# Add the `block` to the dominance frontier of this block
	fun add_df(block: BasicBlock)
	do
		dominance_frontier.add(block)

		# Add this block recursively in super-blocks to compute the iterated
		# dominance frontier
		for successor in block.successors do
			# If this successor has not already been add to the dominance frontier
			if not dominance_frontier.has(successor) then
				add_df(successor)
			end
		end
	end