changeset c2e1ead33662 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=c2e1ead33662
description:
cpu: correct comments in tournament branch predictor
The tournament predictor is presented as doing speculative
update of the global history and non-speculative update
of the local history used to generate the branch prediction.
However, the code does speculative update of both histories.
Signed-off-by: Jason Lowe-Power <[email protected]>
diffstat:
src/cpu/pred/tournament.cc | 4 ++--
src/cpu/pred/tournament.hh | 5 ++---
2 files changed, 4 insertions(+), 5 deletions(-)
diffs (29 lines):
diff -r 1ae84c76066b -r c2e1ead33662 src/cpu/pred/tournament.cc
--- a/src/cpu/pred/tournament.cc Wed Dec 21 15:05:24 2016 -0600
+++ b/src/cpu/pred/tournament.cc Wed Dec 21 15:06:13 2016 -0600
@@ -222,8 +222,8 @@
assert(local_history_idx < localHistoryTableSize);
- // Commented code is for doing speculative update of counters and
- // all histories.
+ // Speculative update of the global history and the
+ // selected local history.
if (choice_prediction) {
if (global_prediction) {
updateGlobalHistTaken(tid);
diff -r 1ae84c76066b -r c2e1ead33662 src/cpu/pred/tournament.hh
--- a/src/cpu/pred/tournament.hh Wed Dec 21 15:05:24 2016 -0600
+++ b/src/cpu/pred/tournament.hh Wed Dec 21 15:06:13 2016 -0600
@@ -57,9 +57,8 @@
* used in the 21264. It has a local predictor, which uses a local history
* table to index into a table of counters, and a global predictor, which
* uses a global history to index into a table of counters. A choice
- * predictor chooses between the two. Only the global history register
- * is speculatively updated, the rest are updated upon branches committing
- * or misspeculating.
+ * predictor chooses between the two. Both the global history register
+ * and the selected local history are speculatively updated.
*/
class TournamentBP : public BPredUnit
{
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