Importance

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Abstract

A branch processing unit (BPU) is used, in an exemplary embodiment, in a superscalar, superpipelined microprocessor compatible with the x86 instruction set architecture. The BPU includes a return stack for call/returns, including return stack pointer repair in the case of the failure of a call/return to confirm (decode) or resolve. Return stack control logic maintains a return stack pointer, incrementing and decrementing the return stack pointer respectively for call/return pairs that hit in the target cache--in addition, the return stack control logic maintains two additional stack pointers used for repair: (a) a confirmation pointer that is incremented when a call is decoded and decremented when a return is decoded; and (b) a resolution pointer that is incremented when a call resolves, and decremented when a return resolves. If a call/return pair that hits in the target cache is not confirmed, the return stack control logic selectively repairs the return stack pointer by replacing it with the confirmation pointer, while if a call/return pair that hits in the target cache does not resolve, the return stack control logic selectively repairs the return stack pointer by replacing it with the resolution pointer.

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