Microsoft KB Archive/195376

= FIX: Incorrect Code Generated with /Og and /Oa or /Ow =

Article ID: 195376

Article Last Modified on 7/5/2005

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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 Q195376



SYMPTOMS
The compiler might generate incorrect code when building with /Og (Global Optimizations) and /Oa (Assume No Aliasing) or /Og and /Ow (Assume Cross-function Aliasing).



RESOLUTION
Turn off /Oa and /Ow to work around the bug.



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
Please refer to Help for more information about the compiler options /Og, /Oa, and /Ow.

The following sample demonstrates the bug. In this case, the problem appears to be related to the final attempt to access an array in a function when that access involves doubling the variable used to index it.

Sample Code
//compiler options : cl /Og /Oa (or /Ow) #include   typedef struct C   { float x,y,z; long index; }C;

float gdIn[3]={1.0,2.0,3.0};

void init(C *gc) {    float fd[3]={1.0,2.0,3.0}; long  i = gc->index; float *pfd = gdIn; gc->x = *(pfd+0); gc->y = *(pfd+i); gc->z = *(pfd+i*2); }

int main {    C c;     c.index = 1; init(&c); printf("Should be 3.0, is %f \n", c.z); return 0; } The program output should be: 3.0.

The program output is: 2.000000.

Keywords: kbbug kbfix kbcompiler kbvs600sp3fix KB195376

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