Technical Report 2002-013

Effects of Branch Predictors on Execution Time

Jakob Engblom

April 2002


This technical report describes the result of a short experimental investigation into the effect of branch predictors on the execution times of tight loops on modern aggressive microprocessors. The same code was tried on Pentium III, Athlon, UltraSparc II, and UltraSparc III processors. For reference, the same experiment was carried out on a simple V850E processor to determine the behaviour without branch prediction.

The results indicate that advanced branch predictors give a very high and hard-to-understand variation in the execution time of loops, and that this effect can be very big relative to the execution time of other instructions.

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