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 <__cstddef/size_t.h> 14 #include <__memory/addressof.h> 15 #include <__memory/construct_at.h> 16 #include <__type_traits/datasizeof.h> 17 #include <__type_traits/enable_if.h> 18 #include <__type_traits/is_always_bitcastable.h> 19 #include <__type_traits/is_assignable.h> 20 #include <__type_traits/is_constant_evaluated.h> 21 #include <__type_traits/is_constructible.h> 22 #include <__type_traits/is_equality_comparable.h> 23 #include <__type_traits/is_integral.h> 24 #include <__type_traits/is_same.h> 25 #include <__type_traits/is_trivially_copyable.h> 26 #include <__type_traits/is_trivially_lexicographically_comparable.h> 27 #include <__type_traits/remove_cv.h> 28 #include <__utility/element_count.h> 29 #include <__utility/is_pointer_in_range.h> 30 31 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 32 # pragma GCC system_header 33 #endif 34 35 _LIBCPP_BEGIN_NAMESPACE_STD 36 37 template <class _Tp> 38 inline const bool __is_char_type = false; 39 40 template <> 41 inline const bool __is_char_type<char> = true; 42 43 #if _LIBCPP_HAS_CHAR8_T 44 template <> 45 inline const bool __is_char_type<char8_t> = true; 46 #endif 47 48 template <class _Tp> 49 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT { 50 static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t"); 51 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation. 52 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816 53 if (__libcpp_is_constant_evaluated()) { 54 #if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED) 55 if constexpr (is_same_v<_Tp, char>) 56 return __builtin_strlen(__str); 57 #endif 58 size_t __i = 0; 59 for (; __str[__i] != '\0'; ++__i) 60 ; 61 return __i; 62 } 63 return __builtin_strlen(reinterpret_cast<const char*>(__str)); 64 } 65 66 // Because of __is_trivially_lexicographically_comparable_v we know that comparing the object representations is 67 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead 68 // of invoking it on every object individually. 69 template <class _Tp, class _Up> 70 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int 71 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 72 static_assert(__is_trivially_lexicographically_comparable_v<_Tp, _Up>, 73 "_Tp and _Up have to be trivially lexicographically comparable"); 74 75 auto __count = static_cast<size_t>(__n); 76 77 if (__libcpp_is_constant_evaluated()) { 78 #ifdef _LIBCPP_COMPILER_CLANG_BASED 79 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value) 80 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 81 #endif 82 83 while (__count != 0) { 84 if (*__lhs < *__rhs) 85 return -1; 86 if (*__rhs < *__lhs) 87 return 1; 88 89 --__count; 90 ++__lhs; 91 ++__rhs; 92 } 93 return 0; 94 } else { 95 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)); 96 } 97 } 98 99 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent 100 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead 101 // of invoking it on every object individually. 102 template <class _Tp, class _Up> 103 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool 104 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) { 105 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 106 "_Tp and _Up have to be trivially equality comparable"); 107 108 auto __count = static_cast<size_t>(__n); 109 110 if (__libcpp_is_constant_evaluated()) { 111 #ifdef _LIBCPP_COMPILER_CLANG_BASED 112 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value) 113 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 114 #endif 115 while (__count != 0) { 116 if (*__lhs != *__rhs) 117 return false; 118 119 --__count; 120 ++__lhs; 121 ++__rhs; 122 } 123 return true; 124 } else { 125 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0; 126 } 127 } 128 129 template <class _Tp, class _Up> 130 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) { 131 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 132 "Calling memchr on non-trivially equality comparable types is unsafe."); 133 134 if (__libcpp_is_constant_evaluated()) { 135 // use __builtin_char_memchr to optimize constexpr evaluation if we can 136 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr) 137 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>) 138 return __builtin_char_memchr(__str, __value, __count); 139 #endif 140 141 for (; __count; --__count) { 142 if (*__str == __value) 143 return __str; 144 ++__str; 145 } 146 return nullptr; 147 } else { 148 char __value_buffer = 0; 149 __builtin_memcpy(&__value_buffer, &__value, sizeof(char)); 150 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count)); 151 } 152 } 153 154 // This function performs an assignment to an existing, already alive TriviallyCopyable object 155 // from another TriviallyCopyable object. 156 // 157 // It basically works around the fact that TriviallyCopyable objects are not required to be 158 // syntactically copy/move constructible or copy/move assignable. Technically, only one of the 159 // four operations is required to be syntactically valid -- but at least one definitely has to 160 // be valid. 161 // 162 // This is necessary in order to implement __constexpr_memmove below in a way that mirrors as 163 // closely as possible what the compiler's __builtin_memmove is able to do. 164 template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0> 165 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 166 __dest = __src; 167 return __dest; 168 } 169 170 // clang-format off 171 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 172 is_assignable<_Tp&, _Up&&>::value, int> = 0> 173 // clang-format on 174 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 175 __dest = 176 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial 177 return __dest; 178 } 179 180 // clang-format off 181 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 182 !is_assignable<_Tp&, _Up&&>::value && 183 is_constructible<_Tp, _Up const&>::value, int> = 0> 184 // clang-format on 185 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) { 186 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 187 // that was there previously 188 std::__construct_at(std::addressof(__dest), __src); 189 return __dest; 190 } 191 192 // clang-format off 193 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value && 194 !is_assignable<_Tp&, _Up&&>::value && 195 !is_constructible<_Tp, _Up const&>::value && 196 is_constructible<_Tp, _Up&&>::value, int> = 0> 197 // clang-format on 198 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) { 199 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object 200 // that was there previously 201 std::__construct_at( 202 std::addressof(__dest), 203 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial 204 return __dest; 205 } 206 207 template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0> 208 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* 209 __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) { 210 size_t __count = static_cast<size_t>(__n); 211 if (__libcpp_is_constant_evaluated()) { 212 #ifdef _LIBCPP_COMPILER_CLANG_BASED 213 if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) { 214 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp)); 215 return __dest; 216 } 217 #endif 218 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) { 219 for (; __count > 0; --__count) 220 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]); 221 } else { 222 for (size_t __i = 0; __i != __count; ++__i) 223 std::__assign_trivially_copyable(__dest[__i], __src[__i]); 224 } 225 } else if (__count > 0) { 226 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>); 227 } 228 return __dest; 229 } 230 231 _LIBCPP_END_NAMESPACE_STD 232 233 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 234