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//===- 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 {

    Value *V = getValPtr();

    assert(V && "Dereferencing deleted ValueHandle");

    return *V;

  }

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; }

};

// Specialize DenseMapInfo to allow WeakVH to participate in DenseMap.

template <> struct DenseMapInfo<WeakVH> {

  static inline WeakVH getEmptyKey() {

    return WeakVH(DenseMapInfo<Value *>::getEmptyKey());

  }

  static inline WeakVH getTombstoneKey() {

    return WeakVH(DenseMapInfo<Value *>::getTombstoneKey());

  }

  static unsigned getHashValue(const WeakVH &Val) {

    return DenseMapInfo<Value *>::getHashValue(Val);

  }

  static bool isEqual(const WeakVH &LHS, const WeakVH &RHS) {

    return DenseMapInfo<Value *>::isEqual(LHS, RHS);

  }

};

/// 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

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

    : public ValueHandleBase

#endif

{

  friend struct DenseMapInfo<AssertingVH<ValueTy>>;

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

  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:

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

  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)) {}

  AssertingVH(const AssertingVH &) = default;

#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(); }

};

// Treat AssertingVH<T> like T* inside maps. This also allows using find_as()

// to look up a value without constructing a value handle.

template<typename T>

struct DenseMapInfo<AssertingVH<T>> : DenseMapInfo<T *> {};

/// 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) {}

  CallbackVH(const Value *P) : CallbackVH(const_cast<Value *>(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 final

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

    : 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); }

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

  /// 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 // LLVM_ENABLE_ABI_BREAKING_CHECKS

  Value *ThePtr = nullptr;

  Value *getRawValPtr() const { return ThePtr; }

  void setRawValPtr(Value *P) { ThePtr = P; }

#endif

  ValueTy *getValPtr() const {

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

    assert(!Poisoned && "Accessed a poisoned value handle!");

#endif

    return static_cast<ValueTy *>(getRawValPtr());

  }

  void setValPtr(ValueTy *P) { setRawValPtr(GetAsValue(P)); }

public:

  PoisoningVH() = default;

#if LLVM_ENABLE_ABI_BREAKING_CHECKS

  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());

  }

  // Allow lookup by T* via find_as(), without constructing a temporary

  // value handle.

  static unsigned getHashValue(const T *Val) {

    return DenseMapInfo<Value *>::getHashValue(Val);

  }

  static bool isEqual(const T *LHS, const PoisoningVH<T> &RHS) {

    return DenseMapInfo<Value *>::isEqual(LHS, RHS.getRawValPtr());

  }

};

} // end namespace llvm

#endif // LLVM_IR_VALUEHANDLE_H