text: //===- llvm/Value.h - Definition of the Value class -------------*- 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 Value class.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_IR_VALUE_H
  #define LLVM_IR_VALUE_H
  
  #include "llvm-c/Types.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/iterator_range.h"
  #include "llvm/IR/Use.h"
  #include "llvm/Support/Alignment.h"
  #include "llvm/Support/CBindingWrapping.h"
  #include "llvm/Support/Casting.h"
  #include <cassert>
  #include <iterator>
  #include <memory>
  
  namespace llvm {
  
  class APInt;
  class Argument;
  class BasicBlock;
  class Constant;
  class ConstantData;
  class ConstantAggregate;
  class DataLayout;
  class Function;
  class GlobalAlias;
  class GlobalIFunc;
  class GlobalIndirectSymbol;
  class GlobalObject;
  class GlobalValue;
  class GlobalVariable;
  class InlineAsm;
  class Instruction;
  class LLVMContext;
  class MDNode;
  class Module;
  class ModuleSlotTracker;
  class raw_ostream;
  template<typename ValueTy> class StringMapEntry;
  class Twine;
  class Type;
  class User;
  
  using ValueName = StringMapEntry<Value *>;
  
  //===----------------------------------------------------------------------===//
  //                                 Value Class
  //===----------------------------------------------------------------------===//
  
  /// LLVM Value Representation
  ///
  /// This is a very important LLVM class. It is the base class of all values
  /// computed by a program that may be used as operands to other values. Value is
  /// the super class of other important classes such as Instruction and Function.
  /// All Values have a Type. Type is not a subclass of Value. Some values can
  /// have a name and they belong to some Module.  Setting the name on the Value
  /// automatically updates the module's symbol table.
  ///
  /// Every value has a "use list" that keeps track of which other Values are
  /// using this Value.  A Value can also have an arbitrary number of ValueHandle
  /// objects that watch it and listen to RAUW and Destroy events.  See
  /// llvm/IR/ValueHandle.h for details.
  class Value {
    Type *VTy;
    Use *UseList;
  
    friend class ValueAsMetadata; // Allow access to IsUsedByMD.
    friend class ValueHandleBase;
  
    const unsigned char SubclassID;   // Subclass identifier (for isa/dyn_cast)
    unsigned char HasValueHandle : 1; // Has a ValueHandle pointing to this?
  
  protected:
    /// Hold subclass data that can be dropped.
    ///
    /// This member is similar to SubclassData, however it is for holding
    /// information which may be used to aid optimization, but which may be
    /// cleared to zero without affecting conservative interpretation.
    unsigned char SubclassOptionalData : 7;
  
  private:
    /// Hold arbitrary subclass data.
    ///
    /// This member is defined by this class, but is not used for anything.
    /// Subclasses can use it to hold whatever state they find useful.  This
    /// field is initialized to zero by the ctor.
    unsigned short SubclassData;
  
  protected:
    /// The number of operands in the subclass.
    ///
    /// This member is defined by this class, but not used for anything.
    /// Subclasses can use it to store their number of operands, if they have
    /// any.
    ///
    /// This is stored here to save space in User on 64-bit hosts.  Since most
    /// instances of Value have operands, 32-bit hosts aren't significantly
    /// affected.
    ///
    /// Note, this should *NOT* be used directly by any class other than User.
    /// User uses this value to find the Use list.
    enum : unsigned { NumUserOperandsBits = 27 };
    unsigned NumUserOperands : NumUserOperandsBits;
  
    // Use the same type as the bitfield above so that MSVC will pack them.
    unsigned IsUsedByMD : 1;
    unsigned HasName : 1;
    unsigned HasMetadata : 1; // Has metadata attached to this?
    unsigned HasHungOffUses : 1;
    unsigned HasDescriptor : 1;
  
  private:
    template <typename UseT> // UseT == 'Use' or 'const Use'
    class use_iterator_impl {
      friend class Value;
  
      UseT *U;
  
      explicit use_iterator_impl(UseT *u) : U(u) {}
  
    public:
      using iterator_category = std::forward_iterator_tag;
      using value_type = UseT *;
      using difference_type = std::ptrdiff_t;
      using pointer = value_type *;
      using reference = value_type &;
  
      use_iterator_impl() : U() {}
  
      bool operator==(const use_iterator_impl &x) const { return U == x.U; }
      bool operator!=(const use_iterator_impl &x) const { return !operator==(x); }
  
      use_iterator_impl &operator++() { // Preincrement
        assert(U && "Cannot increment end iterator!");
        U = U->getNext();
        return *this;
      }
  
      use_iterator_impl operator++(int) { // Postincrement
        auto tmp = *this;
        ++*this;
        return tmp;
      }
  
      UseT &operator*() const {
        assert(U && "Cannot dereference end iterator!");
        return *U;
      }
  
      UseT *operator->() const { return &operator*(); }
  
      operator use_iterator_impl<const UseT>() const {
        return use_iterator_impl<const UseT>(U);
      }
    };
  
    template <typename UserTy> // UserTy == 'User' or 'const User'
    class user_iterator_impl {
      use_iterator_impl<Use> UI;
      explicit user_iterator_impl(Use *U) : UI(U) {}
      friend class Value;
  
    public:
      using iterator_category = std::forward_iterator_tag;
      using value_type = UserTy *;
      using difference_type = std::ptrdiff_t;
      using pointer = value_type *;
      using reference = value_type &;
  
      user_iterator_impl() = default;
  
      bool operator==(const user_iterator_impl &x) const { return UI == x.UI; }
      bool operator!=(const user_iterator_impl &x) const { return !operator==(x); }
  
      /// Returns true if this iterator is equal to user_end() on the value.
      bool atEnd() const { return *this == user_iterator_impl(); }
  
      user_iterator_impl &operator++() { // Preincrement
        ++UI;
        return *this;
      }
  
      user_iterator_impl operator++(int) { // Postincrement
        auto tmp = *this;
        ++*this;
        return tmp;
      }
  
      // Retrieve a pointer to the current User.
      UserTy *operator*() const {
        return UI->getUser();
      }
  
      UserTy *operator->() const { return operator*(); }
  
      operator user_iterator_impl<const UserTy>() const {
        return user_iterator_impl<const UserTy>(*UI);
      }
  
      Use &getUse() const { return *UI; }
    };
  
  protected:
    Value(Type *Ty, unsigned scid);
  
    /// Value's destructor should be virtual by design, but that would require
    /// that Value and all of its subclasses have a vtable that effectively
    /// duplicates the information in the value ID. As a size optimization, the
    /// destructor has been protected, and the caller should manually call
    /// deleteValue.
    ~Value(); // Use deleteValue() to delete a generic Value.
  
  public:
    Value(const Value &) = delete;
    Value &operator=(const Value &) = delete;
  
    /// Delete a pointer to a generic Value.
    void deleteValue();
  
    /// Support for debugging, callable in GDB: V->dump()
    void dump() const;
  
    /// Implement operator<< on Value.
    /// @{
    void print(raw_ostream &O, bool IsForDebug = false) const;
    void print(raw_ostream &O, ModuleSlotTracker &MST,
               bool IsForDebug = false) const;
    /// @}
  
    /// Print the name of this Value out to the specified raw_ostream.
    ///
    /// This is useful when you just want to print 'int %reg126', not the
    /// instruction that generated it. If you specify a Module for context, then
    /// even constanst get pretty-printed; for example, the type of a null
    /// pointer is printed symbolically.
    /// @{
    void printAsOperand(raw_ostream &O, bool PrintType = true,
                        const Module *M = nullptr) const;
    void printAsOperand(raw_ostream &O, bool PrintType,
                        ModuleSlotTracker &MST) const;
    /// @}
  
    /// All values are typed, get the type of this value.
    Type *getType() const { return VTy; }
  
    /// All values hold a context through their type.
    LLVMContext &getContext() const;
  
    // All values can potentially be named.
    bool hasName() const { return HasName; }
    ValueName *getValueName() const;
    void setValueName(ValueName *VN);
  
  private:
    void destroyValueName();
    enum class ReplaceMetadataUses { No, Yes };
    void doRAUW(Value *New, ReplaceMetadataUses);
    void setNameImpl(const Twine &Name);
  
  public:
    /// Return a constant reference to the value's name.
    ///
    /// This guaranteed to return the same reference as long as the value is not
    /// modified.  If the value has a name, this does a hashtable lookup, so it's
    /// not free.
    StringRef getName() const;
  
    /// Change the name of the value.
    ///
    /// Choose a new unique name if the provided name is taken.
    ///
    /// \param Name The new name; or "" if the value's name should be removed.
    void setName(const Twine &Name);
  
    /// Transfer the name from V to this value.
    ///
    /// After taking V's name, sets V's name to empty.
    ///
    /// \note It is an error to call V->takeName(V).
    void takeName(Value *V);
  
  #ifndef NDEBUG
    std::string getNameOrAsOperand() const;
  #endif
  
    /// Change all uses of this to point to a new Value.
    ///
    /// Go through the uses list for this definition and make each use point to
    /// "V" instead of "this".  After this completes, 'this's use list is
    /// guaranteed to be empty.
    void replaceAllUsesWith(Value *V);
  
    /// Change non-metadata uses of this to point to a new Value.
    ///
    /// Go through the uses list for this definition and make each use point to
    /// "V" instead of "this". This function skips metadata entries in the list.
    void replaceNonMetadataUsesWith(Value *V);
  
    /// Go through the uses list for this definition and make each use point
    /// to "V" if the callback ShouldReplace returns true for the given Use.
    /// Unlike replaceAllUsesWith() this function does not support basic block
    /// values.
    void replaceUsesWithIf(Value *New,
                           llvm::function_ref<bool(Use &U)> ShouldReplace);
  
    /// replaceUsesOutsideBlock - Go through the uses list for this definition and
    /// make each use point to "V" instead of "this" when the use is outside the
    /// block. 'This's use list is expected to have at least one element.
    /// Unlike replaceAllUsesWith() this function does not support basic block
    /// values.
    void replaceUsesOutsideBlock(Value *V, BasicBlock *BB);
  
    //----------------------------------------------------------------------
    // Methods for handling the chain of uses of this Value.
    //
    // Materializing a function can introduce new uses, so these methods come in
    // two variants:
    // The methods that start with materialized_ check the uses that are
    // currently known given which functions are materialized. Be very careful
    // when using them since you might not get all uses.
    // The methods that don't start with materialized_ assert that modules is
    // fully materialized.
    void assertModuleIsMaterializedImpl() const;
    // This indirection exists so we can keep assertModuleIsMaterializedImpl()
    // around in release builds of Value.cpp to be linked with other code built
    // in debug mode. But this avoids calling it in any of the release built code.
    void assertModuleIsMaterialized() const {
  #ifndef NDEBUG
      assertModuleIsMaterializedImpl();
  #endif
    }
  
    bool use_empty() const {
      assertModuleIsMaterialized();
      return UseList == nullptr;
    }
  
    bool materialized_use_empty() const {
      return UseList == nullptr;
    }
  
    using use_iterator = use_iterator_impl<Use>;
    using const_use_iterator = use_iterator_impl<const Use>;
  
    use_iterator materialized_use_begin() { return use_iterator(UseList); }
    const_use_iterator materialized_use_begin() const {
      return const_use_iterator(UseList);
    }
    use_iterator use_begin() {
      assertModuleIsMaterialized();
      return materialized_use_begin();
    }
    const_use_iterator use_begin() const {
      assertModuleIsMaterialized();
      return materialized_use_begin();
    }
    use_iterator use_end() { return use_iterator(); }
    const_use_iterator use_end() const { return const_use_iterator(); }
    iterator_range<use_iterator> materialized_uses() {
      return make_range(materialized_use_begin(), use_end());
    }
    iterator_range<const_use_iterator> materialized_uses() const {
      return make_range(materialized_use_begin(), use_end());
    }
    iterator_range<use_iterator> uses() {
      assertModuleIsMaterialized();
      return materialized_uses();
    }
    iterator_range<const_use_iterator> uses() const {
      assertModuleIsMaterialized();
      return materialized_uses();
    }
  
    bool user_empty() const {
      assertModuleIsMaterialized();
      return UseList == nullptr;
    }
  
    using user_iterator = user_iterator_impl<User>;
    using const_user_iterator = user_iterator_impl<const User>;
  
    user_iterator materialized_user_begin() { return user_iterator(UseList); }
    const_user_iterator materialized_user_begin() const {
      return const_user_iterator(UseList);
    }
    user_iterator user_begin() {
      assertModuleIsMaterialized();
      return materialized_user_begin();
    }
    const_user_iterator user_begin() const {
      assertModuleIsMaterialized();
      return materialized_user_begin();
    }
    user_iterator user_end() { return user_iterator(); }
    const_user_iterator user_end() const { return const_user_iterator(); }
    User *user_back() {
      assertModuleIsMaterialized();
      return *materialized_user_begin();
    }
    const User *user_back() const {
      assertModuleIsMaterialized();
      return *materialized_user_begin();
    }
    iterator_range<user_iterator> materialized_users() {
      return make_range(materialized_user_begin(), user_end());
    }
    iterator_range<const_user_iterator> materialized_users() const {
      return make_range(materialized_user_begin(), user_end());
    }
    iterator_range<user_iterator> users() {
      assertModuleIsMaterialized();
      return materialized_users();
    }
    iterator_range<const_user_iterator> users() const {
      assertModuleIsMaterialized();
      return materialized_users();
    }
  
    /// Return true if there is exactly one use of this value.
    ///
    /// This is specialized because it is a common request and does not require
    /// traversing the whole use list.
    bool hasOneUse() const { return hasSingleElement(uses()); }
  
    /// Return true if this Value has exactly N uses.
    bool hasNUses(unsigned N) const;
  
    /// Return true if this value has N uses or more.
    ///
    /// This is logically equivalent to getNumUses() >= N.
    bool hasNUsesOrMore(unsigned N) const;
  
    /// Return true if there is exactly one user of this value.
    ///
    /// Note that this is not the same as "has one use". If a value has one use,
    /// then there certainly is a single user. But if value has several uses,
    /// it is possible that all uses are in a single user, or not.
    ///
    /// This check is potentially costly, since it requires traversing,
    /// in the worst case, the whole use list of a value.
    bool hasOneUser() const;
  
    /// Return true if there is exactly one use of this value that cannot be
    /// dropped.
    Use *getSingleUndroppableUse();
    const Use *getSingleUndroppableUse() const {
      return const_cast<Value *>(this)->getSingleUndroppableUse();
    }
  
    /// Return true if there this value.
    ///
    /// This is specialized because it is a common request and does not require
    /// traversing the whole use list.
    bool hasNUndroppableUses(unsigned N) const;
  
    /// Return true if this value has N uses or more.
    ///
    /// This is logically equivalent to getNumUses() >= N.
    bool hasNUndroppableUsesOrMore(unsigned N) const;
  
    /// Remove every uses that can safely be removed.
    ///
    /// This will remove for example uses in llvm.assume.
    /// This should be used when performing want to perform a tranformation but
    /// some Droppable uses pervent it.
    /// This function optionally takes a filter to only remove some droppable
    /// uses.
    void dropDroppableUses(llvm::function_ref<bool(const Use *)> ShouldDrop =
                               [](const Use *) { return true; });
  
    /// Remove every use of this value in \p User that can safely be removed.
    void dropDroppableUsesIn(User &Usr);
  
    /// Remove the droppable use \p U.
    static void dropDroppableUse(Use &U);
  
    /// Check if this value is used in the specified basic block.
    bool isUsedInBasicBlock(const BasicBlock *BB) const;
  
    /// This method computes the number of uses of this Value.
    ///
    /// This is a linear time operation.  Use hasOneUse, hasNUses, or
    /// hasNUsesOrMore to check for specific values.
    unsigned getNumUses() const;
  
    /// This method should only be used by the Use class.
    void addUse(Use &U) { U.addToList(&UseList); }
  
    /// Concrete subclass of this.
    ///
    /// An enumeration for keeping track of the concrete subclass of Value that
    /// is actually instantiated. Values of this enumeration are kept in the
    /// Value classes SubclassID field. They are used for concrete type
    /// identification.
    enum ValueTy {
  #define HANDLE_VALUE(Name) Name##Val,
  #include "llvm/IR/Value.def"
  
      // Markers:
  #define HANDLE_CONSTANT_MARKER(Marker, Constant) Marker = Constant##Val,
  #include "llvm/IR/Value.def"
    };
  
    /// Return an ID for the concrete type of this object.
    ///
    /// This is used to implement the classof checks.  This should not be used
    /// for any other purpose, as the values may change as LLVM evolves.  Also,
    /// note that for instructions, the Instruction's opcode is added to
    /// InstructionVal. So this means three things:
    /// # there is no value with code InstructionVal (no opcode==0).
    /// # there are more possible values for the value type than in ValueTy enum.
    /// # the InstructionVal enumerator must be the highest valued enumerator in
    ///   the ValueTy enum.
    unsigned getValueID() const {
      return SubclassID;
    }
  
    /// Return the raw optional flags value contained in this value.
    ///
    /// This should only be used when testing two Values for equivalence.
    unsigned getRawSubclassOptionalData() const {
      return SubclassOptionalData;
    }
  
    /// Clear the optional flags contained in this value.
    void clearSubclassOptionalData() {
      SubclassOptionalData = 0;
    }
  
    /// Check the optional flags for equality.
    bool hasSameSubclassOptionalData(const Value *V) const {
      return SubclassOptionalData == V->SubclassOptionalData;
    }
  
    /// Return true if there is a value handle associated with this value.
    bool hasValueHandle() const { return HasValueHandle; }
  
    /// Return true if there is metadata referencing this value.
    bool isUsedByMetadata() const { return IsUsedByMD; }
  
    // Return true if this value is only transitively referenced by metadata.
    bool isTransitiveUsedByMetadataOnly() const;
  
  protected:
    /// Get the current metadata attachments for the given kind, if any.
    ///
    /// These functions require that the value have at most a single attachment
    /// of the given kind, and return \c nullptr if such an attachment is missing.
    /// @{
    MDNode *getMetadata(unsigned KindID) const;
    MDNode *getMetadata(StringRef Kind) const;
    /// @}
  
    /// Appends all attachments with the given ID to \c MDs in insertion order.
    /// If the Value has no attachments with the given ID, or if ID is invalid,
    /// leaves MDs unchanged.
    /// @{
    void getMetadata(unsigned KindID, SmallVectorImpl<MDNode *> &MDs) const;
    void getMetadata(StringRef Kind, SmallVectorImpl<MDNode *> &MDs) const;
    /// @}
  
    /// Appends all metadata attached to this value to \c MDs, sorting by
    /// KindID. The first element of each pair returned is the KindID, the second
    /// element is the metadata value. Attachments with the same ID appear in
    /// insertion order.
    void
    getAllMetadata(SmallVectorImpl<std::pair<unsigned, MDNode *>> &MDs) const;
  
    /// Return true if this value has any metadata attached to it.
    bool hasMetadata() const { return (bool)HasMetadata; }
  
    /// Return true if this value has the given type of metadata attached.
    /// @{
    bool hasMetadata(unsigned KindID) const {
      return getMetadata(KindID) != nullptr;
    }
    bool hasMetadata(StringRef Kind) const {
      return getMetadata(Kind) != nullptr;
    }
    /// @}
  
    /// Set a particular kind of metadata attachment.
    ///
    /// Sets the given attachment to \c MD, erasing it if \c MD is \c nullptr or
    /// replacing it if it already exists.
    /// @{
    void setMetadata(unsigned KindID, MDNode *Node);
    void setMetadata(StringRef Kind, MDNode *Node);
    /// @}
  
    /// Add a metadata attachment.
    /// @{
    void addMetadata(unsigned KindID, MDNode &MD);
    void addMetadata(StringRef Kind, MDNode &MD);
    /// @}
  
    /// Erase all metadata attachments with the given kind.
    ///
    /// \returns true if any metadata was removed.
    bool eraseMetadata(unsigned KindID);
  
    /// Erase all metadata attached to this Value.
    void clearMetadata();
  
  public:
    /// Return true if this value is a swifterror value.
    ///
    /// swifterror values can be either a function argument or an alloca with a
    /// swifterror attribute.
    bool isSwiftError() const;
  
    /// Strip off pointer casts, all-zero GEPs and address space casts.
    ///
    /// Returns the original uncasted value.  If this is called on a non-pointer
    /// value, it returns 'this'.
    const Value *stripPointerCasts() const;
    Value *stripPointerCasts() {
      return const_cast<Value *>(
          static_cast<const Value *>(this)->stripPointerCasts());
    }
  
    /// Strip off pointer casts, all-zero GEPs, address space casts, and aliases.
    ///
    /// Returns the original uncasted value.  If this is called on a non-pointer
    /// value, it returns 'this'.
    const Value *stripPointerCastsAndAliases() const;
    Value *stripPointerCastsAndAliases() {
      return const_cast<Value *>(
          static_cast<const Value *>(this)->stripPointerCastsAndAliases());
    }
  
    /// Strip off pointer casts, all-zero GEPs and address space casts
    /// but ensures the representation of the result stays the same.
    ///
    /// Returns the original uncasted value with the same representation. If this
    /// is called on a non-pointer value, it returns 'this'.
    const Value *stripPointerCastsSameRepresentation() const;
    Value *stripPointerCastsSameRepresentation() {
      return const_cast<Value *>(static_cast<const Value *>(this)
                                     ->stripPointerCastsSameRepresentation());
    }
  
    /// Strip off pointer casts, all-zero GEPs, single-argument phi nodes and
    /// invariant group info.
    ///
    /// Returns the original uncasted value.  If this is called on a non-pointer
    /// value, it returns 'this'. This function should be used only in
    /// Alias analysis.
    const Value *stripPointerCastsForAliasAnalysis() const;
    Value *stripPointerCastsForAliasAnalysis() {
      return const_cast<Value *>(static_cast<const Value *>(this)
                                     ->stripPointerCastsForAliasAnalysis());
    }
  
    /// Strip off pointer casts and all-constant inbounds GEPs.
    ///
    /// Returns the original pointer value.  If this is called on a non-pointer
    /// value, it returns 'this'.
    const Value *stripInBoundsConstantOffsets() const;
    Value *stripInBoundsConstantOffsets() {
      return const_cast<Value *>(
                static_cast<const Value *>(this)->stripInBoundsConstantOffsets());
    }
  
    /// Accumulate the constant offset this value has compared to a base pointer.
    /// Only 'getelementptr' instructions (GEPs) are accumulated but other
    /// instructions, e.g., casts, are stripped away as well.
    /// The accumulated constant offset is added to \p Offset and the base
    /// pointer is returned.
    ///
    /// The APInt \p Offset has to have a bit-width equal to the IntPtr type for
    /// the address space of 'this' pointer value, e.g., use
    /// DataLayout::getIndexTypeSizeInBits(Ty).
    ///
    /// If \p AllowNonInbounds is true, offsets in GEPs are stripped and
    /// accumulated even if the GEP is not "inbounds".
    ///
    /// If \p ExternalAnalysis is provided it will be used to calculate a offset
    /// when a operand of GEP is not constant.
    /// For example, for a value \p ExternalAnalysis might try to calculate a
    /// lower bound. If \p ExternalAnalysis is successful, it should return true.
    ///
    /// If this is called on a non-pointer value, it returns 'this' and the
    /// \p Offset is not modified.
    ///
    /// Note that this function will never return a nullptr. It will also never
    /// manipulate the \p Offset in a way that would not match the difference
    /// between the underlying value and the returned one. Thus, if no constant
    /// offset was found, the returned value is the underlying one and \p Offset
    /// is unchanged.
    const Value *stripAndAccumulateConstantOffsets(
        const DataLayout &DL, APInt &Offset, bool AllowNonInbounds,
        function_ref<bool(Value &Value, APInt &Offset)> ExternalAnalysis =
            nullptr) const;
    Value *stripAndAccumulateConstantOffsets(const DataLayout &DL, APInt &Offset,
                                             bool AllowNonInbounds) {
      return const_cast<Value *>(
          static_cast<const Value *>(this)->stripAndAccumulateConstantOffsets(
              DL, Offset, AllowNonInbounds));
    }
  
    /// This is a wrapper around stripAndAccumulateConstantOffsets with the
    /// in-bounds requirement set to false.
    const Value *stripAndAccumulateInBoundsConstantOffsets(const DataLayout &DL,
                                                           APInt &Offset) const {
      return stripAndAccumulateConstantOffsets(DL, Offset,
                                               /* AllowNonInbounds */ false);
    }
    Value *stripAndAccumulateInBoundsConstantOffsets(const DataLayout &DL,
                                                     APInt &Offset) {
      return stripAndAccumulateConstantOffsets(DL, Offset,
                                               /* AllowNonInbounds */ false);
    }
  
    /// Strip off pointer casts and inbounds GEPs.
    ///
    /// Returns the original pointer value.  If this is called on a non-pointer
    /// value, it returns 'this'.
    const Value *stripInBoundsOffsets(function_ref<void(const Value *)> Func =
                                          [](const Value *) {}) const;
    inline Value *stripInBoundsOffsets(function_ref<void(const Value *)> Func =
                                    [](const Value *) {}) {
      return const_cast<Value *>(
          static_cast<const Value *>(this)->stripInBoundsOffsets(Func));
    }
  
    /// Return true if the memory object referred to by V can by freed in the
    /// scope for which the SSA value defining the allocation is statically
    /// defined.  E.g.  deallocation after the static scope of a value does not
    /// count, but a deallocation before that does.
    bool canBeFreed() const;
  
    /// Returns the number of bytes known to be dereferenceable for the
    /// pointer value.
    ///
    /// If CanBeNull is set by this function the pointer can either be null or be
    /// dereferenceable up to the returned number of bytes.
    ///
    /// IF CanBeFreed is true, the pointer is known to be dereferenceable at
    /// point of definition only.  Caller must prove that allocation is not
    /// deallocated between point of definition and use.
    uint64_t getPointerDereferenceableBytes(const DataLayout &DL,
                                            bool &CanBeNull,
                                            bool &CanBeFreed) const;
  
    /// Returns an alignment of the pointer value.
    ///
    /// Returns an alignment which is either specified explicitly, e.g. via
    /// align attribute of a function argument, or guaranteed by DataLayout.
    Align getPointerAlignment(const DataLayout &DL) const;
  
    /// Translate PHI node to its predecessor from the given basic block.
    ///
    /// If this value is a PHI node with CurBB as its parent, return the value in
    /// the PHI node corresponding to PredBB.  If not, return ourself.  This is
    /// useful if you want to know the value something has in a predecessor
    /// block.
    const Value *DoPHITranslation(const BasicBlock *CurBB,
                                  const BasicBlock *PredBB) const;
    Value *DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB) {
      return const_cast<Value *>(
               static_cast<const Value *>(this)->DoPHITranslation(CurBB, PredBB));
    }
  
    /// The maximum alignment for instructions.
    ///
    /// This is the greatest alignment value supported by load, store, and alloca
    /// instructions, and global values.
    static constexpr unsigned MaxAlignmentExponent = 30;
    static constexpr unsigned MaximumAlignment = 1u << MaxAlignmentExponent;
  
    /// Mutate the type of this Value to be of the specified type.
    ///
    /// Note that this is an extremely dangerous operation which can create
    /// completely invalid IR very easily.  It is strongly recommended that you
    /// recreate IR objects with the right types instead of mutating them in
    /// place.
    void mutateType(Type *Ty) {
      VTy = Ty;
    }
  
    /// Sort the use-list.
    ///
    /// Sorts the Value's use-list by Cmp using a stable mergesort.  Cmp is
    /// expected to compare two \a Use references.
    template <class Compare> void sortUseList(Compare Cmp);
  
    /// Reverse the use-list.
    void reverseUseList();
  
  private:
    /// Merge two lists together.
    ///
    /// Merges \c L and \c R using \c Cmp.  To enable stable sorts, always pushes
    /// "equal" items from L before items from R.
    ///
    /// \return the first element in the list.
    ///
    /// \note Completely ignores \a Use::Prev (doesn't read, doesn't update).
    template <class Compare>
    static Use *mergeUseLists(Use *L, Use *R, Compare Cmp) {
      Use *Merged;
      Use **Next = &Merged;
  
      while (true) {
        if (!L) {
          *Next = R;
          break;
        }
        if (!R) {
          *Next = L;
          break;
        }
        if (Cmp(*R, *L)) {
          *Next = R;
          Next = &R->Next;
          R = R->Next;
        } else {
          *Next = L;
          Next = &L->Next;
          L = L->Next;
        }
      }
  
      return Merged;
    }
  
  protected:
    unsigned short getSubclassDataFromValue() const { return SubclassData; }
    void setValueSubclassData(unsigned short D) { SubclassData = D; }
  };
  
  struct ValueDeleter { void operator()(Value *V) { V->deleteValue(); } };
  
  /// Use this instead of std::unique_ptr<Value> or std::unique_ptr<Instruction>.
  /// Those don't work because Value and Instruction's destructors are protected,
  /// aren't virtual, and won't destroy the complete object.
  using unique_value = std::unique_ptr<Value, ValueDeleter>;
  
  inline raw_ostream &operator<<(raw_ostream &OS, const Value &V) {
    V.print(OS);
    return OS;
  }
  
  void Use::set(Value *V) {
    if (Val) removeFromList();
    Val = V;
    if (V) V->addUse(*this);
  }
  
  Value *Use::operator=(Value *RHS) {
    set(RHS);
    return RHS;
  }
  
  const Use &Use::operator=(const Use &RHS) {
    set(RHS.Val);
    return *this;
  }
  
  template <class Compare> void Value::sortUseList(Compare Cmp) {
    if (!UseList || !UseList->Next)
      // No need to sort 0 or 1 uses.
      return;
  
    // Note: this function completely ignores Prev pointers until the end when
    // they're fixed en masse.
  
    // Create a binomial vector of sorted lists, visiting uses one at a time and
    // merging lists as necessary.
    const unsigned MaxSlots = 32;
    Use *Slots[MaxSlots];
  
    // Collect the first use, turning it into a single-item list.
    Use *Next = UseList->Next;
    UseList->Next = nullptr;
    unsigned NumSlots = 1;
    Slots[0] = UseList;
  
    // Collect all but the last use.
    while (Next->Next) {
      Use *Current = Next;
      Next = Current->Next;
  
      // Turn Current into a single-item list.
      Current->Next = nullptr;
  
      // Save Current in the first available slot, merging on collisions.
      unsigned I;
      for (I = 0; I < NumSlots; ++I) {
        if (!Slots[I])
          break;
  
        // Merge two lists, doubling the size of Current and emptying slot I.
        //
        // Since the uses in Slots[I] originally preceded those in Current, send
        // Slots[I] in as the left parameter to maintain a stable sort.
        Current = mergeUseLists(Slots[I], Current, Cmp);
        Slots[I] = nullptr;
      }
      // Check if this is a new slot.
      if (I == NumSlots) {
        ++NumSlots;
        assert(NumSlots <= MaxSlots && "Use list bigger than 2^32");
      }
  
      // Found an open slot.
      Slots[I] = Current;
    }
  
    // Merge all the lists together.
    assert(Next && "Expected one more Use");
    assert(!Next->Next && "Expected only one Use");
    UseList = Next;
    for (unsigned I = 0; I < NumSlots; ++I)
      if (Slots[I])
        // Since the uses in Slots[I] originally preceded those in UseList, send
        // Slots[I] in as the left parameter to maintain a stable sort.
        UseList = mergeUseLists(Slots[I], UseList, Cmp);
  
    // Fix the Prev pointers.
    for (Use *I = UseList, **Prev = &UseList; I; I = I->Next) {
      I->Prev = Prev;
      Prev = &I->Next;
    }
  }
  
  // isa - Provide some specializations of isa so that we don't have to include
  // the subtype header files to test to see if the value is a subclass...
  //
  template <> struct isa_impl<Constant, Value> {
    static inline bool doit(const Value &Val) {
      static_assert(Value::ConstantFirstVal == 0, "Val.getValueID() >= Value::ConstantFirstVal");
      return Val.getValueID() <= Value::ConstantLastVal;
    }
  };
  
  template <> struct isa_impl<ConstantData, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() >= Value::ConstantDataFirstVal &&
             Val.getValueID() <= Value::ConstantDataLastVal;
    }
  };
  
  template <> struct isa_impl<ConstantAggregate, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() >= Value::ConstantAggregateFirstVal &&
             Val.getValueID() <= Value::ConstantAggregateLastVal;
    }
  };
  
  template <> struct isa_impl<Argument, Value> {
    static inline bool doit (const Value &Val) {
      return Val.getValueID() == Value::ArgumentVal;
    }
  };
  
  template <> struct isa_impl<InlineAsm, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::InlineAsmVal;
    }
  };
  
  template <> struct isa_impl<Instruction, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() >= Value::InstructionVal;
    }
  };
  
  template <> struct isa_impl<BasicBlock, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::BasicBlockVal;
    }
  };
  
  template <> struct isa_impl<Function, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::FunctionVal;
    }
  };
  
  template <> struct isa_impl<GlobalVariable, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::GlobalVariableVal;
    }
  };
  
  template <> struct isa_impl<GlobalAlias, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::GlobalAliasVal;
    }
  };
  
  template <> struct isa_impl<GlobalIFunc, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::GlobalIFuncVal;
    }
  };
  
  template <> struct isa_impl<GlobalIndirectSymbol, Value> {
    static inline bool doit(const Value &Val) {
      return isa<GlobalAlias>(Val) || isa<GlobalIFunc>(Val);
    }
  };
  
  template <> struct isa_impl<GlobalValue, Value> {
    static inline bool doit(const Value &Val) {
      return isa<GlobalObject>(Val) || isa<GlobalIndirectSymbol>(Val);
    }
  };
  
  template <> struct isa_impl<GlobalObject, Value> {
    static inline bool doit(const Value &Val) {
      return isa<GlobalVariable>(Val) || isa<Function>(Val);
    }
  };
  
  // Create wrappers for C Binding types (see CBindingWrapping.h).
  DEFINE_ISA_CONVERSION_FUNCTIONS(Value, LLVMValueRef)
  
  // Specialized opaque value conversions.
  inline Value **unwrap(LLVMValueRef *Vals) {
    return reinterpret_cast<Value**>(Vals);
  }
  
  template<typename T>
  inline T **unwrap(LLVMValueRef *Vals, unsigned Length) {
  #ifndef NDEBUG
    for (LLVMValueRef *I = Vals, *E = Vals + Length; I != E; ++I)
      unwrap<T>(*I); // For side effect of calling assert on invalid usage.
  #endif
    (void)Length;
    return reinterpret_cast<T**>(Vals);
  }
  
  inline LLVMValueRef *wrap(const Value **Vals) {
    return reinterpret_cast<LLVMValueRef*>(const_cast<Value**>(Vals));
  }
  
  } // end namespace llvm
  
  #endif // LLVM_IR_VALUE_H
  