https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62187
--- 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:6abe341558abec40c9c44d76e7fb4fb3978e894b commit r13-1096-g6abe341558abec40c9c44d76e7fb4fb3978e894b Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Jun 14 16:19:32 2022 +0100 libstdc++: Check lengths first in operator== for basic_string [PR62187] As confirmed by LWG 2852, the calls to traits_type::compare do not need to be obsvervable, so we can make operator== compare string lengths first and return immediately for non-equal lengths. This avoids doing a slow string comparison for "abc...xyz" == "abc...xy". Previously we only did this optimization for std::char_traits<char>, but we can enable it unconditionally thanks to LWG 2852. For comparisons with a const char* we can call traits_type::length right away to do the same optimization. That strlen call can be folded away for constant arguments, making it very efficient. For the pre-C++20 operator== and operator!= overloads we can swap the order of the arguments to take advantage of the operator== improvements. libstdc++-v3/ChangeLog: PR libstdc++/62187 * include/bits/basic_string.h (operator==): Always compare lengths before checking string contents. [!__cpp_lib_three_way_comparison] (operator==, operator!=): Reorder arguments.
