From b51483f48f3cc67cf4b508bdd9c4b6a47b44c53a Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Mon, 12 Jun 2017 22:22:39 +0000 Subject: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17 As discussed in PR c++/80265 ("__builtin_{memcmp,memchr,strlen} are not usable in constexpr functions"), use __builtin_constant_p to tell whether we can defer to a constexpr algorithm. I used __always_inline__ just to be thorough. It isn't really really necessary as far as I could determine. Changes like these: if (__n == 0) return 0; - return wmemcmp(__s1, __s2, __n); + else + return wmemcmp(__s1, __s2, __n); are necessary otherwise G++ complains that we're calling a non-constexpr function, which looks like a a manifestation of PR67026 to me. libstdc++-v3: 2017-06-12 Pedro Alves * doc/xml/manual/status_cxx2017.xml: Update C++17 constexpr char_traits status. * doc/html/*: Regenerate. * include/bits/char_traits.h (_GLIBCXX_ALWAYS_INLINE): Define if not already defined. (__cpp_lib_constexpr_char_traits): Uncomment. (__constant_string_p, __constant_char_array_p): New. (std::char_traits, std::char_traits): Add _GLIBCXX17_CONSTEXPR on compare, length and find and use __constant_string_p, __constant_char_array_p and __builtin_constant_p to defer to __gnu_cxx::char_traits at compile time. * testsuite/21_strings/char_traits/requirements/ constexpr_functions_c++17.cc: Uncomment __cpp_lib_constexpr_char_traits tests. Uncomment test_compare, test_length, test_find, test_compare, test_length and test_find static_assert tests. From-SVN: r249137 --- libstdc++-v3/ChangeLog | 23 ++++ .../doc/xml/manual/status_cxx2017.xml | 5 +- libstdc++-v3/include/bits/char_traits.h | 101 ++++++++++++++++-- .../requirements/constexpr_functions_c++17.cc | 16 +-- 4 files changed, 123 insertions(+), 22 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 5ee9e68af68..05efaa06824 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,26 @@ +2017-06-12 Pedro Alves + + * doc/xml/manual/status_cxx2017.xml: Update C++17 constexpr + char_traits status. + * doc/html/*: Regenerate. + + * include/bits/char_traits.h (_GLIBCXX_ALWAYS_INLINE): Define if + not already defined. + (__cpp_lib_constexpr_char_traits): Uncomment. + (__constant_string_p, __constant_char_array_p): New. + (std::char_traits, std::char_traits): Add + _GLIBCXX17_CONSTEXPR on compare, length and find and use + __constant_string_p, __constant_char_array_p and + __builtin_constant_p to defer to __gnu_cxx::char_traits at compile + time. + + * testsuite/21_strings/char_traits/requirements/ + constexpr_functions_c++17.cc: Uncomment + __cpp_lib_constexpr_char_traits tests. Uncomment + test_compare, test_length, test_find, + test_compare, test_length and test_find + static_assert tests. + 2017-06-12 François Dumont * include/bits/stl_tree.h (_Rb_tree_impl()): Restore _Node_allocator diff --git a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml index a2082380043..85e193daffa 100644 --- a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml +++ b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml @@ -482,15 +482,14 @@ Feature-testing recommendations for C++. - Constexpr for std::char_traits P0426R1 - 7 (partial) - ??? + 8 + __cpp_lib_constexpr_char_traits >= 201611 diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h index f19120bd16a..5ccb4396734 100644 --- a/libstdc++-v3/include/bits/char_traits.h +++ b/libstdc++-v3/include/bits/char_traits.h @@ -40,6 +40,10 @@ #include // For streampos #include // For WEOF, wmemmove, wmemset, etc. +#ifndef _GLIBCXX_ALWAYS_INLINE +#define _GLIBCXX_ALWAYS_INLINE inline __attribute__((__always_inline__)) +#endif + namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION @@ -139,7 +143,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return !eq_int_type(__c, eof()) ? __c : to_int_type(char_type()); } }; -// #define __cpp_lib_constexpr_char_traits 201611 +#define __cpp_lib_constexpr_char_traits 201611 template _GLIBCXX14_CONSTEXPR int @@ -212,6 +216,42 @@ namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION +#if __cplusplus > 201402 + /** + * @brief Determine whether the characters of a NULL-terminated + * string are known at compile time. + * @param __s The string. + * + * Assumes that _CharT is a built-in character type. + */ + template + static _GLIBCXX_ALWAYS_INLINE constexpr bool + __constant_string_p(const _CharT* __s) + { + while (__builtin_constant_p(*__s) && *__s) + __s++; + return __builtin_constant_p(*__s); + } + + /** + * @brief Determine whether the characters of a character array are + * known at compile time. + * @param __a The character array. + * @param __n Number of characters. + * + * Assumes that _CharT is a built-in character type. + */ + template + static _GLIBCXX_ALWAYS_INLINE constexpr bool + __constant_char_array_p(const _CharT* __a, size_t __n) + { + size_t __i = 0; + while (__builtin_constant_p(__a[__i]) && __i < __n) + __i++; + return __i == __n; + } +#endif + // 21.1 /** * @brief Basis for explicit traits specializations. @@ -256,21 +296,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION < static_cast(__c2)); } - static /* _GLIBCXX17_CONSTEXPR */ int + static _GLIBCXX17_CONSTEXPR int compare(const char_type* __s1, const char_type* __s2, size_t __n) { +#if __cplusplus > 201402 + if (__builtin_constant_p(__n) + && __constant_char_array_p(__s1, __n) + && __constant_char_array_p(__s2, __n)) + return __gnu_cxx::char_traits::compare(__s1, __s2, __n); +#endif if (__n == 0) return 0; return __builtin_memcmp(__s1, __s2, __n); } - static /* _GLIBCXX17_CONSTEXPR */ size_t + static _GLIBCXX17_CONSTEXPR size_t length(const char_type* __s) - { return __builtin_strlen(__s); } + { +#if __cplusplus > 201402 + if (__constant_string_p(__s)) + return __gnu_cxx::char_traits::length(__s); +#endif + return __builtin_strlen(__s); + } - static /* _GLIBCXX17_CONSTEXPR */ const char_type* + static _GLIBCXX17_CONSTEXPR const char_type* find(const char_type* __s, size_t __n, const char_type& __a) { +#if __cplusplus > 201402 + if (__builtin_constant_p(__n) + && __builtin_constant_p(__a) + && __constant_char_array_p(__s, __n)) + return __gnu_cxx::char_traits::find(__s, __n, __a); +#endif if (__n == 0) return 0; return static_cast(__builtin_memchr(__s, __a, __n)); @@ -347,24 +405,45 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION lt(const char_type& __c1, const char_type& __c2) _GLIBCXX_NOEXCEPT { return __c1 < __c2; } - static /* _GLIBCXX17_CONSTEXPR */ int + static _GLIBCXX17_CONSTEXPR int compare(const char_type* __s1, const char_type* __s2, size_t __n) { +#if __cplusplus > 201402 + if (__builtin_constant_p(__n) + && __constant_char_array_p(__s1, __n) + && __constant_char_array_p(__s2, __n)) + return __gnu_cxx::char_traits::compare(__s1, __s2, __n); +#endif if (__n == 0) return 0; - return wmemcmp(__s1, __s2, __n); + else + return wmemcmp(__s1, __s2, __n); } - static /* _GLIBCXX17_CONSTEXPR */ size_t + static _GLIBCXX17_CONSTEXPR size_t length(const char_type* __s) - { return wcslen(__s); } + { +#if __cplusplus > 201402 + if (__constant_string_p(__s)) + return __gnu_cxx::char_traits::length(__s); + else +#endif + return wcslen(__s); + } - static /* _GLIBCXX17_CONSTEXPR */ const char_type* + static _GLIBCXX17_CONSTEXPR const char_type* find(const char_type* __s, size_t __n, const char_type& __a) { +#if __cplusplus > 201402 + if (__builtin_constant_p(__n) + && __builtin_constant_p(__a) + && __constant_char_array_p(__s, __n)) + return __gnu_cxx::char_traits::find(__s, __n, __a); +#endif if (__n == 0) return 0; - return wmemchr(__s, __a, __n); + else + return wmemchr(__s, __a, __n); } static char_type* diff --git a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc index 014caa02313..efd280fea23 100644 --- a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc +++ b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc @@ -74,20 +74,20 @@ template } #ifndef __cpp_lib_constexpr_char_traits -// #error Feature-test macro for constexpr char_traits is missing +# error Feature-test macro for constexpr char_traits is missing #elif __cpp_lib_constexpr_char_traits != 201611 -// #error Feature-test macro for constexpr char_traits has the wrong value +# error Feature-test macro for constexpr char_traits has the wrong value #endif static_assert( test_assign>() ); -// static_assert( test_compare>() ); -// static_assert( test_length>() ); -// static_assert( test_find>() ); +static_assert( test_compare>() ); +static_assert( test_length>() ); +static_assert( test_find>() ); #ifdef _GLIBCXX_USE_WCHAR_T static_assert( test_assign>() ); -// static_assert( test_compare>() ); -// static_assert( test_length>() ); -// static_assert( test_find>() ); +static_assert( test_compare>() ); +static_assert( test_length>() ); +static_assert( test_find>() ); #endif static_assert( test_assign>() ); static_assert( test_compare>() ); -- 2.30.2