InlineSpiller.cpp

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//===- InlineSpiller.cpp - Insert spills and restores inline --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The inline spiller modifies the machine function directly instead of
// inserting spills and restores in VirtRegMap.
//
//===----------------------------------------------------------------------===//
 
#include "InlineSpiller.h"
#include "AllocationOrder.h"
#include "SplitKit.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/LiveStacks.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineInstrBundle.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/Spiller.h"
#include "llvm/CodeGen/StackMaps.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <iterator>
#include <tuple>
#include <utility>
 
using namespace llvm;
 
#define DEBUG_TYPE "regalloc"
 
STATISTIC(NumSpilledRanges,   "Number of spilled live ranges");
STATISTIC(NumSnippets,        "Number of spilled snippets");
STATISTIC(NumSpills,          "Number of spills inserted");
STATISTIC(NumSpillsRemoved,   "Number of spills removed");
STATISTIC(NumReloads,         "Number of reloads inserted");
STATISTIC(NumReloadsRemoved,  "Number of reloads removed");
STATISTIC(NumFolded,          "Number of folded stack accesses");
STATISTIC(NumFoldedLoads,     "Number of folded loads");
STATISTIC(NumRemats,          "Number of rematerialized defs for spilling");
 
static cl::opt<bool>
RestrictStatepointRemat("restrict-statepoint-remat",
                       cl::init(false), cl::Hidden,
                       cl::desc("Restrict remat for statepoint operands"));
 
namespace {
class HoistSpillHelper : private LiveRangeEdit::Delegate {
  MachineFunction &MF;
  LiveIntervals &LIS;
  LiveStacks &LSS;
  MachineDominatorTree &MDT;
  VirtRegMap &VRM;
  MachineRegisterInfo &MRI;
  const TargetInstrInfo &TII;
  const TargetRegisterInfo &TRI;
  const MachineBlockFrequencyInfo &MBFI;
  LiveRegMatrix *Matrix;
 
  InsertPointAnalysis IPA;
 
  // Map from StackSlot to the LiveInterval of the original register.
  // Note the LiveInterval of the original register may have been deleted
  // after it is spilled. We keep a copy here to track the range where
  // spills can be moved.
  DenseMap<int, std::unique_ptr<LiveInterval>> StackSlotToOrigLI;
 
  // Map from pair of (StackSlot and Original VNI) to a set of spills which
  // have the same stackslot and have equal values defined by Original VNI.
  // These spills are mergeable and are hoist candidates.
  using MergeableSpillsMap =
      MapVector<std::pair<int, VNInfo *>, SmallPtrSet<MachineInstr *, 16>>;
  MergeableSpillsMap MergeableSpills;
 
  /// This is the map from original register to a set containing all its
  /// siblings. To hoist a spill to another BB, we need to find out a live
  /// sibling there and use it as the source of the new spill.
  DenseMap<Register, SmallSetVector<Register, 16>> Virt2SiblingsMap;
 
  bool isSpillCandBB(LiveInterval &OrigLI, VNInfo &OrigVNI,
                     MachineBasicBlock &BB, Register &LiveReg);
 
  void rmRedundantSpills(
      SmallPtrSet<MachineInstr *, 16> &Spills,
      SmallVectorImpl<MachineInstr *> &SpillsToRm,
      DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill);
 
  void getVisitOrders(
      MachineBasicBlock *Root, SmallPtrSet<MachineInstr *, 16> &Spills,
      SmallVectorImpl<MachineDomTreeNode *> &Orders,
      SmallVectorImpl<MachineInstr *> &SpillsToRm,
      DenseMap<MachineDomTreeNode *, Register> &SpillsToKeep,
      DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill);
 
  void runHoistSpills(LiveInterval &OrigLI, VNInfo &OrigVNI,
                      SmallPtrSet<MachineInstr *, 16> &Spills,
                      SmallVectorImpl<MachineInstr *> &SpillsToRm,
                      DenseMap<MachineBasicBlock *, Register> &SpillsToIns);
 
public:
  HoistSpillHelper(const Spiller::RequiredAnalyses &Analyses,
                   MachineFunction &mf, VirtRegMap &vrm, LiveRegMatrix *matrix)
      : MF(mf), LIS(Analyses.LIS), LSS(Analyses.LSS), MDT(Analyses.MDT),
        VRM(vrm), MRI(mf.getRegInfo()), TII(*mf.getSubtarget().getInstrInfo()),
        TRI(*mf.getSubtarget().getRegisterInfo()), MBFI(Analyses.MBFI),
        Matrix(matrix), IPA(LIS, mf.getNumBlockIDs()) {}
 
  void addToMergeableSpills(MachineInstr &Spill, int StackSlot,
                            Register Original);
  bool rmFromMergeableSpills(MachineInstr &Spill, int StackSlot);
  void hoistAllSpills();
  void LRE_WillShrinkVirtReg(Register) override;
  bool LRE_CanEraseVirtReg(Register) override;
  void LRE_DidCloneVirtReg(Register, Register) override;
 
private:
  // Vregs unassigned from the matrix during LRE_WillShrinkVirtReg, pending
  // re-assignment after the interval is shrunk/split.
  DenseMap<Register, MCRegister> PendingReassignments;
};
 
class InlineSpiller : public Spiller {
  MachineFunction &MF;
  LiveIntervals &LIS;
  LiveStacks &LSS;
  VirtRegMap &VRM;
  MachineRegisterInfo &MRI;
  const TargetInstrInfo &TII;
  const TargetRegisterInfo &TRI;
  LiveRegMatrix *Matrix = nullptr;
 
  // Variables that are valid during spill(), but used by multiple methods.
  LiveRangeEdit *Edit = nullptr;
  LiveInterval *StackInt = nullptr;
  int StackSlot;
  Register Original;
  AllocationOrder *Order = nullptr;
 
  // All registers to spill to StackSlot, including the main register.
  SmallVector<Register, 8> RegsToSpill;
 
  // All registers that were replaced by the spiller through some other method,
  // e.g. rematerialization.
  SmallVector<Register, 8> RegsReplaced;
 
  // All COPY instructions to/from snippets.
  // They are ignored since both operands refer to the same stack slot.
  // For bundled copies, this will only include the first header copy.
  SmallPtrSet<MachineInstr*, 8> SnippetCopies;
 
  // Values that failed to remat at some point.
  SmallPtrSet<VNInfo*, 8> UsedValues;
 
  // Dead defs generated during spilling.
  SmallVector<MachineInstr*, 8> DeadDefs;
 
  // Object records spills information and does the hoisting.
  HoistSpillHelper HSpiller;
 
  // Live range weight calculator.
  VirtRegAuxInfo &VRAI;
 
  ~InlineSpiller() override = default;
 
public:
  InlineSpiller(const Spiller::RequiredAnalyses &Analyses, MachineFunction &MF,
                VirtRegMap &VRM, VirtRegAuxInfo &VRAI, LiveRegMatrix *Matrix)
      : MF(MF), LIS(Analyses.LIS), LSS(Analyses.LSS), VRM(VRM),
        MRI(MF.getRegInfo()), TII(*MF.getSubtarget().getInstrInfo()),
        TRI(*MF.getSubtarget().getRegisterInfo()), Matrix(Matrix),
        HSpiller(Analyses, MF, VRM, Matrix), VRAI(VRAI) {}
 
  void spill(LiveRangeEdit &, AllocationOrder *Order = nullptr) override;
  ArrayRef<Register> getSpilledRegs() override { return RegsToSpill; }
  ArrayRef<Register> getReplacedRegs() override { return RegsReplaced; }
  void postOptimization() override;
 
private:
  bool isSnippet(const LiveInterval &SnipLI);
  void collectRegsToSpill();
 
  bool isRegToSpill(Register Reg) { return is_contained(RegsToSpill, Reg); }
 
  bool isSibling(Register Reg);
  bool hoistSpillInsideBB(LiveInterval &SpillLI, MachineInstr &CopyMI);
  void eliminateRedundantSpills(LiveInterval &LI, VNInfo *VNI);
 
  void markValueUsed(LiveInterval *, VNInfo *);
  bool hasPhysRegAvailable(const MachineInstr &MI);
  bool reMaterializeFor(LiveInterval &, MachineInstr &MI);
  void reMaterializeAll();
 
  bool coalesceStackAccess(MachineInstr *MI, Register Reg);
  bool foldMemoryOperand(ArrayRef<std::pair<MachineInstr *, unsigned>>,
                         MachineInstr *LoadMI = nullptr);
  void insertReload(Register VReg, SlotIndex, MachineBasicBlock::iterator MI);
  void insertSpill(Register VReg, MachineBasicBlock::iterator MI);
 
  void spillAroundUses(Register Reg);
  void spillAll();
};
 
} // end anonymous namespace
 
Spiller::~Spiller() = default;
 
void Spiller::anchor() {}
 
Spiller *
llvm::createInlineSpiller(const InlineSpiller::RequiredAnalyses &Analyses,
                          MachineFunction &MF, VirtRegMap &VRM,
                          VirtRegAuxInfo &VRAI, LiveRegMatrix *Matrix) {
  return new InlineSpiller(Analyses, MF, VRM, VRAI, Matrix);
}
 
//===----------------------------------------------------------------------===//
//                                Snippets
//===----------------------------------------------------------------------===//
 
// When spilling a virtual register, we also spill any snippets it is connected
// to. The snippets are small live ranges that only have a single real use,
// leftovers from live range splitting. Spilling them enables memory operand
// folding or tightens the live range around the single use.
//
// This minimizes register pressure and maximizes the store-to-load distance for
// spill slots which can be important in tight loops.
 
/// isFullCopyOf - If MI is a COPY to or from Reg, return the other register,
/// otherwise return 0.
static Register isCopyOf(const MachineInstr &MI, Register Reg,
                         const TargetInstrInfo &TII) {
  if (!TII.isCopyInstr(MI))
    return Register();
 
  const MachineOperand &DstOp = MI.getOperand(0);
  const MachineOperand &SrcOp = MI.getOperand(1);
 
  // TODO: Probably only worth allowing subreg copies with undef dests.
  if (DstOp.getSubReg() != SrcOp.getSubReg())
    return Register();
  if (DstOp.getReg() == Reg)
    return SrcOp.getReg();
  if (SrcOp.getReg() == Reg)
    return DstOp.getReg();
  return Register();
}
 
/// Check for a copy bundle as formed by SplitKit.
static Register isCopyOfBundle(const MachineInstr &FirstMI, Register Reg,
                               const TargetInstrInfo &TII) {
  if (!FirstMI.isBundled())
    return isCopyOf(FirstMI, Reg, TII);
 
  assert(!FirstMI.isBundledWithPred() && FirstMI.isBundledWithSucc() &&
         "expected to see first instruction in bundle");
 
  Register SnipReg;
  MachineBasicBlock::const_instr_iterator I = FirstMI.getIterator();
  while (I->isBundledWithSucc()) {
    const MachineInstr &MI = *I;
    auto CopyInst = TII.isCopyInstr(MI);
    if (!CopyInst)
      return Register();
 
    const MachineOperand &DstOp = *CopyInst->Destination;
    const MachineOperand &SrcOp = *CopyInst->Source;
    if (DstOp.getReg() == Reg) {
      if (!SnipReg)
        SnipReg = SrcOp.getReg();
      else if (SnipReg != SrcOp.getReg())
        return Register();
    } else if (SrcOp.getReg() == Reg) {
      if (!SnipReg)
        SnipReg = DstOp.getReg();
      else if (SnipReg != DstOp.getReg())
        return Register();
    }
 
    ++I;
  }
 
  return Register();
}
 
static void getVDefInterval(const MachineInstr &MI, LiveIntervals &LIS) {
  for (const MachineOperand &MO : MI.all_defs())
    if (MO.getReg().isVirtual())
      LIS.getInterval(MO.getReg());
}
 
/// isSnippet - Identify if a live interval is a snippet that should be spilled.
/// It is assumed that SnipLI is a virtual register with the same original as
/// Edit->getReg().
bool InlineSpiller::isSnippet(const LiveInterval &SnipLI) {
  Register Reg = Edit->getReg();
 
  // A snippet is a tiny live range with only a single instruction using it
  // besides copies to/from Reg or spills/fills.
  // Exception is done for statepoint instructions which will fold fills
  // into their operands.
  // We accept:
  //
  //   %snip = COPY %Reg / FILL fi#
  //   %snip = USE %snip
  //   %snip = STATEPOINT %snip in var arg area
  //   %Reg = COPY %snip / SPILL %snip, fi#
  //
  if (!LIS.intervalIsInOneMBB(SnipLI))
    return false;
 
  // Number of defs should not exceed 2 not accounting defs coming from
  // statepoint instructions.
  unsigned NumValNums = SnipLI.getNumValNums();
  for (auto *VNI : SnipLI.vnis()) {
    MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
    if (MI->getOpcode() == TargetOpcode::STATEPOINT)
      --NumValNums;
  }
  if (NumValNums > 2)
    return false;
 
  MachineInstr *UseMI = nullptr;
 
  // Check that all uses satisfy our criteria.
  for (MachineRegisterInfo::reg_bundle_nodbg_iterator
           RI = MRI.reg_bundle_nodbg_begin(SnipLI.reg()),
           E = MRI.reg_bundle_nodbg_end();
       RI != E;) {
    MachineInstr &MI = *RI++;
 
    // Allow copies to/from Reg.
    if (isCopyOfBundle(MI, Reg, TII))
      continue;
 
    // Allow stack slot loads.
    int FI;
    if (SnipLI.reg() == TII.isLoadFromStackSlot(MI, FI) && FI == StackSlot)
      continue;
 
    // Allow stack slot stores.
    if (SnipLI.reg() == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot)
      continue;
 
    if (StatepointOpers::isFoldableReg(&MI, SnipLI.reg()))
      continue;
 
    // Allow a single additional instruction.
    if (UseMI && &MI != UseMI)
      return false;
    UseMI = &MI;
  }
  return true;
}
 
/// collectRegsToSpill - Collect live range snippets that only have a single
/// real use.
void InlineSpiller::collectRegsToSpill() {
  Register Reg = Edit->getReg();
 
  // Main register always spills.
  RegsToSpill.assign(1, Reg);
  SnippetCopies.clear();
  RegsReplaced.clear();
 
  // Snippets all have the same original, so there can't be any for an original
  // register.
  if (Original == Reg)
    return;
 
  for (MachineInstr &MI : llvm::make_early_inc_range(MRI.reg_bundles(Reg))) {
    Register SnipReg = isCopyOfBundle(MI, Reg, TII);
    if (!isSibling(SnipReg))
      continue;
    LiveInterval &SnipLI = LIS.getInterval(SnipReg);
    if (!isSnippet(SnipLI))
      continue;
    SnippetCopies.insert(&MI);
    if (isRegToSpill(SnipReg))
      continue;
    RegsToSpill.push_back(SnipReg);
    LLVM_DEBUG(dbgs() << "\talso spill snippet " << SnipLI << '\n');
    ++NumSnippets;
  }
}
 
bool InlineSpiller::isSibling(Register Reg) {
  return Reg.isVirtual() && VRM.getOriginal(Reg) == Original;
}
 
/// It is beneficial to spill to earlier place in the same BB in case
/// as follows:
/// There is an alternative def earlier in the same MBB.
/// Hoist the spill as far as possible in SpillMBB. This can ease
/// register pressure:
///
///   x = def
///   y = use x
///   s = copy x
///
/// Hoisting the spill of s to immediately after the def removes the
/// interference between x and y:
///
///   x = def
///   spill x
///   y = use killed x
///
/// This hoist only helps when the copy kills its source.
///
bool InlineSpiller::hoistSpillInsideBB(LiveInterval &SpillLI,
                                       MachineInstr &CopyMI) {
  SlotIndex Idx = LIS.getInstructionIndex(CopyMI);
#ifndef NDEBUG
  VNInfo *VNI = SpillLI.getVNInfoAt(Idx.getRegSlot());
  assert(VNI && VNI->def == Idx.getRegSlot() && "Not defined by copy");
#endif
 
  Register SrcReg = CopyMI.getOperand(1).getReg();
  LiveInterval &SrcLI = LIS.getInterval(SrcReg);
  VNInfo *SrcVNI = SrcLI.getVNInfoAt(Idx);
  LiveQueryResult SrcQ = SrcLI.Query(Idx);
  MachineBasicBlock *DefMBB = LIS.getMBBFromIndex(SrcVNI->def);
  if (DefMBB != CopyMI.getParent() || !SrcQ.isKill())
    return false;
 
  MachineBasicBlock *MBB = DefMBB;
  MachineBasicBlock::iterator MII;
  if (SrcVNI->isPHIDef())
    MII = MBB->SkipPHIsLabelsAndDebug(MBB->begin(), SrcReg);
  else {
    MachineInstr *DefMI = LIS.getInstructionFromIndex(SrcVNI->def);
    assert(DefMI && "Defining instruction disappeared");
    MII = DefMI;
    ++MII;
  }
 
  // When the def is a PHI, the store may be inserted after the prologue
  // instructions. In that case, the segment may need to be extended to the
  // store (see below). Do not hoist if there is an interference between the end
  // of the segment and the insertion point.
  if (SrcVNI->isPHIDef() && Matrix && VRM.hasPhys(SrcReg)) {
    // Here, MII points to the instruction before which the store will be
    // inserted. Using that instruction's base index is a safe upper bound for
    // the interference check.
    SlotIndex InsertIdx = MII == MBB->end()
                              ? LIS.getMBBEndIdx(MBB)
                              : LIS.getInstructionIndex(*MII).getBaseIndex();
    if (SrcQ.endPoint() < InsertIdx &&
        Matrix->checkInterference(SrcQ.endPoint(), InsertIdx,
                                  VRM.getPhys(SrcReg)))
      return false;
  }
 
  // Conservatively extend the stack slot range to the range of the original
  // value. We may be able to do better with stack slot coloring by being more
  // careful here.
  assert(StackInt && "No stack slot assigned yet.");
  LiveInterval &OrigLI = LIS.getInterval(Original);
  VNInfo *OrigVNI = OrigLI.getVNInfoAt(Idx);
  StackInt->MergeValueInAsValue(OrigLI, OrigVNI, StackInt->getValNumInfo(0));
  LLVM_DEBUG(dbgs() << "\tmerged orig valno " << OrigVNI->id << ": "
                    << *StackInt << '\n');
 
  // We are going to spill SrcVNI immediately after its def, so clear out
  // any later spills of the same value.
  eliminateRedundantSpills(SrcLI, SrcVNI);
 
  MachineInstrSpan MIS(MII, MBB);
  // Insert spill without kill flag immediately after def.
  TII.storeRegToStackSlot(*MBB, MII, SrcReg, false, StackSlot,
                          MRI.getRegClass(SrcReg), Register());
  LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MII);
  for (const MachineInstr &MI : make_range(MIS.begin(), MII))
    getVDefInterval(MI, LIS);
  --MII; // Point to store instruction.
  LLVM_DEBUG(dbgs() << "\thoisted: " << SrcVNI->def << '\t' << *MII);
 
  // When the def is a PHI, SkipPHIsLabelsAndDebug may place the store past
  // prologue instructions. Therefore if that copy was the end of a segment
  // we need to extend it to the store.
  if (SrcVNI->isPHIDef()) {
    SlotIndex StoreUseIdx = LIS.getInstructionIndex(*MII).getRegSlot(true);
    SrcLI.extendInBlock(LIS.getMBBStartIdx(MBB), StoreUseIdx);
  }
 
  // If there is only 1 store instruction is required for spill, add it
  // to mergeable list. In X86 AMX, 2 instructions are required to store.
  // We disable the merge for this case.
  if (MIS.begin() == MII)
    HSpiller.addToMergeableSpills(*MII, StackSlot, Original);
  ++NumSpills;
  return true;
}
 
/// eliminateRedundantSpills - SLI:VNI is known to be on the stack. Remove any
/// redundant spills of this value in SLI.reg and sibling copies.
void InlineSpiller::eliminateRedundantSpills(LiveInterval &SLI, VNInfo *VNI) {
  assert(VNI && "Missing value");
  SmallVector<std::pair<LiveInterval*, VNInfo*>, 8> WorkList;
  WorkList.push_back(std::make_pair(&SLI, VNI));
  assert(StackInt && "No stack slot assigned yet.");
 
  do {
    LiveInterval *LI;
    std::tie(LI, VNI) = WorkList.pop_back_val();
    Register Reg = LI->reg();
    LLVM_DEBUG(dbgs() << "Checking redundant spills for " << VNI->id << '@'
                      << VNI->def << " in " << *LI << '\n');
 
    // Regs to spill are taken care of.
    if (isRegToSpill(Reg))
      continue;
 
    // Add all of VNI's live range to StackInt.
    StackInt->MergeValueInAsValue(*LI, VNI, StackInt->getValNumInfo(0));
    LLVM_DEBUG(dbgs() << "Merged to stack int: " << *StackInt << '\n');
 
    // Find all spills and copies of VNI.
    for (MachineInstr &MI :
         llvm::make_early_inc_range(MRI.use_nodbg_bundles(Reg))) {
      if (!MI.mayStore() && !TII.isCopyInstr(MI))
        continue;
      SlotIndex Idx = LIS.getInstructionIndex(MI);
      if (LI->getVNInfoAt(Idx) != VNI)
        continue;
 
      // Follow sibling copies down the dominator tree.
      if (Register DstReg = isCopyOfBundle(MI, Reg, TII)) {
        if (isSibling(DstReg)) {
          LiveInterval &DstLI = LIS.getInterval(DstReg);
          VNInfo *DstVNI = DstLI.getVNInfoAt(Idx.getRegSlot());
          assert(DstVNI && "Missing defined value");
          assert(DstVNI->def == Idx.getRegSlot() && "Wrong copy def slot");
 
          WorkList.push_back(std::make_pair(&DstLI, DstVNI));
        }
        continue;
      }
 
      // Erase spills.
      int FI;
      if (Reg == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot) {
        LLVM_DEBUG(dbgs() << "Redundant spill " << Idx << '\t' << MI);
        // eliminateDeadDefs won't normally remove stores, so switch opcode.
        MI.setDesc(TII.get(TargetOpcode::KILL));
        DeadDefs.push_back(&MI);
        ++NumSpillsRemoved;
        if (HSpiller.rmFromMergeableSpills(MI, StackSlot))
          --NumSpills;
      }
    }
  } while (!WorkList.empty());
}
 
//===----------------------------------------------------------------------===//
//                            Rematerialization
//===----------------------------------------------------------------------===//
 
/// markValueUsed - Remember that VNI failed to rematerialize, so its defining
/// instruction cannot be eliminated. See through snippet copies
void InlineSpiller::markValueUsed(LiveInterval *LI, VNInfo *VNI) {
  SmallVector<std::pair<LiveInterval*, VNInfo*>, 8> WorkList;
  WorkList.push_back(std::make_pair(LI, VNI));
  do {
    std::tie(LI, VNI) = WorkList.pop_back_val();
    if (!UsedValues.insert(VNI).second)
      continue;
 
    if (VNI->isPHIDef()) {
      MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
      for (MachineBasicBlock *P : MBB->predecessors()) {
        VNInfo *PVNI = LI->getVNInfoBefore(LIS.getMBBEndIdx(P));
        if (PVNI)
          WorkList.push_back(std::make_pair(LI, PVNI));
      }
      continue;
    }
 
    // Follow snippet copies.
    MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
    if (!SnippetCopies.count(MI))
      continue;
    LiveInterval &SnipLI = LIS.getInterval(MI->getOperand(1).getReg());
    assert(isRegToSpill(SnipLI.reg()) && "Unexpected register in copy");
    VNInfo *SnipVNI = SnipLI.getVNInfoAt(VNI->def.getRegSlot(true));
    assert(SnipVNI && "Snippet undefined before copy");
    WorkList.push_back(std::make_pair(&SnipLI, SnipVNI));
  } while (!WorkList.empty());
}
 
bool llvm::canGuaranteeAssignmentAfterRemat(Register VReg,
                                            const MachineInstr &MI) {
  if (!RestrictStatepointRemat)
    return true;
  // Here's a quick explanation of the problem we're trying to handle here:
  // * There are some pseudo instructions with more vreg uses than there are
  //   physical registers on the machine.
  // * This is normally handled by spilling the vreg, and folding the reload
  //   into the user instruction.  (Thus decreasing the number of used vregs
  //   until the remainder can be assigned to physregs.)
  // * However, since we may try to spill vregs in any order, we can end up
  //   trying to spill each operand to the instruction, and then rematting it
  //   instead.  When that happens, the new live intervals (for the remats) are
  //   expected to be trivially assignable (i.e. RS_Done).  However, since we
  //   may have more remats than physregs, we're guaranteed to fail to assign
  //   one.
  // At the moment, we only handle this for STATEPOINTs since they're the only
  // pseudo op where we've seen this.  If we start seeing other instructions
  // with the same problem, we need to revisit this.
  if (MI.getOpcode() != TargetOpcode::STATEPOINT)
    return true;
  // For STATEPOINTs we allow re-materialization for fixed arguments only hoping
  // that number of physical registers is enough to cover all fixed arguments.
  // If it is not true we need to revisit it.
  for (unsigned Idx = StatepointOpers(&MI).getVarIdx(),
                EndIdx = MI.getNumOperands();
       Idx < EndIdx; ++Idx) {
    const MachineOperand &MO = MI.getOperand(Idx);
    if (MO.isReg() && MO.getReg() == VReg)
      return false;
  }
  return true;
}
 
/// hasPhysRegAvailable - Check if there is an available physical register for
/// rematerialization.
bool InlineSpiller::hasPhysRegAvailable(const MachineInstr &MI) {
  if (!Order || !Matrix)
    return false;
 
  SlotIndex UseIdx = LIS.getInstructionIndex(MI).getRegSlot(true);
  SlotIndex PrevIdx = UseIdx.getPrevSlot();
 
  for (MCPhysReg PhysReg : *Order) {
    if (!Matrix->checkInterference(PrevIdx, UseIdx, PhysReg))
      return true;
  }
 
  return false;
}
 
/// reMaterializeFor - Attempt to rematerialize before MI instead of reloading.
bool InlineSpiller::reMaterializeFor(LiveInterval &VirtReg, MachineInstr &MI) {
  // Analyze instruction
  SmallVector<std::pair<MachineInstr *, unsigned>, 8> Ops;
  VirtRegInfo RI = AnalyzeVirtRegInBundle(MI, VirtReg.reg(), &Ops);
 
  // Defs without reads will be deleted if unused after remat is
  // completed for other users of the virtual register.
  if (!RI.Reads) {
    LLVM_DEBUG(dbgs() << "\tskipping remat of def " << MI);
    return false;
  }
 
  SlotIndex UseIdx = LIS.getInstructionIndex(MI).getRegSlot(true);
  VNInfo *ParentVNI = VirtReg.getVNInfoAt(UseIdx.getBaseIndex());
 
  if (!ParentVNI) {
    LLVM_DEBUG(dbgs() << "\tadding <undef> flags: ");
    for (MachineOperand &MO : MI.all_uses())
      if (MO.getReg() == VirtReg.reg())
        MO.setIsUndef();
    LLVM_DEBUG(dbgs() << UseIdx << '\t' << MI);
    return true;
  }
 
  // Snippets copies are ignored for remat, and will be deleted if they
  // don't feed a live user after rematerialization completes.
  if (SnippetCopies.count(&MI)) {
    LLVM_DEBUG(dbgs() << "\tskipping remat snippet copy for " << UseIdx << '\t'
                      << MI);
    return false;
  }
 
  LiveInterval &OrigLI = LIS.getInterval(Original);
  VNInfo *OrigVNI = OrigLI.getVNInfoAt(UseIdx);
  assert(OrigVNI && "corrupted sub-interval");
  MachineInstr *DefMI = LIS.getInstructionFromIndex(OrigVNI->def);
  // This can happen if for two reasons: 1) This could be a phi valno,
  // or 2) the remat def has already been removed from the original
  // live interval; this happens if we rematted to all uses, and
  // then further split one of those live ranges.
  if (!DefMI) {
    // Try to find the rematerializable definition by tracing through COPY
    // chains.
    LiveInterval &LI = LIS.getInterval(VirtReg.reg());
    VNInfo *CurVNI = LI.getVNInfoAt(UseIdx);
    MachineInstr *CurDef = nullptr;
 
    LLVM_DEBUG(dbgs() << "\ttracing COPY chain from "
                      << printReg(VirtReg.reg(), &TRI) << "\n");
 
    // Trace backwards through COPY chain using VNInfo
    while (CurVNI) {
      CurDef = LIS.getInstructionFromIndex(CurVNI->def);
 
      LLVM_DEBUG(dbgs() << "\t -> def at " << CurVNI->def << ": "
                        << (CurDef ? TII.getName(CurDef->getOpcode()) : "null")
                        << "\n");
 
      if (!CurDef || !CurDef->isFullCopy())
        break;
 
      Register SrcReg = CurDef->getOperand(1).getReg();
      if (!SrcReg.isVirtual())
        break;
      LLVM_DEBUG(dbgs() << "\t -> tracing through COPY to "
                        << printReg(SrcReg, &TRI) << "\n");
      LiveInterval &SrcLI = LIS.getInterval(SrcReg);
      CurVNI = SrcLI.getVNInfoBefore(CurVNI->def);
    }
    if (CurDef && TII.isReMaterializable(*CurDef)) {
      DefMI = CurDef;
      LLVM_DEBUG(dbgs() << "\tFound remat possibility through COPY chain: "
                        << *DefMI);
    }
    if (!DefMI) {
      markValueUsed(&VirtReg, ParentVNI);
      LLVM_DEBUG(dbgs() << "\tcannot remat missing def for " << UseIdx << '\t'
                        << MI);
      return false;
    }
  }
 
  LiveRangeEdit::Remat RM(ParentVNI);
  RM.OrigMI = DefMI;
  if (!Edit->canRematerializeAt(RM, UseIdx)) {
    markValueUsed(&VirtReg, ParentVNI);
    LLVM_DEBUG(dbgs() << "\tcannot remat for " << UseIdx << '\t' << MI);
    return false;
  }
 
  // If the instruction also writes VirtReg.reg, it had better not require the
  // same register for uses and defs.
  if (RI.Tied) {
    markValueUsed(&VirtReg, ParentVNI);
    LLVM_DEBUG(dbgs() << "\tcannot remat tied reg: " << UseIdx << '\t' << MI);
    return false;
  }
 
  // Before rematerializing into a register for a single instruction, try to
  // fold a load into the instruction. That avoids allocating a new register.
  if (RM.OrigMI->canFoldAsLoad() &&
      (RM.OrigMI->mayLoad() || !hasPhysRegAvailable(MI)) &&
      foldMemoryOperand(Ops, RM.OrigMI)) {
    Edit->markRematerialized(RM.ParentVNI);
    ++NumFoldedLoads;
    return true;
  }
 
  // If we can't guarantee that we'll be able to actually assign the new vreg,
  // we can't remat.
  if (!canGuaranteeAssignmentAfterRemat(VirtReg.reg(), MI)) {
    markValueUsed(&VirtReg, ParentVNI);
    LLVM_DEBUG(dbgs() << "\tcannot remat for " << UseIdx << '\t' << MI);
    return false;
  }
 
  // Allocate a new register for the remat.
  Register NewVReg = Edit->createFrom(Original);
 
  // Constrain it to the register class of MI.
  MRI.constrainRegClass(NewVReg, MRI.getRegClass(VirtReg.reg()));
 
  // Compute which lanes of the virtual register are live at the use point.
  LaneBitmask UsedLanes = LaneBitmask::getAll();
  if (VirtReg.hasSubRanges()) {
    UsedLanes = LaneBitmask::getNone();
    for (const LiveInterval::SubRange &SR : VirtReg.subranges())
      if (SR.liveAt(UseIdx))
        UsedLanes |= SR.LaneMask;
  }
 
  // Finally we can rematerialize OrigMI before MI.
  SlotIndex DefIdx = Edit->rematerializeAt(*MI.getParent(), MI, NewVReg, RM,
                                           TRI, false, 0, nullptr, UsedLanes);
 
  // We take the DebugLoc from MI, since OrigMI may be attributed to a
  // different source location.
  auto *NewMI = LIS.getInstructionFromIndex(DefIdx);
  NewMI->setDebugLoc(MI.getDebugLoc());
 
  (void)DefIdx;
  LLVM_DEBUG(dbgs() << "\tremat:  " << DefIdx << '\t'
                    << *LIS.getInstructionFromIndex(DefIdx));
 
  // Replace operands
  for (const auto &OpPair : Ops) {
    MachineOperand &MO = OpPair.first->getOperand(OpPair.second);
    if (MO.isReg() && MO.isUse() && MO.getReg() == VirtReg.reg())
      MO.setReg(NewVReg);
  }
  LLVM_DEBUG(dbgs() << "\t        " << UseIdx << '\t' << MI << '\n');
 
  ++NumRemats;
  return true;
}
 
/// reMaterializeAll - Try to rematerialize as many uses as possible,
/// and trim the live ranges after.
void InlineSpiller::reMaterializeAll() {
  UsedValues.clear();
 
  // Try to remat before all uses of snippets.
  bool anyRemat = false;
  for (Register Reg : RegsToSpill) {
    LiveInterval &LI = LIS.getInterval(Reg);
    for (MachineInstr &MI : llvm::make_early_inc_range(MRI.reg_bundles(Reg))) {
      // Debug values are not allowed to affect codegen.
      if (MI.isDebugValue())
        continue;
 
      assert(!MI.isDebugInstr() && "Did not expect to find a use in debug "
             "instruction that isn't a DBG_VALUE");
 
      anyRemat |= reMaterializeFor(LI, MI);
    }
  }
  if (!anyRemat)
    return;
 
  // Remove any values that were completely rematted.
  for (Register Reg : RegsToSpill) {
    LiveInterval &LI = LIS.getInterval(Reg);
    for (VNInfo *VNI : LI.vnis()) {
      if (VNI->isUnused() || VNI->isPHIDef() || UsedValues.count(VNI))
        continue;
      MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
      MI->addRegisterDead(Reg, &TRI);
      if (!MI->allDefsAreDead())
        continue;
      LLVM_DEBUG(dbgs() << "All defs dead: " << *MI);
      DeadDefs.push_back(MI);
      // If MI is a bundle header, also try removing copies inside the bundle,
      // otherwise the verifier would complain "live range continues after dead
      // def flag".
      if (MI->isBundledWithSucc() && !MI->isBundledWithPred()) {
        MachineBasicBlock::instr_iterator BeginIt = MI->getIterator(),
                                          EndIt = MI->getParent()->instr_end();
        ++BeginIt; // Skip MI that was already handled.
 
        bool OnlyDeadCopies = true;
        for (MachineBasicBlock::instr_iterator It = BeginIt;
             It != EndIt && It->isBundledWithPred(); ++It) {
 
          auto DestSrc = TII.isCopyInstr(*It);
          bool IsCopyToDeadReg =
              DestSrc && DestSrc->Destination->getReg() == Reg;
          if (!IsCopyToDeadReg) {
            OnlyDeadCopies = false;
            break;
          }
        }
        if (OnlyDeadCopies) {
          for (MachineBasicBlock::instr_iterator It = BeginIt;
               It != EndIt && It->isBundledWithPred(); ++It) {
            It->addRegisterDead(Reg, &TRI);
            LLVM_DEBUG(dbgs() << "All defs dead: " << *It);
            DeadDefs.push_back(&*It);
          }
        }
      }
    }
  }
 
  // Eliminate dead code after remat. Note that some snippet copies may be
  // deleted here.
  if (DeadDefs.empty())
    return;
  LLVM_DEBUG(dbgs() << "Remat created " << DeadDefs.size() << " dead defs.\n");
  Edit->eliminateDeadDefs(DeadDefs, RegsToSpill);
 
  // LiveRangeEdit::eliminateDeadDef is used to remove dead define instructions
  // after rematerialization.  To remove a VNI for a vreg from its LiveInterval,
  // LiveIntervals::removeVRegDefAt is used. However, after non-PHI VNIs are all
  // removed, PHI VNI are still left in the LiveInterval.
  // So to get rid of unused reg, we need to check whether it has non-dbg
  // reference instead of whether it has non-empty interval.
  unsigned ResultPos = 0;
  for (Register Reg : RegsToSpill) {
    if (MRI.reg_nodbg_empty(Reg)) {
      Edit->eraseVirtReg(Reg);
      RegsReplaced.push_back(Reg);
      continue;
    }
 
    assert(LIS.hasInterval(Reg) &&
           (!LIS.getInterval(Reg).empty() || !MRI.reg_nodbg_empty(Reg)) &&
           "Empty and not used live-range?!");
 
    RegsToSpill[ResultPos++] = Reg;
  }
  RegsToSpill.erase(RegsToSpill.begin() + ResultPos, RegsToSpill.end());
  LLVM_DEBUG(dbgs() << RegsToSpill.size()
                    << " registers to spill after remat.\n");
}
 
//===----------------------------------------------------------------------===//
//                                 Spilling
//===----------------------------------------------------------------------===//
 
/// If MI is a load or store of StackSlot, it can be removed.
bool InlineSpiller::coalesceStackAccess(MachineInstr *MI, Register Reg) {
  int FI = 0;
  Register InstrReg = TII.isLoadFromStackSlot(*MI, FI);
  bool IsLoad = InstrReg.isValid();
  if (!IsLoad)
    InstrReg = TII.isStoreToStackSlot(*MI, FI);
 
  // We have a stack access. Is it the right register and slot?
  if (InstrReg != Reg || FI != StackSlot)
    return false;
 
  if (!IsLoad)
    HSpiller.rmFromMergeableSpills(*MI, StackSlot);
 
  LLVM_DEBUG(dbgs() << "Coalescing stack access: " << *MI);
  LIS.RemoveMachineInstrFromMaps(*MI);
  MI->eraseFromParent();
 
  if (IsLoad) {
    ++NumReloadsRemoved;
    --NumReloads;
  } else {
    ++NumSpillsRemoved;
    --NumSpills;
  }
 
  return true;
}
 
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD
// Dump the range of instructions from B to E with their slot indexes.
static void dumpMachineInstrRangeWithSlotIndex(MachineBasicBlock::iterator B,
                                               MachineBasicBlock::iterator E,
                                               LiveIntervals const &LIS,
                                               const char *const header,
                                               Register VReg = Register()) {
  char NextLine = '\n';
  char SlotIndent = '\t';
 
  if (std::next(B) == E) {
    NextLine = ' ';
    SlotIndent = ' ';
  }
 
  dbgs() << '\t' << header << ": " << NextLine;
 
  for (MachineBasicBlock::iterator I = B; I != E; ++I) {
    SlotIndex Idx = LIS.getInstructionIndex(*I).getRegSlot();
 
    // If a register was passed in and this instruction has it as a
    // destination that is marked as an early clobber, print the
    // early-clobber slot index.
    if (VReg) {
      MachineOperand *MO = I->findRegisterDefOperand(VReg, /*TRI=*/nullptr);
      if (MO && MO->isEarlyClobber())
        Idx = Idx.getRegSlot(true);
    }
 
    dbgs() << SlotIndent << Idx << '\t' << *I;
  }
}
#endif
 
/// foldMemoryOperand - Try folding stack slot references in Ops into their
/// instructions.
///
/// @param Ops    Operand indices from AnalyzeVirtRegInBundle().
/// @param LoadMI Load instruction to use instead of stack slot when non-null.
/// @return       True on success.
bool InlineSpiller::
foldMemoryOperand(ArrayRef<std::pair<MachineInstr *, unsigned>> Ops,
                  MachineInstr *LoadMI) {
  if (Ops.empty())
    return false;
  // Don't attempt folding in bundles.
  MachineInstr *MI = Ops.front().first;
  if (Ops.back().first != MI || MI->isBundled())
    return false;
 
  bool WasCopy = TII.isCopyInstr(*MI).has_value();
  Register ImpReg;
 
  // TII::foldMemoryOperand will do what we need here for statepoint
  // (fold load into use and remove corresponding def). We will replace
  // uses of removed def with loads (spillAroundUses).
  // For that to work we need to untie def and use to pass it through
  // foldMemoryOperand and signal foldPatchpoint that it is allowed to
  // fold them.
  bool UntieRegs = MI->getOpcode() == TargetOpcode::STATEPOINT;
 
  // Spill subregs if the target allows it.
  // We always want to spill subregs for stackmap/patchpoint pseudos.
  bool SpillSubRegs = TII.isSubregFoldable() ||
                      MI->getOpcode() == TargetOpcode::STATEPOINT ||
                      MI->getOpcode() == TargetOpcode::PATCHPOINT ||
                      MI->getOpcode() == TargetOpcode::STACKMAP;
 
  // TargetInstrInfo::foldMemoryOperand only expects explicit, non-tied
  // operands.
  SmallVector<unsigned, 8> FoldOps;
  for (const auto &OpPair : Ops) {
    unsigned Idx = OpPair.second;
    assert(MI == OpPair.first && "Instruction conflict during operand folding");
    MachineOperand &MO = MI->getOperand(Idx);
 
    // No point restoring an undef read, and we'll produce an invalid live
    // interval.
    // TODO: Is this really the correct way to handle undef tied uses?
    if (MO.isUse() && !MO.readsReg() && !MO.isTied())
      continue;
 
    if (MO.isImplicit()) {
      ImpReg = MO.getReg();
      continue;
    }
 
    if (!SpillSubRegs && MO.getSubReg())
      return false;
    // We cannot fold a load instruction into a def.
    if (LoadMI && MO.isDef())
      return false;
    // Tied use operands should not be passed to foldMemoryOperand.
    if (UntieRegs || !MI->isRegTiedToDefOperand(Idx))
      FoldOps.push_back(Idx);
  }
 
  // If we only have implicit uses, we won't be able to fold that.
  // Moreover, TargetInstrInfo::foldMemoryOperand will assert if we try!
  if (FoldOps.empty())
    return false;
 
  MachineInstrSpan MIS(MI, MI->getParent());
 
  SmallVector<std::pair<unsigned, unsigned> > TiedOps;
  if (UntieRegs)
    for (unsigned Idx : FoldOps) {
      MachineOperand &MO = MI->getOperand(Idx);
      if (!MO.isTied())
        continue;
      unsigned Tied = MI->findTiedOperandIdx(Idx);
      if (MO.isUse())
        TiedOps.emplace_back(Tied, Idx);
      else {
        assert(MO.isDef() && "Tied to not use and def?");
        TiedOps.emplace_back(Idx, Tied);
      }
      MI->untieRegOperand(Idx);
    }
 
  MachineInstr *CopyMI = nullptr;
  MachineInstr *FoldMI =
      LoadMI
          ? TII.foldMemoryOperand(*MI, FoldOps, *LoadMI, CopyMI, &LIS, &VRM)
          : TII.foldMemoryOperand(*MI, FoldOps, StackSlot, CopyMI, &LIS, &VRM);
  if (!FoldMI) {
    // Re-tie operands.
    for (auto Tied : TiedOps)
      MI->tieOperands(Tied.first, Tied.second);
    return false;
  }
 
  // Remove LIS for any dead defs in the original MI not in FoldMI.
  for (MIBundleOperands MO(*MI); MO.isValid(); ++MO) {
    if (!MO->isReg())
      continue;
    Register Reg = MO->getReg();
    if (!Reg || Reg.isVirtual() || MRI.isReserved(Reg)) {
      continue;
    }
    // Skip non-Defs, including undef uses and internal reads.
    if (MO->isUse())
      continue;
    PhysRegInfo RI = AnalyzePhysRegInBundle(*FoldMI, Reg, &TRI);
    if (RI.FullyDefined)
      continue;
    // FoldMI does not define this physreg. Remove the LI segment.
    assert(MO->isDead() && "Cannot fold physreg def");
    SlotIndex Idx = LIS.getInstructionIndex(*MI).getRegSlot();
    LIS.removePhysRegDefAt(Reg.asMCReg(), Idx);
  }
 
  int FI;
  if (TII.isStoreToStackSlot(*MI, FI) &&
      HSpiller.rmFromMergeableSpills(*MI, FI))
    --NumSpills;
  SlotIndex FoldIdx = LIS.ReplaceMachineInstrInMaps(*MI, *FoldMI);
  if (CopyMI) {
    SlotIndex CopyIdx = LIS.InsertMachineInstrInMaps(*CopyMI).getRegSlot();
    if (!MRI.isSSA()) {
      Register CopyDstReg = CopyMI->getOperand(0).getReg();
      LiveInterval &LI = LIS.getInterval(CopyDstReg);
 
      // The addSegment below extends CopyDstReg's LiveInterval with a new
      // segment for the copy. If CopyDstReg is already assigned in the
      // LiveRegMatrix, we must unassign before the modification and reassign
      // after, so the matrix stays consistent with the updated interval.
      // This can happen when the fold target creates a copy
      // to preserve a source operand, defining a vreg that was already
      // allocated to a physreg.
      bool NeedMatrixReassign =
          Matrix && CopyDstReg.isVirtual() && VRM.hasPhys(CopyDstReg);
      MCRegister PhysReg;
      if (NeedMatrixReassign) {
        PhysReg = VRM.getPhys(CopyDstReg);
        Matrix->unassign(LI);
      }
 
      VNInfo *VNI = LI.getNextValue(CopyIdx, LIS.getVNInfoAllocator());
      LI.addSegment(LiveRange::Segment(CopyIdx, FoldIdx.getRegSlot(), VNI));
 
      if (NeedMatrixReassign)
        Matrix->assign(LI, PhysReg);
 
      Register OrigReg = VRM.getOriginal(CopyDstReg);
      if (OrigReg != CopyDstReg) {
        // Extend the original LI to cover the same range so that the
        // sub-interval invariant holds: the original must be live wherever
        // any of its children are live.  Without this, reMaterializeFor()
        // can query OrigLI at an early-clobber slot that falls inside
        // [CopyIdx, FoldIdx) and get a null VNI, triggering an assertion.
        assert(LIS.hasInterval(OrigReg) && "OrigReg should have live interval");
        LiveInterval &OrigLI = LIS.getInterval(OrigReg);
        if (VNInfo *OrigVNI = OrigLI.getVNInfoAt(FoldIdx.getRegSlot()))
          OrigLI.addSegment(
              LiveRange::Segment(CopyIdx, FoldIdx.getRegSlot(), OrigVNI));
      }
    }
  }
  // Update the call info.
  if (MI->isCandidateForAdditionalCallInfo())
    MI->getMF()->moveAdditionalCallInfo(MI, FoldMI);
 
  // If we've folded a store into an instruction labelled with debug-info,
  // record a substitution from the old operand to the memory operand. Handle
  // the simple common case where operand 0 is the one being folded, plus when
  // the destination operand is also a tied def. More values could be
  // substituted / preserved with more analysis.
  if (MI->peekDebugInstrNum() && Ops[0].second == 0) {
    // Helper lambda.
    auto MakeSubstitution = [this,FoldMI,MI,&Ops]() {
      // Substitute old operand zero to the new instructions memory operand.
      unsigned OldOperandNum = Ops[0].second;
      unsigned NewNum = FoldMI->getDebugInstrNum();
      unsigned OldNum = MI->getDebugInstrNum();
      MF.makeDebugValueSubstitution({OldNum, OldOperandNum},
                         {NewNum, MachineFunction::DebugOperandMemNumber});
    };
 
    const MachineOperand &Op0 = MI->getOperand(Ops[0].second);
    if (Ops.size() == 1 && Op0.isDef()) {
      MakeSubstitution();
    } else if (Ops.size() == 2 && Op0.isDef() && MI->getOperand(1).isTied() &&
               Op0.getReg() == MI->getOperand(1).getReg()) {
      MakeSubstitution();
    }
  } else if (MI->peekDebugInstrNum()) {
    // This is a debug-labelled instruction, but the operand being folded isn't
    // at operand zero. Most likely this means it's a load being folded in.
    // Substitute any register defs from operand zero up to the one being
    // folded -- past that point, we don't know what the new operand indexes
    // will be.
    MF.substituteDebugValuesForInst(*MI, *FoldMI, Ops[0].second);
  }
 
  MI->eraseFromParent();
 
  // Insert any new instructions other than FoldMI into the LIS maps.
  assert(!MIS.empty() && "Unexpected empty span of instructions!");
  for (MachineInstr &MI : MIS)
    if (&MI != FoldMI && &MI != CopyMI)
      LIS.InsertMachineInstrInMaps(MI);
 
  if (CopyMI) {
    Register R = CopyMI->getOperand(1).getReg();
    if (R.isVirtual()) {
      LiveInterval &LI = LIS.getInterval(R);
      LIS.shrinkToUses(&LI);
    } else {
      assert(MRI.isReserved(R) && "Unexpected PhysReg in source operand!");
    }
  }
 
  // TII.foldMemoryOperand may have left some implicit operands on the
  // instruction.  Strip them.
  if (ImpReg)
    for (unsigned i = FoldMI->getNumOperands(); i; --i) {
      MachineOperand &MO = FoldMI->getOperand(i - 1);
      if (!MO.isReg() || !MO.isImplicit())
        break;
      if (MO.getReg() == ImpReg)
        FoldMI->removeOperand(i - 1);
    }
 
  LLVM_DEBUG(dumpMachineInstrRangeWithSlotIndex(MIS.begin(), MIS.end(), LIS,
                                                "folded"));
 
  if (!WasCopy)
    ++NumFolded;
  else if (Ops.front().second == 0) {
    ++NumSpills;
    // If there is only 1 store instruction is required for spill, add it
    // to mergeable list. In X86 AMX, 2 instructions are required to store.
    // We disable the merge for this case.
    if (std::distance(MIS.begin(), MIS.end()) <= 1)
      HSpiller.addToMergeableSpills(*FoldMI, StackSlot, Original);
  } else
    ++NumReloads;
  return true;
}
 
void InlineSpiller::insertReload(Register NewVReg,
                                 SlotIndex Idx,
                                 MachineBasicBlock::iterator MI) {
  MachineBasicBlock &MBB = *MI->getParent();
 
  MachineInstrSpan MIS(MI, &MBB);
  TII.loadRegFromStackSlot(MBB, MI, NewVReg, StackSlot,
                           MRI.getRegClass(NewVReg), Register());
 
  LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MI);
 
  LLVM_DEBUG(dumpMachineInstrRangeWithSlotIndex(MIS.begin(), MI, LIS, "reload",
                                                NewVReg));
  ++NumReloads;
}
 
/// Check if \p Def fully defines a VReg with an undefined value.
/// If that's the case, that means the value of VReg is actually
/// not relevant.
static bool isRealSpill(const MachineInstr &Def) {
  if (!Def.isImplicitDef())
    return true;
 
  // We can say that the VReg defined by Def is undef, only if it is
  // fully defined by Def. Otherwise, some of the lanes may not be
  // undef and the value of the VReg matters.
  return Def.getOperand(0).getSubReg();
}
 
/// insertSpill - Insert a spill of NewVReg after MI.
void InlineSpiller::insertSpill(Register NewVReg,
                                MachineBasicBlock::iterator MI) {
  // Spill are not terminators, so inserting spills after terminators will
  // violate invariants in MachineVerifier.
  assert(!MI->isTerminator() && "Inserting a spill after a terminator");
  MachineBasicBlock &MBB = *MI->getParent();
 
  MachineInstrSpan MIS(MI, &MBB);
  MachineBasicBlock::iterator SpillBefore = std::next(MI);
  bool IsRealSpill = isRealSpill(*MI);
 
  if (IsRealSpill)
    TII.storeRegToStackSlot(MBB, SpillBefore, NewVReg, false, StackSlot,
                            MRI.getRegClass(NewVReg), Register());
  else
    // Don't spill undef value.
    // Anything works for undef, in particular keeping the memory
    // uninitialized is a viable option and it saves code size and
    // run time.
    BuildMI(MBB, SpillBefore, MI->getDebugLoc(), TII.get(TargetOpcode::KILL))
        .addReg(NewVReg);
 
  MachineBasicBlock::iterator Spill = std::next(MI);
  LIS.InsertMachineInstrRangeInMaps(Spill, MIS.end());
  for (const MachineInstr &MI : make_range(Spill, MIS.end()))
    getVDefInterval(MI, LIS);
 
  LLVM_DEBUG(
      dumpMachineInstrRangeWithSlotIndex(Spill, MIS.end(), LIS, "spill"));
  ++NumSpills;
  // If there is only 1 store instruction is required for spill, add it
  // to mergeable list. In X86 AMX, 2 instructions are required to store.
  // We disable the merge for this case.
  if (IsRealSpill && std::distance(Spill, MIS.end()) <= 1)
    HSpiller.addToMergeableSpills(*Spill, StackSlot, Original);
}
 
/// spillAroundUses - insert spill code around each use of Reg.
void InlineSpiller::spillAroundUses(Register Reg) {
  LLVM_DEBUG(dbgs() << "spillAroundUses " << printReg(Reg) << '\n');
  LiveInterval &OldLI = LIS.getInterval(Reg);
 
  // Iterate over instructions using Reg.
  for (MachineInstr &MI : llvm::make_early_inc_range(MRI.reg_bundles(Reg))) {
    // Debug values are not allowed to affect codegen.
    if (MI.isDebugValue()) {
      // Modify DBG_VALUE now that the value is in a spill slot.
      MachineBasicBlock *MBB = MI.getParent();
      LLVM_DEBUG(dbgs() << "Modifying debug info due to spill:\t" << MI);
      buildDbgValueForSpill(*MBB, &MI, MI, StackSlot, Reg);
      MBB->erase(MI);
      continue;
    }
 
    assert(!MI.isDebugInstr() && "Did not expect to find a use in debug "
           "instruction that isn't a DBG_VALUE");
 
    // Ignore copies to/from snippets. We'll delete them.
    if (SnippetCopies.count(&MI))
      continue;
 
    // Stack slot accesses may coalesce away.
    if (coalesceStackAccess(&MI, Reg))
      continue;
 
    // Analyze instruction.
    SmallVector<std::pair<MachineInstr*, unsigned>, 8> Ops;
    VirtRegInfo RI = AnalyzeVirtRegInBundle(MI, Reg, &Ops);
 
    // Find the slot index where this instruction reads and writes OldLI.
    // This is usually the def slot, except for tied early clobbers.
    SlotIndex Idx = LIS.getInstructionIndex(MI).getRegSlot();
    if (VNInfo *VNI = OldLI.getVNInfoAt(Idx.getRegSlot(true)))
      if (SlotIndex::isSameInstr(Idx, VNI->def))
        Idx = VNI->def;
 
    // Check for a sibling copy.
    Register SibReg = isCopyOfBundle(MI, Reg, TII);
    if (SibReg && isSibling(SibReg)) {
      // This may actually be a copy between snippets.
      if (isRegToSpill(SibReg)) {
        LLVM_DEBUG(dbgs() << "Found new snippet copy: " << MI);
        SnippetCopies.insert(&MI);
        continue;
      }
      if (RI.Writes) {
        if (hoistSpillInsideBB(OldLI, MI)) {
          // This COPY is now dead, the value is already in the stack slot.
          MI.getOperand(0).setIsDead();
          DeadDefs.push_back(&MI);
          continue;
        }
      } else {
        // This is a reload for a sib-reg copy. Drop spills downstream.
        LiveInterval &SibLI = LIS.getInterval(SibReg);
        eliminateRedundantSpills(SibLI, SibLI.getVNInfoAt(Idx));
        // The COPY will fold to a reload below.
      }
    }
 
    // Attempt to fold memory ops.
    if (foldMemoryOperand(Ops))
      continue;
 
    // Create a new virtual register for spill/fill.
    // FIXME: Infer regclass from instruction alone.
    Register NewVReg = Edit->createFrom(Reg);
 
    if (RI.Reads)
      insertReload(NewVReg, Idx, &MI);
 
    // Rewrite instruction operands.
    bool hasLiveDef = false;
    for (const auto &OpPair : Ops) {
      MachineOperand &MO = OpPair.first->getOperand(OpPair.second);
      MO.setReg(NewVReg);
      if (MO.isDef() && !MO.isDead())
        hasLiveDef = true;
    }
    LLVM_DEBUG(dbgs() << "\trewrite: " << Idx << '\t' << MI << '\n');
 
    // FIXME: Use a second vreg if instruction has no tied ops.
    if (RI.Writes)
      if (hasLiveDef)
        insertSpill(NewVReg, &MI);
  }
}
 
/// spillAll - Spill all registers remaining after rematerialization.
void InlineSpiller::spillAll() {
  // Update LiveStacks now that we are committed to spilling.
  if (StackSlot == VirtRegMap::NO_STACK_SLOT) {
    StackSlot = VRM.assignVirt2StackSlot(Original);
    StackInt = &LSS.getOrCreateInterval(StackSlot, MRI.getRegClass(Original));
    StackInt->getNextValue(SlotIndex(), LSS.getVNInfoAllocator());
  } else
    StackInt = &LSS.getInterval(StackSlot);
 
  if (Original != Edit->getReg())
    VRM.assignVirt2StackSlot(Edit->getReg(), StackSlot);
 
  assert(StackInt->getNumValNums() == 1 && "Bad stack interval values");
  for (Register Reg : RegsToSpill)
    StackInt->MergeSegmentsInAsValue(LIS.getInterval(Reg),
                                     StackInt->getValNumInfo(0));
  LLVM_DEBUG(dbgs() << "Merged spilled regs: " << *StackInt << '\n');
 
  // Spill around uses of all RegsToSpill.
  for (Register Reg : RegsToSpill) {
    spillAroundUses(Reg);
    // Assign all of the spilled registers to the slot so that
    // LiveDebugVariables knows about these locations later on.
    if (VRM.getStackSlot(Reg) == VirtRegMap::NO_STACK_SLOT)
      VRM.assignVirt2StackSlot(Reg, StackSlot);
  }
 
  // Hoisted spills may cause dead code.
  if (!DeadDefs.empty()) {
    LLVM_DEBUG(dbgs() << "Eliminating " << DeadDefs.size() << " dead defs\n");
    Edit->eliminateDeadDefs(DeadDefs, RegsToSpill);
  }
 
  // Finally delete the SnippetCopies.
  for (Register Reg : RegsToSpill) {
    for (MachineInstr &MI :
         llvm::make_early_inc_range(MRI.reg_instructions(Reg))) {
      assert(SnippetCopies.count(&MI) && "Remaining use wasn't a snippet copy");
      // FIXME: Do this with a LiveRangeEdit callback.
      LIS.getSlotIndexes()->removeSingleMachineInstrFromMaps(MI);
      MI.eraseFromBundle();
    }
  }
 
  // Delete all spilled registers.
  for (Register Reg : RegsToSpill)
    Edit->eraseVirtReg(Reg);
}
 
void InlineSpiller::spill(LiveRangeEdit &edit, AllocationOrder *order) {
  ++NumSpilledRanges;
  Edit = &edit;
  Order = order;
  assert(!edit.getReg().isStack() && "Trying to spill a stack slot.");
  // Share a stack slot among all descendants of Original.
  Original = VRM.getOriginal(edit.getReg());
  StackSlot = VRM.getStackSlot(Original);
  StackInt = nullptr;
 
  LLVM_DEBUG(dbgs() << "Inline spilling "
                    << TRI.getRegClassName(MRI.getRegClass(edit.getReg()))
                    << ':' << edit.getParent() << "\nFrom original "
                    << printReg(Original) << '\n');
  assert(edit.getParent().isSpillable() &&
         "Attempting to spill already spilled value.");
  assert(DeadDefs.empty() && "Previous spill didn't remove dead defs");
 
  collectRegsToSpill();
  reMaterializeAll();
 
  // Remat may handle everything.
  if (!RegsToSpill.empty())
    spillAll();
 
  Edit->calculateRegClassAndHint(MF, VRAI);
}
 
/// Optimizations after all the reg selections and spills are done.
void InlineSpiller::postOptimization() { HSpiller.hoistAllSpills(); }
 
/// When a spill is inserted, add the spill to MergeableSpills map.
void HoistSpillHelper::addToMergeableSpills(MachineInstr &Spill, int StackSlot,
                                            Register Original) {
  BumpPtrAllocator &Allocator = LIS.getVNInfoAllocator();
  LiveInterval &OrigLI = LIS.getInterval(Original);
  // save a copy of LiveInterval in StackSlotToOrigLI because the original
  // LiveInterval may be cleared after all its references are spilled.
 
  auto [Place, Inserted] = StackSlotToOrigLI.try_emplace(StackSlot);
  if (Inserted) {
    auto LI = std::make_unique<LiveInterval>(OrigLI.reg(), OrigLI.weight());
    LI->assign(OrigLI, Allocator);
    Place->second = std::move(LI);
  }
 
  SlotIndex Idx = LIS.getInstructionIndex(Spill);
  VNInfo *OrigVNI = Place->second->getVNInfoAt(Idx.getRegSlot());
  std::pair<int, VNInfo *> MIdx = std::make_pair(StackSlot, OrigVNI);
  MergeableSpills[MIdx].insert(&Spill);
}
 
/// When a spill is removed, remove the spill from MergeableSpills map.
/// Return true if the spill is removed successfully.
bool HoistSpillHelper::rmFromMergeableSpills(MachineInstr &Spill,
                                             int StackSlot) {
  auto It = StackSlotToOrigLI.find(StackSlot);
  if (It == StackSlotToOrigLI.end())
    return false;
  SlotIndex Idx = LIS.getInstructionIndex(Spill);
  VNInfo *OrigVNI = It->second->getVNInfoAt(Idx.getRegSlot());
  std::pair<int, VNInfo *> MIdx = std::make_pair(StackSlot, OrigVNI);
  return MergeableSpills[MIdx].erase(&Spill);
}
 
/// Check BB to see if it is a possible target BB to place a hoisted spill,
/// i.e., there should be a living sibling of OrigReg at the insert point.
bool HoistSpillHelper::isSpillCandBB(LiveInterval &OrigLI, VNInfo &OrigVNI,
                                     MachineBasicBlock &BB, Register &LiveReg) {
  SlotIndex Idx = IPA.getLastInsertPoint(OrigLI, BB);
  // The original def could be after the last insert point in the root block,
  // we can't hoist to here.
  if (Idx < OrigVNI.def) {
    // TODO: We could be better here. If LI is not alive in landing pad
    // we could hoist spill after LIP.
    LLVM_DEBUG(dbgs() << "can't spill in root block - def after LIP\n");
    return false;
  }
  Register OrigReg = OrigLI.reg();
  SmallSetVector<Register, 16> &Siblings = Virt2SiblingsMap[OrigReg];
  assert(OrigLI.getVNInfoAt(Idx) == &OrigVNI && "Unexpected VNI");
 
  for (const Register &SibReg : Siblings) {
    LiveInterval &LI = LIS.getInterval(SibReg);
    if (!LI.getVNInfoAt(Idx))
      continue;
    // All of the sub-ranges should be alive at the prospective slot index.
    // Otherwise, we might risk storing unrelated / compromised values from some
    // sub-registers to the spill slot.
    if (all_of(LI.subranges(), [&](const LiveInterval::SubRange &SR) {
          return SR.getVNInfoAt(Idx) != nullptr;
        })) {
      LiveReg = SibReg;
      return true;
    }
  }
  return false;
}
 
/// Remove redundant spills in the same BB. Save those redundant spills in
/// SpillsToRm, and save the spill to keep and its BB in SpillBBToSpill map.
void HoistSpillHelper::rmRedundantSpills(
    SmallPtrSet<MachineInstr *, 16> &Spills,
    SmallVectorImpl<MachineInstr *> &SpillsToRm,
    DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill) {
  // For each spill saw, check SpillBBToSpill[] and see if its BB already has
  // another spill inside. If a BB contains more than one spill, only keep the
  // earlier spill with smaller SlotIndex.
  for (auto *const CurrentSpill : Spills) {
    MachineBasicBlock *Block = CurrentSpill->getParent();
    MachineDomTreeNode *Node = MDT.getNode(Block);
    MachineInstr *PrevSpill = SpillBBToSpill[Node];
    if (PrevSpill) {
      SlotIndex PIdx = LIS.getInstructionIndex(*PrevSpill);
      SlotIndex CIdx = LIS.getInstructionIndex(*CurrentSpill);
      MachineInstr *SpillToRm = (CIdx > PIdx) ? CurrentSpill : PrevSpill;
      MachineInstr *SpillToKeep = (CIdx > PIdx) ? PrevSpill : CurrentSpill;
      SpillsToRm.push_back(SpillToRm);
      SpillBBToSpill[MDT.getNode(Block)] = SpillToKeep;
    } else {
      SpillBBToSpill[MDT.getNode(Block)] = CurrentSpill;
    }
  }
  for (auto *const SpillToRm : SpillsToRm)
    Spills.erase(SpillToRm);
}
 
/// Starting from \p Root find a top-down traversal order of the dominator
/// tree to visit all basic blocks containing the elements of \p Spills.
/// Redundant spills will be found and put into \p SpillsToRm at the same
/// time. \p SpillBBToSpill will be populated as part of the process and
/// maps a basic block to the first store occurring in the basic block.
/// \post SpillsToRm.union(Spills\@post) == Spills\@pre
void HoistSpillHelper::getVisitOrders(
    MachineBasicBlock *Root, SmallPtrSet<MachineInstr *, 16> &Spills,
    SmallVectorImpl<MachineDomTreeNode *> &Orders,
    SmallVectorImpl<MachineInstr *> &SpillsToRm,
    DenseMap<MachineDomTreeNode *, Register> &SpillsToKeep,
    DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill) {
  // The set contains all the possible BB nodes to which we may hoist
  // original spills.
  SmallPtrSet<MachineDomTreeNode *, 8> WorkSet;
  // Save the BB nodes on the path from the first BB node containing
  // non-redundant spill to the Root node.
  SmallPtrSet<MachineDomTreeNode *, 8> NodesOnPath;
  // All the spills to be hoisted must originate from a single def instruction
  // to the OrigReg. It means the def instruction should dominate all the spills
  // to be hoisted. We choose the BB where the def instruction is located as
  // the Root.
  MachineDomTreeNode *RootIDomNode = MDT[Root]->getIDom();
  // For every node on the dominator tree with spill, walk up on the dominator
  // tree towards the Root node until it is reached. If there is other node
  // containing spill in the middle of the path, the previous spill saw will
  // be redundant and the node containing it will be removed. All the nodes on
  // the path starting from the first node with non-redundant spill to the Root
  // node will be added to the WorkSet, which will contain all the possible
  // locations where spills may be hoisted to after the loop below is done.
  for (auto *const Spill : Spills) {
    MachineBasicBlock *Block = Spill->getParent();
    MachineDomTreeNode *Node = MDT[Block];
    MachineInstr *SpillToRm = nullptr;
    while (Node != RootIDomNode) {
      // If Node dominates Block, and it already contains a spill, the spill in
      // Block will be redundant.
      if (Node != MDT[Block] && SpillBBToSpill[Node]) {
        SpillToRm = SpillBBToSpill[MDT[Block]];
        break;
        /// If we see the Node already in WorkSet, the path from the Node to
        /// the Root node must already be traversed by another spill.
        /// Then no need to repeat.
      } else if (WorkSet.count(Node)) {
        break;
      } else {
        NodesOnPath.insert(Node);
      }
      Node = Node->getIDom();
    }
    if (SpillToRm) {
      SpillsToRm.push_back(SpillToRm);
    } else {
      // Add a BB containing the original spills to SpillsToKeep -- i.e.,
      // set the initial status before hoisting start. The value of BBs
      // containing original spills is set to 0, in order to descriminate
      // with BBs containing hoisted spills which will be inserted to
      // SpillsToKeep later during hoisting.
      SpillsToKeep[MDT[Block]] = Register();
      WorkSet.insert_range(NodesOnPath);
    }
    NodesOnPath.clear();
  }
 
  // Sort the nodes in WorkSet in top-down order and save the nodes
  // in Orders. Orders will be used for hoisting in runHoistSpills.
  unsigned idx = 0;
  Orders.push_back(MDT.getNode(Root));
  do {
    MachineDomTreeNode *Node = Orders[idx++];
    for (MachineDomTreeNode *Child : Node->children()) {
      if (WorkSet.count(Child))
        Orders.push_back(Child);
    }
  } while (idx != Orders.size());
  assert(Orders.size() == WorkSet.size() &&
         "Orders have different size with WorkSet");
 
#ifndef NDEBUG
  LLVM_DEBUG(dbgs() << "Orders size is " << Orders.size() << "\n");
  SmallVector<MachineDomTreeNode *, 32>::reverse_iterator RIt = Orders.rbegin();
  for (; RIt != Orders.rend(); RIt++)
    LLVM_DEBUG(dbgs() << "BB" << (*RIt)->getBlock()->getNumber() << ",");
  LLVM_DEBUG(dbgs() << "\n");
#endif
}
 
/// Try to hoist spills according to BB hotness. The spills to removed will
/// be saved in \p SpillsToRm. The spills to be inserted will be saved in
/// \p SpillsToIns.
void HoistSpillHelper::runHoistSpills(
    LiveInterval &OrigLI, VNInfo &OrigVNI,
    SmallPtrSet<MachineInstr *, 16> &Spills,
    SmallVectorImpl<MachineInstr *> &SpillsToRm,
    DenseMap<MachineBasicBlock *, Register> &SpillsToIns) {
  // Visit order of dominator tree nodes.
  SmallVector<MachineDomTreeNode *, 32> Orders;
  // SpillsToKeep contains all the nodes where spills are to be inserted
  // during hoisting. If the spill to be inserted is an original spill
  // (not a hoisted one), the value of the map entry is 0. If the spill
  // is a hoisted spill, the value of the map entry is the VReg to be used
  // as the source of the spill.
  DenseMap<MachineDomTreeNode *, Register> SpillsToKeep;
  // Map from BB to the first spill inside of it.
  DenseMap<MachineDomTreeNode *, MachineInstr *> SpillBBToSpill;
 
  rmRedundantSpills(Spills, SpillsToRm, SpillBBToSpill);
 
  MachineBasicBlock *Root = LIS.getMBBFromIndex(OrigVNI.def);
  getVisitOrders(Root, Spills, Orders, SpillsToRm, SpillsToKeep,
                 SpillBBToSpill);
 
  // SpillsInSubTreeMap keeps the map from a dom tree node to a pair of
  // nodes set and the cost of all the spills inside those nodes.
  // The nodes set are the locations where spills are to be inserted
  // in the subtree of current node.
  using NodesCostPair =
      std::pair<SmallPtrSet<MachineDomTreeNode *, 16>, BlockFrequency>;
  DenseMap<MachineDomTreeNode *, NodesCostPair> SpillsInSubTreeMap;
 
  // Iterate Orders set in reverse order, which will be a bottom-up order
  // in the dominator tree. Once we visit a dom tree node, we know its
  // children have already been visited and the spill locations in the
  // subtrees of all the children have been determined.
  SmallVector<MachineDomTreeNode *, 32>::reverse_iterator RIt = Orders.rbegin();
  for (; RIt != Orders.rend(); RIt++) {
    MachineBasicBlock *Block = (*RIt)->getBlock();
 
    // If Block contains an original spill, simply continue.
    if (auto It = SpillsToKeep.find(*RIt);
        It != SpillsToKeep.end() && !It->second) {
      auto &SIt = SpillsInSubTreeMap[*RIt];
      SIt.first.insert(*RIt);
      // Sit.second contains the cost of spill.
      SIt.second = MBFI.getBlockFreq(Block);
      continue;
    }
 
    // Collect spills in subtree of current node (*RIt) to
    // SpillsInSubTreeMap[*RIt].first.
    for (MachineDomTreeNode *Child : (*RIt)->children()) {
      if (!SpillsInSubTreeMap.contains(Child))
        continue;
      // The stmt:
      // "auto &[SpillsInSubTree, SubTreeCost] = SpillsInSubTreeMap[*RIt]"
      // below should be placed before getting the begin and end iterators of
      // SpillsInSubTreeMap[Child].first, or else the iterators may be
      // invalidated when SpillsInSubTreeMap[*RIt] is seen the first time
      // and the map grows and then the original buckets in the map are moved.
      auto &[SpillsInSubTree, SubTreeCost] = SpillsInSubTreeMap[*RIt];
      auto ChildIt = SpillsInSubTreeMap.find(Child);
      SubTreeCost += ChildIt->second.second;
      auto BI = ChildIt->second.first.begin();
      auto EI = ChildIt->second.first.end();
      SpillsInSubTree.insert(BI, EI);
      SpillsInSubTreeMap.erase(ChildIt);
    }
 
    auto &[SpillsInSubTree, SubTreeCost] = SpillsInSubTreeMap[*RIt];
    // No spills in subtree, simply continue.
    if (SpillsInSubTree.empty())
      continue;
 
    // Check whether Block is a possible candidate to insert spill.
    Register LiveReg;
    if (!isSpillCandBB(OrigLI, OrigVNI, *Block, LiveReg))
      continue;
 
    // If there are multiple spills that could be merged, bias a little
    // to hoist the spill.
    BranchProbability MarginProb = (SpillsInSubTree.size() > 1)
                                       ? BranchProbability(9, 10)
                                       : BranchProbability(1, 1);
    if (SubTreeCost > MBFI.getBlockFreq(Block) * MarginProb) {
      // Hoist: Move spills to current Block.
      for (auto *const SpillBB : SpillsInSubTree) {
        // When SpillBB is a BB contains original spill, insert the spill
        // to SpillsToRm.
        if (auto It = SpillsToKeep.find(SpillBB);
            It != SpillsToKeep.end() && !It->second) {
          MachineInstr *SpillToRm = SpillBBToSpill[SpillBB];
          SpillsToRm.push_back(SpillToRm);
        }
        // SpillBB will not contain spill anymore, remove it from SpillsToKeep.
        SpillsToKeep.erase(SpillBB);
      }
      // Current Block is the BB containing the new hoisted spill. Add it to
      // SpillsToKeep. LiveReg is the source of the new spill.
      SpillsToKeep[*RIt] = LiveReg;
      LLVM_DEBUG({
        dbgs() << "spills in BB: ";
        for (const auto Rspill : SpillsInSubTree)
          dbgs() << Rspill->getBlock()->getNumber() << " ";
        dbgs() << "were promoted to BB" << (*RIt)->getBlock()->getNumber()
               << "\n";
      });
      SpillsInSubTree.clear();
      SpillsInSubTree.insert(*RIt);
      SubTreeCost = MBFI.getBlockFreq(Block);
    }
  }
  // For spills in SpillsToKeep with LiveReg set (i.e., not original spill),
  // save them to SpillsToIns.
  for (const auto &Ent : SpillsToKeep) {
    if (Ent.second)
      SpillsToIns[Ent.first->getBlock()] = Ent.second;
  }
}
 
/// For spills with equal values, remove redundant spills and hoist those left
/// to less hot spots.
///
/// Spills with equal values will be collected into the same set in
/// MergeableSpills when spill is inserted. These equal spills are originated
/// from the same defining instruction and are dominated by the instruction.
/// Before hoisting all the equal spills, redundant spills inside in the same
/// BB are first marked to be deleted. Then starting from the spills left, walk
/// up on the dominator tree towards the Root node where the define instruction
/// is located, mark the dominated spills to be deleted along the way and
/// collect the BB nodes on the path from non-dominated spills to the define
/// instruction into a WorkSet. The nodes in WorkSet are the candidate places
/// where we are considering to hoist the spills. We iterate the WorkSet in
/// bottom-up order, and for each node, we will decide whether to hoist spills
/// inside its subtree to that node. In this way, we can get benefit locally
/// even if hoisting all the equal spills to one cold place is impossible.
void HoistSpillHelper::hoistAllSpills() {
  SmallVector<Register, 4> NewVRegs;
  LiveRangeEdit Edit(nullptr, NewVRegs, MF, LIS, &VRM, this);
 
  for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) {
    Register Reg = Register::index2VirtReg(i);
    Register Original = VRM.getPreSplitReg(Reg);
    if (!MRI.def_empty(Reg) && Original.isValid())
      Virt2SiblingsMap[Original].insert(Reg);
  }
 
  // Each entry in MergeableSpills contains a spill set with equal values.
  for (auto &Ent : MergeableSpills) {
    int Slot = Ent.first.first;
    LiveInterval &OrigLI = *StackSlotToOrigLI[Slot];
    VNInfo *OrigVNI = Ent.first.second;
    SmallPtrSet<MachineInstr *, 16> &EqValSpills = Ent.second;
    if (Ent.second.empty())
      continue;
 
    LLVM_DEBUG({
      dbgs() << "\nFor Slot" << Slot << " and VN" << OrigVNI->id << ":\n"
             << "Equal spills in BB: ";
      for (const auto spill : EqValSpills)
        dbgs() << spill->getParent()->getNumber() << " ";
      dbgs() << "\n";
    });
 
    // SpillsToRm is the spill set to be removed from EqValSpills.
    SmallVector<MachineInstr *, 16> SpillsToRm;
    // SpillsToIns is the spill set to be newly inserted after hoisting.
    DenseMap<MachineBasicBlock *, Register> SpillsToIns;
 
    runHoistSpills(OrigLI, *OrigVNI, EqValSpills, SpillsToRm, SpillsToIns);
 
    LLVM_DEBUG({
      dbgs() << "Finally inserted spills in BB: ";
      for (const auto &Ispill : SpillsToIns)
        dbgs() << Ispill.first->getNumber() << " ";
      dbgs() << "\nFinally removed spills in BB: ";
      for (const auto Rspill : SpillsToRm)
        dbgs() << Rspill->getParent()->getNumber() << " ";
      dbgs() << "\n";
    });
 
    // Stack live range update.
    LiveInterval &StackIntvl = LSS.getInterval(Slot);
    if (!SpillsToIns.empty() || !SpillsToRm.empty())
      StackIntvl.MergeValueInAsValue(OrigLI, OrigVNI,
                                     StackIntvl.getValNumInfo(0));
 
    // Insert hoisted spills.
    for (auto const &Insert : SpillsToIns) {
      MachineBasicBlock *BB = Insert.first;
      Register LiveReg = Insert.second;
      MachineBasicBlock::iterator MII = IPA.getLastInsertPointIter(OrigLI, *BB);
      MachineInstrSpan MIS(MII, BB);
      TII.storeRegToStackSlot(*BB, MII, LiveReg, false, Slot,
                              MRI.getRegClass(LiveReg), Register());
      LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MII);
      for (const MachineInstr &MI : make_range(MIS.begin(), MII))
        getVDefInterval(MI, LIS);
      ++NumSpills;
    }
 
    // Remove redundant spills or change them to dead instructions.
    NumSpills -= SpillsToRm.size();
    for (auto *const RMEnt : SpillsToRm) {
      RMEnt->setDesc(TII.get(TargetOpcode::KILL));
      for (unsigned i = RMEnt->getNumOperands(); i; --i) {
        MachineOperand &MO = RMEnt->getOperand(i - 1);
        if (MO.isReg() && MO.isImplicit() && MO.isDef() && !MO.isDead())
          RMEnt->removeOperand(i - 1);
      }
    }
    Edit.eliminateDeadDefs(SpillsToRm, {});
  }
 
  // Flush vregs that were unassigned from the matrix during shrinking but
  // were not split (so LRE_DidCloneVirtReg never re-assigned them).
  for (auto &[VReg, PhysReg] : PendingReassignments) {
    assert(Matrix && LIS.hasInterval(VReg) &&
           "Pending reassignment without matrix or live interval");
    Matrix->assign(LIS.getInterval(VReg), PhysReg);
  }
  PendingReassignments.clear();
}
 
/// Called when a virtual register's live interval is about to be shrunk.
/// Unassign from the matrix so the shrunk interval can be re-assigned by a
/// later LRE_DidCloneVirtReg or by hoistAllSpills' flush, and stash the
/// physreg in PendingReassignments since the unassign clears VRM.
void HoistSpillHelper::LRE_WillShrinkVirtReg(Register VirtReg) {
  if (!Matrix || !VRM.hasPhys(VirtReg) || !LIS.hasInterval(VirtReg))
    return;
 
  MCRegister PhysReg = VRM.getPhys(VirtReg);
  LiveInterval &LI = LIS.getInterval(VirtReg);
  Matrix->unassign(LI, /*ClearAllReferencingSegments=*/true);
  PendingReassignments[VirtReg] = PhysReg;
}
 
/// Called before a virtual register is erased from LiveIntervals.
/// Forcibly remove the register from LiveRegMatrix before it's deleted,
/// preventing dangling pointers.
bool HoistSpillHelper::LRE_CanEraseVirtReg(Register VirtReg) {
  PendingReassignments.erase(VirtReg);
  if (Matrix && VRM.hasPhys(VirtReg)) {
    const LiveInterval &LI = LIS.getInterval(VirtReg);
    Matrix->unassign(LI, /*ClearAllReferencingSegments=*/true);
  }
  return true; // Allow deletion to proceed
}
 
/// For VirtReg clone, the \p New register should have the same physreg or
/// stackslot as the \p old register.
void HoistSpillHelper::LRE_DidCloneVirtReg(Register New, Register Old) {
  // New is freshly created by LiveRangeEdit::eliminateDeadDefs and its interval
  // is guaranteed to exist on every path below.
  assert(LIS.hasInterval(New) && "Cloned vreg without live interval");
 
  auto PendingIt = PendingReassignments.find(Old);
  if (PendingIt != PendingReassignments.end()) {
    // Old was already unassigned in LRE_WillShrinkVirtReg, which only
    // enrolls vregs when Matrix is non-null and the interval exists.
    assert(Matrix && LIS.hasInterval(Old) &&
           "Pending reassignment without matrix or live interval");
    MCRegister PhysReg = PendingIt->second;
    PendingReassignments.erase(PendingIt);
 
    // Reassign both Old (with its shrunk interval) and New to the matrix.
    Matrix->assign(LIS.getInterval(Old), PhysReg);
    Matrix->assign(LIS.getInterval(New), PhysReg);
  } else if (VRM.hasPhys(Old)) {
    MCRegister PhysReg = VRM.getPhys(Old);
    if (Matrix) {
      if (LIS.hasInterval(Old)) {
        const LiveInterval &LI = LIS.getInterval(Old);
        // Drop stale pre-clone segments before reassigning Old's current LI.
        Matrix->unassign(LI, /*ClearAllReferencingSegments=*/true);
        Matrix->assign(LI, PhysReg);
      }
      Matrix->assign(LIS.getInterval(New), PhysReg);
    } else {
      VRM.assignVirt2Phys(New, PhysReg);
    }
  } else if (VRM.getStackSlot(Old) != VirtRegMap::NO_STACK_SLOT) {
    VRM.assignVirt2StackSlot(New, VRM.getStackSlot(Old));
  } else {
    llvm_unreachable("VReg should be assigned either physreg or stackslot");
  }
  if (VRM.hasShape(Old))
    VRM.assignVirt2Shape(New, VRM.getShape(Old));
}