[Bug libstdc++/59656] New: weak_ptr::lock function crashes when compiling with -fno-exceptions flag

["chus_flores at hotmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59656

            Bug ID: 59656
           Summary: weak_ptr::lock function crashes when compiling with
                    -fno-exceptions flag
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chus_flores at hotmail dot com

weak_ptr::lock crashes when the code is compiled with the -fno-exceptions flag
and the data pointed by the weak_ptr expires during the execution of the lock
function itself:

(from http://gcc.gnu.org/onlinedocs/gcc-4.8.2/libstdc++/api/a01518_source.html)

shared_ptr<_Tp>
  494       lock() const noexcept
  495       {
  496 #ifdef __GTHREADS
  497     if (this->expired())
  498       return shared_ptr<_Tp>();
  499 
  500     __try
  501       {
  502         return shared_ptr<_Tp>(*this);
  503       }
  504     __catch(const bad_weak_ptr&)
  505       {
  506         return shared_ptr<_Tp>();
  507       }
  508 #else
  509     return this->expired() ? shared_ptr<_Tp>() : shared_ptr<_Tp>(*this);
  510 #endif
  511       }

If the data is valid when line 497 is executed and the data is released in a
different thread just before executing line 502, the program will crash because
it will try to throw an exception (exceptions are disabled because of the flag
-fno-exceptions). This code only works when exceptions are enabled because the
try/catch will resolve the problem, but not otherwise.

The standard definition says that this function must return safely and it
doesn't throw any exception. I presume this must apply even if the exceptions
are not enabled.