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