ltage.cc revision 13433:fd8c49bea81f
1/* 2 * Copyright (c) 2014 The University of Wisconsin 3 * 4 * Copyright (c) 2006 INRIA (Institut National de Recherche en 5 * Informatique et en Automatique / French National Research Institute 6 * for Computer Science and Applied Mathematics) 7 * 8 * All rights reserved. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions are 12 * met: redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer; 14 * redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution; 17 * neither the name of the copyright holders nor the names of its 18 * contributors may be used to endorse or promote products derived from 19 * this software without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 24 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 25 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 26 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 27 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 31 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32 * 33 * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais, 34 * from André Seznec's code. 35 */ 36 37/* @file 38 * Implementation of a L-TAGE branch predictor 39 */ 40 41#include "cpu/pred/ltage.hh" 42 43#include "base/intmath.hh" 44#include "base/logging.hh" 45#include "base/random.hh" 46#include "base/trace.hh" 47#include "debug/Fetch.hh" 48#include "debug/LTage.hh" 49 50LTAGE::LTAGE(const LTAGEParams *params) 51 : BPredUnit(params), 52 logSizeBiMP(params->logSizeBiMP), 53 logRatioBiModalHystEntries(params->logRatioBiModalHystEntries), 54 logSizeTagTables(params->logSizeTagTables), 55 logSizeLoopPred(params->logSizeLoopPred), 56 nHistoryTables(params->nHistoryTables), 57 tagTableCounterBits(params->tagTableCounterBits), 58 histBufferSize(params->histBufferSize), 59 minHist(params->minHist), 60 maxHist(params->maxHist), 61 minTagWidth(params->minTagWidth), 62 threadHistory(params->numThreads) 63{ 64 assert(params->histBufferSize > params->maxHist * 2); 65 useAltPredForNewlyAllocated = 0; 66 logTick = 19; 67 tCounter = ULL(1) << (logTick - 1); 68 69 for (auto& history : threadHistory) { 70 history.pathHist = 0; 71 history.globalHistory = new uint8_t[histBufferSize]; 72 history.gHist = history.globalHistory; 73 memset(history.gHist, 0, histBufferSize); 74 history.ptGhist = 0; 75 } 76 77 histLengths = new int [nHistoryTables+1]; 78 histLengths[1] = minHist; 79 histLengths[nHistoryTables] = maxHist; 80 81 for (int i = 2; i <= nHistoryTables; i++) { 82 histLengths[i] = (int) (((double) minHist * 83 pow ((double) (maxHist) / (double) minHist, 84 (double) (i - 1) / (double) ((nHistoryTables- 1)))) 85 + 0.5); 86 } 87 88 tagWidths[1] = minTagWidth; 89 tagWidths[2] = minTagWidth; 90 tagWidths[3] = minTagWidth + 1; 91 tagWidths[4] = minTagWidth + 1; 92 tagWidths[5] = minTagWidth + 2; 93 tagWidths[6] = minTagWidth + 3; 94 tagWidths[7] = minTagWidth + 4; 95 tagWidths[8] = minTagWidth + 5; 96 tagWidths[9] = minTagWidth + 5; 97 tagWidths[10] = minTagWidth + 6; 98 tagWidths[11] = minTagWidth + 7; 99 tagWidths[12] = minTagWidth + 8; 100 101 for (int i = 1; i <= 2; i++) 102 tagTableSizes[i] = logSizeTagTables - 1; 103 for (int i = 3; i <= 6; i++) 104 tagTableSizes[i] = logSizeTagTables; 105 for (int i = 7; i <= 10; i++) 106 tagTableSizes[i] = logSizeTagTables - 1; 107 for (int i = 11; i <= 12; i++) 108 tagTableSizes[i] = logSizeTagTables - 2; 109 110 for (auto& history : threadHistory) { 111 history.computeIndices = new FoldedHistory[nHistoryTables+1]; 112 history.computeTags[0] = new FoldedHistory[nHistoryTables+1]; 113 history.computeTags[1] = new FoldedHistory[nHistoryTables+1]; 114 115 for (int i = 1; i <= nHistoryTables; i++) { 116 history.computeIndices[i].init(histLengths[i], (tagTableSizes[i])); 117 history.computeTags[0][i].init( 118 history.computeIndices[i].origLength, tagWidths[i]); 119 history.computeTags[1][i].init( 120 history.computeIndices[i].origLength, tagWidths[i] - 1); 121 DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n", 122 histLengths[i], tagTableSizes[i], tagWidths[i]); 123 } 124 } 125 126 const uint64_t bimodalTableSize = ULL(1) << logSizeBiMP; 127 btablePrediction.resize(bimodalTableSize, false); 128 btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries, 129 true); 130 131 ltable = new LoopEntry[ULL(1) << logSizeLoopPred]; 132 gtable = new TageEntry*[nHistoryTables + 1]; 133 for (int i = 1; i <= nHistoryTables; i++) { 134 gtable[i] = new TageEntry[1<<(tagTableSizes[i])]; 135 } 136 137 tableIndices = new int [nHistoryTables+1]; 138 tableTags = new int [nHistoryTables+1]; 139 140 loopUseCounter = 0; 141} 142 143int 144LTAGE::bindex(Addr pc_in) const 145{ 146 return ((pc_in >> instShiftAmt) & ((ULL(1) << (logSizeBiMP)) - 1)); 147} 148 149int 150LTAGE::lindex(Addr pc_in) const 151{ 152 return (((pc_in >> instShiftAmt) & 153 ((ULL(1) << (logSizeLoopPred - 2)) - 1)) << 2); 154} 155 156int 157LTAGE::F(int A, int size, int bank) const 158{ 159 int A1, A2; 160 161 A = A & ((ULL(1) << size) - 1); 162 A1 = (A & ((ULL(1) << tagTableSizes[bank]) - 1)); 163 A2 = (A >> tagTableSizes[bank]); 164 A2 = ((A2 << bank) & ((ULL(1) << tagTableSizes[bank]) - 1)) 165 + (A2 >> (tagTableSizes[bank] - bank)); 166 A = A1 ^ A2; 167 A = ((A << bank) & ((ULL(1) << tagTableSizes[bank]) - 1)) 168 + (A >> (tagTableSizes[bank] - bank)); 169 return (A); 170} 171 172 173// gindex computes a full hash of pc, ghist and pathHist 174int 175LTAGE::gindex(ThreadID tid, Addr pc, int bank) const 176{ 177 int index; 178 int hlen = (histLengths[bank] > 16) ? 16 : histLengths[bank]; 179 index = 180 (pc >> instShiftAmt) ^ 181 ((pc >> instShiftAmt) >> ((int) abs(tagTableSizes[bank] - bank) + 1)) ^ 182 threadHistory[tid].computeIndices[bank].comp ^ 183 F(threadHistory[tid].pathHist, hlen, bank); 184 185 return (index & ((ULL(1) << (tagTableSizes[bank])) - 1)); 186} 187 188 189// Tag computation 190uint16_t 191LTAGE::gtag(ThreadID tid, Addr pc, int bank) const 192{ 193 int tag = (pc >> instShiftAmt) ^ 194 threadHistory[tid].computeTags[0][bank].comp ^ 195 (threadHistory[tid].computeTags[1][bank].comp << 1); 196 197 return (tag & ((ULL(1) << tagWidths[bank]) - 1)); 198} 199 200 201// Up-down saturating counter 202void 203LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits) 204{ 205 assert(nbits <= sizeof(int8_t) << 3); 206 if (taken) { 207 if (ctr < ((1 << (nbits - 1)) - 1)) 208 ctr++; 209 } else { 210 if (ctr > -(1 << (nbits - 1))) 211 ctr--; 212 } 213} 214 215// Bimodal prediction 216bool 217LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const 218{ 219 return btablePrediction[bi->bimodalIndex]; 220} 221 222 223// Update the bimodal predictor: a hysteresis bit is shared among N prediction 224// bits (N = 2 ^ logRatioBiModalHystEntries) 225void 226LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi) 227{ 228 int inter = (btablePrediction[bi->bimodalIndex] << 1) 229 + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries]; 230 if (taken) { 231 if (inter < 3) 232 inter++; 233 } else if (inter > 0) { 234 inter--; 235 } 236 const bool pred = inter >> 1; 237 const bool hyst = inter & 1; 238 btablePrediction[bi->bimodalIndex] = pred; 239 btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst; 240 DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst); 241} 242 243 244//loop prediction: only used if high confidence 245bool 246LTAGE::getLoop(Addr pc, BranchInfo* bi) const 247{ 248 bi->loopHit = -1; 249 bi->loopPredValid = false; 250 bi->loopIndex = lindex(pc); 251 bi->loopTag = ((pc) >> (instShiftAmt + logSizeLoopPred - 2)); 252 253 for (int i = 0; i < 4; i++) { 254 if (ltable[bi->loopIndex + i].tag == bi->loopTag) { 255 bi->loopHit = i; 256 bi->loopPredValid = (ltable[bi->loopIndex + i].confidence >= 3); 257 bi->currentIter = ltable[bi->loopIndex + i].currentIterSpec; 258 if (ltable[bi->loopIndex + i].currentIterSpec + 1 == 259 ltable[bi->loopIndex + i].numIter) { 260 return !(ltable[bi->loopIndex + i].dir); 261 }else { 262 return (ltable[bi->loopIndex + i].dir); 263 } 264 } 265 } 266 return false; 267} 268 269void 270LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi) 271{ 272 if (bi->loopHit>=0) { 273 int index = lindex(pc); 274 if (taken != ltable[index].dir) { 275 ltable[index].currentIterSpec = 0; 276 } else { 277 ltable[index].currentIterSpec++; 278 } 279 } 280} 281 282void 283LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi) 284{ 285 int idx = bi->loopIndex + bi->loopHit; 286 if (bi->loopHit >= 0) { 287 //already a hit 288 if (bi->loopPredValid) { 289 if (taken != bi->loopPred) { 290 // free the entry 291 ltable[idx].numIter = 0; 292 ltable[idx].age = 0; 293 ltable[idx].confidence = 0; 294 ltable[idx].currentIter = 0; 295 return; 296 } else if (bi->loopPred != bi->tagePred) { 297 DPRINTF(LTage, "Loop Prediction success:%lx\n",pc); 298 if (ltable[idx].age < 7) 299 ltable[idx].age++; 300 } 301 } 302 303 ltable[idx].currentIter++; 304 if (ltable[idx].currentIter > ltable[idx].numIter) { 305 ltable[idx].confidence = 0; 306 if (ltable[idx].numIter != 0) { 307 // free the entry 308 ltable[idx].numIter = 0; 309 ltable[idx].age = 0; 310 ltable[idx].confidence = 0; 311 } 312 } 313 314 if (taken != ltable[idx].dir) { 315 if (ltable[idx].currentIter == ltable[idx].numIter) { 316 DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc); 317 318 if (ltable[idx].confidence < 7) { 319 ltable[idx].confidence++; 320 } 321 //just do not predict when the loop count is 1 or 2 322 if (ltable[idx].numIter < 3) { 323 // free the entry 324 ltable[idx].dir = taken; 325 ltable[idx].numIter = 0; 326 ltable[idx].age = 0; 327 ltable[idx].confidence = 0; 328 } 329 } else { 330 DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc); 331 if (ltable[idx].numIter == 0) { 332 // first complete nest; 333 ltable[idx].confidence = 0; 334 ltable[idx].numIter = ltable[idx].currentIter; 335 } else { 336 //not the same number of iterations as last time: free the 337 //entry 338 ltable[idx].numIter = 0; 339 ltable[idx].age = 0; 340 ltable[idx].confidence = 0; 341 } 342 } 343 ltable[idx].currentIter = 0; 344 } 345 346 } else if (taken) { 347 //try to allocate an entry on taken branch 348 int nrand = random_mt.random<int>(); 349 for (int i = 0; i < 4; i++) { 350 int loop_hit = (nrand + i) & 3; 351 idx = bi->loopIndex + loop_hit; 352 if (ltable[idx].age == 0) { 353 DPRINTF(LTage, "Allocating loop pred entry for branch %lx\n", 354 pc); 355 ltable[idx].dir = !taken; 356 ltable[idx].tag = bi->loopTag; 357 ltable[idx].numIter = 0; 358 ltable[idx].age = 7; 359 ltable[idx].confidence = 0; 360 ltable[idx].currentIter = 1; 361 break; 362 363 } 364 else 365 ltable[idx].age--; 366 } 367 } 368 369} 370 371// shifting the global history: we manage the history in a big table in order 372// to reduce simulation time 373void 374LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt) 375{ 376 if (pt == 0) { 377 DPRINTF(LTage, "Rolling over the histories\n"); 378 // Copy beginning of globalHistoryBuffer to end, such that 379 // the last maxHist outcomes are still reachable 380 // through pt[0 .. maxHist - 1]. 381 for (int i = 0; i < maxHist; i++) 382 tab[histBufferSize - maxHist + i] = tab[i]; 383 pt = histBufferSize - maxHist; 384 h = &tab[pt]; 385 } 386 pt--; 387 h--; 388 h[0] = (dir) ? 1 : 0; 389} 390 391// Get GHR for hashing indirect predictor 392// Build history backwards from pointer in 393// bp_history. 394unsigned 395LTAGE::getGHR(ThreadID tid, void *bp_history) const 396{ 397 BranchInfo* bi = static_cast<BranchInfo*>(bp_history); 398 unsigned val = 0; 399 for (unsigned i = 0; i < 32; i++) { 400 // Make sure we don't go out of bounds 401 int gh_offset = bi->ptGhist + i; 402 assert(&(threadHistory[tid].globalHistory[gh_offset]) < 403 threadHistory[tid].globalHistory + histBufferSize); 404 val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i); 405 } 406 407 return val; 408} 409 410//prediction 411bool 412LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) 413{ 414 BranchInfo *bi = new BranchInfo(nHistoryTables+1); 415 b = (void*)(bi); 416 Addr pc = branch_pc; 417 bool pred_taken = true; 418 bi->loopHit = -1; 419 420 if (cond_branch) { 421 // TAGE prediction 422 423 // computes the table addresses and the partial tags 424 for (int i = 1; i <= nHistoryTables; i++) { 425 tableIndices[i] = gindex(tid, pc, i); 426 bi->tableIndices[i] = tableIndices[i]; 427 tableTags[i] = gtag(tid, pc, i); 428 bi->tableTags[i] = tableTags[i]; 429 } 430 431 bi->bimodalIndex = bindex(pc); 432 433 bi->hitBank = 0; 434 bi->altBank = 0; 435 //Look for the bank with longest matching history 436 for (int i = nHistoryTables; i > 0; i--) { 437 if (gtable[i][tableIndices[i]].tag == tableTags[i]) { 438 bi->hitBank = i; 439 bi->hitBankIndex = tableIndices[bi->hitBank]; 440 break; 441 } 442 } 443 //Look for the alternate bank 444 for (int i = bi->hitBank - 1; i > 0; i--) { 445 if (gtable[i][tableIndices[i]].tag == tableTags[i]) { 446 bi->altBank = i; 447 bi->altBankIndex = tableIndices[bi->altBank]; 448 break; 449 } 450 } 451 //computes the prediction and the alternate prediction 452 if (bi->hitBank > 0) { 453 if (bi->altBank > 0) { 454 bi->altTaken = 455 gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0; 456 }else { 457 bi->altTaken = getBimodePred(pc, bi); 458 } 459 460 bi->longestMatchPred = 461 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0; 462 bi->pseudoNewAlloc = 463 abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1; 464 465 //if the entry is recognized as a newly allocated entry and 466 //useAltPredForNewlyAllocated is positive use the alternate 467 //prediction 468 if ((useAltPredForNewlyAllocated < 0) 469 || abs(2 * 470 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1) 471 bi->tagePred = bi->longestMatchPred; 472 else 473 bi->tagePred = bi->altTaken; 474 } else { 475 bi->altTaken = getBimodePred(pc, bi); 476 bi->tagePred = bi->altTaken; 477 bi->longestMatchPred = bi->altTaken; 478 } 479 //end TAGE prediction 480 481 bi->loopPred = getLoop(pc, bi); // loop prediction 482 483 pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ? 484 (bi->loopPred): (bi->tagePred); 485 DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, " 486 "loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n", 487 branch_pc, pred_taken, bi->loopPred, bi->loopPredValid, 488 loopUseCounter, bi->tagePred, bi->altTaken); 489 } 490 bi->branchPC = branch_pc; 491 bi->condBranch = cond_branch; 492 specLoopUpdate(branch_pc, pred_taken, bi); 493 return pred_taken; 494} 495 496// PREDICTOR UPDATE 497void 498LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history, 499 bool squashed) 500{ 501 assert(bp_history); 502 503 BranchInfo *bi = static_cast<BranchInfo*>(bp_history); 504 505 if (squashed) { 506 // This restores the global history, then update it 507 // and recomputes the folded histories. 508 squash(tid, taken, bp_history); 509 return; 510 } 511 512 int nrand = random_mt.random<int>(0,3); 513 Addr pc = branch_pc; 514 if (bi->condBranch) { 515 DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n", 516 branch_pc, taken); 517 // first update the loop predictor 518 loopUpdate(pc, taken, bi); 519 520 if (bi->loopPredValid) { 521 if (bi->tagePred != bi->loopPred) { 522 ctrUpdate(loopUseCounter, (bi->loopPred== taken), 7); 523 } 524 } 525 526 // TAGE UPDATE 527 // try to allocate a new entries only if prediction was wrong 528 bool longest_match_pred = false; 529 bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables); 530 if (bi->hitBank > 0) { 531 // Manage the selection between longest matching and alternate 532 // matching for "pseudo"-newly allocated longest matching entry 533 longest_match_pred = bi->longestMatchPred; 534 bool PseudoNewAlloc = bi->pseudoNewAlloc; 535 // an entry is considered as newly allocated if its prediction 536 // counter is weak 537 if (PseudoNewAlloc) { 538 if (longest_match_pred == taken) { 539 alloc = false; 540 } 541 // if it was delivering the correct prediction, no need to 542 // allocate new entry even if the overall prediction was false 543 if (longest_match_pred != bi->altTaken) { 544 ctrUpdate(useAltPredForNewlyAllocated, 545 bi->altTaken == taken, 4); 546 } 547 } 548 } 549 550 if (alloc) { 551 // is there some "unuseful" entry to allocate 552 int8_t min = 1; 553 for (int i = nHistoryTables; i > bi->hitBank; i--) { 554 if (gtable[i][bi->tableIndices[i]].u < min) { 555 min = gtable[i][bi->tableIndices[i]].u; 556 } 557 } 558 559 // we allocate an entry with a longer history 560 // to avoid ping-pong, we do not choose systematically the next 561 // entry, but among the 3 next entries 562 int Y = nrand & 563 ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1); 564 int X = bi->hitBank + 1; 565 if (Y & 1) { 566 X++; 567 if (Y & 2) 568 X++; 569 } 570 // No entry available, forces one to be available 571 if (min > 0) { 572 gtable[X][bi->tableIndices[X]].u = 0; 573 } 574 575 576 //Allocate only one entry 577 for (int i = X; i <= nHistoryTables; i++) { 578 if ((gtable[i][bi->tableIndices[i]].u == 0)) { 579 gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i]; 580 gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1; 581 gtable[i][bi->tableIndices[i]].u = 0; //? 582 break; 583 } 584 } 585 } 586 //periodic reset of u: reset is not complete but bit by bit 587 tCounter++; 588 if ((tCounter & ((ULL(1) << logTick) - 1)) == 0) { 589 // reset least significant bit 590 // most significant bit becomes least significant bit 591 for (int i = 1; i <= nHistoryTables; i++) { 592 for (int j = 0; j < (ULL(1) << tagTableSizes[i]); j++) { 593 gtable[i][j].u = gtable[i][j].u >> 1; 594 } 595 } 596 } 597 598 if (bi->hitBank > 0) { 599 DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n", 600 bi->hitBank, bi->hitBankIndex, branch_pc); 601 ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken, 602 tagTableCounterBits); 603 // if the provider entry is not certified to be useful also update 604 // the alternate prediction 605 if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) { 606 if (bi->altBank > 0) { 607 ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken, 608 tagTableCounterBits); 609 DPRINTF(LTage, "Updating tag table entry (%d,%d) for" 610 " branch %lx\n", bi->hitBank, bi->hitBankIndex, 611 branch_pc); 612 } 613 if (bi->altBank == 0) { 614 baseUpdate(pc, taken, bi); 615 } 616 } 617 618 // update the u counter 619 if (longest_match_pred != bi->altTaken) { 620 if (longest_match_pred == taken) { 621 if (gtable[bi->hitBank][bi->hitBankIndex].u < 1) { 622 gtable[bi->hitBank][bi->hitBankIndex].u++; 623 } 624 } 625 } 626 } else { 627 baseUpdate(pc, taken, bi); 628 } 629 630 //END PREDICTOR UPDATE 631 } 632 if (!squashed) { 633 delete bi; 634 } 635} 636 637void 638LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b) 639{ 640 BranchInfo* bi = (BranchInfo*)(b); 641 ThreadHistory& tHist = threadHistory[tid]; 642 // UPDATE HISTORIES 643 bool pathbit = ((branch_pc >> instShiftAmt) & 1); 644 //on a squash, return pointers to this and recompute indices. 645 //update user history 646 updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist); 647 tHist.pathHist = (tHist.pathHist << 1) + pathbit; 648 tHist.pathHist = (tHist.pathHist & ((ULL(1) << 16) - 1)); 649 650 bi->ptGhist = tHist.ptGhist; 651 bi->pathHist = tHist.pathHist; 652 //prepare next index and tag computations for user branchs 653 for (int i = 1; i <= nHistoryTables; i++) 654 { 655 bi->ci[i] = tHist.computeIndices[i].comp; 656 bi->ct0[i] = tHist.computeTags[0][i].comp; 657 bi->ct1[i] = tHist.computeTags[1][i].comp; 658 tHist.computeIndices[i].update(tHist.gHist); 659 tHist.computeTags[0][i].update(tHist.gHist); 660 tHist.computeTags[1][i].update(tHist.gHist); 661 } 662 DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, " 663 "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist, 664 tHist.ptGhist); 665} 666 667void 668LTAGE::squash(ThreadID tid, bool taken, void *bp_history) 669{ 670 BranchInfo* bi = (BranchInfo*)(bp_history); 671 ThreadHistory& tHist = threadHistory[tid]; 672 DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, " 673 "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist); 674 tHist.pathHist = bi->pathHist; 675 tHist.ptGhist = bi->ptGhist; 676 tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]); 677 tHist.gHist[0] = (taken ? 1 : 0); 678 for (int i = 1; i <= nHistoryTables; i++) { 679 tHist.computeIndices[i].comp = bi->ci[i]; 680 tHist.computeTags[0][i].comp = bi->ct0[i]; 681 tHist.computeTags[1][i].comp = bi->ct1[i]; 682 tHist.computeIndices[i].update(tHist.gHist); 683 tHist.computeTags[0][i].update(tHist.gHist); 684 tHist.computeTags[1][i].update(tHist.gHist); 685 } 686 687 if (bi->condBranch) { 688 if (bi->loopHit >= 0) { 689 int idx = bi->loopIndex + bi->loopHit; 690 ltable[idx].currentIterSpec = bi->currentIter; 691 } 692 } 693 694} 695 696void 697LTAGE::squash(ThreadID tid, void *bp_history) 698{ 699 BranchInfo* bi = (BranchInfo*)(bp_history); 700 DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC); 701 if (bi->condBranch) { 702 if (bi->loopHit >= 0) { 703 int idx = bi->loopIndex + bi->loopHit; 704 ltable[idx].currentIterSpec = bi->currentIter; 705 } 706 } 707 708 delete bi; 709} 710 711bool 712LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history) 713{ 714 bool retval = predict(tid, branch_pc, true, bp_history); 715 716 DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval); 717 updateHistories(tid, branch_pc, retval, bp_history); 718 assert(threadHistory[tid].gHist == 719 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]); 720 721 return retval; 722} 723 724void 725LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history) 726{ 727 BranchInfo* bi = (BranchInfo*) bp_history; 728 ThreadHistory& tHist = threadHistory[tid]; 729 DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc); 730 assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]); 731 tHist.gHist[0] = 0; 732 for (int i = 1; i <= nHistoryTables; i++) { 733 tHist.computeIndices[i].comp = bi->ci[i]; 734 tHist.computeTags[0][i].comp = bi->ct0[i]; 735 tHist.computeTags[1][i].comp = bi->ct1[i]; 736 tHist.computeIndices[i].update(tHist.gHist); 737 tHist.computeTags[0][i].update(tHist.gHist); 738 tHist.computeTags[1][i].update(tHist.gHist); 739 } 740} 741 742void 743LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history) 744{ 745 DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc); 746 predict(tid, br_pc, false, bp_history); 747 updateHistories(tid, br_pc, true, bp_history); 748 assert(threadHistory[tid].gHist == 749 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]); 750} 751 752LTAGE* 753LTAGEParams::create() 754{ 755 return new LTAGE(this); 756} 757