# Determines wich variables definitions reach each statement.
class ReachingDefsAnalysis
	super ForwardAnalysis

	redef type FLOW: FlowHashSet[VarDef]

	# New initial flows are empty (conservative analysis).
	redef fun new_initial_flow do return new FlowHashSet[VarDef]

	# New initial flows for methods contains the parameters.
	redef fun new_initial_method_flow(n) do
		var flow = new_initial_flow
		var n_signature = n.n_signature
		if n_signature == null then return flow
		for n_param in n_signature.n_params do
			var variable = n_param.variable
			if variable == null then continue
			flow.add(new VarDef(variable, n_param.location))
		end
		return flow
	end

	# Perform set union (used for **some path** analysis).
	redef fun merge(s1, s2) do return s1.flow_union(s2)

	redef fun visit(n) do n.accept_reaching_defs(self)

	# Generate a new variable definition in the `current_outset`.
	fun gen(variable: Variable, location: Location) do
		current_outset.add(new VarDef(variable, location))
	end

	# Kill a variable definition in the `current_outset`.
	fun kill(variable: Variable) do
		for vardef in current_outset.to_a do
			if vardef.variable == variable then current_outset.remove(vardef)
		end
	end

	redef fun pretty_print do
		for node, outset in outsets do
			if outset.is_empty then continue
			var values = outset.to_a
			default_comparator.sort(values)
			print "{node.location.line_end}: {values.join(", ")} out of {node.class_name}"
		end
	end
end