YES(?, a + b + 3)

Initial complexity problem:
1:	T:
		(?, 1)    div(a, b) -> end(a, b) [ 0 >= a ]
		(?, 1)    div(a, b) -> end(a, b) [ a >= b ]
		(?, 1)    div(a, b) -> div(a, b - a) [ b >= a + 1 /\ a >= 1 ]
		(1, 1)    start(a, b) -> div(a, b)
	start location:	start
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 1 produces the following problem:
2:	T:
		(?, 1)    div(a, b) -> div(a, b - a) [ b >= a + 1 /\ a >= 1 ]
		(1, 1)    start(a, b) -> div(a, b)
	start location:	start
	leaf cost:	2

A polynomial rank function with
	Pol(div) = -V_1 + V_2
	Pol(start) = -V_1 + V_2
orients all transitions weakly and the transition
	div(a, b) -> div(a, b - a) [ b >= a + 1 /\ a >= 1 ]
strictly and produces the following problem:
3:	T:
		(a + b, 1)    div(a, b) -> div(a, b - a) [ b >= a + 1 /\ a >= 1 ]
		(1, 1)        start(a, b) -> div(a, b)
	start location:	start
	leaf cost:	2

Complexity upper bound a + b + 3

Time: 0.085 sec (SMT: 0.082 sec)