Add new member functions to look back, or not.
Simplify code.
Don't invalidate the result of regs with no result.
Remove defunct note.
Avoid accessing computations for tokens that aren't fully set up.
Remove note.
Set call and use edges only if computation is local.
Clear ALL computations for WHNF regs.
Change some asserts, and a condition.
Expanded checking for used regs.
Remove old note.
Check more stringently.