Prediction unit that predicts branch history update information produced by multi-fetch block macro-op cache entry

Abstract

A prediction unit (PRU) predicts a sequence of fetch blocks (FBlks). Branch predictors provide, in response to a FBlk start address (FBSA) lookup in combination with branch history state (BHS), information to predict branch history update information (BHUI) produced by the FBlk. A buffer stores accumulated BHUJ. A macro-op (MOP) cache (MOC) includes an unrolled loop multi-FBlk MOC entry (ULP-MF-ME) built from previously observed occurrences of a loop on a loop body of FBlks. A hit on the ULP-MF-ME predicts a current occurrence of a loop on the loop body. In parallel, for N initial iterations of the loop, the PRU updates the BHS with BHUI produced by each FBlk of the N initial iterations using information provided in response to a lookup and accumulates each BHUI into the buffer. The PRU updates the BHS using the accumulated BHUI for subsequent iterations of the loop to avoid more lookups.