Two-level adaptive predictors
Developed by Yeh and Patt at the same time (1992) as the correlation-based prediction scheme.
The basic two-level predictor uses a single global branch history register (BHR) of k bits to index in a pattern history table (PHT) of 2-bit counters.
Global history schemes correspond to correlation-based predictor schemes.
- a single global BHR (denoted G) and
- a single global PHT (denoted g),
- A stands for adaptive.
All PHT implementations of Yeh and Patt use 2-bit predictors.
GAg-predictor with a 4-bit BHR length is denoted as GAg(4).