[lworld] RFR(S): 8220666: [lworld] Nullability information is lost at checkcast in ciTypeFlow

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8220666
http://cr.openjdk.java.net/~thartmann/8220666/webrev.00/

When checkcasting from .box to .val and back .box we should keep track of the information that the
value can never be null.

Thanks,
Tobias