[Bug c++/99066] New: non-weak definition emitted for explicit instantiation declaration

[Bug c++/99066] New: non-weak definition emitted for explicit instantiation declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

            Bug ID: 99066
           Summary: non-weak definition emitted for explicit instantiation
                    declaration
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: link-failure
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

If two TUs both include a header that contains:

template <typename a> struct basic_string {
  static const int npos = 1;
};
template <typename a> const int basic_string<a>::npos;

struct e { template <bool> int f() const; };

template <bool> int e::f() const {
  return basic_string<char>::npos;
}

extern template class basic_string<char>;

then we get a linker error, because both TUs define the npos constant:

/usr/bin/ld: /tmp/ccjy3Spq.o:(.rodata+0x0): multiple definition of
`basic_string<char>::npos'; /tmp/ccMQ33nr.o:(.rodata+0x0): first defined here


Shouldn't the static data member only have weak definitions, unless an explicit
instantiation definition is seen?

/* TU 1 */

#include "str.h"

int main()
{
  return e().f<true>();
}

/* TU 2 */

#include "str.h"


The assembly for both files contains:

        .globl  _ZN12basic_stringIcE4nposE
        .section        .rodata
        .align 4
        .type   _ZN12basic_stringIcE4nposE, @object
        .size   _ZN12basic_stringIcE4nposE, 4
_ZN12basic_stringIcE4nposE:
        .long   1

[Bug c++/99066] non-weak definition emitted for explicit instantiation declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org,
                   |                            |mpolacek at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Note, r104000 still doesn't emit it but r104500 already does, so perhaps a 4.1
GCC era regression?

[Bug c++/99066] [8/9/10/11 Regression] non-weak definition emitted for explicit instantiation declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
            Summary|non-weak definition emitted |[8/9/10/11 Regression]
                   |for explicit instantiation  |non-weak definition emitted
                   |declaration                 |for explicit instantiation
                   |                            |declaration
   Target Milestone|---                         |8.5

[Bug c++/99066] [8/9/10/11 Regression] non-weak definition emitted for explicit instantiation declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-02-10
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps caused by PR23691 changes?

[Bug c++/99066] [8/9/10/11 Regression] non-weak definition emitted for explicit instantiation declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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
             Status|NEW                         |ASSIGNED

[Bug c++/99066] [8/9/10/11 Regression] non-weak definition emitted for explicit instantiation declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> Perhaps caused by PR23691 changes?

r104041, yes.  Bizarre that this went unnoticed for over 15 years.

[Bug c++/99066] [8/9/10/11 Regression] non-weak definition emitted for explicit instantiation declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

--- 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:bd89b8fe9efbdf0a95d827553d1a84fd3cefaa16

commit r11-7986-gbd89b8fe9efbdf0a95d827553d1a84fd3cefaa16
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Apr 4 23:32:32 2021 -0400

    c++: extern template and static data member [PR99066]

    'extern template' should mean that the relevant symbols are never emitted.
    But in this case we were assuming that DECL_EXTERNAL was already set on the
    variable, so we just needed to clear DECL_NOT_REALLY_EXTERN.  Since
    DECL_EXTERNAL was not set, we emitted a definition of npos.

    gcc/cp/ChangeLog:

            PR c++/99066
            * pt.c (mark_decl_instantiated): Set DECL_EXTERNAL.

    gcc/testsuite/ChangeLog:

            PR c++/99066
            * g++.dg/cpp0x/extern_template-6.C: New test.

[Bug c++/99066] [8/9/10 Regression] non-weak definition emitted for explicit instantiation declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[8/9/10/11 Regression]      |[8/9/10 Regression]
                   |non-weak definition emitted |non-weak definition emitted
                   |for explicit instantiation  |for explicit instantiation
                   |declaration                 |declaration

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

[Bug c++/99066] [8/9/10 Regression] non-weak definition emitted for explicit instantiation declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #3)
> r104041, yes.  Bizarre that this went unnoticed for over 15 years.

Very surprising, isn't it!

[Bug c++/99066] [9/10 Regression] non-weak definition emitted for explicit instantiation declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug c++/99066] [9/10 Regression] non-weak definition emitted for explicit instantiation declaration

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug c++/99066] [9/10 Regression] non-weak definition emitted for explicit instantiation declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

--- Comment #9 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:20b503f1125c0b0a7f4b2bb1214d4a3cc6fd9f70

commit r10-10735-g20b503f1125c0b0a7f4b2bb1214d4a3cc6fd9f70
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Apr 4 23:32:32 2021 -0400

    c++: extern template and static data member [PR99066]

    'extern template' should mean that the relevant symbols are never emitted.
    But in this case we were assuming that DECL_EXTERNAL was already set on the
    variable, so we just needed to clear DECL_NOT_REALLY_EXTERN.  Since
    DECL_EXTERNAL was not set, we emitted a definition of npos.

    gcc/cp/ChangeLog:

            PR c++/99066
            * pt.c (mark_decl_instantiated): Set DECL_EXTERNAL.

    gcc/testsuite/ChangeLog:

            PR c++/99066
            * g++.dg/cpp0x/extern_template-6.C: New test.

[Bug c++/99066] [9 Regression] non-weak definition emitted for explicit instantiation declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:950a97a5039c7b96602edfdf8984b5800f5837f3

commit r9-10179-g950a97a5039c7b96602edfdf8984b5800f5837f3
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Apr 4 23:32:32 2021 -0400

    c++: extern template and static data member [PR99066]

    'extern template' should mean that the relevant symbols are never emitted.
    But in this case we were assuming that DECL_EXTERNAL was already set on the
    variable, so we just needed to clear DECL_NOT_REALLY_EXTERN.  Since
    DECL_EXTERNAL was not set, we emitted a definition of npos.

    gcc/cp/ChangeLog:

            PR c++/99066
            * pt.c (mark_decl_instantiated): Set DECL_EXTERNAL.

    gcc/testsuite/ChangeLog:

            PR c++/99066
            * g++.dg/cpp0x/extern_template-6.C: New test.

[Bug c++/99066] [9 Regression] non-weak definition emitted for explicit instantiation declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99066

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

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

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 9.5/10.4/11.