Previously, we had been doing exactly two passes over the event log to
caculate the stack object reference map at each trace point. It turns
out the correct number of passes depends on how many incorrect
assumptions we make about what the stack looks like at instructions with
multiple predecessors (i.e. targets of jumps and branches).
Each time we detect we've made one or more incorrect assumptions during
a pass, we must do another pass to correct those assumptions. That pass
may in turn reveal further incorrect assumptions, and so on.
