[aarch64-port-dev ] RFR(M): 8233743: AArch64: Make r27 conditionally allocatable

[Pengfei Li (Arm Technology China)]

Hi Andrew,

> Why do you think so? UseCompressedOops doesn't usually need r27.

If I understand correctly, your point is to allocate r27 as well for some scenarios when UseCompressedOops or UseCompressedClassPointers is on. This optimization is much more aggressive and I will try to do it carefully.

> We should have a flag which is set if the search for nicely-aligned 
> memory is successful, and then you can use that flag to determine if r27 is needed.

In which file do you think we should add the flag? Can we just check the value of CompressedKlassPointers::base() in reg_mask_init() ?

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Thanks,
Pengfei