# HG changeset patch
# User Taylor Lloyd <taylor@taylorlloyd.ca>
# Date 1373913514 21600
#      Mon Jul 15 12:38:34 2013 -0600
# Node ID 3c2dda87aca0fe25493025216f85e1e2bce6ed14
# Parent  13ffc0066b76a257620b767892c11d58f71b8515
Added GaG (global-global) branch predictor.
-Fixed issues raised during review

diff -r 13ffc0066b76 -r 3c2dda87aca0 src/cpu/pred/BranchPredictor.py
--- a/src/cpu/pred/BranchPredictor.py	Thu Jul 11 21:57:04 2013 -0500
+++ b/src/cpu/pred/BranchPredictor.py	Mon Jul 15 12:38:34 2013 -0600
@@ -36,7 +36,7 @@
 
     numThreads = Param.Unsigned(1, "Number of threads")
     predType = Param.String("tournament",
-        "Branch predictor type ('local', 'tournament')")
+        "Branch predictor type ('local', 'global', 'tournament')")
     localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
     localCtrBits = Param.Unsigned(2, "Bits per counter")
     localHistoryTableSize = Param.Unsigned(2048, "Size of local history table")
diff -r 13ffc0066b76 -r 3c2dda87aca0 src/cpu/pred/SConscript
--- a/src/cpu/pred/SConscript	Thu Jul 11 21:57:04 2013 -0500
+++ b/src/cpu/pred/SConscript	Mon Jul 15 12:38:34 2013 -0600
@@ -35,6 +35,7 @@
 
     Source('bpred_unit.cc')
     Source('2bit_local.cc')
+    Source('global.cc')
     Source('btb.cc')
     Source('ras.cc')
     Source('tournament.cc')
diff -r 13ffc0066b76 -r 3c2dda87aca0 src/cpu/pred/bpred_unit.cc
--- a/src/cpu/pred/bpred_unit.cc	Thu Jul 11 21:57:04 2013 -0500
+++ b/src/cpu/pred/bpred_unit.cc	Mon Jul 15 12:38:34 2013 -0600
@@ -33,6 +33,7 @@
 
 #include "cpu/pred/2bit_local.hh"
 #include "cpu/pred/bpred_unit_impl.hh"
+#include "cpu/pred/global.hh"
 #include "cpu/pred/tournament.hh"
 
 BPredUnit *
@@ -43,6 +44,8 @@
         return new LocalBP(this);
     } else if (predType == "tournament") {
         return new TournamentBP(this);
+    } else if (predType == "global") {
+        return new GlobalBP(this);
     } else {
         fatal("Invalid BP selected!");
     }
diff -r 13ffc0066b76 -r 3c2dda87aca0 src/cpu/pred/global.hh
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/cpu/pred/global.hh	Mon Jul 15 12:38:34 2013 -0600
@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2004-2006 The Regents of The University of Michigan
+ * 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: Kevin Lim
+ *          Taylor Lloyd
+ */
+
+#ifndef __CPU_PRED_GLOBAL_PRED_HH__
+#define __CPU_PRED_GLOBAL_PRED_HH__
+
+#include <vector>
+
+#include "base/types.hh"
+#include "cpu/pred/bpred_unit.hh"
+#include "cpu/pred/sat_counter.hh"
+
+/**
+ * Implements a set global-global (gAG) predictor. It uses the branch history
+ * to index into a table of counters. Global history is speculatively updated,
+ * and corrected during a squash.
+ */
+class GlobalBP : public BPredUnit
+{
+  public:
+    /**
+     * Default branch predictor constructor.
+     */
+    GlobalBP(const Params *params);
+    /**
+     * Looks up the given address in the branch predictor and returns
+     * a true/false value as to whether it is taken.  Also creates a
+     * BPHistory object to store any state it will need on squash/update.
+     * @param branch_addr The address of the branch to look up.
+     * @param bp_history Pointer that will be set to the BPHistory object.
+     * @return Whether or not the branch is taken.
+     */
+    bool lookup(Addr branch_addr, void * &bp_history);
+
+    /**
+     * Records that there was an unconditional branch, and modifies
+     * the bp history to point to an object that has the previous
+     * global history stored in it.
+     * @param bp_history Pointer that will be set to the BPHistory object.
+     */
+    void uncondBranch(void * &bp_history);
+    /**
+     * Updates the branch predictor to Not Taken if a BTB entry is
+     * invalid or not found.
+     * @param branch_addr The address of the branch to look up.
+     * @param bp_history Pointer to any bp history state.
+     * @return Whether or not the branch is taken.
+     */
+    void btbUpdate(Addr branch_addr, void * &bp_history);
+    /**
+     * Updates the branch predictor with the actual result of a branch.
+     * @param branch_addr The address of the branch to update.
+     * @param taken Whether or not the branch was taken.
+     * @param bp_history Pointer to the BPHistory object that was created
+     * when the branch was predicted.
+     * @param squashed is set when this function is called during a squash
+     * operation.
+     */
+    void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
+
+    /**
+     * Restores the global branch history on a squash.
+     * @param bp_history Pointer to the BPHistory object that has the
+     * previous global branch history in it.
+     */
+    void squash(void *bp_history);
+
+  private:
+    /** Updates global history as taken. */
+    inline void updateGlobalHistTaken();
+
+    /** Updates global history as not taken. */
+    inline void updateGlobalHistNotTaken();
+
+    /**
+     * The branch history information that is created with a prediction.
+     * It's used for recovery upon a squash, and discarded for correct
+     * predictions.
+     */
+    struct GlobalHistory {
+      unsigned globalHistory;
+      bool predTaken;
+    };
+
+    /** Table of the global counters */
+    std::vector<SatCounter> globalCtrs;
+
+    /** Number of entries in the global predictor */
+    unsigned globalPredictorSize;
+
+    /** Number of bits required to index the predictor */
+    unsigned globalHistoryBits;
+
+    /** Number of bits in each counter of the global predictor */
+    unsigned globalCtrBits;
+
+    /** Global history register. */
+    unsigned globalHistory;
+
+    /** The mask to ensure no extra history is stored */
+    unsigned globalHistoryMask;
+
+    /** Counter threshold to decide taken/untaken */
+    unsigned threshold;
+};
+#endif // __CPU_PRED_GLOBAL_PRED_HH__
diff -r 13ffc0066b76 -r 3c2dda87aca0 src/cpu/pred/global.cc
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/cpu/pred/global.cc	Mon Jul 15 12:38:34 2013 -0600
@@ -0,0 +1,156 @@
+/*
+ * Copyright (c) 2004-2006 The Regents of The University of Michigan
+ * 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: Kevin Lim
+ *          Taylor Lloyd
+ */
+
+#include "base/intmath.hh"
+#include "base/misc.hh"
+#include "base/trace.hh"
+#include "cpu/pred/global.hh"
+#include "debug/Fetch.hh"
+
+GlobalBP::GlobalBP(const Params *params)
+    : BPredUnit(params),
+      globalPredictorSize(params->globalPredictorSize),
+      globalCtrBits(params->globalCtrBits)
+{
+    if (!isPowerOf2(globalPredictorSize)) {
+        fatal("Invalid global predictor size! (Must be power of 2)\n");
+    }
+
+    //Calculate logarithm to get history bits (cheat for powers of two)
+    int globalHistoryBits = 0;
+    for (int size = globalPredictorSize; size != 0; size = size >> 1)
+    {
+        globalHistoryBits++;
+    }
+
+    // Setup the array of counters for the global predictor.
+    globalCtrs.resize(globalPredictorSize);
+
+    for (unsigned i = 0; i < globalPredictorSize; ++i)
+        globalCtrs[i].setBits(globalCtrBits);
+
+    DPRINTF(Fetch, "Branch predictor: global predictor size: %i\n",
+            globalPredictorSize);
+    DPRINTF(Fetch, "Branch predictor: global history size: %i\n", globalHistoryBits);
+    DPRINTF(Fetch, "Branch predictor: global counter bits: %i\n", globalCtrBits);
+
+    //set the initial history
+    globalHistory = 0;
+    //setup the history mask
+    globalHistoryMask = (1 << globalHistoryBits) - 1;
+    //setup the 'predict taken' threshold
+    threshold = (1 << (globalCtrBits - 1)) - 1;
+}
+
+inline void
+GlobalBP::updateGlobalHistTaken()
+{
+    globalHistory = (globalHistory << 1) | 1;
+    globalHistory = globalHistory & globalHistoryMask;
+}
+
+inline void
+GlobalBP::updateGlobalHistNotTaken()
+{
+    globalHistory = globalHistory << 1;
+    globalHistory = globalHistory & globalHistoryMask;
+}
+
+void 
+GlobalBP::btbUpdate(Addr branch_addr, void * &bp_history)
+{
+    //Update Global History to Not Taken
+    globalHistory = globalHistory & (globalHistoryMask - 1);
+}
+
+bool 
+GlobalBP::lookup(Addr branch_addr, void * &bp_history)
+{
+    bool taken = globalCtrs[globalHistory].read() > threshold;
+
+    DPRINTF(Fetch, "Branch predictor: prediction is %i.\n",
+            (int)taken);
+    GlobalHistory *history = new GlobalHistory;
+    history->globalHistory = globalHistory;
+    history->predTaken = taken;
+    bp_history = (void *)history;
+
+    if (taken) {
+        updateGlobalHistTaken();
+        return true;
+    } else {
+        updateGlobalHistNotTaken();
+        return false;
+    }
+}
+
+void
+GlobalBP::uncondBranch(void * &bp_history)
+{
+    //Create the history
+    GlobalHistory *history = new GlobalHistory;
+    history->globalHistory = globalHistory;
+    history->predTaken = true;
+    bp_history = (void *)history;
+    updateGlobalHistTaken();
+}
+
+void
+GlobalBP::update(Addr branch_addr, bool taken, void *bp_history, bool squashed)
+{
+    DPRINTF(Fetch, "Predictor: Updating predictive counters\n");
+    if (bp_history) {
+        GlobalHistory *history = (GlobalHistory *) bp_history;
+        if(taken) {
+            globalCtrs[history->globalHistory].increment();
+        } else {
+            globalCtrs[history->globalHistory].decrement();
+        }
+        if(squashed) { 
+            // Recover using our past history
+            DPRINTF(Fetch, "Predictor: Update - recovering from squash\n");
+            globalHistory = (history->globalHistory << 1) | taken;
+            globalHistory = globalHistory & globalHistoryMask;
+        }
+        delete history;
+        bp_history = 0;
+    }
+}
+
+void
+GlobalBP::squash(void *bp_history) 
+{
+    DPRINTF(Fetch, "Predictor: Recovering from squash\n");
+    GlobalHistory *history = (GlobalHistory *)bp_history;
+    globalHistory = history->globalHistory;
+    delete history;
+    bp_history = 0;
+}