An improved index function for (D)FCM predictors

The most promising value predictors to date are the finite context method predictor and a recent improvement thereof, the differential finite context method predictor. Both predictors comprise two levels and the index into the second level is a function of the content of the first level. This index function is crucial for good performance. However, our research shows that the currently used select-foldshift-xor function performs poorly on range-limited sequences of values. For example, it does not predict the results of byte loads well. The problem with the current function is that it often cannot reach the predictor's entire second-level table. We propose an improved index function that does not suffer from this shortcoming. On the 15 SPECcpu2000 C programs, our new index function improves the average load-value predictability by about 1% to 5% without increase in predictor size. On byte loads, the improvement is over 6% for 4096-entry predictors.

• Type: Journal
• Year: 2002
• Where: SIGARCH
• Authors: Martin Burtscher
• Keywords: Context Method Predictor, Finite Context Method, Index Function, SIGARCH 2002