1 //===----------------------------------------------------------------------===// 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 _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 10 #define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 11 12 #include <__config> 13 #include <__memory/addressof.h> 14 #include <__memory/construct_at.h> 15 #include <__type_traits/datasizeof.h> 16 #include <__type_traits/is_always_bitcastable.h> 17 #include <__type_traits/is_assignable.h> 18 #include <__type_traits/is_constant_evaluated.h> 19 #include <__type_traits/is_constructible.h> 20 #include <__type_traits/is_equality_comparable.h> 21 #include <__type_traits/is_same.h> 22 #include <__type_traits/is_trivially_copyable.h> 23 #include <__type_traits/is_trivially_lexicographically_comparable.h> 24 #include <__type_traits/remove_cv.h> 25 #include <__utility/is_pointer_in_range.h> 26 #include <cstddef> 27 28 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 29 # pragma GCC system_header 30 #endif 31 32 _LIBCPP_BEGIN_NAMESPACE_STD 33 34 // Type used to encode that a function takes an integer that represents a number 35 // of elements as opposed to a number of bytes. 36 enum class __element_count : size_t {}; 37 38 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const char* __str) { 39 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation. 40 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816 41 #ifdef _LIBCPP_COMPILER_GCC 42 if (__libcpp_is_constant_evaluated()) { 43 size_t __i = 0; 44 for (; __str[__i] != '\0'; ++__i) 45 ; 46 return __i; 47 } 48 #endif 49 return __builtin_strlen(__str); 50 } 51 52 // Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is 53 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead 54 // of invoking it on every object individually. 55 template <class _Tp, class _Up> 56 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int 57 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 58 static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value, 59 "_Tp and _Up have to be trivially lexicographically comparable"); 60 61 auto __count = static_cast<size_t>(__n); 62 63 if (__libcpp_is_constant_evaluated()) { 64 #ifdef _LIBCPP_COMPILER_CLANG_BASED 65 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value) 66 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 67 #endif 68 69 while (__count != 0) { 70 if (*__lhs < *__rhs) 71 return -1; 72 if (*__rhs < *__lhs) 73 return 1; 74 75 --__count; 76 ++__lhs; 77 ++__rhs; 78 } 79 return 0; 80 } else { 81 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 82 } 83 } 84 85 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent 86 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead 87 // of invoking it on every object individually. 88 template <class _Tp, class _Up> 89 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool 90 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 91 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 92 "_Tp and _Up have to be trivially equality comparable"); 93 94 auto __count = static_cast<size_t>(__n); 95 96 if (__libcpp_is_constant_evaluated()) { 97 #ifdef _LIBCPP_COMPILER_CLANG_BASED 98 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value) 99 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 100 #endif 101 while (__count != 0) { 102 if (*__lhs != *__rhs) 103 return false; 104 105 --__count; 106 ++__lhs; 107 ++__rhs; 108 } 109 return true; 110 } else { 111 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 112 } 113 } 114 115 template <class _Tp, class _Up> 116 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) { 117 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 118 "Calling memchr on non-trivially equality comparable types is unsafe."); 119 120 if (__libcpp_is_constant_evaluated()) { 121 // use __builtin_char_memchr to optimize constexpr evaluation if we can 122 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr) 123 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>) 124 return __builtin_char_memchr(__str, __value, __count); 125 #endif 126 127 for (; __count; --__count) { 128 if (*__str == __value) 129 return __str; 130 ++__str; 131 } 132 return nullptr; 133 } else { 134 char __value_buffer = 0; 135 __builtin_memcpy(&__value_buffer, &__value, sizeof(char)); 136 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count)); 137 } 138 } 139 140 // This function performs an assignment to an existing, already alive TriviallyCopyable object 141 // from another TriviallyCopyable object. 142 // 143 // It basically works around the fact that TriviallyCopyable objects are not required to be 144 // syntactically copy/move constructible or copy/move assignable. Technically, only one of the 145 // four operations is required to be syntactically valid -- but at least one definitely has to 146 // be valid. 147 // 148 // This is necessary in order to implement __constexpr_memmove below in a way that mirrors as 149 // closely as possible what the compiler's __builtin_memmove is able to do. 150 template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0> 151 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 152 __dest = __src; 153 return __dest; 154 } 155 156 // clang-format off 157 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 158 is_assignable<_Tp&, _Up&&>::value, int> = 0> 159 // clang-format on 160 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 161 __dest = 162 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial 163 return __dest; 164 } 165 166 // clang-format off 167 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 168 !is_assignable<_Tp&, _Up&&>::value && 169 is_constructible<_Tp, _Up const&>::value, int> = 0> 170 // clang-format on 171 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 172 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 173 // that was there previously 174 std::__construct_at(std::addressof(__dest), __src); 175 return __dest; 176 } 177 178 // clang-format off 179 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 180 !is_assignable<_Tp&, _Up&&>::value && 181 !is_constructible<_Tp, _Up const&>::value && 182 is_constructible<_Tp, _Up&&>::value, int> = 0> 183 // clang-format on 184 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 185 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 186 // that was there previously 187 std::__construct_at( 188 std::addressof(__dest), 189 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial 190 return __dest; 191 } 192 193 template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0> 194 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* 195 __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) { 196 size_t __count = static_cast<size_t>(__n); 197 if (__libcpp_is_constant_evaluated()) { 198 #ifdef _LIBCPP_COMPILER_CLANG_BASED 199 if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) { 200 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp)); 201 return __dest; 202 } 203 #endif 204 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) { 205 for (; __count > 0; --__count) 206 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]); 207 } else { 208 for (size_t __i = 0; __i != __count; ++__i) 209 std::__assign_trivially_copyable(__dest[__i], __src[__i]); 210 } 211 } else if (__count > 0) { 212 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __libcpp_datasizeof<_Tp>::value); 213 } 214 return __dest; 215 } 216 217 _LIBCPP_END_NAMESPACE_STD 218 219 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 220