decode_impl.hh revision 2980:eab855f06b79
1/*
2 * Copyright (c) 2004-2006 The Regents of The University of Michigan
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Kevin Lim
29 */
30
31#include "cpu/o3/decode.hh"
32
33template<class Impl>
34DefaultDecode<Impl>::DefaultDecode(Params *params)
35    : renameToDecodeDelay(params->renameToDecodeDelay),
36      iewToDecodeDelay(params->iewToDecodeDelay),
37      commitToDecodeDelay(params->commitToDecodeDelay),
38      fetchToDecodeDelay(params->fetchToDecodeDelay),
39      decodeWidth(params->decodeWidth),
40      numThreads(params->numberOfThreads)
41{
42    _status = Inactive;
43
44    // Setup status, make sure stall signals are clear.
45    for (int i = 0; i < numThreads; ++i) {
46        decodeStatus[i] = Idle;
47
48        stalls[i].rename = false;
49        stalls[i].iew = false;
50        stalls[i].commit = false;
51
52        squashAfterDelaySlot[i] = false;
53    }
54
55    // @todo: Make into a parameter
56    skidBufferMax = (fetchToDecodeDelay * params->fetchWidth) + decodeWidth;
57}
58
59template <class Impl>
60std::string
61DefaultDecode<Impl>::name() const
62{
63    return cpu->name() + ".decode";
64}
65
66template <class Impl>
67void
68DefaultDecode<Impl>::regStats()
69{
70    decodeIdleCycles
71        .name(name() + ".DECODE:IdleCycles")
72        .desc("Number of cycles decode is idle")
73        .prereq(decodeIdleCycles);
74    decodeBlockedCycles
75        .name(name() + ".DECODE:BlockedCycles")
76        .desc("Number of cycles decode is blocked")
77        .prereq(decodeBlockedCycles);
78    decodeRunCycles
79        .name(name() + ".DECODE:RunCycles")
80        .desc("Number of cycles decode is running")
81        .prereq(decodeRunCycles);
82    decodeUnblockCycles
83        .name(name() + ".DECODE:UnblockCycles")
84        .desc("Number of cycles decode is unblocking")
85        .prereq(decodeUnblockCycles);
86    decodeSquashCycles
87        .name(name() + ".DECODE:SquashCycles")
88        .desc("Number of cycles decode is squashing")
89        .prereq(decodeSquashCycles);
90    decodeBranchResolved
91        .name(name() + ".DECODE:BranchResolved")
92        .desc("Number of times decode resolved a branch")
93        .prereq(decodeBranchResolved);
94    decodeBranchMispred
95        .name(name() + ".DECODE:BranchMispred")
96        .desc("Number of times decode detected a branch misprediction")
97        .prereq(decodeBranchMispred);
98    decodeControlMispred
99        .name(name() + ".DECODE:ControlMispred")
100        .desc("Number of times decode detected an instruction incorrectly"
101              " predicted as a control")
102        .prereq(decodeControlMispred);
103    decodeDecodedInsts
104        .name(name() + ".DECODE:DecodedInsts")
105        .desc("Number of instructions handled by decode")
106        .prereq(decodeDecodedInsts);
107    decodeSquashedInsts
108        .name(name() + ".DECODE:SquashedInsts")
109        .desc("Number of squashed instructions handled by decode")
110        .prereq(decodeSquashedInsts);
111}
112
113template<class Impl>
114void
115DefaultDecode<Impl>::setCPU(O3CPU *cpu_ptr)
116{
117    DPRINTF(Decode, "Setting CPU pointer.\n");
118    cpu = cpu_ptr;
119}
120
121template<class Impl>
122void
123DefaultDecode<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr)
124{
125    DPRINTF(Decode, "Setting time buffer pointer.\n");
126    timeBuffer = tb_ptr;
127
128    // Setup wire to write information back to fetch.
129    toFetch = timeBuffer->getWire(0);
130
131    // Create wires to get information from proper places in time buffer.
132    fromRename = timeBuffer->getWire(-renameToDecodeDelay);
133    fromIEW = timeBuffer->getWire(-iewToDecodeDelay);
134    fromCommit = timeBuffer->getWire(-commitToDecodeDelay);
135}
136
137template<class Impl>
138void
139DefaultDecode<Impl>::setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr)
140{
141    DPRINTF(Decode, "Setting decode queue pointer.\n");
142    decodeQueue = dq_ptr;
143
144    // Setup wire to write information to proper place in decode queue.
145    toRename = decodeQueue->getWire(0);
146}
147
148template<class Impl>
149void
150DefaultDecode<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr)
151{
152    DPRINTF(Decode, "Setting fetch queue pointer.\n");
153    fetchQueue = fq_ptr;
154
155    // Setup wire to read information from fetch queue.
156    fromFetch = fetchQueue->getWire(-fetchToDecodeDelay);
157}
158
159template<class Impl>
160void
161DefaultDecode<Impl>::setActiveThreads(std::list<unsigned> *at_ptr)
162{
163    DPRINTF(Decode, "Setting active threads list pointer.\n");
164    activeThreads = at_ptr;
165}
166
167template <class Impl>
168bool
169DefaultDecode<Impl>::drain()
170{
171    // Decode is done draining at any time.
172    cpu->signalDrained();
173    return true;
174}
175
176template <class Impl>
177void
178DefaultDecode<Impl>::takeOverFrom()
179{
180    _status = Inactive;
181
182    // Be sure to reset state and clear out any old instructions.
183    for (int i = 0; i < numThreads; ++i) {
184        decodeStatus[i] = Idle;
185
186        stalls[i].rename = false;
187        stalls[i].iew = false;
188        stalls[i].commit = false;
189        while (!insts[i].empty())
190            insts[i].pop();
191        while (!skidBuffer[i].empty())
192            skidBuffer[i].pop();
193        branchCount[i] = 0;
194    }
195    wroteToTimeBuffer = false;
196}
197
198template<class Impl>
199bool
200DefaultDecode<Impl>::checkStall(unsigned tid) const
201{
202    bool ret_val = false;
203
204    if (stalls[tid].rename) {
205        DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid);
206        ret_val = true;
207    } else if (stalls[tid].iew) {
208        DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid);
209        ret_val = true;
210    } else if (stalls[tid].commit) {
211        DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid);
212        ret_val = true;
213    }
214
215    return ret_val;
216}
217
218template<class Impl>
219inline bool
220DefaultDecode<Impl>::fetchInstsValid()
221{
222    return fromFetch->size > 0;
223}
224
225template<class Impl>
226bool
227DefaultDecode<Impl>::block(unsigned tid)
228{
229    DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid);
230
231    // Add the current inputs to the skid buffer so they can be
232    // reprocessed when this stage unblocks.
233    skidInsert(tid);
234
235    // If the decode status is blocked or unblocking then decode has not yet
236    // signalled fetch to unblock. In that case, there is no need to tell
237    // fetch to block.
238    if (decodeStatus[tid] != Blocked) {
239        // Set the status to Blocked.
240        decodeStatus[tid] = Blocked;
241
242        if (decodeStatus[tid] != Unblocking) {
243            toFetch->decodeBlock[tid] = true;
244            wroteToTimeBuffer = true;
245        }
246
247        return true;
248    }
249
250    return false;
251}
252
253template<class Impl>
254bool
255DefaultDecode<Impl>::unblock(unsigned tid)
256{
257    // Decode is done unblocking only if the skid buffer is empty.
258    if (skidBuffer[tid].empty()) {
259        DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid);
260        toFetch->decodeUnblock[tid] = true;
261        wroteToTimeBuffer = true;
262
263        decodeStatus[tid] = Running;
264        return true;
265    }
266
267    DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid);
268
269    return false;
270}
271
272template<class Impl>
273void
274DefaultDecode<Impl>::squash(DynInstPtr &inst, unsigned tid)
275{
276    DPRINTF(Decode, "[tid:%i]: Squashing due to incorrect branch prediction "
277            "detected at decode.\n", tid);
278
279    // Send back mispredict information.
280    toFetch->decodeInfo[tid].branchMispredict = true;
281    toFetch->decodeInfo[tid].predIncorrect = true;
282    toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum;
283    toFetch->decodeInfo[tid].squash = true;
284    toFetch->decodeInfo[tid].nextPC = inst->branchTarget();
285#if THE_ISA == ALPHA_ISA
286    toFetch->decodeInfo[tid].branchTaken =
287        inst->readNextPC() != (inst->readPC() + sizeof(TheISA::MachInst));
288
289    InstSeqNum squash_seq_num = inst->seqNum;
290#else
291    toFetch->decodeInfo[tid].branchTaken = inst->readNextNPC() !=
292        (inst->readNextPC() + sizeof(TheISA::MachInst));
293
294    toFetch->decodeInfo[tid].bdelayDoneSeqNum = bdelayDoneSeqNum[tid];
295    squashAfterDelaySlot[tid] = false;
296
297    InstSeqNum squash_seq_num = bdelayDoneSeqNum[tid];
298#endif
299
300    // Might have to tell fetch to unblock.
301    if (decodeStatus[tid] == Blocked ||
302        decodeStatus[tid] == Unblocking) {
303        toFetch->decodeUnblock[tid] = 1;
304    }
305
306    // Set status to squashing.
307    decodeStatus[tid] = Squashing;
308
309    for (int i=0; i<fromFetch->size; i++) {
310        if (fromFetch->insts[i]->threadNumber == tid &&
311            fromFetch->insts[i]->seqNum > squash_seq_num) {
312            fromFetch->insts[i]->setSquashed();
313        }
314    }
315
316    // Clear the instruction list and skid buffer in case they have any
317    // insts in them.
318    while (!insts[tid].empty()) {
319
320#if THE_ISA != ALPHA_ISA
321        if (insts[tid].front()->seqNum <= squash_seq_num) {
322            DPRINTF(Decode, "[tid:%i]: Cannot remove incoming decode "
323                    "instructions before delay slot [sn:%i]. %i insts"
324                    "left in decode.\n", tid, squash_seq_num,
325                    insts[tid].size());
326            break;
327        }
328#endif
329        insts[tid].pop();
330    }
331
332    while (!skidBuffer[tid].empty()) {
333
334#if THE_ISA != ALPHA_ISA
335        if (skidBuffer[tid].front()->seqNum <= squash_seq_num) {
336            DPRINTF(Decode, "[tid:%i]: Cannot remove skidBuffer "
337                    "instructions before delay slot [sn:%i]. %i insts"
338                    "left in decode.\n", tid, squash_seq_num,
339                    insts[tid].size());
340            break;
341        }
342#endif
343        skidBuffer[tid].pop();
344    }
345
346    // Squash instructions up until this one
347    cpu->removeInstsUntil(squash_seq_num, tid);
348}
349
350template<class Impl>
351unsigned
352DefaultDecode<Impl>::squash(unsigned tid)
353{
354    DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid);
355
356    if (decodeStatus[tid] == Blocked ||
357        decodeStatus[tid] == Unblocking) {
358#if !FULL_SYSTEM
359        // In syscall emulation, we can have both a block and a squash due
360        // to a syscall in the same cycle.  This would cause both signals to
361        // be high.  This shouldn't happen in full system.
362        // @todo: Determine if this still happens.
363        if (toFetch->decodeBlock[tid]) {
364            toFetch->decodeBlock[tid] = 0;
365        } else {
366            toFetch->decodeUnblock[tid] = 1;
367        }
368#else
369        toFetch->decodeUnblock[tid] = 1;
370#endif
371    }
372
373    // Set status to squashing.
374    decodeStatus[tid] = Squashing;
375
376    // Go through incoming instructions from fetch and squash them.
377    unsigned squash_count = 0;
378
379    for (int i=0; i<fromFetch->size; i++) {
380        if (fromFetch->insts[i]->threadNumber == tid) {
381            fromFetch->insts[i]->setSquashed();
382            squash_count++;
383        }
384    }
385
386    // Clear the instruction list and skid buffer in case they have any
387    // insts in them.
388    while (!insts[tid].empty()) {
389        insts[tid].pop();
390    }
391
392    while (!skidBuffer[tid].empty()) {
393        skidBuffer[tid].pop();
394    }
395
396    return squash_count;
397}
398
399template<class Impl>
400void
401DefaultDecode<Impl>::skidInsert(unsigned tid)
402{
403    DynInstPtr inst = NULL;
404
405    while (!insts[tid].empty()) {
406        inst = insts[tid].front();
407
408        insts[tid].pop();
409
410        assert(tid == inst->threadNumber);
411
412        DPRINTF(Decode,"Inserting [sn:%lli] PC:%#x into decode skidBuffer %i\n",
413                inst->seqNum, inst->readPC(), inst->threadNumber);
414
415        skidBuffer[tid].push(inst);
416    }
417
418    // @todo: Eventually need to enforce this by not letting a thread
419    // fetch past its skidbuffer
420    assert(skidBuffer[tid].size() <= skidBufferMax);
421}
422
423template<class Impl>
424bool
425DefaultDecode<Impl>::skidsEmpty()
426{
427    std::list<unsigned>::iterator threads = (*activeThreads).begin();
428
429    while (threads != (*activeThreads).end()) {
430        if (!skidBuffer[*threads++].empty())
431            return false;
432    }
433
434    return true;
435}
436
437template<class Impl>
438void
439DefaultDecode<Impl>::updateStatus()
440{
441    bool any_unblocking = false;
442
443    std::list<unsigned>::iterator threads = (*activeThreads).begin();
444
445    threads = (*activeThreads).begin();
446
447    while (threads != (*activeThreads).end()) {
448        unsigned tid = *threads++;
449
450        if (decodeStatus[tid] == Unblocking) {
451            any_unblocking = true;
452            break;
453        }
454    }
455
456    // Decode will have activity if it's unblocking.
457    if (any_unblocking) {
458        if (_status == Inactive) {
459            _status = Active;
460
461            DPRINTF(Activity, "Activating stage.\n");
462
463            cpu->activateStage(O3CPU::DecodeIdx);
464        }
465    } else {
466        // If it's not unblocking, then decode will not have any internal
467        // activity.  Switch it to inactive.
468        if (_status == Active) {
469            _status = Inactive;
470            DPRINTF(Activity, "Deactivating stage.\n");
471
472            cpu->deactivateStage(O3CPU::DecodeIdx);
473        }
474    }
475}
476
477template <class Impl>
478void
479DefaultDecode<Impl>::sortInsts()
480{
481    int insts_from_fetch = fromFetch->size;
482#ifdef DEBUG
483    for (int i=0; i < numThreads; i++)
484        assert(insts[i].empty());
485#endif
486    for (int i = 0; i < insts_from_fetch; ++i) {
487        insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]);
488    }
489}
490
491template<class Impl>
492void
493DefaultDecode<Impl>::readStallSignals(unsigned tid)
494{
495    if (fromRename->renameBlock[tid]) {
496        stalls[tid].rename = true;
497    }
498
499    if (fromRename->renameUnblock[tid]) {
500        assert(stalls[tid].rename);
501        stalls[tid].rename = false;
502    }
503
504    if (fromIEW->iewBlock[tid]) {
505        stalls[tid].iew = true;
506    }
507
508    if (fromIEW->iewUnblock[tid]) {
509        assert(stalls[tid].iew);
510        stalls[tid].iew = false;
511    }
512
513    if (fromCommit->commitBlock[tid]) {
514        stalls[tid].commit = true;
515    }
516
517    if (fromCommit->commitUnblock[tid]) {
518        assert(stalls[tid].commit);
519        stalls[tid].commit = false;
520    }
521}
522
523template <class Impl>
524bool
525DefaultDecode<Impl>::checkSignalsAndUpdate(unsigned tid)
526{
527    // Check if there's a squash signal, squash if there is.
528    // Check stall signals, block if necessary.
529    // If status was blocked
530    //     Check if stall conditions have passed
531    //         if so then go to unblocking
532    // If status was Squashing
533    //     check if squashing is not high.  Switch to running this cycle.
534
535    // Update the per thread stall statuses.
536    readStallSignals(tid);
537
538    // Check squash signals from commit.
539    if (fromCommit->commitInfo[tid].squash) {
540
541        DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash "
542                "from commit.\n", tid);
543
544        squash(tid);
545
546        return true;
547    }
548
549    // Check ROB squash signals from commit.
550    if (fromCommit->commitInfo[tid].robSquashing) {
551        DPRINTF(Decode, "[tid:%u]: ROB is still squashing.\n", tid);
552
553        // Continue to squash.
554        decodeStatus[tid] = Squashing;
555
556        return true;
557    }
558
559    if (checkStall(tid)) {
560        return block(tid);
561    }
562
563    if (decodeStatus[tid] == Blocked) {
564        DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n",
565                tid);
566
567        decodeStatus[tid] = Unblocking;
568
569        unblock(tid);
570
571        return true;
572    }
573
574    if (decodeStatus[tid] == Squashing) {
575        // Switch status to running if decode isn't being told to block or
576        // squash this cycle.
577        DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n",
578                tid);
579
580        decodeStatus[tid] = Running;
581
582        return false;
583    }
584
585    // If we've reached this point, we have not gotten any signals that
586    // cause decode to change its status.  Decode remains the same as before.
587    return false;
588}
589
590template<class Impl>
591void
592DefaultDecode<Impl>::tick()
593{
594    wroteToTimeBuffer = false;
595
596    bool status_change = false;
597
598    toRenameIndex = 0;
599
600    std::list<unsigned>::iterator threads = (*activeThreads).begin();
601
602    sortInsts();
603
604    //Check stall and squash signals.
605    while (threads != (*activeThreads).end()) {
606    unsigned tid = *threads++;
607
608        DPRINTF(Decode,"Processing [tid:%i]\n",tid);
609        status_change =  checkSignalsAndUpdate(tid) || status_change;
610
611        decode(status_change, tid);
612    }
613
614    if (status_change) {
615        updateStatus();
616    }
617
618    if (wroteToTimeBuffer) {
619        DPRINTF(Activity, "Activity this cycle.\n");
620
621        cpu->activityThisCycle();
622    }
623}
624
625template<class Impl>
626void
627DefaultDecode<Impl>::decode(bool &status_change, unsigned tid)
628{
629    // If status is Running or idle,
630    //     call decodeInsts()
631    // If status is Unblocking,
632    //     buffer any instructions coming from fetch
633    //     continue trying to empty skid buffer
634    //     check if stall conditions have passed
635
636    if (decodeStatus[tid] == Blocked) {
637        ++decodeBlockedCycles;
638    } else if (decodeStatus[tid] == Squashing) {
639        ++decodeSquashCycles;
640    }
641
642    // Decode should try to decode as many instructions as its bandwidth
643    // will allow, as long as it is not currently blocked.
644    if (decodeStatus[tid] == Running ||
645        decodeStatus[tid] == Idle) {
646        DPRINTF(Decode, "[tid:%u]: Not blocked, so attempting to run "
647                "stage.\n",tid);
648
649        decodeInsts(tid);
650    } else if (decodeStatus[tid] == Unblocking) {
651        // Make sure that the skid buffer has something in it if the
652        // status is unblocking.
653        assert(!skidsEmpty());
654
655        // If the status was unblocking, then instructions from the skid
656        // buffer were used.  Remove those instructions and handle
657        // the rest of unblocking.
658        decodeInsts(tid);
659
660        if (fetchInstsValid()) {
661            // Add the current inputs to the skid buffer so they can be
662            // reprocessed when this stage unblocks.
663            skidInsert(tid);
664        }
665
666        status_change = unblock(tid) || status_change;
667    }
668}
669
670template <class Impl>
671void
672DefaultDecode<Impl>::decodeInsts(unsigned tid)
673{
674    // Instructions can come either from the skid buffer or the list of
675    // instructions coming from fetch, depending on decode's status.
676    int insts_available = decodeStatus[tid] == Unblocking ?
677        skidBuffer[tid].size() : insts[tid].size();
678
679    if (insts_available == 0) {
680        DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out"
681                " early.\n",tid);
682        // Should I change the status to idle?
683        ++decodeIdleCycles;
684        return;
685    } else if (decodeStatus[tid] == Unblocking) {
686        DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid "
687                "buffer.\n",tid);
688        ++decodeUnblockCycles;
689    } else if (decodeStatus[tid] == Running) {
690        ++decodeRunCycles;
691    }
692
693    DynInstPtr inst;
694
695    std::queue<DynInstPtr>
696        &insts_to_decode = decodeStatus[tid] == Unblocking ?
697        skidBuffer[tid] : insts[tid];
698
699    DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid);
700
701    while (insts_available > 0 && toRenameIndex < decodeWidth) {
702        assert(!insts_to_decode.empty());
703
704        inst = insts_to_decode.front();
705
706        insts_to_decode.pop();
707
708        DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with "
709                "PC %#x\n",
710                tid, inst->seqNum, inst->readPC());
711
712        if (inst->isSquashed()) {
713            DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %#x is "
714                    "squashed, skipping.\n",
715                    tid, inst->seqNum, inst->readPC());
716
717            ++decodeSquashedInsts;
718
719            --insts_available;
720
721            continue;
722        }
723
724        // Also check if instructions have no source registers.  Mark
725        // them as ready to issue at any time.  Not sure if this check
726        // should exist here or at a later stage; however it doesn't matter
727        // too much for function correctness.
728        if (inst->numSrcRegs() == 0) {
729            inst->setCanIssue();
730        }
731
732        // This current instruction is valid, so add it into the decode
733        // queue.  The next instruction may not be valid, so check to
734        // see if branches were predicted correctly.
735        toRename->insts[toRenameIndex] = inst;
736
737        ++(toRename->size);
738        ++toRenameIndex;
739        ++decodeDecodedInsts;
740        --insts_available;
741
742        // Ensure that if it was predicted as a branch, it really is a
743        // branch.
744        if (inst->predTaken() && !inst->isControl()) {
745            DPRINTF(Decode, "PredPC : %#x != NextPC: %#x\n",inst->predPC,
746                    inst->nextPC + 4);
747
748            panic("Instruction predicted as a branch!");
749
750            ++decodeControlMispred;
751
752            // Might want to set some sort of boolean and just do
753            // a check at the end
754            squash(inst, inst->threadNumber);
755
756            break;
757        }
758
759        // Go ahead and compute any PC-relative branches.
760        if (inst->isDirectCtrl() && inst->isUncondCtrl()) {
761            ++decodeBranchResolved;
762
763            if (inst->branchTarget() != inst->readPredTarg()) {
764                ++decodeBranchMispred;
765
766                // Might want to set some sort of boolean and just do
767                // a check at the end
768#if THE_ISA == ALPHA_ISA
769                squash(inst, inst->threadNumber);
770                inst->setPredTarg(inst->branchTarget());
771                break;
772#else
773                // If mispredicted as taken, then ignore delay slot
774                // instruction... else keep delay slot and squash
775                // after it is sent to rename
776                if (inst->predTaken() && inst->isCondDelaySlot()) {
777                    DPRINTF(Decode, "[tid:%i]: Conditional delay slot inst."
778                            "[sn:%i] PC %#x mispredicted as taken.\n", tid,
779                            inst->seqNum, inst->PC);
780                    bdelayDoneSeqNum[tid] = inst->seqNum;
781                    squash(inst, inst->threadNumber);
782                    inst->setPredTarg(inst->branchTarget());
783                    break;
784                } else {
785                    DPRINTF(Decode, "[tid:%i]: Misprediction detected at "
786                            "[sn:%i] PC %#x, will squash after delay slot "
787                            "inst. is sent to Rename\n",
788                            tid, inst->seqNum, inst->PC);
789                    bdelayDoneSeqNum[tid] = inst->seqNum + 1;
790                    squashAfterDelaySlot[tid] = true;
791                    squashInst[tid] = inst;
792                    continue;
793                }
794#endif
795            }
796        }
797
798        if (squashAfterDelaySlot[tid]) {
799            assert(!inst->isSquashed());
800            squash(squashInst[tid], squashInst[tid]->threadNumber);
801            squashInst[tid]->setPredTarg(squashInst[tid]->branchTarget());
802            assert(!inst->isSquashed());
803            break;
804        }
805    }
806
807    // If we didn't process all instructions, then we will need to block
808    // and put all those instructions into the skid buffer.
809    if (!insts_to_decode.empty()) {
810        block(tid);
811    }
812
813    // Record that decode has written to the time buffer for activity
814    // tracking.
815    if (toRenameIndex) {
816        wroteToTimeBuffer = true;
817    }
818}
819