[Bug c++/95686] New: undefined reference to static local variable within inline function

[Bug c++/95686] New: undefined reference to static local variable within inline function

[leni536 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

            Bug ID: 95686
           Summary: undefined reference to static local variable within
                    inline function
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: leni536 at gmail dot com
  Target Milestone: ---

The following code produces an "undefined reference to `foo()::i'" linker
error:

template <const int* ptr>
struct S {
    static constexpr const int* value = ptr;
};

inline
auto foo() {
    static const int i = 0;
    return S<&i>{};
}

#include <iostream>

int main() {
    std::cout << decltype(foo())::value;
}

[Bug c++/95686] undefined reference to static local variable within inline function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|11.0                        |9.3.0
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |9.3.0
   Last reconfirmed|                            |2020-06-16
           Keywords|                            |accepts-invalid

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
clang complains

t.C:9:16: error: non-type template argument refers to object 'i' that does not
      have linkage
            return S<&i>{};
                      ^
t.C:8:26: note: non-type template argument refers to object here
        static const int i = 0;
                         ^

so this means your code is ill-formed.  I can confirm your observation
with GCC 9.3 but GCC 10.1 rejects the code as well:

t.C: In function ?auto foo()?:
t.C:9:17: error: ?& i? is not a valid template argument of type ?const int*?
because ?i? has no linkage
    9 |      return S<&i>{};
      |                 ^

[Bug c++/95686] undefined reference to static local variable within inline function

[leni536 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

--- Comment #2 from Lénárd Szolnoki <leni536 at gmail dot com> ---
I failed to mention that I compiled the example in -std=c++17. With this
compiler option it compiles but fails to link in gcc. It compiles, links and
runs as expected in clang.

The linkage requirement for reference/pointer non-type template arguments were
lifted in C++17.

[Bug c++/95686] undefined reference to static local variable within inline function

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #3 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Lénárd Szolnoki from comment #2)
> I failed to mention that I compiled the example in -std=c++17. With this
> compiler option it compiles but fails to link in gcc. It compiles, links and
> runs as expected in clang.
> 
> The linkage requirement for reference/pointer non-type template arguments
> were lifted in C++17.

According to https://gcc.gnu.org/bugs/ the compile options have to be provided
for every bug report. Here is a slightly simplified reproducer free of any
library dependencies:

Compiler options:

-Wall -Wextra -std=c++2a -pedantic

//---------------
template <const int* ptr>
struct S {
    static constexpr const int* value = ptr;
};

inline
auto foo() {
    static const int i = 0;
    return S<&i>{};
}

void bar(const int*){}

int main() {
    bar(decltype(foo())::value);
}
//---------------

Diagnostic output:

//----------------
/tmp/cci6dPre.o: In function `main':
prog.cc:(.text+0x10): undefined reference to `foo()::i'
collect2: error: ld returned 1 exit status
//----------------

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=53164

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect the same issue as in PR 53164 is the problem here.

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |asolokha at gmx dot com

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 102723 has been marked as a duplicate of this bug. ***

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code, lto

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note this code ICEs with LTO turned on also.

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 109185 has been marked as a duplicate of this bug. ***

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note the testcase is very similar to clang's
test/SemaTemplate/instantiate-static-local.cpp testcase.

[Bug c++/95686] undefined reference to static local variable within inline function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #6)
> Note this code ICEs with LTO turned on also.

The ICE is:

during IPA pass: modref
rls6o5bx.cpp:10:1: internal compiler error: in get_partitioning_class, at
symtab.cc:2096
   10 | }
      | ^
0x7a6b1d symtab_node::get_partitioning_class()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/symtab.cc:2096
0x105d777 lto_output_varpool_node
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/lto-cgraph.cc:631
0x105d777 output_symtab()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/lto-cgraph.cc:999
0x1074fdc lto_output()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/lto-streamer-out.cc:2825
0x1103181 write_lto
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/passes.cc:2784
0x1103181 ipa_write_summaries_1
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/passes.cc:2848
0x1103181 ipa_write_summaries()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/passes.cc:2904
0xd3dd92 ipa_passes
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/cgraphunit.cc:2250
0xd3dd92 symbol_table::compile()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/cgraphunit.cc:2323
0xd405e7 symbol_table::compile()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/cgraphunit.cc:2303
0xd405e7 symbol_table::finalize_compilation_unit()
       
/var/tmp/portage/sys-devel/gcc-13.0.1_p20230312/work/gcc-13-20230312/gcc/cgraphunit.cc:2575