RFR(S): 8238385: CTW: C2 (Shenandoah) compilation fails with "Range check dependent CastII node was not removed"

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8238385/webrev.00/

Barrier expansion modifies the graph in a way that causes 2 subsequent
if to become candidate for folding as a single unsigned test. This
causes the creation of a range check CastII at a point in the
compilation process where none is expected to be created: they are
removed after loop opts but as part of barrier expansion we run an extra
pass of loop opts. The fix simply removes the ones created during
barrier expansion if any the same way they are removed are loop opts.

Roland.