[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-09-04
                 CC|                            |jason at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
The bug is that we aren't emitting ~Foo even though it's marked used; the
vtable is just a side effect.

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |97729
   Last reconfirmed|2015-09-04 00:00:00         |2020-11-5

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We don't emit any constructors or destructors that are marked used.

This is a problem for libstdc++ now.

struct S {
    S();
    ~S();
    S(const S&);
};

[[gnu::used]] inline S::S()  { }
[[gnu::used]] inline S::~S() { }
[[gnu::used]] inline S::S(const S&) { }

This generates no code with GCC. Clang emits all three functions.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97729
[Bug 97729] [11 Regression] Link failure due to basic_stringbuf and others when
building DLL on MinGW

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 49509
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49509&action=edit
gcc11-pr67453.patch

Untested fix.

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

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

https://gcc.gnu.org/g:710508c7b1a2c8e1d75d4c4f1ac79473dbf2b2bb

commit r11-4749-g710508c7b1a2c8e1d75d4c4f1ac79473dbf2b2bb
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 5 16:19:15 2020 +0000

    libstdc++: Fix multiple definitions of std::exception_ptr functions [PR
97729]

    This fixes some multiple definition errors caused by the changes for
    PR libstdc++/90295. The previous solution for inlining the members of
    std::exception_ptr but still exporting them from the library was to
    suppress the 'inline' keyword on those functions when compiling
    libsupc++/eh_ptr.cc, so they get defined in that file. That produces ODR
    violations though, because there are now both inline and non-inline
    definitions in the library, due to the use of std::exception_ptr in
    other files sucg as src/c++11/future.cc.

    The new solution is to define all the relevant members as 'inline'
    unconditionally, but use __attribute__((used)) to cause definitions to
    be emitted in libsupc++/eh_ptr.cc as before. This doesn't quite work
    however, because PR c++/67453 means the attribute is ignored on
    constructors and destructors. As a workaround, the old solution
    (conditionally inline) is still used for those members, but they are
    given the always_inline attribute so that they aren't emitted in
    src/c++11/future.o as inline definitions.

    libstdc++-v3/ChangeLog:

            PR libstdc++/97729
            * include/std/future (__basic_future::_M_get_result): Use
            nullptr for null pointer constant.
            * libsupc++/eh_ptr.cc (operator==, operator!=): Remove
            definitions.
            * libsupc++/exception_ptr.h (_GLIBCXX_EH_PTR_USED): Define
            macro to conditionally add __attribute__((__used__)).
            (operator==, operator!=, exception_ptr::exception_ptr())
            (exception_ptr::exception_ptr(const exception_ptr&))
            (exception_ptr::~exception_ptr())
            (exception_ptr::operator=(const exception_ptr&))
            (exception_ptr::swap(exception_ptr&)): Always define as
            inline. Add macro to be conditionally "used".

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

--- Comment #5 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:6c282c14d1be0bba2bf5d49acd074b349f28ad17

commit r11-4798-g6c282c14d1be0bba2bf5d49acd074b349f28ad17
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Nov 6 20:33:39 2020 +0100

    c++: Propagate attributes to clones in duplicate_decls [PR67453]

    On the following testcase where the cdtor attributes aren't on the
    in-class declaration but on an out-of-class definition, the cdtors
    have their clones created from the in-class declaration, and later on
    duplicate_decls updates attributes on the abstract cdtors, but nothing
    propagates them to the clones.

    2020-11-06  Jakub Jelinek  <jakub@redhat.com>

            PR c++/67453
            * decl.c (duplicate_decls): Propagate DECL_ATTRIBUTES and
            DECL_PRESERVE_P from olddecl to its clones if any.

            * g++.dg/ext/attr-used-2.C: New test.

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:0af3930a497e022597a08fa1bcef5e453bfa636f

commit r11-4839-g0af3930a497e022597a08fa1bcef5e453bfa636f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Nov 9 10:16:07 2020 +0000

    libstdc++: Use 'inline' consistently in std::exception_ptr [PR 97729]

    With PR c++/67453 fixed we can rely on the 'used' attribute to emit
    inline constructors and destructors in libsupc++/eh_ptr.cc. This means
    we don't need to suppress the 'inline' keyword on them in that file, and
    don't need to force 'always_inline' on them in other files.

    libstdc++-v3/ChangeLog:

            PR libstdc++/97729
            * libsupc++/exception_ptr.h (exception_ptr::exception_ptr())
            (exception_ptr::exception_ptr(const exception_ptr&))
            (exception_ptr::~exception_ptr()): Remove 'always_inline'
            attributes. Use 'inline' unconditionally.

[Bug c++/67453] vtable not emitted for class with no key method and defaulted destructor with attribute((used))

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67453

--- Comment #7 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:921661beb90edd14a6102e87f0ff71b5a21a70ee

commit r10-9010-g921661beb90edd14a6102e87f0ff71b5a21a70ee
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Nov 6 20:33:39 2020 +0100

    c++: Propagate attributes to clones in duplicate_decls [PR67453]

    On the following testcase where the cdtor attributes aren't on the
    in-class declaration but on an out-of-class definition, the cdtors
    have their clones created from the in-class declaration, and later on
    duplicate_decls updates attributes on the abstract cdtors, but nothing
    propagates them to the clones.

    2020-11-06  Jakub Jelinek  <jakub@redhat.com>

            PR c++/67453
            * decl.c (duplicate_decls): Propagate DECL_ATTRIBUTES and
            DECL_PRESERVE_P from olddecl to its clones if any.

            * g++.dg/ext/attr-used-2.C: New test.

    (cherry picked from commit 6c282c14d1be0bba2bf5d49acd074b349f28ad17)