Request for reviews (XS): 6883468 for HS16 and HS17

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6883468/webrev.00

Fixed 6883468: C2 compiler enters infinite loop in PhaseIterGVN::transform

Problem:
There is ideal transformation ping-pong between AddPNode::Ideal()
for raw pointer and CastX2PNode::Ideal() transformation which
reconstruct raw AddP node again with the same input SubI(#0, Phi).

Solution:
Avoid transformation in CastX2PNode::Ideal() if input is SubI node
and its in(1) is ConI(#0).

Reviewed by:

Fix verified (y/n): y, by customer

Other testing:
JPRT