[9] RFR(XS) 8059780: SPECjvm2008-MPEG performance regressions on x64 platforms

[Dean Long]

By the way, do we know why the lcm change caused  a regression?  Is 
reordering the worklist
using pop() a design feature?

dl

On 10/31/2014 5:58 PM, Vladimir Kozlov wrote:
> I forgot to say that lcm.cpp changes were small part of 8052081 
> changes. The rest of changes will stay.
>
> Thanks,
> Vladimir
>
> On 10/31/14 5:55 PM, Vladimir Kozlov wrote:
>> http://cr.openjdk.java.net/~kvn/8059780/webrev/
>> https://bugs.openjdk.java.net/browse/JDK-8059780
>>
>> We found performance regression (3-5%) on x64 after changes 8052081 [1]
>> were pushed. It is caused by changes in lcm.cpp. Those changes were done
>> because Atom is in-order cpu and some benchmarks on Atom showed benefit
>> from these changes.
>>
>> But Atom is not our core platform and the regression is big.
>>
>> Backout changes made in lcm.cpp in jdk9 and 8u40 (8052081 was backported
>> to 8u40).
>>
>> We have RFEs to improve block's instructions order which may help both
>> platforms:
>>
>> https://bugs.openjdk.java.net/browse/JDK-6958833
>> https://bugs.openjdk.java.net/browse/JDK-7101232
>>
>> Tested with SPECjvm2008-mpegaudio.
>>
>> Thanks,
>> Vladimir
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8052081