https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265
--- Comment #19 from palves at gcc dot gnu.org --- Author: palves Date: Mon Jun 12 22:22:39 2017 New Revision: 249137 URL: https://gcc.gnu.org/viewcvs?rev=249137&root=gcc&view=rev Log: 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 <pal...@redhat.com> * 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<char>, std::char_traits<wchar_t>): 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<char>, test_length<char>, test_find<char>, test_compare<wchar_t>, test_length<wchar_t> and test_find<wchar_t> static_assert tests. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/doc/xml/manual/status_cxx2017.xml trunk/libstdc++-v3/include/bits/char_traits.h trunk/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
