Scalable dependency matrix with wake-up columns for long latency instructions in an out-of-order processor

Abstract

Aspects of the invention include tracking dependencies between instructions in an issue queue. The tracking includes, for each instruction in the issue queue, tracking a specific dependency on each of a threshold number of instructions most recently added to the issue queue prior to the instruction, tracking as a single group a dependency of the instruction on any instructions in the issue queue that are not in the threshold number of instructions, and tracking for each source register used by the instruction an indicator of whether its content is dependent on results from an instruction in the single group that has not finished execution. Based at least in part on detecting removal from the issue queue of an instruction in the single group that has issued and not finished execution, the method includes indicating that the instruction is ready for issuance or waiting for a notification that the removed instruction has finished execution.