[Bug c++/106784] Add __is_convertible built-in

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106784

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:be4b32b9ef69b86b662cb7511b48cd1048a55403

commit r13-2879-gbe4b32b9ef69b86b662cb7511b48cd1048a55403
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Sep 26 10:21:38 2022 -0400

    c++: Instantiate less when evaluating __is_convertible

    Jon reported that evaluating __is_convertible in a test led to
    instantiating something ill-formed and so we failed to compile the test.
    __is_convertible doesn't and shouldn't need to instantiate so much, so
    let's limit it with a cp_unevaluated guard.  Use a helper function to
    implement both built-ins.

            PR c++/106784

    gcc/cp/ChangeLog:

            * method.cc (is_convertible_helper): New.
            (is_convertible): Use it.
            (is_nothrow_convertible): Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/is_convertible3.C: New test.
            * g++.dg/ext/is_nothrow_convertible3.C: New test.