RFR (S): 8003135: HotSpot inlines and hoists the Thread.currentThread().isInterrupted() out of the loop

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8003135/simple/webrev.00
31 lines changed: 16 ins; 6 del; 9 mod

In the IR produced by Thread.isInterrupted(Z)Z intrinsic it's possible 
to hoist the load of _interrupted flag out of the loop. The fix is to 
add a barrier to forbid such optimization.

Proposed fix is cleaner that [1] (no explicit memory state management).
The place for the barrier is deliberately chosen earlier than necessary 
and it blocks hoisting of some loop invariants when 
Thread.isInterrupted() is called in a loop. But I think it's a fair 
price since I don't think that Thread.isInterrupted(Z)Z performance in 
tight loops is critical.

If you prefer [1] let me know.

Also, cleaned up the code around a little.

Testing: failing test, manual (verified generated code), JPRT (in progress)

Thanks!

Best regards,
Vladimir Ivanov

[1] http://cr.openjdk.java.net/~vlivanov/8003135/fast/webrev.00