Request for reviews (S): 6682236: C2 hits ideal nodes limit during IGVN optimization with EA

[Vladimir Kozlov]

I want this for HS12 (if approved).

http://webrev.invokedynamic.info/kvn/6682236/index.html

Fixed 6682236: C2 hits ideal nodes limit during IGVN optimization with EA

Problem:
I thought I could relay on LoadNode::Identity() call during
IGVN optimization to avoid infinite generation of value Phi
for an instance field loads. But in the failed case it does
not happen since the new Load node (from spit through phi)
is replaced with a new value Phi again during next invocation
of LoadNode::Ideal().

Solution:
Add the check into LoadNode::Ideal() to not generate
a new value Phi if LoadNode::Identity() will find a value.

Reviewed by:
Fix verified (y/n): y, failed test cases.

Other testing:
JPRT, CTW, NSK tests