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 //===- llvm/User.h - User class definition ----------------------*- 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 class defines the interface that one who uses a Value must implement.
 // Each instance of the Value class keeps track of what User's have handles
 // to it.
 //
 //  * Instructions are the largest class of Users.
 //  * Constants may be users of other constants (think arrays and stuff)
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_IR_USER_H
 #define LLVM_IR_USER_H
 
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <iterator>
 
 namespace llvm {
 
 template <typename T> class ArrayRef;
 template <typename T> class MutableArrayRef;
 
 /// Compile-time customization of User operands.
 ///
 /// Customizes operand-related allocators and accessors.
 template <class>
 struct OperandTraits;
 
 class User : public Value {
   friend struct HungoffOperandTraits;
   template <class ConstantClass> friend struct ConstantAggrKeyType;
 
   LLVM_ATTRIBUTE_ALWAYS_INLINE static void *
   allocateFixedOperandUser(size_t, unsigned, unsigned);
 
 protected:
   // Disable the default operator new, as all subclasses must use one of the
   // custom operators below depending on how they store their operands.
   void *operator new(size_t Size) = delete;
 
   /// Indicates this User has operands "hung off" in another allocation.
   struct HungOffOperandsAllocMarker {};
 
   /// Indicates this User has operands co-allocated.
   struct IntrusiveOperandsAllocMarker {
     /// The number of operands for this User.
     const unsigned NumOps;
   };
 
   /// Indicates this User has operands and a descriptor co-allocated .
   struct IntrusiveOperandsAndDescriptorAllocMarker {
     /// The number of operands for this User.
     const unsigned NumOps;
     /// The number of bytes to allocate for the descriptor. Must be divisible by
     /// `sizeof(void *)`.
     const unsigned DescBytes;
   };
 
   /// Information about how a User object was allocated, to be passed into the
   /// User constructor.
   ///
   /// DO NOT USE DIRECTLY. Use one of the `AllocMarker` structs instead, they
   /// call all be implicitly converted to `AllocInfo`.
   struct AllocInfo {
   public:
     const unsigned NumOps : NumUserOperandsBits;
     const bool HasHungOffUses : 1;
     const bool HasDescriptor : 1;
 
     AllocInfo() = delete;
 
     constexpr AllocInfo(const HungOffOperandsAllocMarker)
         : NumOps(0), HasHungOffUses(true), HasDescriptor(false) {}
 
     constexpr AllocInfo(const IntrusiveOperandsAllocMarker Alloc)
         : NumOps(Alloc.NumOps), HasHungOffUses(false), HasDescriptor(false) {}
 
     constexpr AllocInfo(const IntrusiveOperandsAndDescriptorAllocMarker Alloc)
         : NumOps(Alloc.NumOps), HasHungOffUses(false),
           HasDescriptor(Alloc.DescBytes != 0) {}
   };
 
   /// Allocate a User with an operand pointer co-allocated.
   ///
   /// This is used for subclasses which need to allocate a variable number
   /// of operands, ie, 'hung off uses'.
   void *operator new(size_t Size, HungOffOperandsAllocMarker);
 
   /// Allocate a User with the operands co-allocated.
   ///
   /// This is used for subclasses which have a fixed number of operands.
   void *operator new(size_t Size, IntrusiveOperandsAllocMarker allocTrait);
 
   /// Allocate a User with the operands co-allocated.  If DescBytes is non-zero
   /// then allocate an additional DescBytes bytes before the operands. These
   /// bytes can be accessed by calling getDescriptor.
   void *operator new(size_t Size,
                      IntrusiveOperandsAndDescriptorAllocMarker allocTrait);
 
   User(Type *ty, unsigned vty, AllocInfo AllocInfo) : Value(ty, vty) {
     assert(AllocInfo.NumOps < (1u << NumUserOperandsBits) &&
            "Too many operands");
     NumUserOperands = AllocInfo.NumOps;
     assert((!AllocInfo.HasDescriptor || !AllocInfo.HasHungOffUses) &&
            "Cannot have both hung off uses and a descriptor");
     HasHungOffUses = AllocInfo.HasHungOffUses;
     HasDescriptor = AllocInfo.HasDescriptor;
     // If we have hung off uses, then the operand list should initially be
     // null.
     assert((!AllocInfo.HasHungOffUses || !getOperandList()) &&
            "Error in initializing hung off uses for User");
   }
 
   /// Allocate the array of Uses, followed by a pointer
   /// (with bottom bit set) to the User.
   /// \param IsPhi identifies callers which are phi nodes and which need
   /// N BasicBlock* allocated along with N
   void allocHungoffUses(unsigned N, bool IsPhi = false);
 
   /// Grow the number of hung off uses.  Note that allocHungoffUses
   /// should be called if there are no uses.
   void growHungoffUses(unsigned N, bool IsPhi = false);
 
 protected:
   ~User() = default; // Use deleteValue() to delete a generic Instruction.
 
 public:
   User(const User &) = delete;
 
   /// Free memory allocated for User and Use objects.
   void operator delete(void *Usr);
   /// Placement delete - required by std, called if the ctor throws.
   void operator delete(void *Usr, HungOffOperandsAllocMarker) {
     // Note: If a subclass manipulates the information which is required to
     // calculate the Usr memory pointer, e.g. NumUserOperands, the operator
     // delete of that subclass has to restore the changed information to the
     // original value, since the dtor of that class is not called if the ctor
     // fails.
     User::operator delete(Usr);
 
 #ifndef LLVM_ENABLE_EXCEPTIONS
     llvm_unreachable("Constructor throws?");
 #endif
   }
   /// Placement delete - required by std, called if the ctor throws.
   void operator delete(void *Usr, IntrusiveOperandsAllocMarker) {
     // Note: If a subclass manipulates the information which is required to calculate the
     // Usr memory pointer, e.g. NumUserOperands, the operator delete of that subclass has
     // to restore the changed information to the original value, since the dtor of that class
     // is not called if the ctor fails.
     User::operator delete(Usr);
 
 #ifndef LLVM_ENABLE_EXCEPTIONS
     llvm_unreachable("Constructor throws?");
 #endif
   }
   /// Placement delete - required by std, called if the ctor throws.
   void operator delete(void *Usr, IntrusiveOperandsAndDescriptorAllocMarker) {
     // Note: If a subclass manipulates the information which is required to calculate the
     // Usr memory pointer, e.g. NumUserOperands, the operator delete of that subclass has
     // to restore the changed information to the original value, since the dtor of that class
     // is not called if the ctor fails.
     User::operator delete(Usr);
 
 #ifndef LLVM_ENABLE_EXCEPTIONS
     llvm_unreachable("Constructor throws?");
 #endif
   }
 
 protected:
   template <int Idx, typename U> static Use &OpFrom(const U *that) {
     return Idx < 0
       ? OperandTraits<U>::op_end(const_cast<U*>(that))[Idx]
       : OperandTraits<U>::op_begin(const_cast<U*>(that))[Idx];
   }
 
   template <int Idx> Use &Op() {
     return OpFrom<Idx>(this);
   }
   template <int Idx> const Use &Op() const {
     return OpFrom<Idx>(this);
   }
 
 private:
   const Use *getHungOffOperands() const {
     return *(reinterpret_cast<const Use *const *>(this) - 1);
   }
 
   Use *&getHungOffOperands() { return *(reinterpret_cast<Use **>(this) - 1); }
 
   const Use *getIntrusiveOperands() const {
     return reinterpret_cast<const Use *>(this) - NumUserOperands;
   }
 
   Use *getIntrusiveOperands() {
     return reinterpret_cast<Use *>(this) - NumUserOperands;
   }
 
   void setOperandList(Use *NewList) {
     assert(HasHungOffUses &&
            "Setting operand list only required for hung off uses");
     getHungOffOperands() = NewList;
   }
 
 public:
   const Use *getOperandList() const {
     return HasHungOffUses ? getHungOffOperands() : getIntrusiveOperands();
   }
   Use *getOperandList() {
     return const_cast<Use *>(static_cast<const User *>(this)->getOperandList());
   }
 
   Value *getOperand(unsigned i) const {
     assert(i < NumUserOperands && "getOperand() out of range!");
     return getOperandList()[i];
   }
 
   void setOperand(unsigned i, Value *Val) {
     assert(i < NumUserOperands && "setOperand() out of range!");
     assert((!isa<Constant>((const Value*)this) ||
             isa<GlobalValue>((const Value*)this)) &&
            "Cannot mutate a constant with setOperand!");
     getOperandList()[i] = Val;
   }
 
   const Use &getOperandUse(unsigned i) const {
     assert(i < NumUserOperands && "getOperandUse() out of range!");
     return getOperandList()[i];
   }
   Use &getOperandUse(unsigned i) {
     assert(i < NumUserOperands && "getOperandUse() out of range!");
     return getOperandList()[i];
   }
 
   unsigned getNumOperands() const { return NumUserOperands; }
 
   /// Returns the descriptor co-allocated with this User instance.
   ArrayRef<const uint8_t> getDescriptor() const;
 
   /// Returns the descriptor co-allocated with this User instance.
   MutableArrayRef<uint8_t> getDescriptor();
 
   /// Subclasses with hung off uses need to manage the operand count
   /// themselves.  In these instances, the operand count isn't used to find the
   /// OperandList, so there's no issue in having the operand count change.
   void setNumHungOffUseOperands(unsigned NumOps) {
     assert(HasHungOffUses && "Must have hung off uses to use this method");
     assert(NumOps < (1u << NumUserOperandsBits) && "Too many operands");
     NumUserOperands = NumOps;
   }
 
   /// A droppable user is a user for which uses can be dropped without affecting
   /// correctness and should be dropped rather than preventing a transformation
   /// from happening.
   bool isDroppable() const;
 
   // ---------------------------------------------------------------------------
   // Operand Iterator interface...
   //
   using op_iterator = Use*;
   using const_op_iterator = const Use*;
   using op_range = iterator_range<op_iterator>;
   using const_op_range = iterator_range<const_op_iterator>;
 
   op_iterator       op_begin()       { return getOperandList(); }
   const_op_iterator op_begin() const { return getOperandList(); }
   op_iterator       op_end()         {
     return getOperandList() + NumUserOperands;
   }
   const_op_iterator op_end()   const {
     return getOperandList() + NumUserOperands;
   }
   op_range operands() {
     return op_range(op_begin(), op_end());
   }
   const_op_range operands() const {
     return const_op_range(op_begin(), op_end());
   }
 
   /// Iterator for directly iterating over the operand Values.
   struct value_op_iterator
       : iterator_adaptor_base<value_op_iterator, op_iterator,
                               std::random_access_iterator_tag, Value *,
                               ptrdiff_t, Value *, Value *> {
     explicit value_op_iterator(Use *U = nullptr) : iterator_adaptor_base(U) {}
 
     Value *operator*() const { return *I; }
     Value *operator->() const { return operator*(); }
   };
 
   value_op_iterator value_op_begin() {
     return value_op_iterator(op_begin());
   }
   value_op_iterator value_op_end() {
     return value_op_iterator(op_end());
   }
   iterator_range<value_op_iterator> operand_values() {
     return make_range(value_op_begin(), value_op_end());
   }
 
   struct const_value_op_iterator
       : iterator_adaptor_base<const_value_op_iterator, const_op_iterator,
                               std::random_access_iterator_tag, const Value *,
                               ptrdiff_t, const Value *, const Value *> {
     explicit const_value_op_iterator(const Use *U = nullptr) :
       iterator_adaptor_base(U) {}
 
     const Value *operator*() const { return *I; }
     const Value *operator->() const { return operator*(); }
   };
 
   const_value_op_iterator value_op_begin() const {
     return const_value_op_iterator(op_begin());
   }
   const_value_op_iterator value_op_end() const {
     return const_value_op_iterator(op_end());
   }
   iterator_range<const_value_op_iterator> operand_values() const {
     return make_range(value_op_begin(), value_op_end());
   }
 
   /// Drop all references to operands.
   ///
   /// This function is in charge of "letting go" of all objects that this User
   /// refers to.  This allows one to 'delete' a whole class at a time, even
   /// though there may be circular references...  First all references are
   /// dropped, and all use counts go to zero.  Then everything is deleted for
   /// real.  Note that no operations are valid on an object that has "dropped
   /// all references", except operator delete.
   void dropAllReferences() {
     for (Use &U : operands())
       U.set(nullptr);
   }
 
   /// Replace uses of one Value with another.
   ///
   /// Replaces all references to the "From" definition with references to the
   /// "To" definition. Returns whether any uses were replaced.
   bool replaceUsesOfWith(Value *From, Value *To);
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const Value *V) {
     return isa<Instruction>(V) || isa<Constant>(V);
   }
 };
 
 // Either Use objects, or a Use pointer can be prepended to User.
 static_assert(alignof(Use) >= alignof(User),
               "Alignment is insufficient after objects prepended to User");
 static_assert(alignof(Use *) >= alignof(User),
               "Alignment is insufficient after objects prepended to User");
 
 template<> struct simplify_type<User::op_iterator> {
   using SimpleType = Value*;
 
   static SimpleType getSimplifiedValue(User::op_iterator &Val) {
     return Val->get();
   }
 };
 template<> struct simplify_type<User::const_op_iterator> {
   using SimpleType = /*const*/ Value*;
 
   static SimpleType getSimplifiedValue(User::const_op_iterator &Val) {
     return Val->get();
   }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_IR_USER_H

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