FIX: Compiler Performs Illegal Sign Conversion Optimization (151499)

The information in this article applies to:

Microsoft Visual C++, 32-bit Enterprise Edition 5.0
Microsoft Visual C++, 32-bit Professional Edition 5.0

This article was previously published under Q151499

SYMPTOMS

When using the /Og optimization, or an option that includes it such as /Ox, /O2, or /O1, the compiler may incorrectly sign extend a value when performing a conversion.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97, Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

The following sample demonstrates this bug. As you step through this code in the debugger, you will observed that i and j compare as equal when they should not.

Sample Code

   int i, j;
   char c1=-1, c2, c3;
   bool f()
   {
      i = c1 + (unsigned char)c1;
      j = c1 + c1;
      if( i == j )  // this should fail
         return false;
      else
         return true;
   }

Modification Type:	Major	Last Reviewed:	10/17/2003
Keywords:	kbbug kbfix kbVS97sp1fix kbVS97sp2fix KB151499