changeset 8e96720a382c in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=8e96720a382c
description:
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 <[email protected]>
diffstat:
src/cpu/pred/tournament.cc | 7 +++++++
src/cpu/pred/tournament.hh | 1 +
2 files changed, 8 insertions(+), 0 deletions(-)
diffs (42 lines):
diff -r da477ae38907 -r 8e96720a382c src/cpu/pred/tournament.cc
--- a/src/cpu/pred/tournament.cc Tue Sep 15 08:14:06 2015 -0500
+++ b/src/cpu/pred/tournament.cc Tue Sep 15 08:14:07 2015 -0500
@@ -217,6 +217,7 @@
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 @@
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 @@
// 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 -r da477ae38907 -r 8e96720a382c src/cpu/pred/tournament.hh
--- a/src/cpu/pred/tournament.hh Tue Sep 15 08:14:06 2015 -0500
+++ b/src/cpu/pred/tournament.hh Tue Sep 15 08:14:07 2015 -0500
@@ -167,6 +167,7 @@
static int newCount;
#endif
unsigned globalHistory;
+ unsigned localHistoryIdx;
unsigned localHistory;
bool localPredTaken;
bool globalPredTaken;
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