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B-3 Value Range Propagation
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        In  Value Range  Propagation,  for each  variable, a  range  (a pair  of
        max-bound and min-bound) is maintained. Those conditional branches whose
        conditionals lie outside these bounds are eliminated.

        Source file : B-3.c
        Compilation : gcc-4.7.2 -c -O2 -fdump-tree-all B-3.c
        View result : vi -O B-3.c.*.ssa B-3.c.*.vrp1 
        Clear dumps : rm -f B-3.c.* B-3.o


Program
-------
        
        #include <stdio.h>
        int main ()
        {
           int a, b;
           for (a=4 ; a<100; a++) {
               if (a < 4)
        	   b = b + 2;
               else
        	   b = b * 2;
           }
           printf ("%d%d", a, b);
        }
        
Questions
---------

        1   In the file B-3.c, what values  can variable `a' take? Will the `if'
            condition [a  < 4] ever  be true?  Inspect the file  B-3.c.*.vrp1 to
            analyze the dump.