[Bug libstdc++/91488] [9/10 Regression] char_traits::length causes "inlining failed in call to always_inline" error with -fgnu-tm -O2 -std=c++17

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91488

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

https://gcc.gnu.org/g:b7cf6b97fc3f6c02a5d0114fed14f40b08ab3ad8

commit r10-9932-gb7cf6b97fc3f6c02a5d0114fed14f40b08ab3ad8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jun 17 14:11:22 2021 +0100

    libstdc++: Simplify constexpr checks in std::char_traits [PR 91488]

    This removes the 'static' keyword from the helper functions added by
    r8-1294 to detect whether the char_traits member functions can be
    evaluated at compile time. This prevents the "inlining failed" error
    reported in the PR.

    The new testcase from the PR is added to the libitm testsuite, because
    that's where we can be sure it's OK to use the -fgnu-tm option.

    As a drive-by fix, the feature test macros for C++20 P0980R1 support are
    made to depend on whether __cpp_lib_is_constant_evaluated is defined.

    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

            PR libstdc++/91488

    libstdc++-v3/ChangeLog:

            * include/bits/basic_string.h (__cpp_lib_constexpr_string): Only
            define C++20 value when std::is_constant_evaluated is available.
            * include/bits/char_traits.h (__cpp_lib_constexpr_char_traits):
            Likewise.
            (__constant_string_p, __constant_array_p): Give external
            linkage.
            * include/std/version (__cpp_lib_constexpr_char_traits)
            (__cpp_lib_constexpr_string): Only define C++20 values when
            is_constant_evaluated is available.

    libitm/ChangeLog:

            * testsuite/libitm.c++/libstdc++-pr91488.C: New test.

    (cherry picked from commit b376b1ef38971b84975ad1540bf5d2ae0b924e76)