US 6,189,089 B1 · Apparatus and method for retiring instructions in excess of the number of accessible write ports

Abstract

A superscalar microprocessor includes a reorder buffer to correctly handle dependency checking and multiple updates to the same destination. The reorder buffer stores instructions in program order, and retires instructions that have executed and the results obtained. When a instruction is retired, the results of the instruction are stored and the memory space in the reorder buffer is deallocated. The results of the retired instructions are stored to a register file via a retire bus. If the results of two or more retired instructions output to the same register in the register file, then only the newest instruction, the later instruction in the original program sequence, is stored to the program register. The register file has a plurality of write ports for the transfer of data via the retire bus. If two retired instructions output to the same register, then a write port is not utilized. The retire window is the number of instructions monitored for retirement. The present invention advantageously increases the size of the retire window. Accordingly, if two or more retired instructions output to the same register, an additional instruction from the retire window can be retired. The additional instruction utilizes the write port not used by the older of the instructions that output to the same register. Thereby, the reorder buffer is emptied at a faster rate and causes less instruction dispatch stalls.

Claims20

Dependent claims

A reorder buffer comprising:

an instruction storage device, wherein said instruction storage device is configured to store instruction results corresponding to a plurality of instructions, and wherein each of said plurality of instructions includes a register operand that corresponds to a register in a register file having a plurality of write ports;
and
a control unit coupled to said instruction storage device, wherein said control unit is configured to select a subset of said plurality of instructions for retirement during a clock cycle;
wherein a number of instructions retired during said clock cycle exceeds a total number of said plurality of write ports of said register file.

1 more element

An apparatus for retiring instructions, comprising:

a register file, wherein said register file includes a plurality of registers, and wherein said register file includes a plurality of write ports;
and
a reorder buffer coupled to said register file, wherein said reorder buffer includes:
an instruction storage device, wherein said instruction storage device is configured to store instruction results corresponding to a plurality of instructions, and wherein each of said plurality of instructions includes a register operand that corresponds to one of said plurality of registers;
and
a control unit coupled to said instruction storage device, wherein said control unit is configured to select a subset of said plurality of instructions for retirement during a clock cycle;
wherein a number of instructions in said subset exceeds a total number of said plurality of write ports of said register file.

4 more elements

Dependencies are inferred from the claim text.

Apparatus and method for retiring instructions in excess of the number of accessible write ports

Life of this patent

Apparatus and method for retiring instructions in excess of the number of accessible write ports

Life of this patent

Abstract

Claims20