AssertingVH() : ValueHandleBase(Assert
) {}
262 AssertingVH(ValueTy
*P
) : ValueHandleBase(Assert
, GetAsValue(P
)) {}
263 AssertingVH(const AssertingVH
&RHS
) : ValueHandleBase(Assert
, RHS
) {}
265 AssertingVH() : ThePtr(nullptr) {}
266 AssertingVH(ValueTy
*P
) : ThePtr(GetAsValue(P
)) {}
269 operator ValueTy
*() const {
273 ValueTy
*operator=(ValueTy
*RHS
) {
277 ValueTy
*operator=(const AssertingVH
<ValueTy
> &RHS
) {
278 setValPtr(RHS
.getValPtr());
282 ValueTy
*operator->() const { return getValPtr(); }
283 ValueTy
&operator*() const { return *getValPtr(); }
286 // Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap.
288 struct DenseMapInfo
<AssertingVH
<T
>> {
289 static inline AssertingVH
<T
> getEmptyKey() {
291 Res
.setRawValPtr(DenseMapInfo
<Value
*>::getEmptyKey());
295 static inline AssertingVH
<T
> getTombstoneKey() {
297 Res
.setRawValPtr(DenseMapInfo
<Value
*>::getTombstoneKey());
301 static unsigned getHashValue(const AssertingVH
<T
> &Val
) {
302 return DenseMapInfo
<Value
*>::getHashValue(Val
.getRawValPtr());
305 static bool isEqual(const AssertingVH
<T
> &LHS
, const AssertingVH
<T
> &RHS
) {
306 return DenseMapInfo
<Value
*>::isEqual(LHS
.getRawValPtr(),
311 /// Value handle that tracks a Value across RAUW.
313 /// TrackingVH is designed for situations where a client needs to hold a handle
314 /// to a Value (or subclass) across some operations which may move that value,
315 /// but should never destroy it or replace it with some unacceptable type.
317 /// It is an error to attempt to replace a value with one of a type which is
318 /// incompatible with any of its outstanding TrackingVHs.
320 /// It is an error to read from a TrackingVH that does not point to a valid
321 /// value. A TrackingVH is said to not point to a valid value if either it
322 /// hasn't yet been assigned a value yet or because the value it was tracking
323 /// has since been deleted.
325 /// Assigning a value to a TrackingVH is always allowed, even if said TrackingVH
326 /// no longer points to a valid value.
327 template <typename ValueTy
> class TrackingVH
{
328 WeakTrackingVH InnerHandle
;
331 ValueTy
*getValPtr() const {
332 assert(InnerHandle
.pointsToAliveValue() &&
333 "TrackingVH must be non-null and valid on dereference!");
335 // Check that the value is a member of the correct subclass. We would like
336 // to check this property on assignment for better debugging, but we don't
337 // want to require a virtual interface on this VH. Instead we allow RAUW to
338 // replace this value with a value of an invalid type, and check it here.
339 assert(isa
<ValueTy
>(InnerHandle
) &&
340 "Tracked Value was replaced by one with an invalid type!");
341 return cast
<ValueTy
>(InnerHandle
);
344 void setValPtr(ValueTy
*P
) {
345 // Assigning to non-valid TrackingVH's are fine so we just unconditionally
347 InnerHandle
= GetAsValue(P
);
350 // Convert a ValueTy*, which may be const, to the type the base
352 static Value
*GetAsValue(Value
*V
) { return V
; }
353 static Value
*GetAsValue(const Value
*V
) { return const_cast<Value
*>(V
); }
356 TrackingVH() = default;
357 TrackingVH(ValueTy
*P
) { setValPtr(P
); }
359 operator ValueTy
*() const {
363 ValueTy
*operator=(ValueTy
*RHS
) {
368 ValueTy
*operator->() const { return getValPtr(); }
369 ValueTy
&operator*() const { return *getValPtr(); }
372 /// Value handle with callbacks on RAUW and destruction.
374 /// This is a value handle that allows subclasses to define callbacks that run
375 /// when the underlying Value has RAUW called on it or is destroyed. This
376 /// class can be used as the key of a map, as long as the user takes it out of
377 /// the map before calling setValPtr() (since the map has to rearrange itself
378 /// when the pointer changes). Unlike ValueHandleBase, this class has a vtable.
379 class CallbackVH
: public ValueHandleBase
{
380 virtual void anchor();
382 ~CallbackVH() = default;
383 CallbackVH(const CallbackVH
&) = default;
384 CallbackVH
&operator=(const CallbackVH
&) = default;
386 void setValPtr(Value
*P
) {
387 ValueHandleBase::operator=(P
);
391 CallbackVH() : ValueHandleBase(Callback
) {}
392 CallbackVH(Value
*P
) : ValueHandleBase(Callback
, P
) {}
394 operator Value
*() const {
398 /// Callback for Value destruction.
400 /// Called when this->getValPtr() is destroyed, inside ~Value(), so you
401 /// may call any non-virtual Value method on getValPtr(), but no subclass
402 /// methods. If WeakTrackingVH were implemented as a CallbackVH, it would use
404 /// method to call setValPtr(NULL). AssertingVH would use this method to
405 /// cause an assertion failure.
407 /// All implementations must remove the reference from this object to the
408 /// Value that's being destroyed.
409 virtual void deleted() { setValPtr(nullptr); }
411 /// Callback for Value RAUW.
413 /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called,
414 /// _before_ any of the uses have actually been replaced. If WeakTrackingVH
416 /// implemented as a CallbackVH, it would use this method to call
417 /// setValPtr(new_value). AssertingVH would do nothing in this method.
418 virtual void allUsesReplacedWith(Value
*) {}
421 /// Value handle that poisons itself if the Value is deleted.
423 /// This is a Value Handle that points to a value and poisons itself if the
424 /// value is destroyed while the handle is still live. This is very useful for
425 /// catching dangling pointer bugs where an \c AssertingVH cannot be used
426 /// because the dangling handle needs to outlive the value without ever being
429 /// One particularly useful place to use this is as the Key of a map. Dangling
430 /// pointer bugs often lead to really subtle bugs that only occur if another
431 /// object happens to get allocated to the same address as the old one. Using
432 /// a PoisoningVH ensures that an assert is triggered if looking up a new value
433 /// in the map finds a handle from the old value.
435 /// Note that a PoisoningVH handle does *not* follow values across RAUW
436 /// operations. This means that RAUW's need to explicitly update the
437 /// PoisoningVH's as it moves. This is required because in non-assert mode this
438 /// class turns into a trivial wrapper around a pointer.
439 template <typename ValueTy
>
442 final
: public CallbackVH
445 friend struct DenseMapInfo
<PoisoningVH
<ValueTy
>>;
447 // Convert a ValueTy*, which may be const, to the raw Value*.
448 static Value
*GetAsValue(Value
*V
) { return V
; }
449 static Value
*GetAsValue(const Value
*V
) { return const_cast<Value
*>(V
); }
452 /// A flag tracking whether this value has been poisoned.
454 /// On delete and RAUW, we leave the value pointer alone so that as a raw
455 /// pointer it produces the same value (and we fit into the same key of
456 /// a hash table, etc), but we poison the handle so that any top-level usage
458 bool Poisoned
= false;
460 Value
*getRawValPtr() const { return ValueHandleBase::getValPtr(); }
461 void setRawValPtr(Value
*P
) { ValueHandleBase::operator=(P
); }
463 /// Handle deletion by poisoning the handle.
464 void deleted() override
{
465 assert(!Poisoned
&& "Tried to delete an already poisoned handle!");
470 /// Handle RAUW by poisoning the handle.
471 void allUsesReplacedWith(Value
*) override
{
472 assert(!Poisoned
&& "Tried to RAUW an already poisoned handle!");
477 Value
*ThePtr
= nullptr;
479 Value
*getRawValPtr() const { return ThePtr
; }
480 void setRawValPtr(Value
*P
) { ThePtr
= P
; }
483 ValueTy
*getValPtr() const {
484 assert(!Poisoned
&& "Accessed a poisoned value handle!");
485 return static_cast<ValueTy
*>(getRawValPtr());
487 void setValPtr(ValueTy
*P
) { setRawValPtr(GetAsValue(P
)); }
490 PoisoningVH() = default;
492 PoisoningVH(ValueTy
*P
) : CallbackVH(GetAsValue(P
)) {}
493 PoisoningVH(const PoisoningVH
&RHS
)
494 : CallbackVH(RHS
), Poisoned(RHS
.Poisoned
) {}
501 PoisoningVH
&operator=(const PoisoningVH
&RHS
) {
504 CallbackVH::operator=(RHS
);
505 Poisoned
= RHS
.Poisoned
;
509 PoisoningVH(ValueTy
*P
) : ThePtr(GetAsValue(P
)) {}
512 operator ValueTy
*() const { return getValPtr(); }
514 ValueTy
*operator->() const { return getValPtr(); }
515 ValueTy
&operator*() const { return *getValPtr(); }
518 // Specialize DenseMapInfo to allow PoisoningVH to participate in DenseMap.
519 template <typename T
> struct DenseMapInfo
<PoisoningVH
<T
>> {
520 static inline PoisoningVH
<T
> getEmptyKey() {
522 Res
.setRawValPtr(DenseMapInfo
<Value
*>::getEmptyKey());
526 static inline PoisoningVH
<T
> getTombstoneKey() {
528 Res
.setRawValPtr(DenseMapInfo
<Value
*>::getTombstoneKey());
532 static unsigned getHashValue(const PoisoningVH
<T
> &Val
) {
533 return DenseMapInfo
<Value
*>::getHashValue(Val
.getRawValPtr());
536 static bool isEqual(const PoisoningVH
<T
> &LHS
, const PoisoningVH
<T
> &RHS
) {
537 return DenseMapInfo
<Value
*>::isEqual(LHS
.getRawValPtr(),
542 } // end namespace llvm
544 #endif // LLVM_IR_VALUEHANDLE_H