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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?