From: Andrew Lukefahr <lukefahr@umich.edu>
Date: Tue, 15 Sep 2015 13:14:07 +0000 (-0500)
Subject: cpu: pred: Local Predictor Reset in Tournament Predictor
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=543efd5ca687782028fad8873099ad38eeb64085;p=gem5.git

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>
---

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;