Jairo Balart has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/15317
Change subject: cpu: move TAGE predictor code to a base class not
inheriting from BPredUnit.
......................................................................
cpu: move TAGE predictor code to a base class not inheriting from BPredUnit.
This base code can be used for TAGE-based indirect base predictors.
Change-Id: I2251b8b2d7f94124f9955f52b917dc3b064f090e
---
M src/cpu/pred/SConscript
M src/cpu/pred/tage.cc
M src/cpu/pred/tage.hh
A src/cpu/pred/tage_base.cc
A src/cpu/pred/tage_base.hh
5 files changed, 1,295 insertions(+), 1,095 deletions(-)
diff --git a/src/cpu/pred/SConscript b/src/cpu/pred/SConscript
index 5049732..0028445 100644
--- a/src/cpu/pred/SConscript
+++ b/src/cpu/pred/SConscript
@@ -43,6 +43,7 @@
Source('ras.cc')
Source('tournament.cc')
Source ('bi_mode.cc')
+Source('tage_base.cc')
Source('tage.cc')
Source('ltage.cc')
Source('tage_sc_l.cc')
diff --git a/src/cpu/pred/tage.cc b/src/cpu/pred/tage.cc
index 0463b81..c1c1221 100644
--- a/src/cpu/pred/tage.cc
+++ b/src/cpu/pred/tage.cc
@@ -49,23 +49,26 @@
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),
- numUseAltOnNa(params->numUseAltOnNa),
- useAltOnNaBits(params->useAltOnNaBits),
- maxNumAlloc(params->maxNumAlloc),
- noSkip(params->noSkip),
- speculativeHistUpdate(params->speculativeHistUpdate)
+ TAGEBase(
+ params->logRatioBiModalHystEntries,
+ params->nHistoryTables,
+ params->tagTableCounterBits,
+ params->tagTableUBits,
+ params->histBufferSize,
+ params->minHist,
+ params->maxHist,
+ params->pathHistBits,
+ params->tagTableTagWidths,
+ params->logTagTableSizes,
+ params->numThreads,
+ params->logUResetPeriod,
+ params->numUseAltOnNa,
+ params->useAltOnNaBits,
+ params->maxNumAlloc,
+ params->noSkip,
+ params->speculativeHistUpdate,
+ params->instShiftAmt
+ )
{
if (noSkip.empty()) {
// Set all the table to enabled by default
@@ -76,230 +79,8 @@
void
TAGE::init()
{
- // 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(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 = ULL(1) << 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];
-}
-
-void
-TAGE::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
-TAGE::buildTageTables()
-{
- for (int i = 1; i <= nHistoryTables; i++) {
- gtable[i] = new TageEntry[1<<(logTagTableSizes[i])];
- }
-}
-
-void
-TAGE::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);
- }
-}
-
-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 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 & ((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
-template<typename T>
-void
-TAGE::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 TAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits);
-template void TAGE::ctrUpdate(int & ctr, bool taken, int nbits);
-
-// 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;
+ BPredUnit::init();
+ TAGEBase::init();
}
// Get GHR for hashing indirect predictor
@@ -321,112 +102,6 @@
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);
-}
-
-void
-TAGE::calculateIndicesAndTags(ThreadID tid, Addr branch_pc,
TageBranchInfo* 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
-TAGE::getUseAltIdx(TageBranchInfo* bi)
-{
- // There is only 1 counter on the base TAGE implementation
- return 0;
-}
-
-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
-
- 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)] < 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;
-}
-
// PREDICTOR UPDATE
void
TAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
@@ -467,205 +142,6 @@
}
void
-TAGE::adjustAlloc(bool & alloc, bool taken, TageBranchInfo* bi)
-{
- // Nothing for this base class implementation
-}
-
-void
-TAGE::handleAllocAndUReset(bool alloc, bool taken, TageBranchInfo* 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 &
- ((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 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
-TAGE::handleUReset()
-{
- //periodic reset of u: reset is not complete but bit by bit
- 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++) {
- resetUctr(gtable[i][j].u);
- }
- }
- }
-}
-
-void
-TAGE::resetUctr(uint8_t & u)
-{
- u >>= 1;
-}
-
-void
-TAGE::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
- TageBranchInfo* bi, int nrand, Addr corrTarget)
-{
- // TAGE UPDATE
- // try to allocate a new entries only if prediction was wrong
- 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
- 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)],
- bi->altTaken == taken, useAltOnNaBits);
- }
- }
- }
-
- adjustAlloc(alloc, taken, bi);
-
- handleAllocAndUReset(alloc, taken, bi, nrand);
-
- handleTAGEUpdate(branch_pc, taken, bi);
-}
-
-void
-TAGE::handleTAGEUpdate(Addr branch_pc, bool taken, TageBranchInfo* 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
-TAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b,
- bool speculative, const StaticInstPtr &inst, Addr
target)
-{
- 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));
-
- 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);
-}
-
-void
-TAGE::squash(ThreadID tid, bool taken, void *bp_history, Addr target)
-{
- 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);
@@ -722,129 +198,10 @@
}
void
-TAGE::extraAltCalc(TageBranchInfo* bi)
-{
- // do nothing. This is only used in some derived classes
- return;
-}
-
-int
-TAGE::getRandom() const
-{
- return random_mt.random<int>();
-}
-
-void
-TAGE::updateStats(bool taken, TageBranchInfo* bi)
-{
- if (taken == bi->tagePred) {
- // correct prediction
- switch (bi->provider) {
- case BIMODAL_ONLY: tageBimodalProviderCorrect++; break;
- case TAGE_LONGEST_MATCH: tageLongestMatchProviderCorrect++;
break;
- case BIMODAL_ALT_MATCH: bimodalAltMatchProviderCorrect++; break;
- case TAGE_ALT_MATCH: tageAltMatchProviderCorrect++; break;
- }
- } else {
- // wrong prediction
- switch (bi->provider) {
- case BIMODAL_ONLY: tageBimodalProviderWrong++; break;
- case TAGE_LONGEST_MATCH:
- tageLongestMatchProviderWrong++;
- if (bi->altTaken == taken) {
- tageAltMatchProviderWouldHaveHit++;
- }
- break;
- case BIMODAL_ALT_MATCH:
- bimodalAltMatchProviderWrong++;
- break;
- case TAGE_ALT_MATCH:
- tageAltMatchProviderWrong++;
- break;
- }
-
- switch (bi->provider) {
- case BIMODAL_ALT_MATCH:
- case TAGE_ALT_MATCH:
- if (bi->longestMatchPred == taken) {
- tageLongestMatchProviderWouldHaveHit++;
- }
- }
- }
-
- switch (bi->provider) {
- case TAGE_LONGEST_MATCH:
- case TAGE_ALT_MATCH:
- tageLongestMatchProvider[bi->hitBank]++;
- tageAltMatchProvider[bi->altBank]++;
- break;
- }
-}
-
-void
TAGE::regStats()
{
BPredUnit::regStats();
-
- tageLongestMatchProviderCorrect
- .name(name() + ".tageLongestMatchProviderCorrect")
- .desc("Number of times TAGE Longest Match is the provider and "
- "the prediction is correct");
-
- tageAltMatchProviderCorrect
- .name(name() + ".tageAltMatchProviderCorrect")
- .desc("Number of times TAGE Alt Match is the provider and "
- "the prediction is correct");
-
- bimodalAltMatchProviderCorrect
- .name(name() + ".bimodalAltMatchProviderCorrect")
- .desc("Number of times TAGE Alt Match is the bimodal and it is
the "
- "provider and the prediction is correct");
-
- tageBimodalProviderCorrect
- .name(name() + ".tageBimodalProviderCorrect")
- .desc("Number of times there are no hits on the TAGE tables "
- "and the bimodal prediction is correct");
-
- tageLongestMatchProviderWrong
- .name(name() + ".tageLongestMatchProviderWrong")
- .desc("Number of times TAGE Longest Match is the provider and "
- "the prediction is wrong");
-
- tageAltMatchProviderWrong
- .name(name() + ".tageAltMatchProviderWrong")
- .desc("Number of times TAGE Alt Match is the provider and "
- "the prediction is wrong");
-
- bimodalAltMatchProviderWrong
- .name(name() + ".bimodalAltMatchProviderWrong")
- .desc("Number of times TAGE Alt Match is the bimodal and it is
the "
- "provider and the prediction is wrong");
-
- tageBimodalProviderWrong
- .name(name() + ".tageBimodalProviderWrong")
- .desc("Number of times there are no hits on the TAGE tables "
- "and the bimodal prediction is wrong");
-
- tageAltMatchProviderWouldHaveHit
- .name(name() + ".tageAltMatchProviderWouldHaveHit")
- .desc("Number of times TAGE Longest Match is the provider, "
- "the prediction is wrong and Alt Match prediction was
correct");
-
- tageLongestMatchProviderWouldHaveHit
- .name(name() + ".tageLongestMatchProviderWouldHaveHit")
- .desc("Number of times TAGE Alt Match is the provider, the "
- "prediction is wrong and Longest Match prediction was
correct");
-
- tageLongestMatchProvider
- .init(nHistoryTables + 1)
- .name(name() + ".tageLongestMatchProvider")
- .desc("TAGE provider for longest match");
-
- tageAltMatchProvider
- .init(nHistoryTables + 1)
- .name(name() + ".tageAltMatchProvider")
- .desc("TAGE provider for alt match");
+ TAGEBase::regStats();
}
TAGE*
diff --git a/src/cpu/pred/tage.hh b/src/cpu/pred/tage.hh
index f875a18..5b08dd4 100644
--- a/src/cpu/pred/tage.hh
+++ b/src/cpu/pred/tage.hh
@@ -55,11 +55,16 @@
#include "base/types.hh"
#include "cpu/pred/bpred_unit.hh"
+#include "cpu/pred/tage_base.hh"
#include "params/TAGE.hh"
-class TAGE: public BPredUnit
+class TAGE: public BPredUnit, public TAGEBase
{
public:
+ using TAGEBase::predict;
+ using TAGEBase::squash;
+ using TAGEBase::instShiftAmt;
+
TAGE(const TAGEParams *params);
// Base class methods.
@@ -75,434 +80,6 @@
virtual void init() override;
virtual void regStats() 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;
- int bufferSize;
-
- FoldedHistory()
- {
- comp = 0;
- }
-
- void init(int original_length, int compressed_length)
- {
- 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;
- }
- };
-
- // provider type
- enum {
- BIMODAL_ONLY = 0,
- TAGE_LONGEST_MATCH,
- BIMODAL_ALT_MATCH,
- TAGE_ALT_MATCH,
- LAST_TAGE_PROVIDER_TYPE = TAGE_ALT_MATCH
- };
-
- // 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;
-
- // for stats purposes
- unsigned provider;
-
- 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),
- provider(-1)
- {
- 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.
- */
- virtual 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.
- */
- virtual 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.
- */
- virtual 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.
- */
- virtual 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.
- */
- template<typename T>
- void ctrUpdate(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.
- */
- virtual 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).
- */
- virtual void updateHistories(
- ThreadID tid, Addr branch_pc, bool taken, void* b, bool
speculative,
- const StaticInstPtr & inst = StaticInst::nullStaticInstPtr,
- Addr target = MaxAddr);
-
- /**
- * 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).
- * @param target The correct branch target
- * @post bp_history points to valid memory.
- */
- virtual void squash(
- ThreadID tid, bool taken, void *bp_history, Addr target);
-
- /**
- * 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
- * @param corrTarget The correct branch target
- */
- virtual void condBranchUpdate(
- ThreadID tid, Addr branch_pc, bool taken, TageBranchInfo* bi,
- int nrand, Addr corrTarget);
-
- /**
- * 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);
-
- /**
- * Update the stats
- * @param taken Actual branch outcome
- * @param bi Pointer to information on the prediction
- * recorded at prediction time.
- */
- virtual void updateStats(bool taken, TageBranchInfo* bi);
-
- /**
- * Instantiates the TAGE table entries
- */
- virtual void buildTageTables();
-
- /**
- * Calculates the history lengths
- * and some other paramters in derived classes
- */
- virtual void calculateParameters();
-
- /**
- * On a prediction, calculates the TAGE indices and tags for
- * all the different history lengths
- */
- virtual void calculateIndicesAndTags(
- ThreadID tid, Addr branch_pc, TageBranchInfo* bi);
-
- /**
- * Calculation of the index for useAltPredForNewlyAllocated
- * On this base TAGE implementation it is always 0
- */
- virtual unsigned getUseAltIdx(TageBranchInfo* bi);
-
- /**
- * Extra calculation to tell whether TAGE allocaitons may happen or not
- * on an update
- * For this base TAGE implementation it does nothing
- */
- virtual void adjustAlloc(bool & alloc, bool taken, TageBranchInfo* bi);
-
- /**
- * Handles Allocation and U bits reset on an update
- */
- virtual void handleAllocAndUReset(
- bool alloc, bool taken, TageBranchInfo* bi, int nrand);
-
- /**
- * Handles the U bits reset
- */
- virtual void handleUReset();
-
- /**
- * Handles the update of the TAGE entries
- */
- virtual void handleTAGEUpdate(
- Addr branch_pc, bool taken, TageBranchInfo* bi);
-
- /**
- * Algorithm for resetting a single U counter
- */
- virtual void resetUctr(uint8_t & u);
-
- /**
- * Extra steps for calculating altTaken
- * For this base TAGE class it does nothing
- */
- virtual void extraAltCalc(TageBranchInfo* bi);
-
- /**
- * Algorithm for returning a random number
- * This base TAGE class just uses random_mt, but some derived classes
- * may want to use a more realistic implementation or force some values
- */
- int getRandom() const;
-
- const unsigned logRatioBiModalHystEntries;
- const unsigned nHistoryTables;
- const unsigned tagTableCounterBits;
- const unsigned tagTableUBits;
- const unsigned histBufferSize;
- const unsigned minHist;
- const unsigned maxHist;
- const unsigned pathHistBits;
-
- std::vector<unsigned> tagTableTagWidths;
- 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;
-
- /**
- * Initialization of the folded histories
- */
- virtual void initFoldedHistories(ThreadHistory & history);
-
- int *histLengths;
- int *tableIndices;
- int *tableTags;
-
- std::vector<int8_t> useAltPredForNewlyAllocated;
- int64_t tCounter;
- uint64_t logUResetPeriod;
- unsigned numUseAltOnNa;
- unsigned useAltOnNaBits;
- unsigned maxNumAlloc;
-
- // Tells which tables are active
- // (for the base TAGE implementation all are active)
- // Some other classes use this for handling associativity
- std::vector<bool> noSkip;
-
- const bool speculativeHistUpdate;
-
- // stats
- Stats::Scalar tageLongestMatchProviderCorrect;
- Stats::Scalar tageAltMatchProviderCorrect;
- Stats::Scalar bimodalAltMatchProviderCorrect;
- Stats::Scalar tageBimodalProviderCorrect;
- Stats::Scalar tageLongestMatchProviderWrong;
- Stats::Scalar tageAltMatchProviderWrong;
- Stats::Scalar bimodalAltMatchProviderWrong;
- Stats::Scalar tageBimodalProviderWrong;
- Stats::Scalar tageAltMatchProviderWouldHaveHit;
- Stats::Scalar tageLongestMatchProviderWouldHaveHit;
-
- Stats::Vector tageLongestMatchProvider;
- Stats::Vector tageAltMatchProvider;
};
#endif // __CPU_PRED_TAGE
diff --git a/src/cpu/pred/tage_base.cc b/src/cpu/pred/tage_base.cc
new file mode 100644
index 0000000..7fba790
--- /dev/null
+++ b/src/cpu/pred/tage_base.cc
@@ -0,0 +1,748 @@
+/*
+ * 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_base.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"
+
+TAGEBase::TAGEBase(
+ unsigned logRatioBiModalHystEntries,
+ unsigned nHistoryTables,
+ unsigned tagTableCounterBits,
+ unsigned tagTableUBits,
+ unsigned histBufferSize,
+ unsigned minHist,
+ unsigned maxHist,
+ unsigned pathHistBits,
+ std::vector<unsigned> const &tagTableTagWidths,
+ std::vector<int> const &logTagTableSizes,
+ unsigned numThreads,
+ uint64_t logUResetPeriod,
+ unsigned numUseAltOnNa,
+ unsigned useAltOnNaBits,
+ unsigned maxNumAlloc,
+ std::vector<bool> const &noSkip,
+ bool speculativeHistUpdate,
+ unsigned instShiftAmt
+ )
+ : logRatioBiModalHystEntries(logRatioBiModalHystEntries),
+ nHistoryTables(nHistoryTables),
+ tagTableCounterBits(tagTableCounterBits),
+ tagTableUBits(tagTableUBits),
+ histBufferSize(histBufferSize),
+ minHist(minHist),
+ maxHist(maxHist),
+ pathHistBits(pathHistBits),
+ tagTableTagWidths(tagTableTagWidths),
+ logTagTableSizes(logTagTableSizes),
+ threadHistory(numThreads),
+ logUResetPeriod(logUResetPeriod),
+ numUseAltOnNa(numUseAltOnNa),
+ useAltOnNaBits(useAltOnNaBits),
+ maxNumAlloc(maxNumAlloc),
+ noSkip(noSkip),
+ speculativeHistUpdate(speculativeHistUpdate),
+ instShiftAmt(instShiftAmt)
+{
+}
+
+void
+TAGEBase::init()
+{
+ // 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(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 = ULL(1) << 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];
+}
+
+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);
+ }
+}
+
+int
+TAGEBase::bindex(Addr pc_in) const
+{
+ return ((pc_in >> instShiftAmt) & ((ULL(1) << (logTagTableSizes[0])) -
1));
+}
+
+int
+TAGEBase::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
+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 & ((ULL(1) << (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 & ((ULL(1) << 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, TageBranchInfo* 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, 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
+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;
+}
+
+//prediction
+bool
+TAGEBase::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);
+}
+
+void
+TAGEBase::calculateIndicesAndTags(ThreadID tid, Addr branch_pc,
+ TageBranchInfo* 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(TageBranchInfo* bi)
+{
+ // There is only 1 counter on the base TAGE implementation
+ return 0;
+}
+
+bool
+TAGEBase::tagePredict(ThreadID tid, Addr branch_pc,
+ bool cond_branch, TageBranchInfo* 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)] < 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, TageBranchInfo* bi)
+{
+ // Nothing for this base class implementation
+}
+
+void
+TAGEBase::handleAllocAndUReset(bool alloc, bool taken, TageBranchInfo* 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 &
+ ((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 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 & ((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++) {
+ resetUctr(gtable[i][j].u);
+ }
+ }
+ }
+}
+
+void
+TAGEBase::resetUctr(uint8_t & u)
+{
+ u >>= 1;
+}
+
+void
+TAGEBase::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
+ TageBranchInfo* bi, int nrand, Addr corrTarget)
+{
+ // TAGE UPDATE
+ // try to allocate a new entries only if prediction was wrong
+ 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
+ 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)],
+ bi->altTaken == taken, useAltOnNaBits);
+ }
+ }
+ }
+
+ adjustAlloc(alloc, taken, bi);
+
+ handleAllocAndUReset(alloc, taken, bi, nrand);
+
+ handleTAGEUpdate(branch_pc, taken, bi);
+}
+
+void
+TAGEBase::handleTAGEUpdate(Addr branch_pc, bool taken, TageBranchInfo* 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, void*
b,
+ bool speculative, const StaticInstPtr &inst, Addr
target)
+{
+ 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));
+
+ 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);
+}
+
+void
+TAGEBase::squash(ThreadID tid, bool taken, void *bp_history, Addr target)
+{
+ 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
+TAGEBase::extraAltCalc(TageBranchInfo* bi)
+{
+ // do nothing. This is only used in some derived classes
+ return;
+}
+
+int
+TAGEBase::getRandom() const
+{
+ return random_mt.random<int>();
+}
+
+void
+TAGEBase::updateStats(bool taken, TageBranchInfo* bi)
+{
+ if (taken == bi->tagePred) {
+ // correct prediction
+ switch (bi->provider) {
+ case BIMODAL_ONLY: tageBimodalProviderCorrect++; break;
+ case TAGE_LONGEST_MATCH: tageLongestMatchProviderCorrect++;
break;
+ case BIMODAL_ALT_MATCH: bimodalAltMatchProviderCorrect++; break;
+ case TAGE_ALT_MATCH: tageAltMatchProviderCorrect++; break;
+ }
+ } else {
+ // wrong prediction
+ switch (bi->provider) {
+ case BIMODAL_ONLY: tageBimodalProviderWrong++; break;
+ case TAGE_LONGEST_MATCH:
+ tageLongestMatchProviderWrong++;
+ if (bi->altTaken == taken) {
+ tageAltMatchProviderWouldHaveHit++;
+ }
+ break;
+ case BIMODAL_ALT_MATCH:
+ bimodalAltMatchProviderWrong++;
+ break;
+ case TAGE_ALT_MATCH:
+ tageAltMatchProviderWrong++;
+ break;
+ }
+
+ switch (bi->provider) {
+ case BIMODAL_ALT_MATCH:
+ case TAGE_ALT_MATCH:
+ if (bi->longestMatchPred == taken) {
+ tageLongestMatchProviderWouldHaveHit++;
+ }
+ }
+ }
+
+ switch (bi->provider) {
+ case TAGE_LONGEST_MATCH:
+ case TAGE_ALT_MATCH:
+ tageLongestMatchProvider[bi->hitBank]++;
+ tageAltMatchProvider[bi->altBank]++;
+ break;
+ }
+}
+
+void
+TAGEBase::regStats()
+{
+ tageLongestMatchProviderCorrect
+ .name(name() + ".tageLongestMatchProviderCorrect")
+ .desc("Number of times TAGE Longest Match is the provider and "
+ "the prediction is correct");
+
+ tageAltMatchProviderCorrect
+ .name(name() + ".tageAltMatchProviderCorrect")
+ .desc("Number of times TAGE Alt Match is the provider and "
+ "the prediction is correct");
+
+ bimodalAltMatchProviderCorrect
+ .name(name() + ".bimodalAltMatchProviderCorrect")
+ .desc("Number of times TAGE Alt Match is the bimodal and it is
the "
+ "provider and the prediction is correct");
+
+ tageBimodalProviderCorrect
+ .name(name() + ".tageBimodalProviderCorrect")
+ .desc("Number of times there are no hits on the TAGE tables "
+ "and the bimodal prediction is correct");
+
+ tageLongestMatchProviderWrong
+ .name(name() + ".tageLongestMatchProviderWrong")
+ .desc("Number of times TAGE Longest Match is the provider and "
+ "the prediction is wrong");
+
+ tageAltMatchProviderWrong
+ .name(name() + ".tageAltMatchProviderWrong")
+ .desc("Number of times TAGE Alt Match is the provider and "
+ "the prediction is wrong");
+
+ bimodalAltMatchProviderWrong
+ .name(name() + ".bimodalAltMatchProviderWrong")
+ .desc("Number of times TAGE Alt Match is the bimodal and it is
the "
+ "provider and the prediction is wrong");
+
+ tageBimodalProviderWrong
+ .name(name() + ".tageBimodalProviderWrong")
+ .desc("Number of times there are no hits on the TAGE tables "
+ "and the bimodal prediction is wrong");
+
+ tageAltMatchProviderWouldHaveHit
+ .name(name() + ".tageAltMatchProviderWouldHaveHit")
+ .desc("Number of times TAGE Longest Match is the provider, "
+ "the prediction is wrong and Alt Match prediction was
correct");
+
+ tageLongestMatchProviderWouldHaveHit
+ .name(name() + ".tageLongestMatchProviderWouldHaveHit")
+ .desc("Number of times TAGE Alt Match is the provider, the "
+ "prediction is wrong and Longest Match prediction was
correct");
+
+ tageLongestMatchProvider
+ .init(nHistoryTables + 1)
+ .name(name() + ".tageLongestMatchProvider")
+ .desc("TAGE provider for longest match");
+
+ tageAltMatchProvider
+ .init(nHistoryTables + 1)
+ .name(name() + ".tageAltMatchProvider")
+ .desc("TAGE provider for alt match");
+}
diff --git a/src/cpu/pred/tage_base.hh b/src/cpu/pred/tage_base.hh
new file mode 100644
index 0000000..ebd5053
--- /dev/null
+++ b/src/cpu/pred/tage_base.hh
@@ -0,0 +1,517 @@
+/*
+ * 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_BASE
+#define __CPU_PRED_TAGE_BASE
+
+#include <vector>
+
+#include "base/statistics.hh"
+#include "base/types.hh"
+#include "cpu/static_inst.hh"
+
+class TAGEBase
+{
+ public:
+ TAGEBase(
+ unsigned logRatioBiModalHystEntries,
+ unsigned nHistoryTables,
+ unsigned tagTableCounterBits,
+ unsigned tagTableUBits,
+ unsigned histBufferSize,
+ unsigned minHist,
+ unsigned maxHist,
+ unsigned pathHistBits,
+ std::vector<unsigned> const &tagTableTagWidths,
+ std::vector<int> const &logTagTableSizes,
+ unsigned numThreads,
+ uint64_t logUResetPeriod,
+ unsigned numUseAltOnNa,
+ unsigned useAltOnNaBits,
+ unsigned maxNumAlloc,
+ std::vector<bool> const &noSkip,
+ bool speculativeHistUpdate,
+ unsigned instShiftAmt
+ );
+ void regStats();
+ void init();
+
+ 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;
+ int bufferSize;
+
+ FoldedHistory()
+ {
+ comp = 0;
+ }
+
+ void init(int original_length, int compressed_length)
+ {
+ 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;
+ }
+ };
+
+ // provider type
+ enum {
+ BIMODAL_ONLY = 0,
+ TAGE_LONGEST_MATCH,
+ BIMODAL_ALT_MATCH,
+ TAGE_ALT_MATCH,
+ LAST_TAGE_PROVIDER_TYPE = TAGE_ALT_MATCH
+ };
+
+ // 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;
+
+ // for stats purposes
+ unsigned provider;
+
+ 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),
+ provider(-1)
+ {
+ 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.
+ */
+ virtual 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.
+ */
+ virtual 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.
+ */
+ virtual 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.
+ */
+ virtual 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.
+ */
+ template<typename T>
+ void ctrUpdate(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.
+ */
+ virtual 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).
+ */
+ virtual void updateHistories(
+ ThreadID tid, Addr branch_pc, bool taken, void* b, bool
speculative,
+ const StaticInstPtr & inst = StaticInst::nullStaticInstPtr,
+ Addr target = MaxAddr);
+
+ /**
+ * 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).
+ * @param target The correct branch target
+ * @post bp_history points to valid memory.
+ */
+ virtual void squash(
+ ThreadID tid, bool taken, void *bp_history, Addr target);
+
+ /**
+ * 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
+ * @param corrTarget The correct branch target
+ */
+ virtual void condBranchUpdate(
+ ThreadID tid, Addr branch_pc, bool taken, TageBranchInfo* bi,
+ int nrand, Addr corrTarget);
+
+ /**
+ * 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);
+
+ /**
+ * Update the stats
+ * @param taken Actual branch outcome
+ * @param bi Pointer to information on the prediction
+ * recorded at prediction time.
+ */
+ virtual void updateStats(bool taken, TageBranchInfo* bi);
+
+ /**
+ * Instantiates the TAGE table entries
+ */
+ virtual void buildTageTables();
+
+ /**
+ * Calculates the history lengths
+ * and some other paramters in derived classes
+ */
+ virtual void calculateParameters();
+
+ /**
+ * On a prediction, calculates the TAGE indices and tags for
+ * all the different history lengths
+ */
+ virtual void calculateIndicesAndTags(
+ ThreadID tid, Addr branch_pc, TageBranchInfo* bi);
+
+ /**
+ * Calculation of the index for useAltPredForNewlyAllocated
+ * On this base TAGE implementation it is always 0
+ */
+ virtual unsigned getUseAltIdx(TageBranchInfo* bi);
+
+ /**
+ * Extra calculation to tell whether TAGE allocaitons may happen or not
+ * on an update
+ * For this base TAGE implementation it does nothing
+ */
+ virtual void adjustAlloc(bool & alloc, bool taken, TageBranchInfo* bi);
+
+ /**
+ * Handles Allocation and U bits reset on an update
+ */
+ virtual void handleAllocAndUReset(
+ bool alloc, bool taken, TageBranchInfo* bi, int nrand);
+
+ /**
+ * Handles the U bits reset
+ */
+ virtual void handleUReset();
+
+ /**
+ * Handles the update of the TAGE entries
+ */
+ virtual void handleTAGEUpdate(
+ Addr branch_pc, bool taken, TageBranchInfo* bi);
+
+ /**
+ * Algorithm for resetting a single U counter
+ */
+ virtual void resetUctr(uint8_t & u);
+
+ /**
+ * Extra steps for calculating altTaken
+ * For this base TAGE class it does nothing
+ */
+ virtual void extraAltCalc(TageBranchInfo* bi);
+
+ /**
+ * Algorithm for returning a random number
+ * This base TAGE class just uses random_mt, but some derived classes
+ * may want to use a more realistic implementation or force some values
+ */
+ int getRandom() const;
+
+ const unsigned logRatioBiModalHystEntries;
+ const unsigned nHistoryTables;
+ const unsigned tagTableCounterBits;
+ const unsigned tagTableUBits;
+ const unsigned histBufferSize;
+ const unsigned minHist;
+ const unsigned maxHist;
+ const unsigned pathHistBits;
+
+ std::vector<unsigned> tagTableTagWidths;
+ 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;
+
+ /**
+ * Initialization of the folded histories
+ */
+ virtual void initFoldedHistories(ThreadHistory & history);
+
+ int *histLengths;
+ int *tableIndices;
+ int *tableTags;
+
+ std::vector<int8_t> useAltPredForNewlyAllocated;
+ int64_t tCounter;
+ uint64_t logUResetPeriod;
+ unsigned numUseAltOnNa;
+ unsigned useAltOnNaBits;
+ unsigned maxNumAlloc;
+
+ // Tells which tables are active
+ // (for the base TAGE implementation all are active)
+ // Some other classes use this for handling associativity
+ std::vector<bool> noSkip;
+
+ const bool speculativeHistUpdate;
+
+ const unsigned instShiftAmt;
+
+ // stats
+ Stats::Scalar tageLongestMatchProviderCorrect;
+ Stats::Scalar tageAltMatchProviderCorrect;
+ Stats::Scalar bimodalAltMatchProviderCorrect;
+ Stats::Scalar tageBimodalProviderCorrect;
+ Stats::Scalar tageLongestMatchProviderWrong;
+ Stats::Scalar tageAltMatchProviderWrong;
+ Stats::Scalar bimodalAltMatchProviderWrong;
+ Stats::Scalar tageBimodalProviderWrong;
+ Stats::Scalar tageAltMatchProviderWouldHaveHit;
+ Stats::Scalar tageLongestMatchProviderWouldHaveHit;
+
+ Stats::Vector tageLongestMatchProvider;
+ Stats::Vector tageAltMatchProvider;
+};
+
+#endif // __CPU_PRED_TAGE_BASE
--
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Gerrit-Project: public/gem5
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Gerrit-Change-Id: I2251b8b2d7f94124f9955f52b917dc3b064f090e
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Gerrit-Owner: Jairo Balart <jairo.bal...@metempsy.com>
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