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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documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.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:  /Oc
              /Og
 
     Use of either the /Oc or the /Og option allows the compiler to
     calculate the value of a common subexpression once. For example,
     "b + c" is common to the following code. If the values of b and c
     do not change between the three expressions, the compiler can
     calculate the value of b + c once, assign the calculation to a
     temporary variable, and substitute the variable as appropriate.
 
          a = b + c;
 
          d = b + c;
 
          e = b + c;
 
     When you use the /Oc option (default common subexpression
     optimization) the compiler examines short sections of code (basic
     blocks) for common subexpressions. When you use the /Og option
     (enable global common subexpression optimization) the compiler
     searches entire functions for common subexpressions. You can
     disable the default common subexpression optimization with the /Od
     option.
 
     NOTE: You can enable or disable block-scope common subexpression
           optimization on a function-by-function basis using the
           optimize pragma with the c option. You can enable or disable
           global common subexpression optimization on a function-by-
           function basis using the optimize pragma with the g option.
                                    -♦-