LCOV - code coverage report
Current view: top level - lib/CodeGen/SelectionDAG - ScheduleDAGVLIW.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 2 76 2.6 %
Date: 2018-06-17 00:07:59 Functions: 2 10 20.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- ScheduleDAGVLIW.cpp - SelectionDAG list scheduler for VLIW -*- C++ -*-=//
       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 top-down list scheduler, using standard algorithms.
      11             : // The basic approach uses a priority queue of available nodes to schedule.
      12             : // One at a time, nodes are taken from the priority queue (thus in priority
      13             : // order), checked for legality to schedule, and emitted if legal.
      14             : //
      15             : // Nodes may not be legal to schedule either due to structural hazards (e.g.
      16             : // pipeline or resource constraints) or because an input to the instruction has
      17             : // not completed execution.
      18             : //
      19             : //===----------------------------------------------------------------------===//
      20             : 
      21             : #include "ScheduleDAGSDNodes.h"
      22             : #include "llvm/ADT/Statistic.h"
      23             : #include "llvm/CodeGen/LatencyPriorityQueue.h"
      24             : #include "llvm/CodeGen/ResourcePriorityQueue.h"
      25             : #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
      26             : #include "llvm/CodeGen/SchedulerRegistry.h"
      27             : #include "llvm/CodeGen/SelectionDAGISel.h"
      28             : #include "llvm/CodeGen/TargetInstrInfo.h"
      29             : #include "llvm/CodeGen/TargetRegisterInfo.h"
      30             : #include "llvm/CodeGen/TargetSubtargetInfo.h"
      31             : #include "llvm/IR/DataLayout.h"
      32             : #include "llvm/Support/Debug.h"
      33             : #include "llvm/Support/ErrorHandling.h"
      34             : #include "llvm/Support/raw_ostream.h"
      35             : #include <climits>
      36             : using namespace llvm;
      37             : 
      38             : #define DEBUG_TYPE "pre-RA-sched"
      39             : 
      40             : STATISTIC(NumNoops , "Number of noops inserted");
      41             : STATISTIC(NumStalls, "Number of pipeline stalls");
      42             : 
      43             : static RegisterScheduler
      44      101169 :   VLIWScheduler("vliw-td", "VLIW scheduler",
      45             :                 createVLIWDAGScheduler);
      46             : 
      47             : namespace {
      48             : //===----------------------------------------------------------------------===//
      49             : /// ScheduleDAGVLIW - The actual DFA list scheduler implementation.  This
      50             : /// supports / top-down scheduling.
      51             : ///
      52             : class ScheduleDAGVLIW : public ScheduleDAGSDNodes {
      53             : private:
      54             :   /// AvailableQueue - The priority queue to use for the available SUnits.
      55             :   ///
      56             :   SchedulingPriorityQueue *AvailableQueue;
      57             : 
      58             :   /// PendingQueue - This contains all of the instructions whose operands have
      59             :   /// been issued, but their results are not ready yet (due to the latency of
      60             :   /// the operation).  Once the operands become available, the instruction is
      61             :   /// added to the AvailableQueue.
      62             :   std::vector<SUnit*> PendingQueue;
      63             : 
      64             :   /// HazardRec - The hazard recognizer to use.
      65             :   ScheduleHazardRecognizer *HazardRec;
      66             : 
      67             :   /// AA - AliasAnalysis for making memory reference queries.
      68             :   AliasAnalysis *AA;
      69             : 
      70             : public:
      71           0 :   ScheduleDAGVLIW(MachineFunction &mf,
      72             :                   AliasAnalysis *aa,
      73             :                   SchedulingPriorityQueue *availqueue)
      74           0 :     : ScheduleDAGSDNodes(mf), AvailableQueue(availqueue), AA(aa) {
      75           0 :     const TargetSubtargetInfo &STI = mf.getSubtarget();
      76           0 :     HazardRec = STI.getInstrInfo()->CreateTargetHazardRecognizer(&STI, this);
      77           0 :   }
      78             : 
      79           0 :   ~ScheduleDAGVLIW() override {
      80           0 :     delete HazardRec;
      81           0 :     delete AvailableQueue;
      82           0 :   }
      83             : 
      84             :   void Schedule() override;
      85             : 
      86             : private:
      87             :   void releaseSucc(SUnit *SU, const SDep &D);
      88             :   void releaseSuccessors(SUnit *SU);
      89             :   void scheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
      90             :   void listScheduleTopDown();
      91             : };
      92             : }  // end anonymous namespace
      93             : 
      94             : /// Schedule - Schedule the DAG using list scheduling.
      95           0 : void ScheduleDAGVLIW::Schedule() {
      96             :   LLVM_DEBUG(dbgs() << "********** List Scheduling " << printMBBReference(*BB)
      97             :                     << " '" << BB->getName() << "' **********\n");
      98             : 
      99             :   // Build the scheduling graph.
     100           0 :   BuildSchedGraph(AA);
     101             : 
     102           0 :   AvailableQueue->initNodes(SUnits);
     103             : 
     104           0 :   listScheduleTopDown();
     105             : 
     106           0 :   AvailableQueue->releaseState();
     107           0 : }
     108             : 
     109             : //===----------------------------------------------------------------------===//
     110             : //  Top-Down Scheduling
     111             : //===----------------------------------------------------------------------===//
     112             : 
     113             : /// releaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
     114             : /// the PendingQueue if the count reaches zero. Also update its cycle bound.
     115           0 : void ScheduleDAGVLIW::releaseSucc(SUnit *SU, const SDep &D) {
     116           0 :   SUnit *SuccSU = D.getSUnit();
     117             : 
     118             : #ifndef NDEBUG
     119             :   if (SuccSU->NumPredsLeft == 0) {
     120             :     dbgs() << "*** Scheduling failed! ***\n";
     121             :     SuccSU->dump(this);
     122             :     dbgs() << " has been released too many times!\n";
     123             :     llvm_unreachable(nullptr);
     124             :   }
     125             : #endif
     126             :   assert(!D.isWeak() && "unexpected artificial DAG edge");
     127             : 
     128           0 :   --SuccSU->NumPredsLeft;
     129             : 
     130           0 :   SuccSU->setDepthToAtLeast(SU->getDepth() + D.getLatency());
     131             : 
     132             :   // If all the node's predecessors are scheduled, this node is ready
     133             :   // to be scheduled. Ignore the special ExitSU node.
     134           0 :   if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU) {
     135           0 :     PendingQueue.push_back(SuccSU);
     136             :   }
     137           0 : }
     138             : 
     139             : void ScheduleDAGVLIW::releaseSuccessors(SUnit *SU) {
     140             :   // Top down: release successors.
     141           0 :   for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
     142           0 :        I != E; ++I) {
     143             :     assert(!I->isAssignedRegDep() &&
     144             :            "The list-td scheduler doesn't yet support physreg dependencies!");
     145             : 
     146           0 :     releaseSucc(SU, *I);
     147             :   }
     148             : }
     149             : 
     150             : /// scheduleNodeTopDown - Add the node to the schedule. Decrement the pending
     151             : /// count of its successors. If a successor pending count is zero, add it to
     152             : /// the Available queue.
     153           0 : void ScheduleDAGVLIW::scheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
     154             :   LLVM_DEBUG(dbgs() << "*** Scheduling [" << CurCycle << "]: ");
     155             :   LLVM_DEBUG(SU->dump(this));
     156             : 
     157           0 :   Sequence.push_back(SU);
     158             :   assert(CurCycle >= SU->getDepth() && "Node scheduled above its depth!");
     159           0 :   SU->setDepthToAtLeast(CurCycle);
     160             : 
     161           0 :   releaseSuccessors(SU);
     162           0 :   SU->isScheduled = true;
     163           0 :   AvailableQueue->scheduledNode(SU);
     164           0 : }
     165             : 
     166             : /// listScheduleTopDown - The main loop of list scheduling for top-down
     167             : /// schedulers.
     168           0 : void ScheduleDAGVLIW::listScheduleTopDown() {
     169             :   unsigned CurCycle = 0;
     170             : 
     171             :   // Release any successors of the special Entry node.
     172           0 :   releaseSuccessors(&EntrySU);
     173             : 
     174             :   // All leaves to AvailableQueue.
     175           0 :   for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
     176             :     // It is available if it has no predecessors.
     177           0 :     if (SUnits[i].Preds.empty()) {
     178           0 :       AvailableQueue->push(&SUnits[i]);
     179           0 :       SUnits[i].isAvailable = true;
     180             :     }
     181             :   }
     182             : 
     183             :   // While AvailableQueue is not empty, grab the node with the highest
     184             :   // priority. If it is not ready put it back.  Schedule the node.
     185             :   std::vector<SUnit*> NotReady;
     186           0 :   Sequence.reserve(SUnits.size());
     187           0 :   while (!AvailableQueue->empty() || !PendingQueue.empty()) {
     188             :     // Check to see if any of the pending instructions are ready to issue.  If
     189             :     // so, add them to the available queue.
     190           0 :     for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
     191           0 :       if (PendingQueue[i]->getDepth() == CurCycle) {
     192           0 :         AvailableQueue->push(PendingQueue[i]);
     193           0 :         PendingQueue[i]->isAvailable = true;
     194           0 :         PendingQueue[i] = PendingQueue.back();
     195             :         PendingQueue.pop_back();
     196           0 :         --i; --e;
     197             :       }
     198             :       else {
     199             :         assert(PendingQueue[i]->getDepth() > CurCycle && "Negative latency?");
     200             :       }
     201             :     }
     202             : 
     203             :     // If there are no instructions available, don't try to issue anything, and
     204             :     // don't advance the hazard recognizer.
     205           0 :     if (AvailableQueue->empty()) {
     206             :       // Reset DFA state.
     207           0 :       AvailableQueue->scheduledNode(nullptr);
     208           0 :       ++CurCycle;
     209           0 :       continue;
     210             :     }
     211             : 
     212             :     SUnit *FoundSUnit = nullptr;
     213             : 
     214             :     bool HasNoopHazards = false;
     215           0 :     while (!AvailableQueue->empty()) {
     216           0 :       SUnit *CurSUnit = AvailableQueue->pop();
     217             : 
     218             :       ScheduleHazardRecognizer::HazardType HT =
     219           0 :         HazardRec->getHazardType(CurSUnit, 0/*no stalls*/);
     220           0 :       if (HT == ScheduleHazardRecognizer::NoHazard) {
     221           0 :         FoundSUnit = CurSUnit;
     222           0 :         break;
     223             :       }
     224             : 
     225             :       // Remember if this is a noop hazard.
     226           0 :       HasNoopHazards |= HT == ScheduleHazardRecognizer::NoopHazard;
     227             : 
     228           0 :       NotReady.push_back(CurSUnit);
     229             :     }
     230             : 
     231             :     // Add the nodes that aren't ready back onto the available list.
     232           0 :     if (!NotReady.empty()) {
     233           0 :       AvailableQueue->push_all(NotReady);
     234             :       NotReady.clear();
     235             :     }
     236             : 
     237             :     // If we found a node to schedule, do it now.
     238           0 :     if (FoundSUnit) {
     239           0 :       scheduleNodeTopDown(FoundSUnit, CurCycle);
     240           0 :       HazardRec->EmitInstruction(FoundSUnit);
     241             : 
     242             :       // If this is a pseudo-op node, we don't want to increment the current
     243             :       // cycle.
     244           0 :       if (FoundSUnit->Latency)  // Don't increment CurCycle for pseudo-ops!
     245           0 :         ++CurCycle;
     246           0 :     } else if (!HasNoopHazards) {
     247             :       // Otherwise, we have a pipeline stall, but no other problem, just advance
     248             :       // the current cycle and try again.
     249             :       LLVM_DEBUG(dbgs() << "*** Advancing cycle, no work to do\n");
     250           0 :       HazardRec->AdvanceCycle();
     251             :       ++NumStalls;
     252           0 :       ++CurCycle;
     253             :     } else {
     254             :       // Otherwise, we have no instructions to issue and we have instructions
     255             :       // that will fault if we don't do this right.  This is the case for
     256             :       // processors without pipeline interlocks and other cases.
     257             :       LLVM_DEBUG(dbgs() << "*** Emitting noop\n");
     258           0 :       HazardRec->EmitNoop();
     259           0 :       Sequence.push_back(nullptr);   // NULL here means noop
     260             :       ++NumNoops;
     261           0 :       ++CurCycle;
     262             :     }
     263             :   }
     264             : 
     265             : #ifndef NDEBUG
     266             :   VerifyScheduledSequence(/*isBottomUp=*/false);
     267             : #endif
     268           0 : }
     269             : 
     270             : //===----------------------------------------------------------------------===//
     271             : //                         Public Constructor Functions
     272             : //===----------------------------------------------------------------------===//
     273             : 
     274             : /// createVLIWDAGScheduler - This creates a top-down list scheduler.
     275             : ScheduleDAGSDNodes *
     276           0 : llvm::createVLIWDAGScheduler(SelectionDAGISel *IS, CodeGenOpt::Level) {
     277           0 :   return new ScheduleDAGVLIW(*IS->MF, IS->AA, new ResourcePriorityQueue(IS));
     278      303507 : }

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