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
24namespace llvm {
25
26template <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.
39template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
40struct PointerUnionTypeSelector {
41 using Return = typename PointerUnionTypeSelectorReturn<RET_NE>::Return;
42};
43
44template <typename T, typename RET_EQ, typename RET_NE>
45struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> {
46 using Return = typename PointerUnionTypeSelectorReturn<RET_EQ>::Return;
47};
48
49template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
50struct PointerUnionTypeSelectorReturn<
51 PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> {
52 using Return =
53 typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return;
54};
55
56namespace 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 template <typename Derived, typename ValTy, int I, typename ...Types>
97 class PointerUnionMembers;
98
99 template <typename Derived, typename ValTy, int I>
100 class PointerUnionMembers<Derived, ValTy, I> {
101 protected:
102 ValTy Val;
103 PointerUnionMembers() = default;
104 PointerUnionMembers(ValTy Val) : Val(Val) {}
105
106 friend struct PointerLikeTypeTraits<Derived>;
107 };
108
109 template <typename Derived, typename ValTy, int I, typename Type,
110 typename ...Types>
111 class PointerUnionMembers<Derived, ValTy, I, Type, Types...>
112 : public PointerUnionMembers<Derived, ValTy, I + 1, Types...> {
113 using Base = PointerUnionMembers<Derived, ValTy, I + 1, Types...>;
114 public:
115 using Base::Base;
116 PointerUnionMembers() = default;
117 PointerUnionMembers(Type V)
118 : Base(ValTy(const_cast<void *>(
119 PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
120 I)) {}
121
122 using Base::operator=;
123 Derived &operator=(Type V) {
124 this->Val = ValTy(
125 const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
126 I);
127 return static_cast<Derived &>(*this);
128 };
129 };
130}
131
132/// A discriminated union of two or more pointer types, with the discriminator
133/// in the low bit of the pointer.
134///
135/// This implementation is extremely efficient in space due to leveraging the
136/// low bits of the pointer, while exposing a natural and type-safe API.
137///
138/// Common use patterns would be something like this:
139/// PointerUnion<int*, float*> P;
140/// P = (int*)0;
141/// printf("%d %d", P.is<int*>(), P.is<float*>()); // prints "1 0"
142/// X = P.get<int*>(); // ok.
143/// Y = P.get<float*>(); // runtime assertion failure.
144/// Z = P.get<double*>(); // compile time failure.
145/// P = (float*)0;
146/// Y = P.get<float*>(); // ok.
147/// X = P.get<int*>(); // runtime assertion failure.
148template <typename... PTs>
149class PointerUnion
150 : public pointer_union_detail::PointerUnionMembers<
151 PointerUnion<PTs...>,
152 PointerIntPair<
153 void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
154 pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
155 0, PTs...> {
156 // The first type is special because we want to directly cast a pointer to a
157 // default-initialized union to a pointer to the first type. But we don't
158 // want PointerUnion to be a 'template <typename First, typename ...Rest>'
159 // because it's much more convenient to have a name for the whole pack. So
160 // split off the first type here.
161 using First = typename pointer_union_detail::GetFirstType<PTs...>::type;
162 using Base = typename PointerUnion::PointerUnionMembers;
163
164public:
165 PointerUnion() = default;
166
167 PointerUnion(std::nullptr_t) : PointerUnion() {}
168 using Base::Base;
169
170 /// Test if the pointer held in the union is null, regardless of
171 /// which type it is.
172 bool isNull() const { return !this->Val.getPointer(); }
173
174 explicit operator bool() const { return !isNull(); }
175
176 /// Test if the Union currently holds the type matching T.
177 template <typename T> bool is() const {
178 constexpr int Index = pointer_union_detail::TypeIndex<T, PTs...>::Index;
179 static_assert(Index < sizeof...(PTs),
180 "PointerUnion::is<T> given type not in the union");
181 return this->Val.getInt() == Index;
182 }
183
184 /// Returns the value of the specified pointer type.
185 ///
186 /// If the specified pointer type is incorrect, assert.
187 template <typename T> T get() const {
188 assert(is<T>() && "Invalid accessor called");
189 return PointerLikeTypeTraits<T>::getFromVoidPointer(this->Val.getPointer());
190 }
191
192 /// Returns the current pointer if it is of the specified pointer type,
193 /// otherwise returns null.
194 template <typename T> T dyn_cast() const {
195 if (is<T>())
196 return get<T>();
197 return T();
198 }
199
200 /// If the union is set to the first pointer type get an address pointing to
201 /// it.
202 First const *getAddrOfPtr1() const {
203 return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
204 }
205
206 /// If the union is set to the first pointer type get an address pointing to
207 /// it.
208 First *getAddrOfPtr1() {
209 assert(is<First>() && "Val is not the first pointer");
210 assert(
211 PointerLikeTypeTraits<First>::getAsVoidPointer(get<First>()) ==
212 this->Val.getPointer() &&
213 "Can't get the address because PointerLikeTypeTraits changes the ptr");
214 return const_cast<First *>(
215 reinterpret_cast<const First *>(this->Val.getAddrOfPointer()));
216 }
217
218 /// Assignment from nullptr which just clears the union.
219 const PointerUnion &operator=(std::nullptr_t) {
220 this->Val.initWithPointer(nullptr);
221 return *this;
222 }
223
224 /// Assignment from elements of the union.
225 using Base::operator=;
226
227 void *getOpaqueValue() const { return this->Val.getOpaqueValue(); }
228 static inline PointerUnion getFromOpaqueValue(void *VP) {
229 PointerUnion V;
230 V.Val = decltype(V.Val)::getFromOpaqueValue(VP);
231 return V;
232 }
233};
234
235template <typename ...PTs>
236bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
237 return lhs.getOpaqueValue() == rhs.getOpaqueValue();
238}
239
240template <typename ...PTs>
241bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
242 return lhs.getOpaqueValue() != rhs.getOpaqueValue();
243}
244
245template <typename ...PTs>
246bool operator<(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
247 return lhs.getOpaqueValue() < rhs.getOpaqueValue();
248}
249
250// Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
251// # low bits available = min(PT1bits,PT2bits)-1.
252template <typename ...PTs>
253struct PointerLikeTypeTraits<PointerUnion<PTs...>> {
254 static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) {
255 return P.getOpaqueValue();
256 }
257
258 static inline PointerUnion<PTs...> getFromVoidPointer(void *P) {
259 return PointerUnion<PTs...>::getFromOpaqueValue(P);
260 }
261
262 // The number of bits available are the min of the pointer types minus the
263 // bits needed for the discriminator.
264 static constexpr int NumLowBitsAvailable = PointerLikeTypeTraits<decltype(
265 PointerUnion<PTs...>::Val)>::NumLowBitsAvailable;
266};
267
268// Teach DenseMap how to use PointerUnions as keys.
269template <typename ...PTs> struct DenseMapInfo<PointerUnion<PTs...>> {
270 using Union = PointerUnion<PTs...>;
271 using FirstInfo =
272 DenseMapInfo<typename pointer_union_detail::GetFirstType<PTs...>::type>;
273
274 static inline Union getEmptyKey() { return Union(FirstInfo::getEmptyKey()); }
275
276 static inline Union getTombstoneKey() {
277 return Union(FirstInfo::getTombstoneKey());
278 }
279
280 static unsigned getHashValue(const Union &UnionVal) {
281 intptr_t key = (intptr_t)UnionVal.getOpaqueValue();
282 return DenseMapInfo<intptr_t>::getHashValue(key);
283 }
284
285 static bool isEqual(const Union &LHS, const Union &RHS) {
286 return LHS == RHS;
287 }
288};
289
290} // end namespace llvm
291
292#endif // LLVM_ADT_POINTERUNION_H
293