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?

Roman