Out-of-order processor that reduces mis-speculation using a replay scoreboard

Abstract

A pipelined processor includes a dependency scoreboard that tracks dependency or replay of instructions capable of executing out-of-order. Early instructions are termed “producers” that produce data for later dependent instructions. The subsequent instructions are “consumers” that consume the data produced by the producer instructions. The dependency scoreboard is a table of storage cells that tracks producers and consumers and designates whether a particular instruction is dependent on a producer. Active instructions are allocated storage elements for all active instructions. For example, a dependency scoreboard for tracking N active instructions will have N dependency storage cells for ones of the N active instructions. The storage cells for an active instruction may be set for each active instruction that is a “producer” instruction and all levels of dependency are tracked in each cycle. A consumer instruction will have storage cells set not only for all producer instructions, but also for all producers of all producer instructions. The multiple-level dependency tracking technique reduces the number of incorrect speculative instruction executions.

Dependencies are inferred from the claim text.