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Train ITTAGE at resolve stage #630

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Merged
Yakkhini merged 4 commits into from
Dec 5, 2025
Merged

Train ITTAGE at resolve stage #630

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79207b2
cpu-o3: enable ITTAGE predictor
Yakkhini Dec 3, 2025
681b100
cpu-o3: train ittage in resolve stage
Yakkhini Dec 3, 2025
f84a311
cpu-o3: filter not resolved btb entries in ittage resolve update
Yakkhini Dec 3, 2025
ea1a5b2
cpu-o3: only update ubtb & abtb when it enabled
Yakkhini Dec 5, 2025
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3 changes: 2 additions & 1 deletion configs/example/kmhv3.py
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Original file line number Diff line number Diff line change
Expand Up @@ -97,13 +97,14 @@ def setKmhV3Params(args, system):

cpu.branchPred.mbtb.resolvedUpdate = True
cpu.branchPred.tage.resolvedUpdate = True
cpu.branchPred.ittage.resolvedUpdate = True

cpu.branchPred.ubtb.enabled = True
cpu.branchPred.abtb.enabled = False
cpu.branchPred.microtage.enabled = False
cpu.branchPred.mbtb.enabled = True
cpu.branchPred.tage.enabled = True
cpu.branchPred.ittage.enabled = False
cpu.branchPred.ittage.enabled = True
cpu.branchPred.mgsc.enabled = False
cpu.branchPred.ras.enabled = False

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15 changes: 11 additions & 4 deletions src/cpu/pred/btb/btb_ittage.cc
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Expand Up @@ -219,10 +219,17 @@ BTBITTAGE::update(const FetchStream &stream)
all_entries_to_update.push_back(stream.updateNewBTBEntry);
}

// only update indirect branches that are not returns
auto remove_it = std::remove_if(all_entries_to_update.begin(), all_entries_to_update.end(),
[](const BTBEntry &e) { return !(e.isIndirect && !e.isReturn); });
all_entries_to_update.erase(remove_it, all_entries_to_update.end());
// // only update indirect branches that are not returns
if (getResolvedUpdate()) {
auto remove_it =
std::remove_if(all_entries_to_update.begin(), all_entries_to_update.end(),
[](const BTBEntry &e) { return !(e.isIndirect && !e.isReturn && e.resolved); });
all_entries_to_update.erase(remove_it, all_entries_to_update.end());
} else {
auto remove_it = std::remove_if(all_entries_to_update.begin(), all_entries_to_update.end(),
[](const BTBEntry &e) { return !(e.isIndirect && !e.isReturn); });
all_entries_to_update.erase(remove_it, all_entries_to_update.end());
}

// get tage predictions from meta
// TODO: use component idx
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11 changes: 6 additions & 5 deletions src/cpu/pred/btb/decoupled_bpred.cc
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Expand Up @@ -251,15 +251,16 @@ DecoupledBPUWithBTB::generateFinalPredAndCreateBubbles()

// update ubtb/abtb using final S3 prediction
if (predsOfEachStage[numStages - 1].btbEntries.size() > 0) {
ubtb->updateUsingS3Pred(predsOfEachStage[numStages - 1]);
auto it = fetchStreamQueue.find(fsqId-1);
if (it != fetchStreamQueue.end()) {
if (ubtb->isEnabled()) {
ubtb->updateUsingS3Pred(predsOfEachStage[numStages - 1]);
}
auto it = fetchStreamQueue.find(fsqId - 1);
if (it != fetchStreamQueue.end() && abtb->isEnabled()) {
auto previous_block_startpc = it->second.startPC;
abtb->updateUsingS3Pred(predsOfEachStage[numStages - 1], previous_block_startpc);
} else {
} else if (abtb->isEnabled()) {
abtb->updateUsingS3Pred(predsOfEachStage[numStages - 1], 0);
}

}

// 4. Record override bubbles and update statistics
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