[Bug c++/85311] New: const& aggregate parameter with empty default brace initializer results in undefined references to std containers

["vishal at royal-caliber dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85311

            Bug ID: 85311
           Summary: const& aggregate parameter with empty default brace
                    initializer results in undefined references to std
                    containers
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vishal@royal-caliber.com
  Target Milestone: ---

Created attachment 43890
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43890&action=edit
preprocessed output

Hello,

The following code fails to link:

----------test.cpp------------------
#include <vector>

struct Foo
{
  std::vector<int> x;
};

void foo(const Foo& = {})
{
}

int main()
{
  foo();
}
-----------------------------------

$ g++ test.cpp
/tmp/ccJsJY1c.o: In function `main':
test.cpp:(.text+0x2a): undefined reference to `std::vector<int,
std::allocator<int> >::vector()'
collect2: error: ld returned 1 exit status

The problem is triggered by the default value for the parameter to foo(). It
can be avoided by either changing the prototype of foo() to not have a default
value, or by actually providing a value in the call to foo().

The same behavior occurs with several other std containers inside the aggregate
such as deque and list. It can be reproduced in gcc versions 6.4.0, 7.2.0 and
7.3.0 and libstdc++ versions 6.0.22 and 6.0.24.

The preprocessed file is attached. The output of g++ -v follows.

Thank you,
Vishal


Output of "g++-7.3 -v -save-temps test.cpp"

Using built-in specs.
COLLECT_GCC=g++-7.3
COLLECT_LTO_WRAPPER=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --enable-languages=c,c++
--prefix=/home/vishal/localbuild --program-suffix=-7.3 --disable-multilib
Thread model: posix
gcc version 7.3.0 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus -E
-quiet -v -D_GNU_SOURCE test.cpp -mtune=generic -march=x86-64 -fpch-preprocess
-o test.ii
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory
"/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0

/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/x86_64-pc-linux-gnu

/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/backward
 /home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include
 /home/vishal/localbuild/include
 /home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus
-fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64
-auxbase test -version -o test.s
GNU C++14 (GCC) version 7.3.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 7.3.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
warning: GMP header version 6.1.0 differs from library version 6.1.2.
warning: MPFR header version 3.1.3-p4 differs from library version 3.1.6.
warning: MPC header version 1.0.2 differs from library version 1.0.3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (GCC) version 7.3.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 7.3.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
warning: GMP header version 6.1.0 differs from library version 6.1.2.
warning: MPFR header version 3.1.3-p4 differs from library version 3.1.6.
warning: MPC header version 1.0.2 differs from library version 1.0.3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: e93c907a87f28f1e65d001f94ea5afa5
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 as -v --64 -o test.o test.s
GNU assembler version 2.29.1 (x86_64-pc-linux-gnu) using BFD version (Gentoo
2.29.1 p3) 2.29.1
COMPILER_PATH=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/
LIBRARY_PATH=/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/collect2 -plugin
/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/liblto_plugin.so
-plugin-opt=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper
-plugin-opt=-fresolution=test.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc
--eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2
/usr/lib/../lib64/crt1.o /usr/lib/../lib64/crti.o
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/crtbegin.o
-L/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0
-L/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../.. test.o
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/crtend.o
/usr/lib/../lib64/crtn.o
test.o: In function `main':
test.cpp:(.text+0x1b): undefined reference to `std::vector<int,
std::allocator<int> >::vector()'
collect2: error: ld returned 1 exit status