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authorAndrew Lukefahr <lukefahr@umich.edu>2015-09-15 08:14:07 -0500
committerAndrew Lukefahr <lukefahr@umich.edu>2015-09-15 08:14:07 -0500
commit543efd5ca687782028fad8873099ad38eeb64085 (patch)
treef5169ae58d9fda00e1ab708bd5ea4e5698f070aa
parentfb0f9884e27f33c434ef67a5cfd284331a2a89e0 (diff)
downloadgem5-543efd5ca687782028fad8873099ad38eeb64085.tar.xz
cpu: pred: Local Predictor Reset in Tournament Predictor
When a branch gets squashed, it's speculative branch predictor state should get rolled back in squash(). However, only the globalHistory state was being rolled back. This patch adds (at least some) support for rolling back the local predictor state also. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
-rw-r--r--src/cpu/pred/tournament.cc7
-rw-r--r--src/cpu/pred/tournament.hh1
2 files changed, 8 insertions, 0 deletions
diff --git a/src/cpu/pred/tournament.cc b/src/cpu/pred/tournament.cc
index 1d4fe037e..ea6be46fa 100644
--- a/src/cpu/pred/tournament.cc
+++ b/src/cpu/pred/tournament.cc
@@ -217,6 +217,7 @@ TournamentBP::lookup(Addr branch_addr, void * &bp_history)
history->localPredTaken = local_prediction;
history->globalPredTaken = global_prediction;
history->globalUsed = choice_prediction;
+ history->localHistoryIdx = local_history_idx;
history->localHistory = local_predictor_idx;
bp_history = (void *)history;
@@ -256,6 +257,7 @@ TournamentBP::uncondBranch(Addr pc, void * &bp_history)
history->localPredTaken = true;
history->globalPredTaken = true;
history->globalUsed = true;
+ history->localHistoryIdx = invalidPredictorIndex;
history->localHistory = invalidPredictorIndex;
bp_history = static_cast<void *>(history);
@@ -371,6 +373,11 @@ TournamentBP::squash(void *bp_history)
// Restore global history to state prior to this branch.
globalHistory = history->globalHistory;
+ // Restore local history
+ if (history->localHistoryIdx != invalidPredictorIndex) {
+ localHistoryTable[history->localHistoryIdx] = history->localHistory;
+ }
+
// Delete this BPHistory now that we're done with it.
delete history;
}
diff --git a/src/cpu/pred/tournament.hh b/src/cpu/pred/tournament.hh
index d46175610..8fb5b515c 100644
--- a/src/cpu/pred/tournament.hh
+++ b/src/cpu/pred/tournament.hh
@@ -167,6 +167,7 @@ class TournamentBP : public BPredUnit
static int newCount;
#endif
unsigned globalHistory;
+ unsigned localHistoryIdx;
unsigned localHistory;
bool localPredTaken;
bool globalPredTaken;