The Impact of Branch Direction History Combined with Global Branch History in Branch Prediction

Jong Wook KWAK  Ju-Hwan KIM  Chu Shik JHON  

Publication
IEICE TRANSACTIONS on Information and Systems   Vol.E88-D   No.7   pp.1754-1758
Publication Date: 2005/07/01
Online ISSN: 
DOI: 10.1093/ietisy/e88-d.7.1754
Print ISSN: 0916-8532
Type of Manuscript: LETTER
Category: Computer Systems
Keyword: 
branch prediction,  Branch Direction History,  Global Branch History,  gshare predictor,  direction-gshare predictor,  

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Summary: 
Most branch predictors use the PC information of the branch instruction and its dynamic Global Branch History (GBH). In this letter, we suggest a Branch Direction History (BDH) as the third component of the branch prediction and analyze its impact upon the prediction accuracy. Additionally, we propose a new branch predictor, direction-gshare predictor, which utilizes the BDH combined with the GBH. At first, we model a neural network with (PC, GBH, and BDH) and analyze their actual impact upon the branch prediction accuracy, and then we simulate our new predictor, the direction-gshare predictor. The simulation results show that the aliasing in Pattern History Table (PHT) is significantly reduced by the additional use of BDH information. The direction-gshare predictor outperforms bimodal predictor, two-level adaptive predictor and gshare predictor up to 15.32%, 5.41% and 5.74% respectively, without additional hardware costs.