From af2b14a362281f36347728e13dcd6b2c4d3c4991 Mon Sep 17 00:00:00 2001
From: Nathanael Premillieu <npremill@irisa.fr>
Date: Fri, 29 Jun 2012 11:18:29 -0400
Subject: [PATCH] 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.
---
 src/cpu/o3/bpred_unit.hh      | 5 ++++-
 src/cpu/o3/bpred_unit_impl.hh | 7 ++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/cpu/o3/bpred_unit.hh b/src/cpu/o3/bpred_unit.hh
index 8bfab11a9..c1afb4720 100644
--- 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 1e75de90c..6f0e5e3e0 100644
--- 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,
-- 
2.30.2