Q113427: FIX: Incorrect Optimization of Left Shift Operator

Article: Q113427
Product(s): Microsoft C Compiler
Version(s): 1.0
Operating System(s): 
Keyword(s): kbCompilerkbbuglist kbfixlist
Last Modified: 22-JUL-2001

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The information in this article applies to:

- Microsoft C/C++ Compiler (CL.EXE), included with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 1.0 
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SYMPTOMS
========

Optimization of the left shift operator may generate incorrect code in loop
operations when compiled with global optimizations on. In the code sample below,
the "for" loop incorrectly evaluates the "count" variable. The resultant code
causes the loop to execute only once with the following output:

  0

RESOLUTION
==========

Turn off global optimizations (/Og). In the code sample below, turning off
global optimizations will correctly output:

  0
  40000000
  80000000
  C0000000

Global optimizations can be disabled by excluding /Og from the command-line
switches or by the use of a pragma:

     #pragma optimize ("g", off)

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft C/C++ 32-bit
compiler, version 8.0, which is included with Visual C++ 32-bit Edition. This
problem was corrected in C/C++ compiler version 9.0, included with Visual C++
32-bit Edition, version 2.0

Sample Code
-----------

  /*
  * Compile options needed: /Og
  */ 

  #include <stdio.h>

  void main( void )
  {
      unsigned count;
       for ( count = 0 ; count < 4 ; count++ )
           printf(" %X \n", count << 30);
  }

Additional query words: 1.00 8.00

======================================================================
Keywords          : kbCompiler kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : :1.0
Issue type        : kbbug
Solution Type     : kbfix

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