Speculative history forwarding in overriding branch predictors, and related circuits, methods, and computer-readable media

摘要

Speculative history forwarding in overriding branch predictors, and related circuits, methods, and computer-readable media are disclosed. In one embodiment, a branch prediction circuit including a first branch predictor and a second branch predictor is provided. The first branch predictor generates a first branch prediction for a conditional branch instruction, and the first branch prediction is stored in a first branch prediction history. The first branch prediction is also speculatively forwarded to a second branch prediction history. The second branch predictor subsequently generates a second branch prediction based on the second branch prediction history, including the speculatively forwarded first branch prediction. By enabling the second branch predictor to base its branch prediction on the speculatively forwarded first branch prediction, an accuracy of the second branch predictor may be improved.

主权项

1. A branch prediction circuit for performing branch prediction of fetched instructions in a processor, comprising:
a first branch predictor configured to:
predict a first branch prediction of a conditional branch instruction in an instruction queue; andupdate a first branch prediction history register based on the first branch prediction for the conditional branch instruction; a forwarding circuit configured to forward the first branch prediction for the conditional branch instruction to a second branch prediction history register as a speculative prediction; and a second branch predictor configured to predict a second branch prediction of the conditional branch instruction in the instruction queue based on the second branch prediction history register including the speculative prediction.