https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103755
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:b3ac43a3c05744d62a963d656bed782fc867ad79 commit r13-3888-gb3ac43a3c05744d62a963d656bed782fc867ad79 Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed Nov 9 21:44:31 2022 +0000 libstdc++: Avoid redundant checks in std::use_facet [PR103755] We do not need to do bounds checks or a runtime dynamic_cast when using std::has_facet and std::use_facet to access the default facets that are guaranteed to be present in every std::locale object. We can just index straight into the array and use a static_cast for the conversion. This patch adds a new std::__try_use_facet function that is like std::use_facet but returns a pointer, so can be used to implement both std::has_facet and std::use_facet. We can then do the necessary metaprogramming to skip the redundant checks in std::__try_use_facet. To avoid having to export (or hide) instantiations of the new function from libstdc++.so the instantiations are given hidden visibility. This allows them to be used in the library, but user code will instantiate it again using the definition in the header. That would happen anyway, because there are no explicit instantiation declarations for any of std::has_facet, std::use_facet, or the new std::__try_use_facet. libstdc++-v3/ChangeLog: PR libstdc++/103755 * config/abi/pre/gnu.ver: Tighten patterns for facets in the base version. Add exports for __try_use_facet. * include/bits/basic_ios.tcc (basic_ios::_M_cache_locale): Use __try_use_facet instead of has_facet and use_facet. * include/bits/fstream.tcc (basic_filebuf::basic_filebuf()): Likewise. (basic_filebuf::imbue): Likewise. * include/bits/locale_classes.h (locale, locale::id) (locale::_Impl): Declare __try_use_facet as a friend. * include/bits/locale_classes.tcc (__try_use_facet): Define new function template with special cases for default facets. (has_facet, use_facet): Call __try_use_facet. * include/bits/locale_facets.tcc (__try_use_facet): Declare explicit instantiations. * include/bits/locale_facets_nonio.tcc (__try_use_facet): Likewise. * src/c++11/locale-inst-monetary.h (INSTANTIATE_FACET_ACCESSORS): Use new macro for facet accessor instantiations. * src/c++11/locale-inst-numeric.h (INSTANTIATE_FACET_ACCESSORS): Likewise. * src/c++11/locale-inst.cc (INSTANTIATE_USE_FACET): Define new macro for instantiating __try_use_facet and use_facet. (INSTANTIATE_FACET_ACCESSORS): Define new macro for also defining has_facet. * src/c++98/compatibility-ldbl.cc (__try_use_facet): Instantiate. * testsuite/22_locale/ctype/is/string/89728_neg.cc: Adjust expected errors.
