Branch target cache and method for efficiently obtaining target path instructions for tight program loops

摘要

A processor that efficiently obtains target path instructions in the presence of tight program loops includes at least one execution unit for executing instructions and instruction sequencing logic that supplies instructions to the at least one execution unit for execution. The instruction sequencing logic includes an instruction fetch buffer and a branch prediction unit including a branch target cache. In response to prediction of a branch instruction as taken, the branch target cache causes multiple copies of a target instruction group to be loaded into the instruction fetch buffer under the assumption that the branch instruction is a member of the target instruction group. Thereafter, the branch target cache causes all but one of the multiple copies to be canceled from the instruction fetch buffer prior to dispatch if the branch instruction does not belong to the target instruction group. Thus, the branch target cache can meet the instruction fetch cycle time of the processor even for the worst case condition in which the branch instruction is within the target instruction group.