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 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.begin(idx), *E = ItinData.end(idx);
  37       if ((IS->getCycles() == 0) && (IS->getUnits() == 0))
  38         break;
  39
  40       unsigned ItinDepth = 0;
  41       for (; IS != E; ++IS)
  42         ItinDepth += IS->getCycles();
  43
  44       ScoreboardDepth = std::max(ScoreboardDepth, ItinDepth);
  45     }
  46   }
  47
  48   Scoreboard = new unsigned[ScoreboardDepth];
  49   ScoreboardHead = 0;
  50
  51   DEBUG(errs() << "Using exact hazard recognizer: ScoreboardDepth = "
  52         << ScoreboardDepth << '\n');
  53 }
  54
  55 ExactHazardRecognizer::~ExactHazardRecognizer() {
  56   delete Scoreboard;
  57 }
  58
  59 void ExactHazardRecognizer::Reset() {
  60   memset(Scoreboard, 0, ScoreboardDepth * sizeof(unsigned));
  61   ScoreboardHead = 0;
  62 }
  63
  64 unsigned ExactHazardRecognizer::getFutureIndex(unsigned offset) {
  65   return (ScoreboardHead + offset) % ScoreboardDepth;
  66 }
  67
  68 void ExactHazardRecognizer::dumpScoreboard() {
  69   errs() << "Scoreboard:\n";
  70
  71   unsigned last = ScoreboardDepth - 1;
  72   while ((last > 0) && (Scoreboard[getFutureIndex(last)] == 0))
  73     last--;
  74
  75   for (unsigned i = 0; i <= last; i++) {
  76     unsigned FUs = Scoreboard[getFutureIndex(i)];
  77     errs() << "\t";
  78     for (int j = 31; j >= 0; j--)
  79       errs() << ((FUs & (1 << j)) ? '1' : '0');
  80     errs() << '\n';
  81   }
  82 }
  83
  84 ExactHazardRecognizer::HazardType ExactHazardRecognizer::getHazardType(SUnit *SU) {
  85   unsigned cycle = 0;
  86
  87   // Use the itinerary for the underlying instruction to check for
  88   // free FU's in the scoreboard at the appropriate future cycles.
  89   unsigned idx = SU->getInstr()->getDesc().getSchedClass();
  90   for (const InstrStage *IS = ItinData.begin(idx), *E = ItinData.end(idx);
  91        IS != E; ++IS) {
  92     // We must find one of the stage's units free for every cycle the
  93     // stage is occupied. FIXME it would be more accurate to find the
  94     // same unit free in all the cycles.
  95     for (unsigned int i = 0; i < IS->getCycles(); ++i) {
  96       assert(((cycle + i) < ScoreboardDepth) &&
  97              "Scoreboard depth exceeded!");
  98
  99       unsigned index = getFutureIndex(cycle + i);
 100       unsigned freeUnits = IS->getUnits() & ~Scoreboard[index];
 101       if (!freeUnits) {
 102         DEBUG(errs() << "*** Hazard in cycle " << (cycle + i) << ", ");
 103         DEBUG(errs() << "SU(" << SU->NodeNum << "): ");
 104         DEBUG(SU->getInstr()->dump());
 105         return Hazard;
 106       }
 107     }
 108
 109     // Advance the cycle to the next stage.
 110     cycle += IS->getNextCycles();
 111   }
 112
 113   return NoHazard;
 114 }
 115
 116 void ExactHazardRecognizer::EmitInstruction(SUnit *SU) {
 117   unsigned cycle = 0;
 118
 119   // Use the itinerary for the underlying instruction to reserve FU's
 120   // in the scoreboard at the appropriate future cycles.
 121   unsigned idx = SU->getInstr()->getDesc().getSchedClass();
 122   for (const InstrStage *IS = ItinData.begin(idx), *E = ItinData.end(idx);
 123        IS != E; ++IS) {
 124     // We must reserve one of the stage's units for every cycle the
 125     // stage is occupied. FIXME it would be more accurate to reserve
 126     // the same unit free in all the cycles.
 127     for (unsigned int i = 0; i < IS->getCycles(); ++i) {
 128       assert(((cycle + i) < ScoreboardDepth) &&
 129              "Scoreboard depth exceeded!");
 130
 131       unsigned index = getFutureIndex(cycle + i);
 132       unsigned freeUnits = IS->getUnits() & ~Scoreboard[index];
 133
 134       // reduce to a single unit
 135       unsigned freeUnit = 0;
 136       do {
 137         freeUnit = freeUnits;
 138         freeUnits = freeUnit & (freeUnit - 1);
 139       } while (freeUnits);
 140
 141       assert(freeUnit && "No function unit available!");
 142       Scoreboard[index] |= freeUnit;
 143     }
 144
 145     // Advance the cycle to the next stage.
 146     cycle += IS->getNextCycles();
 147   }
 148
 149   DEBUG(dumpScoreboard());
 150 }
 151
 152 void ExactHazardRecognizer::AdvanceCycle() {
 153   Scoreboard[ScoreboardHead] = 0;
 154   ScoreboardHead = getFutureIndex(1);
 155 }
 156
 157 } /* namespace llvm */