IDEA: invariant-related gc hints

[Russell Lewis]

Say that you create a new variable on the heap.  You fill it up with 
data, then cast it to invariant because you know that the contents will 
never change again.

That object might become garbage, of course, but you know that nothing 
it points to can possibly become garbage until the root object (the one 
that you cast to invariant) becomes garbage.

It seems to me that this information would be useful to the GC.  Just 
brainstorming here...but certainly, we could say, "until object X is 
garbage collected, objects A,B,C,D should all get marked 'live' in every 
GC sweep."

Moreover, the GC knows that all accessible data is also invariant, at 
least until the root reference goes away, so none of those objects need 
to be re-swept during a mark-and-sweep pass.

This sort of knowledge might really improve performance on programs that 
had a large set of invariant data.

Other ideas?