This is kind of intentional.
The intent is to measure the number of comparisons needed to implement the switch as a binary search. In f2, there are really only 7 different ranges that need to be distinguished. Consider:

	switch x {
	case 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10:
		println("<11")
	}

That also doesn't use a jump table, as it doesn't take many comparisons to implement it.

We probably shoudn't generate the jump table for f1, but we don't recognize that we can join cases when the first case is a naked fallthrough. (And also we don't recognize duplicate, in your case empty, code blocks either, which would also allow joining cases.)

And of course the number 8 is kind of arbitrary. We had to pick some threshold.

Close as working as intended / not a bug?