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.

diff --git a/src/cpu/o3/bpred_unit.hh b/src/cpu/o3/bpred_unit.hh
index 8bfab11a9939f1c48a89eefe079ba88c022bd991..c1afb4720c9a3aeb51acaab756fc7e46bd85420a 100644 (file)
--- a/src/cpu/o3/bpred_unit.hh
+++ b/src/cpu/o3/bpred_unit.hh
@@ -207,7 +207,7 @@ class BPredUnit
                          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 @@ class BPredUnit
         /** 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 --git a/src/cpu/o3/bpred_unit_impl.hh b/src/cpu/o3/bpred_unit_impl.hh
index 1e75de90c3e054877ae74a597901f691c52bb566..6f0e5e3e0ccf9c89f2a83c353ca698d92902df30 100644 (file)
--- a/src/cpu/o3/bpred_unit_impl.hh
+++ b/src/cpu/o3/bpred_unit_impl.hh
@@ -219,7 +219,7 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
 
             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 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
                               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 @@ BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn, ThreadID tid)
 
             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 @@ BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
                               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,