RFR(S): 8069191: moving predicate out of loops may cause array accesses to bypass null check

[Roland Westrelin]

>> So I guess the test in compile.cpp could simply be n->in(0) != NULL
> 
> That would be safer I think. 

I’m making that change and the ensure_control_or_add_prec() change as well and pushing this.

Thanks for the suggestions, discussion and review.

Roland.