[Bug libstdc++/59768] [DR 2219] std::thread constructor not handling reference_wrapper correctly

["cctsai57 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59768

cctsai57 <cctsai57 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |cctsai57 at gmail dot com

--- Comment #6 from cctsai57 <cctsai57 at gmail dot com> ---
Hi,

Use 'configure CXXFLAGS=-O0' and make gcc successfully, but the generated
libstdc++.so has the following problem:

~~~~~ BEGIN ~~~~~
$ cat test.cc
int main() { return 0; }

$ g++ test.cc
/work2/gcc-x86_64/local/lib/gcc/x86_64-pc-linux-gnu/6.0.0/../../../../lib64/libstdc++.so:
undefined reference to `std::_Unwrap<std::reference_wrapper<std::thread>,
std::decay<std::reference_wrapper<std::thread> >::type>::type
std::__invfwd<std::reference_wrapper<std::thread>
>(std::remove_reference<std::reference_wrapper<std::thread> >::type&)'
collect2: error: ld returned 1 exit status

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/work2/gcc-x86_64/local/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /work2/gcc-x86_64/gcc-src/configure --enable-languages=c,c++
--prefix=/work2/gcc-x86_64/local --disable-bootstrap CXXFLAGS=-O0
Thread model: posix
gcc version 6.0.0 20151222 (experimental) (GCC) 

$ ld -v
GNU ld version 2.25-9.fc22
~~~~~END~~~~~

I guess that '-O0' causes the '__invfwd' not inlined, and the libstdc++.so
building option '-fno-implicit-templates' causes the '__invfwd' template not
instantiated.  I add 'inline' to '__invfwd' to solve this problem, but I'm
not sure if it's right or not:

diff --git a/libstdc++-v3/include/std/functional
b/libstdc++-v3/include/std/functional
index b994df4..9b853e8 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -207,7 +207,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Used by __invoke_impl instead of std::forward<_Tp> so that a
   // reference_wrapper is converted to an lvalue-reference.
   template<typename _Tp>
-    typename _Unwrap<_Tp>::type
+    inline typename _Unwrap<_Tp>::type
     __invfwd(typename remove_reference<_Tp>::type& __t) noexcept
     { return _Unwrap<_Tp>::_S_fwd(__t); }