Re: RFR: heapbase register can be allocated in compressed mode

[Kuai 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?

Thanks,
Kuai Wei


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From:Liu, Xin <xxinliu at amazon.com>
Send Time:2020年4月15日(星期三) 11:17
To:蒯微(麦庶) <kuaiwei.kw at alibaba-inc.com>; Pengfei Li <Pengfei.Li at arm.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, 
LGTM. 

Thanks.
--lx

From: Kuai Wei <kuaiwei.kw at alibaba-inc.com>
Reply-To: Kuai Wei <kuaiwei.kw at alibaba-inc.com>
Date: Tuesday, April 14, 2020 at 6:26 AM
To: "Liu, Xin" <xxinliu at amazon.com>, Pengfei Li <Pengfei.Li at arm.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 Xin and Pengfei,

  Thanks for your comments. I checked change in reinit_heapbase and decide to revert it since it's no harm to set rheapbase. I also made change in verify_heapbase in case someone want to enable this check again.

  The new patch is in http://cr.openjdk.java.net/~wzhuo/8242449/webrev.01/

  It has passed tiered 1 test without new failure.

Thanks,
Kuai Wei

------------------------------------------------------------------
From:Liu, Xin <xxinliu at amazon.com>
Send Time:2020年4月14日(星期二) 17:37
To:Pengfei Li <Pengfei.Li at arm.com>; 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, Pengfei and Kuai, 

Thanks to point out. 
Aarch64.ad does use MacroAssembler::encode_heap_oop, which refers to rheapbase.
That's why we can't use rheapbase as a GP register in C2. Got it. thanks!

--lx


 On 4/14/20, 1:39 AM, "Pengfei Li" <Pengfei.Li at arm.com> wrote:

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    Hi Xin,

    > I read JDK-8234794 but I don't understand why that change involves in r27
    > and CompressedOop.

    JDK-8234794 is the metaspace reservation fix. It also simplifies the encoding/decoding of compressed class pointers. Before that patch, r27 is used for both compressed oops and compressed class pointers. At that time we have to consider if r27 is allocatable if compressed class pointers is on. But after that patch, r27 is for compressed oops only. That's why I could simplify my JDK-8233743 patch after JDK-8234794 was merged.

    --
    Thanks,
    Pengfei