RFR: 8152110: Stabilize C2 loop optimizations

[jamsheed]

Hi,

request for review

jbs: https://bugs.openjdk.java.net/browse/JDK-8152110

webrev: http://cr.openjdk.java.net/~jcm/8152110/webrev.00/

the patch make sure that, there is no heavy loop optimizations performed 
after opaque nodes removal. Only simple loop optimizations like

converting single iteration loops to normal code/ removing empty loops 
are performed after opaque node removal.

this change is done based on discussion here [1]


mach5/perf report attached in jbs

Best regards,
Jamsheed


[1]

http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2016-February/021353.html 

http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2016-March/021967.html