Request for reviews (XS): 6782820: Server VM fails with "unhandled implicit exception in compiled code"

[Vladimir Kozlov]

http://webrev.invokedynamic.info/kvn/6782820/index.html

Fixed 6782820: Server VM fails with "unhandled implicit exception in compiled code"

Problem:
Regression introduced by the fix for 6773078.
LoadKlass node without control edge moved above the oop NULL check.
Note, during parsing LoadKlass node's control edge is not set
because it will be set during CCP phase when a CastPP is removed.

Solution:
Restore the code which sets a control edge for a klass load node.
Add the code which sets a control edge for a klass narrow load
node instead of DecodeN node to fix 6773078 bug.
Add the assert to check that a DecodeN node does not have
a control edge (for 6773078).

Reviewed by:
Fix verified (y/n): y, both tests from 6773078 and 6782820

Other testing:
JPRT, CTW (with -XX:+UseCompressedOops)