RFR (S) 8229016: C2 scalarization crashes with assert(node->Opcode() == Op_CastP2X) failed: ConvP2XNode required

[Aleksey Shipilev]

Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8229016
  https://hg.openjdk.java.net/jdk/jdk/rev/1d2ea8db7083

Patch applies cleanly, but the new test still crashes! And there is still 11.0.6-oracle backport
recorded. Tobias H says we need another line from here:
  https://hg.openjdk.java.net/jdk/jdk/rev/e3d79743f57d#l13.7

After that, new test passes. We could consider backporting the entire JDK-8212243, but it does not
apply cleanly with lots of conflicts, and resolving those would take a lot of time. I believe
picking up that one-liner fix is a better idea.

So, full 11u webrev:
  https://cr.openjdk.java.net/~shade/8229016/webrev.11u.01/

Testing: new test, tier1

-- 
Thanks,
-Aleksey