RFR(S): 8182867: [MVT] Escape analysis does not support value type return with reference field

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8182867
http://cr.openjdk.java.net/~thartmann/valhalla/vt_prototype/webrev.23/

Escape analysis fails with "missing allocation reference path" if a value type is returned as fields and contains a reference field. This is because the reference field value may be an allocation which is then connected to the ReturnNode. Fixed by adding a case for Op_Return and checking if we really return a value type with a reference field.

Thanks,
Tobias