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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H10#define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H11 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_lexicographically_comparable.h>26#include <__type_traits/remove_cv.h>27#include <__utility/element_count.h>28#include <__utility/is_pointer_in_range.h>29 30#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)31# pragma GCC system_header32#endif33 34_LIBCPP_BEGIN_NAMESPACE_STD35 36template <class _Tp>37inline const bool __is_char_type = false;38 39template <>40inline const bool __is_char_type<char> = true;41 42#if _LIBCPP_HAS_CHAR8_T43template <>44inline const bool __is_char_type<char8_t> = true;45#endif46 47template <class _Tp>48inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {49 static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");50 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.51 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7081652 if (__libcpp_is_constant_evaluated()) {53#if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)54 if constexpr (is_same_v<_Tp, char>)55 return __builtin_strlen(__str);56#endif57 size_t __i = 0;58 for (; __str[__i] != '\0'; ++__i)59 ;60 return __i;61 }62 return __builtin_strlen(reinterpret_cast<const char*>(__str));63}64 65// Because of __is_trivially_lexicographically_comparable_v we know that comparing the object representations is66// equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead67// of invoking it on every object individually.68template <class _Tp, class _Up>69_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int70__constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {71 static_assert(__is_trivially_lexicographically_comparable_v<_Tp, _Up>,72 "_Tp and _Up have to be trivially lexicographically comparable");73 74 auto __count = static_cast<size_t>(__n);75 76 if (__libcpp_is_constant_evaluated()) {77#ifdef _LIBCPP_COMPILER_CLANG_BASED78 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)79 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));80#endif81 82 while (__count != 0) {83 if (*__lhs < *__rhs)84 return -1;85 if (*__rhs < *__lhs)86 return 1;87 88 --__count;89 ++__lhs;90 ++__rhs;91 }92 return 0;93 } else {94 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));95 }96}97 98// Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent99// to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead100// of invoking it on every object individually.101template <class _Tp, class _Up>102_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool103__constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {104 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,105 "_Tp and _Up have to be trivially equality comparable");106 107 auto __count = static_cast<size_t>(__n);108 109 if (__libcpp_is_constant_evaluated()) {110#ifdef _LIBCPP_COMPILER_CLANG_BASED111 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)112 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;113#endif114 while (__count != 0) {115 if (*__lhs != *__rhs)116 return false;117 118 --__count;119 ++__lhs;120 ++__rhs;121 }122 return true;123 } else {124 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;125 }126}127 128template <class _Tp, class _Up>129_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {130 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,131 "Calling memchr on non-trivially equality comparable types is unsafe.");132 133 if (__libcpp_is_constant_evaluated()) {134// use __builtin_char_memchr to optimize constexpr evaluation if we can135#if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr)136 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>)137 return __builtin_char_memchr(__str, __value, __count);138#endif139 140 for (; __count; --__count) {141 if (*__str == __value)142 return __str;143 ++__str;144 }145 return nullptr;146 } else {147 char __value_buffer = 0;148 __builtin_memcpy(&__value_buffer, std::addressof(__value), sizeof(char));149 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));150 }151}152 153// This function performs an assignment to an existing, already alive TriviallyCopyable object154// from another TriviallyCopyable object.155//156// It basically works around the fact that TriviallyCopyable objects are not required to be157// syntactically copy/move constructible or copy/move assignable. Technically, only one of the158// four operations is required to be syntactically valid -- but at least one definitely has to159// be valid.160//161// This is necessary in order to implement __constexpr_memmove below in a way that mirrors as162// closely as possible what the compiler's __builtin_memmove is able to do.163template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>164_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {165 __dest = __src;166 return __dest;167}168 169// clang-format off170template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&171 is_assignable<_Tp&, _Up&&>::value, int> = 0>172// clang-format on173_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {174 __dest =175 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial176 return __dest;177}178 179// clang-format off180template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&181 !is_assignable<_Tp&, _Up&&>::value &&182 is_constructible<_Tp, _Up const&>::value, int> = 0>183// clang-format on184_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {185 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object186 // that was there previously187 std::__construct_at(std::addressof(__dest), __src);188 return __dest;189}190 191// clang-format off192template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&193 !is_assignable<_Tp&, _Up&&>::value &&194 !is_constructible<_Tp, _Up const&>::value &&195 is_constructible<_Tp, _Up&&>::value, int> = 0>196// clang-format on197_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {198 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object199 // that was there previously200 std::__construct_at(201 std::addressof(__dest),202 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial203 return __dest;204}205 206template <class _Tp, class _Up>207_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*208__constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {209 static_assert(__is_always_bitcastable<_Up, _Tp>::value);210 size_t __count = static_cast<size_t>(__n);211 if (__libcpp_is_constant_evaluated()) {212#ifdef _LIBCPP_COMPILER_CLANG_BASED213 if _LIBCPP_CONSTEXPR (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {214 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));215 return __dest;216 } else217#endif218 {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 }227 } else if _LIBCPP_CONSTEXPR (sizeof(_Tp) == __datasizeof_v<_Tp>) {228 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));229 } else if (__count > 0) {230 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);231 }232 return __dest;233}234 235_LIBCPP_END_NAMESPACE_STD236 237#endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H238