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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 :
28 : namespace llvm {
29 :
30 : namespace 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 + 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:
50 998 : static inline void *getAsVoidPointer(void *P) { return P; }
51 998 : 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;
62 998 : PointerUnionMembers() = default;
63 998 : 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 1996 : PointerUnionMembers() = default;
76 998 : PointerUnionMembers(Type V)
77 998 : : Base(ValTy(const_cast<void *>(
78 : PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
79 1996 : 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
93 : template <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.
111 : template <typename... PTs>
112 : class PointerUnion
113 : : public pointer_union_detail::PointerUnionMembers<
114 : PointerUnion<PTs...>,
115 : PointerIntPair<
116 : void *, pointer_union_detail::bitsRequired(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 :
134 : public:
135 998 : 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.
142 998 : bool isNull() const { return !this->Val.getPointer(); }
143 :
144 998 : 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 :
193 998 : void *getOpaqueValue() const { return this->Val.getOpaqueValue(); }
194 998 : static inline PointerUnion getFromOpaqueValue(void *VP) {
195 998 : PointerUnion V;
196 998 : V.Val = decltype(V.Val)::getFromOpaqueValue(VP);
197 998 : return V;
198 : }
199 : };
200 :
201 : template <typename ...PTs>
202 : bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
203 : return lhs.getOpaqueValue() == rhs.getOpaqueValue();
204 : }
205 :
206 : template <typename ...PTs>
207 : bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
208 : return lhs.getOpaqueValue() != rhs.getOpaqueValue();
209 : }
210 :
211 : template <typename ...PTs>
212 : bool 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.
226 : template <typename... PTs> struct CastInfoPointerUnionImpl {
227 : using From = PointerUnion<PTs...>;
228 :
229 0 : template <typename To> static inline bool isPossible(From &F) {
230 0 : return F.Val.getInt() == FirstIndexOfType<To, PTs...>::value;
231 : }
232 :
233 0 : template <typename To> static To doCast(From &F) {
234 0 : assert(isPossible<To>(F) && "cast to an incompatible type!");
235 0 : return PointerLikeTypeTraits<To>::getFromVoidPointer(F.Val.getPointer());
236 : }
237 : };
238 :
239 : // Specialization of CastInfo for PointerUnion
240 : template <typename To, typename... PTs>
241 : struct 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 0 : static inline bool isPossible(From &f) {
248 0 : return Impl::template isPossible<To>(f);
249 : }
250 :
251 0 : static To doCast(From &f) { return Impl::template doCast<To>(f); }
252 :
253 : static inline To castFailed() { return To(); }
254 : };
255 :
256 : template <typename To, typename... PTs>
257 : struct 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.
264 : template <typename ...PTs>
265 : struct PointerLikeTypeTraits<PointerUnion<PTs...>> {
266 998 : static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) {
267 998 : return P.getOpaqueValue();
268 : }
269 :
270 998 : static inline PointerUnion<PTs...> getFromVoidPointer(void *P) {
271 998 : 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.
281 : template <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(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
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