cpu: split LTAGE implementation into a base TAGE and a derived LTAGE

The new derived LTAGE is equivalent to the original LTAGE implementation
The default values of the TAGE branch predictor match the settings of the
8C-TAGE configuration described in https://www.jilp.org/vol8/v8paper1.pdf

Change-Id: I8323adbfd5c9a45db23cfff234218280e639f9ed
Signed-off-by: Pau Cabre <pau.cabre@metempsy.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14435
Reviewed-by: Sudhanshu Jha <sudhanshu.jha@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

6 files changed, 1088 insertions, 806 deletions

diff --git a/src/cpu/pred/BranchPredictor.py b/src/cpu/pred/BranchPredictor.py
index 9d83abb0b..2c622cd02 100644
--- a/src/cpu/pred/BranchPredictor.py
+++ b/src/cpu/pred/BranchPredictor.py
@@ -87,34 +87,55 @@ class BiModeBP(BranchPredictor):
     choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
     choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
 
-class LTAGE(BranchPredictor):
-    type = 'LTAGE'
-    cxx_class = 'LTAGE'
-    cxx_header = "cpu/pred/ltage.hh"
+# TAGE branch predictor as described in https://www.jilp.org/vol8/v8paper1.pdf
+# The default sizes below are for the 8C-TAGE configuration (63.5 Kbits)
+class TAGE(BranchPredictor):
+    type = 'TAGE'
+    cxx_class = 'TAGE'
+    cxx_header = "cpu/pred/tage.hh"
 
+    nHistoryTables = Param.Unsigned(7, "Number of history tables")
+    minHist = Param.Unsigned(5, "Minimum history size of LTAGE")
+    maxHist = Param.Unsigned(130, "Maximum history size of LTAGE")
+
+    tagTableTagWidths = VectorParam.Unsigned(
+        [0, 9, 9, 10, 10, 11, 11, 12], "Tag size in TAGE tag tables")
+    logTagTableSizes = VectorParam.Int(
+        [13, 9, 9, 9, 9, 9, 9, 9], "Log2 of TAGE table sizes")
     logRatioBiModalHystEntries = Param.Unsigned(2,
         "Log num of prediction entries for a shared hysteresis bit " \
         "for the Bimodal")
-    logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
-    nHistoryTables = Param.Unsigned(12, "Number of history tables")
+
     tagTableCounterBits = Param.Unsigned(3, "Number of tag table counter bits")
     tagTableUBits = Param.Unsigned(2, "Number of tag table u bits")
+
     histBufferSize = Param.Unsigned(2097152,
             "A large number to track all branch histories(2MEntries default)")
-    minHist = Param.Unsigned(4, "Minimum history size of LTAGE")
-    maxHist = Param.Unsigned(640, "Maximum history size of LTAGE")
+
     pathHistBits = Param.Unsigned(16, "Path history size")
-    tagTableTagWidths = VectorParam.Unsigned(
-        [0, 7, 7, 8, 8, 9, 10, 11, 12, 12, 13, 14, 15],
-        "Tag size in TAGE tag tables")
-    logTagTableSizes = VectorParam.Int(
-        [14, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 9, 9],
-        "Log2 of TAGE table sizes")
-    logUResetPeriod = Param.Unsigned(19,
+    logUResetPeriod = Param.Unsigned(18,
         "Log period in number of branches to reset TAGE useful counters")
     useAltOnNaBits = Param.Unsigned(4, "Size of the USE_ALT_ON_NA counter")
-    withLoopBits = Param.Unsigned(7, "Size of the WITHLOOP counter")
 
+
+# LTAGE branch predictor as described in
+# https://www.irisa.fr/caps/people/seznec/L-TAGE.pdf
+# It is basically a TAGE predictor plus a loop predictor
+# The differnt TAGE sizes are updated according to the paper values (256 Kbits)
+class LTAGE(TAGE):
+    type = 'LTAGE'
+    cxx_class = 'LTAGE'
+    cxx_header = "cpu/pred/ltage.hh"
+
+    nHistoryTables = 12
+    minHist = 4
+    maxHist = 640
+    tagTableTagWidths = [0, 7, 7, 8, 8, 9, 10, 11, 12, 12, 13, 14, 15]
+    logTagTableSizes = [14, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 9, 9]
+    logUResetPeriod = 19
+
+    logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
+    withLoopBits = Param.Unsigned(7, "Size of the WITHLOOP counter")
     loopTableAgeBits = Param.Unsigned(8, "Number of age bits per loop entry")
     loopTableConfidenceBits = Param.Unsigned(2,
             "Number of confidence bits per loop entry")
diff --git a/src/cpu/pred/SConscript b/src/cpu/pred/SConscript
index 1cdf7bbd7..b0e63096a 100644
--- a/src/cpu/pred/SConscript
+++ b/src/cpu/pred/SConscript
@@ -43,7 +43,9 @@ Source('indirect.cc')
 Source('ras.cc')
 Source('tournament.cc')
 Source ('bi_mode.cc')
+Source('tage.cc')
 Source('ltage.cc')
 DebugFlag('FreeList')
 DebugFlag('Branch')
+DebugFlag('Tage')
 DebugFlag('LTage')
diff --git a/src/cpu/pred/ltage.cc b/src/cpu/pred/ltage.cc
index d6cc087e6..3be01936e 100644
--- a/src/cpu/pred/ltage.cc
+++ b/src/cpu/pred/ltage.cc
@@ -48,16 +48,8 @@
 #include "debug/LTage.hh"
 
 LTAGE::LTAGE(const LTAGEParams *params)
-  : BPredUnit(params),
-    logRatioBiModalHystEntries(params->logRatioBiModalHystEntries),
+  : TAGE(params),
     logSizeLoopPred(params->logSizeLoopPred),
-    nHistoryTables(params->nHistoryTables),
-    tagTableCounterBits(params->tagTableCounterBits),
-    tagTableUBits(params->tagTableUBits),
-    histBufferSize(params->histBufferSize),
-    minHist(params->minHist),
-    maxHist(params->maxHist),
-    pathHistBits(params->pathHistBits),
     loopTableAgeBits(params->loopTableAgeBits),
     loopTableConfidenceBits(params->loopTableConfidenceBits),
     loopTableTagBits(params->loopTableTagBits),
@@ -66,18 +58,9 @@ LTAGE::LTAGE(const LTAGEParams *params)
     confidenceThreshold((1 << loopTableConfidenceBits) - 1),
     loopTagMask((1 << loopTableTagBits) - 1),
     loopNumIterMask((1 << loopTableIterBits) - 1),
-    tagTableTagWidths(params->tagTableTagWidths),
-    logTagTableSizes(params->logTagTableSizes),
-    threadHistory(params->numThreads),
-    logUResetPeriod(params->logUResetPeriod),
-    useAltOnNaBits(params->useAltOnNaBits),
+    loopUseCounter(0),
     withLoopBits(params->withLoopBits)
 {
-    // Current method for periodically resetting the u counter bits only
-    // works for 1 or 2 bits
-    // Also make sure that it is not 0
-    assert(tagTableUBits <= 2 && (tagTableUBits > 0));
-
     // we use uint16_t type for these vales, so they cannot be more than
     // 16 bits
     assert(loopTableTagBits <= 16);
@@ -85,81 +68,7 @@ LTAGE::LTAGE(const LTAGEParams *params)
 
     assert(logSizeLoopPred >= logLoopTableAssoc);
 
-    // we use int type for the path history, so it cannot be more than
-    // its size
-    assert(pathHistBits <= (sizeof(int)*8));
-
-    // initialize the counter to half of the period
-    assert(logUResetPeriod != 0);
-    tCounter = ULL(1) << (logUResetPeriod - 1);
-
-    assert(params->histBufferSize > params->maxHist * 2);
-    useAltPredForNewlyAllocated = 0;
-
-    for (auto& history : threadHistory) {
-        history.pathHist = 0;
-        history.globalHistory = new uint8_t[histBufferSize];
-        history.gHist = history.globalHistory;
-        memset(history.gHist, 0, histBufferSize);
-        history.ptGhist = 0;
-    }
-
-    histLengths = new int [nHistoryTables+1];
-    histLengths[1] = minHist;
-    histLengths[nHistoryTables] = maxHist;
-
-    for (int i = 2; i <= nHistoryTables; i++) {
-        histLengths[i] = (int) (((double) minHist *
-                    pow ((double) (maxHist) / (double) minHist,
-                        (double) (i - 1) / (double) ((nHistoryTables- 1))))
-                    + 0.5);
-    }
-
-    assert(tagTableTagWidths.size() == (nHistoryTables+1));
-    assert(logTagTableSizes.size() == (nHistoryTables+1));
-
-    // First entry is for the Bimodal table and it is untagged in this
-    // implementation
-    assert(tagTableTagWidths[0] == 0);
-
-    for (auto& history : threadHistory) {
-        history.computeIndices = new FoldedHistory[nHistoryTables+1];
-        history.computeTags[0] = new FoldedHistory[nHistoryTables+1];
-        history.computeTags[1] = new FoldedHistory[nHistoryTables+1];
-
-        for (int i = 1; i <= nHistoryTables; i++) {
-            history.computeIndices[i].init(
-                histLengths[i], (logTagTableSizes[i]));
-            history.computeTags[0][i].init(
-                history.computeIndices[i].origLength, tagTableTagWidths[i]);
-            history.computeTags[1][i].init(
-                history.computeIndices[i].origLength, tagTableTagWidths[i]-1);
-            DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
-                    histLengths[i], logTagTableSizes[i], tagTableTagWidths[i]);
-        }
-    }
-
-    const uint64_t bimodalTableSize = ULL(1) << logTagTableSizes[0];
-    btablePrediction.resize(bimodalTableSize, false);
-    btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
-                            true);
-
     ltable = new LoopEntry[ULL(1) << logSizeLoopPred];
-    gtable = new TageEntry*[nHistoryTables + 1];
-    for (int i = 1; i <= nHistoryTables; i++) {
-        gtable[i] = new TageEntry[1<<(logTagTableSizes[i])];
-    }
-
-    tableIndices = new int [nHistoryTables+1];
-    tableTags = new int [nHistoryTables+1];
-
-    loopUseCounter = 0;
-}
-
-int
-LTAGE::bindex(Addr pc_in) const
-{
-    return ((pc_in >> instShiftAmt) & ((ULL(1) << (logTagTableSizes[0])) - 1));
 }
 
 int
@@ -176,113 +85,9 @@ LTAGE::lindex(Addr pc_in) const
     return (((pc_in >> instShiftAmt) & mask) << logLoopTableAssoc);
 }
 
-int
-LTAGE::F(int A, int size, int bank) const
-{
-    int A1, A2;
-
-    A = A & ((ULL(1) << size) - 1);
-    A1 = (A & ((ULL(1) << logTagTableSizes[bank]) - 1));
-    A2 = (A >> logTagTableSizes[bank]);
-    A2 = ((A2 << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
-       + (A2 >> (logTagTableSizes[bank] - bank));
-    A = A1 ^ A2;
-    A = ((A << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
-      + (A >> (logTagTableSizes[bank] - bank));
-    return (A);
-}
-
-
-// gindex computes a full hash of pc, ghist and pathHist
-int
-LTAGE::gindex(ThreadID tid, Addr pc, int bank) const
-{
-    int index;
-    int hlen = (histLengths[bank] > pathHistBits) ? pathHistBits :
-                                                    histLengths[bank];
-    const Addr shiftedPc = pc >> instShiftAmt;
-    index =
-        shiftedPc ^
-        (shiftedPc >> ((int) abs(logTagTableSizes[bank] - bank) + 1)) ^
-        threadHistory[tid].computeIndices[bank].comp ^
-        F(threadHistory[tid].pathHist, hlen, bank);
-
-    return (index & ((ULL(1) << (logTagTableSizes[bank])) - 1));
-}
-
-
-// Tag computation
-uint16_t
-LTAGE::gtag(ThreadID tid, Addr pc, int bank) const
-{
-    int tag = (pc >> instShiftAmt) ^
-              threadHistory[tid].computeTags[0][bank].comp ^
-              (threadHistory[tid].computeTags[1][bank].comp << 1);
-
-    return (tag & ((ULL(1) << tagTableTagWidths[bank]) - 1));
-}
-
-
-// Up-down saturating counter
-void
-LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits)
-{
-    assert(nbits <= sizeof(int8_t) << 3);
-    if (taken) {
-        if (ctr < ((1 << (nbits - 1)) - 1))
-            ctr++;
-    } else {
-        if (ctr > -(1 << (nbits - 1)))
-            ctr--;
-    }
-}
-
-// Up-down unsigned saturating counter
-void
-LTAGE::unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits)
-{
-    assert(nbits <= sizeof(uint8_t) << 3);
-    if (up) {
-        if (ctr < ((1 << nbits) - 1))
-            ctr++;
-    } else {
-        if (ctr)
-            ctr--;
-    }
-}
-
-// Bimodal prediction
-bool
-LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const
-{
-    return btablePrediction[bi->bimodalIndex];
-}
-
-
-// Update the bimodal predictor: a hysteresis bit is shared among N prediction
-// bits (N = 2 ^ logRatioBiModalHystEntries)
-void
-LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi)
-{
-    int inter = (btablePrediction[bi->bimodalIndex] << 1)
-        + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries];
-    if (taken) {
-        if (inter < 3)
-            inter++;
-    } else if (inter > 0) {
-        inter--;
-    }
-    const bool pred = inter >> 1;
-    const bool hyst = inter & 1;
-    btablePrediction[bi->bimodalIndex] = pred;
-    btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst;
-    DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst);
-}
-
-
 //loop prediction: only used if high confidence
 bool
-LTAGE::getLoop(Addr pc, BranchInfo* bi) const
+LTAGE::getLoop(Addr pc, LTageBranchInfo* bi) const
 {
     bi->loopHit = -1;
     bi->loopPredValid = false;
@@ -308,7 +113,7 @@ LTAGE::getLoop(Addr pc, BranchInfo* bi) const
 }
 
 void
-LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi)
+LTAGE::specLoopUpdate(Addr pc, bool taken, LTageBranchInfo* bi)
 {
     if (bi->loopHit>=0) {
         int index = lindex(pc);
@@ -322,7 +127,7 @@ LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi)
 }
 
 void
-LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi)
+LTAGE::loopUpdate(Addr pc, bool taken, LTageBranchInfo* bi)
 {
     int idx = bi->loopIndex + bi->loopHit;
     if (bi->loopHit >= 0) {
@@ -409,319 +214,57 @@ LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi)
 
 }
 
-// shifting the global history:  we manage the history in a big table in order
-// to reduce simulation time
-void
-LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt)
-{
-    if (pt == 0) {
-        DPRINTF(LTage, "Rolling over the histories\n");
-         // Copy beginning of globalHistoryBuffer to end, such that
-         // the last maxHist outcomes are still reachable
-         // through pt[0 .. maxHist - 1].
-         for (int i = 0; i < maxHist; i++)
-             tab[histBufferSize - maxHist + i] = tab[i];
-         pt =  histBufferSize - maxHist;
-         h = &tab[pt];
-    }
-    pt--;
-    h--;
-    h[0] = (dir) ? 1 : 0;
-}
-
-// Get GHR for hashing indirect predictor
-// Build history backwards from pointer in
-// bp_history.
-unsigned
-LTAGE::getGHR(ThreadID tid, void *bp_history) const
-{
-    BranchInfo* bi = static_cast<BranchInfo*>(bp_history);
-    unsigned val = 0;
-    for (unsigned i = 0; i < 32; i++) {
-        // Make sure we don't go out of bounds
-        int gh_offset = bi->ptGhist + i;
-        assert(&(threadHistory[tid].globalHistory[gh_offset]) <
-               threadHistory[tid].globalHistory + histBufferSize);
-        val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i);
-    }
-
-    return val;
-}
-
 //prediction
 bool
 LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
 {
-    BranchInfo *bi = new BranchInfo(nHistoryTables+1);
+    LTageBranchInfo *bi = new LTageBranchInfo(nHistoryTables+1);
     b = (void*)(bi);
-    Addr pc = branch_pc;
-    bool pred_taken = true;
-    bi->loopHit = -1;
 
-    if (cond_branch) {
-        // TAGE prediction
-
-        // computes the table addresses and the partial tags
-        for (int i = 1; i <= nHistoryTables; i++) {
-            tableIndices[i] = gindex(tid, pc, i);
-            bi->tableIndices[i] = tableIndices[i];
-            tableTags[i] = gtag(tid, pc, i);
-            bi->tableTags[i] = tableTags[i];
-        }
+    bool pred_taken = tagePredict(tid, branch_pc, cond_branch, bi);
 
-        bi->bimodalIndex = bindex(pc);
-
-        bi->hitBank = 0;
-        bi->altBank = 0;
-        //Look for the bank with longest matching history
-        for (int i = nHistoryTables; i > 0; i--) {
-            if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
-                bi->hitBank = i;
-                bi->hitBankIndex = tableIndices[bi->hitBank];
-                break;
-            }
-        }
-        //Look for the alternate bank
-        for (int i = bi->hitBank - 1; i > 0; i--) {
-            if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
-                bi->altBank = i;
-                bi->altBankIndex = tableIndices[bi->altBank];
-                break;
-            }
-        }
-        //computes the prediction and the alternate prediction
-        if (bi->hitBank > 0) {
-            if (bi->altBank > 0) {
-                bi->altTaken =
-                    gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0;
-            }else {
-                bi->altTaken = getBimodePred(pc, bi);
-            }
+    if (cond_branch) {
+        bi->loopPred = getLoop(branch_pc, bi);	// loop prediction
 
-            bi->longestMatchPred =
-                gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0;
-            bi->pseudoNewAlloc =
-                abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1;
-
-            //if the entry is recognized as a newly allocated entry and
-            //useAltPredForNewlyAllocated is positive use the alternate
-            //prediction
-            if ((useAltPredForNewlyAllocated < 0)
-                   || abs(2 *
-                   gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
-                bi->tagePred = bi->longestMatchPred;
-            else
-                bi->tagePred = bi->altTaken;
-        } else {
-            bi->altTaken = getBimodePred(pc, bi);
-            bi->tagePred = bi->altTaken;
-            bi->longestMatchPred = bi->altTaken;
+        if ((loopUseCounter >= 0) && bi->loopPredValid) {
+            pred_taken = bi->loopPred;
         }
-        //end TAGE prediction
-
-        bi->loopPred = getLoop(pc, bi);	// loop prediction
-
-        pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ?
-                     (bi->loopPred): (bi->tagePred);
         DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, "
                 "loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n",
                 branch_pc, pred_taken, bi->loopPred, bi->loopPredValid,
                 loopUseCounter, bi->tagePred, bi->altTaken);
     }
-    bi->branchPC = branch_pc;
-    bi->condBranch = cond_branch;
+
     specLoopUpdate(branch_pc, pred_taken, bi);
     return pred_taken;
 }
 
-// PREDICTOR UPDATE
 void
-LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
-              bool squashed)
+LTAGE::condBranchUpdate(Addr branch_pc, bool taken,
+                        TageBranchInfo* tage_bi, int nrand)
 {
-    assert(bp_history);
-
-    BranchInfo *bi = static_cast<BranchInfo*>(bp_history);
-
-    if (squashed) {
-        // This restores the global history, then update it
-        // and recomputes the folded histories.
-        squash(tid, taken, bp_history);
-        return;
-    }
-
-    int nrand  = random_mt.random<int>(0,3);
-    Addr pc = branch_pc;
-    if (bi->condBranch) {
-        DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n",
-                branch_pc, taken);
-        // first update the loop predictor
-        loopUpdate(pc, taken, bi);
-
-        if (bi->loopPredValid) {
-            if (bi->tagePred != bi->loopPred) {
-                ctrUpdate(loopUseCounter,
-                          (bi->loopPred == taken),
-                          withLoopBits);
-            }
-        }
-
-        // TAGE UPDATE
-        // try to allocate a  new entries only if prediction was wrong
-        bool longest_match_pred = false;
-        bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
-        if (bi->hitBank > 0) {
-            // Manage the selection between longest matching and alternate
-            // matching for "pseudo"-newly allocated longest matching entry
-             longest_match_pred = bi->longestMatchPred;
-            bool PseudoNewAlloc = bi->pseudoNewAlloc;
-            // an entry is considered as newly allocated if its prediction
-            // counter is weak
-            if (PseudoNewAlloc) {
-                if (longest_match_pred == taken) {
-                    alloc = false;
-                }
-                // if it was delivering the correct prediction, no need to
-                // allocate new entry even if the overall prediction was false
-                if (longest_match_pred != bi->altTaken) {
-                    ctrUpdate(useAltPredForNewlyAllocated,
-                         bi->altTaken == taken, useAltOnNaBits);
-                }
-            }
-        }
-
-        if (alloc) {
-            // is there some "unuseful" entry to allocate
-            uint8_t min = 1;
-            for (int i = nHistoryTables; i > bi->hitBank; i--) {
-                if (gtable[i][bi->tableIndices[i]].u < min) {
-                    min = gtable[i][bi->tableIndices[i]].u;
-                }
-            }
-
-            // we allocate an entry with a longer history
-            // to  avoid ping-pong, we do not choose systematically the next
-            // entry, but among the 3 next entries
-            int Y = nrand &
-                ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1);
-            int X = bi->hitBank + 1;
-            if (Y & 1) {
-                X++;
-                if (Y & 2)
-                    X++;
-            }
-            // No entry available, forces one to be available
-            if (min > 0) {
-                gtable[X][bi->tableIndices[X]].u = 0;
-            }
-
-
-            //Allocate only  one entry
-            for (int i = X; i <= nHistoryTables; i++) {
-                if ((gtable[i][bi->tableIndices[i]].u == 0)) {
-                    gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i];
-                    gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1;
-                    break;
-                }
-            }
-        }
-        //periodic reset of u: reset is not complete but bit by bit
-        tCounter++;
-        if ((tCounter & ((ULL(1) << logUResetPeriod) - 1)) == 0) {
-            // reset least significant bit
-            // most significant bit becomes least significant bit
-            for (int i = 1; i <= nHistoryTables; i++) {
-                for (int j = 0; j < (ULL(1) << logTagTableSizes[i]); j++) {
-                    gtable[i][j].u = gtable[i][j].u >> 1;
-                }
-            }
-        }
+    LTageBranchInfo* bi = static_cast<LTageBranchInfo*>(tage_bi);
 
-        if (bi->hitBank > 0) {
-            DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n",
-                    bi->hitBank, bi->hitBankIndex, branch_pc);
-            ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken,
-                      tagTableCounterBits);
-            // if the provider entry is not certified to be useful also update
-            // the alternate prediction
-            if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) {
-                if (bi->altBank > 0) {
-                    ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken,
-                              tagTableCounterBits);
-                    DPRINTF(LTage, "Updating tag table entry (%d,%d) for"
-                            " branch %lx\n", bi->hitBank, bi->hitBankIndex,
-                            branch_pc);
-                }
-                if (bi->altBank == 0) {
-                    baseUpdate(pc, taken, bi);
-                }
-            }
+    // first update the loop predictor
+    loopUpdate(branch_pc, taken, bi);
 
-            // update the u counter
-            if (bi->tagePred != bi->altTaken) {
-                unsignedCtrUpdate(gtable[bi->hitBank][bi->hitBankIndex].u,
-                                  bi->tagePred == taken, tagTableUBits);
-            }
-        } else {
-            baseUpdate(pc, taken, bi);
+    if (bi->loopPredValid) {
+        if (bi->tagePred != bi->loopPred) {
+            ctrUpdate(loopUseCounter,
+                      (bi->loopPred == taken),
+                      withLoopBits);
         }
-
-        //END PREDICTOR UPDATE
     }
-    if (!squashed) {
-        delete bi;
-    }
-}
 
-void
-LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b)
-{
-    BranchInfo* bi = (BranchInfo*)(b);
-    ThreadHistory& tHist = threadHistory[tid];
-    //  UPDATE HISTORIES
-    bool pathbit = ((branch_pc >> instShiftAmt) & 1);
-    //on a squash, return pointers to this and recompute indices.
-    //update user history
-    updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist);
-    tHist.pathHist = (tHist.pathHist << 1) + pathbit;
-    tHist.pathHist = (tHist.pathHist & ((ULL(1) << pathHistBits) - 1));
-
-    bi->ptGhist = tHist.ptGhist;
-    bi->pathHist = tHist.pathHist;
-    //prepare next index and tag computations for user branchs
-    for (int i = 1; i <= nHistoryTables; i++)
-    {
-        bi->ci[i]  = tHist.computeIndices[i].comp;
-        bi->ct0[i] = tHist.computeTags[0][i].comp;
-        bi->ct1[i] = tHist.computeTags[1][i].comp;
-        tHist.computeIndices[i].update(tHist.gHist);
-        tHist.computeTags[0][i].update(tHist.gHist);
-        tHist.computeTags[1][i].update(tHist.gHist);
-    }
-    DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, "
-            "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist,
-            tHist.ptGhist);
+    TAGE::condBranchUpdate(branch_pc, taken, bi, nrand);
 }
 
 void
 LTAGE::squash(ThreadID tid, bool taken, void *bp_history)
 {
-    BranchInfo* bi = (BranchInfo*)(bp_history);
-    ThreadHistory& tHist = threadHistory[tid];
-    DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, "
-            "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist);
-    tHist.pathHist = bi->pathHist;
-    tHist.ptGhist = bi->ptGhist;
-    tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]);
-    tHist.gHist[0] = (taken ? 1 : 0);
-    for (int i = 1; i <= nHistoryTables; i++) {
-        tHist.computeIndices[i].comp = bi->ci[i];
-        tHist.computeTags[0][i].comp = bi->ct0[i];
-        tHist.computeTags[1][i].comp = bi->ct1[i];
-        tHist.computeIndices[i].update(tHist.gHist);
-        tHist.computeTags[0][i].update(tHist.gHist);
-        tHist.computeTags[1][i].update(tHist.gHist);
-    }
+    TAGE::squash(tid, taken, bp_history);
+
+    LTageBranchInfo* bi = (LTageBranchInfo*)(bp_history);
 
     if (bi->condBranch) {
         if (bi->loopHit >= 0) {
@@ -729,14 +272,12 @@ LTAGE::squash(ThreadID tid, bool taken, void *bp_history)
             ltable[idx].currentIterSpec = bi->currentIter;
         }
     }
-
 }
 
 void
 LTAGE::squash(ThreadID tid, void *bp_history)
 {
-    BranchInfo* bi = (BranchInfo*)(bp_history);
-    DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC);
+    LTageBranchInfo* bi = (LTageBranchInfo*)(bp_history);
     if (bi->condBranch) {
         if (bi->loopHit >= 0) {
             int idx = bi->loopIndex + bi->loopHit;
@@ -744,48 +285,7 @@ LTAGE::squash(ThreadID tid, void *bp_history)
         }
     }
 
-    delete bi;
-}
-
-bool
-LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
-{
-    bool retval = predict(tid, branch_pc, true, bp_history);
-
-    DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
-    updateHistories(tid, branch_pc, retval, bp_history);
-    assert(threadHistory[tid].gHist ==
-           &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
-
-    return retval;
-}
-
-void
-LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
-{
-    BranchInfo* bi = (BranchInfo*) bp_history;
-    ThreadHistory& tHist = threadHistory[tid];
-    DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc);
-    assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]);
-    tHist.gHist[0] = 0;
-    for (int i = 1; i <= nHistoryTables; i++) {
-        tHist.computeIndices[i].comp = bi->ci[i];
-        tHist.computeTags[0][i].comp = bi->ct0[i];
-        tHist.computeTags[1][i].comp = bi->ct1[i];
-        tHist.computeIndices[i].update(tHist.gHist);
-        tHist.computeTags[0][i].update(tHist.gHist);
-        tHist.computeTags[1][i].update(tHist.gHist);
-    }
-}
-
-void
-LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
-{
-    DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc);
-    predict(tid, br_pc, false, bp_history);
-    updateHistories(tid, br_pc, true, bp_history);
-    assert(threadHistory[tid].gHist ==
-           &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
+    TAGE::squash(tid, bp_history);
 }
 
 LTAGE*
diff --git a/src/cpu/pred/ltage.hh b/src/cpu/pred/ltage.hh
index 8b417d44d..d614026d2 100644
--- a/src/cpu/pred/ltage.hh
+++ b/src/cpu/pred/ltage.hh
@@ -52,25 +52,20 @@
 #ifndef __CPU_PRED_LTAGE
 #define __CPU_PRED_LTAGE
 
+
 #include <vector>
 
 #include "base/types.hh"
-#include "cpu/pred/bpred_unit.hh"
+#include "cpu/pred/tage.hh"
 #include "params/LTAGE.hh"
 
-class LTAGE: public BPredUnit
+class LTAGE: public TAGE
 {
   public:
     LTAGE(const LTAGEParams *params);
 
     // Base class methods.
-    void uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history) override;
-    bool lookup(ThreadID tid, Addr branch_addr, void* &bp_history) override;
-    void btbUpdate(ThreadID tid, Addr branch_addr, void* &bp_history) override;
-    void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
-                bool squashed) override;
     void squash(ThreadID tid, void *bp_history) override;
-    unsigned getGHR(ThreadID tid, void *bp_history) const override;
 
   private:
     // Prediction Structures
@@ -89,189 +84,40 @@ class LTAGE: public BPredUnit
                       confidence(0), tag(0), age(0), dir(0) { }
     };
 
-    // Tage Entry
-    struct TageEntry
-    {
-        int8_t ctr;
-        uint16_t tag;
-        uint8_t u;
-        TageEntry() : ctr(0), tag(0), u(0) { }
-    };
-
-    // Folded History Table - compressed history
-    // to mix with instruction PC to index partially
-    // tagged tables.
-    struct FoldedHistory
-    {
-        unsigned comp;
-        int compLength;
-        int origLength;
-        int outpoint;
-
-        void init(int original_length, int compressed_length)
-        {
-            comp = 0;
-            origLength = original_length;
-            compLength = compressed_length;
-            outpoint = original_length % compressed_length;
-        }
-
-        void update(uint8_t * h)
-        {
-            comp = (comp << 1) | h[0];
-            comp ^= h[origLength] << outpoint;
-            comp ^= (comp >> compLength);
-            comp &= (ULL(1) << compLength) - 1;
-        }
-    };
-
     // Primary branch history entry
-    struct BranchInfo
+    struct LTageBranchInfo : public TageBranchInfo
     {
-        int pathHist;
-        int ptGhist;
-        int hitBank;
-        int hitBankIndex;
-        int altBank;
-        int altBankIndex;
-        int bimodalIndex;
         uint16_t loopTag;
         uint16_t currentIter;
 
-        bool tagePred;
-        bool altTaken;
         bool loopPred;
         bool loopPredValid;
         int  loopIndex;
         int loopHit;
-        bool condBranch;
-        bool longestMatchPred;
-        bool pseudoNewAlloc;
-        Addr branchPC;
-
-        // Pointer to dynamically allocated storage
-        // to save table indices and folded histories.
-        // To do one call to new instead of five.
-        int *storage;
-
-        // Pointers to actual saved array within the dynamically
-        // allocated storage.
-        int *tableIndices;
-        int *tableTags;
-        int *ci;
-        int *ct0;
-        int *ct1;
 
-        BranchInfo(int sz)
-            : pathHist(0), ptGhist(0),
-              hitBank(0), hitBankIndex(0),
-              altBank(0), altBankIndex(0),
-              bimodalIndex(0), loopTag(0), currentIter(0),
-              tagePred(false), altTaken(false), loopPred(false),
-              loopPredValid(false), loopIndex(0), loopHit(0),
-              condBranch(false), longestMatchPred(false),
-              pseudoNewAlloc(false), branchPC(0)
-        {
-            storage = new int [sz * 5];
-            tableIndices = storage;
-            tableTags = storage + sz;
-            ci = tableTags + sz;
-            ct0 = ci + sz;
-            ct1 = ct0 + sz;
-        }
-
-        ~BranchInfo()
-        {
-            delete[] storage;
-        }
+        LTageBranchInfo(int sz)
+            : TageBranchInfo(sz),
+              loopTag(0), currentIter(0),
+              loopPred(false),
+              loopPredValid(false), loopIndex(0), loopHit(0)
+        {}
     };
 
     /**
      * Computes the index used to access the
-     * bimodal table.
-     * @param pc_in The unshifted branch PC.
-     */
-    int bindex(Addr pc_in) const;
-
-    /**
-     * Computes the index used to access the
      * loop predictor.
      * @param pc_in The unshifted branch PC.
      */
     int lindex(Addr pc_in) const;
 
     /**
-     * Computes the index used to access a
-     * partially tagged table.
-     * @param tid The thread ID used to select the
-     * global histories to use.
-     * @param pc The unshifted branch PC.
-     * @param bank The partially tagged table to access.
-     */
-    inline int gindex(ThreadID tid, Addr pc, int bank) const;
-
-    /**
-     * Utility function to shuffle the path history
-     * depending on which tagged table we are accessing.
-     * @param phist The path history.
-     * @param size Number of path history bits to use.
-     * @param bank The partially tagged table to access.
-     */
-    int F(int phist, int size, int bank) const;
-
-    /**
-     * Computes the partial tag of a tagged table.
-     * @param tid the thread ID used to select the
-     * global histories to use.
-     * @param pc The unshifted branch PC.
-     * @param bank The partially tagged table to access.
-     */
-    inline uint16_t gtag(ThreadID tid, Addr pc, int bank) const;
-
-    /**
-     * Updates a direction counter based on the actual
-     * branch outcome.
-     * @param ctr Reference to counter to update.
-     * @param taken Actual branch outcome.
-     * @param nbits Counter width.
-     */
-    void ctrUpdate(int8_t & ctr, bool taken, int nbits);
-
-    /**
-     * Updates an unsigned counter based on up/down parameter
-     * @param ctr Reference to counter to update.
-     * @param up Boolean indicating if the counter is incremented/decremented
-     * If true it is incremented, if false it is decremented
-     * @param nbits Counter width.
-     */
-    void unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits);
-
-    /**
-     * Get a branch prediction from the bimodal
-     * predictor.
-     * @param pc The unshifted branch PC.
-     * @param bi Pointer to information on the
-     * prediction.
-     */
-    bool getBimodePred(Addr pc, BranchInfo* bi) const;
-
-    /**
-     * Updates the bimodal predictor.
-     * @param pc The unshifted branch PC.
-     * @param taken The actual branch outcome.
-     * @param bi Pointer to information on the prediction
-     * recorded at prediction time.
-     */
-    void baseUpdate(Addr pc, bool taken, BranchInfo* bi);
-
-    /**
      * Get a branch prediction from the loop
      * predictor.
      * @param pc The unshifted branch PC.
      * @param bi Pointer to information on the
      * prediction.
      */
-    bool getLoop(Addr pc, BranchInfo* bi) const;
+    bool getLoop(Addr pc, LTageBranchInfo* bi) const;
 
    /**
     * Updates the loop predictor.
@@ -280,55 +126,41 @@ class LTAGE: public BPredUnit
     * @param bi Pointer to information on the
     * prediction recorded at prediction time.
     */
-    void loopUpdate(Addr pc, bool Taken, BranchInfo* bi);
-
-   /**
-    * (Speculatively) updates the global branch history.
-    * @param h Reference to pointer to global branch history.
-    * @param dir (Predicted) outcome to update the histories
-    * with.
-    * @param tab
-    * @param PT Reference to path history.
-    */
-    void updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &PT);
+    void loopUpdate(Addr pc, bool Taken, LTageBranchInfo* bi);
 
     /**
-     * Get a branch prediction from L-TAGE. *NOT* an override of
-     * BpredUnit::predict().
-     * @param tid The thread ID to select the global
-     * histories to use.
-     * @param branch_pc The unshifted branch PC.
-     * @param cond_branch True if the branch is conditional.
-     * @param b Reference to wrapping pointer to allow storing
-     * derived class prediction information in the base class.
+     * Speculatively updates the loop predictor
+     * iteration count.
+     * @param pc The unshifted branch PC.
+     * @param taken The predicted branch outcome.
+     * @param bi Pointer to information on the prediction
+     * recorded at prediction time.
      */
-    bool predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b);
+    void specLoopUpdate(Addr pc, bool taken, LTageBranchInfo* bi);
 
     /**
-     * Update L-TAGE. Called at execute to repair histories on a misprediction
-     * and at commit to update the tables.
-     * @param tid The thread ID to select the global
-     * histories to use.
+     * Update LTAGE for conditional branches.
      * @param branch_pc The unshifted branch PC.
      * @param taken Actual branch outcome.
      * @param bi Pointer to information on the prediction
      * recorded at prediction time.
+     * @nrand Random int number from 0 to 3
      */
-    void update(ThreadID tid, Addr branch_pc, bool taken, BranchInfo* bi);
+    void condBranchUpdate(
+        Addr branch_pc, bool taken, TageBranchInfo* bi, int nrand) override;
 
-   /**
-    * (Speculatively) updates global histories (path and direction).
-    * Also recomputes compressed (folded) histories based on the
-    * branch direction.
-    * @param tid The thread ID to select the histories
-    * to update.
-    * @param branch_pc The unshifted branch PC.
-    * @param taken (Predicted) branch direction.
-    * @param b Wrapping pointer to BranchInfo (to allow
-    * storing derived class prediction information in the
-    * base class).
-    */
-    void updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b);
+    /**
+     * Get a branch prediction from LTAGE. *NOT* an override of
+     * BpredUnit::predict().
+     * @param tid The thread ID to select the global
+     * histories to use.
+     * @param branch_pc The unshifted branch PC.
+     * @param cond_branch True if the branch is conditional.
+     * @param b Reference to wrapping pointer to allow storing
+     * derived class prediction information in the base class.
+     */
+    bool predict(
+        ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
 
     /**
      * Restores speculatively updated path and direction histories.
@@ -337,32 +169,15 @@ class LTAGE: public BPredUnit
      * This version of squash() is called once on a branch misprediction.
      * @param tid The Thread ID to select the histories to rollback.
      * @param taken The correct branch outcome.
-     * @param bp_history Wrapping pointer to BranchInfo (to allow
+     * @param bp_history Wrapping pointer to TageBranchInfo (to allow
      * storing derived class prediction information in the
      * base class).
      * @post bp_history points to valid memory.
      */
-    void squash(ThreadID tid, bool taken, void *bp_history);
-
-    /**
-     * Speculatively updates the loop predictor
-     * iteration count.
-     * @param pc The unshifted branch PC.
-     * @param taken The predicted branch outcome.
-     * @param bi Pointer to information on the prediction
-     * recorded at prediction time.
-     */
-    void specLoopUpdate(Addr pc, bool taken, BranchInfo* bi);
+    void squash(
+        ThreadID tid, bool taken, void *bp_history) override;
 
-    const unsigned logRatioBiModalHystEntries;
     const unsigned logSizeLoopPred;
-    const unsigned nHistoryTables;
-    const unsigned tagTableCounterBits;
-    const unsigned tagTableUBits;
-    const unsigned histBufferSize;
-    const unsigned minHist;
-    const unsigned maxHist;
-    const unsigned pathHistBits;
     const unsigned loopTableAgeBits;
     const unsigned loopTableConfidenceBits;
     const unsigned loopTableTagBits;
@@ -372,48 +187,9 @@ class LTAGE: public BPredUnit
     const uint16_t loopTagMask;
     const uint16_t loopNumIterMask;
 
-    const std::vector<unsigned> tagTableTagWidths;
-    const std::vector<int> logTagTableSizes;
-
-    std::vector<bool> btablePrediction;
-    std::vector<bool> btableHysteresis;
-    TageEntry **gtable;
     LoopEntry *ltable;
 
-    // Keep per-thread histories to
-    // support SMT.
-    struct ThreadHistory {
-        // Speculative path history
-        // (LSB of branch address)
-        int pathHist;
-
-        // Speculative branch direction
-        // history (circular buffer)
-        // @TODO Convert to std::vector<bool>
-        uint8_t *globalHistory;
-
-        // Pointer to most recent branch outcome
-        uint8_t* gHist;
-
-        // Index to most recent branch outcome
-        int ptGhist;
-
-        // Speculative folded histories.
-        FoldedHistory *computeIndices;
-        FoldedHistory *computeTags[2];
-    };
-
-    std::vector<ThreadHistory> threadHistory;
-
-    int *histLengths;
-    int *tableIndices;
-    int *tableTags;
-
     int8_t loopUseCounter;
-    int8_t useAltPredForNewlyAllocated;
-    uint64_t tCounter;
-    uint64_t logUResetPeriod;
-    unsigned useAltOnNaBits;
     unsigned withLoopBits;
 };
 
diff --git a/src/cpu/pred/tage.cc b/src/cpu/pred/tage.cc
new file mode 100644
index 000000000..c22e6b7a5
--- /dev/null
+++ b/src/cpu/pred/tage.cc
@@ -0,0 +1,609 @@
+/*
+ * Copyright (c) 2014 The University of Wisconsin
+ *
+ * Copyright (c) 2006 INRIA (Institut National de Recherche en
+ * Informatique et en Automatique  / French National Research Institute
+ * for Computer Science and Applied Mathematics)
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
+ * from André Seznec's code.
+ */
+
+/* @file
+ * Implementation of a TAGE branch predictor
+ */
+
+#include "cpu/pred/tage.hh"
+
+#include "base/intmath.hh"
+#include "base/logging.hh"
+#include "base/random.hh"
+#include "base/trace.hh"
+#include "debug/Fetch.hh"
+#include "debug/Tage.hh"
+
+TAGE::TAGE(const TAGEParams *params)
+  : BPredUnit(params),
+    logRatioBiModalHystEntries(params->logRatioBiModalHystEntries),
+    nHistoryTables(params->nHistoryTables),
+    tagTableCounterBits(params->tagTableCounterBits),
+    tagTableUBits(params->tagTableUBits),
+    histBufferSize(params->histBufferSize),
+    minHist(params->minHist),
+    maxHist(params->maxHist),
+    pathHistBits(params->pathHistBits),
+    tagTableTagWidths(params->tagTableTagWidths),
+    logTagTableSizes(params->logTagTableSizes),
+    threadHistory(params->numThreads),
+    logUResetPeriod(params->logUResetPeriod),
+    useAltOnNaBits(params->useAltOnNaBits)
+{
+    // Current method for periodically resetting the u counter bits only
+    // works for 1 or 2 bits
+    // Also make sure that it is not 0
+    assert(tagTableUBits <= 2 && (tagTableUBits > 0));
+
+    // we use int type for the path history, so it cannot be more than
+    // its size
+    assert(pathHistBits <= (sizeof(int)*8));
+
+    // initialize the counter to half of the period
+    assert(logUResetPeriod != 0);
+    tCounter = ULL(1) << (logUResetPeriod - 1);
+
+    assert(params->histBufferSize > params->maxHist * 2);
+    useAltPredForNewlyAllocated = 0;
+
+    for (auto& history : threadHistory) {
+        history.pathHist = 0;
+        history.globalHistory = new uint8_t[histBufferSize];
+        history.gHist = history.globalHistory;
+        memset(history.gHist, 0, histBufferSize);
+        history.ptGhist = 0;
+    }
+
+    histLengths = new int [nHistoryTables+1];
+    histLengths[1] = minHist;
+    histLengths[nHistoryTables] = maxHist;
+
+    for (int i = 2; i <= nHistoryTables; i++) {
+        histLengths[i] = (int) (((double) minHist *
+                    pow ((double) (maxHist) / (double) minHist,
+                        (double) (i - 1) / (double) ((nHistoryTables- 1))))
+                    + 0.5);
+    }
+
+    assert(tagTableTagWidths.size() == (nHistoryTables+1));
+    assert(logTagTableSizes.size() == (nHistoryTables+1));
+
+    // First entry is for the Bimodal table and it is untagged in this
+    // implementation
+    assert(tagTableTagWidths[0] == 0);
+
+    for (auto& history : threadHistory) {
+        history.computeIndices = new FoldedHistory[nHistoryTables+1];
+        history.computeTags[0] = new FoldedHistory[nHistoryTables+1];
+        history.computeTags[1] = new FoldedHistory[nHistoryTables+1];
+
+        for (int i = 1; i <= nHistoryTables; i++) {
+            history.computeIndices[i].init(
+                histLengths[i], (logTagTableSizes[i]));
+            history.computeTags[0][i].init(
+                history.computeIndices[i].origLength, tagTableTagWidths[i]);
+            history.computeTags[1][i].init(
+                history.computeIndices[i].origLength, tagTableTagWidths[i]-1);
+            DPRINTF(Tage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
+                    histLengths[i], logTagTableSizes[i], tagTableTagWidths[i]);
+        }
+    }
+
+    const uint64_t bimodalTableSize = ULL(1) << logTagTableSizes[0];
+    btablePrediction.resize(bimodalTableSize, false);
+    btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
+                            true);
+
+    gtable = new TageEntry*[nHistoryTables + 1];
+    for (int i = 1; i <= nHistoryTables; i++) {
+        gtable[i] = new TageEntry[1<<(logTagTableSizes[i])];
+    }
+
+    tableIndices = new int [nHistoryTables+1];
+    tableTags = new int [nHistoryTables+1];
+}
+
+int
+TAGE::bindex(Addr pc_in) const
+{
+    return ((pc_in >> instShiftAmt) & ((ULL(1) << (logTagTableSizes[0])) - 1));
+}
+
+int
+TAGE::F(int A, int size, int bank) const
+{
+    int A1, A2;
+
+    A = A & ((ULL(1) << size) - 1);
+    A1 = (A & ((ULL(1) << logTagTableSizes[bank]) - 1));
+    A2 = (A >> logTagTableSizes[bank]);
+    A2 = ((A2 << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
+       + (A2 >> (logTagTableSizes[bank] - bank));
+    A = A1 ^ A2;
+    A = ((A << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
+      + (A >> (logTagTableSizes[bank] - bank));
+    return (A);
+}
+
+
+// gindex computes a full hash of pc, ghist and pathHist
+int
+TAGE::gindex(ThreadID tid, Addr pc, int bank) const
+{
+    int index;
+    int hlen = (histLengths[bank] > pathHistBits) ? pathHistBits :
+                                                    histLengths[bank];
+    const Addr shiftedPc = pc >> instShiftAmt;
+    index =
+        shiftedPc ^
+        (shiftedPc >> ((int) abs(logTagTableSizes[bank] - bank) + 1)) ^
+        threadHistory[tid].computeIndices[bank].comp ^
+        F(threadHistory[tid].pathHist, hlen, bank);
+
+    return (index & ((ULL(1) << (logTagTableSizes[bank])) - 1));
+}
+
+
+// Tag computation
+uint16_t
+TAGE::gtag(ThreadID tid, Addr pc, int bank) const
+{
+    int tag = (pc >> instShiftAmt) ^
+              threadHistory[tid].computeTags[0][bank].comp ^
+              (threadHistory[tid].computeTags[1][bank].comp << 1);
+
+    return (tag & ((ULL(1) << tagTableTagWidths[bank]) - 1));
+}
+
+
+// Up-down saturating counter
+void
+TAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits)
+{
+    assert(nbits <= sizeof(int8_t) << 3);
+    if (taken) {
+        if (ctr < ((1 << (nbits - 1)) - 1))
+            ctr++;
+    } else {
+        if (ctr > -(1 << (nbits - 1)))
+            ctr--;
+    }
+}
+
+// Up-down unsigned saturating counter
+void
+TAGE::unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits)
+{
+    assert(nbits <= sizeof(uint8_t) << 3);
+    if (up) {
+        if (ctr < ((1 << nbits) - 1))
+            ctr++;
+    } else {
+        if (ctr)
+            ctr--;
+    }
+}
+
+// Bimodal prediction
+bool
+TAGE::getBimodePred(Addr pc, TageBranchInfo* bi) const
+{
+    return btablePrediction[bi->bimodalIndex];
+}
+
+
+// Update the bimodal predictor: a hysteresis bit is shared among N prediction
+// bits (N = 2 ^ logRatioBiModalHystEntries)
+void
+TAGE::baseUpdate(Addr pc, bool taken, TageBranchInfo* bi)
+{
+    int inter = (btablePrediction[bi->bimodalIndex] << 1)
+        + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries];
+    if (taken) {
+        if (inter < 3)
+            inter++;
+    } else if (inter > 0) {
+        inter--;
+    }
+    const bool pred = inter >> 1;
+    const bool hyst = inter & 1;
+    btablePrediction[bi->bimodalIndex] = pred;
+    btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst;
+    DPRINTF(Tage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst);
+}
+
+// shifting the global history:  we manage the history in a big table in order
+// to reduce simulation time
+void
+TAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt)
+{
+    if (pt == 0) {
+        DPRINTF(Tage, "Rolling over the histories\n");
+         // Copy beginning of globalHistoryBuffer to end, such that
+         // the last maxHist outcomes are still reachable
+         // through pt[0 .. maxHist - 1].
+         for (int i = 0; i < maxHist; i++)
+             tab[histBufferSize - maxHist + i] = tab[i];
+         pt =  histBufferSize - maxHist;
+         h = &tab[pt];
+    }
+    pt--;
+    h--;
+    h[0] = (dir) ? 1 : 0;
+}
+
+// Get GHR for hashing indirect predictor
+// Build history backwards from pointer in
+// bp_history.
+unsigned
+TAGE::getGHR(ThreadID tid, void *bp_history) const
+{
+    TageBranchInfo* bi = static_cast<TageBranchInfo*>(bp_history);
+    unsigned val = 0;
+    for (unsigned i = 0; i < 32; i++) {
+        // Make sure we don't go out of bounds
+        int gh_offset = bi->ptGhist + i;
+        assert(&(threadHistory[tid].globalHistory[gh_offset]) <
+               threadHistory[tid].globalHistory + histBufferSize);
+        val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i);
+    }
+
+    return val;
+}
+
+//prediction
+bool
+TAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
+{
+    TageBranchInfo *bi = new TageBranchInfo(nHistoryTables+1);
+    b = (void*)(bi);
+    return tagePredict(tid, branch_pc, cond_branch, bi);
+}
+
+bool
+TAGE::tagePredict(ThreadID tid, Addr branch_pc,
+              bool cond_branch, TageBranchInfo* bi)
+{
+    Addr pc = branch_pc;
+    bool pred_taken = true;
+
+    if (cond_branch) {
+        // TAGE prediction
+
+        // computes the table addresses and the partial tags
+        for (int i = 1; i <= nHistoryTables; i++) {
+            tableIndices[i] = gindex(tid, pc, i);
+            bi->tableIndices[i] = tableIndices[i];
+            tableTags[i] = gtag(tid, pc, i);
+            bi->tableTags[i] = tableTags[i];
+        }
+
+        bi->bimodalIndex = bindex(pc);
+
+        bi->hitBank = 0;
+        bi->altBank = 0;
+        //Look for the bank with longest matching history
+        for (int i = nHistoryTables; i > 0; i--) {
+            if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
+                bi->hitBank = i;
+                bi->hitBankIndex = tableIndices[bi->hitBank];
+                break;
+            }
+        }
+        //Look for the alternate bank
+        for (int i = bi->hitBank - 1; i > 0; i--) {
+            if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
+                bi->altBank = i;
+                bi->altBankIndex = tableIndices[bi->altBank];
+                break;
+            }
+        }
+        //computes the prediction and the alternate prediction
+        if (bi->hitBank > 0) {
+            if (bi->altBank > 0) {
+                bi->altTaken =
+                    gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0;
+            }else {
+                bi->altTaken = getBimodePred(pc, bi);
+            }
+
+            bi->longestMatchPred =
+                gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0;
+            bi->pseudoNewAlloc =
+                abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1;
+
+            //if the entry is recognized as a newly allocated entry and
+            //useAltPredForNewlyAllocated is positive use the alternate
+            //prediction
+            if ((useAltPredForNewlyAllocated < 0)
+                   || abs(2 *
+                   gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
+                bi->tagePred = bi->longestMatchPred;
+            else
+                bi->tagePred = bi->altTaken;
+        } else {
+            bi->altTaken = getBimodePred(pc, bi);
+            bi->tagePred = bi->altTaken;
+            bi->longestMatchPred = bi->altTaken;
+        }
+        //end TAGE prediction
+
+        pred_taken = (bi->tagePred);
+        DPRINTF(Tage, "Predict for %lx: taken?:%d, tagePred:%d, altPred:%d\n",
+                branch_pc, pred_taken, bi->tagePred, bi->altTaken);
+    }
+    bi->branchPC = branch_pc;
+    bi->condBranch = cond_branch;
+    return pred_taken;
+}
+
+// PREDICTOR UPDATE
+void
+TAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
+              bool squashed)
+{
+    assert(bp_history);
+
+    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
+
+    if (squashed) {
+        // This restores the global history, then update it
+        // and recomputes the folded histories.
+        squash(tid, taken, bp_history);
+        return;
+    }
+
+    int nrand  = random_mt.random<int>(0,3);
+    if (bi->condBranch) {
+        DPRINTF(Tage, "Updating tables for branch:%lx; taken?:%d\n",
+                branch_pc, taken);
+        condBranchUpdate(branch_pc, taken, bi, nrand);
+    }
+    if (!squashed) {
+        delete bi;
+    }
+}
+
+void
+TAGE::condBranchUpdate(Addr branch_pc, bool taken,
+                       TageBranchInfo* bi, int nrand)
+{
+    // TAGE UPDATE
+    // try to allocate a  new entries only if prediction was wrong
+    bool longest_match_pred = false;
+    bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
+    if (bi->hitBank > 0) {
+        // Manage the selection between longest matching and alternate
+        // matching for "pseudo"-newly allocated longest matching entry
+         longest_match_pred = bi->longestMatchPred;
+        bool PseudoNewAlloc = bi->pseudoNewAlloc;
+        // an entry is considered as newly allocated if its prediction
+        // counter is weak
+        if (PseudoNewAlloc) {
+            if (longest_match_pred == taken) {
+                alloc = false;
+            }
+            // if it was delivering the correct prediction, no need to
+            // allocate new entry even if the overall prediction was false
+            if (longest_match_pred != bi->altTaken) {
+                ctrUpdate(useAltPredForNewlyAllocated,
+                     bi->altTaken == taken, useAltOnNaBits);
+            }
+        }
+    }
+
+    if (alloc) {
+        // is there some "unuseful" entry to allocate
+        uint8_t min = 1;
+        for (int i = nHistoryTables; i > bi->hitBank; i--) {
+            if (gtable[i][bi->tableIndices[i]].u < min) {
+                min = gtable[i][bi->tableIndices[i]].u;
+            }
+        }
+
+        // we allocate an entry with a longer history
+        // to  avoid ping-pong, we do not choose systematically the next
+        // entry, but among the 3 next entries
+        int Y = nrand &
+            ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1);
+        int X = bi->hitBank + 1;
+        if (Y & 1) {
+            X++;
+            if (Y & 2)
+                X++;
+        }
+        // No entry available, forces one to be available
+        if (min > 0) {
+            gtable[X][bi->tableIndices[X]].u = 0;
+        }
+
+
+        //Allocate only  one entry
+        for (int i = X; i <= nHistoryTables; i++) {
+            if ((gtable[i][bi->tableIndices[i]].u == 0)) {
+                gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i];
+                gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1;
+                break;
+            }
+        }
+    }
+    //periodic reset of u: reset is not complete but bit by bit
+    tCounter++;
+    if ((tCounter & ((ULL(1) << logUResetPeriod) - 1)) == 0) {
+        // reset least significant bit
+        // most significant bit becomes least significant bit
+        for (int i = 1; i <= nHistoryTables; i++) {
+            for (int j = 0; j < (ULL(1) << logTagTableSizes[i]); j++) {
+                gtable[i][j].u = gtable[i][j].u >> 1;
+            }
+        }
+    }
+
+    if (bi->hitBank > 0) {
+        DPRINTF(Tage, "Updating tag table entry (%d,%d) for branch %lx\n",
+                bi->hitBank, bi->hitBankIndex, branch_pc);
+        ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken,
+                  tagTableCounterBits);
+        // if the provider entry is not certified to be useful also update
+        // the alternate prediction
+        if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) {
+            if (bi->altBank > 0) {
+                ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken,
+                          tagTableCounterBits);
+                DPRINTF(Tage, "Updating tag table entry (%d,%d) for"
+                        " branch %lx\n", bi->hitBank, bi->hitBankIndex,
+                        branch_pc);
+            }
+            if (bi->altBank == 0) {
+                baseUpdate(branch_pc, taken, bi);
+            }
+        }
+
+        // update the u counter
+        if (bi->tagePred != bi->altTaken) {
+            unsignedCtrUpdate(gtable[bi->hitBank][bi->hitBankIndex].u,
+                              bi->tagePred == taken, tagTableUBits);
+        }
+    } else {
+        baseUpdate(branch_pc, taken, bi);
+    }
+}
+
+void
+TAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b)
+{
+    TageBranchInfo* bi = (TageBranchInfo*)(b);
+    ThreadHistory& tHist = threadHistory[tid];
+    //  UPDATE HISTORIES
+    bool pathbit = ((branch_pc >> instShiftAmt) & 1);
+    //on a squash, return pointers to this and recompute indices.
+    //update user history
+    updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist);
+    tHist.pathHist = (tHist.pathHist << 1) + pathbit;
+    tHist.pathHist = (tHist.pathHist & ((ULL(1) << pathHistBits) - 1));
+
+    bi->ptGhist = tHist.ptGhist;
+    bi->pathHist = tHist.pathHist;
+    //prepare next index and tag computations for user branchs
+    for (int i = 1; i <= nHistoryTables; i++)
+    {
+        bi->ci[i]  = tHist.computeIndices[i].comp;
+        bi->ct0[i] = tHist.computeTags[0][i].comp;
+        bi->ct1[i] = tHist.computeTags[1][i].comp;
+        tHist.computeIndices[i].update(tHist.gHist);
+        tHist.computeTags[0][i].update(tHist.gHist);
+        tHist.computeTags[1][i].update(tHist.gHist);
+    }
+    DPRINTF(Tage, "Updating global histories with branch:%lx; taken?:%d, "
+            "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist,
+            tHist.ptGhist);
+}
+
+void
+TAGE::squash(ThreadID tid, bool taken, void *bp_history)
+{
+    TageBranchInfo* bi = (TageBranchInfo*)(bp_history);
+    ThreadHistory& tHist = threadHistory[tid];
+    DPRINTF(Tage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, "
+            "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist);
+    tHist.pathHist = bi->pathHist;
+    tHist.ptGhist = bi->ptGhist;
+    tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]);
+    tHist.gHist[0] = (taken ? 1 : 0);
+    for (int i = 1; i <= nHistoryTables; i++) {
+        tHist.computeIndices[i].comp = bi->ci[i];
+        tHist.computeTags[0][i].comp = bi->ct0[i];
+        tHist.computeTags[1][i].comp = bi->ct1[i];
+        tHist.computeIndices[i].update(tHist.gHist);
+        tHist.computeTags[0][i].update(tHist.gHist);
+        tHist.computeTags[1][i].update(tHist.gHist);
+    }
+}
+
+void
+TAGE::squash(ThreadID tid, void *bp_history)
+{
+    TageBranchInfo* bi = (TageBranchInfo*)(bp_history);
+    DPRINTF(Tage, "Deleting branch info: %lx\n", bi->branchPC);
+    delete bi;
+}
+
+bool
+TAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
+{
+    bool retval = predict(tid, branch_pc, true, bp_history);
+
+    DPRINTF(Tage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
+    updateHistories(tid, branch_pc, retval, bp_history);
+    assert(threadHistory[tid].gHist ==
+           &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
+
+    return retval;
+}
+
+void
+TAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
+{
+    TageBranchInfo* bi = (TageBranchInfo*) bp_history;
+    ThreadHistory& tHist = threadHistory[tid];
+    DPRINTF(Tage, "BTB miss resets prediction: %lx\n", branch_pc);
+    assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]);
+    tHist.gHist[0] = 0;
+    for (int i = 1; i <= nHistoryTables; i++) {
+        tHist.computeIndices[i].comp = bi->ci[i];
+        tHist.computeTags[0][i].comp = bi->ct0[i];
+        tHist.computeTags[1][i].comp = bi->ct1[i];
+        tHist.computeIndices[i].update(tHist.gHist);
+        tHist.computeTags[0][i].update(tHist.gHist);
+        tHist.computeTags[1][i].update(tHist.gHist);
+    }
+}
+
+void
+TAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
+{
+    DPRINTF(Tage, "UnConditionalBranch: %lx\n", br_pc);
+    predict(tid, br_pc, false, bp_history);
+    updateHistories(tid, br_pc, true, bp_history);
+    assert(threadHistory[tid].gHist ==
+           &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
+}
+
+TAGE*
+TAGEParams::create()
+{
+    return new TAGE(this);
+}
diff --git a/src/cpu/pred/tage.hh b/src/cpu/pred/tage.hh
new file mode 100644
index 000000000..9ba02414c
--- /dev/null
+++ b/src/cpu/pred/tage.hh
@@ -0,0 +1,374 @@
+/*
+ * Copyright (c) 2014 The University of Wisconsin
+ *
+ * Copyright (c) 2006 INRIA (Institut National de Recherche en
+ * Informatique et en Automatique  / French National Research Institute
+ * for Computer Science and Applied Mathematics)
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
+ * from André Seznec's code.
+ */
+
+/* @file
+ * Implementation of a TAGE branch predictor. TAGE is a global-history based
+ * branch predictor. It features a PC-indexed bimodal predictor and N
+ * partially tagged tables, indexed with a hash of the PC and the global
+ * branch history. The different lengths of global branch history used to
+ * index the partially tagged tables grow geometrically. A small path history
+ * is also used in the hash.
+ *
+ * All TAGE tables are accessed in parallel, and the one using the longest
+ * history that matches provides the prediction (some exceptions apply).
+ * Entries are allocated in components using a longer history than the
+ * one that predicted when the prediction is incorrect.
+ */
+
+#ifndef __CPU_PRED_TAGE
+#define __CPU_PRED_TAGE
+
+#include <vector>
+
+#include "base/types.hh"
+#include "cpu/pred/bpred_unit.hh"
+#include "params/TAGE.hh"
+
+class TAGE: public BPredUnit
+{
+  public:
+    TAGE(const TAGEParams *params);
+
+    // Base class methods.
+    void uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history) override;
+    bool lookup(ThreadID tid, Addr branch_addr, void* &bp_history) override;
+    void btbUpdate(ThreadID tid, Addr branch_addr, void* &bp_history) override;
+    void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
+                bool squashed) override;
+    virtual void squash(ThreadID tid, void *bp_history) override;
+    unsigned getGHR(ThreadID tid, void *bp_history) const override;
+
+  protected:
+    // Prediction Structures
+
+    // Tage Entry
+    struct TageEntry
+    {
+        int8_t ctr;
+        uint16_t tag;
+        uint8_t u;
+        TageEntry() : ctr(0), tag(0), u(0) { }
+    };
+
+    // Folded History Table - compressed history
+    // to mix with instruction PC to index partially
+    // tagged tables.
+    struct FoldedHistory
+    {
+        unsigned comp;
+        int compLength;
+        int origLength;
+        int outpoint;
+
+        void init(int original_length, int compressed_length)
+        {
+            comp = 0;
+            origLength = original_length;
+            compLength = compressed_length;
+            outpoint = original_length % compressed_length;
+        }
+
+        void update(uint8_t * h)
+        {
+            comp = (comp << 1) | h[0];
+            comp ^= h[origLength] << outpoint;
+            comp ^= (comp >> compLength);
+            comp &= (ULL(1) << compLength) - 1;
+        }
+    };
+
+    // Primary branch history entry
+    struct TageBranchInfo
+    {
+        int pathHist;
+        int ptGhist;
+        int hitBank;
+        int hitBankIndex;
+        int altBank;
+        int altBankIndex;
+        int bimodalIndex;
+
+        bool tagePred;
+        bool altTaken;
+        bool condBranch;
+        bool longestMatchPred;
+        bool pseudoNewAlloc;
+        Addr branchPC;
+
+        // Pointer to dynamically allocated storage
+        // to save table indices and folded histories.
+        // To do one call to new instead of five.
+        int *storage;
+
+        // Pointers to actual saved array within the dynamically
+        // allocated storage.
+        int *tableIndices;
+        int *tableTags;
+        int *ci;
+        int *ct0;
+        int *ct1;
+
+        TageBranchInfo(int sz)
+            : pathHist(0), ptGhist(0),
+              hitBank(0), hitBankIndex(0),
+              altBank(0), altBankIndex(0),
+              bimodalIndex(0),
+              tagePred(false), altTaken(false),
+              condBranch(false), longestMatchPred(false),
+              pseudoNewAlloc(false), branchPC(0)
+        {
+            storage = new int [sz * 5];
+            tableIndices = storage;
+            tableTags = storage + sz;
+            ci = tableTags + sz;
+            ct0 = ci + sz;
+            ct1 = ct0 + sz;
+        }
+
+        virtual ~TageBranchInfo()
+        {
+            delete[] storage;
+        }
+    };
+
+    /**
+     * Computes the index used to access the
+     * bimodal table.
+     * @param pc_in The unshifted branch PC.
+     */
+    int bindex(Addr pc_in) const;
+
+    /**
+     * Computes the index used to access a
+     * partially tagged table.
+     * @param tid The thread ID used to select the
+     * global histories to use.
+     * @param pc The unshifted branch PC.
+     * @param bank The partially tagged table to access.
+     */
+    inline int gindex(ThreadID tid, Addr pc, int bank) const;
+
+    /**
+     * Utility function to shuffle the path history
+     * depending on which tagged table we are accessing.
+     * @param phist The path history.
+     * @param size Number of path history bits to use.
+     * @param bank The partially tagged table to access.
+     */
+    int F(int phist, int size, int bank) const;
+
+    /**
+     * Computes the partial tag of a tagged table.
+     * @param tid the thread ID used to select the
+     * global histories to use.
+     * @param pc The unshifted branch PC.
+     * @param bank The partially tagged table to access.
+     */
+    inline uint16_t gtag(ThreadID tid, Addr pc, int bank) const;
+
+    /**
+     * Updates a direction counter based on the actual
+     * branch outcome.
+     * @param ctr Reference to counter to update.
+     * @param taken Actual branch outcome.
+     * @param nbits Counter width.
+     */
+    void ctrUpdate(int8_t & ctr, bool taken, int nbits);
+
+    /**
+     * Updates an unsigned counter based on up/down parameter
+     * @param ctr Reference to counter to update.
+     * @param up Boolean indicating if the counter is incremented/decremented
+     * If true it is incremented, if false it is decremented
+     * @param nbits Counter width.
+     */
+    void unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits);
+
+    /**
+     * Get a branch prediction from the bimodal
+     * predictor.
+     * @param pc The unshifted branch PC.
+     * @param bi Pointer to information on the
+     * prediction.
+     */
+    bool getBimodePred(Addr pc, TageBranchInfo* bi) const;
+
+    /**
+     * Updates the bimodal predictor.
+     * @param pc The unshifted branch PC.
+     * @param taken The actual branch outcome.
+     * @param bi Pointer to information on the prediction
+     * recorded at prediction time.
+     */
+    void baseUpdate(Addr pc, bool taken, TageBranchInfo* bi);
+
+   /**
+    * (Speculatively) updates the global branch history.
+    * @param h Reference to pointer to global branch history.
+    * @param dir (Predicted) outcome to update the histories
+    * with.
+    * @param tab
+    * @param PT Reference to path history.
+    */
+    void updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &PT);
+
+    /**
+     * Get a branch prediction from TAGE. *NOT* an override of
+     * BpredUnit::predict().
+     * @param tid The thread ID to select the global
+     * histories to use.
+     * @param branch_pc The unshifted branch PC.
+     * @param cond_branch True if the branch is conditional.
+     * @param b Reference to wrapping pointer to allow storing
+     * derived class prediction information in the base class.
+     */
+    virtual bool predict(
+        ThreadID tid, Addr branch_pc, bool cond_branch, void* &b);
+
+    /**
+     * Update TAGE. Called at execute to repair histories on a misprediction
+     * and at commit to update the tables.
+     * @param tid The thread ID to select the global
+     * histories to use.
+     * @param branch_pc The unshifted branch PC.
+     * @param taken Actual branch outcome.
+     * @param bi Pointer to information on the prediction
+     * recorded at prediction time.
+     */
+    void update(ThreadID tid, Addr branch_pc, bool taken, TageBranchInfo* bi);
+
+   /**
+    * (Speculatively) updates global histories (path and direction).
+    * Also recomputes compressed (folded) histories based on the
+    * branch direction.
+    * @param tid The thread ID to select the histories
+    * to update.
+    * @param branch_pc The unshifted branch PC.
+    * @param taken (Predicted) branch direction.
+    * @param b Wrapping pointer to TageBranchInfo (to allow
+    * storing derived class prediction information in the
+    * base class).
+    */
+    void updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b);
+
+    /**
+     * Restores speculatively updated path and direction histories.
+     * Also recomputes compressed (folded) histories based on the
+     * correct branch outcome.
+     * This version of squash() is called once on a branch misprediction.
+     * @param tid The Thread ID to select the histories to rollback.
+     * @param taken The correct branch outcome.
+     * @param bp_history Wrapping pointer to TageBranchInfo (to allow
+     * storing derived class prediction information in the
+     * base class).
+     * @post bp_history points to valid memory.
+     */
+    virtual void squash(ThreadID tid, bool taken, void *bp_history);
+
+    /**
+     * Update TAGE for conditional branches.
+     * @param branch_pc The unshifted branch PC.
+     * @param taken Actual branch outcome.
+     * @param bi Pointer to information on the prediction
+     * recorded at prediction time.
+     * @nrand Random int number from 0 to 3
+     */
+    virtual void condBranchUpdate(
+        Addr branch_pc, bool taken, TageBranchInfo* bi, int nrand);
+
+    /**
+     * TAGE prediction called from TAGE::predict
+     * @param tid The thread ID to select the global
+     * histories to use.
+     * @param branch_pc The unshifted branch PC.
+     * @param cond_branch True if the branch is conditional.
+     * @param bi Pointer to the TageBranchInfo
+     */
+    bool tagePredict(
+        ThreadID tid, Addr branch_pc, bool cond_branch, TageBranchInfo* bi);
+
+    const unsigned logRatioBiModalHystEntries;
+    const unsigned nHistoryTables;
+    const unsigned tagTableCounterBits;
+    const unsigned tagTableUBits;
+    const unsigned histBufferSize;
+    const unsigned minHist;
+    const unsigned maxHist;
+    const unsigned pathHistBits;
+
+    const std::vector<unsigned> tagTableTagWidths;
+    const std::vector<int> logTagTableSizes;
+
+    std::vector<bool> btablePrediction;
+    std::vector<bool> btableHysteresis;
+    TageEntry **gtable;
+
+    // Keep per-thread histories to
+    // support SMT.
+    struct ThreadHistory {
+        // Speculative path history
+        // (LSB of branch address)
+        int pathHist;
+
+        // Speculative branch direction
+        // history (circular buffer)
+        // @TODO Convert to std::vector<bool>
+        uint8_t *globalHistory;
+
+        // Pointer to most recent branch outcome
+        uint8_t* gHist;
+
+        // Index to most recent branch outcome
+        int ptGhist;
+
+        // Speculative folded histories.
+        FoldedHistory *computeIndices;
+        FoldedHistory *computeTags[2];
+    };
+
+    std::vector<ThreadHistory> threadHistory;
+
+    int *histLengths;
+    int *tableIndices;
+    int *tableTags;
+
+    int8_t useAltPredForNewlyAllocated;
+    uint64_t tCounter;
+    uint64_t logUResetPeriod;
+    unsigned useAltOnNaBits;
+};
+
+#endif // __CPU_PRED_TAGE