1 //===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines the PointerUnion class, which is a discriminated union of 10 // pointer types. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ADT_POINTERUNION_H 15 #define LLVM_ADT_POINTERUNION_H 16 17 #include "llvm/ADT/DenseMapInfo.h" 18 #include "llvm/ADT/PointerIntPair.h" 19 #include "llvm/Support/PointerLikeTypeTraits.h" 20 #include <cassert> 21 #include <cstddef> 22 #include <cstdint> 23 24 namespace llvm { 25 26 template <typename T> struct PointerUnionTypeSelectorReturn { 27 using Return = T; 28 }; 29 30 /// Get a type based on whether two types are the same or not. 31 /// 32 /// For: 33 /// 34 /// \code 35 /// using Ret = typename PointerUnionTypeSelector<T1, T2, EQ, NE>::Return; 36 /// \endcode 37 /// 38 /// Ret will be EQ type if T1 is same as T2 or NE type otherwise. 39 template <typename T1, typename T2, typename RET_EQ, typename RET_NE> 40 struct PointerUnionTypeSelector { 41 using Return = typename PointerUnionTypeSelectorReturn<RET_NE>::Return; 42 }; 43 44 template <typename T, typename RET_EQ, typename RET_NE> 45 struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> { 46 using Return = typename PointerUnionTypeSelectorReturn<RET_EQ>::Return; 47 }; 48 49 template <typename T1, typename T2, typename RET_EQ, typename RET_NE> 50 struct PointerUnionTypeSelectorReturn< 51 PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> { 52 using Return = 53 typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return; 54 }; 55 56 namespace pointer_union_detail { 57 /// Determine the number of bits required to store integers with values < n. 58 /// This is ceil(log2(n)). 59 constexpr int bitsRequired(unsigned n) { 60 return n > 1 ? 1 + bitsRequired((n + 1) / 2) : 0; 61 } 62 63 template <typename... Ts> constexpr int lowBitsAvailable() { 64 return std::min<int>({PointerLikeTypeTraits<Ts>::NumLowBitsAvailable...}); 65 } 66 67 /// Find the index of a type in a list of types. TypeIndex<T, Us...>::Index 68 /// is the index of T in Us, or sizeof...(Us) if T does not appear in the 69 /// list. 70 template <typename T, typename ...Us> struct TypeIndex; 71 template <typename T, typename ...Us> struct TypeIndex<T, T, Us...> { 72 static constexpr int Index = 0; 73 }; 74 template <typename T, typename U, typename... Us> 75 struct TypeIndex<T, U, Us...> { 76 static constexpr int Index = 1 + TypeIndex<T, Us...>::Index; 77 }; 78 template <typename T> struct TypeIndex<T> { 79 static constexpr int Index = 0; 80 }; 81 82 /// Find the first type in a list of types. 83 template <typename T, typename...> struct GetFirstType { 84 using type = T; 85 }; 86 87 /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion 88 /// for the template arguments. 89 template <typename ...PTs> class PointerUnionUIntTraits { 90 public: 91 static inline void *getAsVoidPointer(void *P) { return P; } 92 static inline void *getFromVoidPointer(void *P) { return P; } 93 static constexpr int NumLowBitsAvailable = lowBitsAvailable<PTs...>(); 94 }; 95 96 /// Implement assignment in terms of construction. 97 template <typename Derived, typename T> struct AssignableFrom { 98 Derived &operator=(T t) { 99 return static_cast<Derived &>(*this) = Derived(t); 100 } 101 }; 102 103 template <typename Derived, typename ValTy, int I, typename ...Types> 104 class PointerUnionMembers; 105 106 template <typename Derived, typename ValTy, int I> 107 class PointerUnionMembers<Derived, ValTy, I> { 108 protected: 109 ValTy Val; 110 PointerUnionMembers() = default; 111 PointerUnionMembers(ValTy Val) : Val(Val) {} 112 113 friend struct PointerLikeTypeTraits<Derived>; 114 }; 115 116 template <typename Derived, typename ValTy, int I, typename Type, 117 typename ...Types> 118 class PointerUnionMembers<Derived, ValTy, I, Type, Types...> 119 : public PointerUnionMembers<Derived, ValTy, I + 1, Types...> { 120 using Base = PointerUnionMembers<Derived, ValTy, I + 1, Types...>; 121 public: 122 using Base::Base; 123 PointerUnionMembers() = default; 124 PointerUnionMembers(Type V) 125 : Base(ValTy(const_cast<void *>( 126 PointerLikeTypeTraits<Type>::getAsVoidPointer(V)), 127 I)) {} 128 129 using Base::operator=; 130 Derived &operator=(Type V) { 131 this->Val = ValTy( 132 const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)), 133 I); 134 return static_cast<Derived &>(*this); 135 }; 136 }; 137 } 138 139 /// A discriminated union of two or more pointer types, with the discriminator 140 /// in the low bit of the pointer. 141 /// 142 /// This implementation is extremely efficient in space due to leveraging the 143 /// low bits of the pointer, while exposing a natural and type-safe API. 144 /// 145 /// Common use patterns would be something like this: 146 /// PointerUnion<int*, float*> P; 147 /// P = (int*)0; 148 /// printf("%d %d", P.is<int*>(), P.is<float*>()); // prints "1 0" 149 /// X = P.get<int*>(); // ok. 150 /// Y = P.get<float*>(); // runtime assertion failure. 151 /// Z = P.get<double*>(); // compile time failure. 152 /// P = (float*)0; 153 /// Y = P.get<float*>(); // ok. 154 /// X = P.get<int*>(); // runtime assertion failure. 155 template <typename... PTs> 156 class PointerUnion 157 : public pointer_union_detail::PointerUnionMembers< 158 PointerUnion<PTs...>, 159 PointerIntPair< 160 void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int, 161 pointer_union_detail::PointerUnionUIntTraits<PTs...>>, 162 0, PTs...> { 163 // The first type is special because we want to directly cast a pointer to a 164 // default-initialized union to a pointer to the first type. But we don't 165 // want PointerUnion to be a 'template <typename First, typename ...Rest>' 166 // because it's much more convenient to have a name for the whole pack. So 167 // split off the first type here. 168 using First = typename pointer_union_detail::GetFirstType<PTs...>::type; 169 using Base = typename PointerUnion::PointerUnionMembers; 170 171 public: 172 PointerUnion() = default; 173 174 PointerUnion(std::nullptr_t) : PointerUnion() {} 175 using Base::Base; 176 177 /// Test if the pointer held in the union is null, regardless of 178 /// which type it is. 179 bool isNull() const { return !this->Val.getPointer(); } 180 181 explicit operator bool() const { return !isNull(); } 182 183 /// Test if the Union currently holds the type matching T. 184 template <typename T> int is() const { 185 constexpr int Index = pointer_union_detail::TypeIndex<T, PTs...>::Index; 186 static_assert(Index < sizeof...(PTs), 187 "PointerUnion::is<T> given type not in the union"); 188 return this->Val.getInt() == Index; 189 } 190 191 /// Returns the value of the specified pointer type. 192 /// 193 /// If the specified pointer type is incorrect, assert. 194 template <typename T> T get() const { 195 assert(is<T>() && "Invalid accessor called"); 196 return PointerLikeTypeTraits<T>::getFromVoidPointer(this->Val.getPointer()); 197 } 198 199 /// Returns the current pointer if it is of the specified pointer type, 200 /// otherwises returns null. 201 template <typename T> T dyn_cast() const { 202 if (is<T>()) 203 return get<T>(); 204 return T(); 205 } 206 207 /// If the union is set to the first pointer type get an address pointing to 208 /// it. 209 First const *getAddrOfPtr1() const { 210 return const_cast<PointerUnion *>(this)->getAddrOfPtr1(); 211 } 212 213 /// If the union is set to the first pointer type get an address pointing to 214 /// it. 215 First *getAddrOfPtr1() { 216 assert(is<First>() && "Val is not the first pointer"); 217 assert( 218 PointerLikeTypeTraits<First>::getAsVoidPointer(get<First>()) == 219 this->Val.getPointer() && 220 "Can't get the address because PointerLikeTypeTraits changes the ptr"); 221 return const_cast<First *>( 222 reinterpret_cast<const First *>(this->Val.getAddrOfPointer())); 223 } 224 225 /// Assignment from nullptr which just clears the union. 226 const PointerUnion &operator=(std::nullptr_t) { 227 this->Val.initWithPointer(nullptr); 228 return *this; 229 } 230 231 /// Assignment from elements of the union. 232 using Base::operator=; 233 234 void *getOpaqueValue() const { return this->Val.getOpaqueValue(); } 235 static inline PointerUnion getFromOpaqueValue(void *VP) { 236 PointerUnion V; 237 V.Val = decltype(V.Val)::getFromOpaqueValue(VP); 238 return V; 239 } 240 }; 241 242 template <typename ...PTs> 243 bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) { 244 return lhs.getOpaqueValue() == rhs.getOpaqueValue(); 245 } 246 247 template <typename ...PTs> 248 bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) { 249 return lhs.getOpaqueValue() != rhs.getOpaqueValue(); 250 } 251 252 template <typename ...PTs> 253 bool operator<(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) { 254 return lhs.getOpaqueValue() < rhs.getOpaqueValue(); 255 } 256 257 // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has 258 // # low bits available = min(PT1bits,PT2bits)-1. 259 template <typename ...PTs> 260 struct PointerLikeTypeTraits<PointerUnion<PTs...>> { 261 static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) { 262 return P.getOpaqueValue(); 263 } 264 265 static inline PointerUnion<PTs...> getFromVoidPointer(void *P) { 266 return PointerUnion<PTs...>::getFromOpaqueValue(P); 267 } 268 269 // The number of bits available are the min of the pointer types minus the 270 // bits needed for the discriminator. 271 static constexpr int NumLowBitsAvailable = PointerLikeTypeTraits<decltype( 272 PointerUnion<PTs...>::Val)>::NumLowBitsAvailable; 273 }; 274 275 // Teach DenseMap how to use PointerUnions as keys. 276 template <typename ...PTs> struct DenseMapInfo<PointerUnion<PTs...>> { 277 using Union = PointerUnion<PTs...>; 278 using FirstInfo = 279 DenseMapInfo<typename pointer_union_detail::GetFirstType<PTs...>::type>; 280 281 static inline Union getEmptyKey() { return Union(FirstInfo::getEmptyKey()); } 282 283 static inline Union getTombstoneKey() { 284 return Union(FirstInfo::getTombstoneKey()); 285 } 286 287 static unsigned getHashValue(const Union &UnionVal) { 288 intptr_t key = (intptr_t)UnionVal.getOpaqueValue(); 289 return DenseMapInfo<intptr_t>::getHashValue(key); 290 } 291 292 static bool isEqual(const Union &LHS, const Union &RHS) { 293 return LHS == RHS; 294 } 295 }; 296 297 } // end namespace llvm 298 299 #endif // LLVM_ADT_POINTERUNION_H 300