Head and tail pointer manipulation in a first-in-first-out issue queue

A system comprising:

• a memory having computer readable instructions;
• and
• one or more processors for executing the computer readable instructions, the computer readable instructions controlling the one or more processors to perform operations comprising:
• tracking relative ages of instructions in a first-in-first-out (FIFO) issue queue of an out-of-order (OoO) processor, the FIFO issue queue configured to add instructions to the issue queue in a sequential order and to remove instructions from the issue queue in any order including a non-sequential order, the tracking comprising:
• maintaining a head pointer to a location of an entry allocated to an oldest instruction in the issue queue, wherein upon removal of the oldest instruction from the issue queue, the head pointer is updated to point to a next sequential location in the issue queue;
• maintaining a tail pointer to a location of a last instruction added to the issue queue, wherein upon addition of a new instruction to the issue queue, the tail pointer is updated to point to a next sequential location in the issue queue and the new instruction is inserted at the next sequential location;
• periodically determining whether the tail pointer is pointing to a location that includes an instruction for which continued tracking is needed;
• and
• updating the tail pointer to point to a previous sequential location in the issue queue based at least in part on determining that the tail pointer is not pointing to a location that corresponds to an instruction that needs continued tracking.

A computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform operations comprising:

• tracking relative ages of instructions in a first-in-first-out (FIFO) issue queue of an out-of-order (OoO) processor, the FIFO issue queue configured to add instructions to the issue queue in a sequential order and to remove instructions from the issue queue in any order including a non-sequential order, the tracking comprising:
• maintaining a head pointer to a location of an entry allocated to an oldest instruction in the issue queue, wherein upon removal of the oldest instruction from the issue queue, the head pointer is updated to point to a next sequential location in the issue queue;
• maintaining a tail pointer to a location of a last instruction added to the issue queue, wherein upon addition of a new instruction to the issue queue, the tail pointer is updated to point to a next sequential location in the issue queue and the new instruction is inserted at the next sequential location;
• periodically determining whether the tail pointer is pointing to a location that includes an instruction for which continued tracking is needed;
• and
• updating the tail pointer to point to a previous sequential location in the issue queue based at least in part on determining that the tail pointer is not pointing to a location that corresponds to an instruction that needs continued tracking.