fetch_impl.hh revision 3961:42374ae36922 
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 *          Korey Sewell
30 */
31
32#include "config/use_checker.hh"
33
34#include "arch/isa_traits.hh"
35#include "arch/utility.hh"
36#include "cpu/checker/cpu.hh"
37#include "cpu/exetrace.hh"
38#include "cpu/o3/fetch.hh"
39#include "mem/packet.hh"
40#include "mem/request.hh"
41#include "sim/byteswap.hh"
42#include "sim/host.hh"
43#include "sim/root.hh"
44
45#if FULL_SYSTEM
46#include "arch/tlb.hh"
47#include "arch/vtophys.hh"
48#include "sim/system.hh"
49#endif // FULL_SYSTEM
50
51#include <algorithm>
52
53template<class Impl>
54Tick
55DefaultFetch<Impl>::IcachePort::recvAtomic(PacketPtr pkt)
56{
57    panic("DefaultFetch doesn't expect recvAtomic callback!");
58    return curTick;
59}
60
61template<class Impl>
62void
63DefaultFetch<Impl>::IcachePort::recvFunctional(PacketPtr pkt)
64{
65    DPRINTF(Fetch, "DefaultFetch doesn't update its state from a "
66            "functional call.");
67}
68
69template<class Impl>
70void
71DefaultFetch<Impl>::IcachePort::recvStatusChange(Status status)
72{
73    if (status == RangeChange) {
74        if (!snoopRangeSent) {
75            snoopRangeSent = true;
76            sendStatusChange(Port::RangeChange);
77        }
78        return;
79    }
80
81    panic("DefaultFetch doesn't expect recvStatusChange callback!");
82}
83
84template<class Impl>
85bool
86DefaultFetch<Impl>::IcachePort::recvTiming(PacketPtr pkt)
87{
88    DPRINTF(Fetch, "Received timing\n");
89    if (pkt->isResponse()) {
90        fetch->processCacheCompletion(pkt);
91    }
92    //else Snooped a coherence request, just return
93    return true;
94}
95
96template<class Impl>
97void
98DefaultFetch<Impl>::IcachePort::recvRetry()
99{
100    fetch->recvRetry();
101}
102
103template<class Impl>
104DefaultFetch<Impl>::DefaultFetch(Params *params)
105    : branchPred(params),
106      decodeToFetchDelay(params->decodeToFetchDelay),
107      renameToFetchDelay(params->renameToFetchDelay),
108      iewToFetchDelay(params->iewToFetchDelay),
109      commitToFetchDelay(params->commitToFetchDelay),
110      fetchWidth(params->fetchWidth),
111      cacheBlocked(false),
112      retryPkt(NULL),
113      retryTid(-1),
114      numThreads(params->numberOfThreads),
115      numFetchingThreads(params->smtNumFetchingThreads),
116      interruptPending(false),
117      drainPending(false),
118      switchedOut(false)
119{
120    if (numThreads > Impl::MaxThreads)
121        fatal("numThreads is not a valid value\n");
122
123    // Set fetch stage's status to inactive.
124    _status = Inactive;
125
126    std::string policy = params->smtFetchPolicy;
127
128    // Convert string to lowercase
129    std::transform(policy.begin(), policy.end(), policy.begin(),
130                   (int(*)(int)) tolower);
131
132    // Figure out fetch policy
133    if (policy == "singlethread") {
134        fetchPolicy = SingleThread;
135        if (numThreads > 1)
136            panic("Invalid Fetch Policy for a SMT workload.");
137    } else if (policy == "roundrobin") {
138        fetchPolicy = RoundRobin;
139        DPRINTF(Fetch, "Fetch policy set to Round Robin\n");
140    } else if (policy == "branch") {
141        fetchPolicy = Branch;
142        DPRINTF(Fetch, "Fetch policy set to Branch Count\n");
143    } else if (policy == "iqcount") {
144        fetchPolicy = IQ;
145        DPRINTF(Fetch, "Fetch policy set to IQ count\n");
146    } else if (policy == "lsqcount") {
147        fetchPolicy = LSQ;
148        DPRINTF(Fetch, "Fetch policy set to LSQ count\n");
149    } else {
150        fatal("Invalid Fetch Policy. Options Are: {SingleThread,"
151              " RoundRobin,LSQcount,IQcount}\n");
152    }
153
154    // Get the size of an instruction.
155    instSize = sizeof(TheISA::MachInst);
156}
157
158template <class Impl>
159std::string
160DefaultFetch<Impl>::name() const
161{
162    return cpu->name() + ".fetch";
163}
164
165template <class Impl>
166void
167DefaultFetch<Impl>::regStats()
168{
169    icacheStallCycles
170        .name(name() + ".icacheStallCycles")
171        .desc("Number of cycles fetch is stalled on an Icache miss")
172        .prereq(icacheStallCycles);
173
174    fetchedInsts
175        .name(name() + ".Insts")
176        .desc("Number of instructions fetch has processed")
177        .prereq(fetchedInsts);
178
179    fetchedBranches
180        .name(name() + ".Branches")
181        .desc("Number of branches that fetch encountered")
182        .prereq(fetchedBranches);
183
184    predictedBranches
185        .name(name() + ".predictedBranches")
186        .desc("Number of branches that fetch has predicted taken")
187        .prereq(predictedBranches);
188
189    fetchCycles
190        .name(name() + ".Cycles")
191        .desc("Number of cycles fetch has run and was not squashing or"
192              " blocked")
193        .prereq(fetchCycles);
194
195    fetchSquashCycles
196        .name(name() + ".SquashCycles")
197        .desc("Number of cycles fetch has spent squashing")
198        .prereq(fetchSquashCycles);
199
200    fetchIdleCycles
201        .name(name() + ".IdleCycles")
202        .desc("Number of cycles fetch was idle")
203        .prereq(fetchIdleCycles);
204
205    fetchBlockedCycles
206        .name(name() + ".BlockedCycles")
207        .desc("Number of cycles fetch has spent blocked")
208        .prereq(fetchBlockedCycles);
209
210    fetchedCacheLines
211        .name(name() + ".CacheLines")
212        .desc("Number of cache lines fetched")
213        .prereq(fetchedCacheLines);
214
215    fetchMiscStallCycles
216        .name(name() + ".MiscStallCycles")
217        .desc("Number of cycles fetch has spent waiting on interrupts, or "
218              "bad addresses, or out of MSHRs")
219        .prereq(fetchMiscStallCycles);
220
221    fetchIcacheSquashes
222        .name(name() + ".IcacheSquashes")
223        .desc("Number of outstanding Icache misses that were squashed")
224        .prereq(fetchIcacheSquashes);
225
226    fetchNisnDist
227        .init(/* base value */ 0,
228              /* last value */ fetchWidth,
229              /* bucket size */ 1)
230        .name(name() + ".rateDist")
231        .desc("Number of instructions fetched each cycle (Total)")
232        .flags(Stats::pdf);
233
234    idleRate
235        .name(name() + ".idleRate")
236        .desc("Percent of cycles fetch was idle")
237        .prereq(idleRate);
238    idleRate = fetchIdleCycles * 100 / cpu->numCycles;
239
240    branchRate
241        .name(name() + ".branchRate")
242        .desc("Number of branch fetches per cycle")
243        .flags(Stats::total);
244    branchRate = fetchedBranches / cpu->numCycles;
245
246    fetchRate
247        .name(name() + ".rate")
248        .desc("Number of inst fetches per cycle")
249        .flags(Stats::total);
250    fetchRate = fetchedInsts / cpu->numCycles;
251
252    branchPred.regStats();
253}
254
255template<class Impl>
256void
257DefaultFetch<Impl>::setCPU(O3CPU *cpu_ptr)
258{
259    DPRINTF(Fetch, "Setting the CPU pointer.\n");
260    cpu = cpu_ptr;
261
262    // Name is finally available, so create the port.
263    icachePort = new IcachePort(this);
264
265    icachePort->snoopRangeSent = false;
266
267#if USE_CHECKER
268    if (cpu->checker) {
269        cpu->checker->setIcachePort(icachePort);
270    }
271#endif
272
273    // Schedule fetch to get the correct PC from the CPU
274    // scheduleFetchStartupEvent(1);
275
276    // Fetch needs to start fetching instructions at the very beginning,
277    // so it must start up in active state.
278    switchToActive();
279}
280
281template<class Impl>
282void
283DefaultFetch<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer)
284{
285    DPRINTF(Fetch, "Setting the time buffer pointer.\n");
286    timeBuffer = time_buffer;
287
288    // Create wires to get information from proper places in time buffer.
289    fromDecode = timeBuffer->getWire(-decodeToFetchDelay);
290    fromRename = timeBuffer->getWire(-renameToFetchDelay);
291    fromIEW = timeBuffer->getWire(-iewToFetchDelay);
292    fromCommit = timeBuffer->getWire(-commitToFetchDelay);
293}
294
295template<class Impl>
296void
297DefaultFetch<Impl>::setActiveThreads(std::list<unsigned> *at_ptr)
298{
299    DPRINTF(Fetch, "Setting active threads list pointer.\n");
300    activeThreads = at_ptr;
301}
302
303template<class Impl>
304void
305DefaultFetch<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr)
306{
307    DPRINTF(Fetch, "Setting the fetch queue pointer.\n");
308    fetchQueue = fq_ptr;
309
310    // Create wire to write information to proper place in fetch queue.
311    toDecode = fetchQueue->getWire(0);
312}
313
314template<class Impl>
315void
316DefaultFetch<Impl>::initStage()
317{
318    // Setup PC and nextPC with initial state.
319    for (int tid = 0; tid < numThreads; tid++) {
320        PC[tid] = cpu->readPC(tid);
321        nextPC[tid] = cpu->readNextPC(tid);
322        nextNPC[tid] = cpu->readNextNPC(tid);
323    }
324
325    // Size of cache block.
326    cacheBlkSize = icachePort->peerBlockSize();
327
328    // Create mask to get rid of offset bits.
329    cacheBlkMask = (cacheBlkSize - 1);
330
331    for (int tid=0; tid < numThreads; tid++) {
332
333        fetchStatus[tid] = Running;
334
335        priorityList.push_back(tid);
336
337        memReq[tid] = NULL;
338
339        // Create space to store a cache line.
340        cacheData[tid] = new uint8_t[cacheBlkSize];
341        cacheDataPC[tid] = 0;
342        cacheDataValid[tid] = false;
343
344        delaySlotInfo[tid].branchSeqNum = -1;
345        delaySlotInfo[tid].numInsts = 0;
346        delaySlotInfo[tid].targetAddr = 0;
347        delaySlotInfo[tid].targetReady = false;
348
349        stalls[tid].decode = false;
350        stalls[tid].rename = false;
351        stalls[tid].iew = false;
352        stalls[tid].commit = false;
353    }
354}
355
356template<class Impl>
357void
358DefaultFetch<Impl>::processCacheCompletion(PacketPtr pkt)
359{
360    unsigned tid = pkt->req->getThreadNum();
361
362    DPRINTF(Fetch, "[tid:%u] Waking up from cache miss.\n",tid);
363
364    // Only change the status if it's still waiting on the icache access
365    // to return.
366    if (fetchStatus[tid] != IcacheWaitResponse ||
367        pkt->req != memReq[tid] ||
368        isSwitchedOut()) {
369        ++fetchIcacheSquashes;
370        delete pkt->req;
371        delete pkt;
372        return;
373    }
374
375    memcpy(cacheData[tid], pkt->getPtr<uint8_t *>(), cacheBlkSize);
376    cacheDataValid[tid] = true;
377
378    if (!drainPending) {
379        // Wake up the CPU (if it went to sleep and was waiting on
380        // this completion event).
381        cpu->wakeCPU();
382
383        DPRINTF(Activity, "[tid:%u] Activating fetch due to cache completion\n",
384                tid);
385
386        switchToActive();
387    }
388
389    // Only switch to IcacheAccessComplete if we're not stalled as well.
390    if (checkStall(tid)) {
391        fetchStatus[tid] = Blocked;
392    } else {
393        fetchStatus[tid] = IcacheAccessComplete;
394    }
395
396    // Reset the mem req to NULL.
397    delete pkt->req;
398    delete pkt;
399    memReq[tid] = NULL;
400}
401
402template <class Impl>
403bool
404DefaultFetch<Impl>::drain()
405{
406    // Fetch is ready to drain at any time.
407    cpu->signalDrained();
408    drainPending = true;
409    return true;
410}
411
412template <class Impl>
413void
414DefaultFetch<Impl>::resume()
415{
416    drainPending = false;
417}
418
419template <class Impl>
420void
421DefaultFetch<Impl>::switchOut()
422{
423    switchedOut = true;
424    // Branch predictor needs to have its state cleared.
425    branchPred.switchOut();
426}
427
428template <class Impl>
429void
430DefaultFetch<Impl>::takeOverFrom()
431{
432    // Reset all state
433    for (int i = 0; i < Impl::MaxThreads; ++i) {
434        stalls[i].decode = 0;
435        stalls[i].rename = 0;
436        stalls[i].iew = 0;
437        stalls[i].commit = 0;
438        PC[i] = cpu->readPC(i);
439        nextPC[i] = cpu->readNextPC(i);
440#if ISA_HAS_DELAY_SLOT
441        nextNPC[i] = cpu->readNextNPC(i);
442        delaySlotInfo[i].branchSeqNum = -1;
443        delaySlotInfo[i].numInsts = 0;
444        delaySlotInfo[i].targetAddr = 0;
445        delaySlotInfo[i].targetReady = false;
446#endif
447        fetchStatus[i] = Running;
448    }
449    numInst = 0;
450    wroteToTimeBuffer = false;
451    _status = Inactive;
452    switchedOut = false;
453    interruptPending = false;
454    branchPred.takeOverFrom();
455}
456
457template <class Impl>
458void
459DefaultFetch<Impl>::wakeFromQuiesce()
460{
461    DPRINTF(Fetch, "Waking up from quiesce\n");
462    // Hopefully this is safe
463    // @todo: Allow other threads to wake from quiesce.
464    fetchStatus[0] = Running;
465}
466
467template <class Impl>
468inline void
469DefaultFetch<Impl>::switchToActive()
470{
471    if (_status == Inactive) {
472        DPRINTF(Activity, "Activating stage.\n");
473
474        cpu->activateStage(O3CPU::FetchIdx);
475
476        _status = Active;
477    }
478}
479
480template <class Impl>
481inline void
482DefaultFetch<Impl>::switchToInactive()
483{
484    if (_status == Active) {
485        DPRINTF(Activity, "Deactivating stage.\n");
486
487        cpu->deactivateStage(O3CPU::FetchIdx);
488
489        _status = Inactive;
490    }
491}
492
493template <class Impl>
494bool
495DefaultFetch<Impl>::lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC,
496                                          Addr &next_NPC)
497{
498    // Do branch prediction check here.
499    // A bit of a misnomer...next_PC is actually the current PC until
500    // this function updates it.
501    bool predict_taken;
502
503    if (!inst->isControl()) {
504#if ISA_HAS_DELAY_SLOT
505        next_PC  = next_NPC;
506        next_NPC = next_NPC + instSize;
507        inst->setPredTarg(next_PC, next_NPC);
508#else
509        next_PC = next_PC + instSize;
510        inst->setPredTarg(next_PC, next_PC + sizeof(TheISA::MachInst));
511#endif
512        inst->setPredTaken(false);
513        return false;
514    }
515
516    int tid = inst->threadNumber;
517#if ISA_HAS_DELAY_SLOT
518    Addr pred_PC = next_PC;
519    predict_taken = branchPred.predict(inst, pred_PC, tid);
520
521    if (predict_taken) {
522        DPRINTF(Fetch, "[tid:%i]: Branch predicted to be taken.\n", tid);
523    } else {
524        DPRINTF(Fetch, "[tid:%i]: Branch predicted to be not taken.\n", tid);
525    }
526
527    next_PC = next_NPC;
528    if (predict_taken) {
529        next_NPC = pred_PC;
530        // Update delay slot info
531        ++delaySlotInfo[tid].numInsts;
532        delaySlotInfo[tid].targetAddr = pred_PC;
533        DPRINTF(Fetch, "[tid:%i]: %i delay slot inst(s) to process.\n", tid,
534                delaySlotInfo[tid].numInsts);
535    } else {
536        next_NPC = next_NPC + instSize;
537    }
538#else
539    predict_taken = branchPred.predict(inst, next_PC, tid);
540#endif
541    DPRINTF(Fetch, "[tid:%i]: Branch predicted to go to %#x and then %#x.\n",
542            tid, next_PC, next_NPC);
543    inst->setPredTarg(next_PC, next_NPC);
544    inst->setPredTaken(predict_taken);
545
546    ++fetchedBranches;
547
548    if (predict_taken) {
549        ++predictedBranches;
550    }
551
552    return predict_taken;
553}
554
555template <class Impl>
556bool
557DefaultFetch<Impl>::fetchCacheLine(Addr fetch_PC, Fault &ret_fault, unsigned tid)
558{
559    Fault fault = NoFault;
560
561    //AlphaDep
562    if (cacheBlocked) {
563        DPRINTF(Fetch, "[tid:%i] Can't fetch cache line, cache blocked\n",
564                tid);
565        return false;
566    } else if (isSwitchedOut()) {
567        DPRINTF(Fetch, "[tid:%i] Can't fetch cache line, switched out\n",
568                tid);
569        return false;
570    } else if (interruptPending && !(fetch_PC & 0x3)) {
571        // Hold off fetch from getting new instructions when:
572        // Cache is blocked, or
573        // while an interrupt is pending and we're not in PAL mode, or
574        // fetch is switched out.
575        DPRINTF(Fetch, "[tid:%i] Can't fetch cache line, interrupt pending\n",
576                tid);
577        return false;
578    }
579
580    // Align the fetch PC so it's at the start of a cache block.
581    Addr block_PC = icacheBlockAlignPC(fetch_PC);
582
583    // If we've already got the block, no need to try to fetch it again.
584    if (cacheDataValid[tid] && block_PC == cacheDataPC[tid]) {
585        return true;
586    }
587
588    // Setup the memReq to do a read of the first instruction's address.
589    // Set the appropriate read size and flags as well.
590    // Build request here.
591    RequestPtr mem_req = new Request(tid, block_PC, cacheBlkSize, 0,
592                                     fetch_PC, cpu->readCpuId(), tid);
593
594    memReq[tid] = mem_req;
595
596    // Translate the instruction request.
597    fault = cpu->translateInstReq(mem_req, cpu->thread[tid]);
598
599    // In the case of faults, the fetch stage may need to stall and wait
600    // for the ITB miss to be handled.
601
602    // If translation was successful, attempt to read the first
603    // instruction.
604    if (fault == NoFault) {
605#if 0
606        if (cpu->system->memctrl->badaddr(memReq[tid]->paddr) ||
607            memReq[tid]->isUncacheable()) {
608            DPRINTF(Fetch, "Fetch: Bad address %#x (hopefully on a "
609                    "misspeculating path)!",
610                    memReq[tid]->paddr);
611            ret_fault = TheISA::genMachineCheckFault();
612            return false;
613        }
614#endif
615
616        // Build packet here.
617        PacketPtr data_pkt = new Packet(mem_req,
618                                        Packet::ReadReq, Packet::Broadcast);
619        data_pkt->dataDynamicArray(new uint8_t[cacheBlkSize]);
620
621        cacheDataPC[tid] = block_PC;
622        cacheDataValid[tid] = false;
623
624        DPRINTF(Fetch, "Fetch: Doing instruction read.\n");
625
626        fetchedCacheLines++;
627
628        // Now do the timing access to see whether or not the instruction
629        // exists within the cache.
630        if (!icachePort->sendTiming(data_pkt)) {
631            if (data_pkt->result == Packet::BadAddress) {
632                fault = TheISA::genMachineCheckFault();
633                delete mem_req;
634                memReq[tid] = NULL;
635            }
636            assert(retryPkt == NULL);
637            assert(retryTid == -1);
638            DPRINTF(Fetch, "[tid:%i] Out of MSHRs!\n", tid);
639            fetchStatus[tid] = IcacheWaitRetry;
640            retryPkt = data_pkt;
641            retryTid = tid;
642            cacheBlocked = true;
643            return false;
644        }
645
646        DPRINTF(Fetch, "[tid:%i]: Doing cache access.\n", tid);
647
648        lastIcacheStall[tid] = curTick;
649
650        DPRINTF(Activity, "[tid:%i]: Activity: Waiting on I-cache "
651                "response.\n", tid);
652
653        fetchStatus[tid] = IcacheWaitResponse;
654    } else {
655        delete mem_req;
656        memReq[tid] = NULL;
657    }
658
659    ret_fault = fault;
660    return true;
661}
662
663template <class Impl>
664inline void
665DefaultFetch<Impl>::doSquash(const Addr &new_PC,
666        const Addr &new_NPC, unsigned tid)
667{
668    DPRINTF(Fetch, "[tid:%i]: Squashing, setting PC to: %#x, NPC to: %#x.\n",
669            tid, new_PC, new_NPC);
670
671    PC[tid] = new_PC;
672    nextPC[tid] = new_NPC;
673    nextNPC[tid] = new_NPC + instSize;
674
675    // Clear the icache miss if it's outstanding.
676    if (fetchStatus[tid] == IcacheWaitResponse) {
677        DPRINTF(Fetch, "[tid:%i]: Squashing outstanding Icache miss.\n",
678                tid);
679        memReq[tid] = NULL;
680    }
681
682    // Get rid of the retrying packet if it was from this thread.
683    if (retryTid == tid) {
684        assert(cacheBlocked);
685        cacheBlocked = false;
686        retryTid = -1;
687        delete retryPkt->req;
688        delete retryPkt;
689        retryPkt = NULL;
690    }
691
692    fetchStatus[tid] = Squashing;
693
694    ++fetchSquashCycles;
695}
696
697template<class Impl>
698void
699DefaultFetch<Impl>::squashFromDecode(const Addr &new_PC, const Addr &new_NPC,
700                                     const InstSeqNum &seq_num,
701                                     unsigned tid)
702{
703    DPRINTF(Fetch, "[tid:%i]: Squashing from decode.\n",tid);
704
705    doSquash(new_PC, new_NPC, tid);
706
707#if ISA_HAS_DELAY_SLOT
708    if (seq_num <=  delaySlotInfo[tid].branchSeqNum) {
709        delaySlotInfo[tid].numInsts = 0;
710        delaySlotInfo[tid].targetAddr = 0;
711        delaySlotInfo[tid].targetReady = false;
712    }
713#endif
714
715    // Tell the CPU to remove any instructions that are in flight between
716    // fetch and decode.
717    cpu->removeInstsUntil(seq_num, tid);
718}
719
720template<class Impl>
721bool
722DefaultFetch<Impl>::checkStall(unsigned tid) const
723{
724    bool ret_val = false;
725
726    if (cpu->contextSwitch) {
727        DPRINTF(Fetch,"[tid:%i]: Stalling for a context switch.\n",tid);
728        ret_val = true;
729    } else if (stalls[tid].decode) {
730        DPRINTF(Fetch,"[tid:%i]: Stall from Decode stage detected.\n",tid);
731        ret_val = true;
732    } else if (stalls[tid].rename) {
733        DPRINTF(Fetch,"[tid:%i]: Stall from Rename stage detected.\n",tid);
734        ret_val = true;
735    } else if (stalls[tid].iew) {
736        DPRINTF(Fetch,"[tid:%i]: Stall from IEW stage detected.\n",tid);
737        ret_val = true;
738    } else if (stalls[tid].commit) {
739        DPRINTF(Fetch,"[tid:%i]: Stall from Commit stage detected.\n",tid);
740        ret_val = true;
741    }
742
743    return ret_val;
744}
745
746template<class Impl>
747typename DefaultFetch<Impl>::FetchStatus
748DefaultFetch<Impl>::updateFetchStatus()
749{
750    //Check Running
751    std::list<unsigned>::iterator threads = (*activeThreads).begin();
752
753    while (threads != (*activeThreads).end()) {
754
755        unsigned tid = *threads++;
756
757        if (fetchStatus[tid] == Running ||
758            fetchStatus[tid] == Squashing ||
759            fetchStatus[tid] == IcacheAccessComplete) {
760
761            if (_status == Inactive) {
762                DPRINTF(Activity, "[tid:%i]: Activating stage.\n",tid);
763
764                if (fetchStatus[tid] == IcacheAccessComplete) {
765                    DPRINTF(Activity, "[tid:%i]: Activating fetch due to cache"
766                            "completion\n",tid);
767                }
768
769                cpu->activateStage(O3CPU::FetchIdx);
770            }
771
772            return Active;
773        }
774    }
775
776    // Stage is switching from active to inactive, notify CPU of it.
777    if (_status == Active) {
778        DPRINTF(Activity, "Deactivating stage.\n");
779
780        cpu->deactivateStage(O3CPU::FetchIdx);
781    }
782
783    return Inactive;
784}
785
786template <class Impl>
787void
788DefaultFetch<Impl>::squash(const Addr &new_PC, const Addr &new_NPC,
789                           const InstSeqNum &seq_num,
790                           bool squash_delay_slot, unsigned tid)
791{
792    DPRINTF(Fetch, "[tid:%u]: Squash from commit.\n",tid);
793
794    doSquash(new_PC, new_NPC, tid);
795
796#if ISA_HAS_DELAY_SLOT
797    if (seq_num <=  delaySlotInfo[tid].branchSeqNum) {
798        delaySlotInfo[tid].numInsts = 0;
799        delaySlotInfo[tid].targetAddr = 0;
800        delaySlotInfo[tid].targetReady = false;
801    }
802
803    // Tell the CPU to remove any instructions that are not in the ROB.
804    cpu->removeInstsNotInROB(tid, squash_delay_slot, seq_num);
805#else
806    // Tell the CPU to remove any instructions that are not in the ROB.
807    cpu->removeInstsNotInROB(tid, true, 0);
808#endif
809}
810
811template <class Impl>
812void
813DefaultFetch<Impl>::tick()
814{
815    std::list<unsigned>::iterator threads = (*activeThreads).begin();
816    bool status_change = false;
817
818    wroteToTimeBuffer = false;
819
820    while (threads != (*activeThreads).end()) {
821        unsigned tid = *threads++;
822
823        // Check the signals for each thread to determine the proper status
824        // for each thread.
825        bool updated_status = checkSignalsAndUpdate(tid);
826        status_change =  status_change || updated_status;
827    }
828
829    DPRINTF(Fetch, "Running stage.\n");
830
831    // Reset the number of the instruction we're fetching.
832    numInst = 0;
833
834#if FULL_SYSTEM
835    if (fromCommit->commitInfo[0].interruptPending) {
836        interruptPending = true;
837    }
838
839    if (fromCommit->commitInfo[0].clearInterrupt) {
840        interruptPending = false;
841    }
842#endif
843
844    for (threadFetched = 0; threadFetched < numFetchingThreads;
845         threadFetched++) {
846        // Fetch each of the actively fetching threads.
847        fetch(status_change);
848    }
849
850    // Record number of instructions fetched this cycle for distribution.
851    fetchNisnDist.sample(numInst);
852
853    if (status_change) {
854        // Change the fetch stage status if there was a status change.
855        _status = updateFetchStatus();
856    }
857
858    // If there was activity this cycle, inform the CPU of it.
859    if (wroteToTimeBuffer || cpu->contextSwitch) {
860        DPRINTF(Activity, "Activity this cycle.\n");
861
862        cpu->activityThisCycle();
863    }
864}
865
866template <class Impl>
867bool
868DefaultFetch<Impl>::checkSignalsAndUpdate(unsigned tid)
869{
870    // Update the per thread stall statuses.
871    if (fromDecode->decodeBlock[tid]) {
872        stalls[tid].decode = true;
873    }
874
875    if (fromDecode->decodeUnblock[tid]) {
876        assert(stalls[tid].decode);
877        assert(!fromDecode->decodeBlock[tid]);
878        stalls[tid].decode = false;
879    }
880
881    if (fromRename->renameBlock[tid]) {
882        stalls[tid].rename = true;
883    }
884
885    if (fromRename->renameUnblock[tid]) {
886        assert(stalls[tid].rename);
887        assert(!fromRename->renameBlock[tid]);
888        stalls[tid].rename = false;
889    }
890
891    if (fromIEW->iewBlock[tid]) {
892        stalls[tid].iew = true;
893    }
894
895    if (fromIEW->iewUnblock[tid]) {
896        assert(stalls[tid].iew);
897        assert(!fromIEW->iewBlock[tid]);
898        stalls[tid].iew = false;
899    }
900
901    if (fromCommit->commitBlock[tid]) {
902        stalls[tid].commit = true;
903    }
904
905    if (fromCommit->commitUnblock[tid]) {
906        assert(stalls[tid].commit);
907        assert(!fromCommit->commitBlock[tid]);
908        stalls[tid].commit = false;
909    }
910
911    // Check squash signals from commit.
912    if (fromCommit->commitInfo[tid].squash) {
913
914        DPRINTF(Fetch, "[tid:%u]: Squashing instructions due to squash "
915                "from commit.\n",tid);
916
917#if ISA_HAS_DELAY_SLOT
918    InstSeqNum doneSeqNum = fromCommit->commitInfo[tid].bdelayDoneSeqNum;
919#else
920    InstSeqNum doneSeqNum = fromCommit->commitInfo[tid].doneSeqNum;
921#endif
922        // In any case, squash.
923        squash(fromCommit->commitInfo[tid].nextPC,
924               fromCommit->commitInfo[tid].nextNPC,
925               doneSeqNum,
926               fromCommit->commitInfo[tid].squashDelaySlot,
927               tid);
928
929        // Also check if there's a mispredict that happened.
930        if (fromCommit->commitInfo[tid].branchMispredict) {
931            branchPred.squash(fromCommit->commitInfo[tid].doneSeqNum,
932                              fromCommit->commitInfo[tid].nextPC,
933                              fromCommit->commitInfo[tid].branchTaken,
934                              tid);
935        } else {
936            branchPred.squash(fromCommit->commitInfo[tid].doneSeqNum,
937                              tid);
938        }
939
940        return true;
941    } else if (fromCommit->commitInfo[tid].doneSeqNum) {
942        // Update the branch predictor if it wasn't a squashed instruction
943        // that was broadcasted.
944        branchPred.update(fromCommit->commitInfo[tid].doneSeqNum, tid);
945    }
946
947    // Check ROB squash signals from commit.
948    if (fromCommit->commitInfo[tid].robSquashing) {
949        DPRINTF(Fetch, "[tid:%u]: ROB is still squashing.\n", tid);
950
951        // Continue to squash.
952        fetchStatus[tid] = Squashing;
953
954        return true;
955    }
956
957    // Check squash signals from decode.
958    if (fromDecode->decodeInfo[tid].squash) {
959        DPRINTF(Fetch, "[tid:%u]: Squashing instructions due to squash "
960                "from decode.\n",tid);
961
962        // Update the branch predictor.
963        if (fromDecode->decodeInfo[tid].branchMispredict) {
964            branchPred.squash(fromDecode->decodeInfo[tid].doneSeqNum,
965                              fromDecode->decodeInfo[tid].nextPC,
966                              fromDecode->decodeInfo[tid].branchTaken,
967                              tid);
968        } else {
969            branchPred.squash(fromDecode->decodeInfo[tid].doneSeqNum,
970                              tid);
971        }
972
973        if (fetchStatus[tid] != Squashing) {
974
975#if ISA_HAS_DELAY_SLOT
976            InstSeqNum doneSeqNum = fromDecode->decodeInfo[tid].bdelayDoneSeqNum;
977#else
978            InstSeqNum doneSeqNum = fromDecode->decodeInfo[tid].doneSeqNum;
979#endif
980            // Squash unless we're already squashing
981            squashFromDecode(fromDecode->decodeInfo[tid].nextPC,
982                             fromDecode->decodeInfo[tid].nextNPC,
983                             doneSeqNum,
984                             tid);
985
986            return true;
987        }
988    }
989
990    if (checkStall(tid) &&
991        fetchStatus[tid] != IcacheWaitResponse &&
992        fetchStatus[tid] != IcacheWaitRetry) {
993        DPRINTF(Fetch, "[tid:%i]: Setting to blocked\n",tid);
994
995        fetchStatus[tid] = Blocked;
996
997        return true;
998    }
999
1000    if (fetchStatus[tid] == Blocked ||
1001        fetchStatus[tid] == Squashing) {
1002        // Switch status to running if fetch isn't being told to block or
1003        // squash this cycle.
1004        DPRINTF(Fetch, "[tid:%i]: Done squashing, switching to running.\n",
1005                tid);
1006
1007        fetchStatus[tid] = Running;
1008
1009        return true;
1010    }
1011
1012    // If we've reached this point, we have not gotten any signals that
1013    // cause fetch to change its status.  Fetch remains the same as before.
1014    return false;
1015}
1016
1017template<class Impl>
1018void
1019DefaultFetch<Impl>::fetch(bool &status_change)
1020{
1021    //////////////////////////////////////////
1022    // Start actual fetch
1023    //////////////////////////////////////////
1024    int tid = getFetchingThread(fetchPolicy);
1025
1026    if (tid == -1 || drainPending) {
1027        DPRINTF(Fetch,"There are no more threads available to fetch from.\n");
1028
1029        // Breaks looping condition in tick()
1030        threadFetched = numFetchingThreads;
1031        return;
1032    }
1033
1034    DPRINTF(Fetch, "Attempting to fetch from [tid:%i]\n", tid);
1035
1036    // The current PC.
1037    Addr &fetch_PC = PC[tid];
1038
1039    Addr &fetch_NPC = nextPC[tid];
1040
1041    // Fault code for memory access.
1042    Fault fault = NoFault;
1043
1044    // If returning from the delay of a cache miss, then update the status
1045    // to running, otherwise do the cache access.  Possibly move this up
1046    // to tick() function.
1047    if (fetchStatus[tid] == IcacheAccessComplete) {
1048        DPRINTF(Fetch, "[tid:%i]: Icache miss is complete.\n",
1049                tid);
1050
1051        fetchStatus[tid] = Running;
1052        status_change = true;
1053    } else if (fetchStatus[tid] == Running) {
1054        DPRINTF(Fetch, "[tid:%i]: Attempting to translate and read "
1055                "instruction, starting at PC %08p.\n",
1056                tid, fetch_PC);
1057
1058        bool fetch_success = fetchCacheLine(fetch_PC, fault, tid);
1059        if (!fetch_success) {
1060            if (cacheBlocked) {
1061                ++icacheStallCycles;
1062            } else {
1063                ++fetchMiscStallCycles;
1064            }
1065            return;
1066        }
1067    } else {
1068        if (fetchStatus[tid] == Idle) {
1069            ++fetchIdleCycles;
1070            DPRINTF(Fetch, "[tid:%i]: Fetch is idle!\n", tid);
1071        } else if (fetchStatus[tid] == Blocked) {
1072            ++fetchBlockedCycles;
1073            DPRINTF(Fetch, "[tid:%i]: Fetch is blocked!\n", tid);
1074        } else if (fetchStatus[tid] == Squashing) {
1075            ++fetchSquashCycles;
1076            DPRINTF(Fetch, "[tid:%i]: Fetch is squashing!\n", tid);
1077        } else if (fetchStatus[tid] == IcacheWaitResponse) {
1078            ++icacheStallCycles;
1079            DPRINTF(Fetch, "[tid:%i]: Fetch is waiting cache response!\n", tid);
1080        }
1081
1082        // Status is Idle, Squashing, Blocked, or IcacheWaitResponse, so
1083        // fetch should do nothing.
1084        return;
1085    }
1086
1087    ++fetchCycles;
1088
1089    // If we had a stall due to an icache miss, then return.
1090    if (fetchStatus[tid] == IcacheWaitResponse) {
1091        ++icacheStallCycles;
1092        status_change = true;
1093        return;
1094    }
1095
1096    Addr next_PC = fetch_PC;
1097    Addr next_NPC = fetch_NPC;
1098
1099    InstSeqNum inst_seq;
1100    MachInst inst;
1101    ExtMachInst ext_inst;
1102    // @todo: Fix this hack.
1103    unsigned offset = (fetch_PC & cacheBlkMask) & ~3;
1104
1105    if (fault == NoFault) {
1106        // If the read of the first instruction was successful, then grab the
1107        // instructions from the rest of the cache line and put them into the
1108        // queue heading to decode.
1109
1110        DPRINTF(Fetch, "[tid:%i]: Adding instructions to queue to "
1111                "decode.\n",tid);
1112
1113        // Need to keep track of whether or not a predicted branch
1114        // ended this fetch block.
1115        bool predicted_branch = false;
1116
1117        for (;
1118             offset < cacheBlkSize &&
1119                 numInst < fetchWidth &&
1120                 !predicted_branch;
1121             ++numInst) {
1122
1123            // If we're branching after this instruction, quite fetching
1124            // from the same block then.
1125            predicted_branch =
1126                (fetch_PC + sizeof(TheISA::MachInst) != fetch_NPC);
1127
1128            // Get a sequence number.
1129            inst_seq = cpu->getAndIncrementInstSeq();
1130
1131            // Make sure this is a valid index.
1132            assert(offset <= cacheBlkSize - instSize);
1133
1134            // Get the instruction from the array of the cache line.
1135            inst = TheISA::gtoh(*reinterpret_cast<TheISA::MachInst *>
1136                        (&cacheData[tid][offset]));
1137
1138#if THE_ISA == ALPHA_ISA
1139            ext_inst = TheISA::makeExtMI(inst, fetch_PC);
1140#elif THE_ISA == SPARC_ISA
1141            ext_inst = TheISA::makeExtMI(inst, cpu->thread[tid]->getTC());
1142#elif THE_ISA == MIPS_ISA
1143            ext_inst = TheISA::makeExtMI(inst, cpu->thread[tid]->getTC());
1144#endif
1145
1146            // Create a new DynInst from the instruction fetched.
1147            DynInstPtr instruction = new DynInst(ext_inst,
1148                                                 fetch_PC, fetch_NPC,
1149                                                 next_PC, next_NPC,
1150                                                 inst_seq, cpu);
1151            instruction->setTid(tid);
1152
1153            instruction->setASID(tid);
1154
1155            instruction->setThreadState(cpu->thread[tid]);
1156
1157            DPRINTF(Fetch, "[tid:%i]: Instruction PC %#x created "
1158                    "[sn:%lli]\n",
1159                    tid, instruction->readPC(), inst_seq);
1160
1161            DPRINTF(Fetch, "[tid:%i]: MachInst is %#x\n", tid, ext_inst);
1162
1163            DPRINTF(Fetch, "[tid:%i]: Instruction is: %s\n",
1164                    tid, instruction->staticInst->disassemble(fetch_PC));
1165
1166            instruction->traceData =
1167                Trace::getInstRecord(curTick, cpu->tcBase(tid),
1168                                     instruction->staticInst,
1169                                     instruction->readPC());
1170
1171            lookupAndUpdateNextPC(instruction, next_PC, next_NPC);
1172
1173            // Add instruction to the CPU's list of instructions.
1174            instruction->setInstListIt(cpu->addInst(instruction));
1175
1176            // Write the instruction to the first slot in the queue
1177            // that heads to decode.
1178            toDecode->insts[numInst] = instruction;
1179
1180            toDecode->size++;
1181
1182            // Increment stat of fetched instructions.
1183            ++fetchedInsts;
1184
1185            // Move to the next instruction, unless we have a branch.
1186            fetch_PC = next_PC;
1187            fetch_NPC = next_NPC;
1188
1189            if (instruction->isQuiesce()) {
1190                DPRINTF(Fetch, "Quiesce instruction encountered, halting fetch!",
1191                        curTick);
1192                fetchStatus[tid] = QuiescePending;
1193                ++numInst;
1194                status_change = true;
1195                break;
1196            }
1197
1198            offset += instSize;
1199        }
1200
1201        if (offset >= cacheBlkSize) {
1202            DPRINTF(Fetch, "[tid:%i]: Done fetching, reached the end of cache "
1203                    "block.\n", tid);
1204        } else if (numInst >= fetchWidth) {
1205            DPRINTF(Fetch, "[tid:%i]: Done fetching, reached fetch bandwidth "
1206                    "for this cycle.\n", tid);
1207        } else if (predicted_branch) {
1208            DPRINTF(Fetch, "[tid:%i]: Done fetching, predicted branch "
1209                    "instruction encountered.\n", tid);
1210        }
1211    }
1212
1213    if (numInst > 0) {
1214        wroteToTimeBuffer = true;
1215    }
1216
1217    // Now that fetching is completed, update the PC to signify what the next
1218    // cycle will be.
1219    if (fault == NoFault) {
1220#if ISA_HAS_DELAY_SLOT
1221        if (delaySlotInfo[tid].targetReady &&
1222            delaySlotInfo[tid].numInsts == 0) {
1223            // Set PC to target
1224            PC[tid] = next_PC;
1225            nextPC[tid] = next_NPC;
1226            nextNPC[tid] = next_NPC + instSize;
1227
1228            delaySlotInfo[tid].targetReady = false;
1229        } else {
1230            PC[tid] = next_PC;
1231            nextPC[tid] = next_NPC;
1232            nextNPC[tid] = next_NPC + instSize;
1233        }
1234
1235        DPRINTF(Fetch, "[tid:%i]: Setting PC to %08p.\n", tid, PC[tid]);
1236#else
1237        DPRINTF(Fetch, "[tid:%i]: Setting PC to %08p.\n",tid, next_PC);
1238        PC[tid] = next_PC;
1239        nextPC[tid] = next_PC + instSize;
1240#endif
1241    } else {
1242        // We shouldn't be in an icache miss and also have a fault (an ITB
1243        // miss)
1244        if (fetchStatus[tid] == IcacheWaitResponse) {
1245            panic("Fetch should have exited prior to this!");
1246        }
1247
1248        // Send the fault to commit.  This thread will not do anything
1249        // until commit handles the fault.  The only other way it can
1250        // wake up is if a squash comes along and changes the PC.
1251#if FULL_SYSTEM
1252        assert(numInst != fetchWidth);
1253        // Get a sequence number.
1254        inst_seq = cpu->getAndIncrementInstSeq();
1255        // We will use a nop in order to carry the fault.
1256        ext_inst = TheISA::NoopMachInst;
1257
1258        // Create a new DynInst from the dummy nop.
1259        DynInstPtr instruction = new DynInst(ext_inst,
1260                                             fetch_PC, fetch_NPC,
1261                                             next_PC, next_NPC,
1262                                             inst_seq, cpu);
1263        instruction->setPredTarg(next_PC, next_NPC);
1264        instruction->setTid(tid);
1265
1266        instruction->setASID(tid);
1267
1268        instruction->setThreadState(cpu->thread[tid]);
1269
1270        instruction->traceData = NULL;
1271
1272        instruction->setInstListIt(cpu->addInst(instruction));
1273
1274        instruction->fault = fault;
1275
1276        toDecode->insts[numInst] = instruction;
1277        toDecode->size++;
1278
1279        DPRINTF(Fetch, "[tid:%i]: Blocked, need to handle the trap.\n",tid);
1280
1281        fetchStatus[tid] = TrapPending;
1282        status_change = true;
1283#else // !FULL_SYSTEM
1284        fetchStatus[tid] = TrapPending;
1285        status_change = true;
1286
1287#endif // FULL_SYSTEM
1288        DPRINTF(Fetch, "[tid:%i]: fault (%s) detected @ PC %08p",
1289                tid, fault->name(), PC[tid]);
1290    }
1291}
1292
1293template<class Impl>
1294void
1295DefaultFetch<Impl>::recvRetry()
1296{
1297    if (retryPkt != NULL) {
1298        assert(cacheBlocked);
1299        assert(retryTid != -1);
1300        assert(fetchStatus[retryTid] == IcacheWaitRetry);
1301
1302        if (icachePort->sendTiming(retryPkt)) {
1303            fetchStatus[retryTid] = IcacheWaitResponse;
1304            retryPkt = NULL;
1305            retryTid = -1;
1306            cacheBlocked = false;
1307        }
1308    } else {
1309        assert(retryTid == -1);
1310        // Access has been squashed since it was sent out.  Just clear
1311        // the cache being blocked.
1312        cacheBlocked = false;
1313    }
1314}
1315
1316///////////////////////////////////////
1317//                                   //
1318//  SMT FETCH POLICY MAINTAINED HERE //
1319//                                   //
1320///////////////////////////////////////
1321template<class Impl>
1322int
1323DefaultFetch<Impl>::getFetchingThread(FetchPriority &fetch_priority)
1324{
1325    if (numThreads > 1) {
1326        switch (fetch_priority) {
1327
1328          case SingleThread:
1329            return 0;
1330
1331          case RoundRobin:
1332            return roundRobin();
1333
1334          case IQ:
1335            return iqCount();
1336
1337          case LSQ:
1338            return lsqCount();
1339
1340          case Branch:
1341            return branchCount();
1342
1343          default:
1344            return -1;
1345        }
1346    } else {
1347        int tid = *((*activeThreads).begin());
1348
1349        if (fetchStatus[tid] == Running ||
1350            fetchStatus[tid] == IcacheAccessComplete ||
1351            fetchStatus[tid] == Idle) {
1352            return tid;
1353        } else {
1354            return -1;
1355        }
1356    }
1357
1358}
1359
1360
1361template<class Impl>
1362int
1363DefaultFetch<Impl>::roundRobin()
1364{
1365    std::list<unsigned>::iterator pri_iter = priorityList.begin();
1366    std::list<unsigned>::iterator end      = priorityList.end();
1367
1368    int high_pri;
1369
1370    while (pri_iter != end) {
1371        high_pri = *pri_iter;
1372
1373        assert(high_pri <= numThreads);
1374
1375        if (fetchStatus[high_pri] == Running ||
1376            fetchStatus[high_pri] == IcacheAccessComplete ||
1377            fetchStatus[high_pri] == Idle) {
1378
1379            priorityList.erase(pri_iter);
1380            priorityList.push_back(high_pri);
1381
1382            return high_pri;
1383        }
1384
1385        pri_iter++;
1386    }
1387
1388    return -1;
1389}
1390
1391template<class Impl>
1392int
1393DefaultFetch<Impl>::iqCount()
1394{
1395    std::priority_queue<unsigned> PQ;
1396
1397    std::list<unsigned>::iterator threads = (*activeThreads).begin();
1398
1399    while (threads != (*activeThreads).end()) {
1400        unsigned tid = *threads++;
1401
1402        PQ.push(fromIEW->iewInfo[tid].iqCount);
1403    }
1404
1405    while (!PQ.empty()) {
1406
1407        unsigned high_pri = PQ.top();
1408
1409        if (fetchStatus[high_pri] == Running ||
1410            fetchStatus[high_pri] == IcacheAccessComplete ||
1411            fetchStatus[high_pri] == Idle)
1412            return high_pri;
1413        else
1414            PQ.pop();
1415
1416    }
1417
1418    return -1;
1419}
1420
1421template<class Impl>
1422int
1423DefaultFetch<Impl>::lsqCount()
1424{
1425    std::priority_queue<unsigned> PQ;
1426
1427
1428    std::list<unsigned>::iterator threads = (*activeThreads).begin();
1429
1430    while (threads != (*activeThreads).end()) {
1431        unsigned tid = *threads++;
1432
1433        PQ.push(fromIEW->iewInfo[tid].ldstqCount);
1434    }
1435
1436    while (!PQ.empty()) {
1437
1438        unsigned high_pri = PQ.top();
1439
1440        if (fetchStatus[high_pri] == Running ||
1441            fetchStatus[high_pri] == IcacheAccessComplete ||
1442            fetchStatus[high_pri] == Idle)
1443            return high_pri;
1444        else
1445            PQ.pop();
1446
1447    }
1448
1449    return -1;
1450}
1451
1452template<class Impl>
1453int
1454DefaultFetch<Impl>::branchCount()
1455{
1456    std::list<unsigned>::iterator threads = (*activeThreads).begin();
1457    panic("Branch Count Fetch policy unimplemented\n");
1458    return *threads;
1459}
1460