[Bug c++/83400] g++ -O1 doesn't execute any code in destructors with a throw statement if it sees another throw

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83400

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-12-13
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

extern "C" int puts(const char*);

struct ThrowInDtor{
    ~ThrowInDtor() noexcept(false) {
        puts("in dtor");
        throw 1L;
    }
};

int main() {
    try {
        ThrowInDtor throws;
        throw 1;
    } catch (int) {
        // unreachable
    }
}

terminate called after throwing an instance of 'int'
Aborted (core dumped)


The code is misoptimized to:


;; Function int main() (main, funcdef_no=3, decl_uid=2299, cgraph_uid=3,
symbol_order=3) (executed once)

int main() ()
{
  void * _4;
  void * _11;

  <bb 2> [100.00%]:
  _4 = __cxa_allocate_exception (4);
  MEM[(int *)_4] = 1;
  __cxa_throw (_4, &_ZTIi, 0B);

<L2> [0.00%]:
  puts ("in dtor");
  _11 = __cxa_allocate_exception (8);
  MEM[(long int *)_11] = 1;
  __cxa_throw (_11, &_ZTIl, 0B);

}

It seems the catch(int) has been optimized away and so the destructor never
even runs, we just terminate with an uncaught exception.