XTRAN Demonstration:  Eliminating Dead C Code

The following example uses a rule set written in XTRAN's rules language ("meta-code") that finds and suppresses every statement that is "dead" (cannot execute).  The rules comprise 147 non-comment lines of meta-code.

NOTE that these rules are language-independent; they are exactly the same rules used for similar examples for other languages.

Strategy:

• Use statement navigation facilities provided by XTRAN's rules language to follow every execution path through the code, and mark each visited statement as "live".
  
  
• Use recursive iterator facilities provided by XTRAN's rules language to visit every statement.  If is not marked "live", suppress its output.

 Input to XTRAN

void func(void)
{
        int i;

        if (i == 0 || i == 1)
            goto lbl2;
        i = 1;
        goto lbl3;
/*
 * The following code is dead and should therefore be eliminated:
 */
        if (i > 1)
            goto lbl1;
        i = 2;
lbl1:   i = 3;
        goto lbl3;
/*
 * The following statement is dead and should therefore be eliminated:
 */
        i = 5;
lbl2:   i = 6;
lbl3:   i = 7;
}

 Output from XTRAN

void func(void)
{
        int i;

        if (i == 0 || i == 1)
            goto lbl2;
        i = 1;
        goto lbl3;
lbl2:
        i = 6;
lbl3:
        i = 7;
}

COPYRIGHT 2008; reproduction prohibited without permission.  Revised 2006-11-27

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