ltage.cc revision 12334:e0ab29a34764
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 logSizeTagTables(params->logSizeTagTables), 54 logSizeLoopPred(params->logSizeLoopPred), 55 nHistoryTables(params->nHistoryTables), 56 tagTableCounterBits(params->tagTableCounterBits), 57 histBufferSize(params->histBufferSize), 58 minHist(params->minHist), 59 maxHist(params->maxHist), 60 minTagWidth(params->minTagWidth), 61 threadHistory(params->numThreads) 62{ 63 assert(params->histBufferSize > params->maxHist * 2); 64 useAltPredForNewlyAllocated = 0; 65 logTick = 19; 66 tCounter = ULL(1) << (logTick - 1); 67 68 for (auto& history : threadHistory) { 69 history.pathHist = 0; 70 history.globalHistory = new uint8_t[histBufferSize]; 71 history.gHist = history.globalHistory; 72 memset(history.gHist, 0, histBufferSize); 73 history.ptGhist = 0; 74 } 75 76 histLengths = new int [nHistoryTables+1]; 77 histLengths[1] = minHist; 78 histLengths[nHistoryTables] = maxHist; 79 80 for (int i = 2; i <= nHistoryTables; i++) { 81 histLengths[i] = (int) (((double) minHist * 82 pow ((double) (maxHist) / (double) minHist, 83 (double) (i - 1) / (double) ((nHistoryTables- 1)))) 84 + 0.5); 85 } 86 87 tagWidths[1] = minTagWidth; 88 tagWidths[2] = minTagWidth; 89 tagWidths[3] = minTagWidth + 1; 90 tagWidths[4] = minTagWidth + 1; 91 tagWidths[5] = minTagWidth + 2; 92 tagWidths[6] = minTagWidth + 3; 93 tagWidths[7] = minTagWidth + 4; 94 tagWidths[8] = minTagWidth + 5; 95 tagWidths[9] = minTagWidth + 5; 96 tagWidths[10] = minTagWidth + 6; 97 tagWidths[11] = minTagWidth + 7; 98 tagWidths[12] = minTagWidth + 8; 99 100 for (int i = 1; i <= 2; i++) 101 tagTableSizes[i] = logSizeTagTables - 1; 102 for (int i = 3; i <= 6; i++) 103 tagTableSizes[i] = logSizeTagTables; 104 for (int i = 7; i <= 10; i++) 105 tagTableSizes[i] = logSizeTagTables - 1; 106 for (int i = 11; i <= 12; i++) 107 tagTableSizes[i] = logSizeTagTables - 2; 108 109 for (auto& history : threadHistory) { 110 history.computeIndices = new FoldedHistory[nHistoryTables+1]; 111 history.computeTags[0] = new FoldedHistory[nHistoryTables+1]; 112 history.computeTags[1] = new FoldedHistory[nHistoryTables+1]; 113 114 for (int i = 1; i <= nHistoryTables; i++) { 115 history.computeIndices[i].init(histLengths[i], (tagTableSizes[i])); 116 history.computeTags[0][i].init( 117 history.computeIndices[i].origLength, tagWidths[i]); 118 history.computeTags[1][i].init( 119 history.computeIndices[i].origLength, tagWidths[i] - 1); 120 DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n", 121 histLengths[i], tagTableSizes[i], tagWidths[i]); 122 } 123 } 124 125 btable = new BimodalEntry[ULL(1) << logSizeBiMP]; 126 ltable = new LoopEntry[ULL(1) << logSizeLoopPred]; 127 gtable = new TageEntry*[nHistoryTables + 1]; 128 for (int i = 1; i <= nHistoryTables; i++) { 129 gtable[i] = new TageEntry[1<<(tagTableSizes[i])]; 130 } 131 132 tableIndices = new int [nHistoryTables+1]; 133 tableTags = new int [nHistoryTables+1]; 134 135 loopUseCounter = 0; 136} 137 138int 139LTAGE::bindex(Addr pc_in) const 140{ 141 return ((pc_in) & ((ULL(1) << (logSizeBiMP)) - 1)); 142} 143 144int 145LTAGE::lindex(Addr pc_in) const 146{ 147 return (((pc_in) & ((ULL(1) << (logSizeLoopPred - 2)) - 1)) << 2); 148} 149 150int 151LTAGE::F(int A, int size, int bank) const 152{ 153 int A1, A2; 154 155 A = A & ((ULL(1) << size) - 1); 156 A1 = (A & ((ULL(1) << tagTableSizes[bank]) - 1)); 157 A2 = (A >> tagTableSizes[bank]); 158 A2 = ((A2 << bank) & ((ULL(1) << tagTableSizes[bank]) - 1)) 159 + (A2 >> (tagTableSizes[bank] - bank)); 160 A = A1 ^ A2; 161 A = ((A << bank) & ((ULL(1) << tagTableSizes[bank]) - 1)) 162 + (A >> (tagTableSizes[bank] - bank)); 163 return (A); 164} 165 166 167// gindex computes a full hash of pc, ghist and pathHist 168int 169LTAGE::gindex(ThreadID tid, Addr pc, int bank) const 170{ 171 int index; 172 int hlen = (histLengths[bank] > 16) ? 16 : histLengths[bank]; 173 index = 174 (pc) ^ ((pc) >> ((int) abs(tagTableSizes[bank] - bank) + 1)) ^ 175 threadHistory[tid].computeIndices[bank].comp ^ 176 F(threadHistory[tid].pathHist, hlen, bank); 177 178 return (index & ((ULL(1) << (tagTableSizes[bank])) - 1)); 179} 180 181 182// Tag computation 183uint16_t 184LTAGE::gtag(ThreadID tid, Addr pc, int bank) const 185{ 186 int tag = (pc) ^ threadHistory[tid].computeTags[0][bank].comp 187 ^ (threadHistory[tid].computeTags[1][bank].comp << 1); 188 189 return (tag & ((ULL(1) << tagWidths[bank]) - 1)); 190} 191 192 193// Up-down saturating counter 194void 195LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits) 196{ 197 assert(nbits <= sizeof(int8_t) << 3); 198 if (taken) { 199 if (ctr < ((1 << (nbits - 1)) - 1)) 200 ctr++; 201 } else { 202 if (ctr > -(1 << (nbits - 1))) 203 ctr--; 204 } 205} 206 207// Bimodal prediction 208bool 209LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const 210{ 211 return (btable[bi->bimodalIndex].pred > 0); 212} 213 214 215// Update the bimodal predictor: a hysteresis bit is shared among 4 prediction 216// bits 217void 218LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi) 219{ 220 int inter = (btable[bi->bimodalIndex].pred << 1) 221 + btable[bi->bimodalIndex ].hyst; 222 if (taken) { 223 if (inter < 3) 224 inter++; 225 } else if (inter > 0) { 226 inter--; 227 } 228 btable[bi->bimodalIndex].pred = inter >> 1; 229 btable[bi->bimodalIndex].hyst = (inter & 1); 230 DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", 231 pc, btable[bi->bimodalIndex].pred,btable[bi->bimodalIndex].hyst); 232} 233 234 235//loop prediction: only used if high confidence 236bool 237LTAGE::getLoop(Addr pc, BranchInfo* bi) const 238{ 239 bi->loopHit = -1; 240 bi->loopPredValid = false; 241 bi->loopIndex = lindex(pc); 242 bi->loopTag = ((pc) >> (logSizeLoopPred - 2)); 243 244 for (int i = 0; i < 4; i++) { 245 if (ltable[bi->loopIndex + i].tag == bi->loopTag) { 246 bi->loopHit = i; 247 bi->loopPredValid = (ltable[bi->loopIndex + i].confidence >= 3); 248 bi->currentIter = ltable[bi->loopIndex + i].currentIterSpec; 249 if (ltable[bi->loopIndex + i].currentIterSpec + 1 == 250 ltable[bi->loopIndex + i].numIter) { 251 return !(ltable[bi->loopIndex + i].dir); 252 }else { 253 return (ltable[bi->loopIndex + i].dir); 254 } 255 } 256 } 257 return false; 258} 259 260void 261LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi) 262{ 263 if (bi->loopHit>=0) { 264 int index = lindex(pc); 265 if (taken != ltable[index].dir) { 266 ltable[index].currentIterSpec = 0; 267 } else { 268 ltable[index].currentIterSpec++; 269 } 270 } 271} 272 273void 274LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi) 275{ 276 int idx = bi->loopIndex + bi->loopHit; 277 if (bi->loopHit >= 0) { 278 //already a hit 279 if (bi->loopPredValid) { 280 if (taken != bi->loopPred) { 281 // free the entry 282 ltable[idx].numIter = 0; 283 ltable[idx].age = 0; 284 ltable[idx].confidence = 0; 285 ltable[idx].currentIter = 0; 286 return; 287 } else if (bi->loopPred != bi->tagePred) { 288 DPRINTF(LTage, "Loop Prediction success:%lx\n",pc); 289 if (ltable[idx].age < 7) 290 ltable[idx].age++; 291 } 292 } 293 294 ltable[idx].currentIter++; 295 if (ltable[idx].currentIter > ltable[idx].numIter) { 296 ltable[idx].confidence = 0; 297 if (ltable[idx].numIter != 0) { 298 // free the entry 299 ltable[idx].numIter = 0; 300 ltable[idx].age = 0; 301 ltable[idx].confidence = 0; 302 } 303 } 304 305 if (taken != ltable[idx].dir) { 306 if (ltable[idx].currentIter == ltable[idx].numIter) { 307 DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc); 308 309 if (ltable[idx].confidence < 7) { 310 ltable[idx].confidence++; 311 } 312 //just do not predict when the loop count is 1 or 2 313 if (ltable[idx].numIter < 3) { 314 // free the entry 315 ltable[idx].dir = taken; 316 ltable[idx].numIter = 0; 317 ltable[idx].age = 0; 318 ltable[idx].confidence = 0; 319 } 320 } else { 321 DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc); 322 if (ltable[idx].numIter == 0) { 323 // first complete nest; 324 ltable[idx].confidence = 0; 325 ltable[idx].numIter = ltable[idx].currentIter; 326 } else { 327 //not the same number of iterations as last time: free the 328 //entry 329 ltable[idx].numIter = 0; 330 ltable[idx].age = 0; 331 ltable[idx].confidence = 0; 332 } 333 } 334 ltable[idx].currentIter = 0; 335 } 336 337 } else if (taken) { 338 //try to allocate an entry on taken branch 339 int nrand = random_mt.random<int>(); 340 for (int i = 0; i < 4; i++) { 341 int loop_hit = (nrand + i) & 3; 342 idx = bi->loopIndex + loop_hit; 343 if (ltable[idx].age == 0) { 344 DPRINTF(LTage, "Allocating loop pred entry for branch %lx\n", 345 pc); 346 ltable[idx].dir = !taken; 347 ltable[idx].tag = bi->loopTag; 348 ltable[idx].numIter = 0; 349 ltable[idx].age = 7; 350 ltable[idx].confidence = 0; 351 ltable[idx].currentIter = 1; 352 break; 353 354 } 355 else 356 ltable[idx].age--; 357 } 358 } 359 360} 361 362// shifting the global history: we manage the history in a big table in order 363// to reduce simulation time 364void 365LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt) 366{ 367 if (pt == 0) { 368 DPRINTF(LTage, "Rolling over the histories\n"); 369 // Copy beginning of globalHistoryBuffer to end, such that 370 // the last maxHist outcomes are still reachable 371 // through pt[0 .. maxHist - 1]. 372 for (int i = 0; i < maxHist; i++) 373 tab[histBufferSize - maxHist + i] = tab[i]; 374 pt = histBufferSize - maxHist; 375 h = &tab[pt]; 376 } 377 pt--; 378 h--; 379 h[0] = (dir) ? 1 : 0; 380} 381 382// Get GHR for hashing indirect predictor 383// Build history backwards from pointer in 384// bp_history. 385unsigned 386LTAGE::getGHR(ThreadID tid, void *bp_history) const 387{ 388 BranchInfo* bi = static_cast<BranchInfo*>(bp_history); 389 unsigned val = 0; 390 for (unsigned i = 0; i < 32; i++) { 391 // Make sure we don't go out of bounds 392 int gh_offset = bi->ptGhist + i; 393 assert(&(threadHistory[tid].globalHistory[gh_offset]) < 394 threadHistory[tid].globalHistory + histBufferSize); 395 val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i); 396 } 397 398 return val; 399} 400 401//prediction 402bool 403LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) 404{ 405 BranchInfo *bi = new BranchInfo(nHistoryTables+1); 406 b = (void*)(bi); 407 Addr pc = branch_pc; 408 bool pred_taken = true; 409 bi->loopHit = -1; 410 411 if (cond_branch) { 412 // TAGE prediction 413 414 // computes the table addresses and the partial tags 415 for (int i = 1; i <= nHistoryTables; i++) { 416 tableIndices[i] = gindex(tid, pc, i); 417 bi->tableIndices[i] = tableIndices[i]; 418 tableTags[i] = gtag(tid, pc, i); 419 bi->tableTags[i] = tableTags[i]; 420 } 421 422 bi->bimodalIndex = bindex(pc); 423 424 bi->hitBank = 0; 425 bi->altBank = 0; 426 //Look for the bank with longest matching history 427 for (int i = nHistoryTables; i > 0; i--) { 428 if (gtable[i][tableIndices[i]].tag == tableTags[i]) { 429 bi->hitBank = i; 430 bi->hitBankIndex = tableIndices[bi->hitBank]; 431 break; 432 } 433 } 434 //Look for the alternate bank 435 for (int i = bi->hitBank - 1; i > 0; i--) { 436 if (gtable[i][tableIndices[i]].tag == tableTags[i]) { 437 bi->altBank = i; 438 bi->altBankIndex = tableIndices[bi->altBank]; 439 break; 440 } 441 } 442 //computes the prediction and the alternate prediction 443 if (bi->hitBank > 0) { 444 if (bi->altBank > 0) { 445 bi->altTaken = 446 gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0; 447 }else { 448 bi->altTaken = getBimodePred(pc, bi); 449 } 450 451 bi->longestMatchPred = 452 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0; 453 bi->pseudoNewAlloc = 454 abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1; 455 456 //if the entry is recognized as a newly allocated entry and 457 //useAltPredForNewlyAllocated is positive use the alternate 458 //prediction 459 if ((useAltPredForNewlyAllocated < 0) 460 || abs(2 * 461 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1) 462 bi->tagePred = bi->longestMatchPred; 463 else 464 bi->tagePred = bi->altTaken; 465 } else { 466 bi->altTaken = getBimodePred(pc, bi); 467 bi->tagePred = bi->altTaken; 468 bi->longestMatchPred = bi->altTaken; 469 } 470 //end TAGE prediction 471 472 bi->loopPred = getLoop(pc, bi); // loop prediction 473 474 pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ? 475 (bi->loopPred): (bi->tagePred); 476 DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, " 477 "loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n", 478 branch_pc, pred_taken, bi->loopPred, bi->loopPredValid, 479 loopUseCounter, bi->tagePred, bi->altTaken); 480 } 481 bi->branchPC = branch_pc; 482 bi->condBranch = cond_branch; 483 specLoopUpdate(branch_pc, pred_taken, bi); 484 return pred_taken; 485} 486 487// PREDICTOR UPDATE 488void 489LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history, 490 bool squashed) 491{ 492 assert(bp_history); 493 494 BranchInfo *bi = static_cast<BranchInfo*>(bp_history); 495 496 if (squashed) { 497 // This restores the global history, then update it 498 // and recomputes the folded histories. 499 squash(tid, taken, bp_history); 500 return; 501 } 502 503 int nrand = random_mt.random<int>(0,3); 504 Addr pc = branch_pc; 505 if (bi->condBranch) { 506 DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n", 507 branch_pc, taken); 508 // first update the loop predictor 509 loopUpdate(pc, taken, bi); 510 511 if (bi->loopPredValid) { 512 if (bi->tagePred != bi->loopPred) { 513 ctrUpdate(loopUseCounter, (bi->loopPred== taken), 7); 514 } 515 } 516 517 // TAGE UPDATE 518 // try to allocate a new entries only if prediction was wrong 519 bool longest_match_pred = false; 520 bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables); 521 if (bi->hitBank > 0) { 522 // Manage the selection between longest matching and alternate 523 // matching for "pseudo"-newly allocated longest matching entry 524 longest_match_pred = bi->longestMatchPred; 525 bool PseudoNewAlloc = bi->pseudoNewAlloc; 526 // an entry is considered as newly allocated if its prediction 527 // counter is weak 528 if (PseudoNewAlloc) { 529 if (longest_match_pred == taken) { 530 alloc = false; 531 } 532 // if it was delivering the correct prediction, no need to 533 // allocate new entry even if the overall prediction was false 534 if (longest_match_pred != bi->altTaken) { 535 ctrUpdate(useAltPredForNewlyAllocated, 536 bi->altTaken == taken, 4); 537 } 538 } 539 } 540 541 if (alloc) { 542 // is there some "unuseful" entry to allocate 543 int8_t min = 1; 544 for (int i = nHistoryTables; i > bi->hitBank; i--) { 545 if (gtable[i][bi->tableIndices[i]].u < min) { 546 min = gtable[i][bi->tableIndices[i]].u; 547 } 548 } 549 550 // we allocate an entry with a longer history 551 // to avoid ping-pong, we do not choose systematically the next 552 // entry, but among the 3 next entries 553 int Y = nrand & 554 ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1); 555 int X = bi->hitBank + 1; 556 if (Y & 1) { 557 X++; 558 if (Y & 2) 559 X++; 560 } 561 // No entry available, forces one to be available 562 if (min > 0) { 563 gtable[X][bi->tableIndices[X]].u = 0; 564 } 565 566 567 //Allocate only one entry 568 for (int i = X; i <= nHistoryTables; i++) { 569 if ((gtable[i][bi->tableIndices[i]].u == 0)) { 570 gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i]; 571 gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1; 572 gtable[i][bi->tableIndices[i]].u = 0; //? 573 } 574 } 575 } 576 //periodic reset of u: reset is not complete but bit by bit 577 tCounter++; 578 if ((tCounter & ((ULL(1) << logTick) - 1)) == 0) { 579 // reset least significant bit 580 // most significant bit becomes least significant bit 581 for (int i = 1; i <= nHistoryTables; i++) { 582 for (int j = 0; j < (ULL(1) << tagTableSizes[i]); j++) { 583 gtable[i][j].u = gtable[i][j].u >> 1; 584 } 585 } 586 } 587 588 if (bi->hitBank > 0) { 589 DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n", 590 bi->hitBank, bi->hitBankIndex, branch_pc); 591 ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken, 592 tagTableCounterBits); 593 // if the provider entry is not certified to be useful also update 594 // the alternate prediction 595 if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) { 596 if (bi->altBank > 0) { 597 ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken, 598 tagTableCounterBits); 599 DPRINTF(LTage, "Updating tag table entry (%d,%d) for" 600 " branch %lx\n", bi->hitBank, bi->hitBankIndex, 601 branch_pc); 602 } 603 if (bi->altBank == 0) { 604 baseUpdate(pc, taken, bi); 605 } 606 } 607 608 // update the u counter 609 if (longest_match_pred != bi->altTaken) { 610 if (longest_match_pred == taken) { 611 if (gtable[bi->hitBank][bi->hitBankIndex].u < 1) { 612 gtable[bi->hitBank][bi->hitBankIndex].u++; 613 } 614 } 615 } 616 } else { 617 baseUpdate(pc, taken, bi); 618 } 619 620 //END PREDICTOR UPDATE 621 } 622 if (!squashed) { 623 delete bi; 624 } 625} 626 627void 628LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b) 629{ 630 BranchInfo* bi = (BranchInfo*)(b); 631 ThreadHistory& tHist = threadHistory[tid]; 632 // UPDATE HISTORIES 633 bool pathbit = ((branch_pc) & 1); 634 //on a squash, return pointers to this and recompute indices. 635 //update user history 636 updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist); 637 tHist.pathHist = (tHist.pathHist << 1) + pathbit; 638 tHist.pathHist = (tHist.pathHist & ((ULL(1) << 16) - 1)); 639 640 bi->ptGhist = tHist.ptGhist; 641 bi->pathHist = tHist.pathHist; 642 //prepare next index and tag computations for user branchs 643 for (int i = 1; i <= nHistoryTables; i++) 644 { 645 bi->ci[i] = tHist.computeIndices[i].comp; 646 bi->ct0[i] = tHist.computeTags[0][i].comp; 647 bi->ct1[i] = tHist.computeTags[1][i].comp; 648 tHist.computeIndices[i].update(tHist.gHist); 649 tHist.computeTags[0][i].update(tHist.gHist); 650 tHist.computeTags[1][i].update(tHist.gHist); 651 } 652 DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, " 653 "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist, 654 tHist.ptGhist); 655} 656 657void 658LTAGE::squash(ThreadID tid, bool taken, void *bp_history) 659{ 660 BranchInfo* bi = (BranchInfo*)(bp_history); 661 ThreadHistory& tHist = threadHistory[tid]; 662 DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, " 663 "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist); 664 tHist.pathHist = bi->pathHist; 665 tHist.ptGhist = bi->ptGhist; 666 tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]); 667 tHist.gHist[0] = (taken ? 1 : 0); 668 for (int i = 1; i <= nHistoryTables; i++) { 669 tHist.computeIndices[i].comp = bi->ci[i]; 670 tHist.computeTags[0][i].comp = bi->ct0[i]; 671 tHist.computeTags[1][i].comp = bi->ct1[i]; 672 tHist.computeIndices[i].update(tHist.gHist); 673 tHist.computeTags[0][i].update(tHist.gHist); 674 tHist.computeTags[1][i].update(tHist.gHist); 675 } 676 677 if (bi->condBranch) { 678 if (bi->loopHit >= 0) { 679 int idx = bi->loopIndex + bi->loopHit; 680 ltable[idx].currentIterSpec = bi->currentIter; 681 } 682 } 683 684} 685 686void 687LTAGE::squash(ThreadID tid, void *bp_history) 688{ 689 BranchInfo* bi = (BranchInfo*)(bp_history); 690 DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC); 691 if (bi->condBranch) { 692 if (bi->loopHit >= 0) { 693 int idx = bi->loopIndex + bi->loopHit; 694 ltable[idx].currentIterSpec = bi->currentIter; 695 } 696 } 697 698 delete bi; 699} 700 701bool 702LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history) 703{ 704 bool retval = predict(tid, branch_pc, true, bp_history); 705 706 DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval); 707 updateHistories(tid, branch_pc, retval, bp_history); 708 assert(threadHistory[tid].gHist == 709 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]); 710 711 return retval; 712} 713 714void 715LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history) 716{ 717 BranchInfo* bi = (BranchInfo*) bp_history; 718 ThreadHistory& tHist = threadHistory[tid]; 719 DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc); 720 assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]); 721 tHist.gHist[0] = 0; 722 for (int i = 1; i <= nHistoryTables; i++) { 723 tHist.computeIndices[i].comp = bi->ci[i]; 724 tHist.computeTags[0][i].comp = bi->ct0[i]; 725 tHist.computeTags[1][i].comp = bi->ct1[i]; 726 tHist.computeIndices[i].update(tHist.gHist); 727 tHist.computeTags[0][i].update(tHist.gHist); 728 tHist.computeTags[1][i].update(tHist.gHist); 729 } 730} 731 732void 733LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history) 734{ 735 DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc); 736 predict(tid, br_pc, false, bp_history); 737 updateHistories(tid, br_pc, true, bp_history); 738 assert(threadHistory[tid].gHist == 739 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]); 740} 741 742LTAGE* 743LTAGEParams::create() 744{ 745 return new LTAGE(this); 746} 747