RFR: SFX AddP cloning should check for dependent AddP explicitly

[Aleksey Shipilev]

CTW tests fail with sh/jdk with the assert here:
 1545         assert(addr2->Opcode() == Op_AddP, "expected");

I believe we should instead check for the shape of the graph explicitly here:
  http://cr.openjdk.java.net/~shade/shenandoah/sfx-hard-arr/webrev.01/

Testing: CTW tests, hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey