4. Components of "restricted data flow" execution

4.1 Ordered instruction termination

To allow for clean exceptions, instructions must terminate strictly in program order, as they would in a strictly sequential processor. In-order termination is implemented by a reorder buffer (ROB), which functions as a circular buffer. When an instruction is started, it is allocated an entry in the ROB that will contain the instruction's execution status. An instruction is only completed and removed from the ROB if it is guaranteed (no more speculative execution, no more possibility of interruptions) and all preceding instructions in the program's sequential order are completed from the point of view...