The aliasing issue is supposed to be that if you wind up with two pointers pointing to the same thing, one pointer could alter the "true" variable, and if this variable was also in a register somewhere else, the register would have the wrong value, like volitile variable. There's supposed to be a switch to turn off the aliasing (i.e. you tell the compiler you're smart enough not to do that), but from what I've seen it doesn't always work.