FIX: /Og Increments the Index of a Loop Too Soon

• Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

The array elements in the sample are assigned incorrect values when:

1. You use the compiler option /Og (Global optimizations).

The /Og (Global Optimizations) compiler option increments the index in a loop before executing the body of the loop. As a result, incorrect values are assigned to the array elements.

RESOLUTION

You can disable global optimization on a function-by-function basis using the optimize pragma with the g option. /Og- disables global optimization on a file-by-file basis.

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:

   ARTICLE-ID: Q170365
   TITLE     : INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

The following sample demonstrates the problem.

Sample Code

   /*
   * Compiler option: /Og
   */

   //typedef short* T ;
   //typedef char* T ;

   extern T rg ;

   void f1()
   {
      int ndx = 0 ;
      do
      {
         rg[ndx] = ndx++ ;
      }
      while (ndx < 5)
   }

   void f2()
   {
      int ndx = 0 ;
      while(ndx < 5)
      {
         rg[ndx] = ndx ;
         ndx++ ;
      }
   }

   void f3()
   {
     int ndx = 0 ;
     for(ndx = 0; ndx < 5; ndx++)
     {
        rg[ndx] = ndx ;
     }
   }

Keywords          : CLIss CodeGen vcbuglist500 VS97FixlistSP3 kbcode kbtool VS97FixlistSP2 VS97FixlistSP1
Version           : 5.0
Platform          : NT WINDOWS
Issue type        : kbbug
Solution Type     : kbfix kbservicepack