RFR (XS) 8041351: Crash in src/share/vm/opto/loopnode.cpp:3215 - assert(!had_error) failed: bad dominance

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/8041351/webrev
https://bugs.openjdk.java.net/browse/JDK-8041351

Missed is_mem() check when we collect load nodes in 
SuperWord::co_locate_pack(). As result a Phi node was incorrectly put on 
the list and its edge was wrongly modified producing bad graph.

Thanks,
Vladimir