text: //===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- 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 defines the PointerUnion class, which is a discriminated union of
  // pointer types.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ADT_POINTERUNION_H
  #define LLVM_ADT_POINTERUNION_H
  
  #include "llvm/ADT/DenseMapInfo.h"
  #include "llvm/ADT/PointerIntPair.h"
  #include "llvm/Support/PointerLikeTypeTraits.h"
  #include <cassert>
  #include <cstddef>
  #include <cstdint>
  
  namespace llvm {
  
  template <typename T> struct PointerUnionTypeSelectorReturn {
    using Return = T;
  };
  
  /// Get a type based on whether two types are the same or not.
  ///
  /// For:
  ///
  /// \code
  ///   using Ret = typename PointerUnionTypeSelector<T1, T2, EQ, NE>::Return;
  /// \endcode
  ///
  /// Ret will be EQ type if T1 is same as T2 or NE type otherwise.
  template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
  struct PointerUnionTypeSelector {
    using Return = typename PointerUnionTypeSelectorReturn<RET_NE>::Return;
  };
  
  template <typename T, typename RET_EQ, typename RET_NE>
  struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> {
    using Return = typename PointerUnionTypeSelectorReturn<RET_EQ>::Return;
  };
  
  template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
  struct PointerUnionTypeSelectorReturn<
      PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> {
    using Return =
        typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return;
  };
  
  /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
  /// for the two template arguments.
  template <typename PT1, typename PT2> class PointerUnionUIntTraits {
  public:
    static inline void *getAsVoidPointer(void *P) { return P; }
    static inline void *getFromVoidPointer(void *P) { return P; }
  
    enum {
      PT1BitsAv = (int)(PointerLikeTypeTraits<PT1>::NumLowBitsAvailable),
      PT2BitsAv = (int)(PointerLikeTypeTraits<PT2>::NumLowBitsAvailable),
      NumLowBitsAvailable = PT1BitsAv < PT2BitsAv ? PT1BitsAv : PT2BitsAv
    };
  };
  
  /// A discriminated union of two pointer types, with the discriminator in the
  /// low bit of the pointer.
  ///
  /// This implementation is extremely efficient in space due to leveraging the
  /// low bits of the pointer, while exposing a natural and type-safe API.
  ///
  /// Common use patterns would be something like this:
  ///    PointerUnion<int*, float*> P;
  ///    P = (int*)0;
  ///    printf("%d %d", P.is<int*>(), P.is<float*>());  // prints "1 0"
  ///    X = P.get<int*>();     // ok.
  ///    Y = P.get<float*>();   // runtime assertion failure.
  ///    Z = P.get<double*>();  // compile time failure.
  ///    P = (float*)0;
  ///    Y = P.get<float*>();   // ok.
  ///    X = P.get<int*>();     // runtime assertion failure.
  template <typename PT1, typename PT2> class PointerUnion {
  public:
    using ValTy =
        PointerIntPair<void *, 1, bool, PointerUnionUIntTraits<PT1, PT2>>;
  
  private:
    ValTy Val;
  
    struct IsPT1 {
      static const int Num = 0;
    };
    struct IsPT2 {
      static const int Num = 1;
    };
    template <typename T> struct UNION_DOESNT_CONTAIN_TYPE {};
  
  public:
    PointerUnion() = default;
    PointerUnion(PT1 V)
        : Val(const_cast<void *>(
              PointerLikeTypeTraits<PT1>::getAsVoidPointer(V))) {}
    PointerUnion(PT2 V)
        : Val(const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(V)),
              1) {}
  
    /// Test if the pointer held in the union is null, regardless of
    /// which type it is.
    bool isNull() const {
      // Convert from the void* to one of the pointer types, to make sure that
      // we recursively strip off low bits if we have a nested PointerUnion.
      return !PointerLikeTypeTraits<PT1>::getFromVoidPointer(Val.getPointer());
    }
  
    explicit operator bool() const { return !isNull(); }
  
    /// Test if the Union currently holds the type matching T.
    template <typename T> int is() const {
      using Ty = typename ::llvm::PointerUnionTypeSelector<
          PT1, T, IsPT1,
          ::llvm::PointerUnionTypeSelector<PT2, T, IsPT2,
                                           UNION_DOESNT_CONTAIN_TYPE<T>>>::Return;
      int TyNo = Ty::Num;
      return static_cast<int>(Val.getInt()) == TyNo;
    }
  
    /// Returns the value of the specified pointer type.
    ///
    /// If the specified pointer type is incorrect, assert.
    template <typename T> T get() const {
      assert(is<T>() && "Invalid accessor called");
      return PointerLikeTypeTraits<T>::getFromVoidPointer(Val.getPointer());
    }
  
    /// Returns the current pointer if it is of the specified pointer type,
    /// otherwises returns null.
    template <typename T> T dyn_cast() const {
      if (is<T>())
        return get<T>();
      return T();
    }
  
    /// If the union is set to the first pointer type get an address pointing to
    /// it.
    PT1 const *getAddrOfPtr1() const {
      return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
    }
  
    /// If the union is set to the first pointer type get an address pointing to
    /// it.
    PT1 *getAddrOfPtr1() {
      assert(is<PT1>() && "Val is not the first pointer");
      assert(
          get<PT1>() == Val.getPointer() &&
          "Can't get the address because PointerLikeTypeTraits changes the ptr");
      return const_cast<PT1 *>(
          reinterpret_cast<const PT1 *>(Val.getAddrOfPointer()));
    }
  
    /// Assignment from nullptr which just clears the union.
    const PointerUnion &operator=(std::nullptr_t) {
      Val.initWithPointer(nullptr);
      return *this;
    }
  
    /// Assignment operators - Allow assigning into this union from either
    /// pointer type, setting the discriminator to remember what it came from.
    const PointerUnion &operator=(const PT1 &RHS) {
      Val.initWithPointer(
          const_cast<void *>(PointerLikeTypeTraits<PT1>::getAsVoidPointer(RHS)));
      return *this;
    }
    const PointerUnion &operator=(const PT2 &RHS) {
      Val.setPointerAndInt(
          const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(RHS)),
          1);
      return *this;
    }
  
    void *getOpaqueValue() const { return Val.getOpaqueValue(); }
    static inline PointerUnion getFromOpaqueValue(void *VP) {
      PointerUnion V;
      V.Val = ValTy::getFromOpaqueValue(VP);
      return V;
    }
  };
  
  template <typename PT1, typename PT2>
  bool operator==(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
    return lhs.getOpaqueValue() == rhs.getOpaqueValue();
  }
  
  template <typename PT1, typename PT2>
  bool operator!=(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
    return lhs.getOpaqueValue() != rhs.getOpaqueValue();
  }
  
  template <typename PT1, typename PT2>
  bool operator<(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
    return lhs.getOpaqueValue() < rhs.getOpaqueValue();
  }
  
  // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
  // # low bits available = min(PT1bits,PT2bits)-1.
  template <typename PT1, typename PT2>
  struct PointerLikeTypeTraits<PointerUnion<PT1, PT2>> {
    static inline void *getAsVoidPointer(const PointerUnion<PT1, PT2> &P) {
      return P.getOpaqueValue();
    }
  
    static inline PointerUnion<PT1, PT2> getFromVoidPointer(void *P) {
      return PointerUnion<PT1, PT2>::getFromOpaqueValue(P);
    }
  
    // The number of bits available are the min of the two pointer types.
    enum {
      NumLowBitsAvailable = PointerLikeTypeTraits<
          typename PointerUnion<PT1, PT2>::ValTy>::NumLowBitsAvailable
    };
  };
  
  /// A pointer union of three pointer types. See documentation for PointerUnion
  /// for usage.
  template <typename PT1, typename PT2, typename PT3> class PointerUnion3 {
  public:
    using InnerUnion = PointerUnion<PT1, PT2>;
    using ValTy = PointerUnion<InnerUnion, PT3>;
  
  private:
    ValTy Val;
  
    struct IsInnerUnion {
      ValTy Val;
  
      IsInnerUnion(ValTy val) : Val(val) {}
  
      template <typename T> int is() const {
        return Val.template is<InnerUnion>() &&
               Val.template get<InnerUnion>().template is<T>();
      }
  
      template <typename T> T get() const {
        return Val.template get<InnerUnion>().template get<T>();
      }
    };
  
    struct IsPT3 {
      ValTy Val;
  
      IsPT3(ValTy val) : Val(val) {}
  
      template <typename T> int is() const { return Val.template is<T>(); }
      template <typename T> T get() const { return Val.template get<T>(); }
    };
  
  public:
    PointerUnion3() = default;
    PointerUnion3(PT1 V) { Val = InnerUnion(V); }
    PointerUnion3(PT2 V) { Val = InnerUnion(V); }
    PointerUnion3(PT3 V) { Val = V; }
  
    /// Test if the pointer held in the union is null, regardless of
    /// which type it is.
    bool isNull() const { return Val.isNull(); }
    explicit operator bool() const { return !isNull(); }
  
    /// Test if the Union currently holds the type matching T.
    template <typename T> int is() const {
      // If T is PT1/PT2 choose IsInnerUnion otherwise choose IsPT3.
      using Ty = typename ::llvm::PointerUnionTypeSelector<
          PT1, T, IsInnerUnion,
          ::llvm::PointerUnionTypeSelector<PT2, T, IsInnerUnion, IsPT3>>::Return;
      return Ty(Val).template is<T>();
    }
  
    /// Returns the value of the specified pointer type.
    ///
    /// If the specified pointer type is incorrect, assert.
    template <typename T> T get() const {
      assert(is<T>() && "Invalid accessor called");
      // If T is PT1/PT2 choose IsInnerUnion otherwise choose IsPT3.
      using Ty = typename ::llvm::PointerUnionTypeSelector<
          PT1, T, IsInnerUnion,
          ::llvm::PointerUnionTypeSelector<PT2, T, IsInnerUnion, IsPT3>>::Return;
      return Ty(Val).template get<T>();
    }
  
    /// Returns the current pointer if it is of the specified pointer type,
    /// otherwises returns null.
    template <typename T> T dyn_cast() const {
      if (is<T>())
        return get<T>();
      return T();
    }
  
    /// Assignment from nullptr which just clears the union.
    const PointerUnion3 &operator=(std::nullptr_t) {
      Val = nullptr;
      return *this;
    }
  
    /// Assignment operators - Allow assigning into this union from either
    /// pointer type, setting the discriminator to remember what it came from.
    const PointerUnion3 &operator=(const PT1 &RHS) {
      Val = InnerUnion(RHS);
      return *this;
    }
    const PointerUnion3 &operator=(const PT2 &RHS) {
      Val = InnerUnion(RHS);
      return *this;
    }
    const PointerUnion3 &operator=(const PT3 &RHS) {
      Val = RHS;
      return *this;
    }
  
    void *getOpaqueValue() const { return Val.getOpaqueValue(); }
    static inline PointerUnion3 getFromOpaqueValue(void *VP) {
      PointerUnion3 V;
      V.Val = ValTy::getFromOpaqueValue(VP);
      return V;
    }
  };
  
  // Teach SmallPtrSet that PointerUnion3 is "basically a pointer", that has
  // # low bits available = min(PT1bits,PT2bits,PT2bits)-2.
  template <typename PT1, typename PT2, typename PT3>
  struct PointerLikeTypeTraits<PointerUnion3<PT1, PT2, PT3>> {
    static inline void *getAsVoidPointer(const PointerUnion3<PT1, PT2, PT3> &P) {
      return P.getOpaqueValue();
    }
  
    static inline PointerUnion3<PT1, PT2, PT3> getFromVoidPointer(void *P) {
      return PointerUnion3<PT1, PT2, PT3>::getFromOpaqueValue(P);
    }
  
    // The number of bits available are the min of the two pointer types.
    enum {
      NumLowBitsAvailable = PointerLikeTypeTraits<
          typename PointerUnion3<PT1, PT2, PT3>::ValTy>::NumLowBitsAvailable
    };
  };
  
  template <typename PT1, typename PT2, typename PT3>
  bool operator<(PointerUnion3<PT1, PT2, PT3> lhs,
                 PointerUnion3<PT1, PT2, PT3> rhs) {
    return lhs.getOpaqueValue() < rhs.getOpaqueValue();
  }
  
  /// A pointer union of four pointer types. See documentation for PointerUnion
  /// for usage.
  template <typename PT1, typename PT2, typename PT3, typename PT4>
  class PointerUnion4 {
  public:
    using InnerUnion1 = PointerUnion<PT1, PT2>;
    using InnerUnion2 = PointerUnion<PT3, PT4>;
    using ValTy = PointerUnion<InnerUnion1, InnerUnion2>;
  
  private:
    ValTy Val;
  
  public:
    PointerUnion4() = default;
    PointerUnion4(PT1 V) { Val = InnerUnion1(V); }
    PointerUnion4(PT2 V) { Val = InnerUnion1(V); }
    PointerUnion4(PT3 V) { Val = InnerUnion2(V); }
    PointerUnion4(PT4 V) { Val = InnerUnion2(V); }
  
    /// Test if the pointer held in the union is null, regardless of
    /// which type it is.
    bool isNull() const { return Val.isNull(); }
    explicit operator bool() const { return !isNull(); }
  
    /// Test if the Union currently holds the type matching T.
    template <typename T> int is() const {
      // If T is PT1/PT2 choose InnerUnion1 otherwise choose InnerUnion2.
      using Ty = typename ::llvm::PointerUnionTypeSelector<
          PT1, T, InnerUnion1,
          ::llvm::PointerUnionTypeSelector<PT2, T, InnerUnion1,
                                           InnerUnion2>>::Return;
      return Val.template is<Ty>() && Val.template get<Ty>().template is<T>();
    }
  
    /// Returns the value of the specified pointer type.
    ///
    /// If the specified pointer type is incorrect, assert.
    template <typename T> T get() const {
      assert(is<T>() && "Invalid accessor called");
      // If T is PT1/PT2 choose InnerUnion1 otherwise choose InnerUnion2.
      using Ty = typename ::llvm::PointerUnionTypeSelector<
          PT1, T, InnerUnion1,
          ::llvm::PointerUnionTypeSelector<PT2, T, InnerUnion1,
                                           InnerUnion2>>::Return;
      return Val.template get<Ty>().template get<T>();
    }
  
    /// Returns the current pointer if it is of the specified pointer type,
    /// otherwises returns null.
    template <typename T> T dyn_cast() const {
      if (is<T>())
        return get<T>();
      return T();
    }
  
    /// Assignment from nullptr which just clears the union.
    const PointerUnion4 &operator=(std::nullptr_t) {
      Val = nullptr;
      return *this;
    }
  
    /// Assignment operators - Allow assigning into this union from either
    /// pointer type, setting the discriminator to remember what it came from.
    const PointerUnion4 &operator=(const PT1 &RHS) {
      Val = InnerUnion1(RHS);
      return *this;
    }
    const PointerUnion4 &operator=(const PT2 &RHS) {
      Val = InnerUnion1(RHS);
      return *this;
    }
    const PointerUnion4 &operator=(const PT3 &RHS) {
      Val = InnerUnion2(RHS);
      return *this;
    }
    const PointerUnion4 &operator=(const PT4 &RHS) {
      Val = InnerUnion2(RHS);
      return *this;
    }
  
    void *getOpaqueValue() const { return Val.getOpaqueValue(); }
    static inline PointerUnion4 getFromOpaqueValue(void *VP) {
      PointerUnion4 V;
      V.Val = ValTy::getFromOpaqueValue(VP);
      return V;
    }
  };
  
  // Teach SmallPtrSet that PointerUnion4 is "basically a pointer", that has
  // # low bits available = min(PT1bits,PT2bits,PT2bits)-2.
  template <typename PT1, typename PT2, typename PT3, typename PT4>
  struct PointerLikeTypeTraits<PointerUnion4<PT1, PT2, PT3, PT4>> {
    static inline void *
    getAsVoidPointer(const PointerUnion4<PT1, PT2, PT3, PT4> &P) {
      return P.getOpaqueValue();
    }
  
    static inline PointerUnion4<PT1, PT2, PT3, PT4> getFromVoidPointer(void *P) {
      return PointerUnion4<PT1, PT2, PT3, PT4>::getFromOpaqueValue(P);
    }
  
    // The number of bits available are the min of the two pointer types.
    enum {
      NumLowBitsAvailable = PointerLikeTypeTraits<
          typename PointerUnion4<PT1, PT2, PT3, PT4>::ValTy>::NumLowBitsAvailable
    };
  };
  
  // Teach DenseMap how to use PointerUnions as keys.
  template <typename T, typename U> struct DenseMapInfo<PointerUnion<T, U>> {
    using Pair = PointerUnion<T, U>;
    using FirstInfo = DenseMapInfo<T>;
    using SecondInfo = DenseMapInfo<U>;
  
    static inline Pair getEmptyKey() { return Pair(FirstInfo::getEmptyKey()); }
  
    static inline Pair getTombstoneKey() {
      return Pair(FirstInfo::getTombstoneKey());
    }
  
    static unsigned getHashValue(const Pair &PairVal) {
      intptr_t key = (intptr_t)PairVal.getOpaqueValue();
      return DenseMapInfo<intptr_t>::getHashValue(key);
    }
  
    static bool isEqual(const Pair &LHS, const Pair &RHS) {
      return LHS.template is<T>() == RHS.template is<T>() &&
             (LHS.template is<T>() ? FirstInfo::isEqual(LHS.template get<T>(),
                                                        RHS.template get<T>())
                                   : SecondInfo::isEqual(LHS.template get<U>(),
                                                         RHS.template get<U>()));
    }
  };
  
  } // end namespace llvm
  
  #endif // LLVM_ADT_POINTERUNION_H
  