changeset 6222624550e7 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=6222624550e7
description:
O3: Track if the RAS has been pushed or not to pop the RAS if
neccessary.
Add new flag (named pushedRAS) in the PredictorHistory structure.
This flag tracks whether the RAS has been pushed or not during a
prediction.
Then, in the squash function it is used to pop the RAS if necessary.
diffstat:
src/cpu/o3/bpred_unit.hh | 5 ++++-
src/cpu/o3/bpred_unit_impl.hh | 7 ++++---
2 files changed, 8 insertions(+), 4 deletions(-)
diffs (60 lines):
diff -r e236675714a4 -r 6222624550e7 src/cpu/o3/bpred_unit.hh
--- a/src/cpu/o3/bpred_unit.hh Fri Jun 29 11:18:29 2012 -0400
+++ b/src/cpu/o3/bpred_unit.hh Fri Jun 29 11:18:29 2012 -0400
@@ -207,7 +207,7 @@
bool pred_taken, void *bp_history,
ThreadID _tid)
: seqNum(seq_num), pc(instPC), bpHistory(bp_history), RASTarget(0),
- RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0),
+ RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0),
pushedRAS(0),
wasCall(0), wasReturn(0), validBTB(0)
{}
@@ -242,6 +242,9 @@
/** Whether or not the RAS was used. */
bool usedRAS;
+ /* Wether or not the RAS was pushed */
+ bool pushedRAS;
+
/** Whether or not the instruction was a call. */
bool wasCall;
diff -r e236675714a4 -r 6222624550e7 src/cpu/o3/bpred_unit_impl.hh
--- a/src/cpu/o3/bpred_unit_impl.hh Fri Jun 29 11:18:29 2012 -0400
+++ b/src/cpu/o3/bpred_unit_impl.hh Fri Jun 29 11:18:29 2012 -0400
@@ -219,7 +219,7 @@
if (inst->isCall()) {
RAS[tid].push(pc);
-
+ predict_record.pushedRAS = true;
// Record that it was a call so that the top RAS entry can
// be popped off if the speculation is incorrect.
predict_record.wasCall = true;
@@ -253,6 +253,7 @@
tid, inst->seqNum, inst->pcState());
} else if (inst->isCall() && !inst->isUncondCtrl()) {
RAS[tid].pop();
+ predict_record.pushedRAS = false;
}
TheISA::advancePC(target, inst->staticInst);
}
@@ -308,7 +309,7 @@
RAS[tid].restore(pred_hist.front().RASIndex,
pred_hist.front().RASTarget);
- } else if(pred_hist.front().wasCall && pred_hist.front().validBTB) {
+ } else if(pred_hist.front().wasCall && pred_hist.front().pushedRAS) {
// Was a call but predicated false. Pop RAS here
DPRINTF(Fetch, "BranchPred: [tid: %i] Squashing"
" Call [sn:%i] PC: %s Popping RAS\n", tid,
@@ -408,7 +409,7 @@
hist_it->RASIndex, hist_it->RASTarget);
RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget);
- } else if (hist_it->wasCall && hist_it->validBTB) {
+ } else if (hist_it->wasCall && hist_it->pushedRAS) {
//Was a Call but predicated false. Pop RAS here
DPRINTF(Fetch, "BranchPred: [tid: %i] Incorrectly predicted"
" Call [sn:%i] PC: %s Popping RAS\n", tid,
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