Andrew Scull | 5e1ddfa | 2018-08-14 10:06:54 +0100 | [diff] [blame] | 1 | //===- llvm/ADT/PointerEmbeddedInt.h ----------------------------*- C++ -*-===// |
| 2 | // |
Andrew Walbran | 16937d0 | 2019-10-22 13:54:20 +0100 | [diff] [blame] | 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 |
Andrew Scull | 5e1ddfa | 2018-08-14 10:06:54 +0100 | [diff] [blame] | 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 | |
Olivier Deprez | f4ef2d0 | 2021-04-20 13:36:24 +0200 | [diff] [blame] | 97 | static constexpr int NumLowBitsAvailable = T::Shift; |
Andrew Scull | 5e1ddfa | 2018-08-14 10:06:54 +0100 | [diff] [blame] | 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 |