Microsoft KB Archive/218611

= FIX: Incorrect Code Generated With /Og and /Ob1 =

Article ID: 218611

Article Last Modified on 11/18/2003

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APPLIES TO


 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 6.0 Standard Edition

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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 Error! It should output the following:

i=7 i=6 i=5 i=4 i=3 i=2 i=1 i=0

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

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; }

Keywords: kbbug kbfix kbvs600sp3fix KB218611

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