intel-graphics-compiler/visa/LocalDataflow.cpp

/*========================== begin_copyright_notice ============================

Copyright (C) 2017-2021 Intel Corporation

SPDX-License-Identifier: MIT

============================= end_copyright_notice ===========================*/

#include "Assertions.h"
#include "BitSet.h"
#include "BuildIR.h"
#include "FlowGraph.h"
#include "LocalDataflow.h"
#include <algorithm>
#include <unordered_map>
#include <vector>

using namespace vISA;

namespace {

void getOpndFootprint(G4_Operand *opnd, BitSet &footprint,
                      const IR_Builder &builder) {
  opnd->updateFootPrint(footprint, true, builder);
}

// Combine footprint.
//
// Use DefOnpd's foot print to kill the footprint being defined.
//
void combineFootprint(G4_Operand *DefOpnd, BitSet &footprint,
                      const IR_Builder &builder) {
  DefOpnd->updateFootPrint(footprint, false, builder);
}

struct LocalLivenessInfo;

// This is the basic unit used to track live operands (not fully defined yet).
struct LiveNode {
  LiveNode(G4_INST *Inst, Gen4_Operand_Number OpNum)
      : Inst(Inst), OpNum(OpNum), mask(getMaskSize(Inst, OpNum), 0) {
    auto opnd = getOperand();
    if (opnd)
      getOpndFootprint(opnd, mask, Inst->getBuilder());
  }

  // The instruction being tracked.
  G4_INST *Inst;

  // This indicates which operand being tracked.
  Gen4_Operand_Number OpNum;

  // This tracks byte/bits level of opnd being partially defined.
  BitSet mask;

  // The list of definition nodes seen, sorted in a reversed order.
  //
  // This data structure models the following du/ud chain, and it proves
  // <I3, Src1> is a locally fully-defined operand.
  //
  // I1 : mov (8,  M1) V33(0,0)<1>:d V32(0,0)<1;1,0>:q
  // I2 : mov (8,  M1) V33(1,0)<1>:d V32(2,0)<1;1,0>:q
  // I3 : add (16, M1) V35<1>:d V34<1;1,0>:d V33(0,0)<1;1,0>:d
  //
  // LiveNode <I3, V33> will be partially defined by I2 or I1, and
  // I1 together with I2 fully defines this live node.
  //
  std::vector<std::pair<G4_INST *, Gen4_Operand_Number>> DefNodes;

  G4_Operand *getOperand() const { return Inst->getOperand(OpNum); }

  static unsigned getMaskSize(G4_INST *Inst, Gen4_Operand_Number OpNum) {
    G4_Operand *Opnd = Inst->getOperand(OpNum);
    vISA_ASSERT(Opnd, "null opnd");
    if (Opnd) {
      G4_Declare *Dcl = Opnd->getTopDcl();
      if (Opnd->isAddrExp()) {
        Dcl = Opnd->asAddrExp()->getRegVar()->getDeclare();
      }
      if (Dcl == nullptr) {
        // There is no top declaration for this operand, so this is ARF.
        return 32;
      }
      return Dcl->getRegVar()->isFlag() ? Dcl->getNumberFlagElements()
                                        : Dcl->getByteSize();
    }

    return 0;
  }

  // Propocess a defintion to this live node. If this definition
  // together with existing definitions fully kill this use, return true
  // and add def-use links; return false otherwise.
  bool addDefinition(G4_INST *Inst, Gen4_Operand_Number opndNum,
                     LocalLivenessInfo &LLI);

  // Check if an operand depends on channel mask.
  static bool dependsOnChannelMask(bool IsInSimdFlow, G4_INST *Inst,
                                   Gen4_Operand_Number OpNum);

  // Check if def-use is 'aligned' with channel mask.
  static bool alignedWithChannelMask(G4_INST *DefInst,
                                     Gen4_Operand_Number DefOpNum,
                                     G4_INST *UseInst,
                                     Gen4_Operand_Number UseOpNum);

  friend void swap(LiveNode &a, LiveNode &b) {
    a.DefNodes.swap(b.DefNodes);
    std::swap(a.Inst, b.Inst);
    std::swap(a.OpNum, b.OpNum);
    a.mask.swap(b.mask);
  }
};

struct LocalLivenessInfo {
  // Keep live nodes while scanning the block.
  // Each declare is associated with a list of live nodes.
  std::unordered_map<const G4_Declare *, std::vector<LiveNode>> LiveNodes;

  // This indicates if this block is in simd-cf or not.
  bool IsInSimdFlow;

  // Default constructor.
  explicit LocalLivenessInfo(bool IsInSimdFlow) : IsInSimdFlow(IsInSimdFlow) {}

  // Populate global operands.
  void populateGlobals(GlobalOpndHashTable &globalOpndHT) {
    for (auto &Nodes : LiveNodes) {
      for (auto &LN : Nodes.second) {
        G4_Operand *Opnd = LN.Inst->getOperand(LN.OpNum);
        vISA_ASSERT(Opnd, "null operand");

        // This is a temporal solution to allow optimizations
        // on partially defined local variables.
        //
        // TODO: use pseudo-kill to mark such variables.
        for (auto I = LN.DefNodes.rbegin(), E = LN.DefNodes.rend(); I != E; ++I)
          I->first->addDefUse(LN.Inst, LN.OpNum);

        globalOpndHT.addGlobalOpnd(Opnd);
      }
      Nodes.second.clear();
    }
  }
};

} // namespace

static G4_CmpRelation compOpnd(G4_Operand *Opnd1, G4_Operand *Opnd2,
                               const IR_Builder &builder) {
  if (Opnd1->isDstRegRegion())
    return Opnd1->asDstRegRegion()->compareOperand(Opnd2, builder);
  else if (Opnd1->isCondMod())
    return Opnd1->asCondMod()->compareOperand(Opnd2, builder);
  else if (Opnd1->isSrcRegRegion())
    return Opnd1->asSrcRegRegion()->compareOperand(Opnd2, builder);
  else if (Opnd1->isPredicate())
    return Opnd1->asPredicate()->compareOperand(Opnd2, builder);

  // all other cases, virtual call.
  return Opnd1->compareOperand(Opnd2, builder);
}

bool LiveNode::addDefinition(G4_INST *DefInst, Gen4_Operand_Number DefOpNum,
                             LocalLivenessInfo &LLI) {
  const IR_Builder &builder = Inst->getBuilder();
  // This definition does not overlap with this live node.
  G4_Operand *DefOpnd = DefInst->getOperand(DefOpNum);
  G4_Operand *UseOpnd = getOperand();
  G4_CmpRelation Rel = compOpnd(DefOpnd, UseOpnd, builder);
  if (Rel == G4_CmpRelation::Rel_disjoint)
    return false;

  // Check if this definition will be fully convered by a previous definition.
  // This checks a single definition only. It is not optimal, but should cover
  // common cases.
  for (auto &Node : DefNodes) {
    if (Node.second != DefOpNum)
      continue;
    G4_INST *PrevDefInst = Node.first;
    if (PrevDefInst->getPredicate() || DefInst->getPredicate())
      continue;
    if (PrevDefInst->getMaskOffset() != DefInst->getMaskOffset())
      continue;
    if (!PrevDefInst->isWriteEnableInst() && DefInst->isWriteEnableInst())
      continue;
    G4_Operand *PrevDef = PrevDefInst->getOperand(Node.second);
    G4_Operand *CurrDef = DefInst->getOperand(DefOpNum);
    vASSERT((PrevDef != nullptr) && (CurrDef != nullptr));
    G4_CmpRelation DefRel = compOpnd(PrevDef, CurrDef, builder);
    if (DefRel == G4_CmpRelation::Rel_eq || DefRel == G4_CmpRelation::Rel_gt)
      return false;
  }

  // Determine to count this definition's footprint or not.
  auto CombineBitV = [this, DefInst, DefOpNum, &LLI]() {
    // If definition is predicated and it is not sel, then
    // this definition cannot count, unless use is predicated
    // by the same predicate value.
    if (G4_Predicate *DefPred = DefInst->getPredicate()) {
      if (DefInst->opcode() != G4_opcode::G4_sel) {
        // The following case is a full definition, when predicates
        // have the same value.
        // (+P1) mov (8, M1) V33(0,0)<1>:d 1  // DefInst
        // (+P1) add (8, M1) V34(0,0)<1>:d V33(0,0)<1;1,0>:d V32(0,0)<1;1,0>:d
        G4_Predicate *UsePred = this->Inst->getPredicate();
        if (UsePred == nullptr || !DefPred->samePredicate(*UsePred))
          return false;

        // If UsePred is alive and has no definition, then UsePred should
        // have the same value as DefPred.
        G4_Declare *Dcl = UsePred->getTopDcl();
        auto Iter = LLI.LiveNodes.find(Dcl);
        if (Iter == LLI.LiveNodes.end())
          return false;

        // Find this live node..
        auto NI = std::find_if(
            Iter->second.begin(), Iter->second.end(), [this](const LiveNode &LN) {
              return LN.Inst == this->Inst && LN.OpNum == Opnd_pred;
            });

        // Not alive or alive but partially defined.
        if (NI == Iter->second.end() || !NI->DefNodes.empty())
          return false;
      }
    }

    // If def does not depend on channel mask, then combine its footprint.
    if (!dependsOnChannelMask(LLI.IsInSimdFlow, DefInst, DefOpNum))
      return true;

    // Otherwise, if this use does not depend on channel mask, then do not
    // combine.
    if (!dependsOnChannelMask(LLI.IsInSimdFlow, this->Inst, this->OpNum))
      return false;

    return alignedWithChannelMask(DefInst, DefOpNum, this->Inst, this->OpNum);
  };

  if (CombineBitV()) {
    G4_Operand *DefOpnd = DefInst->getOperand(DefOpNum);
    combineFootprint(DefOpnd, mask, builder);
  }

  if (UseOpnd &&
      mask.isEmpty(UseOpnd->getLeftBound(), UseOpnd->getRightBound())) {
    // Use reverse_iterator as analysis is bottom-up. This makes
    // early defs come first in the def-use lists.
    if (!DefInst->isPseudoKill())
      DefInst->addDefUse(this->Inst, this->OpNum);
    for (auto I = DefNodes.rbegin(), E = DefNodes.rend(); I != E; ++I)
      I->first->addDefUse(this->Inst, this->OpNum);
    return true;
  }

  // This live node is not yet fully killed.
  DefNodes.emplace_back(DefInst, DefOpNum);
  return false;
}

bool LiveNode::dependsOnChannelMask(bool IsInSimdFlow, G4_INST *Inst,
                                    Gen4_Operand_Number OpNum) {
  // Treat non-flag scalar and indirect 1x1/Vx1 uses as noMask. Any non-noMask
  // inst can't kill it.
  auto opnd = Inst->getOperand(OpNum);
  bool isScalarSrc = opnd->isScalarSrc() && !opnd->isFlag();
  bool isIndirect1x1Vx1 = opnd->isIndirect() && !opnd->isVxHIndirect();

  if (!IsInSimdFlow || Inst->isWriteEnableInst() || isScalarSrc ||
      isIndirect1x1Vx1)
    return false;

  // Otherwise.
  return true;
}

// Check if def-use is 'aligned' with channel mask.
//
// CM = 11110000 (M8)
//      00001111 (M0)
//
// mov (8, M0) V33(0,0)<2>:d 1   // defines V33.{0,2,4,6}
// mov (8, M8) V33(0,1)<2>:d 2   // defines V33.{9,11,13,15}
// add (16, M0) V34.0<1>:d V33.0<1;1,0>:d 3 // uses V33.{0,1,2,3,12,13,14,15}
//
// This is not aligned, and it is not a full kill.
//
// mov (8, M0) V33(0,0)<1>:d 1   // defines V33.{0,1,2,3}
// mov (8, M8) V33(1,0)<1>:d 2   // defines V33.{12,13,14,15}
// add (16, M0) V34.0<1>:d V33.0<1;1,0>:d 3 // uses V33.{0,1,2,3,12,13,14,15}
//
// This is aligned, and it is a full kill.
//
bool LiveNode::alignedWithChannelMask(G4_INST *DefInst,
                                      Gen4_Operand_Number DefOpNum,
                                      G4_INST *UseInst,
                                      Gen4_Operand_Number UseOpNum) {
  G4_Operand *DefOpnd = DefInst->getOperand(DefOpNum);
  G4_Operand *UseOpnd = UseInst->getOperand(UseOpNum);
  unsigned DefLB = DefOpnd->getLeftBound();
  unsigned UseLB = UseOpnd->getLeftBound();
  unsigned DefMaskOffset = DefInst->getMaskOffset();
  unsigned UseMaskOffset = UseInst->getMaskOffset();

  // Flag is tracking at bit level.
  G4_Declare *Dcl = DefOpnd->getTopDcl();
  if (Dcl && Dcl->getRegFile() == G4_RegFileKind::G4_FLAG) {
    int DefOffset = int(DefLB - DefMaskOffset);
    int UseOffset = int(UseLB - UseMaskOffset);
    return DefOffset == UseOffset;
  }

  // UseOpnd is indirect VxH
  if (UseOpnd->isVxHIndirect()) {
    int DefOffset = int(DefLB - DefMaskOffset * TypeSize(ADDR_REG_TYPE));
    int UseOffset = int(UseLB - UseMaskOffset * TypeSize(ADDR_REG_TYPE));
    return DefOffset == UseOffset;
  }

  // Do not analyze instructions that may exceed two GRF boundary
  if (DefInst->isSend() || DefInst->isDpas() || UseInst->isSend() ||
      UseInst->isDpas())
    return true;

  // Check that all uses are defined under the righ emask, if defined.
  unsigned DefStride = 1;
  if (DefOpnd->isDstRegRegion()) {
    DefStride = DefOpnd->asDstRegRegion()->getHorzStride();
  }

  bool IsContinguous = false;
  if (UseOpnd->isSrcRegRegion()) {
    G4_SrcRegRegion *UseReg = UseOpnd->asSrcRegRegion();
    const RegionDesc *UseRegDesc = UseReg->getRegion();
    IsContinguous = UseRegDesc->isContiguous(UseInst->getExecSize());
  }

  unsigned DefTySz = DefOpnd->getTypeSize();
  unsigned UseTySz = UseOpnd->getTypeSize();

  // Common cases.
  if (DefStride == 1 && IsContinguous && DefTySz == UseTySz) {
    int DefOffset = int(DefLB - DefMaskOffset * DefTySz);
    int UseOffset = int(UseLB - UseMaskOffset * UseTySz);
    return DefOffset == UseOffset;
  }

  // Other cases.
  //
  // Initial value -1 means byte not defined, for [DefLB, DefRB].
  std::array<int, 256> DefByteMask;
  DefByteMask.fill(-1);

  // Set channel value for each defining byte.
  int Channel = DefInst->getMaskOffset();
  for (unsigned i = 0, n = DefInst->getExecSize(); i < n; ++i) {
    for (unsigned j = 0; j < DefTySz; ++j)
      DefByteMask[i * DefTySz * DefStride + j] = Channel;
    ++Channel;
  }

  // In general, enumerate elements of use region and for each byte
  // check if this byte is defined by a correct emask. Note that
  // it is ok that some bytes are not defined.
  //
  Channel = UseInst->getMaskOffset();
  if (UseOpnd->isSrcRegRegion()) {
    unsigned DefRB = DefOpnd->getRightBound();
    auto Desc = UseOpnd->asSrcRegRegion()->getRegion();
    int hs = Desc->isScalar() ? 1 : Desc->horzStride;
    int vs = Desc->isScalar() ? 0 : Desc->vertStride;
    int numRows = UseInst->getExecSize() / Desc->width;

    for (int i = 0; i < numRows; ++i) {
      for (int j = 0; j < Desc->width; ++j) {
        // Check this element's emask at byte level when defined.
        int eltOffset = i * vs * UseTySz + j * hs * UseTySz;
        if (UseLB + eltOffset >= DefLB &&
            UseLB + eltOffset + UseTySz - 1 <= DefRB) {
          int Offset = UseLB + eltOffset - DefLB;
          for (unsigned k = 0; k < UseTySz; ++k) {
            int Mask = DefByteMask[Offset + k];
            if (Mask != -1 && Mask != Channel)
              return false;
          }
        }
        ++Channel;
      }
    }
  }

  return true;
}

// Remove one element from vector and return the iterator to the next element.
template <typename T, typename AllocatorTy>
typename std::vector<T, AllocatorTy>::iterator
kill(std::vector<T, AllocatorTy> &Elts,
     typename std::vector<T, AllocatorTy>::iterator Iter) {
  vASSERT(Iter != Elts.end());
  vASSERT(!Elts.empty());
  if (&*Iter == &Elts.back()) {
    // This is the last element so the next one is none.
    Elts.pop_back();
    return Elts.end();
  }

  // Not the last one, swap with the tail and keep the iterator unchanged.
  std::swap(*Iter, Elts.back());
  Elts.pop_back();
  return Iter;
}

// Process reads. This simply creates a new live read node.
//
// Note that for an indirect operand, its top dcl is its address variable.
// This models def-use for the underlying address variable, not the
// variable being addressed. An indirect definition introduces a use too.
//
static void processReadOpnds(G4_BB *BB, G4_INST *Inst, LocalLivenessInfo &LLI) {
  if (Inst->isPseudoKill()) {
    return;
  }

  // (1) Indirect dst operand reads address.
  G4_DstRegRegion *Dst = Inst->getDst();
  if (Dst && Dst->isIndirect()) {
    G4_Declare *Dcl = Dst->getTopDcl();
    vISA_ASSERT(Dcl, "out of sync");
    LLI.LiveNodes[Dcl].emplace_back(Inst, Gen4_Operand_Number::Opnd_dst);
  }

  // (2) Direct and indirect source operands.
  for (auto OpNum :
       {Gen4_Operand_Number::Opnd_src0, Gen4_Operand_Number::Opnd_src1,
        Gen4_Operand_Number::Opnd_src2, Gen4_Operand_Number::Opnd_src3,
        Gen4_Operand_Number::Opnd_src4, Gen4_Operand_Number::Opnd_src5,
        Gen4_Operand_Number::Opnd_src6, Gen4_Operand_Number::Opnd_src7,
        Gen4_Operand_Number::Opnd_pred, Gen4_Operand_Number::Opnd_implAccSrc}) {
    G4_Operand *opnd = Inst->getOperand(OpNum);
    if (opnd == nullptr || opnd->isImm() || opnd->isNullReg() ||
        opnd->isLabel())
      continue;

    if (Inst->isPseudoAddrMovIntrinsic()) {
      G4_Declare *Dcl = opnd->asAddrExp()->getRegVar()->getDeclare();
      LLI.LiveNodes[Dcl].emplace_back(Inst, OpNum);
    } else {
      G4_Declare *Dcl = opnd->getTopDcl();
      LLI.LiveNodes[Dcl].emplace_back(Inst, OpNum);
    }
  }
}

static void
processReadOpndsForPseudoKill(G4_BB *BB, G4_INST *Inst,
                              std::unordered_set<G4_Declare *> &pseudoKills) {
  if (Inst->isPseudoKill()) {
    return;
  }
  // (1) Indirect dst operand reads address.
  G4_DstRegRegion *Dst = Inst->getDst();
  if (Dst && Dst->isIndirect()) {
    G4_Declare *dcl = Dst->getTopDcl();
    if (pseudoKills.find(dcl) != pseudoKills.end()) {
      dcl->setIsBBLocal(false);
      pseudoKills.erase(dcl);
    }
  }

  // (2) Direct and indirect source operands.
  for (auto OpNum :
       {Gen4_Operand_Number::Opnd_src0, Gen4_Operand_Number::Opnd_src1,
        Gen4_Operand_Number::Opnd_src2, Gen4_Operand_Number::Opnd_src3,
        Gen4_Operand_Number::Opnd_src4, Gen4_Operand_Number::Opnd_src5,
        Gen4_Operand_Number::Opnd_src6, Gen4_Operand_Number::Opnd_src7,
        Gen4_Operand_Number::Opnd_pred, Gen4_Operand_Number::Opnd_implAccSrc}) {
    G4_Operand *opnd = Inst->getOperand(OpNum);
    if (opnd == nullptr || opnd->isImm() || opnd->isNullReg() ||
        opnd->isLabel())
      continue;

    G4_Declare *dcl = nullptr;
    if (Inst->isPseudoAddrMovIntrinsic()) {
      dcl =opnd->asAddrExp()->getRegVar()->getDeclare();
    } else {
      dcl = opnd->getTopDcl();
    }
    if (pseudoKills.find(dcl) != pseudoKills.end()) {
      dcl->setIsBBLocal(false);
      pseudoKills.erase(dcl);
    }
  }
}

// Process writes. If this is a partial definition, then record this partial
// definition. When all partial definitions together define this live read node,
// it is killed and du/ud links are added.
//
static void processWriteOpnds(G4_BB *BB, G4_INST *Inst,
                              LocalLivenessInfo &LLI) {
  if (Inst->isPseudoKill()) {
    return;
  }
  for (auto OpNum :
       {Gen4_Operand_Number::Opnd_dst, Gen4_Operand_Number::Opnd_condMod,
        Gen4_Operand_Number::Opnd_implAccDst}) {
    G4_Operand *opnd = Inst->getOperand(OpNum);
    if (opnd == nullptr || opnd->isNullReg())
      continue;

    // Do not try to kill uses with indirect definitions.
    if (opnd->isDstRegRegion() && opnd->asDstRegRegion()->isIndirect())
      continue;

    // Iterate all live nodes associated to the same declaration.
    auto &Nodes = LLI.LiveNodes[opnd->getTopDcl()];
    for (auto Iter = Nodes.begin(); Iter != Nodes.end(); /*empty*/) {
      LiveNode &liveNode = *Iter;
      if (liveNode.addDefinition(Inst, OpNum, LLI)) {
        Iter = kill(Nodes, Iter);
        continue;
      }
      ++Iter;
    }
  }
}

void FlowGraph::localDataFlowAnalysis() {
  // For pseudo kill varaible
  // If there is use exposed in a BB, it's treated as global.
  // Otherwise, it's treated as local even the same pseudo kill may appear in
  // multiple BBs
  std::unordered_set<G4_Declare *> pesudoKilledDcls;

  for (auto BB : BBs) {
    LocalLivenessInfo LLI(!BB->isAllLaneActive());
    for (auto I = BB->rbegin(), E = BB->rend(); I != E; ++I) {
      G4_INST *Inst = *I;
      G4_opcode Op = Inst->opcode();
      if (Op == G4_opcode::G4_return || Op == G4_opcode::G4_label)
        continue;
      if (Inst->isOptBarrier()) {
        // Do not try to build def-use accross an optimization barrier,
        // and this effectively disables optimizations across it.
        LLI.populateGlobals(globalOpndHT);

        // A barrier does not kill, but may introduce uses.
        processReadOpnds(BB, Inst, LLI);
        continue;
      }
      processWriteOpnds(BB, Inst, LLI);

      if (Inst->isPseudoKill() && Inst->getDst() && !Inst->getDst()->isNullReg()) {
        G4_Declare *dcl = Inst->getDst()->getTopDcl();
        pesudoKilledDcls.insert(dcl);
        // In case the use in anther BB is analyzed before define
        if (!globalOpndHT.isOpndGlobal(Inst->getDst())) {
          G4_Declare *dcl = Inst->getDst()->getTopDcl();
          dcl->setIsBBLocal(true);
        }
      }

      processReadOpnds(BB, Inst, LLI);
      if (pesudoKilledDcls
              .size()) { // Process the operand using variable which
                         // has psuedo kill. Since the scan is from back to
                         // front, exposed use will make variable global
        processReadOpndsForPseudoKill(BB, Inst, pesudoKilledDcls);
      }
    }

    // All left over live nodes are global.
    LLI.populateGlobals(globalOpndHT);

    // Sort use lists according to their local ids.
    // This matches the use list order produced by forward
    // reaching definition based analysis. It is better for
    // optimizations not to rely on this order.
    BB->resetLocalIds();
    for (auto Inst : *BB) {
      if (Inst->use_size() > 1) {
        using Ty = std::pair<vISA::G4_INST *, Gen4_Operand_Number>;
        auto Cmp = [](const Ty &lhs, const Ty &rhs) -> bool {
          int lhsID = lhs.first->getLocalId();
          int rhsID = rhs.first->getLocalId();
          if (lhsID < rhsID)
            return true;
          else if (lhsID > rhsID)
            return false;
          return lhs.second < rhs.second;
        };
        Inst->sortUses(Cmp);
      }
    }
  }
}

// Reset existing def-use
void FlowGraph::resetLocalDataFlowData() {
  globalOpndHT.clearHashTable();
  for (auto bb : BBs) {
    for (auto inst : *bb) {
      inst->clearDef();
      inst->clearUse();
    }
  }
}

void DefEscapeBBAnalysis::analyzeBB(G4_BB *bb) {
  // active defines in this BB, organized by root declare
  invalidateBB(bb);
  std::unordered_map<G4_Declare *, std::vector<G4_INST *>> activeDefines;
  std::vector<G4_INST *> escapedDefs;
  for (auto inst : *bb) {
    if (!inst->getDst()) {
      continue;
    }

    // analyze GRF/Address dst
    auto dst = inst->getDst();

    if (dst->isIndirect()) {
      escapedDefs.push_back(inst);
    } else if (dst->getTopDcl()) {
      auto dcl = dst->getTopDcl()->getRootDeclare();
      auto &&iter = activeDefines.find(dcl);
      if (iter == activeDefines.end()) {
        // first define for dcl in this BB
        activeDefines[dcl] = {inst};
      } else {
        auto &&vec = iter->second;
        // note size may shrink!
        for (int i = 0; i < (int)vec.size(); ++i) {

          auto prevInst = vec[i];
          if (inst->getMaskOffset() != prevInst->getMaskOffset() ||
              (prevInst->isWriteEnableInst() && !inst->isWriteEnableInst()) ||
              dst->getExecTypeSize() != prevInst->getDst()->getExecTypeSize()) {
            continue;
          }
          auto rel = dst->compareOperand(prevInst->getDst(), *fg.builder);
          if (rel == Rel_eq || rel == Rel_gt) {
            std::swap(vec[i], vec[vec.size() - 1]);
            vec.pop_back();
#ifdef _DEBUG
            // std::cerr << "Inst:\t";
            // prevInst->dump();
            // std::cerr << "killed by Inst:\t";
            // inst->dump();
            auto killIter = killedDefs.find(bb);
            if (killIter == killedDefs.end()) {
              killedDefs[bb] = {prevInst};
            } else {
              auto &&killedVec = killIter->second;
              killedVec.push_back(prevInst);
            }
#endif
          }
        }
        vec.push_back(inst);
      }
    }
  }

  for (auto &&iter : activeDefines) {
    auto &&vec = iter.second;
    for (auto I : vec) {
      escapedDefs.push_back(I);
    }
  }
  escapedInsts[bb] = std::move(escapedDefs);
}

void DefEscapeBBAnalysis::print(std::ostream &OS) const {
  for (auto &&iter : escapedInsts) {
    G4_BB *bb = iter.first;
    OS << "BB" << bb->getId() << ":\n";
    OS << "Escaped inst:\n";
    for (auto &&inst : iter.second) {
      OS << "\t";
      inst->print(OS);
    }
#ifdef _DEBUG
    auto &&killIt = killedDefs.find(bb);
    if (killIt != killedDefs.end()) {
      OS << "Killed inst:\n";
      for (auto &&inst : killIt->second) {
        OS << "\t";
        inst->print(OS);
      }
    }
#endif // _DEBUG
    OS << "\n";
  }
}