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+//===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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