Request for reviews (S): 6819176: Compressed oops causes assert(n != 0L,"Bad immediate dominator info.")

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6819176/webrev.00

Fixed 6819176: Compressed oops causes assert(n != 0L,"Bad immediate dominator info.")

Problem:
PhiNode::Ideal has very unsafe optimization which tries to move
DecodeN through phi down in a hope that it could be consumed by
an address expression or debug info. This optimization is incorrect
since DecodeN is the type node and its type depends on the position
in the graph. The assert is caused by this.

Solution:
Remove incorrect optimization.

Reviewed by:

Fix verified (y/n): y, bug test

Other testing:
JPRT