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[libc++] Optimize char_traits a bit #72799

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Merged
merged 1 commit into from
Apr 20, 2024
Merged

[libc++] Optimize char_traits a bit #72799

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68 changes: 24 additions & 44 deletions libcxx/include/__string/char_traits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,13 +10,15 @@
#define _LIBCPP___STRING_CHAR_TRAITS_H

#include <__algorithm/fill_n.h>
#include <__algorithm/find.h>
#include <__algorithm/find_end.h>
#include <__algorithm/find_first_of.h>
#include <__algorithm/min.h>
#include <__assert>
#include <__compare/ordering.h>
#include <__config>
#include <__functional/hash.h>
#include <__functional/identity.h>
#include <__iterator/iterator_traits.h>
#include <__string/constexpr_c_functions.h>
#include <__type_traits/is_constant_evaluated.h>
Expand Down Expand Up @@ -272,10 +274,14 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char8_t> {
return std::__constexpr_memcmp(__s1, __s2, __element_count(__n));
}

static _LIBCPP_HIDE_FROM_ABI constexpr size_t length(const char_type* __s) _NOEXCEPT;
static _LIBCPP_HIDE_FROM_ABI constexpr size_t length(const char_type* __str) _NOEXCEPT {
return std::__constexpr_strlen(__str);
}

_LIBCPP_HIDE_FROM_ABI static constexpr const char_type*
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
return std::__constexpr_memchr(__s, __a, __n);
}

static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 char_type*
move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT {
Expand Down Expand Up @@ -307,25 +313,6 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char8_t> {
static inline _LIBCPP_HIDE_FROM_ABI constexpr int_type eof() noexcept { return int_type(EOF); }
};

// TODO use '__builtin_strlen' if it ever supports char8_t ??
inline constexpr size_t char_traits<char8_t>::length(const char_type* __s) _NOEXCEPT {
size_t __len = 0;
for (; !eq(*__s, char_type(0)); ++__s)
++__len;
return __len;
}

// TODO use '__builtin_char_memchr' if it ever supports char8_t ??
inline constexpr const char8_t*
char_traits<char8_t>::find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
for (; __n; --__n) {
if (eq(*__s, __a))
return __s;
++__s;
}
return nullptr;
}

#endif // _LIBCPP_HAS_NO_CHAR8_T

template <>
Expand Down Expand Up @@ -353,9 +340,15 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char16_t> {
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 int
compare(const char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT;
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 size_t length(const char_type* __s) _NOEXCEPT;
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 const char_type*
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;

_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 const char_type*
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
__identity __proj;
const char_type* __match = std::__find_impl(__s, __s + __n, __a, __proj);
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Unrelated to this patch, but can we rename __find_impl to __find for consistency?

if (__match == __s + __n)
return nullptr;
return __match;
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static char_type*
move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT {
return std::__constexpr_memmove(__s1, __s2, __element_count(__n));
Expand Down Expand Up @@ -408,16 +401,6 @@ inline _LIBCPP_CONSTEXPR_SINCE_CXX17 size_t char_traits<char16_t>::length(const
return __len;
}

inline _LIBCPP_CONSTEXPR_SINCE_CXX17 const char16_t*
char_traits<char16_t>::find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
for (; __n; --__n) {
if (eq(*__s, __a))
return __s;
++__s;
}
return nullptr;
}

template <>
struct _LIBCPP_TEMPLATE_VIS char_traits<char32_t> {
using char_type = char32_t;
Expand All @@ -443,8 +426,15 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char32_t> {
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 int
compare(const char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT;
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 size_t length(const char_type* __s) _NOEXCEPT;

_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX17 const char_type*
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
__identity __proj;
const char_type* __match = std::__find_impl(__s, __s + __n, __a, __proj);
if (__match == __s + __n)
return nullptr;
return __match;
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static char_type*
move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT {
Expand Down Expand Up @@ -496,16 +486,6 @@ inline _LIBCPP_CONSTEXPR_SINCE_CXX17 size_t char_traits<char32_t>::length(const
return __len;
}

inline _LIBCPP_CONSTEXPR_SINCE_CXX17 const char32_t*
char_traits<char32_t>::find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT {
for (; __n; --__n) {
if (eq(*__s, __a))
return __s;
++__s;
}
return nullptr;
}

// helper fns for basic_string and string_view

// __str_find
Expand Down
23 changes: 19 additions & 4 deletions libcxx/include/__string/constexpr_c_functions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,18 +35,33 @@ _LIBCPP_BEGIN_NAMESPACE_STD
// of elements as opposed to a number of bytes.
enum class __element_count : size_t {};

inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const char* __str) {
template <class _Tp>
inline const bool __is_char_type = false;

template <>
inline const bool __is_char_type<char> = true;

#ifndef _LIBCPP_HAS_NO_CHAR8_T
template <>
inline const bool __is_char_type<char8_t> = true;
#endif

template <class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {
static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");
// GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
#ifdef _LIBCPP_COMPILER_GCC
if (__libcpp_is_constant_evaluated()) {
#if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)
if constexpr (is_same_v<_Tp, char>)
return __builtin_strlen(__str);
#endif
size_t __i = 0;
for (; __str[__i] != '\0'; ++__i)
;
return __i;
}
#endif
return __builtin_strlen(__str);
return __builtin_strlen(reinterpret_cast<const char*>(__str));
}

// Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is
Expand Down