Dynamic Path-Based Branch Correlation
Ravi Nair
Abstract
Misprediction of conditional branches is a major cause for reduced
performance in processor implementations with large numbers of
functional units. We present a hardware scheme which records the path
leading to a conditional branch in order to predict the outcome of the
branch instruction more accurately. The proposed scheme is analyzed
using instruction traces from integer benchmark programs. The results
indicate that knowledge of path information leads to better prediction
than knowledge of simply the previous branch outcomes for a given
number of history items. The results further show that even for
equivalent hardware cost, path-based correlation often outperforms
pattern-based correlation, especially when history information is
periodically destroyed, for example due to context switches.
Keywords
Branch prediction, branch correlation, path-based
correlation, misprediction penalty
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