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BPred: Fix RAS to handle predicated call/return instructions.

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Change RAS to fix issues with predicated call/return instructions.
Handled all cases in the life of a predicated call and return instruction.
This commit is contained in:
Mrinmoy Ghosh
2012-02-13 12:26:25 -06:00
parent fd90c3676d
commit 9b05e96b9e
4 changed files with 122 additions and 56 deletions
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95
src/cpu/pred/tournament.cc
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@@ -258,59 +258,70 @@ TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history,
local_predictor_hist = localHistoryTable[local_history_idx];
local_predictor_idx = local_predictor_hist & localPredictorMask;
// Update the choice predictor to tell it which one was correct if
// there was a prediction.
if (bp_history) {
BPHistory *history = static_cast<BPHistory *>(bp_history);
if (history->localPredTaken != history->globalPredTaken) {
// If the local prediction matches the actual outcome,
// decerement the counter. Otherwise increment the
// counter.
if (history->localPredTaken == taken) {
choiceCtrs[history->globalHistory].decrement();
} else if (history->globalPredTaken == taken){
choiceCtrs[history->globalHistory].increment();
}
}
// Update the counters and local history with the proper
// resolution of the branch. Global history is updated
// speculatively and restored upon squash() calls, so it does not
// need to be updated.
// Update may also be called if the Branch target is incorrect even if
// the prediction is correct. In that case do not update the counters.
bool historyPred = false;
unsigned old_local_pred_index = history->localHistory
& localPredictorMask;
if (taken) {
globalCtrs[history->globalHistory].increment();
if (old_local_pred_index != invalidPredictorIndex) {
localCtrs[old_local_pred_index].increment();
}
& localPredictorMask;
if (history->globalUsed) {
historyPred = history->globalPredTaken;
} else {
globalCtrs[history->globalHistory].decrement();
if (old_local_pred_index != invalidPredictorIndex) {
localCtrs[old_local_pred_index].decrement();
}
}
historyPred = history->localPredTaken;
}
if (historyPred != taken || !squashed) {
// Update the choice predictor to tell it which one was correct if
// there was a prediction.
if (history->localPredTaken != history->globalPredTaken) {
// If the local prediction matches the actual outcome,
// decerement the counter. Otherwise increment the
// counter.
if (history->localPredTaken == taken) {
choiceCtrs[history->globalHistory].decrement();
} else if (history->globalPredTaken == taken) {
choiceCtrs[history->globalHistory].increment();
}
if (squashed) {
if (taken) {
globalHistory = (history->globalHistory << 1) | 1;
globalHistory = globalHistory & globalHistoryMask;
if (history->localHistory != invalidPredictorIndex)
localHistoryTable[local_history_idx] =
}
// Update the counters and local history with the proper
// resolution of the branch. Global history is updated
// speculatively and restored upon squash() calls, so it does not
// need to be updated.
if (taken) {
globalCtrs[history->globalHistory].increment();
if (old_local_pred_index != invalidPredictorIndex) {
localCtrs[old_local_pred_index].increment();
}
} else {
globalCtrs[history->globalHistory].decrement();
if (old_local_pred_index != invalidPredictorIndex) {
localCtrs[old_local_pred_index].decrement();
}
}
}
if (squashed) {
if (taken) {
globalHistory = (history->globalHistory << 1) | 1;
globalHistory = globalHistory & globalHistoryMask;
if (old_local_pred_index != invalidPredictorIndex) {
localHistoryTable[old_local_pred_index] =
(history->localHistory << 1) | 1;
} else {
globalHistory = (history->globalHistory << 1);
globalHistory = globalHistory & globalHistoryMask;
if (history->localHistory != invalidPredictorIndex) {
localHistoryTable[local_history_idx] =
}
} else {
globalHistory = (history->globalHistory << 1);
globalHistory = globalHistory & globalHistoryMask;
if (old_local_pred_index != invalidPredictorIndex) {
localHistoryTable[old_local_pred_index] =
history->localHistory << 1;
}
}
}
}
}
// We're done with this history, now delete it.
delete history;
}
assert(globalHistory < globalPredictorSize &&