From: Korey Sewell <ksewell@umich.edu>
Date: Fri, 4 Feb 2011 05:09:19 +0000 (-0500)
Subject: inorder: pcstate and delay slots bug
X-Git-Tag: stable_2012_02_02~608
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e57613588b15f25b5b912ae98134b6f1007988fd;p=gem5.git

inorder: pcstate and delay slots bug
not taken delay slots were not being advanced correctly to pc+8, so for those ISAs
we 'advance()' the pcstate one more time for the desired effect
---

diff --git a/src/cpu/inorder/resources/bpred_unit.cc b/src/cpu/inorder/resources/bpred_unit.cc
index 310053409..9e15a4fee 100644
--- a/src/cpu/inorder/resources/bpred_unit.cc
+++ b/src/cpu/inorder/resources/bpred_unit.cc
@@ -273,8 +273,6 @@ BPredUnit::predict(DynInstPtr &inst, TheISA::PCState &predPC, ThreadID tid)
             "...predHist.size(): %i\n",
             tid, inst->seqNum, predHist[tid].size());
 
-    inst->setBranchPred(pred_taken);
-
     return pred_taken;
 }
 
diff --git a/src/cpu/inorder/resources/branch_predictor.cc b/src/cpu/inorder/resources/branch_predictor.cc
index dc036df64..c849ba163 100644
--- a/src/cpu/inorder/resources/branch_predictor.cc
+++ b/src/cpu/inorder/resources/branch_predictor.cc
@@ -84,14 +84,20 @@ BranchPredictor::execute(int slot_num)
                 DPRINTF(InOrderStage, "[tid:%u]: [sn:%i]: squashed, "
                         "skipping prediction \n", tid, inst->seqNum);
             } else {
-                TheISA::PCState predPC = inst->pcState();
-                TheISA::advancePC(predPC, inst->staticInst);
+                TheISA::PCState pred_PC = inst->pcState();
+                TheISA::advancePC(pred_PC, inst->staticInst);
+#if ISA_HAS_DELAY_SLOT
+                // By default set target to NNPC (e.g. PC + 8)
+                // so that a not-taken branch will update
+                // correctly
+                pred_PC.advance();
+#endif
 
                 if (inst->isControl()) {
                     // If not, the pred_PC be updated to pc+8
                     // If predicted, the pred_PC will be updated to new target
                     // value
-                    bool predict_taken = branchPred.predict(inst, predPC, tid);
+                    bool predict_taken = branchPred.predict(inst, pred_PC, tid);
 
                     if (predict_taken) {
                         DPRINTF(InOrderBPred, "[tid:%i]: [sn:%i]: Branch "
@@ -103,19 +109,12 @@ BranchPredictor::execute(int slot_num)
                         predictedNotTaken++;
                     }
 
-                    inst->setPredTarg(predPC);
-
                     inst->setBranchPred(predict_taken);
-
-                    DPRINTF(InOrderBPred, "[tid:%i]: [sn:%i]: Predicted PC is "
-                            "%s.\n", tid, seq_num, predPC);
-
-                } else {
-                    inst->setPredTarg(predPC);
-                    //DPRINTF(InOrderBPred, "[tid:%i]: Ignoring [sn:%i] "
-                    //      "because this isn't "
-                    //      "a control instruction.\n", tid, seq_num);
                 }
+
+                inst->setPredTarg(pred_PC);
+                DPRINTF(InOrderBPred, "[tid:%i]: [sn:%i]: Predicted PC is "
+                        "%s.\n", tid, seq_num, pred_PC);
             }
 
             bpred_req->done();
diff --git a/src/cpu/inorder/resources/fetch_seq_unit.cc b/src/cpu/inorder/resources/fetch_seq_unit.cc
index 7fd57cc75..6ed949df3 100644
--- a/src/cpu/inorder/resources/fetch_seq_unit.cc
+++ b/src/cpu/inorder/resources/fetch_seq_unit.cc
@@ -68,8 +68,6 @@ FetchSeqUnit::init()
 void
 FetchSeqUnit::execute(int slot_num)
 {
-    // After this is working, change this to a reinterpret cast
-    // for performance considerations
     ResourceRequest* fs_req = reqMap[slot_num];
     DynInstPtr inst = fs_req->inst;
     ThreadID tid = inst->readTid();
@@ -78,6 +76,9 @@ FetchSeqUnit::execute(int slot_num)
 
     fs_req->fault = NoFault;
 
+    DPRINTF(InOrderFetchSeq, "[tid:%i]: Current PC is %s\n", tid,
+            pc[tid]);
+
     switch (fs_req->cmd)
     {
       case AssignNextPC:
@@ -86,14 +87,13 @@ FetchSeqUnit::execute(int slot_num)
                 inst->pcState(pc[tid]);
                 inst->setMemAddr(pc[tid].instAddr());
 
-                pc[tid].advance(); //XXX HACK!
-                inst->setPredTarg(pc[tid]);
+                // Advance to next PC (typically PC + 4)
+                pc[tid].advance();
 
                 inst->setSeqNum(cpu->getAndIncrementInstSeq(tid));
 
                 DPRINTF(InOrderFetchSeq, "[tid:%i]: Assigning [sn:%i] to "
-                        "PC %s\n", tid, inst->seqNum,
-                        inst->pcState());
+                        "PC %s\n", tid, inst->seqNum, inst->pcState());
 
                 fs_req->done();
             } else {