reference, declarationdefinition
definition → references, declarations, derived classes, virtual overrides
reference to multiple definitions → definitions
unreferenced
    1
    2
    3
    4
    5
    6
    7
    8
    9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
  100
  101
  102
  103
  104
  105
  106
  107
  108
  109
  110
  111
  112
  113
  114
  115
  116
  117
  118
  119
  120
  121
  122
  123
  124
  125
  126
  127
  128
  129
  130
  131
  132
  133
  134
  135
  136
  137
  138
  139
  140
  141
  142
  143
  144
  145
  146
  147
  148
  149
  150
  151
  152
  153
  154
  155
  156
  157
  158
  159
  160
  161
  162
  163
  164
  165
  166
  167
  168
  169
  170
  171
  172
  173
  174
  175
  176
  177
  178
  179
  180
  181
  182
  183
  184
  185
  186
  187
  188
  189
  190
  191
  192
  193
  194
  195
  196
  197
  198
  199
  200
  201
  202
  203
  204
  205
  206
  207
  208
  209
  210
  211
  212
  213
  214
  215
  216
  217
  218
  219
  220
  221
  222
  223
  224
  225
  226
  227
  228
  229
  230
  231
  232
  233
  234
  235
  236
  237
  238
  239
  240
  241
  242
  243
  244
  245
  246
  247
  248
  249
  250
  251
  252
  253
  254
  255
  256
  257
  258
  259
  260
  261
  262
  263
  264
  265
  266
  267
  268
  269
  270
  271
  272
  273
  274
  275
  276
  277
  278
  279
  280
  281
  282
  283
  284
  285
  286
  287
  288
  289
  290
  291
  292
  293
  294
  295
  296
  297
  298
  299
  300
  301
  302
  303
  304
  305
  306
  307
  308
  309
  310
  311
  312
  313
  314
  315
  316
  317
  318
  319
  320
  321
  322
  323
  324
  325
  326
  327
  328
  329
  330
  331
  332
  333
  334
  335
  336
  337
  338
  339
  340
  341
  342
  343
  344
  345
  346
  347
  348
  349
  350
  351
  352
  353
  354
  355
  356
  357
  358
  359
  360
  361
  362
  363
  364
  365
  366
  367
  368
  369
  370
  371
  372
  373
  374
  375
  376
  377
  378
  379
  380
  381
  382
  383
  384
  385
  386
  387
  388
  389
  390
  391
  392
  393
  394
  395
  396
  397
  398
  399
  400
  401
  402
  403
  404
  405
  406
  407
  408
  409
  410
  411
  412
  413
  414
  415
  416
  417
  418
  419
  420
  421
  422
  423
  424
  425
  426
  427
  428
  429
  430
  431
  432
  433
  434
  435
  436
  437
  438
  439
  440
  441
  442
  443
  444
  445
  446
  447
  448
  449
  450
  451
  452
  453
  454
  455
  456
  457
  458
  459
  460
  461
  462
  463
  464
  465
  466
  467
  468
  469
  470
  471
  472
  473
  474
  475
  476
  477
  478
  479
  480
  481
  482
  483
  484
  485
  486
  487
  488
  489
  490
  491
  492
  493
  494
  495
  496
  497
  498
  499
  500
  501
  502
  503
  504
  505
  506
  507
  508
  509
  510
  511
  512
  513
  514
  515
  516
  517
  518
  519
  520
  521
  522
  523
  524
  525
  526
  527
  528
  529
  530
  531
  532
  533
  534
  535
  536
  537
  538
  539
  540
  541
  542
  543
  544
//===- ValueHandle.h - Value Smart Pointer classes --------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file declares the ValueHandle class and its sub-classes.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_VALUEHANDLE_H
#define LLVM_IR_VALUEHANDLE_H

#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include <cassert>

namespace llvm {

/// This is the common base class of value handles.
///
/// ValueHandle's are smart pointers to Value's that have special behavior when
/// the value is deleted or ReplaceAllUsesWith'd.  See the specific handles
/// below for details.
class ValueHandleBase {
  friend class Value;

protected:
  /// This indicates what sub class the handle actually is.
  ///
  /// This is to avoid having a vtable for the light-weight handle pointers. The
  /// fully general Callback version does have a vtable.
  enum HandleBaseKind { Assert, Callback, Weak, WeakTracking };

  ValueHandleBase(const ValueHandleBase &RHS)
      : ValueHandleBase(RHS.PrevPair.getInt(), RHS) {}

  ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS)
      : PrevPair(nullptr, Kind), Val(RHS.getValPtr()) {
    if (isValid(getValPtr()))
      AddToExistingUseList(RHS.getPrevPtr());
  }

private:
  PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair;
  ValueHandleBase *Next = nullptr;
  Value *Val = nullptr;

  void setValPtr(Value *V) { Val = V; }

public:
  explicit ValueHandleBase(HandleBaseKind Kind)
      : PrevPair(nullptr, Kind) {}
  ValueHandleBase(HandleBaseKind Kind, Value *V)
      : PrevPair(nullptr, Kind), Val(V) {
    if (isValid(getValPtr()))
      AddToUseList();
  }

  ~ValueHandleBase() {
    if (isValid(getValPtr()))
      RemoveFromUseList();
  }

  Value *operator=(Value *RHS) {
    if (getValPtr() == RHS)
      return RHS;
    if (isValid(getValPtr()))
      RemoveFromUseList();
    setValPtr(RHS);
    if (isValid(getValPtr()))
      AddToUseList();
    return RHS;
  }

  Value *operator=(const ValueHandleBase &RHS) {
    if (getValPtr() == RHS.getValPtr())
      return RHS.getValPtr();
    if (isValid(getValPtr()))
      RemoveFromUseList();
    setValPtr(RHS.getValPtr());
    if (isValid(getValPtr()))
      AddToExistingUseList(RHS.getPrevPtr());
    return getValPtr();
  }

  Value *operator->() const { return getValPtr(); }
  Value &operator*() const { return *getValPtr(); }

protected:
  Value *getValPtr() const { return Val; }

  static bool isValid(Value *V) {
    return V &&
           V != DenseMapInfo<Value *>::getEmptyKey() &&
           V != DenseMapInfo<Value *>::getTombstoneKey();
  }

  /// Remove this ValueHandle from its current use list.
  void RemoveFromUseList();

  /// Clear the underlying pointer without clearing the use list.
  ///
  /// This should only be used if a derived class has manually removed the
  /// handle from the use list.
  void clearValPtr() { setValPtr(nullptr); }

public:
  // Callbacks made from Value.
  static void ValueIsDeleted(Value *V);
  static void ValueIsRAUWd(Value *Old, Value *New);

private:
  // Internal implementation details.
  ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
  HandleBaseKind getKind() const { return PrevPair.getInt(); }
  void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); }

  /// Add this ValueHandle to the use list for V.
  ///
  /// List is the address of either the head of the list or a Next node within
  /// the existing use list.
  void AddToExistingUseList(ValueHandleBase **List);

  /// Add this ValueHandle to the use list after Node.
  void AddToExistingUseListAfter(ValueHandleBase *Node);

  /// Add this ValueHandle to the use list for V.
  void AddToUseList();
};

/// A nullable Value handle that is nullable.
///
/// This is a value handle that points to a value, and nulls itself
/// out if that value is deleted.
class WeakVH : public ValueHandleBase {
public:
  WeakVH() : ValueHandleBase(Weak) {}
  WeakVH(Value *P) : ValueHandleBase(Weak, P) {}
  WeakVH(const WeakVH &RHS)
      : ValueHandleBase(Weak, RHS) {}

  WeakVH &operator=(const WeakVH &RHS) = default;

  Value *operator=(Value *RHS) {
    return ValueHandleBase::operator=(RHS);
  }
  Value *operator=(const ValueHandleBase &RHS) {
    return ValueHandleBase::operator=(RHS);
  }

  operator Value*() const {
    return getValPtr();
  }
};

// Specialize simplify_type to allow WeakVH to participate in
// dyn_cast, isa, etc.
template <> struct simplify_type<WeakVH> {
  using SimpleType = Value *;

  static SimpleType getSimplifiedValue(WeakVH &WVH) { return WVH; }
};
template <> struct simplify_type<const WeakVH> {
  using SimpleType = Value *;

  static SimpleType getSimplifiedValue(const WeakVH &WVH) { return WVH; }
};

/// Value handle that is nullable, but tries to track the Value.
///
/// This is a value handle that tries hard to point to a Value, even across
/// RAUW operations, but will null itself out if the value is destroyed.  this
/// is useful for advisory sorts of information, but should not be used as the
/// key of a map (since the map would have to rearrange itself when the pointer
/// changes).
class WeakTrackingVH : public ValueHandleBase {
public:
  WeakTrackingVH() : ValueHandleBase(WeakTracking) {}
  WeakTrackingVH(Value *P) : ValueHandleBase(WeakTracking, P) {}
  WeakTrackingVH(const WeakTrackingVH &RHS)
      : ValueHandleBase(WeakTracking, RHS) {}

  WeakTrackingVH &operator=(const WeakTrackingVH &RHS) = default;

  Value *operator=(Value *RHS) {
    return ValueHandleBase::operator=(RHS);
  }
  Value *operator=(const ValueHandleBase &RHS) {
    return ValueHandleBase::operator=(RHS);
  }

  operator Value*() const {
    return getValPtr();
  }

  bool pointsToAliveValue() const {
    return ValueHandleBase::isValid(getValPtr());
  }
};

// Specialize simplify_type to allow WeakTrackingVH to participate in
// dyn_cast, isa, etc.
template <> struct simplify_type<WeakTrackingVH> {
  using SimpleType = Value *;

  static SimpleType getSimplifiedValue(WeakTrackingVH &WVH) { return WVH; }
};
template <> struct simplify_type<const WeakTrackingVH> {
  using SimpleType = Value *;

  static SimpleType getSimplifiedValue(const WeakTrackingVH &WVH) {
    return WVH;
  }
};

/// Value handle that asserts if the Value is deleted.
///
/// This is a Value Handle that points to a value and asserts out if the value
/// is destroyed while the handle is still live.  This is very useful for
/// catching dangling pointer bugs and other things which can be non-obvious.
/// One particularly useful place to use this is as the Key of a map.  Dangling
/// pointer bugs often lead to really subtle bugs that only occur if another
/// object happens to get allocated to the same address as the old one.  Using
/// an AssertingVH ensures that an assert is triggered as soon as the bad
/// delete occurs.
///
/// Note that an AssertingVH handle does *not* follow values across RAUW
/// operations.  This means that RAUW's need to explicitly update the
/// AssertingVH's as it moves.  This is required because in non-assert mode this
/// class turns into a trivial wrapper around a pointer.
template <typename ValueTy>
class AssertingVH
#ifndef NDEBUG
  : public ValueHandleBase
#endif
  {
  friend struct DenseMapInfo<AssertingVH<ValueTy>>;

#ifndef NDEBUG
  Value *getRawValPtr() const { return ValueHandleBase::getValPtr(); }
  void setRawValPtr(Value *P) { ValueHandleBase::operator=(P); }
#else
  Value *ThePtr;
  Value *getRawValPtr() const { return ThePtr; }
  void setRawValPtr(Value *P) { ThePtr = P; }
#endif
  // Convert a ValueTy*, which may be const, to the raw Value*.
  static Value *GetAsValue(Value *V) { return V; }
  static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); }

  ValueTy *getValPtr() const { return static_cast<ValueTy *>(getRawValPtr()); }
  void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); }

public:
#ifndef NDEBUG
  AssertingVH() : ValueHandleBase(Assert) {}
  AssertingVH(ValueTy *P) : ValueHandleBase(Assert, GetAsValue(P)) {}
  AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {}
#else
  AssertingVH() : ThePtr(nullptr) {}
  AssertingVH(ValueTy *P) : ThePtr(GetAsValue(P)) {}
#endif

  operator ValueTy*() const {
    return getValPtr();
  }

  ValueTy *operator=(ValueTy *RHS) {
    setValPtr(RHS);
    return getValPtr();
  }
  ValueTy *operator=(const AssertingVH<ValueTy> &RHS) {
    setValPtr(RHS.getValPtr());
    return getValPtr();
  }

  ValueTy *operator->() const { return getValPtr(); }
  ValueTy &operator*() const { return *getValPtr(); }
};

// Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap.
template<typename T>
struct DenseMapInfo<AssertingVH<T>> {
  static inline AssertingVH<T> getEmptyKey() {
    AssertingVH<T> Res;
    Res.setRawValPtr(DenseMapInfo<Value *>::getEmptyKey());
    return Res;
  }

  static inline AssertingVH<T> getTombstoneKey() {
    AssertingVH<T> Res;
    Res.setRawValPtr(DenseMapInfo<Value *>::getTombstoneKey());
    return Res;
  }

  static unsigned getHashValue(const AssertingVH<T> &Val) {
    return DenseMapInfo<Value *>::getHashValue(Val.getRawValPtr());
  }

  static bool isEqual(const AssertingVH<T> &LHS, const AssertingVH<T> &RHS) {
    return DenseMapInfo<Value *>::isEqual(LHS.getRawValPtr(),
                                          RHS.getRawValPtr());
  }
};

/// Value handle that tracks a Value across RAUW.
///
/// TrackingVH is designed for situations where a client needs to hold a handle
/// to a Value (or subclass) across some operations which may move that value,
/// but should never destroy it or replace it with some unacceptable type.
///
/// It is an error to attempt to replace a value with one of a type which is
/// incompatible with any of its outstanding TrackingVHs.
///
/// It is an error to read from a TrackingVH that does not point to a valid
/// value.  A TrackingVH is said to not point to a valid value if either it
/// hasn't yet been assigned a value yet or because the value it was tracking
/// has since been deleted.
///
/// Assigning a value to a TrackingVH is always allowed, even if said TrackingVH
/// no longer points to a valid value.
template <typename ValueTy> class TrackingVH {
  WeakTrackingVH InnerHandle;

public:
  ValueTy *getValPtr() const {
    assert(InnerHandle.pointsToAliveValue() &&
           "TrackingVH must be non-null and valid on dereference!");

    // Check that the value is a member of the correct subclass. We would like
    // to check this property on assignment for better debugging, but we don't
    // want to require a virtual interface on this VH. Instead we allow RAUW to
    // replace this value with a value of an invalid type, and check it here.
    assert(isa<ValueTy>(InnerHandle) &&
           "Tracked Value was replaced by one with an invalid type!");
    return cast<ValueTy>(InnerHandle);
  }

  void setValPtr(ValueTy *P) {
    // Assigning to non-valid TrackingVH's are fine so we just unconditionally
    // assign here.
    InnerHandle = GetAsValue(P);
  }

  // Convert a ValueTy*, which may be const, to the type the base
  // class expects.
  static Value *GetAsValue(Value *V) { return V; }
  static Value *GetAsValue(const Value *V) { return const_cast<Value*>(V); }

public:
  TrackingVH() = default;
  TrackingVH(ValueTy *P) { setValPtr(P); }

  operator ValueTy*() const {
    return getValPtr();
  }

  ValueTy *operator=(ValueTy *RHS) {
    setValPtr(RHS);
    return getValPtr();
  }

  ValueTy *operator->() const { return getValPtr(); }
  ValueTy &operator*() const { return *getValPtr(); }
};

/// Value handle with callbacks on RAUW and destruction.
///
/// This is a value handle that allows subclasses to define callbacks that run
/// when the underlying Value has RAUW called on it or is destroyed.  This
/// class can be used as the key of a map, as long as the user takes it out of
/// the map before calling setValPtr() (since the map has to rearrange itself
/// when the pointer changes).  Unlike ValueHandleBase, this class has a vtable.
class CallbackVH : public ValueHandleBase {
  virtual void anchor();
protected:
  ~CallbackVH() = default;
  CallbackVH(const CallbackVH &) = default;
  CallbackVH &operator=(const CallbackVH &) = default;

  void setValPtr(Value *P) {
    ValueHandleBase::operator=(P);
  }

public:
  CallbackVH() : ValueHandleBase(Callback) {}
  CallbackVH(Value *P) : ValueHandleBase(Callback, P) {}

  operator Value*() const {
    return getValPtr();
  }

  /// Callback for Value destruction.
  ///
  /// Called when this->getValPtr() is destroyed, inside ~Value(), so you
  /// may call any non-virtual Value method on getValPtr(), but no subclass
  /// methods.  If WeakTrackingVH were implemented as a CallbackVH, it would use
  /// this
  /// method to call setValPtr(NULL).  AssertingVH would use this method to
  /// cause an assertion failure.
  ///
  /// All implementations must remove the reference from this object to the
  /// Value that's being destroyed.
  virtual void deleted() { setValPtr(nullptr); }

  /// Callback for Value RAUW.
  ///
  /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called,
  /// _before_ any of the uses have actually been replaced.  If WeakTrackingVH
  /// were
  /// implemented as a CallbackVH, it would use this method to call
  /// setValPtr(new_value).  AssertingVH would do nothing in this method.
  virtual void allUsesReplacedWith(Value *) {}
};

/// Value handle that poisons itself if the Value is deleted.
///
/// This is a Value Handle that points to a value and poisons itself if the
/// value is destroyed while the handle is still live.  This is very useful for
/// catching dangling pointer bugs where an \c AssertingVH cannot be used
/// because the dangling handle needs to outlive the value without ever being
/// used.
///
/// One particularly useful place to use this is as the Key of a map. Dangling
/// pointer bugs often lead to really subtle bugs that only occur if another
/// object happens to get allocated to the same address as the old one. Using
/// a PoisoningVH ensures that an assert is triggered if looking up a new value
/// in the map finds a handle from the old value.
///
/// Note that a PoisoningVH handle does *not* follow values across RAUW
/// operations. This means that RAUW's need to explicitly update the
/// PoisoningVH's as it moves. This is required because in non-assert mode this
/// class turns into a trivial wrapper around a pointer.
template <typename ValueTy>
class PoisoningVH
#ifndef NDEBUG
    final : public CallbackVH
#endif
{
  friend struct DenseMapInfo<PoisoningVH<ValueTy>>;

  // Convert a ValueTy*, which may be const, to the raw Value*.
  static Value *GetAsValue(Value *V) { return V; }
  static Value *GetAsValue(const Value *V) { return const_cast<Value *>(V); }

#ifndef NDEBUG
  /// A flag tracking whether this value has been poisoned.
  ///
  /// On delete and RAUW, we leave the value pointer alone so that as a raw
  /// pointer it produces the same value (and we fit into the same key of
  /// a hash table, etc), but we poison the handle so that any top-level usage
  /// will fail.
  bool Poisoned = false;

  Value *getRawValPtr() const { return ValueHandleBase::getValPtr(); }
  void setRawValPtr(Value *P) { ValueHandleBase::operator=(P); }

  /// Handle deletion by poisoning the handle.
  void deleted() override {
    assert(!Poisoned && "Tried to delete an already poisoned handle!");
    Poisoned = true;
    RemoveFromUseList();
  }

  /// Handle RAUW by poisoning the handle.
  void allUsesReplacedWith(Value *) override {
    assert(!Poisoned && "Tried to RAUW an already poisoned handle!");
    Poisoned = true;
    RemoveFromUseList();
  }
#else // NDEBUG
  Value *ThePtr = nullptr;

  Value *getRawValPtr() const { return ThePtr; }
  void setRawValPtr(Value *P) { ThePtr = P; }
#endif

  ValueTy *getValPtr() const {
    assert(!Poisoned && "Accessed a poisoned value handle!");
    return static_cast<ValueTy *>(getRawValPtr());
  }
  void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); }

public:
  PoisoningVH() = default;
#ifndef NDEBUG
  PoisoningVH(ValueTy *P) : CallbackVH(GetAsValue(P)) {}
  PoisoningVH(const PoisoningVH &RHS)
      : CallbackVH(RHS), Poisoned(RHS.Poisoned) {}

  ~PoisoningVH() {
    if (Poisoned)
      clearValPtr();
  }

  PoisoningVH &operator=(const PoisoningVH &RHS) {
    if (Poisoned)
      clearValPtr();
    CallbackVH::operator=(RHS);
    Poisoned = RHS.Poisoned;
    return *this;
  }
#else
  PoisoningVH(ValueTy *P) : ThePtr(GetAsValue(P)) {}
#endif

  operator ValueTy *() const { return getValPtr(); }

  ValueTy *operator->() const { return getValPtr(); }
  ValueTy &operator*() const { return *getValPtr(); }
};

// Specialize DenseMapInfo to allow PoisoningVH to participate in DenseMap.
template <typename T> struct DenseMapInfo<PoisoningVH<T>> {
  static inline PoisoningVH<T> getEmptyKey() {
    PoisoningVH<T> Res;
    Res.setRawValPtr(DenseMapInfo<Value *>::getEmptyKey());
    return Res;
  }

  static inline PoisoningVH<T> getTombstoneKey() {
    PoisoningVH<T> Res;
    Res.setRawValPtr(DenseMapInfo<Value *>::getTombstoneKey());
    return Res;
  }

  static unsigned getHashValue(const PoisoningVH<T> &Val) {
    return DenseMapInfo<Value *>::getHashValue(Val.getRawValPtr());
  }

  static bool isEqual(const PoisoningVH<T> &LHS, const PoisoningVH<T> &RHS) {
    return DenseMapInfo<Value *>::isEqual(LHS.getRawValPtr(),
                                          RHS.getRawValPtr());
  }
};

} // end namespace llvm

#endif // LLVM_IR_VALUEHANDLE_H