[Bug c++/97643] New: Accepts invalid qualification conversion involving array of unknown bound [P0388]

[Bug c++/97643] New: Accepts invalid qualification conversion involving array of unknown bound [P0388]

[leni536 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97643

            Bug ID: 97643
           Summary: Accepts invalid qualification conversion involving
                    array of unknown bound [P0388]
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: leni536 at gmail dot com
  Target Milestone: ---

version: g++ (Compiler-Explorer-Build) 11.0.0 20201029 (experimental)

https://godbolt.org/z/a8sKr3

In C++20 the following code is ill-formed, but gcc accepts it:

void foo(int (*arr)[10]);

void bar(int (*arr)[]) {
    int (* ptr)[10];
    int (** ptr2)[] = &ptr; // not allowed
    *ptr2 = arr;
    foo(ptr);
}

The conversion happens from T1 = int (**)[10] to T2 = int (**)[] .

The cv-decomposition of the two types are:
T1 = pointer to | pointer to | array of 10               | int
T2 = pointer to | pointer to | array of unknown bound of | int

The cv-combined type is:
T3 = pointer to | const pointer to | array of unknown bound of | int
= int (*const*)[]

[Bug c++/97643] Accepts invalid qualification conversion involving array of unknown bound [P0388]

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97643

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Accepted since my

commit 89e0a492af5bec8ffa2ec5d99c4858df50d22c16
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Oct 9 20:58:00 2019 +0000

    Implement C++20 P0388R4, DR 1307, and DR 330.

[Bug c++/97643] Accepts invalid qualification conversion involving array of unknown bound [P0388]

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97643

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Michael Meissner <meissner@gcc.gnu.org>:

https://gcc.gnu.org/g:9f1a6501994a2d18ec4fe2a6664637f48021b210

commit r11-5728-g9f1a6501994a2d18ec4fe2a6664637f48021b210
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Thu Dec 3 14:50:26 2020 -0500

    PowerPC: PR libgcc/97543 and libgcc/97643, fix long double issues

    If you use a compiler with long double defaulting to 64-bit instead of
128-bit
    with IBM extended double, you get linker warnings about mis-matches in the
gnu
    attributes for long double (PR libgcc/97543).  Even if the compiler is
    configured to have long double be 64 bit as the default with the
configuration
    option '--without-long-double-128' you get the warnings.

    You also get the same issues if you use a compiler with long double
defaulting
    to IEEE 128-bit instead of IBM extended double (PR libgcc/97643).

    The issue is the way libgcc.a/libgcc.so is built.  Right now when building
    libgcc under Linux, the long double size is set to 128-bits when building
    libgcc.  However, the gnu attributes are set, leading to the warnings.

    One feature of the current GNU attribute implementation is if you have a
shared
    library (such as libgcc_s.so), the GNU attributes for the shared library is
an
    inclusive OR of all of the objects within the library.  This means if any
    object file that uses the -mlong-double-128 option and uses long double,
the GNU
    attributes for the library will indicate that it uses 128-bit IBM long
    doubles.  If you have a static library, you will get the warning only if
you
    actually reference an object file  with the attribute set.

    This patch does two things:

        1)  All of the object files that support IBM 128-bit long doubles
            explicitly set the ABI to IBM extended double.

        2)  I turned off GNU attributes for building the shared library or for
            building the IBM 128-bit long double support.

    libgcc/
    2020-12-03  Michael Meissner  <meissner@linux.ibm.com>

            PR libgcc/97543
            PR libgcc/97643
            * config/rs6000/t-linux (IBM128_STATIC_OBJS): New make variable.
            (IBM128_SHARED_OBJS): New make variable.
            (IBM128_OBJS): New make variable.  Set all objects to use the
            explicit IBM format, and disable gnu attributes.
            (IBM128_CFLAGS): New make variable.
            (gcc_s_compile): Add -mno-gnu-attribute to all shared library
            modules.