RFR(S) 8209651: better TLS poll for x64 C2

[Vladimir Kozlov]

Looks good.

Thanks,
Vladimir

On 8/21/18 1:18 PM, dean.long at oracle.com wrote:
> https://bugs.openjdk.java.net/browse/JDK-8209651
> http://cr.openjdk.java.net/~dlong/8209651/webrev/
> 
> This change allows C2 to use any available register when doing a thread-local GC poll.
> 
> dl
>