[gsg]

Note that you don't need a dumb compiler, register pressure, or an instruction with physical register constraints to require a copy. Two-address instructions suffice: simply have a register for the first operand that contains a value that is used later. A copy is required to preserve the value stomped by the mutating instruction.

In any case I believe the point of the GP is that any necessary copy can be done by going through memory, so register-register moves can be dispensed with where minimalism is the goal.