Proposal for reference annotations

[Richard Kenner]

    Where are you going to put this annotation?  If on the node, then
    you're no different than the current state that Mark hates.  

There's currently a field in each expression for an annotation.  It's
not used for ARRAY_REF and COMPONENT_REF.

Moreover, this is no longer just used for the new fields, but for
a path towards being able to lower the level of references.

    [1] get_expr_operands finds addresses of operands, and optimizers
    assume that they can replace operands just by storing to the address.
    I suppose you could share iff everything is constant.

Yes, that's indeed what I meant.  They wouldn't likely be the same anyway
if they were variable.