[8u] RFR: 8134739: compiler/loopopts/superword/TestVectorizationWithInvariant crashes in loop opts

[Roland Westrelin]

> Backport looks good.

Thanks for reviewing it.

> So the only conflict in jdk8u-dev right now is different "phi()" in loopnode.hpp, and superword.cpp
> actually applies without conflicts, right?

Right.

Roland.