PostRASchedulerList.cpp

//===----- SchedulePostRAList.cpp - list scheduler ------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements a top-down list scheduler, using standard algorithms.
// The basic approach uses a priority queue of available nodes to schedule.
// One at a time, nodes are taken from the priority queue (thus in priority
// order), checked for legality to schedule, and emitted if legal.
//
// Nodes may not be legal to schedule either due to structural hazards (e.g.
// pipeline or resource constraints) or because an input to the instruction has
// not completed execution.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "post-RA-sched"
#include "ExactHazardRecognizer.h"
#include "SimpleHazardRecognizer.h"
#include "ScheduleDAGInstrs.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/LatencyPriorityQueue.h"
#include "llvm/CodeGen/SchedulerRegistry.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/Statistic.h"
#include <map>
#include <set>
using namespace llvm;

STATISTIC(NumNoops, "Number of noops inserted");
STATISTIC(NumStalls, "Number of pipeline stalls");

static cl::opt<bool>
EnableAntiDepBreaking("break-anti-dependencies",
                      cl::desc("Break post-RA scheduling anti-dependencies"),
                      cl::init(true), cl::Hidden);

static cl::opt<bool>
EnablePostRAHazardAvoidance("avoid-hazards",
                      cl::desc("Enable exact hazard avoidance"),
                      cl::init(false), cl::Hidden);

namespace {
  class VISIBILITY_HIDDEN PostRAScheduler : public MachineFunctionPass {
  public:
    static char ID;
    PostRAScheduler() : MachineFunctionPass(&ID) {}

    void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.setPreservesCFG();
      AU.addRequired<MachineDominatorTree>();
      AU.addPreserved<MachineDominatorTree>();
      AU.addRequired<MachineLoopInfo>();
      AU.addPreserved<MachineLoopInfo>();
      MachineFunctionPass::getAnalysisUsage(AU);
    }

    const char *getPassName() const {
      return "Post RA top-down list latency scheduler";
    }

    bool runOnMachineFunction(MachineFunction &Fn);
  };
  char PostRAScheduler::ID = 0;

  class VISIBILITY_HIDDEN SchedulePostRATDList : public ScheduleDAGInstrs {
    /// AvailableQueue - The priority queue to use for the available SUnits.
    ///
    LatencyPriorityQueue AvailableQueue;
  
    /// PendingQueue - This contains all of the instructions whose operands have
    /// been issued, but their results are not ready yet (due to the latency of
    /// the operation).  Once the operands becomes available, the instruction is
    /// added to the AvailableQueue.
    std::vector<SUnit*> PendingQueue;

    /// Topo - A topological ordering for SUnits.
    ScheduleDAGTopologicalSort Topo;

    /// AllocatableSet - The set of allocatable registers.
    /// We'll be ignoring anti-dependencies on non-allocatable registers,
    /// because they may not be safe to break.
    const BitVector AllocatableSet;

    /// HazardRec - The hazard recognizer to use.
    ScheduleHazardRecognizer *HazardRec;

    /// Classes - For live regs that are only used in one register class in a
    /// live range, the register class. If the register is not live, the
    /// corresponding value is null. If the register is live but used in
    /// multiple register classes, the corresponding value is -1 casted to a
    /// pointer.
    const TargetRegisterClass *
      Classes[TargetRegisterInfo::FirstVirtualRegister];

    /// RegRegs - Map registers to all their references within a live range.
    std::multimap<unsigned, MachineOperand *> RegRefs;

    /// The index of the most recent kill (proceding bottom-up), or ~0u if
    /// the register is not live.
    unsigned KillIndices[TargetRegisterInfo::FirstVirtualRegister];

    /// The index of the most recent complete def (proceding bottom up), or ~0u
    /// if the register is live.
    unsigned DefIndices[TargetRegisterInfo::FirstVirtualRegister];

  public:
    SchedulePostRATDList(MachineFunction &MF,
                         const MachineLoopInfo &MLI,
                         const MachineDominatorTree &MDT,
                         ScheduleHazardRecognizer *HR)
      : ScheduleDAGInstrs(MF, MLI, MDT), Topo(SUnits),
        AllocatableSet(TRI->getAllocatableSet(MF)),
        HazardRec(HR) {}

    ~SchedulePostRATDList() {
      delete HazardRec;
    }

    /// StartBlock - Initialize register live-range state for scheduling in
    /// this block.
    ///
    void StartBlock(MachineBasicBlock *BB);

    /// Schedule - Schedule the instruction range using list scheduling.
    ///
    void Schedule();
    
    /// FixupKills - Fix register kill flags that have been made
    /// invalid due to scheduling
    ///
    void FixupKills(MachineBasicBlock *MBB);

    /// Observe - Update liveness information to account for the current
    /// instruction, which will not be scheduled.
    ///
    void Observe(MachineInstr *MI, unsigned Count);

    /// FinishBlock - Clean up register live-range state.
    ///
    void FinishBlock();

    /// GenerateLivenessForKills - If true then generate Def/Kill
    /// information for use in updating register kill. If false then
    /// generate Def/Kill information for anti-dependence breaking.
    bool GenerateLivenessForKills;

  private:
    void PrescanInstruction(MachineInstr *MI);
    void ScanInstruction(MachineInstr *MI, unsigned Count);
    void ReleaseSucc(SUnit *SU, SDep *SuccEdge);
    void ReleaseSuccessors(SUnit *SU);
    void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
    void ListScheduleTopDown();
    bool BreakAntiDependencies();
    unsigned findSuitableFreeRegister(unsigned AntiDepReg,
                                      unsigned LastNewReg,
                                      const TargetRegisterClass *);
  };
}

/// isSchedulingBoundary - Test if the given instruction should be
/// considered a scheduling boundary. This primarily includes labels
/// and terminators.
///
static bool isSchedulingBoundary(const MachineInstr *MI,
                                 const MachineFunction &MF) {
  // Terminators and labels can't be scheduled around.
  if (MI->getDesc().isTerminator() || MI->isLabel())
    return true;

  // Don't attempt to schedule around any instruction that modifies
  // a stack-oriented pointer, as it's unlikely to be profitable. This
  // saves compile time, because it doesn't require every single
  // stack slot reference to depend on the instruction that does the
  // modification.
  const TargetLowering &TLI = *MF.getTarget().getTargetLowering();
  if (MI->modifiesRegister(TLI.getStackPointerRegisterToSaveRestore()))
    return true;

  return false;
}

bool PostRAScheduler::runOnMachineFunction(MachineFunction &Fn) {