Request for reviews (s): 6710487: More than half of JDI Regression tests hang with COOPs in -Xcomp mode

[Vladimir Kozlov]

Thanks to Tom for finding the cause of the problem.

I will move webrev to invokedynamic webpage tomorrow.
http://analemma.sfbay.sun.com/net/jaberwocky/export/home2/work2/hg/6710487/webrev

Fixed 6710487: More than half of JDI Regression tests hang with COOPs in -Xcomp mode

Problem:
DecodeNNode::decode() and EncodePNode::encode() contains
Identity transformation (may return a preexisting ideal node)
which could create a circle during gvn transformation.

Solution:
Don't return a preexisting ideal node when a new node expected.
I think it is OK to return a preexisting node if it used as
an input edge for an other new node (for example, in StoreNode::make()).

Reviewed by:
Fix verified (y/n): y

Other testing:
JPRT