RFR(S): 8155729: C2: Skip transformation of LoadConP for heap-based compressed oops

[Doerr, Martin]

Hi Vladimir,

thank you very much for sponsoring and for the new bug for the other platforms.

Best regards,
Martin

-----Original Message-----
From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com] 
Sent: Dienstag, 4. Oktober 2016 19:13
To: Doerr, Martin <martin.doerr at sap.com>; hotspot-compiler-dev at openjdk.java.net; Andrew Haley (aph at redhat.com) <aph at redhat.com>
Subject: Re: RFR(S): 8155729: C2: Skip transformation of LoadConP for heap-based compressed oops

Looks good. I will sponsor it.

I filed RFE to look on other platforms in JDK 10:

https://bugs.openjdk.java.net/browse/JDK-8167114

Thanks,
Vladimir

On 10/4/16 1:53 AM, Doerr, Martin wrote:
> Hi,
>
> after the bug was approved for 9, I'd like to ask for review of the new webrev:
> http://cr.openjdk.java.net/~mdoerr/8155729_LoadConP/webrev.01/
>
> It is modified to affect only PPC64 and AARCH64.
>
> Thanks and best regards,
> Martin
>
>
> -----Original Message-----
> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
> Sent: Freitag, 29. April 2016 19:05
> To: Doerr, Martin <martin.doerr at sap.com>; hotspot-compiler-dev at openjdk.java.net
> Subject: Re: RFR(S): 8155729: C2: Skip transformation of LoadConP for heap-based compressed oops
>
> Looks good to me. We need corresponding changes in our closed code too.
>
> Thanks,
> Vladimir
>
> On 4/29/16 7:06 AM, Doerr, Martin wrote:
>> Hi,
>>
>>
>>
>> I have opened a new bug for the proposal which was discussed in thread 8154826.
>>
>> The summary is:
>>
>>
>>
>> C2's final graph reshaping performs the following transformation:
>>
>> Original pattern: LoadConP + Storage access
>>
>> Transformed pattern: LoadConN + DecodeN heap-based + Storage access
>>
>>
>>
>> This seems to be fine for simpler compressed oops mode. It also seems to be fine on x86 which can match the decoding
>> into the operand of the Storage access instruction.
>>
>>
>>
>> Other platforms should better skip the transformation:
>>
>> -PPC can load the ConP from constant pool. Decoding takes a lot of instructions, because the heap base needs to get loaded.
>>
>> -SPARC can use that as well.
>>
>> -aarch64: LoadConN+DecodeN has a higher latency than LoadConP.
>>
>>
>>
>> We can always skip the transformation in heap-based compressed klass mode. Matching DecodeNKlass as operand is currently
>> not implemented.
>>
>>
>>
>> Webrev is here:
>>
>> http://cr.openjdk.java.net/~mdoerr/8155729_LoadConP/webrev.00/
>>
>>
>>
>> Please review. I will also need a sponsor, please.
>>
>>
>>
>> Best regards,
>>
>> Martin
>>
>>
>>