[Bug c/113050] New: -Wincompatible-pointer-types emitted as a warning, not an error, for __atomic_load

[Bug c/113050] New: -Wincompatible-pointer-types emitted as a warning, not an error, for __atomic_load

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

            Bug ID: 113050
           Summary: -Wincompatible-pointer-types emitted as a warning, not
                    an error, for __atomic_load
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sjames at gcc dot gnu.org
                CC: arsen at gcc dot gnu.org, fw at gcc dot gnu.org
  Target Milestone: ---

Noticed this when building udisks. I suspect this is actually a dupe of
PR69404, but I felt it was worth filing separately given it's interesting to
have it warn-but-not-error.

The expectation was that this would error (b/c of new 14 default), not just
warn:
```
$ gcc -c udisksenumtypes.i
udisksenumtypes.i: In function ‘udisks_get_type’:
udisksenumtypes.i:5:3: warning: argument 2 of ‘__atomic_load’ discards
‘volatile’ qualifier [-Wincompatible-pointer-types]
    5 |   __atomic_load(in, &out, 5);
      |   ^~~~~~~~~~~~~
```

It does the right thing with explicit -Werror=:
```
$ gcc -c udisksenumtypes.i -Werror=incompatible-pointer-types
udisksenumtypes.i: In function ‘udisks_get_type’:
udisksenumtypes.i:5:3: error: argument 2 of ‘__atomic_load’ discards ‘volatile’
qualifier [-Werror=incompatible-pointer-types]
    5 |   __atomic_load(in, &out, 5);
      |   ^~~~~~~~~~~~~
cc1: some warnings being treated as errors
```

udisksenumtypes.i:
```
volatile long out;
volatile long* in;

void udisks_get_type() {
  __atomic_load(in, &out, 5);
}
```

[Bug c/113050] -Wincompatible-pointer-types emitted as a warning, not an error, for __atomic_load

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

--- Comment #1 from Florian Weimer <fw at gcc dot gnu.org> ---
The warning should be -Wdiscared-qualifiers, which is not an error for C.

What confused me is that the volatile qualifier is already accepted for the
first argument. I believe it's valid for the second argument.

[Bug c/113050] -Wincompatible-pointer-types emitted as a warning, not an error, for __atomic_load

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

--- Comment #2 from Sam James <sjames at gcc dot gnu.org> ---
Yeah, for every attempt I had to reconstruct it manually, I just got the
expected -Wdiscarded-qualifiers, and then realised it was atomic-specific.

[Bug c/113050] -Wincompatible-pointer-types emitted as a warning, not an error, for __atomic_load

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

--- Comment #3 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to Florian Weimer from comment #1)
> The warning should be -Wdiscared-qualifiers, which is not an error for C.
> 
> What confused me is that the volatile qualifier is already accepted for the
> first argument. I believe it's valid for the second argument.

Sorry, I wanted to say: “I believe [the warning is] valid for the second
argument.”

[Bug c/113050] __atomic_* builtins should use -Wdiscarded-qualifiers instead of -Wincompatible-pointer-types

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

Florian Weimer <fw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |fw at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-12-17
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #4 from Florian Weimer <fw at gcc dot gnu.org> ---
Patch submitted:

[PATCH] c-family: Use -Wdiscarded-qualifiers for ignored qualifiers in
__atomic_*
<https://inbox.sourceware.org/gcc-patches/87edfk6dr6.fsf@oldenburg.str.redhat.com/>

[Bug c/113050] __atomic_* builtins should use -Wdiscarded-qualifiers instead of -Wincompatible-pointer-types

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Florian Weimer <fw@gcc.gnu.org>:

https://gcc.gnu.org/g:a48dd581bf917fcd52fb9eab60943825ed96b6d4

commit r14-6751-ga48dd581bf917fcd52fb9eab60943825ed96b6d4
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed Dec 20 17:23:40 2023 +0100

    c-family: Use -Wdiscarded-qualifiers for ignored qualifiers in __atomic_*

    This matches other compiler diagnostics.  No test updates are needed
    because c-c++-common/pr95378.c does not match a specific -W option.

    Fixes commit d2384b7b24f8557b66f6958a05ea99ff4307e75c ("c-family:
    check qualifiers of arguments to __atomic built-ins (PR 95378)").

    gcc/c-family/

            PR c/113050
            * c-common.cc (get_atomic_generic_size): Use
            OPT_Wdiscarded_qualifiers instead of
            OPT_Wincompatible_pointer_types.

[Bug c/113050] __atomic_* builtins should use -Wdiscarded-qualifiers instead of -Wincompatible-pointer-types

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

Florian Weimer <fw at gcc dot gnu.org> changed:

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

--- Comment #6 from Florian Weimer <fw at gcc dot gnu.org> ---
I do not plan to backport this change.

[Bug c/113050] __atomic_* builtins should use -Wdiscarded-qualifiers instead of -Wincompatible-pointer-types

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113050

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0