KB122542 - BUG: Incorrect Code for Loop with Known Value

Article ID: 122542

Article Last Modified on 7/5/2005

Microsoft C/C++ Professional Development System 7.0
Microsoft Visual C++ 1.0 Professional Edition
Microsoft Visual C++ 1.5 Professional Edition
Microsoft Visual C++ 1.51
Microsoft Visual C++ 2.0 Professional Edition

This article was previously published under Q122542

SYMPTOMS

When you use the /Ox, /Og, /O1, or /02 optimizations with the 32-bit compiler or the /Ox and /Ol optimizations with the 16-bit compiler, incorrect code is generated for loops where the number of iterations is a known value. The loop is not executed.

RESOLUTION

Workarounds are:

Remove the optimization from the command line. -or-
Use the optimize pragma to disable optimizations for the function. Use:
```
      #pragma optimize ("",off)
						
```
before the function call, and use:
```
      #pragma optimize ("",on)
						
```
after the function call.

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Sample Code to Reproduce Problem

/* Compile options needed:
/*        32-bit compiler: /Ox, /Og, /O1, or /02
/*        16-bit compiler: /Ox or /Ol
*/ 

/* This sample prints out 11 */ 

#include <stdio.h>

void main(void)
{
   int i = 500;
loop:  i++;
   if( i <= 10 ) goto loop;
      printf( "This should be 501: %d\n", i );
}

Additional query words: 1.00 1.50 1.51 2.00 7.00 8.00 8.00c 9.00

Keywords: KB122542