RFR(XS): 8245714: "Bad graph detected in build_loop_late" when loads are pinned on loop limit check uncommon branch

[Roland Westrelin]

https://bugs.openjdk.java.net/browse/JDK-8245714
http://cr.openjdk.java.net/~roland/8245714/webrev.00/

This triggers when data nodes are pinned on the uncommon trap path of a
predicate. When a new predicate is added, a region is created to merge
the paths comming from the place holder and the new predicate. Data
nodes pinned on the uncommon path for the place holder are then updated
to be pinned on the new region. That logic updates the control edge but
not the control that loop opts keep track of. This causes a crash with
the test case of the webrev where the predicate is a loop limit check.

Roland.