FIX: Incorrect Code Generated With /Og and /Ob1

ID: Q218611

The information in this article applies to:

Microsoft Visual C++, 32-bit Editions, version 6.0

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 this to be a bug in the Microsoft products 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:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 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; 
}

Additional query words:

Keywords : kbservicepack kbVS600sp2 kbVS600SP1 kbVS600sp3fix
Version : winnt:6.0
Platform : winnt
Issue type : kbbug