RFR: Eliminate LoadAddr edge from LoadReferenceBarrier

[Roland Westrelin]

> I've had some observations about Phis though: It seems we see the case
> fairly often that an input load gets split through phis, but the
> corresponding LRB is not. And then we sometimes get values on one path
> of the phi that would allow to optimize away the LRB, e.g. constants or
> allocations. Would it be worth to maybe also split the LRB through phis
> and enable to optimize them on paths that don't need them?

Splitting LRBs through phi makes sense to me. Then the only LRBs that
would be left would have a load as input, right? And figuring the
load address would be straightforward.

Roland.