RFR(M): 8229495: SIGILL in C2 generated OSR compilation

[Roland Westrelin]

Hi Patric,

> I would like to ask for help to review the following change/update:
>
> Issue: https://bugs.openjdk.java.net/browse/JDK-8229495
> Webrev: http://cr.openjdk.java.net/~phedlin/tr8229495/

Running compiler/loopopts/IterationSplitPredicateInconsistency.java with
-XX:LoopUnrollLimit=1024 and your patch causes a crash:

#  Internal Error (/home/roland/jdk-jdk/src/hotspot/share/opto/loopnode.cpp:4016), pid=4004890, tid=4004904
#  assert(!had_error) failed: bad dominance

It doesn't crash without. Loop unrolling heuristics must have changed
recently. I don't see as much unrolling as I used to when I worked on
this.

Roland.