type_traits.h revision 360660 
1//===- llvm/Support/type_traits.h - Simplfied type traits -------*- 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 provides useful additions to the standard type_traits library.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_SUPPORT_TYPE_TRAITS_H
14#define LLVM_SUPPORT_TYPE_TRAITS_H
15
16#include "llvm/Support/Compiler.h"
17#include <type_traits>
18#include <utility>
19
20#ifndef __has_feature
21#define LLVM_DEFINED_HAS_FEATURE
22#define __has_feature(x) 0
23#endif
24
25namespace llvm {
26
27
28/// Metafunction that determines whether the given type is either an
29/// integral type or an enumeration type, including enum classes.
30///
31/// Note that this accepts potentially more integral types than is_integral
32/// because it is based on being implicitly convertible to an integral type.
33/// Also note that enum classes aren't implicitly convertible to integral types,
34/// the value may therefore need to be explicitly converted before being used.
35template <typename T> class is_integral_or_enum {
36  using UnderlyingT = typename std::remove_reference<T>::type;
37
38public:
39  static const bool value =
40      !std::is_class<UnderlyingT>::value && // Filter conversion operators.
41      !std::is_pointer<UnderlyingT>::value &&
42      !std::is_floating_point<UnderlyingT>::value &&
43      (std::is_enum<UnderlyingT>::value ||
44       std::is_convertible<UnderlyingT, unsigned long long>::value);
45};
46
47/// If T is a pointer, just return it. If it is not, return T&.
48template<typename T, typename Enable = void>
49struct add_lvalue_reference_if_not_pointer { using type = T &; };
50
51template <typename T>
52struct add_lvalue_reference_if_not_pointer<
53    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
54  using type = T;
55};
56
57/// If T is a pointer to X, return a pointer to const X. If it is not,
58/// return const T.
59template<typename T, typename Enable = void>
60struct add_const_past_pointer { using type = const T; };
61
62template <typename T>
63struct add_const_past_pointer<
64    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
65  using type = const typename std::remove_pointer<T>::type *;
66};
67
68template <typename T, typename Enable = void>
69struct const_pointer_or_const_ref {
70  using type = const T &;
71};
72template <typename T>
73struct const_pointer_or_const_ref<
74    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
75  using type = typename add_const_past_pointer<T>::type;
76};
77
78namespace detail {
79/// Internal utility to detect trivial copy construction.
80template<typename T> union copy_construction_triviality_helper {
81    T t;
82    copy_construction_triviality_helper() = default;
83    copy_construction_triviality_helper(const copy_construction_triviality_helper&) = default;
84    ~copy_construction_triviality_helper() = default;
85};
86/// Internal utility to detect trivial move construction.
87template<typename T> union move_construction_triviality_helper {
88    T t;
89    move_construction_triviality_helper() = default;
90    move_construction_triviality_helper(move_construction_triviality_helper&&) = default;
91    ~move_construction_triviality_helper() = default;
92};
93
94template<class T>
95union trivial_helper {
96    T t;
97};
98
99} // end namespace detail
100
101/// An implementation of `std::is_trivially_copy_constructible` since we have
102/// users with STLs that don't yet include it.
103template <typename T>
104struct is_trivially_copy_constructible
105    : std::is_copy_constructible<
106          ::llvm::detail::copy_construction_triviality_helper<T>> {};
107template <typename T>
108struct is_trivially_copy_constructible<T &> : std::true_type {};
109template <typename T>
110struct is_trivially_copy_constructible<T &&> : std::false_type {};
111
112/// An implementation of `std::is_trivially_move_constructible` since we have
113/// users with STLs that don't yet include it.
114template <typename T>
115struct is_trivially_move_constructible
116    : std::is_move_constructible<
117          ::llvm::detail::move_construction_triviality_helper<T>> {};
118template <typename T>
119struct is_trivially_move_constructible<T &> : std::true_type {};
120template <typename T>
121struct is_trivially_move_constructible<T &&> : std::true_type {};
122
123
124template <typename T>
125struct is_copy_assignable {
126  template<class F>
127    static auto get(F*) -> decltype(std::declval<F &>() = std::declval<const F &>(), std::true_type{});
128    static std::false_type get(...);
129    static constexpr bool value = decltype(get((T*)nullptr))::value;
130};
131
132template <typename T>
133struct is_move_assignable {
134  template<class F>
135    static auto get(F*) -> decltype(std::declval<F &>() = std::declval<F &&>(), std::true_type{});
136    static std::false_type get(...);
137    static constexpr bool value = decltype(get((T*)nullptr))::value;
138};
139
140
141// An implementation of `std::is_trivially_copyable` since STL version
142// is not equally supported by all compilers, especially GCC 4.9.
143// Uniform implementation of this trait is important for ABI compatibility
144// as it has an impact on SmallVector's ABI (among others).
145template <typename T>
146class is_trivially_copyable {
147
148  // copy constructors
149  static constexpr bool has_trivial_copy_constructor =
150      std::is_copy_constructible<detail::trivial_helper<T>>::value;
151  static constexpr bool has_deleted_copy_constructor =
152      !std::is_copy_constructible<T>::value;
153
154  // move constructors
155  static constexpr bool has_trivial_move_constructor =
156      std::is_move_constructible<detail::trivial_helper<T>>::value;
157  static constexpr bool has_deleted_move_constructor =
158      !std::is_move_constructible<T>::value;
159
160  // copy assign
161  static constexpr bool has_trivial_copy_assign =
162      is_copy_assignable<detail::trivial_helper<T>>::value;
163  static constexpr bool has_deleted_copy_assign =
164      !is_copy_assignable<T>::value;
165
166  // move assign
167  static constexpr bool has_trivial_move_assign =
168      is_move_assignable<detail::trivial_helper<T>>::value;
169  static constexpr bool has_deleted_move_assign =
170      !is_move_assignable<T>::value;
171
172  // destructor
173  static constexpr bool has_trivial_destructor =
174      std::is_destructible<detail::trivial_helper<T>>::value;
175
176  public:
177
178  static constexpr bool value =
179      has_trivial_destructor &&
180      (has_deleted_move_assign || has_trivial_move_assign) &&
181      (has_deleted_move_constructor || has_trivial_move_constructor) &&
182      (has_deleted_copy_assign || has_trivial_copy_assign) &&
183      (has_deleted_copy_constructor || has_trivial_copy_constructor);
184
185#ifdef HAVE_STD_IS_TRIVIALLY_COPYABLE
186  static_assert(value == std::is_trivially_copyable<T>::value,
187                "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
188#endif
189};
190template <typename T>
191class is_trivially_copyable<T*> : public std::true_type {
192};
193
194
195} // end namespace llvm
196
197// If the compiler supports detecting whether a class is final, define
198// an LLVM_IS_FINAL macro. If it cannot be defined properly, this
199// macro will be left undefined.
200#if __cplusplus >= 201402L || defined(_MSC_VER)
201#define LLVM_IS_FINAL(Ty) std::is_final<Ty>()
202#elif __has_feature(is_final) || LLVM_GNUC_PREREQ(4, 7, 0)
203#define LLVM_IS_FINAL(Ty) __is_final(Ty)
204#endif
205
206#ifdef LLVM_DEFINED_HAS_FEATURE
207#undef __has_feature
208#endif
209
210#endif // LLVM_SUPPORT_TYPE_TRAITS_H
211