ScoreboardHazardRecognizer.cpp revision fc992996f751e0941951b6d08d8f1e80ebec1385 
1//===----- ScoreboardHazardRecognizer.cpp - Scheduler Support -------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the ScoreboardHazardRecognizer class, which
11// encapsultes hazard-avoidance heuristics for scheduling, based on the
12// scheduling itineraries specified for the target.
13//
14//===----------------------------------------------------------------------===//
15
16#define DEBUG_TYPE ::llvm::ScoreboardHazardRecognizer::DebugType
17#include "llvm/CodeGen/ScoreboardHazardRecognizer.h"
18#include "llvm/CodeGen/ScheduleDAG.h"
19#include "llvm/MC/MCInstrItineraries.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/ErrorHandling.h"
22#include "llvm/Support/raw_ostream.h"
23#include "llvm/Target/TargetInstrInfo.h"
24
25using namespace llvm;
26
27#ifndef NDEBUG
28const char *ScoreboardHazardRecognizer::DebugType = "";
29#endif
30
31ScoreboardHazardRecognizer::
32ScoreboardHazardRecognizer(const InstrItineraryData *II,
33                           const ScheduleDAG *SchedDAG,
34                           const char *ParentDebugType) :
35  ScheduleHazardRecognizer(), ItinData(II), DAG(SchedDAG), IssueWidth(0),
36  IssueCount(0) {
37
38#ifndef NDEBUG
39  DebugType = ParentDebugType;
40#endif
41
42  // Determine the maximum depth of any itinerary. This determines the depth of
43  // the scoreboard. We always make the scoreboard at least 1 cycle deep to
44  // avoid dealing with the boundary condition.
45  unsigned ScoreboardDepth = 1;
46  if (ItinData && !ItinData->isEmpty()) {
47    for (unsigned idx = 0; ; ++idx) {
48      if (ItinData->isEndMarker(idx))
49        break;
50
51      const InstrStage *IS = ItinData->beginStage(idx);
52      const InstrStage *E = ItinData->endStage(idx);
53      unsigned CurCycle = 0;
54      unsigned ItinDepth = 0;
55      for (; IS != E; ++IS) {
56        unsigned StageDepth = CurCycle + IS->getCycles();
57        if (ItinDepth < StageDepth) ItinDepth = StageDepth;
58        CurCycle += IS->getNextCycles();
59      }
60
61      // Find the next power-of-2 >= ItinDepth
62      while (ItinDepth > ScoreboardDepth) {
63        ScoreboardDepth *= 2;
64        // Don't set MaxLookAhead until we find at least one nonzero stage.
65        // This way, an itinerary with no stages has MaxLookAhead==0, which
66        // completely bypasses the scoreboard hazard logic.
67        MaxLookAhead = ScoreboardDepth;
68      }
69    }
70  }
71
72  ReservedScoreboard.reset(ScoreboardDepth);
73  RequiredScoreboard.reset(ScoreboardDepth);
74
75  if (!isEnabled())
76    DEBUG(dbgs() << "Disabled scoreboard hazard recognizer\n");
77  else {
78    IssueWidth = ItinData->Props.IssueWidth;
79    DEBUG(dbgs() << "Using scoreboard hazard recognizer: Depth = "
80          << ScoreboardDepth << '\n');
81  }
82}
83
84void ScoreboardHazardRecognizer::Reset() {
85  IssueCount = 0;
86  RequiredScoreboard.reset();
87  ReservedScoreboard.reset();
88}
89
90void ScoreboardHazardRecognizer::Scoreboard::dump() const {
91  dbgs() << "Scoreboard:\n";
92
93  unsigned last = Depth - 1;
94  while ((last > 0) && ((*this)[last] == 0))
95    last--;
96
97  for (unsigned i = 0; i <= last; i++) {
98    unsigned FUs = (*this)[i];
99    dbgs() << "\t";
100    for (int j = 31; j >= 0; j--)
101      dbgs() << ((FUs & (1 << j)) ? '1' : '0');
102    dbgs() << '\n';
103  }
104}
105
106bool ScoreboardHazardRecognizer::atIssueLimit() const {
107  if (IssueWidth == 0)
108    return false;
109
110  return IssueCount == IssueWidth;
111}
112
113ScheduleHazardRecognizer::HazardType
114ScoreboardHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
115  if (!ItinData || ItinData->isEmpty())
116    return NoHazard;
117
118  // Note that stalls will be negative for bottom-up scheduling.
119  int cycle = Stalls;
120
121  // Use the itinerary for the underlying instruction to check for
122  // free FU's in the scoreboard at the appropriate future cycles.
123
124  const MCInstrDesc *MCID = DAG->getInstrDesc(SU);
125  if (MCID == NULL) {
126    // Don't check hazards for non-machineinstr Nodes.
127    return NoHazard;
128  }
129  unsigned idx = MCID->getSchedClass();
130  for (const InstrStage *IS = ItinData->beginStage(idx),
131         *E = ItinData->endStage(idx); IS != E; ++IS) {
132    // We must find one of the stage's units free for every cycle the
133    // stage is occupied. FIXME it would be more accurate to find the
134    // same unit free in all the cycles.
135    for (unsigned int i = 0; i < IS->getCycles(); ++i) {
136      int StageCycle = cycle + (int)i;
137      if (StageCycle < 0)
138        continue;
139
140      if (StageCycle >= (int)RequiredScoreboard.getDepth()) {
141        assert((StageCycle - Stalls) < (int)RequiredScoreboard.getDepth() &&
142               "Scoreboard depth exceeded!");
143        // This stage was stalled beyond pipeline depth, so cannot conflict.
144        break;
145      }
146
147      unsigned freeUnits = IS->getUnits();
148      switch (IS->getReservationKind()) {
149      case InstrStage::Required:
150        // Required FUs conflict with both reserved and required ones
151        freeUnits &= ~ReservedScoreboard[StageCycle];
152        // FALLTHROUGH
153      case InstrStage::Reserved:
154        // Reserved FUs can conflict only with required ones.
155        freeUnits &= ~RequiredScoreboard[StageCycle];
156        break;
157      }
158
159      if (!freeUnits) {
160        DEBUG(dbgs() << "*** Hazard in cycle +" << StageCycle << ", ");
161        DEBUG(dbgs() << "SU(" << SU->NodeNum << "): ");
162        DEBUG(DAG->dumpNode(SU));
163        return Hazard;
164      }
165    }
166
167    // Advance the cycle to the next stage.
168    cycle += IS->getNextCycles();
169  }
170
171  return NoHazard;
172}
173
174void ScoreboardHazardRecognizer::EmitInstruction(SUnit *SU) {
175  if (!ItinData || ItinData->isEmpty())
176    return;
177
178  // Use the itinerary for the underlying instruction to reserve FU's
179  // in the scoreboard at the appropriate future cycles.
180  const MCInstrDesc *MCID = DAG->getInstrDesc(SU);
181  assert(MCID && "The scheduler must filter non-machineinstrs");
182  if (DAG->TII->isZeroCost(MCID->Opcode))
183    return;
184
185  ++IssueCount;
186
187  unsigned cycle = 0;
188
189  unsigned idx = MCID->getSchedClass();
190  for (const InstrStage *IS = ItinData->beginStage(idx),
191         *E = ItinData->endStage(idx); IS != E; ++IS) {
192    // We must reserve one of the stage's units for every cycle the
193    // stage is occupied. FIXME it would be more accurate to reserve
194    // the same unit free in all the cycles.
195    for (unsigned int i = 0; i < IS->getCycles(); ++i) {
196      assert(((cycle + i) < RequiredScoreboard.getDepth()) &&
197             "Scoreboard depth exceeded!");
198
199      unsigned freeUnits = IS->getUnits();
200      switch (IS->getReservationKind()) {
201      case InstrStage::Required:
202        // Required FUs conflict with both reserved and required ones
203        freeUnits &= ~ReservedScoreboard[cycle + i];
204        // FALLTHROUGH
205      case InstrStage::Reserved:
206        // Reserved FUs can conflict only with required ones.
207        freeUnits &= ~RequiredScoreboard[cycle + i];
208        break;
209      }
210
211      // reduce to a single unit
212      unsigned freeUnit = 0;
213      do {
214        freeUnit = freeUnits;
215        freeUnits = freeUnit & (freeUnit - 1);
216      } while (freeUnits);
217
218      if (IS->getReservationKind() == InstrStage::Required)
219        RequiredScoreboard[cycle + i] |= freeUnit;
220      else
221        ReservedScoreboard[cycle + i] |= freeUnit;
222    }
223
224    // Advance the cycle to the next stage.
225    cycle += IS->getNextCycles();
226  }
227
228  DEBUG(ReservedScoreboard.dump());
229  DEBUG(RequiredScoreboard.dump());
230}
231
232void ScoreboardHazardRecognizer::AdvanceCycle() {
233  IssueCount = 0;
234  ReservedScoreboard[0] = 0; ReservedScoreboard.advance();
235  RequiredScoreboard[0] = 0; RequiredScoreboard.advance();
236}
237
238void ScoreboardHazardRecognizer::RecedeCycle() {
239  IssueCount = 0;
240  ReservedScoreboard[ReservedScoreboard.getDepth()-1] = 0;
241  ReservedScoreboard.recede();
242  RequiredScoreboard[RequiredScoreboard.getDepth()-1] = 0;
243  RequiredScoreboard.recede();
244}
245