RFR(M): 8233743: AArch64: Make r27 conditionally allocatable

[dean.long at oracle.com]

Hi Pengfei,

I took a quick look and didn't notice any problems.  Nice work! This 
seems to match the x64 approach, however please get other reviews.

dl

On 11/13/19 1:55 AM, Pengfei Li (Arm Technology China) wrote:
> Hi,
>
> JBS: https://bugs.openjdk.java.net/browse/JDK-8233743
> Webrev: http://cr.openjdk.java.net/~pli/rfr/8233743/webrev.00/
>
> This is a follow-up patch of JDK-8217909[1] to make the AArch64 register
> r27 allocatable when CompressedOops and CompressedClassPointers are both
> turned off.
>
> Below changes have been made:
> - Massage the RegMask(s) in reg_mask_init() at C2 initialization and
> remove r27 from some of the masks conditionally to make it allocatable.
> - Also make r29 conditionally reserved in this similar way.
> - Make r29 allocatable for pointers as well as integers.
> - Replace an rheapbase use to rscratch1 in AArch64 ZGC.
> - Revert JDK-8231754[2] which makes r27 always reserved in JVMCI.
>
> This patch aligns with the implementation in [1] which makes the x86_64
> r12 register allocatable. Please let me know if I have missed anything
> for AArch64.
>
> Tests:
> Full jtreg with default options and extra options "-XX:-UseCompressedOops
> -XX:+PreserveFramePointer". No new failure is found.
>
> [1] https://hg.openjdk.java.net/jdk/jdk/rev/48b50573dee4
> [2] https://hg.openjdk.java.net/jdk/jdk/rev/d068b1e534de
>
> --
> Thanks,
> Pengfei
>