RFR: heapbase register can be allocated in compressed mode

[Liu, Xin]

Hi, Wei, 

Your change of aarch64.ad is definitely correct, but I feel that's the only place c2 refers to reg_class  heapbase_reg. 
If it's gone, is that possible we use R27 no matter what UseCompressedOops is? I read JDK-8234794 but I don't understand why that change involves in r27 and CompressedOop. 

Btw, I think you can just keep the assignment in MacroAssembler::reinit_heapbase() for simplicity.  Leaving a comment is better. 
I think Assignment of rheapbase is harmless. Only c2-generated code will use rheapbase and it's for locals. I still can pass hotspot-tier1 without your change of macroAssembler_aarch64.cpp.
Another argument is that your change of reinit_heapbase() makes verify_heapbase() more complex.  I don't know why it is commented out, but it looks quite easy to fix currently. 

Thanks,
--lx




On 4/13/20, 2:55 AM, "hotspot-compiler-dev on behalf of Kuai Wei" <hotspot-compiler-dev-bounces at openjdk.java.net on behalf of kuaiwei.kw at alibaba-inc.com> wrote:

    CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
    
    
    
    Hi Pengfei,
    
      Thanks for your help.
    
    Kuai Wei
    
    
    ------------------------------------------------------------------
    From:Pengfei Li <Pengfei.Li at arm.com>
    Send Time:2020年4月13日(星期一) 10:37
    To:蒯微(麦庶) <kuaiwei.kw at alibaba-inc.com>; Andrew Haley <aph at redhat.com>; hotspot compiler <hotspot-compiler-dev at openjdk.java.net>
    Cc:nd <nd at arm.com>
    Subject:RE: RFR: heapbase register can be allocated in compressed mode
    
    Hi Wei,
    
    > I can not push to tip branch. Can you help me to push it ? Or do we need
    > other reivew?
    
    Thanks for your enhancement patch. I ran full jtreg in the weekend and found no new failure after this change.
    
    We could also help push if there's no other review comments.
    
    --
    Thanks,
    Pengfei