[Bug c++/78919] New: Lambdas, default parameters and std::functional cause assembly error

[kirit.saelensminde at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78919

            Bug ID: 78919
           Summary: Lambdas, default parameters and std::functional cause
                    assembly error
           Product: gcc
           Version: 5.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kirit.saelensminde at gmail dot com
  Target Milestone: ---

There seems to be some odd interaction with default parameters, lambdas and
std::function.

    // Compile with:
    //      g++ --std=c++11 -Wall -Wextra bug.cpp
    //      g++ --std=c++14 -Wall -Wextra bug.cpp
    #include <functional>
    #include <iostream>

    template<typename F>
    void foo(F fn, std::function<void(void)> = [](){}) {
        fn();
    }

    int main() {
        foo([](){ std::cout << "First" << std::endl;});
        foo([](){ std::cout << "Second" << std::endl;});
    }


If the second call to `foo` is removed then it works fine. Otherwise there are
assembler errors like the below:

    /tmp/ccwG9slS.s: Assembler messages:                                        
    /tmp/ccwG9slS.s:252: Error: symbol `_ZNKUlvE_clEv' is already defined
    /tmp/ccwG9slS.s:537: Error: symbol
`_ZSt4moveIRUlvE_EONSt16remove_referenceIT_E4typeEOS3_' is already defined
    /tmp/ccwG9slS.s:555: Error: symbol `_ZNSt8functionIFvvEEC2IUlvE_vvEET_' is
already defined
    /tmp/ccwG9slS.s:813: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E21_M_not_empty_functionIS1_EEbRKT_'
is already defined
    /tmp/ccwG9slS.s:830: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E15_M_init_functorERSt9_Any_dataOS1_'
is already defined
    /tmp/ccwG9slS.s:871: Error: symbol
`_ZNSt17_Function_handlerIFvvEUlvE_E9_M_invokeERKSt9_Any_data' is already
defined
    /tmp/ccwG9slS.s:894: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E10_M_managerERSt9_Any_dataRKS3_St18_Manager_operation'
is already defined
    /tmp/ccwG9slS.s:1122: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E15_M_init_functorERSt9_Any_dataOS1_St17integral_constantIbLb1EE'
is already defined
    /tmp/ccwG9slS.s:1151: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E14_M_get_pointerERKSt9_Any_data' is
already defined
    /tmp/ccwG9slS.s:1176: Error: symbol
`_ZNSt9_Any_data9_M_accessIPUlvE_EERT_v' is already defined
    /tmp/ccwG9slS.s:1196: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E8_M_cloneERSt9_Any_dataRKS3_St17integral_constantIbLb1EE'
is already defined
    /tmp/ccwG9slS.s:1225: Error: symbol
`_ZNSt14_Function_base13_Base_managerIUlvE_E10_M_destroyERSt9_Any_dataSt17integral_constantIbLb1EE'
is already defined
    /tmp/ccwG9slS.s:1306: Error: symbol
`_ZNKSt9_Any_data9_M_accessIUlvE_EERKT_v' is already defined
    /tmp/ccwG9slS.s:1326: Error: symbol `_ZSt11__addressofIKUlvE_EPT_RS2_' is
already defined
    /tmp/ccwG9slS.s:1344: Error: symbol `_ZNSt9_Any_data9_M_accessIUlvE_EERT_v'
is already defined


As well as 5.4.1 this bug happens in 6.2.0 and 6.2.1. We've tried this on
Ubuntu versions and Arch linux versions of the compilers.


This looks somewhat similar to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65919 but the errors appear quite
different.