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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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─────C/C++ Compiler─────────────────────────────────────────────────────────
 
     Syntax:  /Oa
              /Ow
 
     The /Oa and /Ow options control the assumptions the compiler makes
     regarding "aliasing" when it performs optimizations. These options
     can significantly improve the performance of your program, but
     there are a few situations in which these options are not
     appropriate.
 
     The /Oa option tells the compiler that your program does not
     perform any aliasing (other than the very simple forms that the
     compiler can detect) and that function calls are safe. This allows
     the compiler to optimize your code more fully. However, if you
     specify this option when compiling a program that does perform
     aliasing, the compiler may produce incorrect code.
 
     When you use the /Ow option, you specify that aliasing might occur
     across function calls. Therefore, after each function call, pointer
     variables must be reloaded from memory. For more information on the
     /Oa and /Ow options and aliasing, see the "Programming Techniques"
     manual.
 
     Microsoft Windows can change the values of handles during the
     execution of a function. Therefore, always use /Ow when you
     program using Windows.
 
     NOTE: You can instruct the compiler to disable optimizations
           that are unsafe with code that does aliasing by using the
           optimize pragma with either the a or w option.
                                    -♦-