1 files changed, 238 insertions, 4 deletions

diff --git a/cpu/beta_cpu/bpred_unit_impl.hh b/cpu/beta_cpu/bpred_unit_impl.hh
index 47415ce9b..02c613d34 100644
--- a/cpu/beta_cpu/bpred_unit_impl.hh
+++ b/cpu/beta_cpu/bpred_unit_impl.hh
@@ -1,13 +1,247 @@
 
 #include "cpu/beta_cpu/bpred_unit.hh"
+#include "base/traceflags.hh"
+#include "base/trace.hh"
 
 template<class Impl>
-DefaultBPredUnit<Impl>::DefaultBPredUnit(Params &params)
-  : BP(params.localPredictorSize,
-       params.localPredictorCtrBits,
+TwobitBPredUnit<Impl>::TwobitBPredUnit(Params &params)
+  : BP(params.local_predictor_size,
+       params.local_ctr_bits,
        params.instShiftAmt),
     BTB(params.BTBEntries,
         params.BTBTagSize,
-        params.instShiftAmt)
+        params.instShiftAmt),
+    RAS(params.RASSize)
 {
 }
+
+template <class Impl>
+void
+TwobitBPredUnit<Impl>::regStats()
+{
+    lookups
+        .name(name() + ".BPredUnit.lookups")
+        .desc("Number of BP lookups")
+        ;
+
+    condPredicted
+        .name(name() + ".BPredUnit.condPredicted")
+        .desc("Number of conditional branches predicted")
+        ;
+
+    condIncorrect
+        .name(name() + ".BPredUnit.condIncorrect")
+        .desc("Number of conditional branches incorrect")
+        ;
+
+    BTBLookups
+        .name(name() + ".BPredUnit.BTBLookups")
+        .desc("Number of BTB lookups")
+        ;
+
+    BTBHits
+        .name(name() + ".BPredUnit.BTBHits")
+        .desc("Number of BTB hits")
+        ;
+
+    BTBCorrect
+        .name(name() + ".BPredUnit.BTBCorrect")
+        .desc("Number of correct BTB predictions (this stat may not "
+              "work properly.")
+        ;
+
+    usedRAS
+        .name(name() + ".BPredUnit.usedRAS")
+        .desc("Number of times the RAS was used.")
+        ;
+
+    RASIncorrect
+        .name(name() + ".BPredUnit.RASInCorrect")
+        .desc("Number of incorrect RAS predictions.")
+        ;
+}
+
+template <class Impl>
+bool
+TwobitBPredUnit<Impl>::predict(DynInstPtr &inst, Addr &PC)
+{
+    // See if branch predictor predicts taken.
+    // If so, get its target addr either from the BTB or the RAS.
+    // Once that's done, speculatively update the predictor?
+    // Save off record of branch stuff so the RAS can be fixed
+    // up once it's done.
+
+    bool pred_taken = false;
+    Addr target;
+
+    ++lookups;
+
+    if (inst->isUncondCtrl()) {
+        DPRINTF(Fetch, "BranchPred: Unconditional control.\n");
+        pred_taken = true;
+    } else {
+        ++condPredicted;
+
+        pred_taken = BPLookup(PC);
+
+        DPRINTF(Fetch, "BranchPred: Branch predictor predicted %i for PC %#x"
+                "\n", pred_taken, inst->readPC());
+    }
+
+    PredictorHistory predict_record(inst->seqNum, PC, pred_taken);
+
+    // Now lookup in the BTB or RAS.
+    if (pred_taken) {
+        if (inst->isReturn()) {
+            ++usedRAS;
+
+            // If it's a function return call, then look up the address
+            // in the RAS.
+            target = RAS.top();
+
+            // Record the top entry of the RAS, and its index.
+            predict_record.usedRAS = true;
+            predict_record.RASIndex = RAS.topIdx();
+            predict_record.RASTarget = target;
+
+            RAS.pop();
+
+            DPRINTF(Fetch, "BranchPred: Instruction %#x is a return, RAS "
+                    "predicted target: %#x, RAS index: %i.\n",
+                    inst->readPC(), target, predict_record.RASIndex);
+        } else {
+            ++BTBLookups;
+
+            if (inst->isCall()) {
+                RAS.push(PC+sizeof(MachInst));
+
+                // 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;
+
+                DPRINTF(Fetch, "BranchPred: Instruction %#x was a call, "
+                        "adding %#x to the RAS.\n",
+                        inst->readPC(), PC+sizeof(MachInst));
+            }
+
+            if (BTB.valid(PC)) {
+                ++BTBHits;
+
+                //If it's anything else, use the BTB to get the target addr.
+                target = BTB.lookup(PC);
+
+                DPRINTF(Fetch, "BranchPred: Instruction %#x predicted target "
+                        "is %#x.\n", inst->readPC(), target);
+
+            } else {
+                DPRINTF(Fetch, "BranchPred: BTB doesn't have a valid entry."
+                        "\n");
+                pred_taken = false;
+            }
+
+        }
+    }
+
+    if (pred_taken) {
+        // Set the PC and the instruction's predicted target.
+        PC = target;
+        inst->setPredTarg(target);
+    } else {
+        PC = PC + sizeof(MachInst);
+        inst->setPredTarg(PC);
+    }
+
+    predHist.push_front(predict_record);
+
+    assert(!predHist.empty());
+
+    return pred_taken;
+}
+
+template <class Impl>
+void
+TwobitBPredUnit<Impl>::update(const InstSeqNum &done_sn)
+{
+    DPRINTF(Fetch, "BranchPred: Commiting branches until sequence number "
+            "%i.\n", done_sn);
+
+    while (!predHist.empty() && predHist.back().seqNum <= done_sn) {
+        assert(!predHist.empty());
+
+        // Update the branch predictor with the correct results of branches.
+        BP.update(predHist.back().PC, predHist.back().predTaken);
+
+        predHist.pop_back();
+    }
+}
+
+template <class Impl>
+void
+TwobitBPredUnit<Impl>::squash(const InstSeqNum &squashed_sn)
+{
+    while (!predHist.empty() && predHist.front().seqNum > squashed_sn) {
+        if (predHist.front().usedRAS) {
+            DPRINTF(Fetch, "BranchPred: Restoring top of RAS to: %i, "
+                    "target: %#x.\n",
+                    predHist.front().RASIndex,
+                    predHist.front().RASTarget);
+
+            RAS.restore(predHist.front().RASIndex,
+                        predHist.front().RASTarget);
+        } else if (predHist.front().wasCall) {
+            DPRINTF(Fetch, "BranchPred: Removing speculative entry added "
+                    "to the RAS.\n");
+
+            RAS.pop();
+        }
+
+        predHist.pop_front();
+    }
+}
+
+template <class Impl>
+void
+TwobitBPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
+                              const Addr &corr_target,
+                              const bool actually_taken)
+{
+    // Now that we know that a branch was mispredicted, we need to undo
+    // all the branches that have been seen up until this branch and
+    // fix up everything.
+
+    ++condIncorrect;
+
+    DPRINTF(Fetch, "BranchPred: Squashing from sequence number %i, "
+            "setting target to %#x.\n",
+            squashed_sn, corr_target);
+
+    while (!predHist.empty() && predHist.front().seqNum > squashed_sn) {
+
+        if (predHist.front().usedRAS) {
+            DPRINTF(Fetch, "BranchPred: Restoring top of RAS to: %i, "
+                    "target: %#x.\n",
+                    predHist.front().RASIndex,
+                    predHist.front().RASTarget);
+
+            RAS.restore(predHist.front().RASIndex,
+                        predHist.front().RASTarget);
+        } else if (predHist.front().wasCall) {
+            DPRINTF(Fetch, "BranchPred: Removing speculative entry added "
+                    "to the RAS.\n");
+
+            RAS.pop();
+        }
+
+        predHist.pop_front();
+    }
+
+    predHist.front().predTaken = actually_taken;
+
+    if (predHist.front().usedRAS) {
+        ++RASIncorrect;
+    }
+
+    BP.update(predHist.front().PC, actually_taken);
+
+    BTB.update(predHist.front().PC, corr_target);
+}