[Bug c++/78761] New: C++14, compiler generate mangled name that can not be demangled

["chihin.ko at oracle dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78761

            Bug ID: 78761
           Summary: C++14, compiler generate mangled name that can not be
                    demangled
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chihin.ko at oracle dot com
  Target Milestone: ---

cat t.cc

template <class T>
decltype(auto) g_1(T t) {
    return t;
}

template <class T>
auto g_2(T t) {
    return t;
}

int main() {
    decltype(auto) res = g_1<int>(10);
    decltype(auto) res2 = g_2<int>(10);
    return 0;
}
==========================================
g++ -g t.cc

> nm a.out | grep g_2
[71]    |     4198535|   12|FUNC |WEAK |0    |20     |_Z3g_2IiEDaT_
> /pkg/gnu/bin/gnu-c++filt _Z3g_2IiEDaT_
auto g_2<int>(int) <=== this is OK

> nm a.out | grep g_1
[84]    |      4198523|   12|FUNC |WEAK |0    |19     |_Z3g_1IiEDcT_
> /pkg/gnu/bin/gnu-c++filt _Z3g_1IiEDcT_
_Z3g_1IiEDcT_   <=== can not be demangled