The invention provides a method for executing instructions. The method includes dispatching and executing a first and second plurality of instructions in a portion of a pipeline without first determining whether stages of the portion of the pipeline are ready. The method further includes determining if an execution problem is encountered and replaying the first plurality of instructions in response to determining that the first plurality of instructions encountered an execution problem. The invention also provides a processor pipeline. The processor pipeline includes a front end to fetch a plurality of instructions for execution and a back end to execute the plurality of instructions fetched by the front end. The back end includes a retirement stage to determine if an instruction had an execution problem. The back end is non-stallable. The processor pipeline also includes a channel to send an indication that the instruction encountered an execution problem from the retirement stage to a replay point of the pipeline from which the instruction may be re-executed.
This patent application is a continuation-inpart application of U.S. patent application Ser. No. 08/998,341, filed Dec. 24, 1997, now U.S. Pat. No. 6,076,153.
An executed first instruction having a first logical operand as a destination is retired. A register assigned to the first logical operand is identified to back out of an architectural state. The identifying may be performed when an executed second instruction having a second logical operand as a destination is ready to retire or is retired. The register may be assigned to a third logical operand for an instruction to be executed.
A decentralized exception processing system includes a plurality of local exception units. Each local exception unit is coupled to process local exception signals from one or more processing resources that are proximate to it. Each local exception unit generates local commit signals, using order information for the instruction in an issue group and any local exception signals it receives. The local commit signals are combined to generate a global commit signal for each instruction in the issue group. Local exception signals are collected at a selected one of the local exception units and processed to generate a global exception unit. The selected local exception unit resteers control of the processing resources to an exception handler associated with the global exception unit.
Rescheduling multiple micro-operations in a processor using a replay queue. The processor comprises a replay queue to receive a plurality of instructions and an execution unit to execute the plurality of instructions. A scheduler is coupled between the replay queue and the execution unit. The scheduler speculatively schedules instructions for execution and dispatches each instruction to the execution unit. A checker is coupled to the execution unit to determine whether each instruction has executed successfully. The checker is also coupled to the replay queue to communicate to the replay queue each instruction that has not executed successfully.
When a branch misprediction in a pipelined processor is discovered, if the mispredicted branch instruction is not the last uncommitted instruction in the pipelines, older uncommitted instructions are checked for dependency on a long latency operation. If one is discovered, all uncommitted instructions are flushed from the pipelines without waiting for the dependency to be resolved. The branch prediction is corrected, and the branch instruction and all flushed instructions older than the branch instruction are re-fetched and executed.
The present invention is related to a processor capable of speculatively executing an instruction having a data dependence upon a preceding instruction in order to improve the efficiency of dynamically scheduling instructions. The reissue of instructions is possible without lowering the efficiency of the instruction scheduling process by dividing the function of scheduling instructions and the function of the reissue of instructions.
