[Bug c++/96078] New: [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[Bug c++/96078] New: [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[rs2740 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

            Bug ID: 96078
           Summary: [10/11 Regression] flatten attribute on constructor
                    and destructor causes spurious warning
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

struct A {
    [[gnu::flatten]] A() {}
    [[gnu::flatten]] ~A() {}
};

A a;

Produces no warnings with GCC 9 but on GCC 10 and trunk warns:

<source>:3:22: warning: 'flatten' attribute is ignored on aliases
[-Wattributes]

    3 |     [[gnu::flatten]] ~A() {}

      |                      ^

<source>:2:22: warning: 'flatten' attribute is ignored on aliases
[-Wattributes]

    2 |     [[gnu::flatten]] A() {}

      |                      ^

The warning appears to be introduced by the fix to PR92372.

Marking `A` as `final` eliminates the warnings, as does giving it an virtual
base class. Presumably the issue is that in the problematic case one of the
complete/base object c/dtors was treated as an alias for the other?

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |9.3.0
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2020-07-06
     Ever confirmed|0                           |1
      Known to fail|                            |10.1.0, 11.0

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |10.2

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Martin Liška <marxin at gcc dot gnu.org> changed:

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

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r10-7279-gf22712bd8a2ed57d.

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.2                        |10.3

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10.2 is released, adjusting target milestone.

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Jason Merrill <jason at gcc dot gnu.org> changed:

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

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 50174
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50174&action=edit
proposed patch

[Bug c++/96078] [10/11 Regression] flatten attribute on constructor and destructor causes spurious warning

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

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

https://gcc.gnu.org/g:f8e7f3f3f33e22721a28772cc3f9b616e48cd1c9

commit r11-7469-gf8e7f3f3f33e22721a28772cc3f9b616e48cd1c9
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 11 22:01:19 2021 -0500

    cgraph: flatten and same_body aliases [PR96078]

    The patch for PR92372 made us start warning about a flatten attribute on an
    alias.  But in the case of C++ 'tor base/complete variants, the user didn't
    create the alias.  If the alias target also has the attribute, the alias
    points to a flattened function, so we shouldn't warn.

    gcc/ChangeLog:

            PR c++/96078
            * cgraphunit.c (process_function_and_variable_attributes): Don't
            warn about flatten on an alias if the target also has it.
            * cgraph.h (symtab_node::get_alias_target_tree): New.

    gcc/testsuite/ChangeLog:

            PR c++/96078
            * g++.dg/ext/attr-flatten1.C: New test.

[Bug c++/96078] [10 Regression] flatten attribute on constructor and destructor causes spurious warning

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |11.0
      Known to fail|11.0                        |
            Summary|[10/11 Regression] flatten  |[10 Regression] flatten
                   |attribute on constructor    |attribute on constructor
                   |and destructor causes       |and destructor causes
                   |spurious warning            |spurious warning

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for GCC 11 so far.

[Bug c++/96078] [10 Regression] flatten attribute on constructor and destructor causes spurious warning

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:d455130553544ee838b5215e76ccad22304cde39

commit r10-9413-gd455130553544ee838b5215e76ccad22304cde39
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 11 22:01:19 2021 -0500

    cgraph: flatten and same_body aliases [PR96078]

    The patch for PR92372 made us start warning about a flatten attribute on an
    alias.  But in the case of C++ 'tor base/complete variants, the user didn't
    create the alias.  If the alias target also has the attribute, the alias
    points to a flattened function, so we shouldn't warn.

    gcc/ChangeLog:

            PR c++/96078
            * cgraphunit.c (process_function_and_variable_attributes): Don't
            warn about flatten on an alias if the target also has it.
            * cgraph.h (symtab_node::get_alias_target_tree): New.

    gcc/testsuite/ChangeLog:

            PR c++/96078
            * g++.dg/ext/attr-flatten1.C: New test.

[Bug c++/96078] [10 Regression] flatten attribute on constructor and destructor causes spurious warning

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Jason Merrill <jason at gcc dot gnu.org> changed:

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

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
And 10.3.

[Bug c++/96078] [10 Regression] flatten attribute on constructor and destructor causes spurious warning

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96078

Alexandre Oliva <aoliva at gcc dot gnu.org> changed:

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

--- Comment #8 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
FWIW, I've just confirmed a fail of attr-flatten-1.c in gcc-10, targeting
ppc64-vxw7r2.  The expected warning is not issued.  I haven't tried other
targets or branches yet.