[Bug c++/96090] noexcept operator of potentially-throwing defaulted function gives the wrong result

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96090

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:

https://gcc.gnu.org/g:4719b6f5ae4d758f193a17bbd5fb6cbacd702a23

commit r14-6395-g4719b6f5ae4d758f193a17bbd5fb6cbacd702a23
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Sat Oct 28 16:04:52 2023 +1100

    c++: Fix noexcept checking for trivial operations [PR96090]

    This patch stops eager folding of trivial operations (construction and
    assignment) from occurring when checking for noexceptness. This was
    previously done in PR c++/53025, but only for copy/move construction,
    and the __is_nothrow_xible builtins did not receive the same treatment
    when they were added.

    To handle `is_nothrow_default_constructible`, the patch also ensures
    that when no parameters are passed we do value initialisation instead of
    just building the constructor call: in particular, value-initialisation
    doesn't necessarily actually invoke the constructor for trivial default
    constructors, and so we need to handle this case as well.

    This is contrary to the proposed resolution of CWG2820; for now we just
    ensure it matches the behaviour of the `noexcept` operator and create
    testcases formalising this, and if that issue gets accepted we can
    revisit.

            PR c++/96090
            PR c++/100470

    gcc/cp/ChangeLog:

            * call.cc (build_over_call): Prevent folding of trivial special
            members when checking for noexcept.
            * method.cc (constructible_expr): Perform value-initialisation
            for empty parameter lists.
            (is_nothrow_xible): Treat as noexcept operator.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept81.C: New test.
            * g++.dg/ext/is_nothrow_constructible7.C: New test.
            * g++.dg/ext/is_nothrow_constructible8.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>