possible gcse failure: not able to eliminate redundant loads

[Robert Dewar]

> i.e. the dereference is protected by a conditional.  Thus
> we can't hoist the dereference past the conditional (and
> thence out of the loop that started this thread).


it is interesting to note that the IBM compiler group decided that
ensuring that null could be safetly dereferenced, and hence such
references can be hoisted etc, was a major win in C code efficiency.