cpu-o3: enhance source prediction alignment

Change-Id: Ic8a5757f4f87dbaf448df998fcd714e46f80d9a8

Author: Cao Jiaming

src/cpu/pred/btb/abtb.cc

@@ -215,7 +215,7 @@ AheadBTB::fillStagePredictions(const std::vector<TickedBTBEntry>& entries,
         mixed_entries = entries;
         for (auto &entry : mixed_entries) {
             if (entry.pc == ubtb_pred_entry.pc) {
-                entry.valid = false; // invalidate duplicated entry from aBTB
+                entry.valid = false; // invalidate duplicated entry from aBTB (only use for align counter)
                 break;
             }
         }

src/cpu/pred/btb/btb_ittage.cc

@@ -495,6 +495,21 @@ BTBITTAGE::doUpdateHist(const boost::dynamic_bitset<> &history, bool taken, Addr
     }
 }
 
+bool
+BTBITTAGE::tageHit()
+{
+    auto meta = getPredictionMeta();
+    auto preds = std::static_pointer_cast<TageMeta>(meta)->preds;
+    bool hit = false;
+    for (auto & [pc, pred] : preds) {
+        if (pred.mainInfo.found) {
+            hit = true;
+            break;
+        }
+    }
+    return hit;
+}
+
 /**
  * @brief Updates branch history for speculative execution
  *

src/cpu/pred/btb/btb_ittage.hh

@@ -140,7 +140,6 @@ class BTBITTAGE : public TimedBaseBTBPredictor
     // Update branch history
     void doUpdateHist(const bitset &history, bool taken, Addr pc, Addr target);
 
-
     const unsigned numPredictors;
 
     std::vector<unsigned> tableSizes;
@@ -270,6 +269,7 @@ public:
     bool debugFlag = false;
 
     void recoverFoldedHist(const bitset& history);
+    bool tageHit();
 
     // void checkFoldedHist(const bitset& history);
 };

src/cpu/pred/btb/decoupled_bpred.cc

@@ -245,34 +245,39 @@ DecoupledBPUWithBTB::generateFinalPredAndCreateBubbles()
 
     if (predsOfEachStage[0].btbEntries.size() != 0) {
         for (auto entry : predsOfEachStage[0].btbEntries){
-            if (entry.isIndirect || entry.isDirect || entry.ctr >=0 ||entry.alwaysTaken){
+            if (entry.isIndirect || entry.isDirect || entry.ctr >= 0 ||entry.alwaysTaken){
                 finalPred.s1Source = entry.source;
                 break;
             }
         }
     }
 
-    if (predsOfEachStage[2].btbEntries.size() != 0) {
+    bool found_s3_taken = false;
+    bool na_s3_taken_but_have_cond = false;
+
+    for (BTBEntry entry : predsOfEachStage[2].btbEntries) {
+        if (entry.isDirect || entry.isIndirect || entry.ctr >= 0 || entry.alwaysTaken) {
+            found_s3_taken = true;
+        }else if (entry.isCond){
+            //only use when there's no taken prediction in s3
+            na_s3_taken_but_have_cond = true;
+        }
+    }
+
+    if (found_s3_taken) {
         auto pred_taken_entry = finalPred.getTakenEntry();
         if (pred_taken_entry.valid) {
             if (pred_taken_entry.isReturn) {
                 finalPred.s3Source = ras->getComponentIdx();
-            } else if (pred_taken_entry.isIndirect) {
+            } else if (pred_taken_entry.isIndirect && ittage->tageHit()) {
                 finalPred.s3Source = ittage->getComponentIdx();
             }else if (pred_taken_entry.isCond) {
                 finalPred.s3Source = tage->getComponentIdx();
             } else {
                 finalPred.s3Source = mbtb->getComponentIdx();
             }
         }else {
-            bool found = false;
-            for (auto entry : predsOfEachStage[2].btbEntries) {
-                if (entry.isCond){
-                    found = true;
-                    break;
-                }
-            }
-            if (found) {
+            if (na_s3_taken_but_have_cond) {
                 finalPred.s3Source = tage->getComponentIdx();
             }else {
                 finalPred.s3Source = -1;

src/cpu/pred/btb/decoupled_bpred_stats.cc

@@ -905,7 +905,6 @@ DecoupledBPUWithBTB::commitPredWrongSource(const FetchStream &entry)
         dbpBtbStats.s1PredWrongFallthrough++;
     }
 
-    int s3blame = mbtbid;
     if (s3PredSource == rasid) {
         if (exeBranchInfo.isCond) {
             dbpBtbStats.s3PredWrongTage++;
@@ -947,7 +946,6 @@ DecoupledBPUWithBTB::commitPredWrongSource(const FetchStream &entry)
     }else if (s3PredSource == -1) {
         dbpBtbStats.s3PredWrongMbtb++;
     }
-    //components[s3blame]->predwrongSource();
 }
 /**
  * @brief Handle instruction commits and phase-based statistics