We present a general way of making use of may- and must-alias information
to achieve flow-sensitive type systems that allow for flow-sensitivity on
the heap. In particular, we show how may-alias information can be used for
a limited form of flow-sensitivity — structural weakening — that allows
type changes on the heap that are compatible with the subtype hierarchy.

Further, we show how the combination of may- and must-alias information
can be used to achieve strong updates, i.e., type changes on the heap that
are not compatible with the subtype hierarchy, resembling the typical type
rule for updates of variables in flow sensitive type systems.

This work has been enabled by the use of our plugin framework — a framework
for parameterizing type systems over the results of abstract interpretations —
that allows us to abstract away from the computation of the alias information.
In addition, our successful use of the plugin mechanism to extract both may-
and must-alias information shows its strength.