[Bug c++/109096] New: __has_unique_object_representations does not account for unnamed bitfield

[Bug c++/109096] New: __has_unique_object_representations does not account for unnamed bitfield

[gcc at jonathanmueller dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

            Bug ID: 109096
           Summary: __has_unique_object_representations does not account
                    for unnamed bitfield
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at jonathanmueller dot dev
  Target Milestone: ---

__has_unique_object_representations should return false for types that contain
an unnamed bit field of non-zero bit-width, since that introduces padding bits;
yet it doesn't:

```
#include <cassert>
#include <cstring>

struct foo
{
    int member : 8;
    // We explitly introduce 24 padding bits here.
    int : 24;

    bool operator==(const foo&) const = default;
};

// Yet this assertion passes?!
static_assert(__has_unique_object_representations(foo));

// But we clearly don't have unique object representations:
int main()
{
    // Create two objects with different object representations.
    foo a, b;
    std::memset(&a, 0xFF, sizeof(foo));
    std::memset(&b, 0x99, sizeof(foo));

    // Make all members identical to give them the same value representation.
    a.member = 0;
    b.member = 0;
    // This passes; they have the same value representation.
    assert(a == b);

    // But this fails; they don't have unique object representations!
    assert(std::memcmp(&a, &b, sizeof(foo)) == 0);
}
```

https://godbolt.org/z/Y4GzqYE8s

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[gcc at jonathanmueller dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #1 from Jonathan Müller <gcc at jonathanmueller dot dev> ---
Sorry, wrong godbolt link: https://godbolt.org/z/f1fGExsr7

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-03-10
     Ever confirmed|0                           |1
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |jakub at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 54647
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54647&action=edit
gcc13-pr109096.patch

Untested fix.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:c35cf160a0ed81570cff6600dba465cf95fa80fa

commit r13-6663-gc35cf160a0ed81570cff6600dba465cf95fa80fa
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 14 16:17:32 2023 +0100

    c++: Treat unnamed bitfields as padding for
__has_unique_object_representations [PR109096]

    As reported in the PR, for __has_unique_object_representations we
    were treating unnamed bitfields as named ones, which is wrong, they
    are actually padding.

    THe following patch fixes that.

    2023-03-14  Jakub Jelinek  <jakub@redhat.com>

            PR c++/109096
            * tree.cc (record_has_unique_obj_representations): Ignore unnamed
            bitfields.

            * g++.dg/cpp1z/has-unique-obj-representations3.C: New test.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk so far.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:9dc438900f77cf47e4e89522bc68c85b289dd52a

commit r12-9290-g9dc438900f77cf47e4e89522bc68c85b289dd52a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 14 16:17:32 2023 +0100

    c++: Treat unnamed bitfields as padding for
__has_unique_object_representations [PR109096]

    As reported in the PR, for __has_unique_object_representations we
    were treating unnamed bitfields as named ones, which is wrong, they
    are actually padding.

    THe following patch fixes that.

    2023-03-14  Jakub Jelinek  <jakub@redhat.com>

            PR c++/109096
            * tree.cc (record_has_unique_obj_representations): Ignore unnamed
            bitfields.

            * g++.dg/cpp1z/has-unique-obj-representations3.C: New test.

    (cherry picked from commit c35cf160a0ed81570cff6600dba465cf95fa80fa)

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 12.3 too.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

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

https://gcc.gnu.org/g:66d35a0cb88f83f085b2ba4c46d0429ba0cfe574

commit r11-10724-g66d35a0cb88f83f085b2ba4c46d0429ba0cfe574
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 14 16:17:32 2023 +0100

    c++: Treat unnamed bitfields as padding for
__has_unique_object_representations [PR109096]

    As reported in the PR, for __has_unique_object_representations we
    were treating unnamed bitfields as named ones, which is wrong, they
    are actually padding.

    THe following patch fixes that.

    2023-03-14  Jakub Jelinek  <jakub@redhat.com>

            PR c++/109096
            * tree.c (record_has_unique_obj_representations): Ignore unnamed
            bitfields.

            * g++.dg/cpp1z/has-unique-obj-representations3.C: New test.

    (cherry picked from commit c35cf160a0ed81570cff6600dba465cf95fa80fa)

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 11.4 as well.

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:066de3a9bb2bc796cfc02767ab4d4440660f7086

commit r10-11377-g066de3a9bb2bc796cfc02767ab4d4440660f7086
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 14 16:17:32 2023 +0100

    c++: Treat unnamed bitfields as padding for
__has_unique_object_representations [PR109096]

    As reported in the PR, for __has_unique_object_representations we
    were treating unnamed bitfields as named ones, which is wrong, they
    are actually padding.

    THe following patch fixes that.

    2023-03-14  Jakub Jelinek  <jakub@redhat.com>

            PR c++/109096
            * tree.c (record_has_unique_obj_representations): Ignore unnamed
            bitfields.

            * g++.dg/cpp1z/has-unique-obj-representations3.C: New test.

    (cherry picked from commit c35cf160a0ed81570cff6600dba465cf95fa80fa)

[Bug c++/109096] __has_unique_object_representations does not account for unnamed bitfield

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109096

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 10.5 too.