From: Arthur Perais <arthur.perais@inria.fr>
Date: Wed, 21 Dec 2016 21:06:13 +0000 (-0600)
Subject: cpu: correct comments in tournament branch predictor
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=34065f8d5f51e165b56d12a6d88092332809f0b9;p=gem5.git

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 <jason@lowepower.com>
---

diff --git a/src/cpu/pred/tournament.cc b/src/cpu/pred/tournament.cc
index 319606871..96f03eb30 100644
--- a/src/cpu/pred/tournament.cc
+++ b/src/cpu/pred/tournament.cc
@@ -222,8 +222,8 @@ TournamentBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
 
     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 --git a/src/cpu/pred/tournament.hh b/src/cpu/pred/tournament.hh
index 3aa17e030..0febd21bc 100644
--- a/src/cpu/pred/tournament.hh
+++ b/src/cpu/pred/tournament.hh
@@ -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
 {