Considering the call-return pattern in Figure 4.21, number of overflows and underflows (each of which causes a register save/restore) will occur with a window size of

8 -> window size 8 : Why total number of underflows and overflows are 8?

16 -> window size 16: Why total number of underflows and overflows are 0?

Time (in units of calls/returns) Return Call Nesting depth Figure 4.21 Example Call-Return Behavior of a Program