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/// \file
10/// This file defines the PointerUnion class, which is a discriminated union of
11/// pointer types.
12///
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_POINTERUNION_H
16#define LLVM_ADT_POINTERUNION_H
17
18#include "llvm/ADT/DenseMapInfo.h"
19#include "llvm/ADT/PointerIntPair.h"
20#include "llvm/ADT/STLExtras.h"
21#include "llvm/Support/Casting.h"
22#include "llvm/Support/PointerLikeTypeTraits.h"
23#include <algorithm>
24#include <cassert>
25#include <cstddef>
26#include <cstdint>
27
28namespace llvm {
29
30namespace pointer_union_detail {
31 /// Determine the number of bits required to store integers with values < n.
32 /// This is ceil(log2(n)).
33 constexpr int bitsRequired(unsigned n) {
34 return n > 1 ? 1 + bitsRequired(n: (n + 1) / 2) : 0;
35 }
36
37 template <typename... Ts> constexpr int lowBitsAvailable() {
38 return std::min<int>({PointerLikeTypeTraits<Ts>::NumLowBitsAvailable...});
39 }
40
41 /// Find the first type in a list of types.
42 template <typename T, typename...> struct GetFirstType {
43 using type = T;
44 };
45
46 /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
47 /// for the template arguments.
48 template <typename ...PTs> class PointerUnionUIntTraits {
49 public:
50 static inline void *getAsVoidPointer(void *P) { return P; }
51 static inline void *getFromVoidPointer(void *P) { return P; }
52 static constexpr int NumLowBitsAvailable = lowBitsAvailable<PTs...>();
53 };
54
55 template <typename Derived, typename ValTy, int I, typename ...Types>
56 class PointerUnionMembers;
57
58 template <typename Derived, typename ValTy, int I>
59 class PointerUnionMembers<Derived, ValTy, I> {
60 protected:
61 ValTy Val;
62 PointerUnionMembers() = default;
63 PointerUnionMembers(ValTy Val) : Val(Val) {}
64
65 friend struct PointerLikeTypeTraits<Derived>;
66 };
67
68 template <typename Derived, typename ValTy, int I, typename Type,
69 typename ...Types>
70 class PointerUnionMembers<Derived, ValTy, I, Type, Types...>
71 : public PointerUnionMembers<Derived, ValTy, I + 1, Types...> {
72 using Base = PointerUnionMembers<Derived, ValTy, I + 1, Types...>;
73 public:
74 using Base::Base;
75 PointerUnionMembers() = default;
76 PointerUnionMembers(Type V)
77 : Base(ValTy(const_cast<void *>(
78 PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
79 I)) {}
80
81 using Base::operator=;
82 Derived &operator=(Type V) {
83 this->Val = ValTy(
84 const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
85 I);
86 return static_cast<Derived &>(*this);
87 };
88 };
89}
90
91// This is a forward declaration of CastInfoPointerUnionImpl
92// Refer to its definition below for further details
93template <typename... PTs> struct CastInfoPointerUnionImpl;
94/// A discriminated union of two or more pointer types, with the discriminator
95/// in the low bit of the pointer.
96///
97/// This implementation is extremely efficient in space due to leveraging the
98/// low bits of the pointer, while exposing a natural and type-safe API.
99///
100/// Common use patterns would be something like this:
101/// PointerUnion<int*, float*> P;
102/// P = (int*)0;
103/// printf("%d %d", P.is<int*>(), P.is<float*>()); // prints "1 0"
104/// X = P.get<int*>(); // ok.
105/// Y = P.get<float*>(); // runtime assertion failure.
106/// Z = P.get<double*>(); // compile time failure.
107/// P = (float*)0;
108/// Y = P.get<float*>(); // ok.
109/// X = P.get<int*>(); // runtime assertion failure.
110/// PointerUnion<int*, int*> Q; // compile time failure.
111template <typename... PTs>
112class PointerUnion
113 : public pointer_union_detail::PointerUnionMembers<
114 PointerUnion<PTs...>,
115 PointerIntPair<
116 void *, pointer_union_detail::bitsRequired(n: sizeof...(PTs)), int,
117 pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
118 0, PTs...> {
119 static_assert(TypesAreDistinct<PTs...>::value,
120 "PointerUnion alternative types cannot be repeated");
121 // The first type is special because we want to directly cast a pointer to a
122 // default-initialized union to a pointer to the first type. But we don't
123 // want PointerUnion to be a 'template <typename First, typename ...Rest>'
124 // because it's much more convenient to have a name for the whole pack. So
125 // split off the first type here.
126 using First = TypeAtIndex<0, PTs...>;
127 using Base = typename PointerUnion::PointerUnionMembers;
128
129 /// This is needed to give the CastInfo implementation below access
130 /// to protected members.
131 /// Refer to its definition for further details.
132 friend struct CastInfoPointerUnionImpl<PTs...>;
133
134public:
135 PointerUnion() = default;
136
137 PointerUnion(std::nullptr_t) : PointerUnion() {}
138 using Base::Base;
139
140 /// Test if the pointer held in the union is null, regardless of
141 /// which type it is.
142 bool isNull() const { return !this->Val.getPointer(); }
143
144 explicit operator bool() const { return !isNull(); }
145
146 // FIXME: Replace the uses of is(), get() and dyn_cast() with
147 // isa<T>, cast<T> and the llvm::dyn_cast<T>
148
149 /// Test if the Union currently holds the type matching T.
150 template <typename T> inline bool is() const { return isa<T>(*this); }
151
152 /// Returns the value of the specified pointer type.
153 ///
154 /// If the specified pointer type is incorrect, assert.
155 template <typename T> inline T get() const {
156 assert(isa<T>(*this) && "Invalid accessor called");
157 return cast<T>(*this);
158 }
159
160 /// Returns the current pointer if it is of the specified pointer type,
161 /// otherwise returns null.
162 template <typename T> inline T dyn_cast() const {
163 return llvm::dyn_cast_if_present<T>(*this);
164 }
165
166 /// If the union is set to the first pointer type get an address pointing to
167 /// it.
168 First const *getAddrOfPtr1() const {
169 return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
170 }
171
172 /// If the union is set to the first pointer type get an address pointing to
173 /// it.
174 First *getAddrOfPtr1() {
175 assert(isa<First>(*this) && "Val is not the first pointer");
176 assert(
177 PointerLikeTypeTraits<First>::getAsVoidPointer(cast<First>(*this)) ==
178 this->Val.getPointer() &&
179 "Can't get the address because PointerLikeTypeTraits changes the ptr");
180 return const_cast<First *>(
181 reinterpret_cast<const First *>(this->Val.getAddrOfPointer()));
182 }
183
184 /// Assignment from nullptr which just clears the union.
185 const PointerUnion &operator=(std::nullptr_t) {
186 this->Val.initWithPointer(nullptr);
187 return *this;
188 }
189
190 /// Assignment from elements of the union.
191 using Base::operator=;
192
193 void *getOpaqueValue() const { return this->Val.getOpaqueValue(); }
194 static inline PointerUnion getFromOpaqueValue(void *VP) {
195 PointerUnion V;
196 V.Val = decltype(V.Val)::getFromOpaqueValue(VP);
197 return V;
198 }
199};
200
201template <typename ...PTs>
202bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
203 return lhs.getOpaqueValue() == rhs.getOpaqueValue();
204}
205
206template <typename ...PTs>
207bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
208 return lhs.getOpaqueValue() != rhs.getOpaqueValue();
209}
210
211template <typename ...PTs>
212bool operator<(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
213 return lhs.getOpaqueValue() < rhs.getOpaqueValue();
214}
215
216/// We can't (at least, at this moment with C++14) declare CastInfo
217/// as a friend of PointerUnion like this:
218/// ```
219/// template<typename To>
220/// friend struct CastInfo<To, PointerUnion<PTs...>>;
221/// ```
222/// The compiler complains 'Partial specialization cannot be declared as a
223/// friend'.
224/// So we define this struct to be a bridge between CastInfo and
225/// PointerUnion.
226template <typename... PTs> struct CastInfoPointerUnionImpl {
227 using From = PointerUnion<PTs...>;
228
229 template <typename To> static inline bool isPossible(From &F) {
230 return F.Val.getInt() == FirstIndexOfType<To, PTs...>::value;
231 }
232
233 template <typename To> static To doCast(From &F) {
234 assert(isPossible<To>(F) && "cast to an incompatible type!");
235 return PointerLikeTypeTraits<To>::getFromVoidPointer(F.Val.getPointer());
236 }
237};
238
239// Specialization of CastInfo for PointerUnion
240template <typename To, typename... PTs>
241struct CastInfo<To, PointerUnion<PTs...>>
242 : public DefaultDoCastIfPossible<To, PointerUnion<PTs...>,
243 CastInfo<To, PointerUnion<PTs...>>> {
244 using From = PointerUnion<PTs...>;
245 using Impl = CastInfoPointerUnionImpl<PTs...>;
246
247 static inline bool isPossible(From &f) {
248 return Impl::template isPossible<To>(f);
249 }
250
251 static To doCast(From &f) { return Impl::template doCast<To>(f); }
252
253 static inline To castFailed() { return To(); }
254};
255
256template <typename To, typename... PTs>
257struct CastInfo<To, const PointerUnion<PTs...>>
258 : public ConstStrippingForwardingCast<To, const PointerUnion<PTs...>,
259 CastInfo<To, PointerUnion<PTs...>>> {
260};
261
262// Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
263// # low bits available = min(PT1bits,PT2bits)-1.
264template <typename ...PTs>
265struct PointerLikeTypeTraits<PointerUnion<PTs...>> {
266 static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) {
267 return P.getOpaqueValue();
268 }
269
270 static inline PointerUnion<PTs...> getFromVoidPointer(void *P) {
271 return PointerUnion<PTs...>::getFromOpaqueValue(P);
272 }
273
274 // The number of bits available are the min of the pointer types minus the
275 // bits needed for the discriminator.
276 static constexpr int NumLowBitsAvailable = PointerLikeTypeTraits<decltype(
277 PointerUnion<PTs...>::Val)>::NumLowBitsAvailable;
278};
279
280// Teach DenseMap how to use PointerUnions as keys.
281template <typename ...PTs> struct DenseMapInfo<PointerUnion<PTs...>> {
282 using Union = PointerUnion<PTs...>;
283 using FirstInfo =
284 DenseMapInfo<typename pointer_union_detail::GetFirstType<PTs...>::type>;
285
286 static inline Union getEmptyKey() { return Union(FirstInfo::getEmptyKey()); }
287
288 static inline Union getTombstoneKey() {
289 return Union(FirstInfo::getTombstoneKey());
290 }
291
292 static unsigned getHashValue(const Union &UnionVal) {
293 intptr_t key = (intptr_t)UnionVal.getOpaqueValue();
294 return DenseMapInfo<intptr_t>::getHashValue(Val: key);
295 }
296
297 static bool isEqual(const Union &LHS, const Union &RHS) {
298 return LHS == RHS;
299 }
300};
301
302} // end namespace llvm
303
304#endif // LLVM_ADT_POINTERUNION_H
305

source code of include/llvm-17/llvm/ADT/PointerUnion.h