Q281424: FIX: Bad Code Is Generated with /Og Enabled

Article: Q281424
Product(s): Microsoft C Compiler
Version(s): 6.0sp4
Operating System(s): 
Keyword(s): kbCompiler kbVC600fix kbDSupport
Last Modified: 28-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0sp4 
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0sp4 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0sp4 
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SYMPTOMS
========

With the global optimizations (/Og) compiler option enabled, the Visual C++ 6.0
Service Pack 4 (SP4) compiler may generate incorrect code for return values to
functions. See the "More Information" section for a detailed reproducible
sample.

CAUSE
=====

This is a regression bug that occurred in Visual Studio Service Pack 4.

RESOLUTION
==========

To work around this bug, do one of the following:

- Replace the following line in the sample code

  Test (MyClass::Testfunc(), y, z);

  with the following:

  MyClass x = MyClass::Testfunc();
  Test (x , y, z); 

  -or-

- In the sample code, use #pragma optimize("g", off) before the main function
  to disable the optimizations only in main.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.

This problem was corrected in Visual Studio 6.0 Service Pack 5.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

  // Test.cpp<BR/>
  // Command line : cl test.cpp /Og

  #include <iostream.h>

  class MyClass
  {
  public:
     unsigned long mID;
     MyClass(unsigned long id);
     MyClass(const MyClass & other);
     MyClass & operator = (const MyClass & other) ;
     unsigned long getID()
     {
  	   return mID;
     }
     static MyClass Testfunc()
     {
  	   return 0;
     };
  };

  MyClass::MyClass (unsigned long id /* = 0 */)
  {
     mID = id;
  }

  MyClass::MyClass(const MyClass & other) : mID(other.mID) 
  {
     cout << "In Copy Constructor" << endl;
  }

  MyClass & MyClass::operator = (const MyClass & other) 
  {
      cout << "In Operator =" << endl;
      mID = other.mID;
      return *this;
  }

  void Test (MyClass x, int y, int z)
  {
     cout << "In Function Test" << endl;
     cout << x.getID() << ' ' << y << ' ' << z << endl;
  }

  int main ()
  {
     int y = 1;
     int z = 2;
     Test (MyClass::Testfunc(), y, z);
     // expected output is 0 1 2
     return 0;
  }

The following is the expected output:

In Function Test
0 1 2

Actual Output:

In Function Test
1245052 0 2

Additional query words: kbbug kbfix

======================================================================
Keywords          : kbCompiler kbVC600fix kbDSupport 
Technology        : kbVCsearch kbAudDeveloper kbVC32bitSearch kbVC600SP4
Version           : :6.0sp4
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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