[Bug c++/97420] [9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:bbad9d7cfdb8dd8e28589160120546a61adeeedf

commit r11-8726-gbbad9d7cfdb8dd8e28589160120546a61adeeedf
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed May 26 08:35:31 2021 -0400

    c++: Fix reference NTTP binding to noexcept fn [PR97420]

    Here, in C++17 mode, convert_nontype_argument_function is rejecting
    binding a non-noexcept function reference template parameter to a
    noexcept function (encoded as the template argument '*(int (&) (int)) &f').

    The first roadblock to making this work is that the argument is wrapped
    an an implicit INDIRECT_REF, so we need to unwrap it before calling
    strip_fnptr_conv.

    The second roadblock is that the NOP_EXPR cast converts from a function
    pointer type to a reference type while simultaneously removing the
    noexcept qualification, and fnptr_conv_p doesn't consider this cast to
    be a function pointer conversion.  This patch fixes this by making
    fnptr_conv_p treat REFERENCE_TYPEs and POINTER_TYPEs interchangeably.

    Finally, in passing, this patch also simplifies noexcept_conv_p by
    removing a bunch of redundant checks already performed by its only
    caller fnptr_conv_p.

            PR c++/97420

    gcc/cp/ChangeLog:

            * cvt.c (noexcept_conv_p): Remove redundant checks and simplify.
            (fnptr_conv_p): Don't call non_reference.  Use INDIRECT_TYPE_P
            instead of TYPE_PTR_P.
            * pt.c (convert_nontype_argument_function): Look through
            implicit INDIRECT_REFs before calling strip_fnptr_conv.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept68.C: New test.

    (cherry picked from commit b4329e3dd6fb7c78948fcf9d2f5b9d873deec284)