RFR(S): 8161652 Crash with assert(ft == _type) failed in PhiNode::Value()

[Roland Westrelin]

> Changes seems fine but conditions in code are difficult to
> follow. Please, add comments.

Thanks for looking at this, Vladimir. Here is a new webrev with extra
comments:

http://cr.openjdk.java.net/~roland/8161652/webrev.01/

Roland.