This refers to the machine's condition code register. It has no operands and may not have a machine mode. This is best on most machines, where each comparison sets the entire series of flags. To stand for a single flag that is the result of a single condition. This is useful on machines that have only a single flag bit, and in which comparison instructions must specify the condition to test.
Instructions can set the condition code implicitly.
On many machines, nearly all instructions set the condition code based on the value that they compute or store. See Condition Code . This is usually the preferable approach if only a small subset of instructions modify the condition code. This represents the machine's program counter. It has no operands and may not have a machine mode.