LRB midpath code quality

[Roman Kennke]

>>> Well yes, an implicit null-check would be good. It would never fire,
>>> because if the value is null, it would blow up earlier in the cset
>>> check. Or am I missing something?
>>
>> I suppose PhaseCFG::implicit_null_check() doesn't recognize the barrier
>> load as a candidate for implicit null checks for some reason.
> 
> Yes, maybe.
> 
> But can you explain to me why it should be needed at all? If a
> dominating (implicit?) null-check before the in-cset-check should catch
> all nulls on that path already? Why does it matter?

Also, I don't think we want to generate an NPE/SEGV on that path. We
want to skip a bunch of stuff if the value is NULL.

Roman