commit_impl.hh revision 8581:56f97760eadd 
1/*
2 * Copyright (c) 2010 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder.  You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2004-2006 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Kevin Lim
41 *          Korey Sewell
42 */
43
44#include <algorithm>
45#include <string>
46
47#include "arch/utility.hh"
48#include "base/loader/symtab.hh"
49#include "base/cp_annotate.hh"
50#include "config/full_system.hh"
51#include "config/the_isa.hh"
52#include "config/use_checker.hh"
53#include "cpu/o3/commit.hh"
54#include "cpu/o3/thread_state.hh"
55#include "cpu/exetrace.hh"
56#include "cpu/timebuf.hh"
57#include "debug/Activity.hh"
58#include "debug/Commit.hh"
59#include "debug/CommitRate.hh"
60#include "debug/ExecFaulting.hh"
61#include "debug/O3PipeView.hh"
62#include "params/DerivO3CPU.hh"
63#include "sim/faults.hh"
64
65#if USE_CHECKER
66#include "cpu/checker/cpu.hh"
67#endif
68
69using namespace std;
70
71template <class Impl>
72DefaultCommit<Impl>::TrapEvent::TrapEvent(DefaultCommit<Impl> *_commit,
73                                          ThreadID _tid)
74    : Event(CPU_Tick_Pri, AutoDelete), commit(_commit), tid(_tid)
75{
76}
77
78template <class Impl>
79void
80DefaultCommit<Impl>::TrapEvent::process()
81{
82    // This will get reset by commit if it was switched out at the
83    // time of this event processing.
84    commit->trapSquash[tid] = true;
85}
86
87template <class Impl>
88const char *
89DefaultCommit<Impl>::TrapEvent::description() const
90{
91    return "Trap";
92}
93
94template <class Impl>
95DefaultCommit<Impl>::DefaultCommit(O3CPU *_cpu, DerivO3CPUParams *params)
96    : cpu(_cpu),
97      squashCounter(0),
98      iewToCommitDelay(params->iewToCommitDelay),
99      commitToIEWDelay(params->commitToIEWDelay),
100      renameToROBDelay(params->renameToROBDelay),
101      fetchToCommitDelay(params->commitToFetchDelay),
102      renameWidth(params->renameWidth),
103      commitWidth(params->commitWidth),
104      numThreads(params->numThreads),
105      drainPending(false),
106      switchedOut(false),
107      trapLatency(params->trapLatency)
108{
109    _status = Active;
110    _nextStatus = Inactive;
111    std::string policy = params->smtCommitPolicy;
112
113    //Convert string to lowercase
114    std::transform(policy.begin(), policy.end(), policy.begin(),
115                   (int(*)(int)) tolower);
116
117    //Assign commit policy
118    if (policy == "aggressive"){
119        commitPolicy = Aggressive;
120
121        DPRINTF(Commit,"Commit Policy set to Aggressive.\n");
122    } else if (policy == "roundrobin"){
123        commitPolicy = RoundRobin;
124
125        //Set-Up Priority List
126        for (ThreadID tid = 0; tid < numThreads; tid++) {
127            priority_list.push_back(tid);
128        }
129
130        DPRINTF(Commit,"Commit Policy set to Round Robin.\n");
131    } else if (policy == "oldestready"){
132        commitPolicy = OldestReady;
133
134        DPRINTF(Commit,"Commit Policy set to Oldest Ready.");
135    } else {
136        assert(0 && "Invalid SMT Commit Policy. Options Are: {Aggressive,"
137               "RoundRobin,OldestReady}");
138    }
139
140    for (ThreadID tid = 0; tid < numThreads; tid++) {
141        commitStatus[tid] = Idle;
142        changedROBNumEntries[tid] = false;
143        checkEmptyROB[tid] = false;
144        trapInFlight[tid] = false;
145        committedStores[tid] = false;
146        trapSquash[tid] = false;
147        tcSquash[tid] = false;
148        pc[tid].set(0);
149        lastCommitedSeqNum[tid] = 0;
150    }
151#if FULL_SYSTEM
152    interrupt = NoFault;
153#endif
154}
155
156template <class Impl>
157std::string
158DefaultCommit<Impl>::name() const
159{
160    return cpu->name() + ".commit";
161}
162
163template <class Impl>
164void
165DefaultCommit<Impl>::regStats()
166{
167    using namespace Stats;
168    commitCommittedInsts
169        .name(name() + ".commitCommittedInsts")
170        .desc("The number of committed instructions")
171        .prereq(commitCommittedInsts);
172    commitSquashedInsts
173        .name(name() + ".commitSquashedInsts")
174        .desc("The number of squashed insts skipped by commit")
175        .prereq(commitSquashedInsts);
176    commitSquashEvents
177        .name(name() + ".commitSquashEvents")
178        .desc("The number of times commit is told to squash")
179        .prereq(commitSquashEvents);
180    commitNonSpecStalls
181        .name(name() + ".commitNonSpecStalls")
182        .desc("The number of times commit has been forced to stall to "
183              "communicate backwards")
184        .prereq(commitNonSpecStalls);
185    branchMispredicts
186        .name(name() + ".branchMispredicts")
187        .desc("The number of times a branch was mispredicted")
188        .prereq(branchMispredicts);
189    numCommittedDist
190        .init(0,commitWidth,1)
191        .name(name() + ".committed_per_cycle")
192        .desc("Number of insts commited each cycle")
193        .flags(Stats::pdf)
194        ;
195
196    statComInst
197        .init(cpu->numThreads)
198        .name(name() + ".count")
199        .desc("Number of instructions committed")
200        .flags(total)
201        ;
202
203    statComSwp
204        .init(cpu->numThreads)
205        .name(name() + ".swp_count")
206        .desc("Number of s/w prefetches committed")
207        .flags(total)
208        ;
209
210    statComRefs
211        .init(cpu->numThreads)
212        .name(name() +  ".refs")
213        .desc("Number of memory references committed")
214        .flags(total)
215        ;
216
217    statComLoads
218        .init(cpu->numThreads)
219        .name(name() +  ".loads")
220        .desc("Number of loads committed")
221        .flags(total)
222        ;
223
224    statComMembars
225        .init(cpu->numThreads)
226        .name(name() +  ".membars")
227        .desc("Number of memory barriers committed")
228        .flags(total)
229        ;
230
231    statComBranches
232        .init(cpu->numThreads)
233        .name(name() + ".branches")
234        .desc("Number of branches committed")
235        .flags(total)
236        ;
237
238    statComFloating
239        .init(cpu->numThreads)
240        .name(name() + ".fp_insts")
241        .desc("Number of committed floating point instructions.")
242        .flags(total)
243        ;
244
245    statComInteger
246        .init(cpu->numThreads)
247        .name(name()+".int_insts")
248        .desc("Number of committed integer instructions.")
249        .flags(total)
250        ;
251
252    statComFunctionCalls
253        .init(cpu->numThreads)
254        .name(name()+".function_calls")
255        .desc("Number of function calls committed.")
256        .flags(total)
257        ;
258
259    commitEligible
260        .init(cpu->numThreads)
261        .name(name() + ".bw_limited")
262        .desc("number of insts not committed due to BW limits")
263        .flags(total)
264        ;
265
266    commitEligibleSamples
267        .name(name() + ".bw_lim_events")
268        .desc("number cycles where commit BW limit reached")
269        ;
270}
271
272template <class Impl>
273void
274DefaultCommit<Impl>::setThreads(std::vector<Thread *> &threads)
275{
276    thread = threads;
277}
278
279template <class Impl>
280void
281DefaultCommit<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr)
282{
283    timeBuffer = tb_ptr;
284
285    // Setup wire to send information back to IEW.
286    toIEW = timeBuffer->getWire(0);
287
288    // Setup wire to read data from IEW (for the ROB).
289    robInfoFromIEW = timeBuffer->getWire(-iewToCommitDelay);
290}
291
292template <class Impl>
293void
294DefaultCommit<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr)
295{
296    fetchQueue = fq_ptr;
297
298    // Setup wire to get instructions from rename (for the ROB).
299    fromFetch = fetchQueue->getWire(-fetchToCommitDelay);
300}
301
302template <class Impl>
303void
304DefaultCommit<Impl>::setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr)
305{
306    renameQueue = rq_ptr;
307
308    // Setup wire to get instructions from rename (for the ROB).
309    fromRename = renameQueue->getWire(-renameToROBDelay);
310}
311
312template <class Impl>
313void
314DefaultCommit<Impl>::setIEWQueue(TimeBuffer<IEWStruct> *iq_ptr)
315{
316    iewQueue = iq_ptr;
317
318    // Setup wire to get instructions from IEW.
319    fromIEW = iewQueue->getWire(-iewToCommitDelay);
320}
321
322template <class Impl>
323void
324DefaultCommit<Impl>::setIEWStage(IEW *iew_stage)
325{
326    iewStage = iew_stage;
327}
328
329template<class Impl>
330void
331DefaultCommit<Impl>::setActiveThreads(list<ThreadID> *at_ptr)
332{
333    activeThreads = at_ptr;
334}
335
336template <class Impl>
337void
338DefaultCommit<Impl>::setRenameMap(RenameMap rm_ptr[])
339{
340    for (ThreadID tid = 0; tid < numThreads; tid++)
341        renameMap[tid] = &rm_ptr[tid];
342}
343
344template <class Impl>
345void
346DefaultCommit<Impl>::setROB(ROB *rob_ptr)
347{
348    rob = rob_ptr;
349}
350
351template <class Impl>
352void
353DefaultCommit<Impl>::initStage()
354{
355    rob->setActiveThreads(activeThreads);
356    rob->resetEntries();
357
358    // Broadcast the number of free entries.
359    for (ThreadID tid = 0; tid < numThreads; tid++) {
360        toIEW->commitInfo[tid].usedROB = true;
361        toIEW->commitInfo[tid].freeROBEntries = rob->numFreeEntries(tid);
362        toIEW->commitInfo[tid].emptyROB = true;
363    }
364
365    // Commit must broadcast the number of free entries it has at the
366    // start of the simulation, so it starts as active.
367    cpu->activateStage(O3CPU::CommitIdx);
368
369    cpu->activityThisCycle();
370    trapLatency = cpu->ticks(trapLatency);
371}
372
373template <class Impl>
374bool
375DefaultCommit<Impl>::drain()
376{
377    drainPending = true;
378
379    return false;
380}
381
382template <class Impl>
383void
384DefaultCommit<Impl>::switchOut()
385{
386    switchedOut = true;
387    drainPending = false;
388    rob->switchOut();
389}
390
391template <class Impl>
392void
393DefaultCommit<Impl>::resume()
394{
395    drainPending = false;
396}
397
398template <class Impl>
399void
400DefaultCommit<Impl>::takeOverFrom()
401{
402    switchedOut = false;
403    _status = Active;
404    _nextStatus = Inactive;
405    for (ThreadID tid = 0; tid < numThreads; tid++) {
406        commitStatus[tid] = Idle;
407        changedROBNumEntries[tid] = false;
408        trapSquash[tid] = false;
409        tcSquash[tid] = false;
410    }
411    squashCounter = 0;
412    rob->takeOverFrom();
413}
414
415template <class Impl>
416void
417DefaultCommit<Impl>::updateStatus()
418{
419    // reset ROB changed variable
420    list<ThreadID>::iterator threads = activeThreads->begin();
421    list<ThreadID>::iterator end = activeThreads->end();
422
423    while (threads != end) {
424        ThreadID tid = *threads++;
425
426        changedROBNumEntries[tid] = false;
427
428        // Also check if any of the threads has a trap pending
429        if (commitStatus[tid] == TrapPending ||
430            commitStatus[tid] == FetchTrapPending) {
431            _nextStatus = Active;
432        }
433    }
434
435    if (_nextStatus == Inactive && _status == Active) {
436        DPRINTF(Activity, "Deactivating stage.\n");
437        cpu->deactivateStage(O3CPU::CommitIdx);
438    } else if (_nextStatus == Active && _status == Inactive) {
439        DPRINTF(Activity, "Activating stage.\n");
440        cpu->activateStage(O3CPU::CommitIdx);
441    }
442
443    _status = _nextStatus;
444}
445
446template <class Impl>
447void
448DefaultCommit<Impl>::setNextStatus()
449{
450    int squashes = 0;
451
452    list<ThreadID>::iterator threads = activeThreads->begin();
453    list<ThreadID>::iterator end = activeThreads->end();
454
455    while (threads != end) {
456        ThreadID tid = *threads++;
457
458        if (commitStatus[tid] == ROBSquashing) {
459            squashes++;
460        }
461    }
462
463    squashCounter = squashes;
464
465    // If commit is currently squashing, then it will have activity for the
466    // next cycle. Set its next status as active.
467    if (squashCounter) {
468        _nextStatus = Active;
469    }
470}
471
472template <class Impl>
473bool
474DefaultCommit<Impl>::changedROBEntries()
475{
476    list<ThreadID>::iterator threads = activeThreads->begin();
477    list<ThreadID>::iterator end = activeThreads->end();
478
479    while (threads != end) {
480        ThreadID tid = *threads++;
481
482        if (changedROBNumEntries[tid]) {
483            return true;
484        }
485    }
486
487    return false;
488}
489
490template <class Impl>
491size_t
492DefaultCommit<Impl>::numROBFreeEntries(ThreadID tid)
493{
494    return rob->numFreeEntries(tid);
495}
496
497template <class Impl>
498void
499DefaultCommit<Impl>::generateTrapEvent(ThreadID tid)
500{
501    DPRINTF(Commit, "Generating trap event for [tid:%i]\n", tid);
502
503    TrapEvent *trap = new TrapEvent(this, tid);
504
505    cpu->schedule(trap, curTick() + trapLatency);
506    trapInFlight[tid] = true;
507    thread[tid]->trapPending = true;
508}
509
510template <class Impl>
511void
512DefaultCommit<Impl>::generateTCEvent(ThreadID tid)
513{
514    assert(!trapInFlight[tid]);
515    DPRINTF(Commit, "Generating TC squash event for [tid:%i]\n", tid);
516
517    tcSquash[tid] = true;
518}
519
520template <class Impl>
521void
522DefaultCommit<Impl>::squashAll(ThreadID tid)
523{
524    // If we want to include the squashing instruction in the squash,
525    // then use one older sequence number.
526    // Hopefully this doesn't mess things up.  Basically I want to squash
527    // all instructions of this thread.
528    InstSeqNum squashed_inst = rob->isEmpty() ?
529        lastCommitedSeqNum[tid] : rob->readHeadInst(tid)->seqNum - 1;
530
531    // All younger instructions will be squashed. Set the sequence
532    // number as the youngest instruction in the ROB (0 in this case.
533    // Hopefully nothing breaks.)
534    youngestSeqNum[tid] = lastCommitedSeqNum[tid];
535
536    rob->squash(squashed_inst, tid);
537    changedROBNumEntries[tid] = true;
538
539    // Send back the sequence number of the squashed instruction.
540    toIEW->commitInfo[tid].doneSeqNum = squashed_inst;
541
542    // Send back the squash signal to tell stages that they should
543    // squash.
544    toIEW->commitInfo[tid].squash = true;
545
546    // Send back the rob squashing signal so other stages know that
547    // the ROB is in the process of squashing.
548    toIEW->commitInfo[tid].robSquashing = true;
549
550    toIEW->commitInfo[tid].mispredictInst = NULL;
551    toIEW->commitInfo[tid].squashInst = NULL;
552
553    toIEW->commitInfo[tid].pc = pc[tid];
554}
555
556template <class Impl>
557void
558DefaultCommit<Impl>::squashFromTrap(ThreadID tid)
559{
560    squashAll(tid);
561
562    DPRINTF(Commit, "Squashing from trap, restarting at PC %s\n", pc[tid]);
563
564    thread[tid]->trapPending = false;
565    thread[tid]->inSyscall = false;
566    trapInFlight[tid] = false;
567
568    trapSquash[tid] = false;
569
570    commitStatus[tid] = ROBSquashing;
571    cpu->activityThisCycle();
572}
573
574template <class Impl>
575void
576DefaultCommit<Impl>::squashFromTC(ThreadID tid)
577{
578    squashAll(tid);
579
580    DPRINTF(Commit, "Squashing from TC, restarting at PC %s\n", pc[tid]);
581
582    thread[tid]->inSyscall = false;
583    assert(!thread[tid]->trapPending);
584
585    commitStatus[tid] = ROBSquashing;
586    cpu->activityThisCycle();
587
588    tcSquash[tid] = false;
589}
590
591template <class Impl>
592void
593DefaultCommit<Impl>::squashAfter(ThreadID tid, DynInstPtr &head_inst,
594        uint64_t squash_after_seq_num)
595{
596    youngestSeqNum[tid] = squash_after_seq_num;
597
598    rob->squash(squash_after_seq_num, tid);
599    changedROBNumEntries[tid] = true;
600
601    // Send back the sequence number of the squashed instruction.
602    toIEW->commitInfo[tid].doneSeqNum = squash_after_seq_num;
603
604    toIEW->commitInfo[tid].squashInst = head_inst;
605    // Send back the squash signal to tell stages that they should squash.
606    toIEW->commitInfo[tid].squash = true;
607
608    // Send back the rob squashing signal so other stages know that
609    // the ROB is in the process of squashing.
610    toIEW->commitInfo[tid].robSquashing = true;
611
612    toIEW->commitInfo[tid].mispredictInst = NULL;
613
614    toIEW->commitInfo[tid].pc = pc[tid];
615    DPRINTF(Commit, "Executing squash after for [tid:%i] inst [sn:%lli]\n",
616            tid, squash_after_seq_num);
617    commitStatus[tid] = ROBSquashing;
618}
619
620template <class Impl>
621void
622DefaultCommit<Impl>::tick()
623{
624    wroteToTimeBuffer = false;
625    _nextStatus = Inactive;
626
627    if (drainPending && rob->isEmpty() && !iewStage->hasStoresToWB()) {
628        cpu->signalDrained();
629        drainPending = false;
630        return;
631    }
632
633    if (activeThreads->empty())
634        return;
635
636    list<ThreadID>::iterator threads = activeThreads->begin();
637    list<ThreadID>::iterator end = activeThreads->end();
638
639    // Check if any of the threads are done squashing.  Change the
640    // status if they are done.
641    while (threads != end) {
642        ThreadID tid = *threads++;
643
644        // Clear the bit saying if the thread has committed stores
645        // this cycle.
646        committedStores[tid] = false;
647
648        if (commitStatus[tid] == ROBSquashing) {
649
650            if (rob->isDoneSquashing(tid)) {
651                commitStatus[tid] = Running;
652            } else {
653                DPRINTF(Commit,"[tid:%u]: Still Squashing, cannot commit any"
654                        " insts this cycle.\n", tid);
655                rob->doSquash(tid);
656                toIEW->commitInfo[tid].robSquashing = true;
657                wroteToTimeBuffer = true;
658            }
659        }
660    }
661
662    commit();
663
664    markCompletedInsts();
665
666    threads = activeThreads->begin();
667
668    while (threads != end) {
669        ThreadID tid = *threads++;
670
671        if (!rob->isEmpty(tid) && rob->readHeadInst(tid)->readyToCommit()) {
672            // The ROB has more instructions it can commit. Its next status
673            // will be active.
674            _nextStatus = Active;
675
676            DynInstPtr inst = rob->readHeadInst(tid);
677
678            DPRINTF(Commit,"[tid:%i]: Instruction [sn:%lli] PC %s is head of"
679                    " ROB and ready to commit\n",
680                    tid, inst->seqNum, inst->pcState());
681
682        } else if (!rob->isEmpty(tid)) {
683            DynInstPtr inst = rob->readHeadInst(tid);
684
685            DPRINTF(Commit,"[tid:%i]: Can't commit, Instruction [sn:%lli] PC "
686                    "%s is head of ROB and not ready\n",
687                    tid, inst->seqNum, inst->pcState());
688        }
689
690        DPRINTF(Commit, "[tid:%i]: ROB has %d insts & %d free entries.\n",
691                tid, rob->countInsts(tid), rob->numFreeEntries(tid));
692    }
693
694
695    if (wroteToTimeBuffer) {
696        DPRINTF(Activity, "Activity This Cycle.\n");
697        cpu->activityThisCycle();
698    }
699
700    updateStatus();
701}
702
703#if FULL_SYSTEM
704template <class Impl>
705void
706DefaultCommit<Impl>::handleInterrupt()
707{
708    // Verify that we still have an interrupt to handle
709    if (!cpu->checkInterrupts(cpu->tcBase(0))) {
710        DPRINTF(Commit, "Pending interrupt is cleared by master before "
711                "it got handled. Restart fetching from the orig path.\n");
712        toIEW->commitInfo[0].clearInterrupt = true;
713        interrupt = NoFault;
714        return;
715    }
716
717    // Wait until all in flight instructions are finished before enterring
718    // the interrupt.
719    if (cpu->instList.empty()) {
720        // Squash or record that I need to squash this cycle if
721        // an interrupt needed to be handled.
722        DPRINTF(Commit, "Interrupt detected.\n");
723
724        // Clear the interrupt now that it's going to be handled
725        toIEW->commitInfo[0].clearInterrupt = true;
726
727        assert(!thread[0]->inSyscall);
728        thread[0]->inSyscall = true;
729
730        // CPU will handle interrupt.
731        cpu->processInterrupts(interrupt);
732
733        thread[0]->inSyscall = false;
734
735        commitStatus[0] = TrapPending;
736
737        // Generate trap squash event.
738        generateTrapEvent(0);
739
740        interrupt = NoFault;
741    } else {
742        DPRINTF(Commit, "Interrupt pending, waiting for ROB to empty.\n");
743    }
744}
745
746template <class Impl>
747void
748DefaultCommit<Impl>::propagateInterrupt()
749{
750    if (commitStatus[0] == TrapPending || interrupt || trapSquash[0] ||
751            tcSquash[0])
752        return;
753
754    // Process interrupts if interrupts are enabled, not in PAL
755    // mode, and no other traps or external squashes are currently
756    // pending.
757    // @todo: Allow other threads to handle interrupts.
758
759    // Get any interrupt that happened
760    interrupt = cpu->getInterrupts();
761
762    // Tell fetch that there is an interrupt pending.  This
763    // will make fetch wait until it sees a non PAL-mode PC,
764    // at which point it stops fetching instructions.
765    if (interrupt != NoFault)
766        toIEW->commitInfo[0].interruptPending = true;
767}
768
769#endif // FULL_SYSTEM
770
771template <class Impl>
772void
773DefaultCommit<Impl>::commit()
774{
775
776#if FULL_SYSTEM
777    // Check for any interrupt that we've already squashed for and start processing it.
778    if (interrupt != NoFault)
779        handleInterrupt();
780
781    // Check if we have a interrupt and get read to handle it
782    if (cpu->checkInterrupts(cpu->tcBase(0)))
783        propagateInterrupt();
784#endif // FULL_SYSTEM
785
786    ////////////////////////////////////
787    // Check for any possible squashes, handle them first
788    ////////////////////////////////////
789    list<ThreadID>::iterator threads = activeThreads->begin();
790    list<ThreadID>::iterator end = activeThreads->end();
791
792    while (threads != end) {
793        ThreadID tid = *threads++;
794
795        // Not sure which one takes priority.  I think if we have
796        // both, that's a bad sign.
797        if (trapSquash[tid] == true) {
798            assert(!tcSquash[tid]);
799            squashFromTrap(tid);
800        } else if (tcSquash[tid] == true) {
801            assert(commitStatus[tid] != TrapPending);
802            squashFromTC(tid);
803        }
804
805        // Squashed sequence number must be older than youngest valid
806        // instruction in the ROB. This prevents squashes from younger
807        // instructions overriding squashes from older instructions.
808        if (fromIEW->squash[tid] &&
809            commitStatus[tid] != TrapPending &&
810            fromIEW->squashedSeqNum[tid] <= youngestSeqNum[tid]) {
811
812            if (fromIEW->mispredictInst[tid]) {
813                DPRINTF(Commit,
814                    "[tid:%i]: Squashing due to branch mispred PC:%#x [sn:%i]\n",
815                    tid,
816                    fromIEW->mispredictInst[tid]->instAddr(),
817                    fromIEW->squashedSeqNum[tid]);
818            } else {
819                DPRINTF(Commit,
820                    "[tid:%i]: Squashing due to order violation [sn:%i]\n",
821                    tid, fromIEW->squashedSeqNum[tid]);
822            }
823
824            DPRINTF(Commit, "[tid:%i]: Redirecting to PC %#x\n",
825                    tid,
826                    fromIEW->pc[tid].nextInstAddr());
827
828            commitStatus[tid] = ROBSquashing;
829
830            // If we want to include the squashing instruction in the squash,
831            // then use one older sequence number.
832            InstSeqNum squashed_inst = fromIEW->squashedSeqNum[tid];
833
834            if (fromIEW->includeSquashInst[tid] == true) {
835                squashed_inst--;
836            }
837
838            // All younger instructions will be squashed. Set the sequence
839            // number as the youngest instruction in the ROB.
840            youngestSeqNum[tid] = squashed_inst;
841
842            rob->squash(squashed_inst, tid);
843            changedROBNumEntries[tid] = true;
844
845            toIEW->commitInfo[tid].doneSeqNum = squashed_inst;
846
847            toIEW->commitInfo[tid].squash = true;
848
849            // Send back the rob squashing signal so other stages know that
850            // the ROB is in the process of squashing.
851            toIEW->commitInfo[tid].robSquashing = true;
852
853            toIEW->commitInfo[tid].mispredictInst =
854                fromIEW->mispredictInst[tid];
855            toIEW->commitInfo[tid].branchTaken =
856                fromIEW->branchTaken[tid];
857            toIEW->commitInfo[tid].squashInst = NULL;
858
859            toIEW->commitInfo[tid].pc = fromIEW->pc[tid];
860
861            if (toIEW->commitInfo[tid].mispredictInst) {
862                ++branchMispredicts;
863            }
864        }
865
866    }
867
868    setNextStatus();
869
870    if (squashCounter != numThreads) {
871        // If we're not currently squashing, then get instructions.
872        getInsts();
873
874        // Try to commit any instructions.
875        commitInsts();
876    }
877
878    //Check for any activity
879    threads = activeThreads->begin();
880
881    while (threads != end) {
882        ThreadID tid = *threads++;
883
884        if (changedROBNumEntries[tid]) {
885            toIEW->commitInfo[tid].usedROB = true;
886            toIEW->commitInfo[tid].freeROBEntries = rob->numFreeEntries(tid);
887
888            wroteToTimeBuffer = true;
889            changedROBNumEntries[tid] = false;
890            if (rob->isEmpty(tid))
891                checkEmptyROB[tid] = true;
892        }
893
894        // ROB is only considered "empty" for previous stages if: a)
895        // ROB is empty, b) there are no outstanding stores, c) IEW
896        // stage has received any information regarding stores that
897        // committed.
898        // c) is checked by making sure to not consider the ROB empty
899        // on the same cycle as when stores have been committed.
900        // @todo: Make this handle multi-cycle communication between
901        // commit and IEW.
902        if (checkEmptyROB[tid] && rob->isEmpty(tid) &&
903            !iewStage->hasStoresToWB(tid) && !committedStores[tid]) {
904            checkEmptyROB[tid] = false;
905            toIEW->commitInfo[tid].usedROB = true;
906            toIEW->commitInfo[tid].emptyROB = true;
907            toIEW->commitInfo[tid].freeROBEntries = rob->numFreeEntries(tid);
908            wroteToTimeBuffer = true;
909        }
910
911    }
912}
913
914template <class Impl>
915void
916DefaultCommit<Impl>::commitInsts()
917{
918    ////////////////////////////////////
919    // Handle commit
920    // Note that commit will be handled prior to putting new
921    // instructions in the ROB so that the ROB only tries to commit
922    // instructions it has in this current cycle, and not instructions
923    // it is writing in during this cycle.  Can't commit and squash
924    // things at the same time...
925    ////////////////////////////////////
926
927    DPRINTF(Commit, "Trying to commit instructions in the ROB.\n");
928
929    unsigned num_committed = 0;
930
931    DynInstPtr head_inst;
932
933    // Commit as many instructions as possible until the commit bandwidth
934    // limit is reached, or it becomes impossible to commit any more.
935    while (num_committed < commitWidth) {
936        int commit_thread = getCommittingThread();
937
938        if (commit_thread == -1 || !rob->isHeadReady(commit_thread))
939            break;
940
941        head_inst = rob->readHeadInst(commit_thread);
942
943        ThreadID tid = head_inst->threadNumber;
944
945        assert(tid == commit_thread);
946
947        DPRINTF(Commit, "Trying to commit head instruction, [sn:%i] [tid:%i]\n",
948                head_inst->seqNum, tid);
949
950        // If the head instruction is squashed, it is ready to retire
951        // (be removed from the ROB) at any time.
952        if (head_inst->isSquashed()) {
953
954            DPRINTF(Commit, "Retiring squashed instruction from "
955                    "ROB.\n");
956
957            rob->retireHead(commit_thread);
958
959            ++commitSquashedInsts;
960
961            // Record that the number of ROB entries has changed.
962            changedROBNumEntries[tid] = true;
963        } else {
964            pc[tid] = head_inst->pcState();
965
966            // Increment the total number of non-speculative instructions
967            // executed.
968            // Hack for now: it really shouldn't happen until after the
969            // commit is deemed to be successful, but this count is needed
970            // for syscalls.
971            thread[tid]->funcExeInst++;
972
973            // Try to commit the head instruction.
974            bool commit_success = commitHead(head_inst, num_committed);
975
976            if (commit_success) {
977                ++num_committed;
978
979                changedROBNumEntries[tid] = true;
980
981                // Set the doneSeqNum to the youngest committed instruction.
982                toIEW->commitInfo[tid].doneSeqNum = head_inst->seqNum;
983
984                ++commitCommittedInsts;
985
986                // To match the old model, don't count nops and instruction
987                // prefetches towards the total commit count.
988                if (!head_inst->isNop() && !head_inst->isInstPrefetch()) {
989                    cpu->instDone(tid);
990                }
991
992                // Updates misc. registers.
993                head_inst->updateMiscRegs();
994
995                TheISA::advancePC(pc[tid], head_inst->staticInst);
996
997                // Keep track of the last sequence number commited
998                lastCommitedSeqNum[tid] = head_inst->seqNum;
999
1000                // If this is an instruction that doesn't play nicely with
1001                // others squash everything and restart fetch
1002                if (head_inst->isSquashAfter())
1003                    squashAfter(tid, head_inst, head_inst->seqNum);
1004
1005                int count = 0;
1006                Addr oldpc;
1007                // Debug statement.  Checks to make sure we're not
1008                // currently updating state while handling PC events.
1009                assert(!thread[tid]->inSyscall && !thread[tid]->trapPending);
1010                do {
1011                    oldpc = pc[tid].instAddr();
1012                    cpu->system->pcEventQueue.service(thread[tid]->getTC());
1013                    count++;
1014                } while (oldpc != pc[tid].instAddr());
1015                if (count > 1) {
1016                    DPRINTF(Commit,
1017                            "PC skip function event, stopping commit\n");
1018                    break;
1019                }
1020            } else {
1021                DPRINTF(Commit, "Unable to commit head instruction PC:%s "
1022                        "[tid:%i] [sn:%i].\n",
1023                        head_inst->pcState(), tid ,head_inst->seqNum);
1024                break;
1025            }
1026        }
1027    }
1028
1029    DPRINTF(CommitRate, "%i\n", num_committed);
1030    numCommittedDist.sample(num_committed);
1031
1032    if (num_committed == commitWidth) {
1033        commitEligibleSamples++;
1034    }
1035}
1036
1037template <class Impl>
1038bool
1039DefaultCommit<Impl>::commitHead(DynInstPtr &head_inst, unsigned inst_num)
1040{
1041    assert(head_inst);
1042
1043    ThreadID tid = head_inst->threadNumber;
1044
1045    // If the instruction is not executed yet, then it will need extra
1046    // handling.  Signal backwards that it should be executed.
1047    if (!head_inst->isExecuted()) {
1048        // Keep this number correct.  We have not yet actually executed
1049        // and committed this instruction.
1050        thread[tid]->funcExeInst--;
1051
1052        if (head_inst->isNonSpeculative() ||
1053            head_inst->isStoreConditional() ||
1054            head_inst->isMemBarrier() ||
1055            head_inst->isWriteBarrier()) {
1056
1057            DPRINTF(Commit, "Encountered a barrier or non-speculative "
1058                    "instruction [sn:%lli] at the head of the ROB, PC %s.\n",
1059                    head_inst->seqNum, head_inst->pcState());
1060
1061            if (inst_num > 0 || iewStage->hasStoresToWB(tid)) {
1062                DPRINTF(Commit, "Waiting for all stores to writeback.\n");
1063                return false;
1064            }
1065
1066            toIEW->commitInfo[tid].nonSpecSeqNum = head_inst->seqNum;
1067
1068            // Change the instruction so it won't try to commit again until
1069            // it is executed.
1070            head_inst->clearCanCommit();
1071
1072            ++commitNonSpecStalls;
1073
1074            return false;
1075        } else if (head_inst->isLoad()) {
1076            if (inst_num > 0 || iewStage->hasStoresToWB(tid)) {
1077                DPRINTF(Commit, "Waiting for all stores to writeback.\n");
1078                return false;
1079            }
1080
1081            assert(head_inst->uncacheable());
1082            DPRINTF(Commit, "[sn:%lli]: Uncached load, PC %s.\n",
1083                    head_inst->seqNum, head_inst->pcState());
1084
1085            // Send back the non-speculative instruction's sequence
1086            // number.  Tell the lsq to re-execute the load.
1087            toIEW->commitInfo[tid].nonSpecSeqNum = head_inst->seqNum;
1088            toIEW->commitInfo[tid].uncached = true;
1089            toIEW->commitInfo[tid].uncachedLoad = head_inst;
1090
1091            head_inst->clearCanCommit();
1092
1093            return false;
1094        } else {
1095            panic("Trying to commit un-executed instruction "
1096                  "of unknown type!\n");
1097        }
1098    }
1099
1100    if (head_inst->isThreadSync()) {
1101        // Not handled for now.
1102        panic("Thread sync instructions are not handled yet.\n");
1103    }
1104
1105    // Check if the instruction caused a fault.  If so, trap.
1106    Fault inst_fault = head_inst->getFault();
1107
1108    // Stores mark themselves as completed.
1109    if (!head_inst->isStore() && inst_fault == NoFault) {
1110        head_inst->setCompleted();
1111    }
1112
1113#if USE_CHECKER
1114    // Use checker prior to updating anything due to traps or PC
1115    // based events.
1116    if (cpu->checker) {
1117        cpu->checker->verify(head_inst);
1118    }
1119#endif
1120
1121    if (inst_fault != NoFault) {
1122        DPRINTF(Commit, "Inst [sn:%lli] PC %s has a fault\n",
1123                head_inst->seqNum, head_inst->pcState());
1124
1125        if (iewStage->hasStoresToWB(tid) || inst_num > 0) {
1126            DPRINTF(Commit, "Stores outstanding, fault must wait.\n");
1127            return false;
1128        }
1129
1130        head_inst->setCompleted();
1131
1132#if USE_CHECKER
1133        if (cpu->checker && head_inst->isStore()) {
1134            cpu->checker->verify(head_inst);
1135        }
1136#endif
1137
1138        assert(!thread[tid]->inSyscall);
1139
1140        // Mark that we're in state update mode so that the trap's
1141        // execution doesn't generate extra squashes.
1142        thread[tid]->inSyscall = true;
1143
1144        // Execute the trap.  Although it's slightly unrealistic in
1145        // terms of timing (as it doesn't wait for the full timing of
1146        // the trap event to complete before updating state), it's
1147        // needed to update the state as soon as possible.  This
1148        // prevents external agents from changing any specific state
1149        // that the trap need.
1150        cpu->trap(inst_fault, tid, head_inst->staticInst);
1151
1152        // Exit state update mode to avoid accidental updating.
1153        thread[tid]->inSyscall = false;
1154
1155        commitStatus[tid] = TrapPending;
1156
1157        DPRINTF(Commit, "Committing instruction with fault [sn:%lli]\n",
1158            head_inst->seqNum);
1159        if (head_inst->traceData) {
1160            if (DTRACE(ExecFaulting)) {
1161                head_inst->traceData->setFetchSeq(head_inst->seqNum);
1162                head_inst->traceData->setCPSeq(thread[tid]->numInst);
1163                head_inst->traceData->dump();
1164            }
1165            delete head_inst->traceData;
1166            head_inst->traceData = NULL;
1167        }
1168
1169        // Generate trap squash event.
1170        generateTrapEvent(tid);
1171        return false;
1172    }
1173
1174    updateComInstStats(head_inst);
1175
1176#if FULL_SYSTEM
1177    if (thread[tid]->profile) {
1178        thread[tid]->profilePC = head_inst->instAddr();
1179        ProfileNode *node = thread[tid]->profile->consume(thread[tid]->getTC(),
1180                                                          head_inst->staticInst);
1181
1182        if (node)
1183            thread[tid]->profileNode = node;
1184    }
1185    if (CPA::available()) {
1186        if (head_inst->isControl()) {
1187            ThreadContext *tc = thread[tid]->getTC();
1188            CPA::cpa()->swAutoBegin(tc, head_inst->nextInstAddr());
1189        }
1190    }
1191#endif
1192    DPRINTF(Commit, "Committing instruction with [sn:%lli] PC %s\n",
1193            head_inst->seqNum, head_inst->pcState());
1194    if (head_inst->traceData) {
1195        head_inst->traceData->setFetchSeq(head_inst->seqNum);
1196        head_inst->traceData->setCPSeq(thread[tid]->numInst);
1197        head_inst->traceData->dump();
1198        delete head_inst->traceData;
1199        head_inst->traceData = NULL;
1200    }
1201
1202    // Update the commit rename map
1203    for (int i = 0; i < head_inst->numDestRegs(); i++) {
1204        renameMap[tid]->setEntry(head_inst->flattenedDestRegIdx(i),
1205                                 head_inst->renamedDestRegIdx(i));
1206    }
1207
1208    // Finally clear the head ROB entry.
1209    rob->retireHead(tid);
1210
1211#if TRACING_ON
1212    // Print info needed by the pipeline activity viewer.
1213    DPRINTFR(O3PipeView, "O3PipeView:fetch:%llu:0x%08llx:%d:%llu:%s\n",
1214             head_inst->fetchTick,
1215             head_inst->instAddr(),
1216             head_inst->microPC(),
1217             head_inst->seqNum,
1218             head_inst->staticInst->disassemble(head_inst->instAddr()));
1219    DPRINTFR(O3PipeView, "O3PipeView:decode:%llu\n", head_inst->decodeTick);
1220    DPRINTFR(O3PipeView, "O3PipeView:rename:%llu\n", head_inst->renameTick);
1221    DPRINTFR(O3PipeView, "O3PipeView:dispatch:%llu\n", head_inst->dispatchTick);
1222    DPRINTFR(O3PipeView, "O3PipeView:issue:%llu\n", head_inst->issueTick);
1223    DPRINTFR(O3PipeView, "O3PipeView:complete:%llu\n", head_inst->completeTick);
1224    DPRINTFR(O3PipeView, "O3PipeView:retire:%llu\n", curTick());
1225#endif
1226
1227    // If this was a store, record it for this cycle.
1228    if (head_inst->isStore())
1229        committedStores[tid] = true;
1230
1231    // Return true to indicate that we have committed an instruction.
1232    return true;
1233}
1234
1235template <class Impl>
1236void
1237DefaultCommit<Impl>::getInsts()
1238{
1239    DPRINTF(Commit, "Getting instructions from Rename stage.\n");
1240
1241    // Read any renamed instructions and place them into the ROB.
1242    int insts_to_process = std::min((int)renameWidth, fromRename->size);
1243
1244    for (int inst_num = 0; inst_num < insts_to_process; ++inst_num) {
1245        DynInstPtr inst;
1246
1247        inst = fromRename->insts[inst_num];
1248        ThreadID tid = inst->threadNumber;
1249
1250        if (!inst->isSquashed() &&
1251            commitStatus[tid] != ROBSquashing &&
1252            commitStatus[tid] != TrapPending) {
1253            changedROBNumEntries[tid] = true;
1254
1255            DPRINTF(Commit, "Inserting PC %s [sn:%i] [tid:%i] into ROB.\n",
1256                    inst->pcState(), inst->seqNum, tid);
1257
1258            rob->insertInst(inst);
1259
1260            assert(rob->getThreadEntries(tid) <= rob->getMaxEntries(tid));
1261
1262            youngestSeqNum[tid] = inst->seqNum;
1263        } else {
1264            DPRINTF(Commit, "Instruction PC %s [sn:%i] [tid:%i] was "
1265                    "squashed, skipping.\n",
1266                    inst->pcState(), inst->seqNum, tid);
1267        }
1268    }
1269}
1270
1271template <class Impl>
1272void
1273DefaultCommit<Impl>::skidInsert()
1274{
1275    DPRINTF(Commit, "Attempting to any instructions from rename into "
1276            "skidBuffer.\n");
1277
1278    for (int inst_num = 0; inst_num < fromRename->size; ++inst_num) {
1279        DynInstPtr inst = fromRename->insts[inst_num];
1280
1281        if (!inst->isSquashed()) {
1282            DPRINTF(Commit, "Inserting PC %s [sn:%i] [tid:%i] into ",
1283                    "skidBuffer.\n", inst->pcState(), inst->seqNum,
1284                    inst->threadNumber);
1285            skidBuffer.push(inst);
1286        } else {
1287            DPRINTF(Commit, "Instruction PC %s [sn:%i] [tid:%i] was "
1288                    "squashed, skipping.\n",
1289                    inst->pcState(), inst->seqNum, inst->threadNumber);
1290        }
1291    }
1292}
1293
1294template <class Impl>
1295void
1296DefaultCommit<Impl>::markCompletedInsts()
1297{
1298    // Grab completed insts out of the IEW instruction queue, and mark
1299    // instructions completed within the ROB.
1300    for (int inst_num = 0;
1301         inst_num < fromIEW->size && fromIEW->insts[inst_num];
1302         ++inst_num)
1303    {
1304        if (!fromIEW->insts[inst_num]->isSquashed()) {
1305            DPRINTF(Commit, "[tid:%i]: Marking PC %s, [sn:%lli] ready "
1306                    "within ROB.\n",
1307                    fromIEW->insts[inst_num]->threadNumber,
1308                    fromIEW->insts[inst_num]->pcState(),
1309                    fromIEW->insts[inst_num]->seqNum);
1310
1311            // Mark the instruction as ready to commit.
1312            fromIEW->insts[inst_num]->setCanCommit();
1313        }
1314    }
1315}
1316
1317template <class Impl>
1318bool
1319DefaultCommit<Impl>::robDoneSquashing()
1320{
1321    list<ThreadID>::iterator threads = activeThreads->begin();
1322    list<ThreadID>::iterator end = activeThreads->end();
1323
1324    while (threads != end) {
1325        ThreadID tid = *threads++;
1326
1327        if (!rob->isDoneSquashing(tid))
1328            return false;
1329    }
1330
1331    return true;
1332}
1333
1334template <class Impl>
1335void
1336DefaultCommit<Impl>::updateComInstStats(DynInstPtr &inst)
1337{
1338    ThreadID tid = inst->threadNumber;
1339
1340    //
1341    //  Pick off the software prefetches
1342    //
1343#ifdef TARGET_ALPHA
1344    if (inst->isDataPrefetch()) {
1345        statComSwp[tid]++;
1346    } else {
1347        statComInst[tid]++;
1348    }
1349#else
1350    statComInst[tid]++;
1351#endif
1352
1353    //
1354    //  Control Instructions
1355    //
1356    if (inst->isControl())
1357        statComBranches[tid]++;
1358
1359    //
1360    //  Memory references
1361    //
1362    if (inst->isMemRef()) {
1363        statComRefs[tid]++;
1364
1365        if (inst->isLoad()) {
1366            statComLoads[tid]++;
1367        }
1368    }
1369
1370    if (inst->isMemBarrier()) {
1371        statComMembars[tid]++;
1372    }
1373
1374    // Integer Instruction
1375    if (inst->isInteger())
1376        statComInteger[tid]++;
1377
1378    // Floating Point Instruction
1379    if (inst->isFloating())
1380        statComFloating[tid]++;
1381
1382    // Function Calls
1383    if (inst->isCall())
1384        statComFunctionCalls[tid]++;
1385
1386}
1387
1388////////////////////////////////////////
1389//                                    //
1390//  SMT COMMIT POLICY MAINTAINED HERE //
1391//                                    //
1392////////////////////////////////////////
1393template <class Impl>
1394ThreadID
1395DefaultCommit<Impl>::getCommittingThread()
1396{
1397    if (numThreads > 1) {
1398        switch (commitPolicy) {
1399
1400          case Aggressive:
1401            //If Policy is Aggressive, commit will call
1402            //this function multiple times per
1403            //cycle
1404            return oldestReady();
1405
1406          case RoundRobin:
1407            return roundRobin();
1408
1409          case OldestReady:
1410            return oldestReady();
1411
1412          default:
1413            return InvalidThreadID;
1414        }
1415    } else {
1416        assert(!activeThreads->empty());
1417        ThreadID tid = activeThreads->front();
1418
1419        if (commitStatus[tid] == Running ||
1420            commitStatus[tid] == Idle ||
1421            commitStatus[tid] == FetchTrapPending) {
1422            return tid;
1423        } else {
1424            return InvalidThreadID;
1425        }
1426    }
1427}
1428
1429template<class Impl>
1430ThreadID
1431DefaultCommit<Impl>::roundRobin()
1432{
1433    list<ThreadID>::iterator pri_iter = priority_list.begin();
1434    list<ThreadID>::iterator end      = priority_list.end();
1435
1436    while (pri_iter != end) {
1437        ThreadID tid = *pri_iter;
1438
1439        if (commitStatus[tid] == Running ||
1440            commitStatus[tid] == Idle ||
1441            commitStatus[tid] == FetchTrapPending) {
1442
1443            if (rob->isHeadReady(tid)) {
1444                priority_list.erase(pri_iter);
1445                priority_list.push_back(tid);
1446
1447                return tid;
1448            }
1449        }
1450
1451        pri_iter++;
1452    }
1453
1454    return InvalidThreadID;
1455}
1456
1457template<class Impl>
1458ThreadID
1459DefaultCommit<Impl>::oldestReady()
1460{
1461    unsigned oldest = 0;
1462    bool first = true;
1463
1464    list<ThreadID>::iterator threads = activeThreads->begin();
1465    list<ThreadID>::iterator end = activeThreads->end();
1466
1467    while (threads != end) {
1468        ThreadID tid = *threads++;
1469
1470        if (!rob->isEmpty(tid) &&
1471            (commitStatus[tid] == Running ||
1472             commitStatus[tid] == Idle ||
1473             commitStatus[tid] == FetchTrapPending)) {
1474
1475            if (rob->isHeadReady(tid)) {
1476
1477                DynInstPtr head_inst = rob->readHeadInst(tid);
1478
1479                if (first) {
1480                    oldest = tid;
1481                    first = false;
1482                } else if (head_inst->seqNum < oldest) {
1483                    oldest = tid;
1484                }
1485            }
1486        }
1487    }
1488
1489    if (!first) {
1490        return oldest;
1491    } else {
1492        return InvalidThreadID;
1493    }
1494}
1495