Question

We have been debugging a strange case for some days now, and have somewhat isolated the bug, but it still doesn’t make any sense. Perhaps anyone here can give me a clue about what is going on.

The problem is an access violation that occur in a part of the code.

Basically we have something like this:

void aclass::somefunc() {
  try {
    erroneous_member_function(*someptr);
  } 
  catch (AnException) {
  }
}

void aclass::erroneous_member_function(const SomeObject& ref) {
  // { //<--scope here error goes away
  LargeObject obj = Singleton()->Object.someLargeObj; //<-remove this error goes away

  //DummyDestruct dummy1//<-- this is not destroyed before the unreachable

  throw AnException();

  // } //<--end scope here error goes away 

  UnreachableClass unreachable; //<- remove this, and the error goes away

  DummyDestruct dummy2; //<- destructor of this object is called! 
}

While in the debugger it actually looks like it is destructing the UnreachableClass, and when I insert the DummyDestruct object this does not get destroyed before the strange destructor are called. So it is not seem like the destruction of the LargeObject is going awry.

All this is in the middle of production code, and it is very hard to isolate it to a small example.

My question is, does anyone have a clue about what is causing this, and what is happening? I have a quite full featured debugger available (Embarcadero RAD studio), but now I am not sure what to do with it.

Can anyone give me some advise on how to proceed?

Update:

I placed a DummyDestruct object beneath the throw clause, and placed a breakpoint in the destructor. The destructor for this object is entered (and its only us is in this piece of code).

Answer 1

With the information you have provided, and if everything is as you state, the only possible answer is a bug in the compiler/optimizer. Just add the extra scope with a comment (This is, again, if everything is exactly as you have stated).