1 //===- llvm/ADT/PointerIntPair.h - Pair for pointer and int -----*- 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 PointerIntPair class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_ADT_POINTERINTPAIR_H
14 #define LLVM_ADT_POINTERINTPAIR_H
15 
16 #include "llvm/Support/Compiler.h"
17 #include "llvm/Support/PointerLikeTypeTraits.h"
18 #include "llvm/Support/type_traits.h"
19 #include <cassert>
20 #include <cstdint>
21 #include <limits>
22 
23 namespace llvm {
24 
25 template <typename T> struct DenseMapInfo;
26 template <typename PointerT, unsigned IntBits, typename PtrTraits>
27 struct PointerIntPairInfo;
28 
29 /// PointerIntPair - This class implements a pair of a pointer and small
30 /// integer.  It is designed to represent this in the space required by one
31 /// pointer by bitmangling the integer into the low part of the pointer.  This
32 /// can only be done for small integers: typically up to 3 bits, but it depends
33 /// on the number of bits available according to PointerLikeTypeTraits for the
34 /// type.
35 ///
36 /// Note that PointerIntPair always puts the IntVal part in the highest bits
37 /// possible.  For example, PointerIntPair<void*, 1, bool> will put the bit for
38 /// the bool into bit #2, not bit #0, which allows the low two bits to be used
39 /// for something else.  For example, this allows:
40 ///   PointerIntPair<PointerIntPair<void*, 1, bool>, 1, bool>
41 /// ... and the two bools will land in different bits.
42 template <typename PointerTy, unsigned IntBits, typename IntType = unsigned,
43           typename PtrTraits = PointerLikeTypeTraits<PointerTy>,
44           typename Info = PointerIntPairInfo<PointerTy, IntBits, PtrTraits>>
45 class PointerIntPair {
46   // Used by MSVC visualizer and generally helpful for debugging/visualizing.
47   using InfoTy = Info;
48   intptr_t Value = 0;
49 
50 public:
51   constexpr PointerIntPair() = default;
52 
53   PointerIntPair(PointerTy PtrVal, IntType IntVal) {
54     setPointerAndInt(PtrVal, IntVal);
55   }
56 
57   explicit PointerIntPair(PointerTy PtrVal) { initWithPointer(PtrVal); }
58 
59   PointerTy getPointer() const { return Info::getPointer(Value); }
60 
61   IntType getInt() const { return (IntType)Info::getInt(Value); }
62 
63   void setPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
64     Value = Info::updatePointer(Value, PtrVal);
65   }
66 
67   void setInt(IntType IntVal) LLVM_LVALUE_FUNCTION {
68     Value = Info::updateInt(Value, static_cast<intptr_t>(IntVal));
69   }
70 
71   void initWithPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
72     Value = Info::updatePointer(0, PtrVal);
73   }
74 
75   void setPointerAndInt(PointerTy PtrVal, IntType IntVal) LLVM_LVALUE_FUNCTION {
76     Value = Info::updateInt(Info::updatePointer(0, PtrVal),
77                             static_cast<intptr_t>(IntVal));
78   }
79 
80   PointerTy const *getAddrOfPointer() const {
81     return const_cast<PointerIntPair *>(this)->getAddrOfPointer();
82   }
83 
84   PointerTy *getAddrOfPointer() {
85     assert(Value == reinterpret_cast<intptr_t>(getPointer()) &&
86            "Can only return the address if IntBits is cleared and "
87            "PtrTraits doesn't change the pointer");
88     return reinterpret_cast<PointerTy *>(&Value);
89   }
90 
91   void *getOpaqueValue() const { return reinterpret_cast<void *>(Value); }
92 
93   void setFromOpaqueValue(void *Val) LLVM_LVALUE_FUNCTION {
94     Value = reinterpret_cast<intptr_t>(Val);
95   }
96 
97   static PointerIntPair getFromOpaqueValue(void *V) {
98     PointerIntPair P;
99     P.setFromOpaqueValue(V);
100     return P;
101   }
102 
103   // Allow PointerIntPairs to be created from const void * if and only if the
104   // pointer type could be created from a const void *.
105   static PointerIntPair getFromOpaqueValue(const void *V) {
106     (void)PtrTraits::getFromVoidPointer(V);
107     return getFromOpaqueValue(const_cast<void *>(V));
108   }
109 
110   bool operator==(const PointerIntPair &RHS) const {
111     return Value == RHS.Value;
112   }
113 
114   bool operator!=(const PointerIntPair &RHS) const {
115     return Value != RHS.Value;
116   }
117 
118   bool operator<(const PointerIntPair &RHS) const { return Value < RHS.Value; }
119   bool operator>(const PointerIntPair &RHS) const { return Value > RHS.Value; }
120 
121   bool operator<=(const PointerIntPair &RHS) const {
122     return Value <= RHS.Value;
123   }
124 
125   bool operator>=(const PointerIntPair &RHS) const {
126     return Value >= RHS.Value;
127   }
128 };
129 
130 // Specialize is_trivially_copyable to avoid limitation of llvm::is_trivially_copyable
131 // when compiled with gcc 4.9.
132 template <typename PointerTy, unsigned IntBits, typename IntType,
133           typename PtrTraits,
134           typename Info>
135 struct is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>> : std::true_type {
136 #ifdef HAVE_STD_IS_TRIVIALLY_COPYABLE
137   static_assert(std::is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>>::value,
138                 "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
139 #endif
140 };
141 
142 
143 template <typename PointerT, unsigned IntBits, typename PtrTraits>
144 struct PointerIntPairInfo {
145   static_assert(PtrTraits::NumLowBitsAvailable <
146                     std::numeric_limits<uintptr_t>::digits,
147                 "cannot use a pointer type that has all bits free");
148   static_assert(IntBits <= PtrTraits::NumLowBitsAvailable,
149                 "PointerIntPair with integer size too large for pointer");
150   enum MaskAndShiftConstants : uintptr_t {
151     /// PointerBitMask - The bits that come from the pointer.
152     PointerBitMask =
153         ~(uintptr_t)(((intptr_t)1 << PtrTraits::NumLowBitsAvailable) - 1),
154 
155     /// IntShift - The number of low bits that we reserve for other uses, and
156     /// keep zero.
157     IntShift = (uintptr_t)PtrTraits::NumLowBitsAvailable - IntBits,
158 
159     /// IntMask - This is the unshifted mask for valid bits of the int type.
160     IntMask = (uintptr_t)(((intptr_t)1 << IntBits) - 1),
161 
162     // ShiftedIntMask - This is the bits for the integer shifted in place.
163     ShiftedIntMask = (uintptr_t)(IntMask << IntShift)
164   };
165 
166   static PointerT getPointer(intptr_t Value) {
167     return PtrTraits::getFromVoidPointer(
168         reinterpret_cast<void *>(Value & PointerBitMask));
169   }
170 
171   static intptr_t getInt(intptr_t Value) {
172     return (Value >> IntShift) & IntMask;
173   }
174 
175   static intptr_t updatePointer(intptr_t OrigValue, PointerT Ptr) {
176     intptr_t PtrWord =
177         reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(Ptr));
178     assert((PtrWord & ~PointerBitMask) == 0 &&
179            "Pointer is not sufficiently aligned");
180     // Preserve all low bits, just update the pointer.
181     return PtrWord | (OrigValue & ~PointerBitMask);
182   }
183 
184   static intptr_t updateInt(intptr_t OrigValue, intptr_t Int) {
185     intptr_t IntWord = static_cast<intptr_t>(Int);
186     assert((IntWord & ~IntMask) == 0 && "Integer too large for field");
187 
188     // Preserve all bits other than the ones we are updating.
189     return (OrigValue & ~ShiftedIntMask) | IntWord << IntShift;
190   }
191 };
192 
193 // Provide specialization of DenseMapInfo for PointerIntPair.
194 template <typename PointerTy, unsigned IntBits, typename IntType>
195 struct DenseMapInfo<PointerIntPair<PointerTy, IntBits, IntType>> {
196   using Ty = PointerIntPair<PointerTy, IntBits, IntType>;
197 
198   static Ty getEmptyKey() {
199     uintptr_t Val = static_cast<uintptr_t>(-1);
200     Val <<= PointerLikeTypeTraits<Ty>::NumLowBitsAvailable;
201     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
202   }
203 
204   static Ty getTombstoneKey() {
205     uintptr_t Val = static_cast<uintptr_t>(-2);
206     Val <<= PointerLikeTypeTraits<PointerTy>::NumLowBitsAvailable;
207     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
208   }
209 
210   static unsigned getHashValue(Ty V) {
211     uintptr_t IV = reinterpret_cast<uintptr_t>(V.getOpaqueValue());
212     return unsigned(IV) ^ unsigned(IV >> 9);
213   }
214 
215   static bool isEqual(const Ty &LHS, const Ty &RHS) { return LHS == RHS; }
216 };
217 
218 // Teach SmallPtrSet that PointerIntPair is "basically a pointer".
219 template <typename PointerTy, unsigned IntBits, typename IntType,
220           typename PtrTraits>
221 struct PointerLikeTypeTraits<
222     PointerIntPair<PointerTy, IntBits, IntType, PtrTraits>> {
223   static inline void *
224   getAsVoidPointer(const PointerIntPair<PointerTy, IntBits, IntType> &P) {
225     return P.getOpaqueValue();
226   }
227 
228   static inline PointerIntPair<PointerTy, IntBits, IntType>
229   getFromVoidPointer(void *P) {
230     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
231   }
232 
233   static inline PointerIntPair<PointerTy, IntBits, IntType>
234   getFromVoidPointer(const void *P) {
235     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
236   }
237 
238   static constexpr int NumLowBitsAvailable =
239       PtrTraits::NumLowBitsAvailable - IntBits;
240 };
241 
242 } // end namespace llvm
243 
244 #endif // LLVM_ADT_POINTERINTPAIR_H
245