Request for reviews (S): 7035946: Up to 15% regression on JDK 7 b136 vs b135 on specjvm2008.crypto.rsa on x64

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7035946/webrev

7035946: Up to 15% regression on JDK 7 b136 vs b135 on specjvm2008.crypto.rsa on x64

It is almost exact anti-delta of my changes in 7008866. I kept 
replace_parallel_iv() as separate method and added new TraceLoopOpts output.

I traced down the most of regression to my changes for "replace parallel 
induction variables" optimization in 7008866 fix. I replaced new nodes IGVN 
registration with immediate Ideal transformation. As result Split_If 
optimization reversed it back by doing spit through Phi and it prevents loop 
predicates (which follow Split_If) execute RCE. If local transformation in 
replace_parallel_iv() is not executed the created new code matches RCE shape: 
iv*ratio+(init2-init*ratio) where (init2-init*ratio) is loop invariant. And 
Split_If optimization does not execute spit through Phi for AddI nodes in 
Counted loops. Yes, a lot of hidden dependences.

An other part of regression came from always creation of new loop iteration Phi 
node. I was not able to find why it has regression affect. I returned code back 
to keep original Phi.

I do not see affect on refworkload benchmark after this fix.

Thanks,
Vladimir