//===- 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