FIX: Incorrect Code Generated With /Og and /Ob1 (218611)


The information in this article applies to:

  • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
  • Microsoft Visual C++, 32-bit Professional Edition 6.0
  • Microsoft Visual C++, 32-bit Learning Edition 6.0
This article was previously published under Q218611

SYMPTOMS

Incorrect code is generated for a comparison such as 
   if (!(i > 0))
when it is compiled with both the /Og and /Ob1.

RESOLUTION

To work around the problem disable either the /Ob1 or /Og optimization.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:

194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

MORE INFORMATION


The following code is output. 

     i=7<BR/>
     Error!<BR/><BR/>
It should output the following:
     i=7<BR/>
     i=6<BR/>
     i=5<BR/>
     i=4<BR/>
     i=3<BR/>
     i=2<BR/>
     i=1<BR/>
     i=0<BR/>

Steps to Reproduce Behavior


Compile the following code with /Og and /Ob1. 
#include <stdio.h>
class C
{
public:
    C(int i) { mLow = i; mHigh = 0; }
    int getByte(int i) const;
    unsigned long mLow;
    unsigned long mHigh;
};

inline int C::getByte(int i) const
{
    if (i < 4)
	return (mLow >> (i << 3)) & 0xFF;
    else
	return (mHigh >> ((i - 4) << 3)) & 0xFF;
}

int main()
{
    C h (1);
    int i = 7;
    for ( i = 7; ; i--) {
		printf("i=%d\n",i);
        if (h.getByte(i) != 0)
            break;
        if (!(i > 0)) {				// Incorrect code
            printf("Error!\n");
            break;
        }
    }
    return 1; 
}
Modification Type:MajorLast Reviewed:11/18/2003
Keywords:kbbug kbfix kbVS600sp3fix KB218611
©2003 Microsoft Corporation. All rights reserved.