Why does he write such code?

["zhangsong" <happynodyandhappyyogo@xxxxxxxxx>]

Hello all, 

I read linux-2.4 and found a line of confused code:

In kernel/sched.c:
       
     void do_timer(struct pt_regs * regs)
     {
　　	   (*(unsigned long *)&jiffies)++; /* confused code */
　　　　…
     }

1. Why not to use something link atomic_inc insead of the above code?
2. Can the GCC optimize the above code to jiffies++ ?

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