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/enable_if.h> 17 #include <__type_traits/is_always_bitcastable.h> 18 #include <__type_traits/is_assignable.h> 19 #include <__type_traits/is_constant_evaluated.h> 20 #include <__type_traits/is_constructible.h> 21 #include <__type_traits/is_equality_comparable.h> 22 #include <__type_traits/is_integral.h> 23 #include <__type_traits/is_same.h> 24 #include <__type_traits/is_trivially_copyable.h> 25 #include <__type_traits/is_trivially_lexicographically_comparable.h> 26 #include <__type_traits/remove_cv.h> 27 #include <__utility/is_pointer_in_range.h> 28 #include <cstddef> 29 30 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 31 # pragma GCC system_header 32 #endif 33 34 _LIBCPP_BEGIN_NAMESPACE_STD 35 36 // Type used to encode that a function takes an integer that represents a number 37 // of elements as opposed to a number of bytes. 38 enum class __element_count : size_t {}; 39 40 template <class _Tp> 41 inline const bool __is_char_type = false; 42 43 template <> 44 inline const bool __is_char_type<char> = true; 45 46 #ifndef _LIBCPP_HAS_NO_CHAR8_T 47 template <> 48 inline const bool __is_char_type<char8_t> = true; 49 #endif 50 51 template <class _Tp> 52 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT { 53 static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t"); 54 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation. 55 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816 56 if (__libcpp_is_constant_evaluated()) { 57 #if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED) 58 if constexpr (is_same_v<_Tp, char>) 59 return __builtin_strlen(__str); 60 #endif 61 size_t __i = 0; 62 for (; __str[__i] != '\0'; ++__i) 63 ; 64 return __i; 65 } 66 return __builtin_strlen(reinterpret_cast<const char*>(__str)); 67 } 68 69 // Because of __is_trivially_lexicographically_comparable_v we know that comparing the object representations is 70 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead 71 // of invoking it on every object individually. 72 template <class _Tp, class _Up> 73 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int 74 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 75 static_assert(__is_trivially_lexicographically_comparable_v<_Tp, _Up>, 76 "_Tp and _Up have to be trivially lexicographically comparable"); 77 78 auto __count = static_cast<size_t>(__n); 79 80 if (__libcpp_is_constant_evaluated()) { 81 #ifdef _LIBCPP_COMPILER_CLANG_BASED 82 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value) 83 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 84 #endif 85 86 while (__count != 0) { 87 if (*__lhs < *__rhs) 88 return -1; 89 if (*__rhs < *__lhs) 90 return 1; 91 92 --__count; 93 ++__lhs; 94 ++__rhs; 95 } 96 return 0; 97 } else { 98 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 99 } 100 } 101 102 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent 103 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead 104 // of invoking it on every object individually. 105 template <class _Tp, class _Up> 106 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool 107 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 108 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 109 "_Tp and _Up have to be trivially equality comparable"); 110 111 auto __count = static_cast<size_t>(__n); 112 113 if (__libcpp_is_constant_evaluated()) { 114 #ifdef _LIBCPP_COMPILER_CLANG_BASED 115 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value) 116 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 117 #endif 118 while (__count != 0) { 119 if (*__lhs != *__rhs) 120 return false; 121 122 --__count; 123 ++__lhs; 124 ++__rhs; 125 } 126 return true; 127 } else { 128 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 129 } 130 } 131 132 template <class _Tp, class _Up> 133 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) { 134 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 135 "Calling memchr on non-trivially equality comparable types is unsafe."); 136 137 if (__libcpp_is_constant_evaluated()) { 138 // use __builtin_char_memchr to optimize constexpr evaluation if we can 139 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr) 140 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>) 141 return __builtin_char_memchr(__str, __value, __count); 142 #endif 143 144 for (; __count; --__count) { 145 if (*__str == __value) 146 return __str; 147 ++__str; 148 } 149 return nullptr; 150 } else { 151 char __value_buffer = 0; 152 __builtin_memcpy(&__value_buffer, &__value, sizeof(char)); 153 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count)); 154 } 155 } 156 157 // This function performs an assignment to an existing, already alive TriviallyCopyable object 158 // from another TriviallyCopyable object. 159 // 160 // It basically works around the fact that TriviallyCopyable objects are not required to be 161 // syntactically copy/move constructible or copy/move assignable. Technically, only one of the 162 // four operations is required to be syntactically valid -- but at least one definitely has to 163 // be valid. 164 // 165 // This is necessary in order to implement __constexpr_memmove below in a way that mirrors as 166 // closely as possible what the compiler's __builtin_memmove is able to do. 167 template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0> 168 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 169 __dest = __src; 170 return __dest; 171 } 172 173 // clang-format off 174 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 175 is_assignable<_Tp&, _Up&&>::value, int> = 0> 176 // clang-format on 177 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 178 __dest = 179 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial 180 return __dest; 181 } 182 183 // clang-format off 184 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 185 !is_assignable<_Tp&, _Up&&>::value && 186 is_constructible<_Tp, _Up const&>::value, int> = 0> 187 // clang-format on 188 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 189 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 190 // that was there previously 191 std::__construct_at(std::addressof(__dest), __src); 192 return __dest; 193 } 194 195 // clang-format off 196 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 197 !is_assignable<_Tp&, _Up&&>::value && 198 !is_constructible<_Tp, _Up const&>::value && 199 is_constructible<_Tp, _Up&&>::value, int> = 0> 200 // clang-format on 201 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 202 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 203 // that was there previously 204 std::__construct_at( 205 std::addressof(__dest), 206 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial 207 return __dest; 208 } 209 210 template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0> 211 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* 212 __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) { 213 size_t __count = static_cast<size_t>(__n); 214 if (__libcpp_is_constant_evaluated()) { 215 #ifdef _LIBCPP_COMPILER_CLANG_BASED 216 if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) { 217 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp)); 218 return __dest; 219 } 220 #endif 221 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) { 222 for (; __count > 0; --__count) 223 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]); 224 } else { 225 for (size_t __i = 0; __i != __count; ++__i) 226 std::__assign_trivially_copyable(__dest[__i], __src[__i]); 227 } 228 } else if (__count > 0) { 229 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>); 230 } 231 return __dest; 232 } 233 234 _LIBCPP_END_NAMESPACE_STD 235 236 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 237