ScoreboardHazardRecognizer.cpp revision 9632f77f8dde9d2c9c9cb9d022b846a82c918cbd 
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
43  // depth of the scoreboard. We always make the scoreboard at least 1
44  // cycle deep to avoid dealing with the boundary condition.
45  unsigned ScoreboardDepth = 1;
46  if (ItinData && !ItinData->isEmpty()) {
47    IssueWidth = ItinData->IssueWidth;
48
49    for (unsigned idx = 0; ; ++idx) {
50      if (ItinData->isEndMarker(idx))
51        break;
52
53      const InstrStage *IS = ItinData->beginStage(idx);
54      const InstrStage *E = ItinData->endStage(idx);
55      unsigned CurCycle = 0;
56      unsigned ItinDepth = 0;
57      for (; IS != E; ++IS) {
58        unsigned StageDepth = CurCycle + IS->getCycles();
59        if (ItinDepth < StageDepth) ItinDepth = StageDepth;
60        CurCycle += IS->getNextCycles();
61      }
62
63      // Find the next power-of-2 >= ItinDepth
64      while (ItinDepth > ScoreboardDepth) {
65        ScoreboardDepth *= 2;
66      }
67    }
68    MaxLookAhead = ScoreboardDepth;
69  }
70
71  ReservedScoreboard.reset(ScoreboardDepth);
72  RequiredScoreboard.reset(ScoreboardDepth);
73
74  DEBUG(dbgs() << "Using scoreboard hazard recognizer: Depth = "
75               << ScoreboardDepth << '\n');
76}
77
78void ScoreboardHazardRecognizer::Reset() {
79  IssueCount = 0;
80  RequiredScoreboard.reset();
81  ReservedScoreboard.reset();
82}
83
84void ScoreboardHazardRecognizer::Scoreboard::dump() const {
85  dbgs() << "Scoreboard:\n";
86
87  unsigned last = Depth - 1;
88  while ((last > 0) && ((*this)[last] == 0))
89    last--;
90
91  for (unsigned i = 0; i <= last; i++) {
92    unsigned FUs = (*this)[i];
93    dbgs() << "\t";
94    for (int j = 31; j >= 0; j--)
95      dbgs() << ((FUs & (1 << j)) ? '1' : '0');
96    dbgs() << '\n';
97  }
98}
99
100bool ScoreboardHazardRecognizer::atIssueLimit() const {
101  if (IssueWidth == 0)
102    return false;
103
104  return IssueCount == IssueWidth;
105}
106
107ScheduleHazardRecognizer::HazardType
108ScoreboardHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
109  if (!ItinData || ItinData->isEmpty())
110    return NoHazard;
111
112  // Note that stalls will be negative for bottom-up scheduling.
113  int cycle = Stalls;
114
115  // Use the itinerary for the underlying instruction to check for
116  // free FU's in the scoreboard at the appropriate future cycles.
117
118  const MCInstrDesc *MCID = DAG->getInstrDesc(SU);
119  if (MCID == NULL) {
120    // Don't check hazards for non-machineinstr Nodes.
121    return NoHazard;
122  }
123  unsigned idx = MCID->getSchedClass();
124  for (const InstrStage *IS = ItinData->beginStage(idx),
125         *E = ItinData->endStage(idx); IS != E; ++IS) {
126    // We must find one of the stage's units free for every cycle the
127    // stage is occupied. FIXME it would be more accurate to find the
128    // same unit free in all the cycles.
129    for (unsigned int i = 0; i < IS->getCycles(); ++i) {
130      int StageCycle = cycle + (int)i;
131      if (StageCycle < 0)
132        continue;
133
134      if (StageCycle >= (int)RequiredScoreboard.getDepth()) {
135        assert((StageCycle - Stalls) < (int)RequiredScoreboard.getDepth() &&
136               "Scoreboard depth exceeded!");
137        // This stage was stalled beyond pipeline depth, so cannot conflict.
138        break;
139      }
140
141      unsigned freeUnits = IS->getUnits();
142      switch (IS->getReservationKind()) {
143      case InstrStage::Required:
144        // Required FUs conflict with both reserved and required ones
145        freeUnits &= ~ReservedScoreboard[StageCycle];
146        // FALLTHROUGH
147      case InstrStage::Reserved:
148        // Reserved FUs can conflict only with required ones.
149        freeUnits &= ~RequiredScoreboard[StageCycle];
150        break;
151      }
152
153      if (!freeUnits) {
154        DEBUG(dbgs() << "*** Hazard in cycle +" << StageCycle << ", ");
155        DEBUG(dbgs() << "SU(" << SU->NodeNum << "): ");
156        DEBUG(DAG->dumpNode(SU));
157        return Hazard;
158      }
159    }
160
161    // Advance the cycle to the next stage.
162    cycle += IS->getNextCycles();
163  }
164
165  return NoHazard;
166}
167
168void ScoreboardHazardRecognizer::EmitInstruction(SUnit *SU) {
169  if (!ItinData || ItinData->isEmpty())
170    return;
171
172  // Use the itinerary for the underlying instruction to reserve FU's
173  // in the scoreboard at the appropriate future cycles.
174  const MCInstrDesc *MCID = DAG->getInstrDesc(SU);
175  assert(MCID && "The scheduler must filter non-machineinstrs");
176  if (DAG->TII->isZeroCost(MCID->Opcode))
177    return;
178
179  ++IssueCount;
180
181  unsigned cycle = 0;
182
183  unsigned idx = MCID->getSchedClass();
184  for (const InstrStage *IS = ItinData->beginStage(idx),
185         *E = ItinData->endStage(idx); IS != E; ++IS) {
186    // We must reserve one of the stage's units for every cycle the
187    // stage is occupied. FIXME it would be more accurate to reserve
188    // the same unit free in all the cycles.
189    for (unsigned int i = 0; i < IS->getCycles(); ++i) {
190      assert(((cycle + i) < RequiredScoreboard.getDepth()) &&
191             "Scoreboard depth exceeded!");
192
193      unsigned freeUnits = IS->getUnits();
194      switch (IS->getReservationKind()) {
195      case InstrStage::Required:
196        // Required FUs conflict with both reserved and required ones
197        freeUnits &= ~ReservedScoreboard[cycle + i];
198        // FALLTHROUGH
199      case InstrStage::Reserved:
200        // Reserved FUs can conflict only with required ones.
201        freeUnits &= ~RequiredScoreboard[cycle + i];
202        break;
203      }
204
205      // reduce to a single unit
206      unsigned freeUnit = 0;
207      do {
208        freeUnit = freeUnits;
209        freeUnits = freeUnit & (freeUnit - 1);
210      } while (freeUnits);
211
212      if (IS->getReservationKind() == InstrStage::Required)
213        RequiredScoreboard[cycle + i] |= freeUnit;
214      else
215        ReservedScoreboard[cycle + i] |= freeUnit;
216    }
217
218    // Advance the cycle to the next stage.
219    cycle += IS->getNextCycles();
220  }
221
222  DEBUG(ReservedScoreboard.dump());
223  DEBUG(RequiredScoreboard.dump());
224}
225
226void ScoreboardHazardRecognizer::AdvanceCycle() {
227  IssueCount = 0;
228  ReservedScoreboard[0] = 0; ReservedScoreboard.advance();
229  RequiredScoreboard[0] = 0; RequiredScoreboard.advance();
230}
231
232void ScoreboardHazardRecognizer::RecedeCycle() {
233  IssueCount = 0;
234  ReservedScoreboard[ReservedScoreboard.getDepth()-1] = 0;
235  ReservedScoreboard.recede();
236  RequiredScoreboard[RequiredScoreboard.getDepth()-1] = 0;
237  RequiredScoreboard.recede();
238}
239