1//===-- llvm/ADT/BitmaskEnum.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_BITMASKENUM_H
10#define LLVM_ADT_BITMASKENUM_H
11
12#include <cassert>
13#include <type_traits>
14#include <utility>
15
16#include "llvm/Support/MathExtras.h"
17
18/// LLVM_MARK_AS_BITMASK_ENUM lets you opt in an individual enum type so you can
19/// perform bitwise operations on it without putting static_cast everywhere.
20///
21/// \code
22///   enum MyEnum {
23///     E1 = 1, E2 = 2, E3 = 4, E4 = 8,
24///     LLVM_MARK_AS_BITMASK_ENUM(/* LargestValue = */ E4)
25///   };
26///
27///   void Foo() {
28///     MyEnum A = (E1 | E2) & E3 ^ ~E4; // Look, ma: No static_cast!
29///   }
30/// \endcode
31///
32/// Normally when you do a bitwise operation on an enum value, you get back an
33/// instance of the underlying type (e.g. int).  But using this macro, bitwise
34/// ops on your enum will return you back instances of the enum.  This is
35/// particularly useful for enums which represent a combination of flags.
36///
37/// The parameter to LLVM_MARK_AS_BITMASK_ENUM should be the largest individual
38/// value in your enum.
39///
40/// All of the enum's values must be non-negative.
41#define LLVM_MARK_AS_BITMASK_ENUM(LargestValue)                                \
42  LLVM_BITMASK_LARGEST_ENUMERATOR = LargestValue
43
44/// LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE() pulls the operator overloads used
45/// by LLVM_MARK_AS_BITMASK_ENUM into the current namespace.
46///
47/// Suppose you have an enum foo::bar::MyEnum.  Before using
48/// LLVM_MARK_AS_BITMASK_ENUM on MyEnum, you must put
49/// LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE() somewhere inside namespace foo or
50/// namespace foo::bar.  This allows the relevant operator overloads to be found
51/// by ADL.
52///
53/// You don't need to use this macro in namespace llvm; it's done at the bottom
54/// of this file.
55#define LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE()                               \
56  using ::llvm::BitmaskEnumDetail::operator~;                                  \
57  using ::llvm::BitmaskEnumDetail::operator|;                                  \
58  using ::llvm::BitmaskEnumDetail::operator&;                                  \
59  using ::llvm::BitmaskEnumDetail::operator^;                                  \
60  using ::llvm::BitmaskEnumDetail::operator|=;                                 \
61  using ::llvm::BitmaskEnumDetail::operator&=;                                 \
62  /* Force a semicolon at the end of this macro. */                            \
63  using ::llvm::BitmaskEnumDetail::operator^=
64
65namespace llvm {
66
67/// Traits class to determine whether an enum has a
68/// LLVM_BITMASK_LARGEST_ENUMERATOR enumerator.
69template <typename E, typename Enable = void>
70struct is_bitmask_enum : std::false_type {};
71
72template <typename E>
73struct is_bitmask_enum<
74    E, std::enable_if_t<sizeof(E::LLVM_BITMASK_LARGEST_ENUMERATOR) >= 0>>
75    : std::true_type {};
76namespace BitmaskEnumDetail {
77
78/// Get a bitmask with 1s in all places up to the high-order bit of E's largest
79/// value.
80template <typename E> std::underlying_type_t<E> Mask() {
81  // On overflow, NextPowerOf2 returns zero with the type uint64_t, so
82  // subtracting 1 gives us the mask with all bits set, like we want.
83  return NextPowerOf2(static_cast<std::underlying_type_t<E>>(
84             E::LLVM_BITMASK_LARGEST_ENUMERATOR)) -
85         1;
86}
87
88/// Check that Val is in range for E, and return Val cast to E's underlying
89/// type.
90template <typename E> std::underlying_type_t<E> Underlying(E Val) {
91  auto U = static_cast<std::underlying_type_t<E>>(Val);
92  assert(U >= 0 && "Negative enum values are not allowed.");
93  assert(U <= Mask<E>() && "Enum value too large (or largest val too small?)");
94  return U;
95}
96
97constexpr unsigned bitWidth(uint64_t Value) {
98  return Value ? 1 + bitWidth(Value >> 1) : 0;
99}
100
101template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
102E operator~(E Val) {
103  return static_cast<E>(~Underlying(Val) & Mask<E>());
104}
105
106template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
107E operator|(E LHS, E RHS) {
108  return static_cast<E>(Underlying(LHS) | Underlying(RHS));
109}
110
111template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
112E operator&(E LHS, E RHS) {
113  return static_cast<E>(Underlying(LHS) & Underlying(RHS));
114}
115
116template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
117E operator^(E LHS, E RHS) {
118  return static_cast<E>(Underlying(LHS) ^ Underlying(RHS));
119}
120
121// |=, &=, and ^= return a reference to LHS, to match the behavior of the
122// operators on builtin types.
123
124template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
125E &operator|=(E &LHS, E RHS) {
126  LHS = LHS | RHS;
127  return LHS;
128}
129
130template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
131E &operator&=(E &LHS, E RHS) {
132  LHS = LHS & RHS;
133  return LHS;
134}
135
136template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
137E &operator^=(E &LHS, E RHS) {
138  LHS = LHS ^ RHS;
139  return LHS;
140}
141
142} // namespace BitmaskEnumDetail
143
144// Enable bitmask enums in namespace ::llvm and all nested namespaces.
145LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
146template <typename E, typename = std::enable_if_t<is_bitmask_enum<E>::value>>
147constexpr unsigned BitWidth = BitmaskEnumDetail::bitWidth(uint64_t{
148    static_cast<std::underlying_type_t<E>>(
149        E::LLVM_BITMASK_LARGEST_ENUMERATOR)});
150
151} // namespace llvm
152
153#endif
154