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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/108243] Missed optimization for static const std::string_view(const char*) Date: Wed, 04 Jan 2023 13:05:35 +0000 [thread overview] Message-ID: <bug-108243-4-GJlImz0ZjJ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-108243-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108243 --- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- This is caused by a change in libstdc++ headers: @@ -230,9 +230,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION static _GLIBCXX_ALWAYS_INLINE constexpr bool __constant_string_p(const _CharT* __s) { +#ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED + (void) __s; + // In constexpr contexts all strings should be constant. + return __builtin_is_constant_evaluated(); +#else while (__builtin_constant_p(*__s) && *__s) __s++; return __builtin_constant_p(*__s); +#endif } /** That affects the definition of std::char_traits<char>::length: static constexpr size_t length(const char_type* __s) { if (__constant_string_p(__s)) return __gnu_cxx::char_traits<char_type>::length(__s); return __builtin_strlen(__s); } So since GCC 9.1.0 we only treat the length as a constant expression if the string_view object is constexpr, otherwise we call strlen, which requires the object to exist. I think the compiler _should_ be able to optimize this case anyway, but maybe we need to partially revert the libstdc++ changes.
next prev parent reply other threads:[~2023-01-04 13:05 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-12-28 16:31 [Bug c++/108243] New: " erosenberger at kinetica dot com 2023-01-04 11:42 ` [Bug c++/108243] " redi at gcc dot gnu.org 2023-01-04 13:05 ` redi at gcc dot gnu.org [this message] 2023-01-04 13:15 ` redi at gcc dot gnu.org 2023-01-04 13:20 ` [Bug c++/108243] [10/11/12/13 Regression] " redi at gcc dot gnu.org 2023-01-04 13:21 ` redi at gcc dot gnu.org 2023-01-04 16:47 ` ppalka at gcc dot gnu.org 2023-01-04 17:22 ` jakub at gcc dot gnu.org 2023-01-09 14:05 ` rguenth at gcc dot gnu.org 2023-01-27 19:13 ` ppalka at gcc dot gnu.org 2023-02-17 20:21 ` cvs-commit at gcc dot gnu.org 2023-02-20 5:23 ` de34 at live dot cn 2023-02-20 18:33 ` ppalka at gcc dot gnu.org 2023-02-21 13:38 ` rguenth at gcc dot gnu.org 2023-02-21 14:09 ` ppalka at gcc dot gnu.org 2023-03-02 19:05 ` cvs-commit at gcc dot gnu.org 2023-03-02 19:05 ` cvs-commit at gcc dot gnu.org 2023-03-02 19:51 ` [Bug c++/108243] [10/11/12 " ppalka at gcc dot gnu.org 2023-07-07 10:44 ` [Bug c++/108243] [11/12 " rguenth at gcc dot gnu.org 2023-12-13 16:48 ` cvs-commit at gcc dot gnu.org
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