1. A method for encoding an instruction to save processor core register values, comprising: encoding in a first field of the instruction whether a first value in a first register is to be saved at one of a first location or a second location in a stack memory; if, based on the encoding in the first field of the instruction, the first value is to be saved as a value associated with storage already allocated on the stack, saving the first value in the stack memory at the first location having an address value equal to A plus a second value in a second register; and if, based on the encoding in the first field of the instruction, the first value is to be saved as a value associated with storage not yet allocated on the stack, saving the first value at the second location in the stack memory having an address value equal to B plus the second value in the second register, wherein only one of A and B is a positive number.