System and method for instruction unwinding in an out-of-order processor

Abstract

A system and corresponding method unwind instructions in an out-of-order (OoO) processor. The system comprises a mapper. In response to a restart event causing at least one instruction to be unwound, the mapper restores a present integer mapper state and present floating-point (FP) mapper state, used for mapping instructions, to a former integer mapper state and former FP mapper state, respectively. The mapper stores integer snapshots and FP snapshots of the present integer and FP mapper state, respectively, to expedite restoration to the former integer and FP mapper state, respectively. Access to the FP snapshots is blocked, intermittently, as a function of at least one FP present indicator used by the mapper to record presence of FP registers used as destinations in the instructions. Blocking the access, intermittently, improves power efficiency of the OoO processor.