Method and system for enhanced branch history prediction accurac

Details Method and system for enhanced branch history prediction accurac Method and system for enhanced branch history prediction accurac

1993-01-08

1994-11-22

Bowler, Alyssa H.

Boots, shoes, and leggings

395375, 364DIG1, 3642617, 3642613, 3642626, 36473223, 3642318, 364DIG2, 36493155, 364938, 3649382, 3649575, 364957, 364960, 36496424, G06F 932, G06F 1300

Patent

active

053677030

ABSTRACT:
A method and system for enhanced branch history prediction accuracy in a superscalar processor system by maintaining branch history tables which include a separate branch history for each instruction fetch position within a multi-instruction access. In a superscalar processor system which is capable of accessing multiple instructions simultaneously, a branch history table is established which includes a predictive field for each possible instruction fetch position within a multi-instruction access. Each group of predictive fields is accessed within the branch history table utilizing a portion of the instruction fetch address, such as the low order address bits. A particular predictive field within the group is then selected which corresponds to the position of the branch instruction within the instruction fetch. The content of the selected predictive field is then utilized to predict whether or not a branch is taken for the corresponding branch instruction. Each predictive field preferably comprises a two bit binary counter which is incremented or decremented in response to a branch being "taken" or "not taken" and then stored again within the branch history table.

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Oehler et al. "IBM Disc System/6000: Architecture and Performance" IEEE Micro Jun. 1991.

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