[Bug c++/51316] New: alignof doesn't work with arrays of unknown bound

[Bug c++/51316] New: alignof doesn't work with arrays of unknown bound

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

             Bug #: 51316
           Summary: alignof doesn't work with arrays of unknown bound
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tsoae@mail.ru


gcc 4.7.0 rejects the following code:

    int main()
    {
        // error: invalid application of '__alignof__' to incomplete type 'int
[]'
        alignof(int []);
    }

5.3.6/1:

    An alignof expression yields the alignment requirement of its operand type.
The operand shall be a type-id representing a complete object type or an array
thereof or a reference to a complete object type.

int[] is array of complete object type.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-11-26 23:11:11 UTC ---
Note that this usage is not valid in C1X.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #2 from Nikolka <tsoae at mail dot ru> 2011-11-27 08:37:37 UTC ---
> Note that this usage is not valid in C1X.

Could you explain?

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-11-27 15:58:15 UTC ---
On Sun, 27 Nov 2011, tsoae at mail dot ru wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316
> 
> --- Comment #2 from Nikolka <tsoae at mail dot ru> 2011-11-27 08:37:37 UTC ---
> > Note that this usage is not valid in C1X.
> 
> Could you explain?

See C1X 6.5.3.4 paragraph 1, "The _Alignof operator shall not be applied 
to a function type or an incomplete type.".  This is a constraint, so a 
diagnostic is required.  Thus, if C++ allows this case, the diagnostic 
(which is in code shared between C and C++) must be appropriately 
conditional on the language being compiled.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011-12-28
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
     Ever Confirmed|0                           |1

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-12-28 20:24:44 UTC ---
On it.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[tsoae at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #5 from Nikolka <tsoae at mail dot ru> 2011-12-28 22:06:18 UTC ---
> On it.

There is an active core issue about alignof:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3309.html#1305

Probably, you should take into account the proposed resolution.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-12-28 22:31:02 UTC ---
Yeah, just allow the types at issue, that was clarified in core/930 actually.

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

--- Comment #7 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2011-12-30 21:11:24 UTC ---
Author: paolo
Date: Fri Dec 30 21:11:20 2011
New Revision: 182746

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=182746
Log:
/c-family
2011-12-30  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/51316
    * c-common.c (c_sizeof_or_alignof_type): In C++ allow for alignof
    of array types with an unknown bound.

/testsuite
2011-12-30  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/51316
    * g++.dg/cpp0x/alignof4.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/alignof4.C
Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c-common.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/51316] alignof doesn't work with arrays of unknown bound

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51316

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.0

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-12-30 21:13:01 UTC ---
Fixed for 4.7.0.