RFR: heapbase register can be allocated in compressed mode

[Pengfei Li]

Hi Wei,

> Thanks for all feedback. I think this patch has enough review and can be merged.
> 
> Hi Pengfei,
>
>  I need help to push it. Could you help to merge it?

I'm not a reviewer, and not sure whether your updated webrev.01 [1] still requires an official reviewer to confirm.

Maybe Andrew Haley or other AArch64 reviewers can help?

[1] http://cr.openjdk.java.net/~wzhuo/8242449/webrev.01/

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Thanks,
Pengfei