1/* 2 * Copyright (c) 2004-2006 The Regents of The University of Michigan 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are 7 * met: redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer; 9 * redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution; 12 * neither the name of the copyright holders nor the names of its 13 * contributors may be used to endorse or promote products derived from 14 * this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 * Authors: Kevin Lim 29 */ 30
| 1/* 2 * Copyright (c) 2004-2006 The Regents of The University of Michigan 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are 7 * met: redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer; 9 * redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution; 12 * neither the name of the copyright holders nor the names of its 13 * contributors may be used to endorse or promote products derived from 14 * this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 * Authors: Kevin Lim 29 */ 30
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33#include "params/DerivO3CPU.hh" 34 35using namespace std; 36 37template<class Impl> 38DefaultDecode<Impl>::DefaultDecode(O3CPU *_cpu, DerivO3CPUParams *params) 39 : cpu(_cpu), 40 renameToDecodeDelay(params->renameToDecodeDelay), 41 iewToDecodeDelay(params->iewToDecodeDelay), 42 commitToDecodeDelay(params->commitToDecodeDelay), 43 fetchToDecodeDelay(params->fetchToDecodeDelay), 44 decodeWidth(params->decodeWidth), 45 numThreads(params->numThreads) 46{ 47 _status = Inactive; 48 49 // Setup status, make sure stall signals are clear. 50 for (ThreadID tid = 0; tid < numThreads; ++tid) { 51 decodeStatus[tid] = Idle; 52 53 stalls[tid].rename = false; 54 stalls[tid].iew = false; 55 stalls[tid].commit = false; 56 } 57 58 // @todo: Make into a parameter 59 skidBufferMax = (fetchToDecodeDelay * params->fetchWidth) + decodeWidth; 60} 61 62template <class Impl> 63std::string 64DefaultDecode<Impl>::name() const 65{ 66 return cpu->name() + ".decode"; 67} 68 69template <class Impl> 70void 71DefaultDecode<Impl>::regStats() 72{ 73 decodeIdleCycles 74 .name(name() + ".DECODE:IdleCycles") 75 .desc("Number of cycles decode is idle") 76 .prereq(decodeIdleCycles); 77 decodeBlockedCycles 78 .name(name() + ".DECODE:BlockedCycles") 79 .desc("Number of cycles decode is blocked") 80 .prereq(decodeBlockedCycles); 81 decodeRunCycles 82 .name(name() + ".DECODE:RunCycles") 83 .desc("Number of cycles decode is running") 84 .prereq(decodeRunCycles); 85 decodeUnblockCycles 86 .name(name() + ".DECODE:UnblockCycles") 87 .desc("Number of cycles decode is unblocking") 88 .prereq(decodeUnblockCycles); 89 decodeSquashCycles 90 .name(name() + ".DECODE:SquashCycles") 91 .desc("Number of cycles decode is squashing") 92 .prereq(decodeSquashCycles); 93 decodeBranchResolved 94 .name(name() + ".DECODE:BranchResolved") 95 .desc("Number of times decode resolved a branch") 96 .prereq(decodeBranchResolved); 97 decodeBranchMispred 98 .name(name() + ".DECODE:BranchMispred") 99 .desc("Number of times decode detected a branch misprediction") 100 .prereq(decodeBranchMispred); 101 decodeControlMispred 102 .name(name() + ".DECODE:ControlMispred") 103 .desc("Number of times decode detected an instruction incorrectly" 104 " predicted as a control") 105 .prereq(decodeControlMispred); 106 decodeDecodedInsts 107 .name(name() + ".DECODE:DecodedInsts") 108 .desc("Number of instructions handled by decode") 109 .prereq(decodeDecodedInsts); 110 decodeSquashedInsts 111 .name(name() + ".DECODE:SquashedInsts") 112 .desc("Number of squashed instructions handled by decode") 113 .prereq(decodeSquashedInsts); 114} 115 116template<class Impl> 117void 118DefaultDecode<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr) 119{ 120 timeBuffer = tb_ptr; 121 122 // Setup wire to write information back to fetch. 123 toFetch = timeBuffer->getWire(0); 124 125 // Create wires to get information from proper places in time buffer. 126 fromRename = timeBuffer->getWire(-renameToDecodeDelay); 127 fromIEW = timeBuffer->getWire(-iewToDecodeDelay); 128 fromCommit = timeBuffer->getWire(-commitToDecodeDelay); 129} 130 131template<class Impl> 132void 133DefaultDecode<Impl>::setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr) 134{ 135 decodeQueue = dq_ptr; 136 137 // Setup wire to write information to proper place in decode queue. 138 toRename = decodeQueue->getWire(0); 139} 140 141template<class Impl> 142void 143DefaultDecode<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr) 144{ 145 fetchQueue = fq_ptr; 146 147 // Setup wire to read information from fetch queue. 148 fromFetch = fetchQueue->getWire(-fetchToDecodeDelay); 149} 150 151template<class Impl> 152void 153DefaultDecode<Impl>::setActiveThreads(std::list<ThreadID> *at_ptr) 154{ 155 activeThreads = at_ptr; 156} 157 158template <class Impl> 159bool 160DefaultDecode<Impl>::drain() 161{ 162 // Decode is done draining at any time. 163 cpu->signalDrained(); 164 return true; 165} 166 167template <class Impl> 168void 169DefaultDecode<Impl>::takeOverFrom() 170{ 171 _status = Inactive; 172 173 // Be sure to reset state and clear out any old instructions. 174 for (ThreadID tid = 0; tid < numThreads; ++tid) { 175 decodeStatus[tid] = Idle; 176 177 stalls[tid].rename = false; 178 stalls[tid].iew = false; 179 stalls[tid].commit = false; 180 while (!insts[tid].empty()) 181 insts[tid].pop(); 182 while (!skidBuffer[tid].empty()) 183 skidBuffer[tid].pop(); 184 branchCount[tid] = 0; 185 } 186 wroteToTimeBuffer = false; 187} 188 189template<class Impl> 190bool 191DefaultDecode<Impl>::checkStall(ThreadID tid) const 192{ 193 bool ret_val = false; 194 195 if (stalls[tid].rename) { 196 DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid); 197 ret_val = true; 198 } else if (stalls[tid].iew) { 199 DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid); 200 ret_val = true; 201 } else if (stalls[tid].commit) { 202 DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid); 203 ret_val = true; 204 } 205 206 return ret_val; 207} 208 209template<class Impl> 210inline bool 211DefaultDecode<Impl>::fetchInstsValid() 212{ 213 return fromFetch->size > 0; 214} 215 216template<class Impl> 217bool 218DefaultDecode<Impl>::block(ThreadID tid) 219{ 220 DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid); 221 222 // Add the current inputs to the skid buffer so they can be 223 // reprocessed when this stage unblocks. 224 skidInsert(tid); 225 226 // If the decode status is blocked or unblocking then decode has not yet 227 // signalled fetch to unblock. In that case, there is no need to tell 228 // fetch to block. 229 if (decodeStatus[tid] != Blocked) { 230 // Set the status to Blocked. 231 decodeStatus[tid] = Blocked; 232 233 if (decodeStatus[tid] != Unblocking) { 234 toFetch->decodeBlock[tid] = true; 235 wroteToTimeBuffer = true; 236 } 237 238 return true; 239 } 240 241 return false; 242} 243 244template<class Impl> 245bool 246DefaultDecode<Impl>::unblock(ThreadID tid) 247{ 248 // Decode is done unblocking only if the skid buffer is empty. 249 if (skidBuffer[tid].empty()) { 250 DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid); 251 toFetch->decodeUnblock[tid] = true; 252 wroteToTimeBuffer = true; 253 254 decodeStatus[tid] = Running; 255 return true; 256 } 257 258 DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid); 259 260 return false; 261} 262 263template<class Impl> 264void 265DefaultDecode<Impl>::squash(DynInstPtr &inst, ThreadID tid) 266{ 267 DPRINTF(Decode, "[tid:%i]: [sn:%i] Squashing due to incorrect branch " 268 "prediction detected at decode.\n", tid, inst->seqNum); 269 270 // Send back mispredict information. 271 toFetch->decodeInfo[tid].branchMispredict = true; 272 toFetch->decodeInfo[tid].predIncorrect = true; 273 toFetch->decodeInfo[tid].squash = true; 274 toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum; 275 toFetch->decodeInfo[tid].nextPC = inst->branchTarget(); 276 toFetch->decodeInfo[tid].branchTaken = inst->pcState().branching(); 277 278 InstSeqNum squash_seq_num = inst->seqNum; 279 280 // Might have to tell fetch to unblock. 281 if (decodeStatus[tid] == Blocked || 282 decodeStatus[tid] == Unblocking) { 283 toFetch->decodeUnblock[tid] = 1; 284 } 285 286 // Set status to squashing. 287 decodeStatus[tid] = Squashing; 288 289 for (int i=0; i<fromFetch->size; i++) { 290 if (fromFetch->insts[i]->threadNumber == tid && 291 fromFetch->insts[i]->seqNum > squash_seq_num) { 292 fromFetch->insts[i]->setSquashed(); 293 } 294 } 295 296 // Clear the instruction list and skid buffer in case they have any 297 // insts in them. 298 while (!insts[tid].empty()) { 299 insts[tid].pop(); 300 } 301 302 while (!skidBuffer[tid].empty()) { 303 skidBuffer[tid].pop(); 304 } 305 306 // Squash instructions up until this one 307 cpu->removeInstsUntil(squash_seq_num, tid); 308} 309 310template<class Impl> 311unsigned 312DefaultDecode<Impl>::squash(ThreadID tid) 313{ 314 DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid); 315 316 if (decodeStatus[tid] == Blocked || 317 decodeStatus[tid] == Unblocking) { 318#if !FULL_SYSTEM 319 // In syscall emulation, we can have both a block and a squash due 320 // to a syscall in the same cycle. This would cause both signals to 321 // be high. This shouldn't happen in full system. 322 // @todo: Determine if this still happens. 323 if (toFetch->decodeBlock[tid]) { 324 toFetch->decodeBlock[tid] = 0; 325 } else { 326 toFetch->decodeUnblock[tid] = 1; 327 } 328#else 329 toFetch->decodeUnblock[tid] = 1; 330#endif 331 } 332 333 // Set status to squashing. 334 decodeStatus[tid] = Squashing; 335 336 // Go through incoming instructions from fetch and squash them. 337 unsigned squash_count = 0; 338 339 for (int i=0; i<fromFetch->size; i++) { 340 if (fromFetch->insts[i]->threadNumber == tid) { 341 fromFetch->insts[i]->setSquashed(); 342 squash_count++; 343 } 344 } 345 346 // Clear the instruction list and skid buffer in case they have any 347 // insts in them. 348 while (!insts[tid].empty()) { 349 insts[tid].pop(); 350 } 351 352 while (!skidBuffer[tid].empty()) { 353 skidBuffer[tid].pop(); 354 } 355 356 return squash_count; 357} 358 359template<class Impl> 360void 361DefaultDecode<Impl>::skidInsert(ThreadID tid) 362{ 363 DynInstPtr inst = NULL; 364 365 while (!insts[tid].empty()) { 366 inst = insts[tid].front(); 367 368 insts[tid].pop(); 369 370 assert(tid == inst->threadNumber); 371 372 DPRINTF(Decode,"Inserting [sn:%lli] PC: %s into decode skidBuffer %i\n", 373 inst->seqNum, inst->pcState(), inst->threadNumber); 374 375 skidBuffer[tid].push(inst); 376 } 377 378 // @todo: Eventually need to enforce this by not letting a thread 379 // fetch past its skidbuffer 380 assert(skidBuffer[tid].size() <= skidBufferMax); 381} 382 383template<class Impl> 384bool 385DefaultDecode<Impl>::skidsEmpty() 386{ 387 list<ThreadID>::iterator threads = activeThreads->begin(); 388 list<ThreadID>::iterator end = activeThreads->end(); 389 390 while (threads != end) { 391 ThreadID tid = *threads++; 392 if (!skidBuffer[tid].empty()) 393 return false; 394 } 395 396 return true; 397} 398 399template<class Impl> 400void 401DefaultDecode<Impl>::updateStatus() 402{ 403 bool any_unblocking = false; 404 405 list<ThreadID>::iterator threads = activeThreads->begin(); 406 list<ThreadID>::iterator end = activeThreads->end(); 407 408 while (threads != end) { 409 ThreadID tid = *threads++; 410 411 if (decodeStatus[tid] == Unblocking) { 412 any_unblocking = true; 413 break; 414 } 415 } 416 417 // Decode will have activity if it's unblocking. 418 if (any_unblocking) { 419 if (_status == Inactive) { 420 _status = Active; 421 422 DPRINTF(Activity, "Activating stage.\n"); 423 424 cpu->activateStage(O3CPU::DecodeIdx); 425 } 426 } else { 427 // If it's not unblocking, then decode will not have any internal 428 // activity. Switch it to inactive. 429 if (_status == Active) { 430 _status = Inactive; 431 DPRINTF(Activity, "Deactivating stage.\n"); 432 433 cpu->deactivateStage(O3CPU::DecodeIdx); 434 } 435 } 436} 437 438template <class Impl> 439void 440DefaultDecode<Impl>::sortInsts() 441{ 442 int insts_from_fetch = fromFetch->size; 443#ifdef DEBUG 444 for (ThreadID tid = 0; tid < numThreads; tid++) 445 assert(insts[tid].empty()); 446#endif 447 for (int i = 0; i < insts_from_fetch; ++i) { 448 insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]); 449 } 450} 451 452template<class Impl> 453void 454DefaultDecode<Impl>::readStallSignals(ThreadID tid) 455{ 456 if (fromRename->renameBlock[tid]) { 457 stalls[tid].rename = true; 458 } 459 460 if (fromRename->renameUnblock[tid]) { 461 assert(stalls[tid].rename); 462 stalls[tid].rename = false; 463 } 464 465 if (fromIEW->iewBlock[tid]) { 466 stalls[tid].iew = true; 467 } 468 469 if (fromIEW->iewUnblock[tid]) { 470 assert(stalls[tid].iew); 471 stalls[tid].iew = false; 472 } 473 474 if (fromCommit->commitBlock[tid]) { 475 stalls[tid].commit = true; 476 } 477 478 if (fromCommit->commitUnblock[tid]) { 479 assert(stalls[tid].commit); 480 stalls[tid].commit = false; 481 } 482} 483 484template <class Impl> 485bool 486DefaultDecode<Impl>::checkSignalsAndUpdate(ThreadID tid) 487{ 488 // Check if there's a squash signal, squash if there is. 489 // Check stall signals, block if necessary. 490 // If status was blocked 491 // Check if stall conditions have passed 492 // if so then go to unblocking 493 // If status was Squashing 494 // check if squashing is not high. Switch to running this cycle. 495 496 // Update the per thread stall statuses. 497 readStallSignals(tid); 498 499 // Check squash signals from commit. 500 if (fromCommit->commitInfo[tid].squash) { 501 502 DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash " 503 "from commit.\n", tid); 504 505 squash(tid); 506 507 return true; 508 } 509 510 // Check ROB squash signals from commit. 511 if (fromCommit->commitInfo[tid].robSquashing) { 512 DPRINTF(Decode, "[tid:%u]: ROB is still squashing.\n", tid); 513 514 // Continue to squash. 515 decodeStatus[tid] = Squashing; 516 517 return true; 518 } 519 520 if (checkStall(tid)) { 521 return block(tid); 522 } 523 524 if (decodeStatus[tid] == Blocked) { 525 DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n", 526 tid); 527 528 decodeStatus[tid] = Unblocking; 529 530 unblock(tid); 531 532 return true; 533 } 534 535 if (decodeStatus[tid] == Squashing) { 536 // Switch status to running if decode isn't being told to block or 537 // squash this cycle. 538 DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n", 539 tid); 540 541 decodeStatus[tid] = Running; 542 543 return false; 544 } 545 546 // If we've reached this point, we have not gotten any signals that 547 // cause decode to change its status. Decode remains the same as before. 548 return false; 549} 550 551template<class Impl> 552void 553DefaultDecode<Impl>::tick() 554{ 555 wroteToTimeBuffer = false; 556 557 bool status_change = false; 558 559 toRenameIndex = 0; 560 561 list<ThreadID>::iterator threads = activeThreads->begin(); 562 list<ThreadID>::iterator end = activeThreads->end(); 563 564 sortInsts(); 565 566 //Check stall and squash signals. 567 while (threads != end) { 568 ThreadID tid = *threads++; 569 570 DPRINTF(Decode,"Processing [tid:%i]\n",tid); 571 status_change = checkSignalsAndUpdate(tid) || status_change; 572 573 decode(status_change, tid); 574 } 575 576 if (status_change) { 577 updateStatus(); 578 } 579 580 if (wroteToTimeBuffer) { 581 DPRINTF(Activity, "Activity this cycle.\n"); 582 583 cpu->activityThisCycle(); 584 } 585} 586 587template<class Impl> 588void 589DefaultDecode<Impl>::decode(bool &status_change, ThreadID tid) 590{ 591 // If status is Running or idle, 592 // call decodeInsts() 593 // If status is Unblocking, 594 // buffer any instructions coming from fetch 595 // continue trying to empty skid buffer 596 // check if stall conditions have passed 597 598 if (decodeStatus[tid] == Blocked) { 599 ++decodeBlockedCycles; 600 } else if (decodeStatus[tid] == Squashing) { 601 ++decodeSquashCycles; 602 } 603 604 // Decode should try to decode as many instructions as its bandwidth 605 // will allow, as long as it is not currently blocked. 606 if (decodeStatus[tid] == Running || 607 decodeStatus[tid] == Idle) { 608 DPRINTF(Decode, "[tid:%u]: Not blocked, so attempting to run " 609 "stage.\n",tid); 610 611 decodeInsts(tid); 612 } else if (decodeStatus[tid] == Unblocking) { 613 // Make sure that the skid buffer has something in it if the 614 // status is unblocking. 615 assert(!skidsEmpty()); 616 617 // If the status was unblocking, then instructions from the skid 618 // buffer were used. Remove those instructions and handle 619 // the rest of unblocking. 620 decodeInsts(tid); 621 622 if (fetchInstsValid()) { 623 // Add the current inputs to the skid buffer so they can be 624 // reprocessed when this stage unblocks. 625 skidInsert(tid); 626 } 627 628 status_change = unblock(tid) || status_change; 629 } 630} 631 632template <class Impl> 633void 634DefaultDecode<Impl>::decodeInsts(ThreadID tid) 635{ 636 // Instructions can come either from the skid buffer or the list of 637 // instructions coming from fetch, depending on decode's status. 638 int insts_available = decodeStatus[tid] == Unblocking ? 639 skidBuffer[tid].size() : insts[tid].size(); 640 641 if (insts_available == 0) { 642 DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out" 643 " early.\n",tid); 644 // Should I change the status to idle? 645 ++decodeIdleCycles; 646 return; 647 } else if (decodeStatus[tid] == Unblocking) { 648 DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid " 649 "buffer.\n",tid); 650 ++decodeUnblockCycles; 651 } else if (decodeStatus[tid] == Running) { 652 ++decodeRunCycles; 653 } 654 655 DynInstPtr inst; 656 657 std::queue<DynInstPtr> 658 &insts_to_decode = decodeStatus[tid] == Unblocking ? 659 skidBuffer[tid] : insts[tid]; 660 661 DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid); 662 663 while (insts_available > 0 && toRenameIndex < decodeWidth) { 664 assert(!insts_to_decode.empty()); 665 666 inst = insts_to_decode.front(); 667 668 insts_to_decode.pop(); 669 670 DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with " 671 "PC %s\n", tid, inst->seqNum, inst->pcState()); 672 673 if (inst->isSquashed()) { 674 DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %s is " 675 "squashed, skipping.\n", 676 tid, inst->seqNum, inst->pcState()); 677 678 ++decodeSquashedInsts; 679 680 --insts_available; 681 682 continue; 683 } 684 685 // Also check if instructions have no source registers. Mark 686 // them as ready to issue at any time. Not sure if this check 687 // should exist here or at a later stage; however it doesn't matter 688 // too much for function correctness. 689 if (inst->numSrcRegs() == 0) { 690 inst->setCanIssue(); 691 } 692 693 // This current instruction is valid, so add it into the decode 694 // queue. The next instruction may not be valid, so check to 695 // see if branches were predicted correctly. 696 toRename->insts[toRenameIndex] = inst; 697 698 ++(toRename->size); 699 ++toRenameIndex; 700 ++decodeDecodedInsts; 701 --insts_available; 702 703 // Ensure that if it was predicted as a branch, it really is a 704 // branch. 705 if (inst->readPredTaken() && !inst->isControl()) { 706 panic("Instruction predicted as a branch!"); 707 708 ++decodeControlMispred; 709 710 // Might want to set some sort of boolean and just do 711 // a check at the end 712 squash(inst, inst->threadNumber); 713 714 break; 715 } 716 717 // Go ahead and compute any PC-relative branches. 718 if (inst->isDirectCtrl() && inst->isUncondCtrl()) { 719 ++decodeBranchResolved; 720 721 if (!(inst->branchTarget() == inst->readPredTarg())) { 722 ++decodeBranchMispred; 723 724 // Might want to set some sort of boolean and just do 725 // a check at the end 726 squash(inst, inst->threadNumber); 727 TheISA::PCState target = inst->branchTarget(); 728 729 DPRINTF(Decode, "[sn:%i]: Updating predictions: PredPC: %s\n", 730 inst->seqNum, target); 731 //The micro pc after an instruction level branch should be 0 732 inst->setPredTarg(target); 733 break; 734 } 735 } 736 } 737 738 // If we didn't process all instructions, then we will need to block 739 // and put all those instructions into the skid buffer. 740 if (!insts_to_decode.empty()) { 741 block(tid); 742 } 743 744 // Record that decode has written to the time buffer for activity 745 // tracking. 746 if (toRenameIndex) { 747 wroteToTimeBuffer = true; 748 } 749}
| 37#include "params/DerivO3CPU.hh" 38 39using namespace std; 40 41template<class Impl> 42DefaultDecode<Impl>::DefaultDecode(O3CPU *_cpu, DerivO3CPUParams *params) 43 : cpu(_cpu), 44 renameToDecodeDelay(params->renameToDecodeDelay), 45 iewToDecodeDelay(params->iewToDecodeDelay), 46 commitToDecodeDelay(params->commitToDecodeDelay), 47 fetchToDecodeDelay(params->fetchToDecodeDelay), 48 decodeWidth(params->decodeWidth), 49 numThreads(params->numThreads) 50{ 51 _status = Inactive; 52 53 // Setup status, make sure stall signals are clear. 54 for (ThreadID tid = 0; tid < numThreads; ++tid) { 55 decodeStatus[tid] = Idle; 56 57 stalls[tid].rename = false; 58 stalls[tid].iew = false; 59 stalls[tid].commit = false; 60 } 61 62 // @todo: Make into a parameter 63 skidBufferMax = (fetchToDecodeDelay * params->fetchWidth) + decodeWidth; 64} 65 66template <class Impl> 67std::string 68DefaultDecode<Impl>::name() const 69{ 70 return cpu->name() + ".decode"; 71} 72 73template <class Impl> 74void 75DefaultDecode<Impl>::regStats() 76{ 77 decodeIdleCycles 78 .name(name() + ".DECODE:IdleCycles") 79 .desc("Number of cycles decode is idle") 80 .prereq(decodeIdleCycles); 81 decodeBlockedCycles 82 .name(name() + ".DECODE:BlockedCycles") 83 .desc("Number of cycles decode is blocked") 84 .prereq(decodeBlockedCycles); 85 decodeRunCycles 86 .name(name() + ".DECODE:RunCycles") 87 .desc("Number of cycles decode is running") 88 .prereq(decodeRunCycles); 89 decodeUnblockCycles 90 .name(name() + ".DECODE:UnblockCycles") 91 .desc("Number of cycles decode is unblocking") 92 .prereq(decodeUnblockCycles); 93 decodeSquashCycles 94 .name(name() + ".DECODE:SquashCycles") 95 .desc("Number of cycles decode is squashing") 96 .prereq(decodeSquashCycles); 97 decodeBranchResolved 98 .name(name() + ".DECODE:BranchResolved") 99 .desc("Number of times decode resolved a branch") 100 .prereq(decodeBranchResolved); 101 decodeBranchMispred 102 .name(name() + ".DECODE:BranchMispred") 103 .desc("Number of times decode detected a branch misprediction") 104 .prereq(decodeBranchMispred); 105 decodeControlMispred 106 .name(name() + ".DECODE:ControlMispred") 107 .desc("Number of times decode detected an instruction incorrectly" 108 " predicted as a control") 109 .prereq(decodeControlMispred); 110 decodeDecodedInsts 111 .name(name() + ".DECODE:DecodedInsts") 112 .desc("Number of instructions handled by decode") 113 .prereq(decodeDecodedInsts); 114 decodeSquashedInsts 115 .name(name() + ".DECODE:SquashedInsts") 116 .desc("Number of squashed instructions handled by decode") 117 .prereq(decodeSquashedInsts); 118} 119 120template<class Impl> 121void 122DefaultDecode<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr) 123{ 124 timeBuffer = tb_ptr; 125 126 // Setup wire to write information back to fetch. 127 toFetch = timeBuffer->getWire(0); 128 129 // Create wires to get information from proper places in time buffer. 130 fromRename = timeBuffer->getWire(-renameToDecodeDelay); 131 fromIEW = timeBuffer->getWire(-iewToDecodeDelay); 132 fromCommit = timeBuffer->getWire(-commitToDecodeDelay); 133} 134 135template<class Impl> 136void 137DefaultDecode<Impl>::setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr) 138{ 139 decodeQueue = dq_ptr; 140 141 // Setup wire to write information to proper place in decode queue. 142 toRename = decodeQueue->getWire(0); 143} 144 145template<class Impl> 146void 147DefaultDecode<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr) 148{ 149 fetchQueue = fq_ptr; 150 151 // Setup wire to read information from fetch queue. 152 fromFetch = fetchQueue->getWire(-fetchToDecodeDelay); 153} 154 155template<class Impl> 156void 157DefaultDecode<Impl>::setActiveThreads(std::list<ThreadID> *at_ptr) 158{ 159 activeThreads = at_ptr; 160} 161 162template <class Impl> 163bool 164DefaultDecode<Impl>::drain() 165{ 166 // Decode is done draining at any time. 167 cpu->signalDrained(); 168 return true; 169} 170 171template <class Impl> 172void 173DefaultDecode<Impl>::takeOverFrom() 174{ 175 _status = Inactive; 176 177 // Be sure to reset state and clear out any old instructions. 178 for (ThreadID tid = 0; tid < numThreads; ++tid) { 179 decodeStatus[tid] = Idle; 180 181 stalls[tid].rename = false; 182 stalls[tid].iew = false; 183 stalls[tid].commit = false; 184 while (!insts[tid].empty()) 185 insts[tid].pop(); 186 while (!skidBuffer[tid].empty()) 187 skidBuffer[tid].pop(); 188 branchCount[tid] = 0; 189 } 190 wroteToTimeBuffer = false; 191} 192 193template<class Impl> 194bool 195DefaultDecode<Impl>::checkStall(ThreadID tid) const 196{ 197 bool ret_val = false; 198 199 if (stalls[tid].rename) { 200 DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid); 201 ret_val = true; 202 } else if (stalls[tid].iew) { 203 DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid); 204 ret_val = true; 205 } else if (stalls[tid].commit) { 206 DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid); 207 ret_val = true; 208 } 209 210 return ret_val; 211} 212 213template<class Impl> 214inline bool 215DefaultDecode<Impl>::fetchInstsValid() 216{ 217 return fromFetch->size > 0; 218} 219 220template<class Impl> 221bool 222DefaultDecode<Impl>::block(ThreadID tid) 223{ 224 DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid); 225 226 // Add the current inputs to the skid buffer so they can be 227 // reprocessed when this stage unblocks. 228 skidInsert(tid); 229 230 // If the decode status is blocked or unblocking then decode has not yet 231 // signalled fetch to unblock. In that case, there is no need to tell 232 // fetch to block. 233 if (decodeStatus[tid] != Blocked) { 234 // Set the status to Blocked. 235 decodeStatus[tid] = Blocked; 236 237 if (decodeStatus[tid] != Unblocking) { 238 toFetch->decodeBlock[tid] = true; 239 wroteToTimeBuffer = true; 240 } 241 242 return true; 243 } 244 245 return false; 246} 247 248template<class Impl> 249bool 250DefaultDecode<Impl>::unblock(ThreadID tid) 251{ 252 // Decode is done unblocking only if the skid buffer is empty. 253 if (skidBuffer[tid].empty()) { 254 DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid); 255 toFetch->decodeUnblock[tid] = true; 256 wroteToTimeBuffer = true; 257 258 decodeStatus[tid] = Running; 259 return true; 260 } 261 262 DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid); 263 264 return false; 265} 266 267template<class Impl> 268void 269DefaultDecode<Impl>::squash(DynInstPtr &inst, ThreadID tid) 270{ 271 DPRINTF(Decode, "[tid:%i]: [sn:%i] Squashing due to incorrect branch " 272 "prediction detected at decode.\n", tid, inst->seqNum); 273 274 // Send back mispredict information. 275 toFetch->decodeInfo[tid].branchMispredict = true; 276 toFetch->decodeInfo[tid].predIncorrect = true; 277 toFetch->decodeInfo[tid].squash = true; 278 toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum; 279 toFetch->decodeInfo[tid].nextPC = inst->branchTarget(); 280 toFetch->decodeInfo[tid].branchTaken = inst->pcState().branching(); 281 282 InstSeqNum squash_seq_num = inst->seqNum; 283 284 // Might have to tell fetch to unblock. 285 if (decodeStatus[tid] == Blocked || 286 decodeStatus[tid] == Unblocking) { 287 toFetch->decodeUnblock[tid] = 1; 288 } 289 290 // Set status to squashing. 291 decodeStatus[tid] = Squashing; 292 293 for (int i=0; i<fromFetch->size; i++) { 294 if (fromFetch->insts[i]->threadNumber == tid && 295 fromFetch->insts[i]->seqNum > squash_seq_num) { 296 fromFetch->insts[i]->setSquashed(); 297 } 298 } 299 300 // Clear the instruction list and skid buffer in case they have any 301 // insts in them. 302 while (!insts[tid].empty()) { 303 insts[tid].pop(); 304 } 305 306 while (!skidBuffer[tid].empty()) { 307 skidBuffer[tid].pop(); 308 } 309 310 // Squash instructions up until this one 311 cpu->removeInstsUntil(squash_seq_num, tid); 312} 313 314template<class Impl> 315unsigned 316DefaultDecode<Impl>::squash(ThreadID tid) 317{ 318 DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid); 319 320 if (decodeStatus[tid] == Blocked || 321 decodeStatus[tid] == Unblocking) { 322#if !FULL_SYSTEM 323 // In syscall emulation, we can have both a block and a squash due 324 // to a syscall in the same cycle. This would cause both signals to 325 // be high. This shouldn't happen in full system. 326 // @todo: Determine if this still happens. 327 if (toFetch->decodeBlock[tid]) { 328 toFetch->decodeBlock[tid] = 0; 329 } else { 330 toFetch->decodeUnblock[tid] = 1; 331 } 332#else 333 toFetch->decodeUnblock[tid] = 1; 334#endif 335 } 336 337 // Set status to squashing. 338 decodeStatus[tid] = Squashing; 339 340 // Go through incoming instructions from fetch and squash them. 341 unsigned squash_count = 0; 342 343 for (int i=0; i<fromFetch->size; i++) { 344 if (fromFetch->insts[i]->threadNumber == tid) { 345 fromFetch->insts[i]->setSquashed(); 346 squash_count++; 347 } 348 } 349 350 // Clear the instruction list and skid buffer in case they have any 351 // insts in them. 352 while (!insts[tid].empty()) { 353 insts[tid].pop(); 354 } 355 356 while (!skidBuffer[tid].empty()) { 357 skidBuffer[tid].pop(); 358 } 359 360 return squash_count; 361} 362 363template<class Impl> 364void 365DefaultDecode<Impl>::skidInsert(ThreadID tid) 366{ 367 DynInstPtr inst = NULL; 368 369 while (!insts[tid].empty()) { 370 inst = insts[tid].front(); 371 372 insts[tid].pop(); 373 374 assert(tid == inst->threadNumber); 375 376 DPRINTF(Decode,"Inserting [sn:%lli] PC: %s into decode skidBuffer %i\n", 377 inst->seqNum, inst->pcState(), inst->threadNumber); 378 379 skidBuffer[tid].push(inst); 380 } 381 382 // @todo: Eventually need to enforce this by not letting a thread 383 // fetch past its skidbuffer 384 assert(skidBuffer[tid].size() <= skidBufferMax); 385} 386 387template<class Impl> 388bool 389DefaultDecode<Impl>::skidsEmpty() 390{ 391 list<ThreadID>::iterator threads = activeThreads->begin(); 392 list<ThreadID>::iterator end = activeThreads->end(); 393 394 while (threads != end) { 395 ThreadID tid = *threads++; 396 if (!skidBuffer[tid].empty()) 397 return false; 398 } 399 400 return true; 401} 402 403template<class Impl> 404void 405DefaultDecode<Impl>::updateStatus() 406{ 407 bool any_unblocking = false; 408 409 list<ThreadID>::iterator threads = activeThreads->begin(); 410 list<ThreadID>::iterator end = activeThreads->end(); 411 412 while (threads != end) { 413 ThreadID tid = *threads++; 414 415 if (decodeStatus[tid] == Unblocking) { 416 any_unblocking = true; 417 break; 418 } 419 } 420 421 // Decode will have activity if it's unblocking. 422 if (any_unblocking) { 423 if (_status == Inactive) { 424 _status = Active; 425 426 DPRINTF(Activity, "Activating stage.\n"); 427 428 cpu->activateStage(O3CPU::DecodeIdx); 429 } 430 } else { 431 // If it's not unblocking, then decode will not have any internal 432 // activity. Switch it to inactive. 433 if (_status == Active) { 434 _status = Inactive; 435 DPRINTF(Activity, "Deactivating stage.\n"); 436 437 cpu->deactivateStage(O3CPU::DecodeIdx); 438 } 439 } 440} 441 442template <class Impl> 443void 444DefaultDecode<Impl>::sortInsts() 445{ 446 int insts_from_fetch = fromFetch->size; 447#ifdef DEBUG 448 for (ThreadID tid = 0; tid < numThreads; tid++) 449 assert(insts[tid].empty()); 450#endif 451 for (int i = 0; i < insts_from_fetch; ++i) { 452 insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]); 453 } 454} 455 456template<class Impl> 457void 458DefaultDecode<Impl>::readStallSignals(ThreadID tid) 459{ 460 if (fromRename->renameBlock[tid]) { 461 stalls[tid].rename = true; 462 } 463 464 if (fromRename->renameUnblock[tid]) { 465 assert(stalls[tid].rename); 466 stalls[tid].rename = false; 467 } 468 469 if (fromIEW->iewBlock[tid]) { 470 stalls[tid].iew = true; 471 } 472 473 if (fromIEW->iewUnblock[tid]) { 474 assert(stalls[tid].iew); 475 stalls[tid].iew = false; 476 } 477 478 if (fromCommit->commitBlock[tid]) { 479 stalls[tid].commit = true; 480 } 481 482 if (fromCommit->commitUnblock[tid]) { 483 assert(stalls[tid].commit); 484 stalls[tid].commit = false; 485 } 486} 487 488template <class Impl> 489bool 490DefaultDecode<Impl>::checkSignalsAndUpdate(ThreadID tid) 491{ 492 // Check if there's a squash signal, squash if there is. 493 // Check stall signals, block if necessary. 494 // If status was blocked 495 // Check if stall conditions have passed 496 // if so then go to unblocking 497 // If status was Squashing 498 // check if squashing is not high. Switch to running this cycle. 499 500 // Update the per thread stall statuses. 501 readStallSignals(tid); 502 503 // Check squash signals from commit. 504 if (fromCommit->commitInfo[tid].squash) { 505 506 DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash " 507 "from commit.\n", tid); 508 509 squash(tid); 510 511 return true; 512 } 513 514 // Check ROB squash signals from commit. 515 if (fromCommit->commitInfo[tid].robSquashing) { 516 DPRINTF(Decode, "[tid:%u]: ROB is still squashing.\n", tid); 517 518 // Continue to squash. 519 decodeStatus[tid] = Squashing; 520 521 return true; 522 } 523 524 if (checkStall(tid)) { 525 return block(tid); 526 } 527 528 if (decodeStatus[tid] == Blocked) { 529 DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n", 530 tid); 531 532 decodeStatus[tid] = Unblocking; 533 534 unblock(tid); 535 536 return true; 537 } 538 539 if (decodeStatus[tid] == Squashing) { 540 // Switch status to running if decode isn't being told to block or 541 // squash this cycle. 542 DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n", 543 tid); 544 545 decodeStatus[tid] = Running; 546 547 return false; 548 } 549 550 // If we've reached this point, we have not gotten any signals that 551 // cause decode to change its status. Decode remains the same as before. 552 return false; 553} 554 555template<class Impl> 556void 557DefaultDecode<Impl>::tick() 558{ 559 wroteToTimeBuffer = false; 560 561 bool status_change = false; 562 563 toRenameIndex = 0; 564 565 list<ThreadID>::iterator threads = activeThreads->begin(); 566 list<ThreadID>::iterator end = activeThreads->end(); 567 568 sortInsts(); 569 570 //Check stall and squash signals. 571 while (threads != end) { 572 ThreadID tid = *threads++; 573 574 DPRINTF(Decode,"Processing [tid:%i]\n",tid); 575 status_change = checkSignalsAndUpdate(tid) || status_change; 576 577 decode(status_change, tid); 578 } 579 580 if (status_change) { 581 updateStatus(); 582 } 583 584 if (wroteToTimeBuffer) { 585 DPRINTF(Activity, "Activity this cycle.\n"); 586 587 cpu->activityThisCycle(); 588 } 589} 590 591template<class Impl> 592void 593DefaultDecode<Impl>::decode(bool &status_change, ThreadID tid) 594{ 595 // If status is Running or idle, 596 // call decodeInsts() 597 // If status is Unblocking, 598 // buffer any instructions coming from fetch 599 // continue trying to empty skid buffer 600 // check if stall conditions have passed 601 602 if (decodeStatus[tid] == Blocked) { 603 ++decodeBlockedCycles; 604 } else if (decodeStatus[tid] == Squashing) { 605 ++decodeSquashCycles; 606 } 607 608 // Decode should try to decode as many instructions as its bandwidth 609 // will allow, as long as it is not currently blocked. 610 if (decodeStatus[tid] == Running || 611 decodeStatus[tid] == Idle) { 612 DPRINTF(Decode, "[tid:%u]: Not blocked, so attempting to run " 613 "stage.\n",tid); 614 615 decodeInsts(tid); 616 } else if (decodeStatus[tid] == Unblocking) { 617 // Make sure that the skid buffer has something in it if the 618 // status is unblocking. 619 assert(!skidsEmpty()); 620 621 // If the status was unblocking, then instructions from the skid 622 // buffer were used. Remove those instructions and handle 623 // the rest of unblocking. 624 decodeInsts(tid); 625 626 if (fetchInstsValid()) { 627 // Add the current inputs to the skid buffer so they can be 628 // reprocessed when this stage unblocks. 629 skidInsert(tid); 630 } 631 632 status_change = unblock(tid) || status_change; 633 } 634} 635 636template <class Impl> 637void 638DefaultDecode<Impl>::decodeInsts(ThreadID tid) 639{ 640 // Instructions can come either from the skid buffer or the list of 641 // instructions coming from fetch, depending on decode's status. 642 int insts_available = decodeStatus[tid] == Unblocking ? 643 skidBuffer[tid].size() : insts[tid].size(); 644 645 if (insts_available == 0) { 646 DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out" 647 " early.\n",tid); 648 // Should I change the status to idle? 649 ++decodeIdleCycles; 650 return; 651 } else if (decodeStatus[tid] == Unblocking) { 652 DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid " 653 "buffer.\n",tid); 654 ++decodeUnblockCycles; 655 } else if (decodeStatus[tid] == Running) { 656 ++decodeRunCycles; 657 } 658 659 DynInstPtr inst; 660 661 std::queue<DynInstPtr> 662 &insts_to_decode = decodeStatus[tid] == Unblocking ? 663 skidBuffer[tid] : insts[tid]; 664 665 DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid); 666 667 while (insts_available > 0 && toRenameIndex < decodeWidth) { 668 assert(!insts_to_decode.empty()); 669 670 inst = insts_to_decode.front(); 671 672 insts_to_decode.pop(); 673 674 DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with " 675 "PC %s\n", tid, inst->seqNum, inst->pcState()); 676 677 if (inst->isSquashed()) { 678 DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %s is " 679 "squashed, skipping.\n", 680 tid, inst->seqNum, inst->pcState()); 681 682 ++decodeSquashedInsts; 683 684 --insts_available; 685 686 continue; 687 } 688 689 // Also check if instructions have no source registers. Mark 690 // them as ready to issue at any time. Not sure if this check 691 // should exist here or at a later stage; however it doesn't matter 692 // too much for function correctness. 693 if (inst->numSrcRegs() == 0) { 694 inst->setCanIssue(); 695 } 696 697 // This current instruction is valid, so add it into the decode 698 // queue. The next instruction may not be valid, so check to 699 // see if branches were predicted correctly. 700 toRename->insts[toRenameIndex] = inst; 701 702 ++(toRename->size); 703 ++toRenameIndex; 704 ++decodeDecodedInsts; 705 --insts_available; 706 707 // Ensure that if it was predicted as a branch, it really is a 708 // branch. 709 if (inst->readPredTaken() && !inst->isControl()) { 710 panic("Instruction predicted as a branch!"); 711 712 ++decodeControlMispred; 713 714 // Might want to set some sort of boolean and just do 715 // a check at the end 716 squash(inst, inst->threadNumber); 717 718 break; 719 } 720 721 // Go ahead and compute any PC-relative branches. 722 if (inst->isDirectCtrl() && inst->isUncondCtrl()) { 723 ++decodeBranchResolved; 724 725 if (!(inst->branchTarget() == inst->readPredTarg())) { 726 ++decodeBranchMispred; 727 728 // Might want to set some sort of boolean and just do 729 // a check at the end 730 squash(inst, inst->threadNumber); 731 TheISA::PCState target = inst->branchTarget(); 732 733 DPRINTF(Decode, "[sn:%i]: Updating predictions: PredPC: %s\n", 734 inst->seqNum, target); 735 //The micro pc after an instruction level branch should be 0 736 inst->setPredTarg(target); 737 break; 738 } 739 } 740 } 741 742 // If we didn't process all instructions, then we will need to block 743 // and put all those instructions into the skid buffer. 744 if (!insts_to_decode.empty()) { 745 block(tid); 746 } 747 748 // Record that decode has written to the time buffer for activity 749 // tracking. 750 if (toRenameIndex) { 751 wroteToTimeBuffer = true; 752 } 753}
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