RFR(S): 8219448: split-if update_uses accesses stale idom data

[Nils Eliasson]

Hi,

This patch fixes some of the idom updates in split-if. The updates are 
there, but at the end, which is to late. They need to be correct when 
handling the uses of the region being split. When the stale idom is seen 
we end up asserting or crashing.

https://bugs.openjdk.java.net/browse/JDK-8219448

http://cr.openjdk.java.net/~neliasso/8219448/webrev.01/

Please review,

Nils Eliasson