lib/CodeGen/ExactHazardRecognizer.cpp

   1 //===----- ExactHazardRecognizer.cpp - hazard recognizer -------- ---------===//
   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 implements a a hazard recognizer using the instructions itineraries
  11 // defined for the current target.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "exact-hazards"
  16 #include "ExactHazardRecognizer.h"
  17 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
  18 #include "llvm/Support/Debug.h"
  19 #include "llvm/Support/ErrorHandling.h"
  20 #include "llvm/Support/raw_ostream.h"
  21 #include "llvm/Target/TargetInstrItineraries.h"
  22
  23 using namespace llvm;
  24
  25 ExactHazardRecognizer::ExactHazardRecognizer(const InstrItineraryData &LItinData) :
  26   ScheduleHazardRecognizer(), ItinData(LItinData)
  27 {
  28   // Determine the maximum depth of any itinerary. This determines the
  29   // depth of the scoreboard. We always make the scoreboard at least 1
  30   // cycle deep to avoid dealing with the boundary condition.
  31   ScoreboardDepth = 1;
  32   if (!ItinData.isEmpty()) {
  33     for (unsigned idx = 0; ; ++idx) {
  34       // If the begin stage of an itinerary has 0 cycles and units,
  35       // then we have reached the end of the itineraries.
  36       const InstrStage *IS = ItinData.beginStage(idx);
  37       const InstrStage *E = ItinData.endStage(idx);
  38       if ((IS->getCycles() == 0) && (IS->getUnits() == 0))
  39         break;
  40
  41       unsigned ItinDepth = 0;
  42       for (; IS != E; ++IS)
  43         ItinDepth += IS->getCycles();
  44
  45       ScoreboardDepth = std::max(ScoreboardDepth, ItinDepth);
  46     }
  47   }
  48
  49   Scoreboard = new unsigned[ScoreboardDepth];
  50   ScoreboardHead = 0;
  51
  52   DEBUG(errs() << "Using exact hazard recognizer: ScoreboardDepth = "
  53                << ScoreboardDepth << '\n');
  54 }
  55
  56 ExactHazardRecognizer::~ExactHazardRecognizer() {
  57   delete [] Scoreboard;
  58 }
  59
  60 void ExactHazardRecognizer::Reset() {
  61   memset(Scoreboard, 0, ScoreboardDepth * sizeof(unsigned));
  62   ScoreboardHead = 0;
  63 }
  64
  65 unsigned ExactHazardRecognizer::getFutureIndex(unsigned offset) {
  66   return (ScoreboardHead + offset) % ScoreboardDepth;
  67 }
  68
  69 void ExactHazardRecognizer::dumpScoreboard() {
  70   errs() << "Scoreboard:\n";
  71
  72   unsigned last = ScoreboardDepth - 1;
  73   while ((last > 0) && (Scoreboard[getFutureIndex(last)] == 0))
  74     last--;
  75
  76   for (unsigned i = 0; i <= last; i++) {
  77     unsigned FUs = Scoreboard[getFutureIndex(i)];
  78     errs() << "\t";
  79     for (int j = 31; j >= 0; j--)
  80       errs() << ((FUs & (1 << j)) ? '1' : '0');
  81     errs() << '\n';
  82   }
  83 }
  84
  85 ExactHazardRecognizer::HazardType ExactHazardRecognizer::getHazardType(SUnit *SU) {
  86   if (!ItinData.isEmpty()) {
  87     unsigned cycle = 0;
  88
  89     // Use the itinerary for the underlying instruction to check for
  90     // free FU's in the scoreboard at the appropriate future cycles.
  91     unsigned idx = SU->getInstr()->getDesc().getSchedClass();
  92     for (const InstrStage *IS = ItinData.beginStage(idx),
  93            *E = ItinData.endStage(idx); IS != E; ++IS) {
  94       // We must find one of the stage's units free for every cycle the
  95       // stage is occupied. FIXME it would be more accurate to find the
  96       // same unit free in all the cycles.
  97       for (unsigned int i = 0; i < IS->getCycles(); ++i) {
  98         assert(((cycle + i) < ScoreboardDepth) &&
  99                "Scoreboard depth exceeded!");
 100
 101         unsigned index = getFutureIndex(cycle + i);
 102         unsigned freeUnits = IS->getUnits() & ~Scoreboard[index];
 103         if (!freeUnits) {
 104           DEBUG(errs() << "*** Hazard in cycle " << (cycle + i) << ", ");
 105           DEBUG(errs() << "SU(" << SU->NodeNum << "): ");
 106           DEBUG(SU->getInstr()->dump());
 107           return Hazard;
 108         }
 109       }
 110
 111       // Advance the cycle to the next stage.
 112       cycle += IS->getNextCycles();
 113     }
 114   }
 115
 116   return NoHazard;
 117 }
 118
 119 void ExactHazardRecognizer::EmitInstruction(SUnit *SU) {
 120   if (!ItinData.isEmpty()) {
 121     unsigned cycle = 0;
 122
 123     // Use the itinerary for the underlying instruction to reserve FU's
 124     // in the scoreboard at the appropriate future cycles.
 125     unsigned idx = SU->getInstr()->getDesc().getSchedClass();
 126     for (const InstrStage *IS = ItinData.beginStage(idx),
 127            *E = ItinData.endStage(idx); IS != E; ++IS) {
 128       // We must reserve one of the stage's units for every cycle the
 129       // stage is occupied. FIXME it would be more accurate to reserve
 130       // the same unit free in all the cycles.
 131       for (unsigned int i = 0; i < IS->getCycles(); ++i) {
 132         assert(((cycle + i) < ScoreboardDepth) &&
 133                "Scoreboard depth exceeded!");
 134
 135         unsigned index = getFutureIndex(cycle + i);
 136         unsigned freeUnits = IS->getUnits() & ~Scoreboard[index];
 137
 138         // reduce to a single unit
 139         unsigned freeUnit = 0;
 140         do {
 141           freeUnit = freeUnits;
 142           freeUnits = freeUnit & (freeUnit - 1);
 143         } while (freeUnits);
 144
 145         assert(freeUnit && "No function unit available!");
 146         Scoreboard[index] |= freeUnit;
 147       }
 148
 149       // Advance the cycle to the next stage.
 150       cycle += IS->getNextCycles();
 151     }
 152
 153     DEBUG(dumpScoreboard());
 154   }
 155 }
 156
 157 void ExactHazardRecognizer::AdvanceCycle() {
 158   Scoreboard[ScoreboardHead] = 0;
 159   ScoreboardHead = getFutureIndex(1);
 160 }