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
33using namespace std;
34
35template<class Impl>
36DefaultDecode<Impl>::DefaultDecode(Params *params)
37 : renameToDecodeDelay(params->renameToDecodeDelay),
38 iewToDecodeDelay(params->iewToDecodeDelay),
39 commitToDecodeDelay(params->commitToDecodeDelay),
40 fetchToDecodeDelay(params->fetchToDecodeDelay),
41 decodeWidth(params->decodeWidth),
42 numThreads(params->numberOfThreads)
43{
44 _status = Inactive;
45
46 // Setup status, make sure stall signals are clear.
47 for (int i = 0; i < numThreads; ++i) {
48 decodeStatus[i] = Idle;
49
50 stalls[i].rename = false;
51 stalls[i].iew = false;
52 stalls[i].commit = 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(list<unsigned> *at_ptr)
162{
163 DPRINTF(Decode, "Setting active threads list pointer.\n");
164 activeThreads = at_ptr;
165}
166
167template <class Impl>
| 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
33using namespace std;
34
35template<class Impl>
36DefaultDecode<Impl>::DefaultDecode(Params *params)
37 : renameToDecodeDelay(params->renameToDecodeDelay),
38 iewToDecodeDelay(params->iewToDecodeDelay),
39 commitToDecodeDelay(params->commitToDecodeDelay),
40 fetchToDecodeDelay(params->fetchToDecodeDelay),
41 decodeWidth(params->decodeWidth),
42 numThreads(params->numberOfThreads)
43{
44 _status = Inactive;
45
46 // Setup status, make sure stall signals are clear.
47 for (int i = 0; i < numThreads; ++i) {
48 decodeStatus[i] = Idle;
49
50 stalls[i].rename = false;
51 stalls[i].iew = false;
52 stalls[i].commit = 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(list<unsigned> *at_ptr)
162{
163 DPRINTF(Decode, "Setting active threads list pointer.\n");
164 activeThreads = at_ptr;
165}
166
167template <class Impl>
|
173}
174
175template <class Impl>
176void
177DefaultDecode<Impl>::takeOverFrom()
178{
179 _status = Inactive;
180
181 // Be sure to reset state and clear out any old instructions.
182 for (int i = 0; i < numThreads; ++i) {
183 decodeStatus[i] = Idle;
184
185 stalls[i].rename = false;
186 stalls[i].iew = false;
187 stalls[i].commit = false;
188 while (!insts[i].empty())
189 insts[i].pop();
190 while (!skidBuffer[i].empty())
191 skidBuffer[i].pop();
192 branchCount[i] = 0;
193 }
194 wroteToTimeBuffer = false;
195}
196
197template<class Impl>
198bool
199DefaultDecode<Impl>::checkStall(unsigned tid) const
200{
201 bool ret_val = false;
202
203 if (stalls[tid].rename) {
204 DPRINTF(Decode,"[tid:%i]: Stall fom Rename stage detected.\n", tid);
205 ret_val = true;
206 } else if (stalls[tid].iew) {
207 DPRINTF(Decode,"[tid:%i]: Stall fom IEW stage detected.\n", tid);
208 ret_val = true;
209 } else if (stalls[tid].commit) {
210 DPRINTF(Decode,"[tid:%i]: Stall fom Commit stage detected.\n", tid);
211 ret_val = true;
212 }
213
214 return ret_val;
215}
216
217template<class Impl>
218inline bool
219DefaultDecode<Impl>::fetchInstsValid()
220{
221 return fromFetch->size > 0;
222}
223
224template<class Impl>
225bool
226DefaultDecode<Impl>::block(unsigned tid)
227{
228 DPRINTF(Decode, "[tid:%u]: Blocking.\n", tid);
229
230 // Add the current inputs to the skid buffer so they can be
231 // reprocessed when this stage unblocks.
232 skidInsert(tid);
233
234 // If the decode status is blocked or unblocking then decode has not yet
235 // signalled fetch to unblock. In that case, there is no need to tell
236 // fetch to block.
237 if (decodeStatus[tid] != Blocked) {
238 // Set the status to Blocked.
239 decodeStatus[tid] = Blocked;
240
241 if (decodeStatus[tid] != Unblocking) {
242 toFetch->decodeBlock[tid] = true;
243 wroteToTimeBuffer = true;
244 }
245
246 return true;
247 }
248
249 return false;
250}
251
252template<class Impl>
253bool
254DefaultDecode<Impl>::unblock(unsigned tid)
255{
256 // Decode is done unblocking only if the skid buffer is empty.
257 if (skidBuffer[tid].empty()) {
258 DPRINTF(Decode, "[tid:%u]: Done unblocking.\n", tid);
259 toFetch->decodeUnblock[tid] = true;
260 wroteToTimeBuffer = true;
261
262 decodeStatus[tid] = Running;
263 return true;
264 }
265
266 DPRINTF(Decode, "[tid:%u]: Currently unblocking.\n", tid);
267
268 return false;
269}
270
271template<class Impl>
272void
273DefaultDecode<Impl>::squash(DynInstPtr &inst, unsigned tid)
274{
275 DPRINTF(Decode, "[tid:%i]: Squashing due to incorrect branch prediction "
276 "detected at decode.\n", tid);
277
278 // Send back mispredict information.
279 toFetch->decodeInfo[tid].branchMispredict = true;
280 toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum;
281 toFetch->decodeInfo[tid].predIncorrect = true;
282 toFetch->decodeInfo[tid].squash = true;
283 toFetch->decodeInfo[tid].nextPC = inst->branchTarget();
284 toFetch->decodeInfo[tid].branchTaken =
285 inst->readNextPC() != (inst->readPC() + sizeof(TheISA::MachInst));
286
287 // Might have to tell fetch to unblock.
288 if (decodeStatus[tid] == Blocked ||
289 decodeStatus[tid] == Unblocking) {
290 toFetch->decodeUnblock[tid] = 1;
291 }
292
293 // Set status to squashing.
294 decodeStatus[tid] = Squashing;
295
296 for (int i=0; i<fromFetch->size; i++) {
297 if (fromFetch->insts[i]->threadNumber == tid &&
298 fromFetch->insts[i]->seqNum > inst->seqNum) {
299 fromFetch->insts[i]->setSquashed();
300 }
301 }
302
303 // Clear the instruction list and skid buffer in case they have any
304 // insts in them.
305 while (!insts[tid].empty()) {
306 insts[tid].pop();
307 }
308
309 while (!skidBuffer[tid].empty()) {
310 skidBuffer[tid].pop();
311 }
312
313 // Squash instructions up until this one
314 cpu->removeInstsUntil(inst->seqNum, tid);
315}
316
317template<class Impl>
318unsigned
319DefaultDecode<Impl>::squash(unsigned tid)
320{
321 DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid);
322
323 if (decodeStatus[tid] == Blocked ||
324 decodeStatus[tid] == Unblocking) {
325#if !FULL_SYSTEM
326 // In syscall emulation, we can have both a block and a squash due
327 // to a syscall in the same cycle. This would cause both signals to
328 // be high. This shouldn't happen in full system.
329 // @todo: Determine if this still happens.
330 if (toFetch->decodeBlock[tid]) {
331 toFetch->decodeBlock[tid] = 0;
332 } else {
333 toFetch->decodeUnblock[tid] = 1;
334 }
335#else
336 toFetch->decodeUnblock[tid] = 1;
337#endif
338 }
339
340 // Set status to squashing.
341 decodeStatus[tid] = Squashing;
342
343 // Go through incoming instructions from fetch and squash them.
344 unsigned squash_count = 0;
345
346 for (int i=0; i<fromFetch->size; i++) {
347 if (fromFetch->insts[i]->threadNumber == tid) {
348 fromFetch->insts[i]->setSquashed();
349 squash_count++;
350 }
351 }
352
353 // Clear the instruction list and skid buffer in case they have any
354 // insts in them.
355 while (!insts[tid].empty()) {
356 insts[tid].pop();
357 }
358
359 while (!skidBuffer[tid].empty()) {
360 skidBuffer[tid].pop();
361 }
362
363 return squash_count;
364}
365
366template<class Impl>
367void
368DefaultDecode<Impl>::skidInsert(unsigned tid)
369{
370 DynInstPtr inst = NULL;
371
372 while (!insts[tid].empty()) {
373 inst = insts[tid].front();
374
375 insts[tid].pop();
376
377 assert(tid == inst->threadNumber);
378
379 DPRINTF(Decode,"Inserting [sn:%lli] PC:%#x into decode skidBuffer %i\n",
380 inst->seqNum, inst->readPC(), inst->threadNumber);
381
382 skidBuffer[tid].push(inst);
383 }
384
385 // @todo: Eventually need to enforce this by not letting a thread
386 // fetch past its skidbuffer
387 assert(skidBuffer[tid].size() <= skidBufferMax);
388}
389
390template<class Impl>
391bool
392DefaultDecode<Impl>::skidsEmpty()
393{
394 list<unsigned>::iterator threads = (*activeThreads).begin();
395
396 while (threads != (*activeThreads).end()) {
397 if (!skidBuffer[*threads++].empty())
398 return false;
399 }
400
401 return true;
402}
403
404template<class Impl>
405void
406DefaultDecode<Impl>::updateStatus()
407{
408 bool any_unblocking = false;
409
410 list<unsigned>::iterator threads = (*activeThreads).begin();
411
412 threads = (*activeThreads).begin();
413
414 while (threads != (*activeThreads).end()) {
415 unsigned tid = *threads++;
416
417 if (decodeStatus[tid] == Unblocking) {
418 any_unblocking = true;
419 break;
420 }
421 }
422
423 // Decode will have activity if it's unblocking.
424 if (any_unblocking) {
425 if (_status == Inactive) {
426 _status = Active;
427
428 DPRINTF(Activity, "Activating stage.\n");
429
430 cpu->activateStage(O3CPU::DecodeIdx);
431 }
432 } else {
433 // If it's not unblocking, then decode will not have any internal
434 // activity. Switch it to inactive.
435 if (_status == Active) {
436 _status = Inactive;
437 DPRINTF(Activity, "Deactivating stage.\n");
438
439 cpu->deactivateStage(O3CPU::DecodeIdx);
440 }
441 }
442}
443
444template <class Impl>
445void
446DefaultDecode<Impl>::sortInsts()
447{
448 int insts_from_fetch = fromFetch->size;
449#ifdef DEBUG
450 for (int i=0; i < numThreads; i++)
451 assert(insts[i].empty());
452#endif
453 for (int i = 0; i < insts_from_fetch; ++i) {
454 insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]);
455 }
456}
457
458template<class Impl>
459void
460DefaultDecode<Impl>::readStallSignals(unsigned tid)
461{
462 if (fromRename->renameBlock[tid]) {
463 stalls[tid].rename = true;
464 }
465
466 if (fromRename->renameUnblock[tid]) {
467 assert(stalls[tid].rename);
468 stalls[tid].rename = false;
469 }
470
471 if (fromIEW->iewBlock[tid]) {
472 stalls[tid].iew = true;
473 }
474
475 if (fromIEW->iewUnblock[tid]) {
476 assert(stalls[tid].iew);
477 stalls[tid].iew = false;
478 }
479
480 if (fromCommit->commitBlock[tid]) {
481 stalls[tid].commit = true;
482 }
483
484 if (fromCommit->commitUnblock[tid]) {
485 assert(stalls[tid].commit);
486 stalls[tid].commit = false;
487 }
488}
489
490template <class Impl>
491bool
492DefaultDecode<Impl>::checkSignalsAndUpdate(unsigned tid)
493{
494 // Check if there's a squash signal, squash if there is.
495 // Check stall signals, block if necessary.
496 // If status was blocked
497 // Check if stall conditions have passed
498 // if so then go to unblocking
499 // If status was Squashing
500 // check if squashing is not high. Switch to running this cycle.
501
502 // Update the per thread stall statuses.
503 readStallSignals(tid);
504
505 // Check squash signals from commit.
506 if (fromCommit->commitInfo[tid].squash) {
507
508 DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash "
509 "from commit.\n", tid);
510
511 squash(tid);
512
513 return true;
514 }
515
516 // Check ROB squash signals from commit.
517 if (fromCommit->commitInfo[tid].robSquashing) {
518 DPRINTF(Decode, "[tid:%u]: ROB is still squashing.\n", tid);
519
520 // Continue to squash.
521 decodeStatus[tid] = Squashing;
522
523 return true;
524 }
525
526 if (checkStall(tid)) {
527 return block(tid);
528 }
529
530 if (decodeStatus[tid] == Blocked) {
531 DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n",
532 tid);
533
534 decodeStatus[tid] = Unblocking;
535
536 unblock(tid);
537
538 return true;
539 }
540
541 if (decodeStatus[tid] == Squashing) {
542 // Switch status to running if decode isn't being told to block or
543 // squash this cycle.
544 DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n",
545 tid);
546
547 decodeStatus[tid] = Running;
548
549 return false;
550 }
551
552 // If we've reached this point, we have not gotten any signals that
553 // cause decode to change its status. Decode remains the same as before.
554 return false;
555}
556
557template<class Impl>
558void
559DefaultDecode<Impl>::tick()
560{
561 wroteToTimeBuffer = false;
562
563 bool status_change = false;
564
565 toRenameIndex = 0;
566
567 list<unsigned>::iterator threads = (*activeThreads).begin();
568
569 sortInsts();
570
571 //Check stall and squash signals.
572 while (threads != (*activeThreads).end()) {
573 unsigned tid = *threads++;
574
575 DPRINTF(Decode,"Processing [tid:%i]\n",tid);
576 status_change = checkSignalsAndUpdate(tid) || status_change;
577
578 decode(status_change, tid);
579 }
580
581 if (status_change) {
582 updateStatus();
583 }
584
585 if (wroteToTimeBuffer) {
586 DPRINTF(Activity, "Activity this cycle.\n");
587
588 cpu->activityThisCycle();
589 }
590}
591
592template<class Impl>
593void
594DefaultDecode<Impl>::decode(bool &status_change, unsigned tid)
595{
596 // If status is Running or idle,
597 // call decodeInsts()
598 // If status is Unblocking,
599 // buffer any instructions coming from fetch
600 // continue trying to empty skid buffer
601 // check if stall conditions have passed
602
603 if (decodeStatus[tid] == Blocked) {
604 ++decodeBlockedCycles;
605 } else if (decodeStatus[tid] == Squashing) {
606 ++decodeSquashCycles;
607 }
608
609 // Decode should try to decode as many instructions as its bandwidth
610 // will allow, as long as it is not currently blocked.
611 if (decodeStatus[tid] == Running ||
612 decodeStatus[tid] == Idle) {
613 DPRINTF(Decode, "[tid:%u] Not blocked, so attempting to run "
614 "stage.\n",tid);
615
616 decodeInsts(tid);
617 } else if (decodeStatus[tid] == Unblocking) {
618 // Make sure that the skid buffer has something in it if the
619 // status is unblocking.
620 assert(!skidsEmpty());
621
622 // If the status was unblocking, then instructions from the skid
623 // buffer were used. Remove those instructions and handle
624 // the rest of unblocking.
625 decodeInsts(tid);
626
627 if (fetchInstsValid()) {
628 // Add the current inputs to the skid buffer so they can be
629 // reprocessed when this stage unblocks.
630 skidInsert(tid);
631 }
632
633 status_change = unblock(tid) || status_change;
634 }
635}
636
637template <class Impl>
638void
639DefaultDecode<Impl>::decodeInsts(unsigned tid)
640{
641 // Instructions can come either from the skid buffer or the list of
642 // instructions coming from fetch, depending on decode's status.
643 int insts_available = decodeStatus[tid] == Unblocking ?
644 skidBuffer[tid].size() : insts[tid].size();
645
646 if (insts_available == 0) {
647 DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out"
648 " early.\n",tid);
649 // Should I change the status to idle?
650 ++decodeIdleCycles;
651 return;
652 } else if (decodeStatus[tid] == Unblocking) {
653 DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid "
654 "buffer.\n",tid);
655 ++decodeUnblockCycles;
656 } else if (decodeStatus[tid] == Running) {
657 ++decodeRunCycles;
658 }
659
660 DynInstPtr inst;
661
662 std::queue<DynInstPtr>
663 &insts_to_decode = decodeStatus[tid] == Unblocking ?
664 skidBuffer[tid] : insts[tid];
665
666 DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid);
667
668 while (insts_available > 0 && toRenameIndex < decodeWidth) {
669 assert(!insts_to_decode.empty());
670
671 inst = insts_to_decode.front();
672
673 insts_to_decode.pop();
674
675 DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with "
676 "PC %#x\n",
677 tid, inst->seqNum, inst->readPC());
678
679 if (inst->isSquashed()) {
680 DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %#x is "
681 "squashed, skipping.\n",
682 tid, inst->seqNum, inst->readPC());
683
684 ++decodeSquashedInsts;
685
686 --insts_available;
687
688 continue;
689 }
690
691 // Also check if instructions have no source registers. Mark
692 // them as ready to issue at any time. Not sure if this check
693 // should exist here or at a later stage; however it doesn't matter
694 // too much for function correctness.
695 if (inst->numSrcRegs() == 0) {
696 inst->setCanIssue();
697 }
698
699 // This current instruction is valid, so add it into the decode
700 // queue. The next instruction may not be valid, so check to
701 // see if branches were predicted correctly.
702 toRename->insts[toRenameIndex] = inst;
703
704 ++(toRename->size);
705 ++toRenameIndex;
706 ++decodeDecodedInsts;
707 --insts_available;
708
709 // Ensure that if it was predicted as a branch, it really is a
710 // branch.
711 if (inst->predTaken() && !inst->isControl()) {
712 panic("Instruction predicted as a branch!");
713
714 ++decodeControlMispred;
715
716 // Might want to set some sort of boolean and just do
717 // a check at the end
718 squash(inst, inst->threadNumber);
719
720 break;
721 }
722
723 // Go ahead and compute any PC-relative branches.
724 if (inst->isDirectCtrl() && inst->isUncondCtrl()) {
725 ++decodeBranchResolved;
726
727 if (inst->branchTarget() != inst->readPredTarg()) {
728 ++decodeBranchMispred;
729
730 // Might want to set some sort of boolean and just do
731 // a check at the end
732 squash(inst, inst->threadNumber);
733 inst->setPredTarg(inst->branchTarget());
734
735 break;
736 }
737 }
738 }
739
740 // If we didn't process all instructions, then we will need to block
741 // and put all those instructions into the skid buffer.
742 if (!insts_to_decode.empty()) {
743 block(tid);
744 }
745
746 // Record that decode has written to the time buffer for activity
747 // tracking.
748 if (toRenameIndex) {
749 wroteToTimeBuffer = true;
750 }
751}
| 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].doneSeqNum = inst->seqNum;
282 toFetch->decodeInfo[tid].predIncorrect = true;
283 toFetch->decodeInfo[tid].squash = true;
284 toFetch->decodeInfo[tid].nextPC = inst->branchTarget();
285 toFetch->decodeInfo[tid].branchTaken =
286 inst->readNextPC() != (inst->readPC() + sizeof(TheISA::MachInst));
287
288 // Might have to tell fetch to unblock.
289 if (decodeStatus[tid] == Blocked ||
290 decodeStatus[tid] == Unblocking) {
291 toFetch->decodeUnblock[tid] = 1;
292 }
293
294 // Set status to squashing.
295 decodeStatus[tid] = Squashing;
296
297 for (int i=0; i<fromFetch->size; i++) {
298 if (fromFetch->insts[i]->threadNumber == tid &&
299 fromFetch->insts[i]->seqNum > inst->seqNum) {
300 fromFetch->insts[i]->setSquashed();
301 }
302 }
303
304 // Clear the instruction list and skid buffer in case they have any
305 // insts in them.
306 while (!insts[tid].empty()) {
307 insts[tid].pop();
308 }
309
310 while (!skidBuffer[tid].empty()) {
311 skidBuffer[tid].pop();
312 }
313
314 // Squash instructions up until this one
315 cpu->removeInstsUntil(inst->seqNum, tid);
316}
317
318template<class Impl>
319unsigned
320DefaultDecode<Impl>::squash(unsigned tid)
321{
322 DPRINTF(Decode, "[tid:%i]: Squashing.\n",tid);
323
324 if (decodeStatus[tid] == Blocked ||
325 decodeStatus[tid] == Unblocking) {
326#if !FULL_SYSTEM
327 // In syscall emulation, we can have both a block and a squash due
328 // to a syscall in the same cycle. This would cause both signals to
329 // be high. This shouldn't happen in full system.
330 // @todo: Determine if this still happens.
331 if (toFetch->decodeBlock[tid]) {
332 toFetch->decodeBlock[tid] = 0;
333 } else {
334 toFetch->decodeUnblock[tid] = 1;
335 }
336#else
337 toFetch->decodeUnblock[tid] = 1;
338#endif
339 }
340
341 // Set status to squashing.
342 decodeStatus[tid] = Squashing;
343
344 // Go through incoming instructions from fetch and squash them.
345 unsigned squash_count = 0;
346
347 for (int i=0; i<fromFetch->size; i++) {
348 if (fromFetch->insts[i]->threadNumber == tid) {
349 fromFetch->insts[i]->setSquashed();
350 squash_count++;
351 }
352 }
353
354 // Clear the instruction list and skid buffer in case they have any
355 // insts in them.
356 while (!insts[tid].empty()) {
357 insts[tid].pop();
358 }
359
360 while (!skidBuffer[tid].empty()) {
361 skidBuffer[tid].pop();
362 }
363
364 return squash_count;
365}
366
367template<class Impl>
368void
369DefaultDecode<Impl>::skidInsert(unsigned tid)
370{
371 DynInstPtr inst = NULL;
372
373 while (!insts[tid].empty()) {
374 inst = insts[tid].front();
375
376 insts[tid].pop();
377
378 assert(tid == inst->threadNumber);
379
380 DPRINTF(Decode,"Inserting [sn:%lli] PC:%#x into decode skidBuffer %i\n",
381 inst->seqNum, inst->readPC(), inst->threadNumber);
382
383 skidBuffer[tid].push(inst);
384 }
385
386 // @todo: Eventually need to enforce this by not letting a thread
387 // fetch past its skidbuffer
388 assert(skidBuffer[tid].size() <= skidBufferMax);
389}
390
391template<class Impl>
392bool
393DefaultDecode<Impl>::skidsEmpty()
394{
395 list<unsigned>::iterator threads = (*activeThreads).begin();
396
397 while (threads != (*activeThreads).end()) {
398 if (!skidBuffer[*threads++].empty())
399 return false;
400 }
401
402 return true;
403}
404
405template<class Impl>
406void
407DefaultDecode<Impl>::updateStatus()
408{
409 bool any_unblocking = false;
410
411 list<unsigned>::iterator threads = (*activeThreads).begin();
412
413 threads = (*activeThreads).begin();
414
415 while (threads != (*activeThreads).end()) {
416 unsigned tid = *threads++;
417
418 if (decodeStatus[tid] == Unblocking) {
419 any_unblocking = true;
420 break;
421 }
422 }
423
424 // Decode will have activity if it's unblocking.
425 if (any_unblocking) {
426 if (_status == Inactive) {
427 _status = Active;
428
429 DPRINTF(Activity, "Activating stage.\n");
430
431 cpu->activateStage(O3CPU::DecodeIdx);
432 }
433 } else {
434 // If it's not unblocking, then decode will not have any internal
435 // activity. Switch it to inactive.
436 if (_status == Active) {
437 _status = Inactive;
438 DPRINTF(Activity, "Deactivating stage.\n");
439
440 cpu->deactivateStage(O3CPU::DecodeIdx);
441 }
442 }
443}
444
445template <class Impl>
446void
447DefaultDecode<Impl>::sortInsts()
448{
449 int insts_from_fetch = fromFetch->size;
450#ifdef DEBUG
451 for (int i=0; i < numThreads; i++)
452 assert(insts[i].empty());
453#endif
454 for (int i = 0; i < insts_from_fetch; ++i) {
455 insts[fromFetch->insts[i]->threadNumber].push(fromFetch->insts[i]);
456 }
457}
458
459template<class Impl>
460void
461DefaultDecode<Impl>::readStallSignals(unsigned tid)
462{
463 if (fromRename->renameBlock[tid]) {
464 stalls[tid].rename = true;
465 }
466
467 if (fromRename->renameUnblock[tid]) {
468 assert(stalls[tid].rename);
469 stalls[tid].rename = false;
470 }
471
472 if (fromIEW->iewBlock[tid]) {
473 stalls[tid].iew = true;
474 }
475
476 if (fromIEW->iewUnblock[tid]) {
477 assert(stalls[tid].iew);
478 stalls[tid].iew = false;
479 }
480
481 if (fromCommit->commitBlock[tid]) {
482 stalls[tid].commit = true;
483 }
484
485 if (fromCommit->commitUnblock[tid]) {
486 assert(stalls[tid].commit);
487 stalls[tid].commit = false;
488 }
489}
490
491template <class Impl>
492bool
493DefaultDecode<Impl>::checkSignalsAndUpdate(unsigned tid)
494{
495 // Check if there's a squash signal, squash if there is.
496 // Check stall signals, block if necessary.
497 // If status was blocked
498 // Check if stall conditions have passed
499 // if so then go to unblocking
500 // If status was Squashing
501 // check if squashing is not high. Switch to running this cycle.
502
503 // Update the per thread stall statuses.
504 readStallSignals(tid);
505
506 // Check squash signals from commit.
507 if (fromCommit->commitInfo[tid].squash) {
508
509 DPRINTF(Decode, "[tid:%u]: Squashing instructions due to squash "
510 "from commit.\n", tid);
511
512 squash(tid);
513
514 return true;
515 }
516
517 // Check ROB squash signals from commit.
518 if (fromCommit->commitInfo[tid].robSquashing) {
519 DPRINTF(Decode, "[tid:%u]: ROB is still squashing.\n", tid);
520
521 // Continue to squash.
522 decodeStatus[tid] = Squashing;
523
524 return true;
525 }
526
527 if (checkStall(tid)) {
528 return block(tid);
529 }
530
531 if (decodeStatus[tid] == Blocked) {
532 DPRINTF(Decode, "[tid:%u]: Done blocking, switching to unblocking.\n",
533 tid);
534
535 decodeStatus[tid] = Unblocking;
536
537 unblock(tid);
538
539 return true;
540 }
541
542 if (decodeStatus[tid] == Squashing) {
543 // Switch status to running if decode isn't being told to block or
544 // squash this cycle.
545 DPRINTF(Decode, "[tid:%u]: Done squashing, switching to running.\n",
546 tid);
547
548 decodeStatus[tid] = Running;
549
550 return false;
551 }
552
553 // If we've reached this point, we have not gotten any signals that
554 // cause decode to change its status. Decode remains the same as before.
555 return false;
556}
557
558template<class Impl>
559void
560DefaultDecode<Impl>::tick()
561{
562 wroteToTimeBuffer = false;
563
564 bool status_change = false;
565
566 toRenameIndex = 0;
567
568 list<unsigned>::iterator threads = (*activeThreads).begin();
569
570 sortInsts();
571
572 //Check stall and squash signals.
573 while (threads != (*activeThreads).end()) {
574 unsigned tid = *threads++;
575
576 DPRINTF(Decode,"Processing [tid:%i]\n",tid);
577 status_change = checkSignalsAndUpdate(tid) || status_change;
578
579 decode(status_change, tid);
580 }
581
582 if (status_change) {
583 updateStatus();
584 }
585
586 if (wroteToTimeBuffer) {
587 DPRINTF(Activity, "Activity this cycle.\n");
588
589 cpu->activityThisCycle();
590 }
591}
592
593template<class Impl>
594void
595DefaultDecode<Impl>::decode(bool &status_change, unsigned tid)
596{
597 // If status is Running or idle,
598 // call decodeInsts()
599 // If status is Unblocking,
600 // buffer any instructions coming from fetch
601 // continue trying to empty skid buffer
602 // check if stall conditions have passed
603
604 if (decodeStatus[tid] == Blocked) {
605 ++decodeBlockedCycles;
606 } else if (decodeStatus[tid] == Squashing) {
607 ++decodeSquashCycles;
608 }
609
610 // Decode should try to decode as many instructions as its bandwidth
611 // will allow, as long as it is not currently blocked.
612 if (decodeStatus[tid] == Running ||
613 decodeStatus[tid] == Idle) {
614 DPRINTF(Decode, "[tid:%u] Not blocked, so attempting to run "
615 "stage.\n",tid);
616
617 decodeInsts(tid);
618 } else if (decodeStatus[tid] == Unblocking) {
619 // Make sure that the skid buffer has something in it if the
620 // status is unblocking.
621 assert(!skidsEmpty());
622
623 // If the status was unblocking, then instructions from the skid
624 // buffer were used. Remove those instructions and handle
625 // the rest of unblocking.
626 decodeInsts(tid);
627
628 if (fetchInstsValid()) {
629 // Add the current inputs to the skid buffer so they can be
630 // reprocessed when this stage unblocks.
631 skidInsert(tid);
632 }
633
634 status_change = unblock(tid) || status_change;
635 }
636}
637
638template <class Impl>
639void
640DefaultDecode<Impl>::decodeInsts(unsigned tid)
641{
642 // Instructions can come either from the skid buffer or the list of
643 // instructions coming from fetch, depending on decode's status.
644 int insts_available = decodeStatus[tid] == Unblocking ?
645 skidBuffer[tid].size() : insts[tid].size();
646
647 if (insts_available == 0) {
648 DPRINTF(Decode, "[tid:%u] Nothing to do, breaking out"
649 " early.\n",tid);
650 // Should I change the status to idle?
651 ++decodeIdleCycles;
652 return;
653 } else if (decodeStatus[tid] == Unblocking) {
654 DPRINTF(Decode, "[tid:%u] Unblocking, removing insts from skid "
655 "buffer.\n",tid);
656 ++decodeUnblockCycles;
657 } else if (decodeStatus[tid] == Running) {
658 ++decodeRunCycles;
659 }
660
661 DynInstPtr inst;
662
663 std::queue<DynInstPtr>
664 &insts_to_decode = decodeStatus[tid] == Unblocking ?
665 skidBuffer[tid] : insts[tid];
666
667 DPRINTF(Decode, "[tid:%u]: Sending instruction to rename.\n",tid);
668
669 while (insts_available > 0 && toRenameIndex < decodeWidth) {
670 assert(!insts_to_decode.empty());
671
672 inst = insts_to_decode.front();
673
674 insts_to_decode.pop();
675
676 DPRINTF(Decode, "[tid:%u]: Processing instruction [sn:%lli] with "
677 "PC %#x\n",
678 tid, inst->seqNum, inst->readPC());
679
680 if (inst->isSquashed()) {
681 DPRINTF(Decode, "[tid:%u]: Instruction %i with PC %#x is "
682 "squashed, skipping.\n",
683 tid, inst->seqNum, inst->readPC());
684
685 ++decodeSquashedInsts;
686
687 --insts_available;
688
689 continue;
690 }
691
692 // Also check if instructions have no source registers. Mark
693 // them as ready to issue at any time. Not sure if this check
694 // should exist here or at a later stage; however it doesn't matter
695 // too much for function correctness.
696 if (inst->numSrcRegs() == 0) {
697 inst->setCanIssue();
698 }
699
700 // This current instruction is valid, so add it into the decode
701 // queue. The next instruction may not be valid, so check to
702 // see if branches were predicted correctly.
703 toRename->insts[toRenameIndex] = inst;
704
705 ++(toRename->size);
706 ++toRenameIndex;
707 ++decodeDecodedInsts;
708 --insts_available;
709
710 // Ensure that if it was predicted as a branch, it really is a
711 // branch.
712 if (inst->predTaken() && !inst->isControl()) {
713 panic("Instruction predicted as a branch!");
714
715 ++decodeControlMispred;
716
717 // Might want to set some sort of boolean and just do
718 // a check at the end
719 squash(inst, inst->threadNumber);
720
721 break;
722 }
723
724 // Go ahead and compute any PC-relative branches.
725 if (inst->isDirectCtrl() && inst->isUncondCtrl()) {
726 ++decodeBranchResolved;
727
728 if (inst->branchTarget() != inst->readPredTarg()) {
729 ++decodeBranchMispred;
730
731 // Might want to set some sort of boolean and just do
732 // a check at the end
733 squash(inst, inst->threadNumber);
734 inst->setPredTarg(inst->branchTarget());
735
736 break;
737 }
738 }
739 }
740
741 // If we didn't process all instructions, then we will need to block
742 // and put all those instructions into the skid buffer.
743 if (!insts_to_decode.empty()) {
744 block(tid);
745 }
746
747 // Record that decode has written to the time buffer for activity
748 // tracking.
749 if (toRenameIndex) {
750 wroteToTimeBuffer = true;
751 }
752}
|