blob: 1ff8eba9f47a6faefdf7367b21d9cbe22532f0c2 [file] [log] [blame]
/*
* 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.
*/
/* @file
* Implementation of a TAGE branch predictor
*/
#include "cpu/pred/tage_base.hh"
#include "base/intmath.hh"
#include "base/logging.hh"
#include "debug/Fetch.hh"
#include "debug/Tage.hh"
namespace gem5
{
namespace branch_prediction
{
TAGEBase::TAGEBase(const TAGEBaseParams &p)
: SimObject(p),
logRatioBiModalHystEntries(p.logRatioBiModalHystEntries),
nHistoryTables(p.nHistoryTables),
tagTableCounterBits(p.tagTableCounterBits),
tagTableUBits(p.tagTableUBits),
histBufferSize(p.histBufferSize),
minHist(p.minHist),
maxHist(p.maxHist),
pathHistBits(p.pathHistBits),
tagTableTagWidths(p.tagTableTagWidths),
logTagTableSizes(p.logTagTableSizes),
threadHistory(p.numThreads),
logUResetPeriod(p.logUResetPeriod),
initialTCounterValue(p.initialTCounterValue),
numUseAltOnNa(p.numUseAltOnNa),
useAltOnNaBits(p.useAltOnNaBits),
maxNumAlloc(p.maxNumAlloc),
noSkip(p.noSkip),
speculativeHistUpdate(p.speculativeHistUpdate),
instShiftAmt(p.instShiftAmt),
initialized(false),
stats(this, nHistoryTables)
{
if (noSkip.empty()) {
// Set all the table to enabled by default
noSkip.resize(nHistoryTables + 1, true);
}
}
TAGEBase::BranchInfo*
TAGEBase::makeBranchInfo() {
return new BranchInfo(*this);
}
void
TAGEBase::init()
{
if (initialized) {
return;
}
// 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 = initialTCounterValue;
assert(histBufferSize > maxHist * 2);
useAltPredForNewlyAllocated.resize(numUseAltOnNa, 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];
calculateParameters();
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];
initFoldedHistories(history);
}
const uint64_t bimodalTableSize = 1ULL << logTagTableSizes[0];
btablePrediction.resize(bimodalTableSize, false);
btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
true);
gtable = new TageEntry*[nHistoryTables + 1];
buildTageTables();
tableIndices = new int [nHistoryTables+1];
tableTags = new int [nHistoryTables+1];
initialized = true;
}
void
TAGEBase::initFoldedHistories(ThreadHistory & history)
{
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]);
}
}
void
TAGEBase::buildTageTables()
{
for (int i = 1; i <= nHistoryTables; i++) {
gtable[i] = new TageEntry[1<<(logTagTableSizes[i])];
}
}
void
TAGEBase::calculateParameters()
{
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);
}
}
void
TAGEBase::btbUpdate(ThreadID tid, Addr branch_pc, BranchInfo* &bi)
{
if (speculativeHistUpdate) {
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);
}
}
}
int
TAGEBase::bindex(Addr pc_in) const
{
return ((pc_in >> instShiftAmt) & ((1ULL << (logTagTableSizes[0])) - 1));
}
int
TAGEBase::F(int A, int size, int bank) const
{
int A1, A2;
A = A & ((1ULL << size) - 1);
A1 = (A & ((1ULL << logTagTableSizes[bank]) - 1));
A2 = (A >> logTagTableSizes[bank]);
A2 = ((A2 << bank) & ((1ULL << logTagTableSizes[bank]) - 1))
+ (A2 >> (logTagTableSizes[bank] - bank));
A = A1 ^ A2;
A = ((A << bank) & ((1ULL << logTagTableSizes[bank]) - 1))
+ (A >> (logTagTableSizes[bank] - bank));
return (A);
}
// gindex computes a full hash of pc, ghist and pathHist
int
TAGEBase::gindex(ThreadID tid, Addr pc, int bank) const
{
int index;
int hlen = (histLengths[bank] > pathHistBits) ? pathHistBits :
histLengths[bank];
const unsigned int 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 & ((1ULL << (logTagTableSizes[bank])) - 1));
}
// Tag computation
uint16_t
TAGEBase::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 & ((1ULL << tagTableTagWidths[bank]) - 1));
}
// Up-down saturating counter
template<typename T>
void
TAGEBase::ctrUpdate(T & ctr, bool taken, int nbits)
{
assert(nbits <= sizeof(T) << 3);
if (taken) {
if (ctr < ((1 << (nbits - 1)) - 1))
ctr++;
} else {
if (ctr > -(1 << (nbits - 1)))
ctr--;
}
}
// int8_t and int versions of this function may be needed
template void TAGEBase::ctrUpdate(int8_t & ctr, bool taken, int nbits);
template void TAGEBase::ctrUpdate(int & ctr, bool taken, int nbits);
// Up-down unsigned saturating counter
void
TAGEBase::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
TAGEBase::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
TAGEBase::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(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
TAGEBase::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;
}
void
TAGEBase::calculateIndicesAndTags(ThreadID tid, Addr branch_pc,
BranchInfo* bi)
{
// computes the table addresses and the partial tags
for (int i = 1; i <= nHistoryTables; i++) {
tableIndices[i] = gindex(tid, branch_pc, i);
bi->tableIndices[i] = tableIndices[i];
tableTags[i] = gtag(tid, branch_pc, i);
bi->tableTags[i] = tableTags[i];
}
}
unsigned
TAGEBase::getUseAltIdx(BranchInfo* bi, Addr branch_pc)
{
// There is only 1 counter on the base TAGE implementation
return 0;
}
bool
TAGEBase::tagePredict(ThreadID tid, Addr branch_pc,
bool cond_branch, BranchInfo* bi)
{
Addr pc = branch_pc;
bool pred_taken = true;
if (cond_branch) {
// TAGE prediction
calculateIndicesAndTags(tid, pc, 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 (noSkip[i] &&
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 (noSkip[i] &&
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;
extraAltCalc(bi);
}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[getUseAltIdx(bi, branch_pc)] < 0)
|| ! bi->pseudoNewAlloc) {
bi->tagePred = bi->longestMatchPred;
bi->provider = TAGE_LONGEST_MATCH;
} else {
bi->tagePred = bi->altTaken;
bi->provider = bi->altBank ? TAGE_ALT_MATCH
: BIMODAL_ALT_MATCH;
}
} else {
bi->altTaken = getBimodePred(pc, bi);
bi->tagePred = bi->altTaken;
bi->longestMatchPred = bi->altTaken;
bi->provider = BIMODAL_ONLY;
}
//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;
}
void
TAGEBase::adjustAlloc(bool & alloc, bool taken, bool pred_taken)
{
// Nothing for this base class implementation
}
void
TAGEBase::handleAllocAndUReset(bool alloc, bool taken, BranchInfo* bi,
int nrand)
{
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 &
((1ULL << (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 entries
unsigned numAllocated = 0;
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;
++numAllocated;
if (numAllocated == maxNumAlloc) {
break;
}
}
}
}
tCounter++;
handleUReset();
}
void
TAGEBase::handleUReset()
{
//periodic reset of u: reset is not complete but bit by bit
if ((tCounter & ((1ULL << 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 < (1ULL << logTagTableSizes[i]); j++) {
resetUctr(gtable[i][j].u);
}
}
}
}
void
TAGEBase::resetUctr(uint8_t & u)
{
u >>= 1;
}
void
TAGEBase::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
BranchInfo* bi, int nrand, Addr corrTarget, bool pred, bool preAdjustAlloc)
{
// TAGE UPDATE
// try to allocate a new entries only if prediction was wrong
bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
if (preAdjustAlloc) {
adjustAlloc(alloc, taken, pred);
}
if (bi->hitBank > 0) {
// Manage the selection between longest matching and alternate
// matching for "pseudo"-newly allocated longest matching entry
bool PseudoNewAlloc = bi->pseudoNewAlloc;
// an entry is considered as newly allocated if its prediction
// counter is weak
if (PseudoNewAlloc) {
if (bi->longestMatchPred == taken) {
alloc = false;
}
// if it was delivering the correct prediction, no need to
// allocate new entry even if the overall prediction was false
if (bi->longestMatchPred != bi->altTaken) {
ctrUpdate(
useAltPredForNewlyAllocated[getUseAltIdx(bi, branch_pc)],
bi->altTaken == taken, useAltOnNaBits);
}
}
}
if (!preAdjustAlloc) {
adjustAlloc(alloc, taken, pred);
}
handleAllocAndUReset(alloc, taken, bi, nrand);
handleTAGEUpdate(branch_pc, taken, bi);
}
void
TAGEBase::handleTAGEUpdate(Addr branch_pc, bool taken, BranchInfo* bi)
{
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
TAGEBase::updateHistories(ThreadID tid, Addr branch_pc, bool taken,
BranchInfo* bi, bool speculative,
const StaticInstPtr &inst, Addr target)
{
if (speculative != speculativeHistUpdate) {
return;
}
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 & ((1ULL << pathHistBits) - 1));
if (speculative) {
bi->ptGhist = tHist.ptGhist;
bi->pathHist = tHist.pathHist;
}
//prepare next index and tag computations for user branchs
for (int i = 1; i <= nHistoryTables; i++)
{
if (speculative) {
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);
assert(threadHistory[tid].gHist ==
&threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
}
void
TAGEBase::squash(ThreadID tid, bool taken, TAGEBase::BranchInfo *bi,
Addr target)
{
if (!speculativeHistUpdate) {
/* If there are no speculative updates, no actions are needed */
return;
}
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
TAGEBase::extraAltCalc(BranchInfo* bi)
{
// do nothing. This is only used in some derived classes
return;
}
void
TAGEBase::updateStats(bool taken, BranchInfo* bi)
{
if (taken == bi->tagePred) {
// correct prediction
switch (bi->provider) {
case BIMODAL_ONLY: stats.bimodalProviderCorrect++; break;
case TAGE_LONGEST_MATCH: stats.longestMatchProviderCorrect++; break;
case BIMODAL_ALT_MATCH:
stats.bimodalAltMatchProviderCorrect++;
break;
case TAGE_ALT_MATCH: stats.altMatchProviderCorrect++; break;
}
} else {
// wrong prediction
switch (bi->provider) {
case BIMODAL_ONLY: stats.bimodalProviderWrong++; break;
case TAGE_LONGEST_MATCH:
stats.longestMatchProviderWrong++;
if (bi->altTaken == taken) {
stats.altMatchProviderWouldHaveHit++;
}
break;
case BIMODAL_ALT_MATCH:
stats.bimodalAltMatchProviderWrong++;
break;
case TAGE_ALT_MATCH:
stats.altMatchProviderWrong++;
break;
}
switch (bi->provider) {
case BIMODAL_ALT_MATCH:
case TAGE_ALT_MATCH:
if (bi->longestMatchPred == taken) {
stats.longestMatchProviderWouldHaveHit++;
}
}
}
switch (bi->provider) {
case TAGE_LONGEST_MATCH:
case TAGE_ALT_MATCH:
stats.longestMatchProvider[bi->hitBank]++;
stats.altMatchProvider[bi->altBank]++;
break;
}
}
unsigned
TAGEBase::getGHR(ThreadID tid, BranchInfo *bi) const
{
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;
}
TAGEBase::TAGEBaseStats::TAGEBaseStats(
statistics::Group *parent, unsigned nHistoryTables)
: statistics::Group(parent),
ADD_STAT(longestMatchProviderCorrect, statistics::units::Count::get(),
"Number of times TAGE Longest Match is the provider and the "
"prediction is correct"),
ADD_STAT(altMatchProviderCorrect, statistics::units::Count::get(),
"Number of times TAGE Alt Match is the provider and the "
"prediction is correct"),
ADD_STAT(bimodalAltMatchProviderCorrect, statistics::units::Count::get(),
"Number of times TAGE Alt Match is the bimodal and it is the "
"provider and the prediction is correct"),
ADD_STAT(bimodalProviderCorrect, statistics::units::Count::get(),
"Number of times there are no hits on the TAGE tables and the "
"bimodal prediction is correct"),
ADD_STAT(longestMatchProviderWrong, statistics::units::Count::get(),
"Number of times TAGE Longest Match is the provider and the "
"prediction is wrong"),
ADD_STAT(altMatchProviderWrong, statistics::units::Count::get(),
"Number of times TAGE Alt Match is the provider and the "
"prediction is wrong"),
ADD_STAT(bimodalAltMatchProviderWrong, statistics::units::Count::get(),
"Number of times TAGE Alt Match is the bimodal and it is the "
"provider and the prediction is wrong"),
ADD_STAT(bimodalProviderWrong, statistics::units::Count::get(),
"Number of times there are no hits on the TAGE tables and the "
"bimodal prediction is wrong"),
ADD_STAT(altMatchProviderWouldHaveHit, statistics::units::Count::get(),
"Number of times TAGE Longest Match is the provider, the "
"prediction is wrong and Alt Match prediction was correct"),
ADD_STAT(longestMatchProviderWouldHaveHit, statistics::units::Count::get(),
"Number of times TAGE Alt Match is the provider, the "
"prediction is wrong and Longest Match prediction was correct"),
ADD_STAT(longestMatchProvider, statistics::units::Count::get(),
"TAGE provider for longest match"),
ADD_STAT(altMatchProvider, statistics::units::Count::get(),
"TAGE provider for alt match")
{
longestMatchProvider.init(nHistoryTables + 1);
altMatchProvider.init(nHistoryTables + 1);
}
int8_t
TAGEBase::getCtr(int hitBank, int hitBankIndex) const
{
return gtable[hitBank][hitBankIndex].ctr;
}
unsigned
TAGEBase::getTageCtrBits() const
{
return tagTableCounterBits;
}
int
TAGEBase::getPathHist(ThreadID tid) const
{
return threadHistory[tid].pathHist;
}
bool
TAGEBase::isSpeculativeUpdateEnabled() const
{
return speculativeHistUpdate;
}
size_t
TAGEBase::getSizeInBits() const {
size_t bits = 0;
for (int i = 1; i <= nHistoryTables; i++) {
bits += (1 << logTagTableSizes[i]) *
(tagTableCounterBits + tagTableUBits + tagTableTagWidths[i]);
}
uint64_t bimodalTableSize = 1ULL << logTagTableSizes[0];
bits += numUseAltOnNa * useAltOnNaBits;
bits += bimodalTableSize;
bits += (bimodalTableSize >> logRatioBiModalHystEntries);
bits += histLengths[nHistoryTables];
bits += pathHistBits;
bits += logUResetPeriod;
return bits;
}
} // namespace branch_prediction
} // namespace gem5