BUG: Incorrect / inconsistent program behaviour when the "Remove Integer Overflow Checks" option is

  • Thread starter Thread starter Ralph Purtcher-Wydenbruck
  • Start date Start date
R

Ralph Purtcher-Wydenbruck

This is a worrying bug, and indicates a potential problem in the Framework
CLR. This bug affected a project I was working on, which behaved differently
when run from the Visual Studio IDE than when run by double clicking on the
project's EXE file. The problem can be replicated easily:

Create a new project in Visual Studio 2003 and add the following code.


Module Main
Sub Main()
Dim xmlDoc As New System.Xml.XmlDocument
xmlDoc.AppendChild(xmlDoc.CreateElement("Root"))
Dim o, n As Object
Dim count As Integer
For Each o In xmlDoc.ChildNodes
For n = 0 To 9
count += 1
Next
Next
System.Windows.Forms.MessageBox.Show("Count: " & count)
End Sub
End Module


IMPORTANT: To replicate the bug, you must

(1) Set the project compile mode to "Release"
(2) Enable the following option: Project Configuration Properties /
Optimisations / "Remove Integer Overflow Checks"

Finally, run the program from the Visual Studio IDE. The expected message,
"Count: 10", is displayed. Now run the program from it's EXE file via
Windows Explorer. A message, "Count: 1" is displayed, which is incorrect.
 
Ralph,

Interesting, that does indeed look like some kind of JIT compiler bug.

FYI, changing the loop variable n to an Integer fixes the problem. Why
did you have it declared as Object anyway?



Mattias
 
I know it fixes it, but I wanted to show the problem. Actually, changing the
code in almost any way fixes the problem.

It's a rather worrying thought that this kind arbitrary JIT compiler problem
might affect anyone's code.

So, there was no specific reason for the Object declaration, other than the
fact that I wanted to provide a simple example that did not break the
problem. (In my shipping code I used a For / Each for the inner loop, not an
object).
 
Ralph,
I know it fixes it, but I wanted to show the problem. Actually, changing the
code in almost any way fixes the problem.
Click to expand...

OK, fine. FWIW, the bug seems to be fixed in Whidbey.

It's a rather worrying thought that this kind arbitrary JIT compiler problem
might affect anyone's code.
Click to expand...

Well, there will always be bugs.



Mattias
 
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