[LLVMdev] Possible SelectionDAG Bug

[Dan Gohman]

On Mar 2, 2010, at 8:57 AM, David Greene wrote:

> On Monday 01 March 2010 20:32:07 Dan Gohman wrote:
> 
>>> No, what I mean is the thing under UI at the point of call to
>>> AddModifiedNodeToCSEMaps gets deleted.  So UI is invalid and when
>>> we loop back around and check it against UE we blow up with a
>>> singular iterator error.
>> 
>> UI is incremented before AddModifiedNodeToCSEMaps is called, so
>> I'm still not seeing what you're describing here.
> 
> It's not the increment that trips, it's the loop top compare to UE.  It 
> doesn't matter where UI points at the call to AddModifiedNodeToCSEMaps.
> The fact that AddModifiedNodeToCSEMaps can recursively call 
> ReplaceAllUsesOf means that we can potentially delete the node
> out from under UI.

Ok, I think I've finally managed to draw on my whiteboard a theoretical
situation which could have a problem like this.

The attached patch should theoretically fix this bug, though I have no
way to confirm this right now. Does it fix the bug you're seeing?

Dan

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