Question

I have what I’m pretty sure is a bug in the optimizer in Visual studio 2005. The problem is with an STL map.

Here’s the relevant code:

MyMapIterator myIt = m_myMap.find(otherID);

if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_A)
{
    //Prints stuff.  No side-effects whatsoever.
}
else if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_B && myIt->second.foo == FOO_A)
{
    //Prints stuff.  No side-effects whatsoever.
}
else if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_B && myIt->second.foo == FOO_B && /*other meaningless conditions */)
{
    //Prints stuff.  No side-effects whatsoever.
}

Works flawlessly in debug, used to crash in release, and disabling global optimizations “fixed it” Now, nothing works. I get a:

Microsoft Visual Studio C Runtime Library has detected a fatal error in [...]

Press Break to debug the program or Continue to terminate the program. 

This happens on the first MyMapIterator::operator-> of the last else if

The map is empty, I know that find should have returned end(), The first two comparisons to that effect work. But somehow, the third time ‘myIt != m_myMap.end()’ returns true, and the right side of the && is executed.

Various other places fail like this with a variant of ‘myIt != m_myMap.end()’ returning true in that same file, but this is, to me, the one that rules out most other possibilities. I used to think it was a buffer overflow that was stomping on my map, but take a look back at the code. I am positive that no other thread is stomping on it, and this is 100% reproductible.

So, what do I do from here. This is not performance sensitive in the slightest. I just need it to work as it should. Any option is acceptable. Yes I know I could surround the whole thing with the iterator equality check and it isn’t the nicest code. The point is, it should still work, and if that fails, anything else can.

EDIT

The last else-if doesn’t generate any jump !

    if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_A)
009270BE  mov         ecx,dword ptr [this] 
009270C4  add         ecx,0Ch 
009270C7  lea         eax,[ebp-90h] 
009270CD  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::end (8A21E0h) 
009270D2  mov         esi,eax 
009270D4  lea         edi,[myIt] 
009270D7  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::const_iterator::operator!= (8A2220h) 
009270DC  movzx       ecx,al 
009270DF  test        ecx,ecx 
009270E1  je          lux::Bar::DoStuff+0E4h (927154h) 
009270E3  lea         esi,[myIt] 
009270E6  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::iterator::operator-> (8A21F0h) 
009270EB  cmp         dword ptr [eax+8],1 
009270EF  jne         lux::Bar::DoStuff+0E4h (927154h) 
    {
         Stuff
    }
    else if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_B)
00927154  mov         ecx,dword ptr [this] 
0092715A  add         ecx,0Ch 
0092715D  lea         eax,[ebp-98h] 
00927163  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::end (8A21E0h) 
00927168  mov         esi,eax 
0092716A  lea         edi,[myIt] 
0092716D  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::const_iterator::operator!= (8A2220h) 
00927172  movzx       edx,al 
00927175  test        edx,edx 
00927177  je          lux::Bar::DoStuff+17Ah (9271EAh) 
00927179  lea         esi,[myIt] 
0092717C  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::iterator::operator-> (8A21F0h) 
00927181  cmp         dword ptr [eax+8],2 
00927185  jne         lux::Bar::DoStuff+17Ah (9271EAh) 
    {
            //Stuff
     }
    else if (myIt != m_myMap.end() && myIt->second.userStatus == STATUS_C)
009271EA  mov         ecx,dword ptr [this] 
009271F0  add         ecx,0Ch 
009271F3  lea         eax,[ebp-0A0h] 
009271F9  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::end (8A21E0h) 
009271FE  mov         esi,eax 
00927200  lea         edi,[myIt] 
00927203  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::const_iterator::operator!= (8A2220h) 
00927208  lea         esi,[myIt] 
0092720B  call        std::_Tree<std::_Tmap_traits<unsigned __int64,lux::Foo,std::less<unsigned __int64>,std::allocator<std::pair<unsigned __int64 const ,lux::Foo> >,0> >::iterator::operator-> (8A21F0h) 
    {
            //Stuff in the condition and after

Answer 1

Well guys. After much pain and tears. To fix it at least temporarily I had to rework the code a bit to the form suggested by most people, which is how it should have been in the first case:

if (myIt != m_myMap.end())
{
    if (myIt->second.userStatus == STATUS_A) 
    {
        //Prints stuff.  No side-effects whatsoever.
    }
    else if (myIt->second.userStatus == STATUS_B && myIt->second->foo == FOO_A)
    {        
        //Prints stuff.  No side-effects whatsoever.
    }
    else if (myIt->second.userStatus == STATUS_B && myIt->second->foo == FOO_B && /*other meaningless conditions */)
    {
        //Prints stuff.  No side-effects whatsoever.
    }
}

However, the bug was still present. This gem fixed it:

if (myIt != m_myMap.end())
if (myIt != m_myMap.end())
{
    if (myIt->second.userStatus == STATUS_A) 
    {
        //Prints stuff.  No side-effects whatsoever.
    }
    else if (myIt->second.userStatus == STATUS_B && myIt->second->foo == FOO_A)
    {        
        //Prints stuff.  No side-effects whatsoever.
    }
    else if (myIt->second.userStatus == STATUS_B && myIt->second->foo == FOO_B && /*other meaningless conditions */)
    {
        //Prints stuff.  No side-effects whatsoever.
    }
}

Yes. Doubling the if resulted in a jump instruction being emitted after the test.