Global weak pattern history table filtering

摘要

Embodiments relate to global weak pattern history table (PHT) filtering. An aspect includes receiving a search address associated with a branch prediction, and receiving a prediction strength indicator and a tag from a PHT. Based on determining that the tag matches the search address and the prediction strength indicator is weak, an accuracy counter is compared to a comparison threshold to determine whether a PHT direction prediction from the PHT is more likely accurate than a branch history table (BHT) direction prediction from a BHT. The PHT direction prediction is selected as a direction prediction based on determining that the accuracy counter indicates that the PHT direction prediction is more likely accurate than the BHT direction prediction. The BHT direction prediction is selected as the direction prediction based on determining that the accuracy counter indicates that the BHT direction prediction is more likely accurate than the PHT direction prediction.

主权项

1. A system for pattern history table filtering, the system comprising:
a pattern history table; a branch history table; an accuracy counter; and a processing circuit configured to perform a method comprising:
receiving a search address associated with a branch prediction;receiving a prediction strength indicator and a tag from the pattern history table, the prediction strength indicator having a value of weak or strong defined relative to a pattern history table direction prediction of a corresponding branch as taken or not taken wherein the prediction strength indicator transitions between weak and strong based on receiving a resolved branch indication of taken or not taken such that a combination of the prediction strength indicator and the pattern history table direction prediction supports transitions between a range of predictions comprising: strong not taken, weak not taken, weak taken, and strong taken; determining whether a pattern history table match exists based on the tag matching the search address; based on determining that the pattern history table match exists and the prediction strength indicator is weak, comparing the accuracy counter to a comparison threshold to determine whether a pattern history table direction prediction from the pattern history table is more likely accurate than the branch history table direction prediction from the branch history table; selecting the pattern history table direction prediction as a direction prediction based on determining that the accuracy counter indicates that the pattern history table direction prediction is more likely accurate than the branch history table direction prediction, the pattern history table match exists, and the prediction strength indicator is weak; selecting the branch history table direction prediction as the direction prediction based on determining that the accuracy counter indicates that the branch history table direction prediction is more likely accurate than the pattern history table direction prediction, the pattern history table match exists, and the prediction strength indicator is weak; selecting, by the processing circuit, the pattern history table direction prediction as the direction prediction based on determining that the pattern history table match exists and the prediction strength indicator is strong; and selecting, by the processing circuit, the branch history table direction prediction as the direction prediction based on determining that the pattern history table match does not exist.