decode.cc revision 11793:ef606668d247 
1/*
2 * Copyright (c) 2013-2014 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 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions are
16 * met: redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer;
18 * redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution;
21 * neither the name of the copyright holders nor the names of its
22 * contributors may be used to endorse or promote products derived from
23 * this software without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
26 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
27 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
28 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
29 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
35 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 *
37 * Authors: Andrew Bardsley
38 */
39
40#include "cpu/minor/decode.hh"
41
42#include "cpu/minor/pipeline.hh"
43#include "debug/Decode.hh"
44
45namespace Minor
46{
47
48Decode::Decode(const std::string &name,
49    MinorCPU &cpu_,
50    MinorCPUParams &params,
51    Latch<ForwardInstData>::Output inp_,
52    Latch<ForwardInstData>::Input out_,
53    std::vector<InputBuffer<ForwardInstData>> &next_stage_input_buffer) :
54    Named(name),
55    cpu(cpu_),
56    inp(inp_),
57    out(out_),
58    nextStageReserve(next_stage_input_buffer),
59    outputWidth(params.executeInputWidth),
60    processMoreThanOneInput(params.decodeCycleInput),
61    decodeInfo(params.numThreads),
62    threadPriority(0)
63{
64    if (outputWidth < 1)
65        fatal("%s: executeInputWidth must be >= 1 (%d)\n", name, outputWidth);
66
67    if (params.decodeInputBufferSize < 1) {
68        fatal("%s: decodeInputBufferSize must be >= 1 (%d)\n", name,
69        params.decodeInputBufferSize);
70    }
71
72    /* Per-thread input buffers */
73    for (ThreadID tid = 0; tid < params.numThreads; tid++) {
74        inputBuffer.push_back(
75            InputBuffer<ForwardInstData>(
76                name + ".inputBuffer" + std::to_string(tid), "insts",
77                params.decodeInputBufferSize));
78    }
79}
80
81const ForwardInstData *
82Decode::getInput(ThreadID tid)
83{
84    /* Get insts from the inputBuffer to work with */
85    if (!inputBuffer[tid].empty()) {
86        const ForwardInstData &head = inputBuffer[tid].front();
87
88        return (head.isBubble() ? NULL : &(inputBuffer[tid].front()));
89    } else {
90        return NULL;
91    }
92}
93
94void
95Decode::popInput(ThreadID tid)
96{
97    if (!inputBuffer[tid].empty())
98        inputBuffer[tid].pop();
99
100    decodeInfo[tid].inputIndex = 0;
101    decodeInfo[tid].inMacroop = false;
102}
103
104#if TRACING_ON
105/** Add the tracing data to an instruction.  This originates in
106 *  decode because this is the first place that execSeqNums are known
107 *  (these are used as the 'FetchSeq' in tracing data) */
108static void
109dynInstAddTracing(MinorDynInstPtr inst, StaticInstPtr static_inst,
110    MinorCPU &cpu)
111{
112    inst->traceData = cpu.getTracer()->getInstRecord(curTick(),
113        cpu.getContext(inst->id.threadId),
114        inst->staticInst, inst->pc, static_inst);
115
116    /* Use the execSeqNum as the fetch sequence number as this most closely
117     *  matches the other processor models' idea of fetch sequence */
118    if (inst->traceData)
119        inst->traceData->setFetchSeq(inst->id.execSeqNum);
120}
121#endif
122
123void
124Decode::evaluate()
125{
126    /* Push input onto appropriate input buffer */
127    if (!inp.outputWire->isBubble())
128        inputBuffer[inp.outputWire->threadId].setTail(*inp.outputWire);
129
130    ForwardInstData &insts_out = *out.inputWire;
131
132    assert(insts_out.isBubble());
133
134    for (ThreadID tid = 0; tid < cpu.numThreads; tid++)
135        decodeInfo[tid].blocked = !nextStageReserve[tid].canReserve();
136
137    ThreadID tid = getScheduledThread();
138
139    if (tid != InvalidThreadID) {
140        DecodeThreadInfo &decode_info = decodeInfo[tid];
141        const ForwardInstData *insts_in = getInput(tid);
142
143        unsigned int output_index = 0;
144
145        /* Pack instructions into the output while we can.  This may involve
146         * using more than one input line */
147        while (insts_in &&
148           decode_info.inputIndex < insts_in->width() && /* Still more input */
149           output_index < outputWidth /* Still more output to fill */)
150        {
151            MinorDynInstPtr inst = insts_in->insts[decode_info.inputIndex];
152
153            if (inst->isBubble()) {
154                /* Skip */
155                decode_info.inputIndex++;
156                decode_info.inMacroop = false;
157            } else {
158                StaticInstPtr static_inst = inst->staticInst;
159                /* Static inst of a macro-op above the output_inst */
160                StaticInstPtr parent_static_inst = NULL;
161                MinorDynInstPtr output_inst = inst;
162
163                if (inst->isFault()) {
164                    DPRINTF(Decode, "Fault being passed: %d\n",
165                        inst->fault->name());
166
167                    decode_info.inputIndex++;
168                    decode_info.inMacroop = false;
169                } else if (static_inst->isMacroop()) {
170                    /* Generate a new micro-op */
171                    StaticInstPtr static_micro_inst;
172
173                    /* Set up PC for the next micro-op emitted */
174                    if (!decode_info.inMacroop) {
175                        decode_info.microopPC = inst->pc;
176                        decode_info.inMacroop = true;
177                    }
178
179                    /* Get the micro-op static instruction from the
180                     * static_inst. */
181                    static_micro_inst =
182                        static_inst->fetchMicroop(
183                                decode_info.microopPC.microPC());
184
185                    output_inst = new MinorDynInst(inst->id);
186                    output_inst->pc = decode_info.microopPC;
187                    output_inst->staticInst = static_micro_inst;
188                    output_inst->fault = NoFault;
189
190                    /* Allow a predicted next address only on the last
191                     *  microop */
192                    if (static_micro_inst->isLastMicroop()) {
193                        output_inst->predictedTaken = inst->predictedTaken;
194                        output_inst->predictedTarget = inst->predictedTarget;
195                    }
196
197                    DPRINTF(Decode, "Microop decomposition inputIndex:"
198                        " %d output_index: %d lastMicroop: %s microopPC:"
199                        " %d.%d inst: %d\n",
200                        decode_info.inputIndex, output_index,
201                        (static_micro_inst->isLastMicroop() ?
202                            "true" : "false"),
203                        decode_info.microopPC.instAddr(),
204                        decode_info.microopPC.microPC(),
205                        *output_inst);
206
207                    /* Acknowledge that the static_inst isn't mine, it's my
208                     * parent macro-op's */
209                    parent_static_inst = static_inst;
210
211                    static_micro_inst->advancePC(decode_info.microopPC);
212
213                    /* Step input if this is the last micro-op */
214                    if (static_micro_inst->isLastMicroop()) {
215                        decode_info.inputIndex++;
216                        decode_info.inMacroop = false;
217                    }
218                } else {
219                    /* Doesn't need decomposing, pass on instruction */
220                    DPRINTF(Decode, "Passing on inst: %s inputIndex:"
221                        " %d output_index: %d\n",
222                        *output_inst, decode_info.inputIndex, output_index);
223
224                    parent_static_inst = static_inst;
225
226                    /* Step input */
227                    decode_info.inputIndex++;
228                    decode_info.inMacroop = false;
229                }
230
231                /* Set execSeqNum of output_inst */
232                output_inst->id.execSeqNum = decode_info.execSeqNum;
233                /* Add tracing */
234#if TRACING_ON
235                dynInstAddTracing(output_inst, parent_static_inst, cpu);
236#endif
237
238                /* Step to next sequence number */
239                decode_info.execSeqNum++;
240
241                /* Correctly size the output before writing */
242                if (output_index == 0) insts_out.resize(outputWidth);
243                /* Push into output */
244                insts_out.insts[output_index] = output_inst;
245                output_index++;
246            }
247
248            /* Have we finished with the input? */
249            if (decode_info.inputIndex == insts_in->width()) {
250                /* If we have just been producing micro-ops, we *must* have
251                 * got to the end of that for inputIndex to be pushed past
252                 * insts_in->width() */
253                assert(!decode_info.inMacroop);
254                popInput(tid);
255                insts_in = NULL;
256
257                if (processMoreThanOneInput) {
258                    DPRINTF(Decode, "Wrapping\n");
259                    insts_in = getInput(tid);
260                }
261            }
262        }
263
264        /* The rest of the output (if any) should already have been packed
265         *  with bubble instructions by insts_out's initialisation
266         *
267         *  for (; output_index < outputWidth; output_index++)
268         *      assert(insts_out.insts[output_index]->isBubble());
269         */
270    }
271
272    /* If we generated output, reserve space for the result in the next stage
273     *  and mark the stage as being active this cycle */
274    if (!insts_out.isBubble()) {
275        /* Note activity of following buffer */
276        cpu.activityRecorder->activity();
277        insts_out.threadId = tid;
278        nextStageReserve[tid].reserve();
279    }
280
281    /* If we still have input to process and somewhere to put it,
282     *  mark stage as active */
283    for (ThreadID i = 0; i < cpu.numThreads; i++)
284    {
285        if (getInput(i) && nextStageReserve[i].canReserve()) {
286            cpu.activityRecorder->activateStage(Pipeline::DecodeStageId);
287            break;
288        }
289    }
290
291    /* Make sure the input (if any left) is pushed */
292    if (!inp.outputWire->isBubble())
293        inputBuffer[inp.outputWire->threadId].pushTail();
294}
295
296inline ThreadID
297Decode::getScheduledThread()
298{
299    /* Select thread via policy. */
300    std::vector<ThreadID> priority_list;
301
302    switch (cpu.threadPolicy) {
303      case Enums::SingleThreaded:
304        priority_list.push_back(0);
305        break;
306      case Enums::RoundRobin:
307        priority_list = cpu.roundRobinPriority(threadPriority);
308        break;
309      case Enums::Random:
310        priority_list = cpu.randomPriority();
311        break;
312      default:
313        panic("Unknown fetch policy");
314    }
315
316    for (auto tid : priority_list) {
317        if (getInput(tid) && !decodeInfo[tid].blocked) {
318            threadPriority = tid;
319            return tid;
320        }
321    }
322
323   return InvalidThreadID;
324}
325
326bool
327Decode::isDrained()
328{
329    for (const auto &buffer : inputBuffer) {
330        if (!buffer.empty())
331            return false;
332    }
333
334    return (*inp.outputWire).isBubble();
335}
336
337void
338Decode::minorTrace() const
339{
340    std::ostringstream data;
341
342    if (decodeInfo[0].blocked)
343        data << 'B';
344    else
345        (*out.inputWire).reportData(data);
346
347    MINORTRACE("insts=%s\n", data.str());
348    inputBuffer[0].minorTrace();
349}
350
351}
352