src/cpu/pred/tournament.cc - public/gem5 - Git at Google

 /*
  * Copyright (c) 2011, 2014 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * 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
  */

 #include "cpu/pred/tournament.hh"

 #include "base/bitfield.hh"
 #include "base/intmath.hh"

 TournamentBP::TournamentBP(const TournamentBPParams *params)
     : BPredUnit(params),
       localPredictorSize(params->localPredictorSize),
       localCtrBits(params->localCtrBits),
       localHistoryTableSize(params->localHistoryTableSize),
       localHistoryBits(ceilLog2(params->localPredictorSize)),
       globalPredictorSize(params->globalPredictorSize),
       globalCtrBits(params->globalCtrBits),
       globalHistory(params->numThreads, 0),
       globalHistoryBits(
           ceilLog2(params->globalPredictorSize) >
           ceilLog2(params->choicePredictorSize) ?
           ceilLog2(params->globalPredictorSize) :
           ceilLog2(params->choicePredictorSize)),
       choicePredictorSize(params->choicePredictorSize),
       choiceCtrBits(params->choiceCtrBits)
 {
     if (!isPowerOf2(localPredictorSize)) {
         fatal("Invalid local predictor size!\n");
     }

     if (!isPowerOf2(globalPredictorSize)) {
         fatal("Invalid global predictor size!\n");
     }

     //Set up the array of counters for the local predictor
     localCtrs.resize(localPredictorSize);

     for (int i = 0; i < localPredictorSize; ++i)
         localCtrs[i].setBits(localCtrBits);

     localPredictorMask = mask(localHistoryBits);

     if (!isPowerOf2(localHistoryTableSize)) {
         fatal("Invalid local history table size!\n");
     }

     //Setup the history table for the local table
     localHistoryTable.resize(localHistoryTableSize);

     for (int i = 0; i < localHistoryTableSize; ++i)
         localHistoryTable[i] = 0;

     //Setup the array of counters for the global predictor
     globalCtrs.resize(globalPredictorSize);

     for (int i = 0; i < globalPredictorSize; ++i)
         globalCtrs[i].setBits(globalCtrBits);

     // Set up the global history mask
     // this is equivalent to mask(log2(globalPredictorSize)
     globalHistoryMask = globalPredictorSize - 1;

     if (!isPowerOf2(choicePredictorSize)) {
         fatal("Invalid choice predictor size!\n");
     }

     // Set up choiceHistoryMask
     // this is equivalent to mask(log2(choicePredictorSize)
     choiceHistoryMask = choicePredictorSize - 1;

     //Setup the array of counters for the choice predictor
     choiceCtrs.resize(choicePredictorSize);

     for (int i = 0; i < choicePredictorSize; ++i)
         choiceCtrs[i].setBits(choiceCtrBits);

     //Set up historyRegisterMask
     historyRegisterMask = mask(globalHistoryBits);

     //Check that predictors don't use more bits than they have available
     if (globalHistoryMask > historyRegisterMask) {
         fatal("Global predictor too large for global history bits!\n");
     }
     if (choiceHistoryMask > historyRegisterMask) {
         fatal("Choice predictor too large for global history bits!\n");
     }

     if (globalHistoryMask < historyRegisterMask &&
         choiceHistoryMask < historyRegisterMask) {
         inform("More global history bits than required by predictors\n");
     }

     // Set thresholds for the three predictors' counters
     // This is equivalent to (2^(Ctr))/2 - 1
     localThreshold  = (ULL(1) << (localCtrBits  - 1)) - 1;
     globalThreshold = (ULL(1) << (globalCtrBits - 1)) - 1;
     choiceThreshold = (ULL(1) << (choiceCtrBits - 1)) - 1;
 }

 inline
 unsigned
 TournamentBP::calcLocHistIdx(Addr &branch_addr)
 {
     // Get low order bits after removing instruction offset.
     return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
 }

 inline
 void
 TournamentBP::updateGlobalHistTaken(ThreadID tid)
 {
     globalHistory[tid] = (globalHistory[tid] << 1) | 1;
     globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
 }

 inline
 void
 TournamentBP::updateGlobalHistNotTaken(ThreadID tid)
 {
     globalHistory[tid] = (globalHistory[tid] << 1);
     globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
 }

 inline
 void
 TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
 {
     localHistoryTable[local_history_idx] =
         (localHistoryTable[local_history_idx] << 1) | 1;
 }

 inline
 void
 TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
 {
     localHistoryTable[local_history_idx] =
         (localHistoryTable[local_history_idx] << 1);
 }


 void
 TournamentBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history)
 {
     unsigned local_history_idx = calcLocHistIdx(branch_addr);
     //Update Global History to Not Taken (clear LSB)
     globalHistory[tid] &= (historyRegisterMask & ~ULL(1));
     //Update Local History to Not Taken
     localHistoryTable[local_history_idx] =
        localHistoryTable[local_history_idx] & (localPredictorMask & ~ULL(1));
 }

 bool
 TournamentBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
 {
     bool local_prediction;
     unsigned local_history_idx;
     unsigned local_predictor_idx;

     bool global_prediction;
     bool choice_prediction;

     //Lookup in the local predictor to get its branch prediction
     local_history_idx = calcLocHistIdx(branch_addr);
     local_predictor_idx = localHistoryTable[local_history_idx]
         & localPredictorMask;
     local_prediction = localCtrs[local_predictor_idx].read() > localThreshold;

     //Lookup in the global predictor to get its branch prediction
     global_prediction = globalThreshold <
       globalCtrs[globalHistory[tid] & globalHistoryMask].read();

     //Lookup in the choice predictor to see which one to use
     choice_prediction = choiceThreshold <
       choiceCtrs[globalHistory[tid] & choiceHistoryMask].read();

     // Create BPHistory and pass it back to be recorded.
     BPHistory *history = new BPHistory;
     history->globalHistory = globalHistory[tid];
     history->localPredTaken = local_prediction;
     history->globalPredTaken = global_prediction;
     history->globalUsed = choice_prediction;
     history->localHistoryIdx = local_history_idx;
     history->localHistory = local_predictor_idx;
     bp_history = (void *)history;

     assert(local_history_idx < localHistoryTableSize);

     // Speculative update of the global history and the
     // selected local history.
     if (choice_prediction) {
         if (global_prediction) {
             updateGlobalHistTaken(tid);
             updateLocalHistTaken(local_history_idx);
             return true;
         } else {
             updateGlobalHistNotTaken(tid);
             updateLocalHistNotTaken(local_history_idx);
             return false;
         }
     } else {
         if (local_prediction) {
             updateGlobalHistTaken(tid);
             updateLocalHistTaken(local_history_idx);
             return true;
         } else {
             updateGlobalHistNotTaken(tid);
             updateLocalHistNotTaken(local_history_idx);
             return false;
         }
     }
 }

 void
 TournamentBP::uncondBranch(ThreadID tid, Addr pc, void * &bp_history)
 {
     // Create BPHistory and pass it back to be recorded.
     BPHistory *history = new BPHistory;
     history->globalHistory = globalHistory[tid];
     history->localPredTaken = true;
     history->globalPredTaken = true;
     history->globalUsed = true;
     history->localHistoryIdx = invalidPredictorIndex;
     history->localHistory = invalidPredictorIndex;
     bp_history = static_cast<void *>(history);

     updateGlobalHistTaken(tid);
 }

 void
 TournamentBP::update(ThreadID tid, Addr branch_addr, bool taken,
                      void *bp_history, bool squashed,
                      const StaticInstPtr & inst, Addr corrTarget)
 {
     assert(bp_history);

     BPHistory *history = static_cast<BPHistory *>(bp_history);

     unsigned local_history_idx = calcLocHistIdx(branch_addr);

     assert(local_history_idx < localHistoryTableSize);

     // Unconditional branches do not use local history.
     bool old_local_pred_valid = history->localHistory !=
             invalidPredictorIndex;

     // If this is a misprediction, restore the speculatively
     // updated state (global history register and local history)
     // and update again.
     if (squashed) {
         // Global history restore and update
         globalHistory[tid] = (history->globalHistory << 1) | taken;
         globalHistory[tid] &= historyRegisterMask;

         // Local history restore and update.
         if (old_local_pred_valid) {
             localHistoryTable[local_history_idx] =
                         (history->localHistory << 1) | taken;
         }

         return;
     }

     unsigned old_local_pred_index = history->localHistory &
         localPredictorMask;

     assert(old_local_pred_index < localPredictorSize);

     // Update the choice predictor to tell it which one was correct if
     // there was a prediction.
     if (history->localPredTaken != history->globalPredTaken &&
         old_local_pred_valid)
     {
          // If the local prediction matches the actual outcome,
          // decrement the counter. Otherwise increment the
          // counter.
          unsigned choice_predictor_idx =
            history->globalHistory & choiceHistoryMask;
          if (history->localPredTaken == taken) {
              choiceCtrs[choice_predictor_idx].decrement();
          } else if (history->globalPredTaken == taken) {
              choiceCtrs[choice_predictor_idx].increment();
          }
     }

     // Update the counters with the proper
     // resolution of the branch. Histories are updated
     // speculatively, restored upon squash() calls, and
     // recomputed upon update(squash = true) calls,
     // so they do not need to be updated.
     unsigned global_predictor_idx =
             history->globalHistory & globalHistoryMask;
     if (taken) {
           globalCtrs[global_predictor_idx].increment();
           if (old_local_pred_valid) {
                  localCtrs[old_local_pred_index].increment();
           }
     } else {
           globalCtrs[global_predictor_idx].decrement();
           if (old_local_pred_valid) {
               localCtrs[old_local_pred_index].decrement();
           }
     }

     // We're done with this history, now delete it.
     delete history;
 }

 void
 TournamentBP::squash(ThreadID tid, void *bp_history)
 {
     BPHistory *history = static_cast<BPHistory *>(bp_history);

     // Restore global history to state prior to this branch.
     globalHistory[tid] = history->globalHistory;

     // Restore local history
     if (history->localHistoryIdx != invalidPredictorIndex) {
         localHistoryTable[history->localHistoryIdx] = history->localHistory;
     }

     // Delete this BPHistory now that we're done with it.
     delete history;
 }

 TournamentBP*
 TournamentBPParams::create()
 {
     return new TournamentBP(this);
 }

 #ifdef DEBUG
 int
 TournamentBP::BPHistory::newCount = 0;
 #endif
	/*
	* Copyright (c) 2011, 2014 ARM Limited
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* 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
	*/

	#include "cpu/pred/tournament.hh"

	#include "base/bitfield.hh"
	#include "base/intmath.hh"

	TournamentBP::TournamentBP(const TournamentBPParams *params)
	: BPredUnit(params),
	localPredictorSize(params->localPredictorSize),
	localCtrBits(params->localCtrBits),
	localHistoryTableSize(params->localHistoryTableSize),
	localHistoryBits(ceilLog2(params->localPredictorSize)),
	globalPredictorSize(params->globalPredictorSize),
	globalCtrBits(params->globalCtrBits),
	globalHistory(params->numThreads, 0),
	globalHistoryBits(
	ceilLog2(params->globalPredictorSize) >
	ceilLog2(params->choicePredictorSize) ?
	ceilLog2(params->globalPredictorSize) :
	ceilLog2(params->choicePredictorSize)),
	choicePredictorSize(params->choicePredictorSize),
	choiceCtrBits(params->choiceCtrBits)
	{
	if (!isPowerOf2(localPredictorSize)) {
	fatal("Invalid local predictor size!\n");
	}

	if (!isPowerOf2(globalPredictorSize)) {
	fatal("Invalid global predictor size!\n");
	}

	//Set up the array of counters for the local predictor
	localCtrs.resize(localPredictorSize);

	for (int i = 0; i < localPredictorSize; ++i)
	localCtrs[i].setBits(localCtrBits);

	localPredictorMask = mask(localHistoryBits);

	if (!isPowerOf2(localHistoryTableSize)) {
	fatal("Invalid local history table size!\n");
	}

	//Setup the history table for the local table
	localHistoryTable.resize(localHistoryTableSize);

	for (int i = 0; i < localHistoryTableSize; ++i)
	localHistoryTable[i] = 0;

	//Setup the array of counters for the global predictor
	globalCtrs.resize(globalPredictorSize);

	for (int i = 0; i < globalPredictorSize; ++i)
	globalCtrs[i].setBits(globalCtrBits);

	// Set up the global history mask
	// this is equivalent to mask(log2(globalPredictorSize)
	globalHistoryMask = globalPredictorSize - 1;

	if (!isPowerOf2(choicePredictorSize)) {
	fatal("Invalid choice predictor size!\n");
	}

	// Set up choiceHistoryMask
	// this is equivalent to mask(log2(choicePredictorSize)
	choiceHistoryMask = choicePredictorSize - 1;

	//Setup the array of counters for the choice predictor
	choiceCtrs.resize(choicePredictorSize);

	for (int i = 0; i < choicePredictorSize; ++i)
	choiceCtrs[i].setBits(choiceCtrBits);

	//Set up historyRegisterMask
	historyRegisterMask = mask(globalHistoryBits);

	//Check that predictors don't use more bits than they have available
	if (globalHistoryMask > historyRegisterMask) {
	fatal("Global predictor too large for global history bits!\n");
	}
	if (choiceHistoryMask > historyRegisterMask) {
	fatal("Choice predictor too large for global history bits!\n");
	}

	if (globalHistoryMask < historyRegisterMask &&
	choiceHistoryMask < historyRegisterMask) {
	inform("More global history bits than required by predictors\n");
	}

	// Set thresholds for the three predictors' counters
	// This is equivalent to (2^(Ctr))/2 - 1
	localThreshold = (ULL(1) << (localCtrBits - 1)) - 1;
	globalThreshold = (ULL(1) << (globalCtrBits - 1)) - 1;
	choiceThreshold = (ULL(1) << (choiceCtrBits - 1)) - 1;
	}

	inline
	unsigned
	TournamentBP::calcLocHistIdx(Addr &branch_addr)
	{
	// Get low order bits after removing instruction offset.
	return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
	}

	inline
	void
	TournamentBP::updateGlobalHistTaken(ThreadID tid)
	{
	globalHistory[tid] = (globalHistory[tid] << 1) \| 1;
	globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
	}

	inline
	void
	TournamentBP::updateGlobalHistNotTaken(ThreadID tid)
	{
	globalHistory[tid] = (globalHistory[tid] << 1);
	globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
	}

	inline
	void
	TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
	{
	localHistoryTable[local_history_idx] =
	(localHistoryTable[local_history_idx] << 1) \| 1;
	}

	inline
	void
	TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
	{
	localHistoryTable[local_history_idx] =
	(localHistoryTable[local_history_idx] << 1);
	}


	void
	TournamentBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history)
	{
	unsigned local_history_idx = calcLocHistIdx(branch_addr);
	//Update Global History to Not Taken (clear LSB)
	globalHistory[tid] &= (historyRegisterMask & ~ULL(1));
	//Update Local History to Not Taken
	localHistoryTable[local_history_idx] =
	localHistoryTable[local_history_idx] & (localPredictorMask & ~ULL(1));
	}

	bool
	TournamentBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
	{
	bool local_prediction;
	unsigned local_history_idx;
	unsigned local_predictor_idx;

	bool global_prediction;
	bool choice_prediction;

	//Lookup in the local predictor to get its branch prediction
	local_history_idx = calcLocHistIdx(branch_addr);
	local_predictor_idx = localHistoryTable[local_history_idx]
	& localPredictorMask;
	local_prediction = localCtrs[local_predictor_idx].read() > localThreshold;

	//Lookup in the global predictor to get its branch prediction
	global_prediction = globalThreshold <
	globalCtrs[globalHistory[tid] & globalHistoryMask].read();

	//Lookup in the choice predictor to see which one to use
	choice_prediction = choiceThreshold <
	choiceCtrs[globalHistory[tid] & choiceHistoryMask].read();

	// Create BPHistory and pass it back to be recorded.
	BPHistory *history = new BPHistory;
	history->globalHistory = globalHistory[tid];
	history->localPredTaken = local_prediction;
	history->globalPredTaken = global_prediction;
	history->globalUsed = choice_prediction;
	history->localHistoryIdx = local_history_idx;
	history->localHistory = local_predictor_idx;
	bp_history = (void *)history;

	assert(local_history_idx < localHistoryTableSize);

	// Speculative update of the global history and the
	// selected local history.
	if (choice_prediction) {
	if (global_prediction) {
	updateGlobalHistTaken(tid);
	updateLocalHistTaken(local_history_idx);
	return true;
	} else {
	updateGlobalHistNotTaken(tid);
	updateLocalHistNotTaken(local_history_idx);
	return false;
	}
	} else {
	if (local_prediction) {
	updateGlobalHistTaken(tid);
	updateLocalHistTaken(local_history_idx);
	return true;
	} else {
	updateGlobalHistNotTaken(tid);
	updateLocalHistNotTaken(local_history_idx);
	return false;
	}
	}
	}

	void
	TournamentBP::uncondBranch(ThreadID tid, Addr pc, void * &bp_history)
	{
	// Create BPHistory and pass it back to be recorded.
	BPHistory *history = new BPHistory;
	history->globalHistory = globalHistory[tid];
	history->localPredTaken = true;
	history->globalPredTaken = true;
	history->globalUsed = true;
	history->localHistoryIdx = invalidPredictorIndex;
	history->localHistory = invalidPredictorIndex;
	bp_history = static_cast<void *>(history);

	updateGlobalHistTaken(tid);
	}

	void
	TournamentBP::update(ThreadID tid, Addr branch_addr, bool taken,
	void *bp_history, bool squashed,
	const StaticInstPtr & inst, Addr corrTarget)
	{
	assert(bp_history);

	BPHistory history = static_cast<BPHistory >(bp_history);

	unsigned local_history_idx = calcLocHistIdx(branch_addr);

	assert(local_history_idx < localHistoryTableSize);

	// Unconditional branches do not use local history.
	bool old_local_pred_valid = history->localHistory !=
	invalidPredictorIndex;

	// If this is a misprediction, restore the speculatively
	// updated state (global history register and local history)
	// and update again.
	if (squashed) {
	// Global history restore and update
	globalHistory[tid] = (history->globalHistory << 1) \| taken;
	globalHistory[tid] &= historyRegisterMask;

	// Local history restore and update.
	if (old_local_pred_valid) {
	localHistoryTable[local_history_idx] =
	(history->localHistory << 1) \| taken;
	}

	return;
	}

	unsigned old_local_pred_index = history->localHistory &
	localPredictorMask;

	assert(old_local_pred_index < localPredictorSize);

	// Update the choice predictor to tell it which one was correct if
	// there was a prediction.
	if (history->localPredTaken != history->globalPredTaken &&
	old_local_pred_valid)
	{
	// If the local prediction matches the actual outcome,
	// decrement the counter. Otherwise increment the
	// counter.
	unsigned choice_predictor_idx =
	history->globalHistory & choiceHistoryMask;
	if (history->localPredTaken == taken) {
	choiceCtrs[choice_predictor_idx].decrement();
	} else if (history->globalPredTaken == taken) {
	choiceCtrs[choice_predictor_idx].increment();
	}
	}

	// Update the counters with the proper
	// resolution of the branch. Histories are updated
	// speculatively, restored upon squash() calls, and
	// recomputed upon update(squash = true) calls,
	// so they do not need to be updated.
	unsigned global_predictor_idx =
	history->globalHistory & globalHistoryMask;
	if (taken) {
	globalCtrs[global_predictor_idx].increment();
	if (old_local_pred_valid) {
	localCtrs[old_local_pred_index].increment();
	}
	} else {
	globalCtrs[global_predictor_idx].decrement();
	if (old_local_pred_valid) {
	localCtrs[old_local_pred_index].decrement();
	}
	}

	// We're done with this history, now delete it.
	delete history;
	}

	void
	TournamentBP::squash(ThreadID tid, void *bp_history)
	{
	BPHistory history = static_cast<BPHistory >(bp_history);

	// Restore global history to state prior to this branch.
	globalHistory[tid] = history->globalHistory;

	// Restore local history
	if (history->localHistoryIdx != invalidPredictorIndex) {
	localHistoryTable[history->localHistoryIdx] = history->localHistory;
	}

	// Delete this BPHistory now that we're done with it.
	delete history;
	}

	TournamentBP*
	TournamentBPParams::create()
	{
	return new TournamentBP(this);
	}

	#ifdef DEBUG
	int
	TournamentBP::BPHistory::newCount = 0;
	#endif