[9] RFR (XXS): 8173404: C2: wrong nmethod dependency can be recorded for CallSite.target

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8173404/webrev.00
https://jbs.oracle.com/browse/JDK-8173404

When C2 constant folds mutable call site target, it records a dependency 
on the value, but repeatedly reads the value from the call site. Since 
there's a race between compilation thread and application thread doing 
CallSite.setTarget(), it's possible to end up with different values used 
as the constant and recorded in the dependency.

The fix is to reuse target constant when recording the dependency.

Testing: regression test, RBT (in progress)

Thanks!

Best regards,
Vladimir Ivanov