[Bug c++/67632] New: explicit instantiation omits copy constructor and others

[Bug c++/67632] New: explicit instantiation omits copy constructor and others

[jlink at drw dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

            Bug ID: 67632
           Summary: explicit instantiation omits copy constructor and
                    others
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlink at drw dot com
  Target Milestone: ---

When I compile the follow test case with g++ -std=c++11 -c, and view the output
with nm, it shows that the std::unordered_map copy constructor is never
emitted:

% cat t.cc 
#include <unordered_map>
template class std::unordered_map<int, int>;
% g++ -std=c++11 -c t.cc
% 

If I compile the following and link it with the above, I'll get the undefined
reference:

% cat x.cc 
#include <unordered_map>
extern template class std::unordered_map<int, int>;
std::unordered_map<int, int> copy(
   const std::unordered_map<int, int> & a) { return a; }

main() {}

% g++ -std=c++11 t.o x.cc     
/tmp/cc0dF94P.o: In function `copy(std::unordered_map<int, int, std::hash<int>,
std::equal_to<int>, std::allocator<std::pair<int const, int> > > const&)':
x.cc:(.text+0x1f): undefined reference to `std::unordered_map<int, int,
std::hash<int>, std::equal_to<int>, std::allocator<std::pair<int const, int> >
>::unordered_map(std::unordered_map<int, int, std::hash<int>,
std::equal_to<int>, std::allocator<std::pair<int const, int> > > const&)'
collect2: error: ld returned 1 exit status

This seems like a clear bug, right?  Either the explicit instantiation should
emit everything, or the use of extern template should know what still needs to
be emitted locally.

[Bug c++/67632] explicit instantiation omits copy constructor and others

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|WORKSFORME                  |---

--- Comment #2 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Reopened. I've tested for the wrong symbol.
I let others handle this.

[Bug c++/67632] explicit instantiation omits copy constructor and others

[jlink at drw dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

--- Comment #3 from Joseph Link <jlink at drw dot com> ---
Yeah, watch out for the copy constructor that takes an allocator.  That one's
there.  The compiler generated one is not.

[Bug libstdc++/67632] explicit instantiation omits copy constructor and others

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |redi at gcc dot gnu.org
          Component|c++                         |libstdc++

--- Comment #4 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Might be a libstdc++ issue. Adding CC.

markus@x4 /tmp % g++ -c -O0 -std=c++11 t.cpp
markus@x4 /tmp % nm t.o | grep
_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_
0000000000000000 W
_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_RKS7_
markus@x4 /tmp % g++ -Wl,--no-demangle -O0 -std=c++11 t.cpp x.cpp
/tmp/ccMHoCTz.o:x.cpp:function
_Z4copyRKSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEE: error:
undefined reference to
'_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_'
collect2: error: ld returned 1 exit status
markus@x4 /tmp % c++filt
_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_
std::unordered_map<int, int, std::hash<int>, std::equal_to<int>,
std::allocator<std::pair<int const, int> >
>::unordered_map(std::unordered_map<int, int, std::hash<int>,
std::equal_to<int>, std::allocator<std::pair<int const, int> > > const&)
markus@x4 /tmp % c++filt
_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_RKS7_
std::unordered_map<int, int, std::hash<int>, std::equal_to<int>,
std::allocator<std::pair<int const, int> >
>::unordered_map(std::unordered_map<int, int, std::hash<int>,
std::equal_to<int>, std::allocator<std::pair<int const, int> > > const&,
std::allocator<std::pair<int const, int> > const&)

[Bug libstdc++/67632] explicit instantiation omits copy constructor and others

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Not sure how it can be a libstdc++ issue, the copy constructor exists, the
library can't force the front-end to instantiate it.

I'm travelling without access to proper computers, but as far as I can tell
from coliru.stacked-crooked.com it links fine using clang++ -stdlib=libstdc++
(with libstdc++ 5.2.0).

[Bug libstdc++/67632] explicit instantiation omits copy constructor and others

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

--- Comment #6 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #5)
> Not sure how it can be a libstdc++ issue, the copy constructor exists, the
> library can't force the front-end to instantiate it.
> 
> I'm travelling without access to proper computers, but as far as I can tell
> from coliru.stacked-crooked.com it links fine using clang++
> -stdlib=libstdc++ (with libstdc++ 5.2.0).

No, it doesn't for -O0. Higher -O values make the issue go away.

markus@x4 /tmp % clang++ -stdlib=libc++ -O0 -std=c++11 t.cpp x.cpp
markus@x4 /tmp % clang++ -Wl,--no-demangle -O0 -std=c++11 t.cpp x.cpp
/tmp/x-5ef538.o:x.cpp:function
_Z4copyRKSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEE: error:
undefined reference to
'_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_'
clang-3.8: error: linker command failed with exit code 1 (use -v to see
invocation)
markus@x4 /tmp % icpc -Wl,--no-demangle -O0 -std=c++11 t.cpp x.cpp
/tmp/icpcMamJXz.o:x.cpp:function
_Z4copyRKSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEE: error:
undefined reference to
'_ZNSt13unordered_mapIiiSt4hashIiESt8equal_toIiESaISt4pairIKiiEEEC1ERKS8_'

[Bug libstdc++/67632] explicit instantiation omits copy constructor and others

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67632

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-09-19
     Ever confirmed|0                           |1

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Markus Trippelsdorf from comment #6)
> No, it doesn't for -O0. Higher -O values make the issue go away.

Oh, ok, weird. I probably won't be able to look into this further until Monday.