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

[Vladimir Kozlov]

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