RFR: 6869327: Add new C2 flag to keep safepoints in counted loops.

[Vladimir Kozlov]

Looks good.

Did you run it in JPRT?

Add -XX:+IgnoreUrecognizedVMOptions flags to the list of flags (put it 
first) in the test because UseCountedLoopSafepoints is only C2 flag and 
TieredCompilation is Server VM flag.

Thanks,
Vladimir

On 11/27/15 5:01 AM, Andreas Eriksson wrote:
> Hi,
>
> Please review this change that adds a flag to keep a safepoint in counted loops.
>
> Currently C2 removes safepoints in counted loops.
> This can force other safepointing threads to wait for the counted loop thread for long periods of time.
> This change adds a flag, UseCountedLoopSafepoints, which keeps a safepoint in the loop. Its default value is false.
>
> Bug: 6869327: Add new C2 flag to keep safepoints in counted loops.
> https://bugs.openjdk.java.net/browse/JDK-6869327
>
> Webrev: http://cr.openjdk.java.net/~aeriksso/6869327/webrev.00/
>
> Thanks,
> Andreas