compound assignment operators are split during lowering.

<<<

main = fun () {
    var x int = 0
    x += 1
    x *= 2
    x -= 3
}

>>>

(unit
	(types
		(type 0 int primitive)
		(type 1 uint primitive)
		(type 2 bool primitive)
		(type 3 string primitive)
		(type 4 float primitive)
		(type 5 byte primitive)
		(type 6 ascii primitive)
		(type 7 void primitive))
	(functions
		(function 0 main main (returns (ref void)) (block
			(declaration x (ref int) (initializer (expr 0)))
			(assign (expr (name x)) (expr (binary + (expr (name x)) (expr 1))))
			(assign (expr (name x)) (expr (binary * (expr (name x)) (expr 2))))
			(assign (expr (name x)) (expr (binary - (expr (name x)) (expr 3))))
		)))
	(emission_order 0 1 2 3 4 5 6 7))