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Subject: [Bug libstdc++/105027] Missing constraints on std::bit_cast
Date: Wed, 23 Mar 2022 12:17:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105027

--- Comment #4 from CVS 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:4894d69a1f37d54b6a612e58053db477ff5ba832

commit r12-7781-g4894d69a1f37d54b6a612e58053db477ff5ba832
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.=