cpu: update info related direction into BP if mispredicted.

Update direction info of a branch into BP if, the branch is not
found in the target buffer. Therefore, this  updated direction is
used to squash the branch later on. Previously, some mispredicted
branches were not sqaushed as the BP had old info.

Reported-by: Dimitrios Chasapis
Change-Id: I4be2eb706edc5ffa9935948fb52a01667286c721
jira-issue: https://gem5.atlassian.net/browse/GEM5-355
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25903
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Ayaz Akram <yazakram@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Dimitrios Chasapis <k4s4s.heavener@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

diff --git a/src/cpu/pred/bpred_unit.cc b/src/cpu/pred/bpred_unit.cc
index 3d9e3ea5aba403e9b1c2965942586e2bf72e6f69..4b93e30b39c849a2268893b09fa4596b5afa807a 100644 (file)
--- a/src/cpu/pred/bpred_unit.cc
+++ b/src/cpu/pred/bpred_unit.cc
@@ -263,6 +263,7 @@ BPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
                     DPRINTF(Branch, "[tid:%i] [sn:%llu] BTB doesn't have a "
                             "valid entry\n",tid,seqNum);
                     pred_taken = false;
+                    predict_record.predTaken = pred_taken;
                     // The Direction of the branch predictor is altered
                     // because the BTB did not have an entry
                     // The predictor needs to be updated accordingly
@@ -293,6 +294,7 @@ BPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
                 } else {
                     ++indirectMisses;
                     pred_taken = false;
+                    predict_record.predTaken = pred_taken;
                     DPRINTF(Branch,
                             "[tid:%i] [sn:%llu] "
                             "Instruction %s no indirect "