1. Let's suppose that an instruction requires one of its arguments to
be in a particular register. For example: instruction Op requires
its first argument to be in register R1. Modify graph coloring
register allocation to take this into account.
2. Modify graph coloring register allocation to enable one to ensure
that instructions that require a register pair for some operand or result
are assigned a pair.
3. Problem 17.1 in Muchnick
4. Problem 17.5 in Muchnick