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Up: Control Hazards, Branch Prediction
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Q:
- Suppose the loop is executed 9 times
- Branch is taken 9 times, not taken once
- What is the prediction accuracy, assuming
the prediction bit for the branch remains
in the prediction buffer?
A:
- Will inevitably mispredict on 10
iteration
- Will also mispredict on first
- Because prediction bit was flipped on previous
execution of the loop's last iteration
- Branch is taken 90% of the time
- But correctly predicted only 80% of the
time
How can we do better?