diff options
Diffstat (limited to 'src/cpu/pred/tournament.cc')
-rw-r--r-- | src/cpu/pred/tournament.cc | 147 |
1 files changed, 62 insertions, 85 deletions
diff --git a/src/cpu/pred/tournament.cc b/src/cpu/pred/tournament.cc index 96f03eb30..c0c1c12cf 100644 --- a/src/cpu/pred/tournament.cc +++ b/src/cpu/pred/tournament.cc @@ -267,100 +267,77 @@ void TournamentBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, bool squashed) { - unsigned local_history_idx; - unsigned local_predictor_idx M5_VAR_USED; - unsigned local_predictor_hist; + assert(bp_history); - // Get the local predictor's current prediction - local_history_idx = calcLocHistIdx(branch_addr); - local_predictor_hist = localHistoryTable[local_history_idx]; - local_predictor_idx = local_predictor_hist & localPredictorMask; - - if (bp_history) { - BPHistory *history = static_cast<BPHistory *>(bp_history); - // 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; - - bool old_local_pred_valid = history->localHistory != - invalidPredictorIndex; + BPHistory *history = static_cast<BPHistory *>(bp_history); - assert(old_local_pred_index < localPredictorSize); + unsigned local_history_idx = calcLocHistIdx(branch_addr); - if (history->globalUsed) { - historyPred = history->globalPredTaken; - } else { - 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. - unsigned choice_predictor_idx = - history->globalHistory & choiceHistoryMask; - if (history->localPredTaken == taken) { - choiceCtrs[choice_predictor_idx].decrement(); - } else if (history->globalPredTaken == taken) { - choiceCtrs[choice_predictor_idx].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. - unsigned global_predictor_idx = - history->globalHistory & globalHistoryMask; - if (taken) { - globalCtrs[global_predictor_idx].increment(); - if (old_local_pred_valid) { - localCtrs[old_local_pred_index].increment(); - } - } else { - globalCtrs[global_predictor_idx].decrement(); - if (old_local_pred_valid) { - localCtrs[old_local_pred_index].decrement(); - } - } - } - if (squashed) { - if (taken) { - globalHistory[tid] = (history->globalHistory << 1) | 1; - globalHistory[tid] = globalHistory[tid] & historyRegisterMask; - if (old_local_pred_valid) { - localHistoryTable[local_history_idx] = - (history->localHistory << 1) | 1; - } - } else { - globalHistory[tid] = (history->globalHistory << 1); - globalHistory[tid] = globalHistory[tid] & historyRegisterMask; - if (old_local_pred_valid) { - localHistoryTable[local_history_idx] = - history->localHistory << 1; - } - } + assert(local_history_idx < localHistoryTableSize); - } else { - // We're done with this history, now delete it. - delete history; + // Unconditional branches do not use local history. + bool old_local_pred_valid = history->localHistory != + invalidPredictorIndex; + + // If this is a misprediction, restore the speculatively + // updated state (global history register and local history) + // and update again. + if (squashed) { + // Global history restore and update + globalHistory[tid] = (history->globalHistory << 1) | taken; + globalHistory[tid] &= historyRegisterMask; + + // Local history restore and update. + if (old_local_pred_valid) { + localHistoryTable[local_history_idx] = + (history->localHistory << 1) | taken; } - } - assert(local_history_idx < localHistoryTableSize); + return; + } + unsigned old_local_pred_index = history->localHistory & + localPredictorMask; + + assert(old_local_pred_index < localPredictorSize); + + // Update the choice predictor to tell it which one was correct if + // there was a prediction. + if (history->localPredTaken != history->globalPredTaken && + old_local_pred_valid) + { + // If the local prediction matches the actual outcome, + // decrement the counter. Otherwise increment the + // counter. + unsigned choice_predictor_idx = + history->globalHistory & choiceHistoryMask; + if (history->localPredTaken == taken) { + choiceCtrs[choice_predictor_idx].decrement(); + } else if (history->globalPredTaken == taken) { + choiceCtrs[choice_predictor_idx].increment(); + } + } -} + // Update the counters with the proper + // resolution of the branch. Histories are updated + // speculatively, restored upon squash() calls, and + // recomputed upon update(squash = true) calls, + // so they do not need to be updated. + unsigned global_predictor_idx = + history->globalHistory & globalHistoryMask; + if (taken) { + globalCtrs[global_predictor_idx].increment(); + if (old_local_pred_valid) { + localCtrs[old_local_pred_index].increment(); + } + } else { + globalCtrs[global_predictor_idx].decrement(); + if (old_local_pred_valid) { + localCtrs[old_local_pred_index].decrement(); + } + } -void -TournamentBP::retireSquashed(ThreadID tid, void *bp_history) -{ - BPHistory *history = static_cast<BPHistory *>(bp_history); + // We're done with this history, now delete it. delete history; } |