1 | //===- llvm/ADT/PointerEmbeddedInt.h ----------------------------*- 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 | #ifndef LLVM_ADT_POINTEREMBEDDEDINT_H |
10 | #define LLVM_ADT_POINTEREMBEDDEDINT_H |
11 | |
12 | #include "llvm/ADT/DenseMapInfo.h" |
13 | #include "llvm/Support/MathExtras.h" |
14 | #include "llvm/Support/PointerLikeTypeTraits.h" |
15 | #include <cassert> |
16 | #include <climits> |
17 | #include <cstdint> |
18 | #include <type_traits> |
19 | |
20 | namespace llvm { |
21 | |
22 | /// Utility to embed an integer into a pointer-like type. This is specifically |
23 | /// intended to allow embedding integers where fewer bits are required than |
24 | /// exist in a pointer, and the integer can participate in abstractions along |
25 | /// side other pointer-like types. For example it can be placed into a \c |
26 | /// PointerSumType or \c PointerUnion. |
27 | /// |
28 | /// Note that much like pointers, an integer value of zero has special utility |
29 | /// due to boolean conversions. For example, a non-null value can be tested for |
30 | /// in the above abstractions without testing the particular active member. |
31 | /// Also, the default constructed value zero initializes the integer. |
32 | template <typename IntT, int Bits = sizeof(IntT) * CHAR_BIT> |
33 | class PointerEmbeddedInt { |
34 | uintptr_t Value = 0; |
35 | |
36 | // Note: This '<' is correct; using '<=' would result in some shifts |
37 | // overflowing their storage types. |
38 | static_assert(Bits < sizeof(uintptr_t) * CHAR_BIT, |
39 | "Cannot embed more bits than we have in a pointer!" ); |
40 | |
41 | enum : uintptr_t { |
42 | // We shift as many zeros into the value as we can while preserving the |
43 | // number of bits desired for the integer. |
44 | Shift = sizeof(uintptr_t) * CHAR_BIT - Bits, |
45 | |
46 | // We also want to be able to mask out the preserved bits for asserts. |
47 | Mask = static_cast<uintptr_t>(-1) << Bits |
48 | }; |
49 | |
50 | struct RawValueTag { |
51 | explicit RawValueTag() = default; |
52 | }; |
53 | |
54 | friend struct PointerLikeTypeTraits<PointerEmbeddedInt>; |
55 | |
56 | explicit PointerEmbeddedInt(uintptr_t Value, RawValueTag) : Value(Value) {} |
57 | |
58 | public: |
59 | PointerEmbeddedInt() = default; |
60 | |
61 | PointerEmbeddedInt(IntT I) { *this = I; } |
62 | |
63 | PointerEmbeddedInt &operator=(IntT I) { |
64 | assert((std::is_signed<IntT>::value ? isInt<Bits>(I) : isUInt<Bits>(I)) && |
65 | "Integer has bits outside those preserved!" ); |
66 | Value = static_cast<uintptr_t>(I) << Shift; |
67 | return *this; |
68 | } |
69 | |
70 | // Note that this implicit conversion additionally allows all of the basic |
71 | // comparison operators to work transparently, etc. |
72 | operator IntT() const { |
73 | if (std::is_signed<IntT>::value) |
74 | return static_cast<IntT>(static_cast<intptr_t>(Value) >> Shift); |
75 | return static_cast<IntT>(Value >> Shift); |
76 | } |
77 | }; |
78 | |
79 | // Provide pointer like traits to support use with pointer unions and sum |
80 | // types. |
81 | template <typename IntT, int Bits> |
82 | struct PointerLikeTypeTraits<PointerEmbeddedInt<IntT, Bits>> { |
83 | using T = PointerEmbeddedInt<IntT, Bits>; |
84 | |
85 | static inline void *getAsVoidPointer(const T &P) { |
86 | return reinterpret_cast<void *>(P.Value); |
87 | } |
88 | |
89 | static inline T getFromVoidPointer(void *P) { |
90 | return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag()); |
91 | } |
92 | |
93 | static inline T getFromVoidPointer(const void *P) { |
94 | return T(reinterpret_cast<uintptr_t>(P), typename T::RawValueTag()); |
95 | } |
96 | |
97 | static constexpr int NumLowBitsAvailable = T::Shift; |
98 | }; |
99 | |
100 | // Teach DenseMap how to use PointerEmbeddedInt objects as keys if the Int type |
101 | // itself can be a key. |
102 | template <typename IntT, int Bits> |
103 | struct DenseMapInfo<PointerEmbeddedInt<IntT, Bits>> { |
104 | using T = PointerEmbeddedInt<IntT, Bits>; |
105 | using IntInfo = DenseMapInfo<IntT>; |
106 | |
107 | static inline T getEmptyKey() { return IntInfo::getEmptyKey(); } |
108 | static inline T getTombstoneKey() { return IntInfo::getTombstoneKey(); } |
109 | |
110 | static unsigned getHashValue(const T &Arg) { |
111 | return IntInfo::getHashValue(Arg); |
112 | } |
113 | |
114 | static bool isEqual(const T &LHS, const T &RHS) { return LHS == RHS; } |
115 | }; |
116 | |
117 | } // end namespace llvm |
118 | |
119 | #endif // LLVM_ADT_POINTEREMBEDDEDINT_H |
120 | |