FIX: Incorrect Code Generated With /Og and /Ob1

View products that this article applies to.

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.

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RESOLUTION

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

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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 (http://support.microsoft.com/kb/194022/EN-US/ ) INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 (http://support.microsoft.com/kb/194295/EN-US/ ) HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

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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/>

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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; 
}

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