RFR(S): 8203215: IdealLoopTree::split_outer_loop leaves phi-nodes with only one input

[Nils Eliasson]

Hi,

I ran into an issue in the ZGC repo caused by optimizations encountering 
loop-phi-nodes having only one input. I tracked down the source of these 
to IdealLoopTree::split_outer_loop that is a part of beautify_loops.

This patch makes sure that the phis that may need a transform is 
processed after beautify_loops is completed, but before the loop tree is 
rebuilt.

Bug: https://bugs.openjdk.java.net/browse/JDK-8203215

Webrev: http://cr.openjdk.java.net/~neliasso/8203215/webrev.01/

Please review,

Nils