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📄 AggressiveAntiDepBreaker.cpp(37.23 KB)
📄 AggressiveAntiDepBreaker.h(6.8 KB)
📄 AllocationOrder.cpp(1.96 KB)
📄 AllocationOrder.h(2.96 KB)
📄 Analysis.cpp(32.62 KB)
📁 AsmPrinter
📄 AtomicExpandPass.cpp(71.86 KB)
📄 BBSectionsPrepare.cpp(18.8 KB)
📄 BasicTargetTransformInfo.cpp(1.53 KB)
📄 BranchFolding.cpp(77.92 KB)
📄 BranchFolding.h(7.36 KB)
📄 BranchRelaxation.cpp(19.45 KB)
📄 BreakFalseDeps.cpp(9.79 KB)
📄 BuiltinGCs.cpp(4.88 KB)
📄 CFGuardLongjmp.cpp(3.73 KB)
📄 CFIInstrInserter.cpp(17.53 KB)
📄 CalcSpillWeights.cpp(10.22 KB)
📄 CallingConvLower.cpp(10.4 KB)
📄 CodeGen.cpp(5.28 KB)
📄 CodeGenPrepare.cpp(295.01 KB)
📄 CommandFlags.cpp(24.89 KB)
📄 CriticalAntiDepBreaker.cpp(27.91 KB)
📄 CriticalAntiDepBreaker.h(4.22 KB)
📄 DFAPacketizer.cpp(10.91 KB)
📄 DeadMachineInstructionElim.cpp(6.52 KB)
📄 DetectDeadLanes.cpp(20.74 KB)
📄 DwarfEHPrepare.cpp(9.01 KB)
📄 EarlyIfConversion.cpp(37.51 KB)
📄 EdgeBundles.cpp(3.21 KB)
📄 ExecutionDomainFix.cpp(14.67 KB)
📄 ExpandMemCmp.cpp(33.66 KB)
📄 ExpandPostRAPseudos.cpp(7.28 KB)
📄 ExpandReductions.cpp(7.23 KB)
📄 FEntryInserter.cpp(1.81 KB)
📄 FaultMaps.cpp(4.99 KB)
📄 FinalizeISel.cpp(2.65 KB)
📄 FixupStatepointCallerSaved.cpp(11.06 KB)
📄 FuncletLayout.cpp(2.21 KB)
📄 GCMetadata.cpp(5.1 KB)
📄 GCMetadataPrinter.cpp(748 B)
📄 GCRootLowering.cpp(11.46 KB)
📄 GCStrategy.cpp(708 B)
📁 GlobalISel
📄 GlobalMerge.cpp(24.52 KB)
📄 HardwareLoops.cpp(18.44 KB)
📄 IfConversion.cpp(89.43 KB)
📄 ImplicitNullChecks.cpp(25.14 KB)
📄 IndirectBrExpandPass.cpp(7.79 KB)
📄 InlineSpiller.cpp(58.24 KB)
📄 InterferenceCache.cpp(8.83 KB)
📄 InterferenceCache.h(7.22 KB)
📄 InterleavedAccessPass.cpp(16.59 KB)
📄 InterleavedLoadCombinePass.cpp(42.35 KB)
📄 IntrinsicLowering.cpp(17.08 KB)
📄 LLVMTargetMachine.cpp(10.25 KB)
📄 LatencyPriorityQueue.cpp(5.64 KB)
📄 LazyMachineBlockFrequencyInfo.cpp(3.36 KB)
📄 LexicalScopes.cpp(12.16 KB)
📄 LiveDebugValues.cpp(78.98 KB)
📄 LiveDebugVariables.cpp(51.79 KB)
📄 LiveDebugVariables.h(2.15 KB)
📄 LiveInterval.cpp(46.67 KB)
📄 LiveIntervalCalc.cpp(7.62 KB)
📄 LiveIntervalUnion.cpp(6.36 KB)
📄 LiveIntervals.cpp(64.59 KB)
📄 LivePhysRegs.cpp(11.08 KB)
📄 LiveRangeCalc.cpp(15.72 KB)
📄 LiveRangeEdit.cpp(17.03 KB)
📄 LiveRangeShrink.cpp(8.69 KB)
📄 LiveRangeUtils.h(2.12 KB)
📄 LiveRegMatrix.cpp(7.47 KB)
📄 LiveRegUnits.cpp(4.72 KB)
📄 LiveStacks.cpp(2.95 KB)
📄 LiveVariables.cpp(30.26 KB)
📄 LocalStackSlotAllocation.cpp(17.26 KB)
📄 LoopTraversal.cpp(2.89 KB)
📄 LowLevelType.cpp(1.93 KB)
📄 LowerEmuTLS.cpp(5.66 KB)
📄 MBFIWrapper.cpp(1.57 KB)
📄 MIRCanonicalizerPass.cpp(12.46 KB)
📄 MIRNamerPass.cpp(2.16 KB)
📁 MIRParser
📄 MIRPrinter.cpp(32.67 KB)
📄 MIRPrintingPass.cpp(1.99 KB)
📄 MIRVRegNamerUtils.cpp(6.04 KB)
📄 MIRVRegNamerUtils.h(3.25 KB)
📄 MachineBasicBlock.cpp(50.47 KB)
📄 MachineBlockFrequencyInfo.cpp(10.13 KB)
📄 MachineBlockPlacement.cpp(137.61 KB)
📄 MachineBranchProbabilityInfo.cpp(3.5 KB)
📄 MachineCSE.cpp(31.82 KB)
📄 MachineCombiner.cpp(28.13 KB)
📄 MachineCopyPropagation.cpp(29.21 KB)
📄 MachineDebugify.cpp(6.47 KB)
📄 MachineDominanceFrontier.cpp(1.83 KB)
📄 MachineDominators.cpp(4.86 KB)
📄 MachineFrameInfo.cpp(9.77 KB)
📄 MachineFunction.cpp(42.97 KB)
📄 MachineFunctionPass.cpp(4.78 KB)
📄 MachineFunctionPrinterPass.cpp(2.3 KB)
📄 MachineInstr.cpp(76.39 KB)
📄 MachineInstrBundle.cpp(11.49 KB)
📄 MachineLICM.cpp(57.05 KB)
📄 MachineLoopInfo.cpp(4.98 KB)
📄 MachineLoopUtils.cpp(5.16 KB)
📄 MachineModuleInfo.cpp(9.9 KB)
📄 MachineModuleInfoImpls.cpp(1.5 KB)
📄 MachineOperand.cpp(39.6 KB)
📄 MachineOptimizationRemarkEmitter.cpp(3.29 KB)
📄 MachineOutliner.cpp(42.13 KB)
📄 MachinePipeliner.cpp(111.33 KB)
📄 MachinePostDominators.cpp(2.42 KB)
📄 MachineRegionInfo.cpp(4.75 KB)
📄 MachineRegisterInfo.cpp(22.97 KB)
📄 MachineSSAUpdater.cpp(12.99 KB)
📄 MachineScheduler.cpp(136.89 KB)
📄 MachineSink.cpp(51.94 KB)
📄 MachineSizeOpts.cpp(8.76 KB)
📄 MachineStripDebug.cpp(3.76 KB)
📄 MachineTraceMetrics.cpp(49.58 KB)
📄 MachineVerifier.cpp(107.98 KB)
📄 MacroFusion.cpp(7.55 KB)
📄 ModuloSchedule.cpp(85.09 KB)
📄 NonRelocatableStringpool.cpp(1.65 KB)
📄 OptimizePHIs.cpp(6.7 KB)
📄 PHIElimination.cpp(27.73 KB)
📄 PHIEliminationUtils.cpp(2.56 KB)
📄 PHIEliminationUtils.h(972 B)
📄 ParallelCG.cpp(3.71 KB)
📄 PatchableFunction.cpp(3.44 KB)
📄 PeepholeOptimizer.cpp(78.41 KB)
📄 PostRAHazardRecognizer.cpp(3.5 KB)
📄 PostRASchedulerList.cpp(24.31 KB)
📄 PreISelIntrinsicLowering.cpp(7.91 KB)
📄 ProcessImplicitDefs.cpp(5.4 KB)
📄 PrologEpilogInserter.cpp(50.45 KB)
📄 PseudoSourceValue.cpp(4.71 KB)
📄 RDFGraph.cpp(58.39 KB)
📄 RDFLiveness.cpp(40.7 KB)
📄 RDFRegisters.cpp(11.29 KB)
📄 ReachingDefAnalysis.cpp(21.74 KB)
📄 RegAllocBase.cpp(6.31 KB)
📄 RegAllocBase.h(4.63 KB)
📄 RegAllocBasic.cpp(11.33 KB)
📄 RegAllocFast.cpp(45.78 KB)
📄 RegAllocGreedy.cpp(123.32 KB)
📄 RegAllocPBQP.cpp(33.14 KB)
📄 RegUsageInfoCollector.cpp(7.39 KB)
📄 RegUsageInfoPropagate.cpp(5.07 KB)
📄 RegisterClassInfo.cpp(6.62 KB)
📄 RegisterCoalescer.cpp(151.71 KB)
📄 RegisterCoalescer.h(4.04 KB)
📄 RegisterPressure.cpp(48.86 KB)
📄 RegisterScavenging.cpp(27.48 KB)
📄 RegisterUsageInfo.cpp(3.18 KB)
📄 RenameIndependentSubregs.cpp(14.79 KB)
📄 ResetMachineFunctionPass.cpp(3.48 KB)
📄 SafeStack.cpp(34.12 KB)
📄 SafeStackLayout.cpp(5.3 KB)
📄 SafeStackLayout.h(2.41 KB)
📄 ScalarizeMaskedMemIntrin.cpp(31.46 KB)
📄 ScheduleDAG.cpp(21.34 KB)
📄 ScheduleDAGInstrs.cpp(54.59 KB)
📄 ScheduleDAGPrinter.cpp(3.21 KB)
📄 ScoreboardHazardRecognizer.cpp(7.96 KB)
📁 SelectionDAG
📄 ShadowStackGCLowering.cpp(14.16 KB)
📄 ShrinkWrap.cpp(23.03 KB)
📄 SjLjEHPrepare.cpp(18.93 KB)
📄 SlotIndexes.cpp(9.35 KB)
📄 SpillPlacement.cpp(12.58 KB)
📄 SpillPlacement.h(6.67 KB)
📄 SplitKit.cpp(66.39 KB)
📄 SplitKit.h(23.7 KB)
📄 StackColoring.cpp(49.03 KB)
📄 StackMapLivenessAnalysis.cpp(6.16 KB)
📄 StackMaps.cpp(19.74 KB)
📄 StackProtector.cpp(22.94 KB)
📄 StackSlotColoring.cpp(17.12 KB)
📄 SwiftErrorValueTracking.cpp(11.37 KB)
📄 SwitchLoweringUtils.cpp(18.33 KB)
📄 TailDuplication.cpp(3.32 KB)
📄 TailDuplicator.cpp(38.29 KB)
📄 TargetFrameLoweringImpl.cpp(6.24 KB)
📄 TargetInstrInfo.cpp(51.1 KB)
📄 TargetLoweringBase.cpp(82.53 KB)
📄 TargetLoweringObjectFileImpl.cpp(80.52 KB)
📄 TargetOptionsImpl.cpp(2 KB)
📄 TargetPassConfig.cpp(48.89 KB)
📄 TargetRegisterInfo.cpp(19.15 KB)
📄 TargetSchedule.cpp(13.16 KB)
📄 TargetSubtargetInfo.cpp(1.89 KB)
📄 TwoAddressInstructionPass.cpp(62.08 KB)
📄 TypePromotion.cpp(32.46 KB)
📄 UnreachableBlockElim.cpp(7.48 KB)
📄 ValueTypes.cpp(19.87 KB)
📄 VirtRegMap.cpp(21.4 KB)
📄 WasmEHPrepare.cpp(17.48 KB)
📄 WinEHPrepare.cpp(51.16 KB)
📄 XRayInstrumentation.cpp(9.66 KB)

Editing: LiveRangeCalc.cpp

//===- LiveRangeCalc.cpp - Calculate live ranges -------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Implementation of the LiveRangeCalc class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/LiveRangeCalc.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <tuple>
#include <utility>

using namespace llvm;

#define DEBUG_TYPE "regalloc"

// Reserve an address that indicates a value that is known to be "undef".
static VNInfo UndefVNI(0xbad, SlotIndex());

void LiveRangeCalc::resetLiveOutMap() {
  unsigned NumBlocks = MF->getNumBlockIDs();
  Seen.clear();
  Seen.resize(NumBlocks);
  EntryInfos.clear();
  Map.resize(NumBlocks);
}

void LiveRangeCalc::reset(const MachineFunction *mf,
                          SlotIndexes *SI,
                          MachineDominatorTree *MDT,
                          VNInfo::Allocator *VNIA) {
  MF = mf;
  MRI = &MF->getRegInfo();
  Indexes = SI;
  DomTree = MDT;
  Alloc = VNIA;
  resetLiveOutMap();
  LiveIn.clear();
}

void LiveRangeCalc::updateFromLiveIns() {
  LiveRangeUpdater Updater;
  for (const LiveInBlock &I : LiveIn) {
    if (!I.DomNode)
      continue;
    MachineBasicBlock *MBB = I.DomNode->getBlock();
    assert(I.Value && "No live-in value found");
    SlotIndex Start, End;
    std::tie(Start, End) = Indexes->getMBBRange(MBB);

if (I.Kill.isValid())
      // Value is killed inside this block.
      End = I.Kill;
    else {
      // The value is live-through, update LiveOut as well.
      // Defer the Domtree lookup until it is needed.
      assert(Seen.test(MBB->getNumber()));
      Map[MBB] = LiveOutPair(I.Value, nullptr);
    }
    Updater.setDest(&I.LR);
    Updater.add(Start, End, I.Value);
  }
  LiveIn.clear();
}

void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
                           ArrayRef<SlotIndex> Undefs) {
  assert(Use.isValid() && "Invalid SlotIndex");
  assert(Indexes && "Missing SlotIndexes");
  assert(DomTree && "Missing dominator tree");

MachineBasicBlock *UseMBB = Indexes->getMBBFromIndex(Use.getPrevSlot());
  assert(UseMBB && "No MBB at Use");

// Is there a def in the same MBB we can extend?
  auto EP = LR.extendInBlock(Undefs, Indexes->getMBBStartIdx(UseMBB), Use);
  if (EP.first != nullptr || EP.second)
    return;

// Find the single reaching def, or determine if Use is jointly dominated by
  // multiple values, and we may need to create even more phi-defs to preserve
  // VNInfo SSA form.  Perform a search for all predecessor blocks where we
  // know the dominating VNInfo.
  if (findReachingDefs(LR, *UseMBB, Use, PhysReg, Undefs))
    return;

// When there were multiple different values, we may need new PHIs.
  calculateValues();
}

// This function is called by a client after using the low-level API to add
// live-out and live-in blocks.  The unique value optimization is not
// available, SplitEditor::transferValues handles that case directly anyway.
void LiveRangeCalc::calculateValues() {
  assert(Indexes && "Missing SlotIndexes");
  assert(DomTree && "Missing dominator tree");
  updateSSA();
  updateFromLiveIns();
}

bool LiveRangeCalc::isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
                                 MachineBasicBlock &MBB, BitVector &DefOnEntry,
                                 BitVector &UndefOnEntry) {
  unsigned BN = MBB.getNumber();
  if (DefOnEntry[BN])
    return true;
  if (UndefOnEntry[BN])
    return false;

auto MarkDefined = [BN, &DefOnEntry](MachineBasicBlock &B) -> bool {
    for (MachineBasicBlock *S : B.successors())
      DefOnEntry[S->getNumber()] = true;
    DefOnEntry[BN] = true;
    return true;
  };

SetVector<unsigned> WorkList;
  // Checking if the entry of MBB is reached by some def: add all predecessors
  // that are potentially defined-on-exit to the work list.
  for (MachineBasicBlock *P : MBB.predecessors())
    WorkList.insert(P->getNumber());

for (unsigned i = 0; i != WorkList.size(); ++i) {
    // Determine if the exit from the block is reached by some def.
    unsigned N = WorkList[i];
    MachineBasicBlock &B = *MF->getBlockNumbered(N);
    if (Seen[N]) {
      const LiveOutPair &LOB = Map[&B];
      if (LOB.first != nullptr && LOB.first != &UndefVNI)
        return MarkDefined(B);
    }
    SlotIndex Begin, End;
    std::tie(Begin, End) = Indexes->getMBBRange(&B);
    // Treat End as not belonging to B.
    // If LR has a segment S that starts at the next block, i.e. [End, ...),
    // std::upper_bound will return the segment following S. Instead,
    // S should be treated as the first segment that does not overlap B.
    LiveRange::iterator UB = std::upper_bound(LR.begin(), LR.end(),
                                              End.getPrevSlot());
    if (UB != LR.begin()) {
      LiveRange::Segment &Seg = *std::prev(UB);
      if (Seg.end > Begin) {
        // There is a segment that overlaps B. If the range is not explicitly
        // undefined between the end of the segment and the end of the block,
        // treat the block as defined on exit. If it is, go to the next block
        // on the work list.
        if (LR.isUndefIn(Undefs, Seg.end, End))
          continue;
        return MarkDefined(B);
      }
    }

// No segment overlaps with this block. If this block is not defined on
    // entry, or it undefines the range, do not process its predecessors.
    if (UndefOnEntry[N] || LR.isUndefIn(Undefs, Begin, End)) {
      UndefOnEntry[N] = true;
      continue;
    }
    if (DefOnEntry[N])
      return MarkDefined(B);

// Still don't know: add all predecessors to the work list.
    for (MachineBasicBlock *P : B.predecessors())
      WorkList.insert(P->getNumber());
  }

UndefOnEntry[BN] = true;
  return false;
}

bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
                                     SlotIndex Use, unsigned PhysReg,
                                     ArrayRef<SlotIndex> Undefs) {
  unsigned UseMBBNum = UseMBB.getNumber();

// Block numbers where LR should be live-in.
  SmallVector<unsigned, 16> WorkList(1, UseMBBNum);

// Remember if we have seen more than one value.
  bool UniqueVNI = true;
  VNInfo *TheVNI = nullptr;

bool FoundUndef = false;

// Using Seen as a visited set, perform a BFS for all reaching defs.
  for (unsigned i = 0; i != WorkList.size(); ++i) {
    MachineBasicBlock *MBB = MF->getBlockNumbered(WorkList[i]);

#ifndef NDEBUG
    if (MBB->pred_empty()) {
      MBB->getParent()->verify();
      errs() << "Use of " << printReg(PhysReg, MRI->getTargetRegisterInfo())
             << " does not have a corresponding definition on every path:\n";
      const MachineInstr *MI = Indexes->getInstructionFromIndex(Use);
      if (MI != nullptr)
        errs() << Use << " " << *MI;
      report_fatal_error("Use not jointly dominated by defs.");
    }

if (Register::isPhysicalRegister(PhysReg) && !MBB->isLiveIn(PhysReg)) {
      MBB->getParent()->verify();
      const TargetRegisterInfo *TRI = MRI->getTargetRegisterInfo();
      errs() << "The register " << printReg(PhysReg, TRI)
             << " needs to be live in to " << printMBBReference(*MBB)
             << ", but is missing from the live-in list.\n";
      report_fatal_error("Invalid global physical register");
    }
#endif
    FoundUndef |= MBB->pred_empty();

for (MachineBasicBlock *Pred : MBB->predecessors()) {
       // Is this a known live-out block?
       if (Seen.test(Pred->getNumber())) {
         if (VNInfo *VNI = Map[Pred].first) {
           if (TheVNI && TheVNI != VNI)
             UniqueVNI = false;
           TheVNI = VNI;
         }
         continue;
       }

SlotIndex Start, End;
       std::tie(Start, End) = Indexes->getMBBRange(Pred);

// First time we see Pred.  Try to determine the live-out value, but set
       // it as null if Pred is live-through with an unknown value.
       auto EP = LR.extendInBlock(Undefs, Start, End);
       VNInfo *VNI = EP.first;
       FoundUndef |= EP.second;
       setLiveOutValue(Pred, EP.second ? &UndefVNI : VNI);
       if (VNI) {
         if (TheVNI && TheVNI != VNI)
           UniqueVNI = false;
         TheVNI = VNI;
       }
       if (VNI || EP.second)
         continue;

// No, we need a live-in value for Pred as well
       if (Pred != &UseMBB)
         WorkList.push_back(Pred->getNumber());
       else
          // Loopback to UseMBB, so value is really live through.
         Use = SlotIndex();
    }
  }

LiveIn.clear();
  FoundUndef |= (TheVNI == nullptr || TheVNI == &UndefVNI);
  if (!Undefs.empty() && FoundUndef)
    UniqueVNI = false;

// Both updateSSA() and LiveRangeUpdater benefit from ordered blocks, but
  // neither require it. Skip the sorting overhead for small updates.
  if (WorkList.size() > 4)
    array_pod_sort(WorkList.begin(), WorkList.end());

// If a unique reaching def was found, blit in the live ranges immediately.
  if (UniqueVNI) {
    assert(TheVNI != nullptr && TheVNI != &UndefVNI);
    LiveRangeUpdater Updater(&LR);
    for (unsigned BN : WorkList) {
      SlotIndex Start, End;
      std::tie(Start, End) = Indexes->getMBBRange(BN);
      // Trim the live range in UseMBB.
      if (BN == UseMBBNum && Use.isValid())
        End = Use;
      else
        Map[MF->getBlockNumbered(BN)] = LiveOutPair(TheVNI, nullptr);
      Updater.add(Start, End, TheVNI);
    }
    return true;
  }

// Prepare the defined/undefined bit vectors.
  EntryInfoMap::iterator Entry;
  bool DidInsert;
  std::tie(Entry, DidInsert) = EntryInfos.insert(
      std::make_pair(&LR, std::make_pair(BitVector(), BitVector())));
  if (DidInsert) {
    // Initialize newly inserted entries.
    unsigned N = MF->getNumBlockIDs();
    Entry->second.first.resize(N);
    Entry->second.second.resize(N);
  }
  BitVector &DefOnEntry = Entry->second.first;
  BitVector &UndefOnEntry = Entry->second.second;

// Multiple values were found, so transfer the work list to the LiveIn array
  // where UpdateSSA will use it as a work list.
  LiveIn.reserve(WorkList.size());
  for (unsigned BN : WorkList) {
    MachineBasicBlock *MBB = MF->getBlockNumbered(BN);
    if (!Undefs.empty() &&
        !isDefOnEntry(LR, Undefs, *MBB, DefOnEntry, UndefOnEntry))
      continue;
    addLiveInBlock(LR, DomTree->getNode(MBB));
    if (MBB == &UseMBB)
      LiveIn.back().Kill = Use;
  }

return false;
}

// This is essentially the same iterative algorithm that SSAUpdater uses,
// except we already have a dominator tree, so we don't have to recompute it.
void LiveRangeCalc::updateSSA() {
  assert(Indexes && "Missing SlotIndexes");
  assert(DomTree && "Missing dominator tree");

// Interate until convergence.
  bool Changed;
  do {
    Changed = false;
    // Propagate live-out values down the dominator tree, inserting phi-defs
    // when necessary.
    for (LiveInBlock &I : LiveIn) {
      MachineDomTreeNode *Node = I.DomNode;
      // Skip block if the live-in value has already been determined.
      if (!Node)
        continue;
      MachineBasicBlock *MBB = Node->getBlock();
      MachineDomTreeNode *IDom = Node->getIDom();
      LiveOutPair IDomValue;

// We need a live-in value to a block with no immediate dominator?
      // This is probably an unreachable block that has survived somehow.
      bool needPHI = !IDom || !Seen.test(IDom->getBlock()->getNumber());

// IDom dominates all of our predecessors, but it may not be their
      // immediate dominator. Check if any of them have live-out values that are
      // properly dominated by IDom. If so, we need a phi-def here.
      if (!needPHI) {
        IDomValue = Map[IDom->getBlock()];

// Cache the DomTree node that defined the value.
        if (IDomValue.first && IDomValue.first != &UndefVNI &&
            !IDomValue.second) {
          Map[IDom->getBlock()].second = IDomValue.second =
            DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));
        }

for (MachineBasicBlock *Pred : MBB->predecessors()) {
          LiveOutPair &Value = Map[Pred];
          if (!Value.first || Value.first == IDomValue.first)
            continue;
          if (Value.first == &UndefVNI) {
            needPHI = true;
            break;
          }

// Cache the DomTree node that defined the value.
          if (!Value.second)
            Value.second =
              DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));

// This predecessor is carrying something other than IDomValue.
          // It could be because IDomValue hasn't propagated yet, or it could be
          // because MBB is in the dominance frontier of that value.
          if (DomTree->dominates(IDom, Value.second)) {
            needPHI = true;
            break;
          }
        }
      }

// The value may be live-through even if Kill is set, as can happen when
      // we are called from extendRange. In that case LiveOutSeen is true, and
      // LiveOut indicates a foreign or missing value.
      LiveOutPair &LOP = Map[MBB];

// Create a phi-def if required.
      if (needPHI) {
        Changed = true;
        assert(Alloc && "Need VNInfo allocator to create PHI-defs");
        SlotIndex Start, End;
        std::tie(Start, End) = Indexes->getMBBRange(MBB);
        LiveRange &LR = I.LR;
        VNInfo *VNI = LR.getNextValue(Start, *Alloc);
        I.Value = VNI;
        // This block is done, we know the final value.
        I.DomNode = nullptr;

// Add liveness since updateFromLiveIns now skips this node.
        if (I.Kill.isValid()) {
          if (VNI)
            LR.addSegment(LiveInterval::Segment(Start, I.Kill, VNI));
        } else {
          if (VNI)
            LR.addSegment(LiveInterval::Segment(Start, End, VNI));
          LOP = LiveOutPair(VNI, Node);
        }
      } else if (IDomValue.first && IDomValue.first != &UndefVNI) {
        // No phi-def here. Remember incoming value.
        I.Value = IDomValue.first;

// If the IDomValue is killed in the block, don't propagate through.
        if (I.Kill.isValid())
          continue;

// Propagate IDomValue if it isn't killed:
        // MBB is live-out and doesn't define its own value.
        if (LOP.first == IDomValue.first)
          continue;
        Changed = true;
        LOP = IDomValue;
      }
    }
  } while (Changed);
}

bool LiveRangeCalc::isJointlyDominated(const MachineBasicBlock *MBB,
                                       ArrayRef<SlotIndex> Defs,
                                       const SlotIndexes &Indexes) {
  const MachineFunction &MF = *MBB->getParent();
  BitVector DefBlocks(MF.getNumBlockIDs());
  for (SlotIndex I : Defs)
    DefBlocks.set(Indexes.getMBBFromIndex(I)->getNumber());

SetVector<unsigned> PredQueue;
  PredQueue.insert(MBB->getNumber());
  for (unsigned i = 0; i != PredQueue.size(); ++i) {
    unsigned BN = PredQueue[i];
    if (DefBlocks[BN])
      return true;
    const MachineBasicBlock *B = MF.getBlockNumbered(BN);
    for (const MachineBasicBlock *P : B->predecessors())
      PredQueue.insert(P->getNumber());
  }
  return false;
}

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