Oracle Branch Predictor

[aaku...@ncsu.edu]

Hello,

I had questions regarding the Oracle BP in ESESC. The code snippet is:

PredType BPOracle::predict(DInst *dinst, bool doUpdate, bool doStats) {

    if(!dinst->isTaken())

      return CorrectPrediction; // NT

 

    return btb.predict(dinst, doUpdate, doStats);

 }

For an oracle BP the direction should always be what dinst->isTaken says correct? If this condition (!dinst->isTaken())  is false, then why do we wait for prediction from the BTB and not directly do a T? 

Thank you,
Aishwarya

[Jose Renau]

the BPOracle is just for the Taken/No-Taken predictor. If both BPOracle and BTB are oracle, you get perfect predction all the time.

Jose Renau Professor, Computer Science & Engineering W // http://masc.soe.ucsc.edu

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