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>

1 files changed, 7 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;
 }