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Subject: [Bug libstdc++/113200] std::char_traits<char>::move is not constexpr
 when the argument is a string literal
Date: Fri, 05 Jan 2024 10:23:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113200

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:15cc291887dc9dd92b2c93f4545e20eb6c190122

commit r14-6944-g15cc291887dc9dd92b2c93f4545e20eb6c190122
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 3 15:01:09 2024 +0000

    libstdc++: Fix std::char_traits<C>::move [PR113200]

    The current constexpr implementation of std::char_traits<C>::move relies
    on being able to compare the pointer parameters, which is not allowed
    for unrelated pointers. We can use __builtin_constant_p to determine
    whether it's safe to compare the pointers directly. If not, then we know
    the ranges must be disjoint and so we can use char_traits<C>::copy to
    copy forwards from the first character to the last. If the pointers can
    be compared directly, then we can simplify the condition for copying
    backwards to just two pointer comparisons.

    libstdc++-v3/ChangeLog:

            PR libstdc++/113200
            * include/bits/char_traits.h (__gnu_cxx::char_traits::move): Use
            __builtin_constant_p to check for unrelated pointers that cannot
            be compared during constant evaluation.
            * testsuite/21_strings/char_traits/requirements/113200.cc: New
            test.=