[Bug libstdc++/105027] Missing constraints on std::bit_cast

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105027

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:20f2303b0ce6bbe412e852e6423daabd04c39ebb

commit r11-9773-g20f2303b0ce6bbe412e852e6423daabd04c39ebb
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 23 09:57:20 2022 +0000

    libstdc++: Add missing constraints to std::bit_cast [PR105027]

    Our std::bit_cast was relying on the compiler to check for errors inside
    __builtin_bit_cast, instead of checking them as constraints. That means
    std::bit_cast was not SFINAE-friendly.

    This fix uses a requires-clause, so for old versions of Clang without
    concepts support the function will still be unconstrained. At some point
    in future we can remove the #ifdef __cpp_concepts check and rely on all
    compilers having full concepts support in C++20 mode.

    libstdc++-v3/ChangeLog:

            PR libstdc++/105027
            * include/std/bit (bit_cast): Add constraints.
            * testsuite/26_numerics/bit/bit.cast/105027.cc: New test.

    (cherry picked from commit 4894d69a1f37d54b6a612e58053db477ff5ba832)