llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp

//===- SIInsertWaitcnts.cpp - Insert Wait Instructions --------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file
/// \brief Insert wait instructions for memory reads and writes.
///
/// Memory reads and writes are issued asynchronously, so we need to insert
/// S_WAITCNT instructions when we want to access any of their results or
/// overwrite any register that's used asynchronously.
//
//===----------------------------------------------------------------------===//

#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIDefines.h"
#include "SIInstrInfo.h"
#include "SIMachineFunctionInfo.h"
#include "SIRegisterInfo.h"
#include "Utils/AMDGPUBaseInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <cstring>
#include <memory>
#include <utility>
#include <vector>

#define DEBUG_TYPE "si-insert-waitcnts"

using namespace llvm;

namespace {

// Class of object that encapsulates latest instruction counter score
// associated with the operand.  Used for determining whether
// s_waitcnt instruction needs to be emited.

#define CNT_MASK(t) (1u << (t))

enum InstCounterType { VM_CNT = 0, LGKM_CNT, EXP_CNT, NUM_INST_CNTS };

using RegInterval = std::pair<signed, signed>;

struct {
  int32_t VmcntMax;
  int32_t ExpcntMax;
  int32_t LgkmcntMax;
  int32_t NumVGPRsMax;
  int32_t NumSGPRsMax;
} HardwareLimits;

struct {
  unsigned VGPR0;
  unsigned VGPRL;
  unsigned SGPR0;
  unsigned SGPRL;
} RegisterEncoding;

enum WaitEventType {
  VMEM_ACCESS,      // vector-memory read & write
  LDS_ACCESS,       // lds read & write
  GDS_ACCESS,       // gds read & write
  SQ_MESSAGE,       // send message
  SMEM_ACCESS,      // scalar-memory read & write
  EXP_GPR_LOCK,     // export holding on its data src
  GDS_GPR_LOCK,     // GDS holding on its data and addr src
  EXP_POS_ACCESS,   // write to export position
  EXP_PARAM_ACCESS, // write to export parameter
  VMW_GPR_LOCK,     // vector-memory write holding on its data src
  NUM_WAIT_EVENTS,
};

// The mapping is:
//  0                .. SQ_MAX_PGM_VGPRS-1               real VGPRs
//  SQ_MAX_PGM_VGPRS .. NUM_ALL_VGPRS-1                  extra VGPR-like slots
//  NUM_ALL_VGPRS    .. NUM_ALL_VGPRS+SQ_MAX_PGM_SGPRS-1 real SGPRs
// We reserve a fixed number of VGPR slots in the scoring tables for
// special tokens like SCMEM_LDS (needed for buffer load to LDS).
enum RegisterMapping {
  SQ_MAX_PGM_VGPRS = 256, // Maximum programmable VGPRs across all targets.
  SQ_MAX_PGM_SGPRS = 256, // Maximum programmable SGPRs across all targets.
  NUM_EXTRA_VGPRS = 1,    // A reserved slot for DS.
  EXTRA_VGPR_LDS = 0,     // This is a placeholder the Shader algorithm uses.
  NUM_ALL_VGPRS = SQ_MAX_PGM_VGPRS + NUM_EXTRA_VGPRS, // Where SGPR starts.
};

#define ForAllWaitEventType(w)                                                 \
  for (enum WaitEventType w = (enum WaitEventType)0;                           \
       (w) < (enum WaitEventType)NUM_WAIT_EVENTS;                              \
       (w) = (enum WaitEventType)((w) + 1))

// This is a per-basic-block object that maintains current score brackets
// of each wait-counter, and a per-register scoreboard for each wait-couner.
// We also maintain the latest score for every event type that can change the
// waitcnt in order to know if there are multiple types of events within
// the brackets. When multiple types of event happen in the bracket,
// wait-count may get decreased out of order, therefore we need to put in
// "s_waitcnt 0" before use.
class BlockWaitcntBrackets {
public:
  BlockWaitcntBrackets() {
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      memset(VgprScores[T], 0, sizeof(VgprScores[T]));
    }
  }

  ~BlockWaitcntBrackets() = default;

  static int32_t getWaitCountMax(InstCounterType T) {
    switch (T) {
    case VM_CNT:
      return HardwareLimits.VmcntMax;
    case LGKM_CNT:
      return HardwareLimits.LgkmcntMax;
    case EXP_CNT:
      return HardwareLimits.ExpcntMax;
    default:
      break;
    }
    return 0;
  }

  void setScoreLB(InstCounterType T, int32_t Val) {
    assert(T < NUM_INST_CNTS);
    if (T >= NUM_INST_CNTS)
      return;
    ScoreLBs[T] = Val;
  }

  void setScoreUB(InstCounterType T, int32_t Val) {
    assert(T < NUM_INST_CNTS);
    if (T >= NUM_INST_CNTS)
      return;
    ScoreUBs[T] = Val;
    if (T == EXP_CNT) {
      int32_t UB = (int)(ScoreUBs[T] - getWaitCountMax(EXP_CNT));
      if (ScoreLBs[T] < UB)
        ScoreLBs[T] = UB;
    }
  }

  int32_t getScoreLB(InstCounterType T) {
    assert(T < NUM_INST_CNTS);
    if (T >= NUM_INST_CNTS)
      return 0;
    return ScoreLBs[T];
  }

  int32_t getScoreUB(InstCounterType T) {
    assert(T < NUM_INST_CNTS);
    if (T >= NUM_INST_CNTS)
      return 0;
    return ScoreUBs[T];
  }

  // Mapping from event to counter.
  InstCounterType eventCounter(WaitEventType E) {
    switch (E) {
    case VMEM_ACCESS:
      return VM_CNT;
    case LDS_ACCESS:
    case GDS_ACCESS:
    case SQ_MESSAGE:
    case SMEM_ACCESS:
      return LGKM_CNT;
    case EXP_GPR_LOCK:
    case GDS_GPR_LOCK:
    case VMW_GPR_LOCK:
    case EXP_POS_ACCESS:
    case EXP_PARAM_ACCESS:
      return EXP_CNT;
    default:
      llvm_unreachable("unhandled event type");
    }
    return NUM_INST_CNTS;
  }

  void setRegScore(int GprNo, InstCounterType T, int32_t Val) {
    if (GprNo < NUM_ALL_VGPRS) {
      if (GprNo > VgprUB) {
        VgprUB = GprNo;
      }
      VgprScores[T][GprNo] = Val;
    } else {
      assert(T == LGKM_CNT);
      if (GprNo - NUM_ALL_VGPRS > SgprUB) {
        SgprUB = GprNo - NUM_ALL_VGPRS;
      }
      SgprScores[GprNo - NUM_ALL_VGPRS] = Val;
    }
  }

  int32_t getRegScore(int GprNo, InstCounterType T) {
    if (GprNo < NUM_ALL_VGPRS) {
      return VgprScores[T][GprNo];
    }
    return SgprScores[GprNo - NUM_ALL_VGPRS];
  }

  void clear() {
    memset(ScoreLBs, 0, sizeof(ScoreLBs));
    memset(ScoreUBs, 0, sizeof(ScoreUBs));
    memset(EventUBs, 0, sizeof(EventUBs));
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      memset(VgprScores[T], 0, sizeof(VgprScores[T]));
    }
    memset(SgprScores, 0, sizeof(SgprScores));
  }

  RegInterval getRegInterval(const MachineInstr *MI, const SIInstrInfo *TII,
                             const MachineRegisterInfo *MRI,
                             const SIRegisterInfo *TRI, unsigned OpNo,
                             bool Def) const;

  void setExpScore(const MachineInstr *MI, const SIInstrInfo *TII,
                   const SIRegisterInfo *TRI, const MachineRegisterInfo *MRI,
                   unsigned OpNo, int32_t Val);

  void setWaitAtBeginning() { WaitAtBeginning = true; }
  void clearWaitAtBeginning() { WaitAtBeginning = false; }
  bool getWaitAtBeginning() const { return WaitAtBeginning; }
  void setEventUB(enum WaitEventType W, int32_t Val) { EventUBs[W] = Val; }
  int32_t getMaxVGPR() const { return VgprUB; }
  int32_t getMaxSGPR() const { return SgprUB; }

  int32_t getEventUB(enum WaitEventType W) const {
    assert(W < NUM_WAIT_EVENTS);
    return EventUBs[W];
  }

  bool counterOutOfOrder(InstCounterType T);
  unsigned int updateByWait(InstCounterType T, int ScoreToWait);
  void updateByEvent(const SIInstrInfo *TII, const SIRegisterInfo *TRI,
                     const MachineRegisterInfo *MRI, WaitEventType E,
                     MachineInstr &MI);

  bool hasPendingSMEM() const {
    return (EventUBs[SMEM_ACCESS] > ScoreLBs[LGKM_CNT] &&
            EventUBs[SMEM_ACCESS] <= ScoreUBs[LGKM_CNT]);
  }

  bool hasPendingFlat() const {
    return ((LastFlat[LGKM_CNT] > ScoreLBs[LGKM_CNT] &&
             LastFlat[LGKM_CNT] <= ScoreUBs[LGKM_CNT]) ||
            (LastFlat[VM_CNT] > ScoreLBs[VM_CNT] &&
             LastFlat[VM_CNT] <= ScoreUBs[VM_CNT]));
  }

  void setPendingFlat() {
    LastFlat[VM_CNT] = ScoreUBs[VM_CNT];
    LastFlat[LGKM_CNT] = ScoreUBs[LGKM_CNT];
  }

  int pendingFlat(InstCounterType Ct) const { return LastFlat[Ct]; }

  void setLastFlat(InstCounterType Ct, int Val) { LastFlat[Ct] = Val; }

  bool getRevisitLoop() const { return RevisitLoop; }
  void setRevisitLoop(bool RevisitLoopIn) { RevisitLoop = RevisitLoopIn; }

  void setPostOrder(int32_t PostOrderIn) { PostOrder = PostOrderIn; }
  int32_t getPostOrder() const { return PostOrder; }

  void setWaitcnt(MachineInstr *WaitcntIn) { Waitcnt = WaitcntIn; }
  void clearWaitcnt() { Waitcnt = nullptr; }
  MachineInstr *getWaitcnt() const { return Waitcnt; }

  bool mixedExpTypes() const { return MixedExpTypes; }
  void setMixedExpTypes(bool MixedExpTypesIn) {
    MixedExpTypes = MixedExpTypesIn;
  }

  void print(raw_ostream &);
  void dump() { print(dbgs()); }

private:
  bool WaitAtBeginning = false;
  bool RevisitLoop = false;
  bool MixedExpTypes = false;
  int32_t PostOrder = 0;
  MachineInstr *Waitcnt = nullptr;
  int32_t ScoreLBs[NUM_INST_CNTS] = {0};
  int32_t ScoreUBs[NUM_INST_CNTS] = {0};
  int32_t EventUBs[NUM_WAIT_EVENTS] = {0};
  // Remember the last flat memory operation.
  int32_t LastFlat[NUM_INST_CNTS] = {0};
  // wait_cnt scores for every vgpr.
  // Keep track of the VgprUB and SgprUB to make merge at join efficient.
  int32_t VgprUB = 0;
  int32_t SgprUB = 0;
  int32_t VgprScores[NUM_INST_CNTS][NUM_ALL_VGPRS];
  // Wait cnt scores for every sgpr, only lgkmcnt is relevant.
  int32_t SgprScores[SQ_MAX_PGM_SGPRS] = {0};
};

// This is a per-loop-region object that records waitcnt status at the end of
// loop footer from the previous iteration. We also maintain an iteration
// count to track the number of times the loop has been visited. When it
// doesn't converge naturally, we force convergence by inserting s_waitcnt 0
// at the end of the loop footer.
class LoopWaitcntData {
public:
  LoopWaitcntData() = default;
  ~LoopWaitcntData() = default;

  void incIterCnt() { IterCnt++; }
  void resetIterCnt() { IterCnt = 0; }
  int32_t getIterCnt() { return IterCnt; }

  void setWaitcnt(MachineInstr *WaitcntIn) { LfWaitcnt = WaitcntIn; }
  MachineInstr *getWaitcnt() const { return LfWaitcnt; }

  void print() {
    DEBUG(dbgs() << "  iteration " << IterCnt << '\n';);
  }

private:
  // s_waitcnt added at the end of loop footer to stablize wait scores
  // at the end of the loop footer.
  MachineInstr *LfWaitcnt = nullptr;
  // Number of iterations the loop has been visited, not including the initial
  // walk over.
  int32_t IterCnt = 0;
};

class SIInsertWaitcnts : public MachineFunctionPass {
private:
  const SISubtarget *ST = nullptr;
  const SIInstrInfo *TII = nullptr;
  const SIRegisterInfo *TRI = nullptr;
  const MachineRegisterInfo *MRI = nullptr;
  const MachineLoopInfo *MLI = nullptr;
  AMDGPU::IsaInfo::IsaVersion IV;
  AMDGPUAS AMDGPUASI;

  DenseSet<MachineBasicBlock *> BlockVisitedSet;
  DenseSet<MachineInstr *> TrackedWaitcntSet;
  DenseSet<MachineInstr *> VCCZBugHandledSet;

  DenseMap<MachineBasicBlock *, std::unique_ptr<BlockWaitcntBrackets>>
      BlockWaitcntBracketsMap;

  DenseSet<MachineBasicBlock *> BlockWaitcntProcessedSet;

  DenseMap<MachineLoop *, std::unique_ptr<LoopWaitcntData>> LoopWaitcntDataMap;

  std::vector<std::unique_ptr<BlockWaitcntBrackets>> KillWaitBrackets;

public:
  static char ID;

  SIInsertWaitcnts() : MachineFunctionPass(ID) {}

  bool runOnMachineFunction(MachineFunction &MF) override;

  StringRef getPassName() const override {
    return "SI insert wait instructions";
  }

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

  void addKillWaitBracket(BlockWaitcntBrackets *Bracket) {
    // The waitcnt information is copied because it changes as the block is
    // traversed.
    KillWaitBrackets.push_back(
        llvm::make_unique<BlockWaitcntBrackets>(*Bracket));
  }

  bool mayAccessLDSThroughFlat(const MachineInstr &MI) const;
  MachineInstr *generateSWaitCntInstBefore(MachineInstr &MI,
                                           BlockWaitcntBrackets *ScoreBrackets);
  void updateEventWaitCntAfter(MachineInstr &Inst,
                               BlockWaitcntBrackets *ScoreBrackets);
  void mergeInputScoreBrackets(MachineBasicBlock &Block);
  MachineBasicBlock *loopBottom(const MachineLoop *Loop);
  void insertWaitcntInBlock(MachineFunction &MF, MachineBasicBlock &Block);
  void insertWaitcntBeforeCF(MachineBasicBlock &Block, MachineInstr *Inst);
};

} // end anonymous namespace

RegInterval BlockWaitcntBrackets::getRegInterval(const MachineInstr *MI,
                                                 const SIInstrInfo *TII,
                                                 const MachineRegisterInfo *MRI,
                                                 const SIRegisterInfo *TRI,
                                                 unsigned OpNo,
                                                 bool Def) const {
  const MachineOperand &Op = MI->getOperand(OpNo);
  if (!Op.isReg() || !TRI->isInAllocatableClass(Op.getReg()) ||
      (Def && !Op.isDef()))
    return {-1, -1};

  // A use via a PW operand does not need a waitcnt.
  // A partial write is not a WAW.
  assert(!Op.getSubReg() || !Op.isUndef());

  RegInterval Result;
  const MachineRegisterInfo &MRIA = *MRI;

  unsigned Reg = TRI->getEncodingValue(Op.getReg());

  if (TRI->isVGPR(MRIA, Op.getReg())) {
    assert(Reg >= RegisterEncoding.VGPR0 && Reg <= RegisterEncoding.VGPRL);
    Result.first = Reg - RegisterEncoding.VGPR0;
    assert(Result.first >= 0 && Result.first < SQ_MAX_PGM_VGPRS);
  } else if (TRI->isSGPRReg(MRIA, Op.getReg())) {
    assert(Reg >= RegisterEncoding.SGPR0 && Reg < SQ_MAX_PGM_SGPRS);
    Result.first = Reg - RegisterEncoding.SGPR0 + NUM_ALL_VGPRS;
    assert(Result.first >= NUM_ALL_VGPRS &&
           Result.first < SQ_MAX_PGM_SGPRS + NUM_ALL_VGPRS);
  }
  // TODO: Handle TTMP
  // else if (TRI->isTTMP(MRIA, Reg.getReg())) ...
  else
    return {-1, -1};

  const MachineInstr &MIA = *MI;
  const TargetRegisterClass *RC = TII->getOpRegClass(MIA, OpNo);
  unsigned Size = TRI->getRegSizeInBits(*RC);
  Result.second = Result.first + (Size / 32);

  return Result;
}

void BlockWaitcntBrackets::setExpScore(const MachineInstr *MI,
                                       const SIInstrInfo *TII,
                                       const SIRegisterInfo *TRI,
                                       const MachineRegisterInfo *MRI,
                                       unsigned OpNo, int32_t Val) {
  RegInterval Interval = getRegInterval(MI, TII, MRI, TRI, OpNo, false);
  DEBUG({
    const MachineOperand &Opnd = MI->getOperand(OpNo);
    assert(TRI->isVGPR(*MRI, Opnd.getReg()));
  });
  for (signed RegNo = Interval.first; RegNo < Interval.second; ++RegNo) {
    setRegScore(RegNo, EXP_CNT, Val);
  }
}

void BlockWaitcntBrackets::updateByEvent(const SIInstrInfo *TII,
                                         const SIRegisterInfo *TRI,
                                         const MachineRegisterInfo *MRI,
                                         WaitEventType E, MachineInstr &Inst) {
  const MachineRegisterInfo &MRIA = *MRI;
  InstCounterType T = eventCounter(E);
  int32_t CurrScore = getScoreUB(T) + 1;
  // EventUB and ScoreUB need to be update regardless if this event changes
  // the score of a register or not.
  // Examples including vm_cnt when buffer-store or lgkm_cnt when send-message.
  EventUBs[E] = CurrScore;
  setScoreUB(T, CurrScore);

  if (T == EXP_CNT) {
    // Check for mixed export types. If they are mixed, then a waitcnt exp(0)
    // is required.
    if (!MixedExpTypes) {
      MixedExpTypes = counterOutOfOrder(EXP_CNT);
    }

    // Put score on the source vgprs. If this is a store, just use those
    // specific register(s).
    if (TII->isDS(Inst) && (Inst.mayStore() || Inst.mayLoad())) {
      // All GDS operations must protect their address register (same as
      // export.)
      if (Inst.getOpcode() != AMDGPU::DS_APPEND &&
          Inst.getOpcode() != AMDGPU::DS_CONSUME) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::addr),
            CurrScore);
      }
      if (Inst.mayStore()) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::data0),
            CurrScore);
        if (AMDGPU::getNamedOperandIdx(Inst.getOpcode(),
                                       AMDGPU::OpName::data1) != -1) {
          setExpScore(&Inst, TII, TRI, MRI,
                      AMDGPU::getNamedOperandIdx(Inst.getOpcode(),
                                                 AMDGPU::OpName::data1),
                      CurrScore);
        }
      } else if (AMDGPU::getAtomicNoRetOp(Inst.getOpcode()) != -1 &&
                 Inst.getOpcode() != AMDGPU::DS_GWS_INIT &&
                 Inst.getOpcode() != AMDGPU::DS_GWS_SEMA_V &&
                 Inst.getOpcode() != AMDGPU::DS_GWS_SEMA_BR &&
                 Inst.getOpcode() != AMDGPU::DS_GWS_SEMA_P &&
                 Inst.getOpcode() != AMDGPU::DS_GWS_BARRIER &&
                 Inst.getOpcode() != AMDGPU::DS_APPEND &&
                 Inst.getOpcode() != AMDGPU::DS_CONSUME &&
                 Inst.getOpcode() != AMDGPU::DS_ORDERED_COUNT) {
        for (unsigned I = 0, E = Inst.getNumOperands(); I != E; ++I) {
          const MachineOperand &Op = Inst.getOperand(I);
          if (Op.isReg() && !Op.isDef() && TRI->isVGPR(MRIA, Op.getReg())) {
            setExpScore(&Inst, TII, TRI, MRI, I, CurrScore);
          }
        }
      }
    } else if (TII->isFLAT(Inst)) {
      if (Inst.mayStore()) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::data),
            CurrScore);
      } else if (AMDGPU::getAtomicNoRetOp(Inst.getOpcode()) != -1) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::data),
            CurrScore);
      }
    } else if (TII->isMIMG(Inst)) {
      if (Inst.mayStore()) {
        setExpScore(&Inst, TII, TRI, MRI, 0, CurrScore);
      } else if (AMDGPU::getAtomicNoRetOp(Inst.getOpcode()) != -1) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::data),
            CurrScore);
      }
    } else if (TII->isMTBUF(Inst)) {
      if (Inst.mayStore()) {
        setExpScore(&Inst, TII, TRI, MRI, 0, CurrScore);
      }
    } else if (TII->isMUBUF(Inst)) {
      if (Inst.mayStore()) {
        setExpScore(&Inst, TII, TRI, MRI, 0, CurrScore);
      } else if (AMDGPU::getAtomicNoRetOp(Inst.getOpcode()) != -1) {
        setExpScore(
            &Inst, TII, TRI, MRI,
            AMDGPU::getNamedOperandIdx(Inst.getOpcode(), AMDGPU::OpName::data),
            CurrScore);
      }
    } else {
      if (TII->isEXP(Inst)) {
        // For export the destination registers are really temps that
        // can be used as the actual source after export patching, so
        // we need to treat them like sources and set the EXP_CNT
        // score.
        for (unsigned I = 0, E = Inst.getNumOperands(); I != E; ++I) {
          MachineOperand &DefMO = Inst.getOperand(I);
          if (DefMO.isReg() && DefMO.isDef() &&
              TRI->isVGPR(MRIA, DefMO.getReg())) {
            setRegScore(TRI->getEncodingValue(DefMO.getReg()), EXP_CNT,
                        CurrScore);
          }
        }
      }
      for (unsigned I = 0, E = Inst.getNumOperands(); I != E; ++I) {
        MachineOperand &MO = Inst.getOperand(I);
        if (MO.isReg() && !MO.isDef() && TRI->isVGPR(MRIA, MO.getReg())) {
          setExpScore(&Inst, TII, TRI, MRI, I, CurrScore);
        }
      }
    }
#if 0 // TODO: check if this is handled by MUBUF code above.
  } else if (Inst.getOpcode() == AMDGPU::BUFFER_STORE_DWORD ||
       Inst.getOpcode() == AMDGPU::BUFFER_STORE_DWORDX2 ||
       Inst.getOpcode() == AMDGPU::BUFFER_STORE_DWORDX4) {
    MachineOperand *MO = TII->getNamedOperand(Inst, AMDGPU::OpName::data);
    unsigned OpNo;//TODO: find the OpNo for this operand;
    RegInterval Interval = getRegInterval(&Inst, TII, MRI, TRI, OpNo, false);
    for (signed RegNo = Interval.first; RegNo < Interval.second;
    ++RegNo) {
      setRegScore(RegNo + NUM_ALL_VGPRS, t, CurrScore);
    }
#endif
  } else {
    // Match the score to the destination registers.
    for (unsigned I = 0, E = Inst.getNumOperands(); I != E; ++I) {
      RegInterval Interval = getRegInterval(&Inst, TII, MRI, TRI, I, true);
      if (T == VM_CNT && Interval.first >= NUM_ALL_VGPRS)
        continue;
      for (signed RegNo = Interval.first; RegNo < Interval.second; ++RegNo) {
        setRegScore(RegNo, T, CurrScore);
      }
    }
    if (TII->isDS(Inst) && Inst.mayStore()) {
      setRegScore(SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS, T, CurrScore);
    }
  }
}

void BlockWaitcntBrackets::print(raw_ostream &OS) {
  OS << '\n';
  for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
       T = (enum InstCounterType)(T + 1)) {
    int LB = getScoreLB(T);
    int UB = getScoreUB(T);

    switch (T) {
    case VM_CNT:
      OS << "    VM_CNT(" << UB - LB << "): ";
      break;
    case LGKM_CNT:
      OS << "    LGKM_CNT(" << UB - LB << "): ";
      break;
    case EXP_CNT:
      OS << "    EXP_CNT(" << UB - LB << "): ";
      break;
    default:
      OS << "    UNKNOWN(" << UB - LB << "): ";
      break;
    }

    if (LB < UB) {
      // Print vgpr scores.
      for (int J = 0; J <= getMaxVGPR(); J++) {
        int RegScore = getRegScore(J, T);
        if (RegScore <= LB)
          continue;
        int RelScore = RegScore - LB - 1;
        if (J < SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS) {
          OS << RelScore << ":v" << J << " ";
        } else {
          OS << RelScore << ":ds ";
        }
      }
      // Also need to print sgpr scores for lgkm_cnt.
      if (T == LGKM_CNT) {
        for (int J = 0; J <= getMaxSGPR(); J++) {
          int RegScore = getRegScore(J + NUM_ALL_VGPRS, LGKM_CNT);
          if (RegScore <= LB)
            continue;
          int RelScore = RegScore - LB - 1;
          OS << RelScore << ":s" << J << " ";
        }
      }
    }
    OS << '\n';
  }
  OS << '\n';
}

unsigned int BlockWaitcntBrackets::updateByWait(InstCounterType T,
                                                int ScoreToWait) {
  unsigned int NeedWait = 0;
  if (ScoreToWait == -1) {
    // The score to wait is unknown. This implies that it was not encountered
    // during the path of the CFG walk done during the current traversal but
    // may be seen on a different path. Emit an s_wait counter with a
    // conservative value of 0 for the counter.
    NeedWait = CNT_MASK(T);
    setScoreLB(T, getScoreUB(T));
    return NeedWait;
  }

  // If the score of src_operand falls within the bracket, we need an
  // s_waitcnt instruction.
  const int32_t LB = getScoreLB(T);
  const int32_t UB = getScoreUB(T);
  if ((UB >= ScoreToWait) && (ScoreToWait > LB)) {
    if (T == VM_CNT && hasPendingFlat()) {
      // If there is a pending FLAT operation, and this is a VM waitcnt,
      // then we need to force a waitcnt 0 for VM.
      NeedWait = CNT_MASK(T);
      setScoreLB(T, getScoreUB(T));
    } else if (counterOutOfOrder(T)) {
      // Counter can get decremented out-of-order when there
      // are multiple types event in the brack. Also emit an s_wait counter
      // with a conservative value of 0 for the counter.
      NeedWait = CNT_MASK(T);
      setScoreLB(T, getScoreUB(T));
    } else {
      NeedWait = CNT_MASK(T);
      setScoreLB(T, ScoreToWait);
    }
  }

  return NeedWait;
}

// Where there are multiple types of event in the bracket of a counter,
// the decrement may go out of order.
bool BlockWaitcntBrackets::counterOutOfOrder(InstCounterType T) {
  switch (T) {
  case VM_CNT:
    return false;
  case LGKM_CNT: {
    if (EventUBs[SMEM_ACCESS] > ScoreLBs[LGKM_CNT] &&
        EventUBs[SMEM_ACCESS] <= ScoreUBs[LGKM_CNT]) {
      // Scalar memory read always can go out of order.
      return true;
    }
    int NumEventTypes = 0;
    if (EventUBs[LDS_ACCESS] > ScoreLBs[LGKM_CNT] &&
        EventUBs[LDS_ACCESS] <= ScoreUBs[LGKM_CNT]) {
      NumEventTypes++;
    }
    if (EventUBs[GDS_ACCESS] > ScoreLBs[LGKM_CNT] &&
        EventUBs[GDS_ACCESS] <= ScoreUBs[LGKM_CNT]) {
      NumEventTypes++;
    }
    if (EventUBs[SQ_MESSAGE] > ScoreLBs[LGKM_CNT] &&
        EventUBs[SQ_MESSAGE] <= ScoreUBs[LGKM_CNT]) {
      NumEventTypes++;
    }
    if (NumEventTypes <= 1) {
      return false;
    }
    break;
  }
  case EXP_CNT: {
    // If there has been a mixture of export types, then a waitcnt exp(0) is
    // required.
    if (MixedExpTypes)
      return true;
    int NumEventTypes = 0;
    if (EventUBs[EXP_GPR_LOCK] > ScoreLBs[EXP_CNT] &&
        EventUBs[EXP_GPR_LOCK] <= ScoreUBs[EXP_CNT]) {
      NumEventTypes++;
    }
    if (EventUBs[GDS_GPR_LOCK] > ScoreLBs[EXP_CNT] &&
        EventUBs[GDS_GPR_LOCK] <= ScoreUBs[EXP_CNT]) {
      NumEventTypes++;
    }
    if (EventUBs[VMW_GPR_LOCK] > ScoreLBs[EXP_CNT] &&
        EventUBs[VMW_GPR_LOCK] <= ScoreUBs[EXP_CNT]) {
      NumEventTypes++;
    }
    if (EventUBs[EXP_PARAM_ACCESS] > ScoreLBs[EXP_CNT] &&
        EventUBs[EXP_PARAM_ACCESS] <= ScoreUBs[EXP_CNT]) {
      NumEventTypes++;
    }

    if (EventUBs[EXP_POS_ACCESS] > ScoreLBs[EXP_CNT] &&
        EventUBs[EXP_POS_ACCESS] <= ScoreUBs[EXP_CNT]) {
      NumEventTypes++;
    }

    if (NumEventTypes <= 1) {
      return false;
    }
    break;
  }
  default:
    break;
  }
  return true;
}

INITIALIZE_PASS_BEGIN(SIInsertWaitcnts, DEBUG_TYPE, "SI Insert Waitcnts", false,
                      false)
INITIALIZE_PASS_END(SIInsertWaitcnts, DEBUG_TYPE, "SI Insert Waitcnts", false,
                    false)

char SIInsertWaitcnts::ID = 0;

char &llvm::SIInsertWaitcntsID = SIInsertWaitcnts::ID;

FunctionPass *llvm::createSIInsertWaitcntsPass() {
  return new SIInsertWaitcnts();
}

static bool readsVCCZ(const MachineInstr &MI) {
  unsigned Opc = MI.getOpcode();
  return (Opc == AMDGPU::S_CBRANCH_VCCNZ || Opc == AMDGPU::S_CBRANCH_VCCZ) &&
         !MI.getOperand(1).isUndef();
}

///  \brief Generate s_waitcnt instruction to be placed before cur_Inst.
///  Instructions of a given type are returned in order,
///  but instructions of different types can complete out of order.
///  We rely on this in-order completion
///  and simply assign a score to the memory access instructions.
///  We keep track of the active "score bracket" to determine
///  if an access of a memory read requires an s_waitcnt
///  and if so what the value of each counter is.
///  The "score bracket" is bound by the lower bound and upper bound
///  scores (*_score_LB and *_score_ub respectively).
MachineInstr *SIInsertWaitcnts::generateSWaitCntInstBefore(
    MachineInstr &MI, BlockWaitcntBrackets *ScoreBrackets) {
  // To emit, or not to emit - that's the question!
  // Start with an assumption that there is no need to emit.
  unsigned int EmitSwaitcnt = 0;
  // s_waitcnt instruction to return; default is NULL.
  MachineInstr *SWaitInst = nullptr;
  // No need to wait before phi. If a phi-move exists, then the wait should
  // has been inserted before the move. If a phi-move does not exist, then
  // wait should be inserted before the real use. The same is true for
  // sc-merge. It is not a coincident that all these cases correspond to the
  // instructions that are skipped in the assembling loop.
  bool NeedLineMapping = false; // TODO: Check on this.
  if (MI.isDebugValue() &&
      // TODO: any other opcode?
      !NeedLineMapping) {
    return SWaitInst;
  }

  // See if an s_waitcnt is forced at block entry, or is needed at
  // program end.
  if (ScoreBrackets->getWaitAtBeginning()) {
    // Note that we have already cleared the state, so we don't need to update
    // it.
    ScoreBrackets->clearWaitAtBeginning();
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      EmitSwaitcnt |= CNT_MASK(T);
      ScoreBrackets->setScoreLB(T, ScoreBrackets->getScoreUB(T));
    }
  }

  // See if this instruction has a forced S_WAITCNT VM.
  // TODO: Handle other cases of NeedsWaitcntVmBefore()
  else if (MI.getOpcode() == AMDGPU::BUFFER_WBINVL1 ||
           MI.getOpcode() == AMDGPU::BUFFER_WBINVL1_SC ||
           MI.getOpcode() == AMDGPU::BUFFER_WBINVL1_VOL) {
    EmitSwaitcnt |=
        ScoreBrackets->updateByWait(VM_CNT, ScoreBrackets->getScoreUB(VM_CNT));
  }

  // All waits must be resolved at call return.
  // NOTE: this could be improved with knowledge of all call sites or
  //   with knowledge of the called routines.
  if (MI.getOpcode() == AMDGPU::RETURN ||
      MI.getOpcode() == AMDGPU::SI_RETURN_TO_EPILOG ||
      MI.getOpcode() == AMDGPU::S_SETPC_B64_return) {
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      if (ScoreBrackets->getScoreUB(T) > ScoreBrackets->getScoreLB(T)) {
        ScoreBrackets->setScoreLB(T, ScoreBrackets->getScoreUB(T));
        EmitSwaitcnt |= CNT_MASK(T);
      }
    }
  }
  // Resolve vm waits before gs-done.
  else if ((MI.getOpcode() == AMDGPU::S_SENDMSG ||
            MI.getOpcode() == AMDGPU::S_SENDMSGHALT) &&
           ((MI.getOperand(0).getImm() & AMDGPU::SendMsg::ID_MASK_) ==
            AMDGPU::SendMsg::ID_GS_DONE)) {
    if (ScoreBrackets->getScoreUB(VM_CNT) > ScoreBrackets->getScoreLB(VM_CNT)) {
      ScoreBrackets->setScoreLB(VM_CNT, ScoreBrackets->getScoreUB(VM_CNT));
      EmitSwaitcnt |= CNT_MASK(VM_CNT);
    }
  }
#if 0 // TODO: the following blocks of logic when we have fence.
  else if (MI.getOpcode() == SC_FENCE) {
    const unsigned int group_size =
      context->shader_info->GetMaxThreadGroupSize();
    // group_size == 0 means thread group size is unknown at compile time
    const bool group_is_multi_wave =
      (group_size == 0 || group_size > target_info->GetWaveFrontSize());
    const bool fence_is_global = !((SCInstInternalMisc*)Inst)->IsGroupFence();

    for (unsigned int i = 0; i < Inst->NumSrcOperands(); i++) {
      SCRegType src_type = Inst->GetSrcType(i);
      switch (src_type) {
        case SCMEM_LDS:
          if (group_is_multi_wave ||
            context->OptFlagIsOn(OPT_R1100_LDSMEM_FENCE_CHICKEN_BIT)) {
            EmitSwaitcnt |= ScoreBrackets->updateByWait(LGKM_CNT,
                               ScoreBrackets->getScoreUB(LGKM_CNT));
            // LDS may have to wait for VM_CNT after buffer load to LDS
            if (target_info->HasBufferLoadToLDS()) {
              EmitSwaitcnt |= ScoreBrackets->updateByWait(VM_CNT,
                                 ScoreBrackets->getScoreUB(VM_CNT));
            }
          }
          break;

        case SCMEM_GDS:
          if (group_is_multi_wave || fence_is_global) {
            EmitSwaitcnt |= ScoreBrackets->updateByWait(EXP_CNT,
              ScoreBrackets->getScoreUB(EXP_CNT));
            EmitSwaitcnt |= ScoreBrackets->updateByWait(LGKM_CNT,
              ScoreBrackets->getScoreUB(LGKM_CNT));
          }
          break;

        case SCMEM_UAV:
        case SCMEM_TFBUF:
        case SCMEM_RING:
        case SCMEM_SCATTER:
          if (group_is_multi_wave || fence_is_global) {
            EmitSwaitcnt |= ScoreBrackets->updateByWait(EXP_CNT,
              ScoreBrackets->getScoreUB(EXP_CNT));
            EmitSwaitcnt |= ScoreBrackets->updateByWait(VM_CNT,
              ScoreBrackets->getScoreUB(VM_CNT));
          }
          break;

        case SCMEM_SCRATCH:
        default:
          break;
      }
    }
  }
#endif

  // Export & GDS instructions do not read the EXEC mask until after the export
  // is granted (which can occur well after the instruction is issued).
  // The shader program must flush all EXP operations on the export-count
  // before overwriting the EXEC mask.
  else {
    if (MI.modifiesRegister(AMDGPU::EXEC, TRI)) {
      // Export and GDS are tracked individually, either may trigger a waitcnt
      // for EXEC.
      EmitSwaitcnt |= ScoreBrackets->updateByWait(
          EXP_CNT, ScoreBrackets->getEventUB(EXP_GPR_LOCK));
      EmitSwaitcnt |= ScoreBrackets->updateByWait(
          EXP_CNT, ScoreBrackets->getEventUB(EXP_PARAM_ACCESS));
      EmitSwaitcnt |= ScoreBrackets->updateByWait(
          EXP_CNT, ScoreBrackets->getEventUB(EXP_POS_ACCESS));
      EmitSwaitcnt |= ScoreBrackets->updateByWait(
          EXP_CNT, ScoreBrackets->getEventUB(GDS_GPR_LOCK));
    }

#if 0 // TODO: the following code to handle CALL.
    // The argument passing for CALLs should suffice for VM_CNT and LGKM_CNT.
    // However, there is a problem with EXP_CNT, because the call cannot
    // easily tell if a register is used in the function, and if it did, then
    // the referring instruction would have to have an S_WAITCNT, which is
    // dependent on all call sites. So Instead, force S_WAITCNT for EXP_CNTs
    // before the call.
    if (MI.getOpcode() == SC_CALL) {
      if (ScoreBrackets->getScoreUB(EXP_CNT) >
        ScoreBrackets->getScoreLB(EXP_CNT)) {
        ScoreBrackets->setScoreLB(EXP_CNT, ScoreBrackets->getScoreUB(EXP_CNT));
        EmitSwaitcnt |= CNT_MASK(EXP_CNT);
      }
    }
#endif

    // FIXME: Should not be relying on memoperands.
    // Look at the source operands of every instruction to see if
    // any of them results from a previous memory operation that affects
    // its current usage. If so, an s_waitcnt instruction needs to be
    // emitted.
    // If the source operand was defined by a load, add the s_waitcnt
    // instruction.
    for (const MachineMemOperand *Memop : MI.memoperands()) {
      unsigned AS = Memop->getAddrSpace();
      if (AS != AMDGPUASI.LOCAL_ADDRESS)
        continue;
      unsigned RegNo = SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS;
      // VM_CNT is only relevant to vgpr or LDS.
      EmitSwaitcnt |= ScoreBrackets->updateByWait(
          VM_CNT, ScoreBrackets->getRegScore(RegNo, VM_CNT));
    }

    for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
      const MachineOperand &Op = MI.getOperand(I);
      const MachineRegisterInfo &MRIA = *MRI;
      RegInterval Interval =
          ScoreBrackets->getRegInterval(&MI, TII, MRI, TRI, I, false);
      for (signed RegNo = Interval.first; RegNo < Interval.second; ++RegNo) {
        if (TRI->isVGPR(MRIA, Op.getReg())) {
          // VM_CNT is only relevant to vgpr or LDS.
          EmitSwaitcnt |= ScoreBrackets->updateByWait(
              VM_CNT, ScoreBrackets->getRegScore(RegNo, VM_CNT));
        }
        EmitSwaitcnt |= ScoreBrackets->updateByWait(
            LGKM_CNT, ScoreBrackets->getRegScore(RegNo, LGKM_CNT));
      }
    }
    // End of for loop that looks at all source operands to decide vm_wait_cnt
    // and lgk_wait_cnt.

    // Two cases are handled for destination operands:
    // 1) If the destination operand was defined by a load, add the s_waitcnt
    // instruction to guarantee the right WAW order.
    // 2) If a destination operand that was used by a recent export/store ins,
    // add s_waitcnt on exp_cnt to guarantee the WAR order.
    if (MI.mayStore()) {
      // FIXME: Should not be relying on memoperands.
      for (const MachineMemOperand *Memop : MI.memoperands()) {
        unsigned AS = Memop->getAddrSpace();
        if (AS != AMDGPUASI.LOCAL_ADDRESS)
          continue;
        unsigned RegNo = SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS;
        EmitSwaitcnt |= ScoreBrackets->updateByWait(
            VM_CNT, ScoreBrackets->getRegScore(RegNo, VM_CNT));
        EmitSwaitcnt |= ScoreBrackets->updateByWait(
            EXP_CNT, ScoreBrackets->getRegScore(RegNo, EXP_CNT));
      }
    }
    for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
      MachineOperand &Def = MI.getOperand(I);
      const MachineRegisterInfo &MRIA = *MRI;
      RegInterval Interval =
          ScoreBrackets->getRegInterval(&MI, TII, MRI, TRI, I, true);
      for (signed RegNo = Interval.first; RegNo < Interval.second; ++RegNo) {
        if (TRI->isVGPR(MRIA, Def.getReg())) {
          EmitSwaitcnt |= ScoreBrackets->updateByWait(
              VM_CNT, ScoreBrackets->getRegScore(RegNo, VM_CNT));
          EmitSwaitcnt |= ScoreBrackets->updateByWait(
              EXP_CNT, ScoreBrackets->getRegScore(RegNo, EXP_CNT));
        }
        EmitSwaitcnt |= ScoreBrackets->updateByWait(
            LGKM_CNT, ScoreBrackets->getRegScore(RegNo, LGKM_CNT));
      }
    } // End of for loop that looks at all dest operands.
  }

  // TODO: Tie force zero to a compiler triage option.
  bool ForceZero = false;

  // Check to see if this is an S_BARRIER, and if an implicit S_WAITCNT 0
  // occurs before the instruction. Doing it here prevents any additional
  // S_WAITCNTs from being emitted if the instruction was marked as
  // requiring a WAITCNT beforehand.
  if (MI.getOpcode() == AMDGPU::S_BARRIER &&
      !ST->hasAutoWaitcntBeforeBarrier()) {
    EmitSwaitcnt |=
        ScoreBrackets->updateByWait(VM_CNT, ScoreBrackets->getScoreUB(VM_CNT));
    EmitSwaitcnt |= ScoreBrackets->updateByWait(
        EXP_CNT, ScoreBrackets->getScoreUB(EXP_CNT));
    EmitSwaitcnt |= ScoreBrackets->updateByWait(
        LGKM_CNT, ScoreBrackets->getScoreUB(LGKM_CNT));
  }

  // TODO: Remove this work-around, enable the assert for Bug 457939
  //       after fixing the scheduler. Also, the Shader Compiler code is
  //       independent of target.
  if (readsVCCZ(MI) && ST->getGeneration() <= SISubtarget::SEA_ISLANDS) {
    if (ScoreBrackets->getScoreLB(LGKM_CNT) <
            ScoreBrackets->getScoreUB(LGKM_CNT) &&
        ScoreBrackets->hasPendingSMEM()) {
      // Wait on everything, not just LGKM.  vccz reads usually come from
      // terminators, and we always wait on everything at the end of the
      // block, so if we only wait on LGKM here, we might end up with
      // another s_waitcnt inserted right after this if there are non-LGKM
      // instructions still outstanding.
      ForceZero = true;
      EmitSwaitcnt = true;
    }
  }

  // Does this operand processing indicate s_wait counter update?
  if (EmitSwaitcnt) {
    int CntVal[NUM_INST_CNTS];

    bool UseDefaultWaitcntStrategy = true;
    if (ForceZero) {
      // Force all waitcnts to 0.
      for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
           T = (enum InstCounterType)(T + 1)) {
        ScoreBrackets->setScoreLB(T, ScoreBrackets->getScoreUB(T));
      }
      CntVal[VM_CNT] = 0;
      CntVal[EXP_CNT] = 0;
      CntVal[LGKM_CNT] = 0;
      UseDefaultWaitcntStrategy = false;
    }

    if (UseDefaultWaitcntStrategy) {
      for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
           T = (enum InstCounterType)(T + 1)) {
        if (EmitSwaitcnt & CNT_MASK(T)) {
          int Delta =
              ScoreBrackets->getScoreUB(T) - ScoreBrackets->getScoreLB(T);
          int MaxDelta = ScoreBrackets->getWaitCountMax(T);
          if (Delta >= MaxDelta) {
            Delta = -1;
            if (T != EXP_CNT) {
              ScoreBrackets->setScoreLB(
                  T, ScoreBrackets->getScoreUB(T) - MaxDelta);
            }
            EmitSwaitcnt &= ~CNT_MASK(T);
          }
          CntVal[T] = Delta;
        } else {
          // If we are not waiting for a particular counter then encode
          // it as -1 which means "don't care."
          CntVal[T] = -1;
        }
      }
    }

    // If we are not waiting on any counter we can skip the wait altogether.
    if (EmitSwaitcnt != 0) {
      MachineInstr *OldWaitcnt = ScoreBrackets->getWaitcnt();
      int Imm = (!OldWaitcnt) ? 0 : OldWaitcnt->getOperand(0).getImm();
      if (!OldWaitcnt || (AMDGPU::decodeVmcnt(IV, Imm) !=
                          (CntVal[VM_CNT] & AMDGPU::getVmcntBitMask(IV))) ||
          (AMDGPU::decodeExpcnt(IV, Imm) !=
           (CntVal[EXP_CNT] & AMDGPU::getExpcntBitMask(IV))) ||
          (AMDGPU::decodeLgkmcnt(IV, Imm) !=
           (CntVal[LGKM_CNT] & AMDGPU::getLgkmcntBitMask(IV)))) {
        MachineLoop *ContainingLoop = MLI->getLoopFor(MI.getParent());
        if (ContainingLoop) {
          MachineBasicBlock *TBB = ContainingLoop->getHeader();
          BlockWaitcntBrackets *ScoreBracket =
              BlockWaitcntBracketsMap[TBB].get();
          if (!ScoreBracket) {
            assert(!BlockVisitedSet.count(TBB));
            BlockWaitcntBracketsMap[TBB] =
                llvm::make_unique<BlockWaitcntBrackets>();
            ScoreBracket = BlockWaitcntBracketsMap[TBB].get();
          }
          ScoreBracket->setRevisitLoop(true);
          DEBUG(dbgs() << "set-revisit: block"
                       << ContainingLoop->getHeader()->getNumber() << '\n';);
        }
      }

      // Update an existing waitcount, or make a new one.
      MachineFunction &MF = *MI.getParent()->getParent();
      if (OldWaitcnt && OldWaitcnt->getOpcode() != AMDGPU::S_WAITCNT) {
        SWaitInst = OldWaitcnt;
      } else {
        SWaitInst = MF.CreateMachineInstr(TII->get(AMDGPU::S_WAITCNT),
                                          MI.getDebugLoc());
        TrackedWaitcntSet.insert(SWaitInst);
      }

      const MachineOperand &Op =
          MachineOperand::CreateImm(AMDGPU::encodeWaitcnt(
              IV, CntVal[VM_CNT], CntVal[EXP_CNT], CntVal[LGKM_CNT]));
      SWaitInst->addOperand(MF, Op);

      if (CntVal[EXP_CNT] == 0) {
        ScoreBrackets->setMixedExpTypes(false);
      }
    }
  }

  return SWaitInst;
}

void SIInsertWaitcnts::insertWaitcntBeforeCF(MachineBasicBlock &MBB,
                                             MachineInstr *Waitcnt) {
  if (MBB.empty()) {
    MBB.push_back(Waitcnt);
    return;
  }

  MachineBasicBlock::iterator It = MBB.end();
  MachineInstr *MI = &*(--It);
  if (MI->isBranch()) {
    MBB.insert(It, Waitcnt);
  } else {
    MBB.push_back(Waitcnt);
  }
}

// This is a flat memory operation. Check to see if it has memory
// tokens for both LDS and Memory, and if so mark it as a flat.
bool SIInsertWaitcnts::mayAccessLDSThroughFlat(const MachineInstr &MI) const {
  if (MI.memoperands_empty())
    return true;

  for (const MachineMemOperand *Memop : MI.memoperands()) {
    unsigned AS = Memop->getAddrSpace();
    if (AS == AMDGPUASI.LOCAL_ADDRESS || AS == AMDGPUASI.FLAT_ADDRESS)
      return true;
  }

  return false;
}

void SIInsertWaitcnts::updateEventWaitCntAfter(
    MachineInstr &Inst, BlockWaitcntBrackets *ScoreBrackets) {
  // Now look at the instruction opcode. If it is a memory access
  // instruction, update the upper-bound of the appropriate counter's
  // bracket and the destination operand scores.
  // TODO: Use the (TSFlags & SIInstrFlags::LGKM_CNT) property everywhere.
  if (TII->isDS(Inst) && TII->usesLGKM_CNT(Inst)) {
    if (TII->hasModifiersSet(Inst, AMDGPU::OpName::gds)) {
      ScoreBrackets->updateByEvent(TII, TRI, MRI, GDS_ACCESS, Inst);
      ScoreBrackets->updateByEvent(TII, TRI, MRI, GDS_GPR_LOCK, Inst);
    } else {
      ScoreBrackets->updateByEvent(TII, TRI, MRI, LDS_ACCESS, Inst);
    }
  } else if (TII->isFLAT(Inst)) {
    assert(Inst.mayLoad() || Inst.mayStore());

    if (TII->usesVM_CNT(Inst))
      ScoreBrackets->updateByEvent(TII, TRI, MRI, VMEM_ACCESS, Inst);

    if (TII->usesLGKM_CNT(Inst)) {
      ScoreBrackets->updateByEvent(TII, TRI, MRI, LDS_ACCESS, Inst);

      // This is a flat memory operation, so note it - it will require
      // that both the VM and LGKM be flushed to zero if it is pending when
      // a VM or LGKM dependency occurs.
      if (mayAccessLDSThroughFlat(Inst))
        ScoreBrackets->setPendingFlat();
    }
  } else if (SIInstrInfo::isVMEM(Inst) &&
             // TODO: get a better carve out.
             Inst.getOpcode() != AMDGPU::BUFFER_WBINVL1 &&
             Inst.getOpcode() != AMDGPU::BUFFER_WBINVL1_SC &&
             Inst.getOpcode() != AMDGPU::BUFFER_WBINVL1_VOL) {
    ScoreBrackets->updateByEvent(TII, TRI, MRI, VMEM_ACCESS, Inst);
    if ( // TODO: assumed yes -- target_info->MemWriteNeedsExpWait() &&
        (Inst.mayStore() || AMDGPU::getAtomicNoRetOp(Inst.getOpcode()) != -1)) {
      ScoreBrackets->updateByEvent(TII, TRI, MRI, VMW_GPR_LOCK, Inst);
    }
  } else if (TII->isSMRD(Inst)) {
    ScoreBrackets->updateByEvent(TII, TRI, MRI, SMEM_ACCESS, Inst);
  } else {
    switch (Inst.getOpcode()) {
    case AMDGPU::S_SENDMSG:
    case AMDGPU::S_SENDMSGHALT:
      ScoreBrackets->updateByEvent(TII, TRI, MRI, SQ_MESSAGE, Inst);
      break;
    case AMDGPU::EXP:
    case AMDGPU::EXP_DONE: {
      int Imm = TII->getNamedOperand(Inst, AMDGPU::OpName::tgt)->getImm();
      if (Imm >= 32 && Imm <= 63)
        ScoreBrackets->updateByEvent(TII, TRI, MRI, EXP_PARAM_ACCESS, Inst);
      else if (Imm >= 12 && Imm <= 15)
        ScoreBrackets->updateByEvent(TII, TRI, MRI, EXP_POS_ACCESS, Inst);
      else
        ScoreBrackets->updateByEvent(TII, TRI, MRI, EXP_GPR_LOCK, Inst);
      break;
    }
    case AMDGPU::S_MEMTIME:
    case AMDGPU::S_MEMREALTIME:
      ScoreBrackets->updateByEvent(TII, TRI, MRI, SMEM_ACCESS, Inst);
      break;
    default:
      break;
    }
  }
}

void SIInsertWaitcnts::mergeInputScoreBrackets(MachineBasicBlock &Block) {
  BlockWaitcntBrackets *ScoreBrackets = BlockWaitcntBracketsMap[&Block].get();
  int32_t MaxPending[NUM_INST_CNTS] = {0};
  int32_t MaxFlat[NUM_INST_CNTS] = {0};
  bool MixedExpTypes = false;

  // Clear the score bracket state.
  ScoreBrackets->clear();

  // Compute the number of pending elements on block entry.

  // IMPORTANT NOTE: If iterative handling of loops is added, the code will
  // need to handle single BBs with backedges to themselves. This means that
  // they will need to retain and not clear their initial state.

  // See if there are any uninitialized predecessors. If so, emit an
  // s_waitcnt 0 at the beginning of the block.
  for (MachineBasicBlock *pred : Block.predecessors()) {
    BlockWaitcntBrackets *PredScoreBrackets =
        BlockWaitcntBracketsMap[pred].get();
    bool Visited = BlockVisitedSet.count(pred);
    if (!Visited || PredScoreBrackets->getWaitAtBeginning()) {
      continue;
    }
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      int span =
          PredScoreBrackets->getScoreUB(T) - PredScoreBrackets->getScoreLB(T);
      MaxPending[T] = std::max(MaxPending[T], span);
      span =
          PredScoreBrackets->pendingFlat(T) - PredScoreBrackets->getScoreLB(T);
      MaxFlat[T] = std::max(MaxFlat[T], span);
    }

    MixedExpTypes |= PredScoreBrackets->mixedExpTypes();
  }

  // TODO: Is SC Block->IsMainExit() same as Block.succ_empty()?
  // Also handle kills for exit block.
  if (Block.succ_empty() && !KillWaitBrackets.empty()) {
    for (unsigned int I = 0; I < KillWaitBrackets.size(); I++) {
      for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
           T = (enum InstCounterType)(T + 1)) {
        int Span = KillWaitBrackets[I]->getScoreUB(T) -
                   KillWaitBrackets[I]->getScoreLB(T);
        MaxPending[T] = std::max(MaxPending[T], Span);
        Span = KillWaitBrackets[I]->pendingFlat(T) -
               KillWaitBrackets[I]->getScoreLB(T);
        MaxFlat[T] = std::max(MaxFlat[T], Span);
      }

      MixedExpTypes |= KillWaitBrackets[I]->mixedExpTypes();
    }
  }

  // Special handling for GDS_GPR_LOCK and EXP_GPR_LOCK.
  for (MachineBasicBlock *Pred : Block.predecessors()) {
    BlockWaitcntBrackets *PredScoreBrackets =
        BlockWaitcntBracketsMap[Pred].get();
    bool Visited = BlockVisitedSet.count(Pred);
    if (!Visited || PredScoreBrackets->getWaitAtBeginning()) {
      continue;
    }

    int GDSSpan = PredScoreBrackets->getEventUB(GDS_GPR_LOCK) -
                  PredScoreBrackets->getScoreLB(EXP_CNT);
    MaxPending[EXP_CNT] = std::max(MaxPending[EXP_CNT], GDSSpan);
    int EXPSpan = PredScoreBrackets->getEventUB(EXP_GPR_LOCK) -
                  PredScoreBrackets->getScoreLB(EXP_CNT);
    MaxPending[EXP_CNT] = std::max(MaxPending[EXP_CNT], EXPSpan);
  }

  // TODO: Is SC Block->IsMainExit() same as Block.succ_empty()?
  if (Block.succ_empty() && !KillWaitBrackets.empty()) {
    for (unsigned int I = 0; I < KillWaitBrackets.size(); I++) {
      int GDSSpan = KillWaitBrackets[I]->getEventUB(GDS_GPR_LOCK) -
                    KillWaitBrackets[I]->getScoreLB(EXP_CNT);
      MaxPending[EXP_CNT] = std::max(MaxPending[EXP_CNT], GDSSpan);
      int EXPSpan = KillWaitBrackets[I]->getEventUB(EXP_GPR_LOCK) -
                    KillWaitBrackets[I]->getScoreLB(EXP_CNT);
      MaxPending[EXP_CNT] = std::max(MaxPending[EXP_CNT], EXPSpan);
    }
  }

#if 0
  // LC does not (unlike) add a waitcnt at beginning. Leaving it as marker.
  // TODO: how does LC distinguish between function entry and main entry?
  // If this is the entry to a function, force a wait.
  MachineBasicBlock &Entry = Block.getParent()->front();
  if (Entry.getNumber() == Block.getNumber()) {
    ScoreBrackets->setWaitAtBeginning();
    return;
  }
#endif

  // Now set the current Block's brackets to the largest ending bracket.
  for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
       T = (enum InstCounterType)(T + 1)) {
    ScoreBrackets->setScoreUB(T, MaxPending[T]);
    ScoreBrackets->setScoreLB(T, 0);
    ScoreBrackets->setLastFlat(T, MaxFlat[T]);
  }

  ScoreBrackets->setMixedExpTypes(MixedExpTypes);

  // Set the register scoreboard.
  for (MachineBasicBlock *Pred : Block.predecessors()) {
    if (!BlockVisitedSet.count(Pred)) {
      continue;
    }

    BlockWaitcntBrackets *PredScoreBrackets =
        BlockWaitcntBracketsMap[Pred].get();

    // Now merge the gpr_reg_score information
    for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
         T = (enum InstCounterType)(T + 1)) {
      int PredLB = PredScoreBrackets->getScoreLB(T);
      int PredUB = PredScoreBrackets->getScoreUB(T);
      if (PredLB < PredUB) {
        int PredScale = MaxPending[T] - PredUB;
        // Merge vgpr scores.
        for (int J = 0; J <= PredScoreBrackets->getMaxVGPR(); J++) {
          int PredRegScore = PredScoreBrackets->getRegScore(J, T);
          if (PredRegScore <= PredLB)
            continue;
          int NewRegScore = PredScale + PredRegScore;
          ScoreBrackets->setRegScore(
              J, T, std::max(ScoreBrackets->getRegScore(J, T), NewRegScore));
        }
        // Also need to merge sgpr scores for lgkm_cnt.
        if (T == LGKM_CNT) {
          for (int J = 0; J <= PredScoreBrackets->getMaxSGPR(); J++) {
            int PredRegScore =
                PredScoreBrackets->getRegScore(J + NUM_ALL_VGPRS, LGKM_CNT);
            if (PredRegScore <= PredLB)
              continue;
            int NewRegScore = PredScale + PredRegScore;
            ScoreBrackets->setRegScore(
                J + NUM_ALL_VGPRS, LGKM_CNT,
                std::max(
                    ScoreBrackets->getRegScore(J + NUM_ALL_VGPRS, LGKM_CNT),
                    NewRegScore));
          }
        }
      }
    }

    // Also merge the WaitEvent information.
    ForAllWaitEventType(W) {
      enum InstCounterType T = PredScoreBrackets->eventCounter(W);
      int PredEventUB = PredScoreBrackets->getEventUB(W);
      if (PredEventUB > PredScoreBrackets->getScoreLB(T)) {
        int NewEventUB =
            MaxPending[T] + PredEventUB - PredScoreBrackets->getScoreUB(T);
        if (NewEventUB > 0) {
          ScoreBrackets->setEventUB(
              W, std::max(ScoreBrackets->getEventUB(W), NewEventUB));
        }
      }
    }
  }

  // TODO: Is SC Block->IsMainExit() same as Block.succ_empty()?
  // Set the register scoreboard.
  if (Block.succ_empty() && !KillWaitBrackets.empty()) {
    for (unsigned int I = 0; I < KillWaitBrackets.size(); I++) {
      // Now merge the gpr_reg_score information.
      for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
           T = (enum InstCounterType)(T + 1)) {
        int PredLB = KillWaitBrackets[I]->getScoreLB(T);
        int PredUB = KillWaitBrackets[I]->getScoreUB(T);
        if (PredLB < PredUB) {
          int PredScale = MaxPending[T] - PredUB;
          // Merge vgpr scores.
          for (int J = 0; J <= KillWaitBrackets[I]->getMaxVGPR(); J++) {
            int PredRegScore = KillWaitBrackets[I]->getRegScore(J, T);
            if (PredRegScore <= PredLB)
              continue;
            int NewRegScore = PredScale + PredRegScore;
            ScoreBrackets->setRegScore(
                J, T, std::max(ScoreBrackets->getRegScore(J, T), NewRegScore));
          }
          // Also need to merge sgpr scores for lgkm_cnt.
          if (T == LGKM_CNT) {
            for (int J = 0; J <= KillWaitBrackets[I]->getMaxSGPR(); J++) {
              int PredRegScore =
                  KillWaitBrackets[I]->getRegScore(J + NUM_ALL_VGPRS, LGKM_CNT);
              if (PredRegScore <= PredLB)
                continue;
              int NewRegScore = PredScale + PredRegScore;
              ScoreBrackets->setRegScore(
                  J + NUM_ALL_VGPRS, LGKM_CNT,
                  std::max(
                      ScoreBrackets->getRegScore(J + NUM_ALL_VGPRS, LGKM_CNT),
                      NewRegScore));
            }
          }
        }
      }

      // Also merge the WaitEvent information.
      ForAllWaitEventType(W) {
        enum InstCounterType T = KillWaitBrackets[I]->eventCounter(W);
        int PredEventUB = KillWaitBrackets[I]->getEventUB(W);
        if (PredEventUB > KillWaitBrackets[I]->getScoreLB(T)) {
          int NewEventUB =
              MaxPending[T] + PredEventUB - KillWaitBrackets[I]->getScoreUB(T);
          if (NewEventUB > 0) {
            ScoreBrackets->setEventUB(
                W, std::max(ScoreBrackets->getEventUB(W), NewEventUB));
          }
        }
      }
    }
  }

  // Special case handling of GDS_GPR_LOCK and EXP_GPR_LOCK. Merge this for the
  // sequencing predecessors, because changes to EXEC require waitcnts due to
  // the delayed nature of these operations.
  for (MachineBasicBlock *Pred : Block.predecessors()) {
    if (!BlockVisitedSet.count(Pred)) {
      continue;
    }

    BlockWaitcntBrackets *PredScoreBrackets =
        BlockWaitcntBracketsMap[Pred].get();

    int pred_gds_ub = PredScoreBrackets->getEventUB(GDS_GPR_LOCK);
    if (pred_gds_ub > PredScoreBrackets->getScoreLB(EXP_CNT)) {
      int new_gds_ub = MaxPending[EXP_CNT] + pred_gds_ub -
                       PredScoreBrackets->getScoreUB(EXP_CNT);
      if (new_gds_ub > 0) {
        ScoreBrackets->setEventUB(
            GDS_GPR_LOCK,
            std::max(ScoreBrackets->getEventUB(GDS_GPR_LOCK), new_gds_ub));
      }
    }
    int pred_exp_ub = PredScoreBrackets->getEventUB(EXP_GPR_LOCK);
    if (pred_exp_ub > PredScoreBrackets->getScoreLB(EXP_CNT)) {
      int new_exp_ub = MaxPending[EXP_CNT] + pred_exp_ub -
                       PredScoreBrackets->getScoreUB(EXP_CNT);
      if (new_exp_ub > 0) {
        ScoreBrackets->setEventUB(
            EXP_GPR_LOCK,
            std::max(ScoreBrackets->getEventUB(EXP_GPR_LOCK), new_exp_ub));
      }
    }
  }
}

/// Return the "bottom" block of a loop. This differs from
/// MachineLoop::getBottomBlock in that it works even if the loop is
/// discontiguous.
MachineBasicBlock *SIInsertWaitcnts::loopBottom(const MachineLoop *Loop) {
  MachineBasicBlock *Bottom = Loop->getHeader();
  for (MachineBasicBlock *MBB : Loop->blocks())
    if (MBB->getNumber() > Bottom->getNumber())
      Bottom = MBB;
  return Bottom;
}

// Generate s_waitcnt instructions where needed.
void SIInsertWaitcnts::insertWaitcntInBlock(MachineFunction &MF,
                                            MachineBasicBlock &Block) {
  // Initialize the state information.
  mergeInputScoreBrackets(Block);

  BlockWaitcntBrackets *ScoreBrackets = BlockWaitcntBracketsMap[&Block].get();

  DEBUG({
    dbgs() << "Block" << Block.getNumber();
    ScoreBrackets->dump();
  });

  // Walk over the instructions.
  for (MachineBasicBlock::iterator Iter = Block.begin(), E = Block.end();
       Iter != E;) {
    MachineInstr &Inst = *Iter;
    // Remove any previously existing waitcnts.
    if (Inst.getOpcode() == AMDGPU::S_WAITCNT) {
      // TODO: Register the old waitcnt and optimize the following waitcnts.
      // Leaving the previously existing waitcnts is conservatively correct.
      if (!TrackedWaitcntSet.count(&Inst))
        ++Iter;
      else {
        ScoreBrackets->setWaitcnt(&Inst);
        ++Iter;
        Inst.removeFromParent();
      }
      continue;
    }

    // Kill instructions generate a conditional branch to the endmain block.
    // Merge the current waitcnt state into the endmain block information.
    // TODO: Are there other flavors of KILL instruction?
    if (Inst.getOpcode() == AMDGPU::KILL) {
      addKillWaitBracket(ScoreBrackets);
    }

    bool VCCZBugWorkAround = false;
    if (readsVCCZ(Inst) &&
        (!VCCZBugHandledSet.count(&Inst))) {
      if (ScoreBrackets->getScoreLB(LGKM_CNT) <
              ScoreBrackets->getScoreUB(LGKM_CNT) &&
          ScoreBrackets->hasPendingSMEM()) {
        if (ST->getGeneration() <= SISubtarget::SEA_ISLANDS)
          VCCZBugWorkAround = true;
      }
    }

    // Generate an s_waitcnt instruction to be placed before
    // cur_Inst, if needed.
    MachineInstr *SWaitInst = generateSWaitCntInstBefore(Inst, ScoreBrackets);

    if (SWaitInst) {
      // We don't (yet) track waitcnts that existed prior to the waitcnt
      // pass (we just skip over them); because the waitcnt pass is ignorant
      // of them, it may insert a redundant waitcnt. To avoid this, check
      // the prev instr. If it and the to-be-inserted waitcnt are the
      // same, keep the prev waitcnt and skip the insertion. We assume that
      // whomever. e.g., for memory model, inserted the prev waitcnt really
      // wants it there.
      bool insertSWaitInst = true;
      if (Iter != Block.begin()) {
        MachineInstr *MIPrevInst = &*std::prev(Iter);
        if (MIPrevInst &&
            MIPrevInst->getOpcode() == AMDGPU::S_WAITCNT &&
            MIPrevInst->getOperand(0).getImm() == SWaitInst->getOperand(0).getImm()) {
          insertSWaitInst = false;
        }
      }
      if (insertSWaitInst) {
        Block.insert(Inst, SWaitInst);
        if (ScoreBrackets->getWaitcnt() != SWaitInst) {
          DEBUG(dbgs() << "insertWaitcntInBlock\n"
                       << "Old Instr: " << Inst << '\n'
                       << "New Instr: " << *SWaitInst << '\n';);
        }
      }
    }

    updateEventWaitCntAfter(Inst, ScoreBrackets);

#if 0 // TODO: implement resource type check controlled by options with ub = LB.
    // If this instruction generates a S_SETVSKIP because it is an
    // indexed resource, and we are on Tahiti, then it will also force
    // an S_WAITCNT vmcnt(0)
    if (RequireCheckResourceType(Inst, context)) {
      // Force the score to as if an S_WAITCNT vmcnt(0) is emitted.
      ScoreBrackets->setScoreLB(VM_CNT,
      ScoreBrackets->getScoreUB(VM_CNT));
    }
#endif

    ScoreBrackets->clearWaitcnt();

    if (SWaitInst) {
      DEBUG({ SWaitInst->print(dbgs() << '\n'); });
    }
    DEBUG({
      Inst.print(dbgs());
      ScoreBrackets->dump();
    });

    // Check to see if this is a GWS instruction. If so, and if this is CI or
    // VI, then the generated code sequence will include an S_WAITCNT 0.
    // TODO: Are these the only GWS instructions?
    if (Inst.getOpcode() == AMDGPU::DS_GWS_INIT ||
        Inst.getOpcode() == AMDGPU::DS_GWS_SEMA_V ||
        Inst.getOpcode() == AMDGPU::DS_GWS_SEMA_BR ||
        Inst.getOpcode() == AMDGPU::DS_GWS_SEMA_P ||
        Inst.getOpcode() == AMDGPU::DS_GWS_BARRIER) {
      // TODO: && context->target_info->GwsRequiresMemViolTest() ) {
      ScoreBrackets->updateByWait(VM_CNT, ScoreBrackets->getScoreUB(VM_CNT));
      ScoreBrackets->updateByWait(EXP_CNT, ScoreBrackets->getScoreUB(EXP_CNT));
      ScoreBrackets->updateByWait(LGKM_CNT,
                                  ScoreBrackets->getScoreUB(LGKM_CNT));
    }

    // TODO: Remove this work-around after fixing the scheduler and enable the
    // assert above.
    if (VCCZBugWorkAround) {
      // Restore the vccz bit.  Any time a value is written to vcc, the vcc
      // bit is updated, so we can restore the bit by reading the value of
      // vcc and then writing it back to the register.
      BuildMI(Block, Inst, Inst.getDebugLoc(), TII->get(AMDGPU::S_MOV_B64),
              AMDGPU::VCC)
          .addReg(AMDGPU::VCC);
      VCCZBugHandledSet.insert(&Inst);
    }

    ++Iter;
  }

  // Check if we need to force convergence at loop footer.
  MachineLoop *ContainingLoop = MLI->getLoopFor(&Block);
  if (ContainingLoop && loopBottom(ContainingLoop) == &Block) {
    LoopWaitcntData *WaitcntData = LoopWaitcntDataMap[ContainingLoop].get();
    WaitcntData->print();
    DEBUG(dbgs() << '\n';);

    // The iterative waitcnt insertion algorithm aims for optimal waitcnt
    // placement and doesn't always guarantee convergence for a loop. Each
    // loop should take at most 2 iterations for it to converge naturally.
    // When this max is reached and result doesn't converge, we force
    // convergence by inserting a s_waitcnt at the end of loop footer.
    if (WaitcntData->getIterCnt() > 2) {
      // To ensure convergence, need to make wait events at loop footer be no
      // more than those from the previous iteration.
      // As a simplification, Instead of tracking individual scores and
      // generate the precise wait count, just wait on 0.
      bool HasPending = false;
      MachineInstr *SWaitInst = WaitcntData->getWaitcnt();
      for (enum InstCounterType T = VM_CNT; T < NUM_INST_CNTS;
           T = (enum InstCounterType)(T + 1)) {
        if (ScoreBrackets->getScoreUB(T) > ScoreBrackets->getScoreLB(T)) {
          ScoreBrackets->setScoreLB(T, ScoreBrackets->getScoreUB(T));
          HasPending = true;
        }
      }

      if (HasPending) {
        if (!SWaitInst) {
          SWaitInst = Block.getParent()->CreateMachineInstr(
              TII->get(AMDGPU::S_WAITCNT), DebugLoc());
          TrackedWaitcntSet.insert(SWaitInst);
          const MachineOperand &Op = MachineOperand::CreateImm(0);
          SWaitInst->addOperand(MF, Op);
#if 0 // TODO: Format the debug output
          OutputTransformBanner("insertWaitcntInBlock",0,"Create:",context);
          OutputTransformAdd(SWaitInst, context);
#endif
        }
#if 0 // TODO: ??
        _DEV( REPORTED_STATS->force_waitcnt_converge = 1; )
#endif
      }

      if (SWaitInst) {
        DEBUG({
          SWaitInst->print(dbgs());
          dbgs() << "\nAdjusted score board:";
          ScoreBrackets->dump();
        });

        // Add this waitcnt to the block. It is either newly created or
        // created in previous iterations and added back since block traversal
        // always remove waitcnt.
        insertWaitcntBeforeCF(Block, SWaitInst);
        WaitcntData->setWaitcnt(SWaitInst);
      }
    }
  }
}

bool SIInsertWaitcnts::runOnMachineFunction(MachineFunction &MF) {
  ST = &MF.getSubtarget<SISubtarget>();
  TII = ST->getInstrInfo();
  TRI = &TII->getRegisterInfo();
  MRI = &MF.getRegInfo();
  MLI = &getAnalysis<MachineLoopInfo>();
  IV = AMDGPU::IsaInfo::getIsaVersion(ST->getFeatureBits());
  const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
  AMDGPUASI = ST->getAMDGPUAS();

  HardwareLimits.VmcntMax = AMDGPU::getVmcntBitMask(IV);
  HardwareLimits.ExpcntMax = AMDGPU::getExpcntBitMask(IV);
  HardwareLimits.LgkmcntMax = AMDGPU::getLgkmcntBitMask(IV);

  HardwareLimits.NumVGPRsMax = ST->getAddressableNumVGPRs();
  HardwareLimits.NumSGPRsMax = ST->getAddressableNumSGPRs();
  assert(HardwareLimits.NumVGPRsMax <= SQ_MAX_PGM_VGPRS);
  assert(HardwareLimits.NumSGPRsMax <= SQ_MAX_PGM_SGPRS);

  RegisterEncoding.VGPR0 = TRI->getEncodingValue(AMDGPU::VGPR0);
  RegisterEncoding.VGPRL =
      RegisterEncoding.VGPR0 + HardwareLimits.NumVGPRsMax - 1;
  RegisterEncoding.SGPR0 = TRI->getEncodingValue(AMDGPU::SGPR0);
  RegisterEncoding.SGPRL =
      RegisterEncoding.SGPR0 + HardwareLimits.NumSGPRsMax - 1;

  TrackedWaitcntSet.clear();
  BlockVisitedSet.clear();
  VCCZBugHandledSet.clear();

  // Walk over the blocks in reverse post-dominator order, inserting
  // s_waitcnt where needed.
  ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
  bool Modified = false;
  for (ReversePostOrderTraversal<MachineFunction *>::rpo_iterator
           I = RPOT.begin(),
           E = RPOT.end(), J = RPOT.begin();
       I != E;) {
    MachineBasicBlock &MBB = **I;

    BlockVisitedSet.insert(&MBB);

    BlockWaitcntBrackets *ScoreBrackets = BlockWaitcntBracketsMap[&MBB].get();
    if (!ScoreBrackets) {
      BlockWaitcntBracketsMap[&MBB] = llvm::make_unique<BlockWaitcntBrackets>();
      ScoreBrackets = BlockWaitcntBracketsMap[&MBB].get();
    }
    ScoreBrackets->setPostOrder(MBB.getNumber());
    MachineLoop *ContainingLoop = MLI->getLoopFor(&MBB);
    if (ContainingLoop && LoopWaitcntDataMap[ContainingLoop] == nullptr)
      LoopWaitcntDataMap[ContainingLoop] = llvm::make_unique<LoopWaitcntData>();

    // If we are walking into the block from before the loop, then guarantee
    // at least 1 re-walk over the loop to propagate the information, even if
    // no S_WAITCNT instructions were generated.
    if (ContainingLoop && ContainingLoop->getHeader() == &MBB && J < I &&
        (!BlockWaitcntProcessedSet.count(&MBB))) {
      BlockWaitcntBracketsMap[&MBB]->setRevisitLoop(true);
      DEBUG(dbgs() << "set-revisit: block"
                   << ContainingLoop->getHeader()->getNumber() << '\n';);
    }

    // Walk over the instructions.
    insertWaitcntInBlock(MF, MBB);

    // Flag that waitcnts have been processed at least once.
    BlockWaitcntProcessedSet.insert(&MBB);

    // See if we want to revisit the loop.
    if (ContainingLoop && loopBottom(ContainingLoop) == &MBB) {
      MachineBasicBlock *EntryBB = ContainingLoop->getHeader();
      BlockWaitcntBrackets *EntrySB = BlockWaitcntBracketsMap[EntryBB].get();
      if (EntrySB && EntrySB->getRevisitLoop()) {
        EntrySB->setRevisitLoop(false);
        J = I;
        int32_t PostOrder = EntrySB->getPostOrder();
        // TODO: Avoid this loop. Find another way to set I.
        for (ReversePostOrderTraversal<MachineFunction *>::rpo_iterator
                 X = RPOT.begin(),
                 Y = RPOT.end();
             X != Y; ++X) {
          MachineBasicBlock &MBBX = **X;
          if (MBBX.getNumber() == PostOrder) {
            I = X;
            break;
          }
        }
        LoopWaitcntData *WaitcntData = LoopWaitcntDataMap[ContainingLoop].get();
        WaitcntData->incIterCnt();
        DEBUG(dbgs() << "revisit: block" << EntryBB->getNumber() << '\n';);
        continue;
      } else {
        LoopWaitcntData *WaitcntData = LoopWaitcntDataMap[ContainingLoop].get();
        // Loop converged, reset iteration count. If this loop gets revisited,
        // it must be from an outer loop, the counter will restart, this will
        // ensure we don't force convergence on such revisits.
        WaitcntData->resetIterCnt();
      }
    }

    J = I;
    ++I;
  }

  SmallVector<MachineBasicBlock *, 4> EndPgmBlocks;

  bool HaveScalarStores = false;

  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end(); BI != BE;
       ++BI) {
    MachineBasicBlock &MBB = *BI;

    for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E;
         ++I) {
      if (!HaveScalarStores && TII->isScalarStore(*I))
        HaveScalarStores = true;

      if (I->getOpcode() == AMDGPU::S_ENDPGM ||
          I->getOpcode() == AMDGPU::SI_RETURN_TO_EPILOG)
        EndPgmBlocks.push_back(&MBB);
    }
  }

  if (HaveScalarStores) {
    // If scalar writes are used, the cache must be flushed or else the next
    // wave to reuse the same scratch memory can be clobbered.
    //
    // Insert s_dcache_wb at wave termination points if there were any scalar
    // stores, and only if the cache hasn't already been flushed. This could be
    // improved by looking across blocks for flushes in postdominating blocks
    // from the stores but an explicitly requested flush is probably very rare.
    for (MachineBasicBlock *MBB : EndPgmBlocks) {
      bool SeenDCacheWB = false;

      for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
           ++I) {
        if (I->getOpcode() == AMDGPU::S_DCACHE_WB)
          SeenDCacheWB = true;
        else if (TII->isScalarStore(*I))
          SeenDCacheWB = false;

        // FIXME: It would be better to insert this before a waitcnt if any.
        if ((I->getOpcode() == AMDGPU::S_ENDPGM ||
             I->getOpcode() == AMDGPU::SI_RETURN_TO_EPILOG) &&
            !SeenDCacheWB) {
          Modified = true;
          BuildMI(*MBB, I, I->getDebugLoc(), TII->get(AMDGPU::S_DCACHE_WB));
        }
      }
    }
  }

  if (!MFI->isEntryFunction()) {
    // Wait for any outstanding memory operations that the input registers may
    // depend on. We can't track them and it's better to the wait after the
    // costly call sequence.

    // TODO: Could insert earlier and schedule more liberally with operations
    // that only use caller preserved registers.
    MachineBasicBlock &EntryBB = MF.front();
    BuildMI(EntryBB, EntryBB.getFirstNonPHI(), DebugLoc(), TII->get(AMDGPU::S_WAITCNT))
      .addImm(0);

    Modified = true;
  }

  return Modified;
}