RFR: SFX AddP cloning should check for dependent AddP explicitly

[Roman Kennke]

>> 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/
> 
> This also apparently fixes a lot of x86_32 CTW tests.

It looks ok to me.
I assume the failure case is rare enough that we can accept the register
mess-up there?

Roman