DwarfDebug.cpp

  // Add to map.
  TheCU->insertDIE(N, VariableDIE);
  // Add to context owner.
  DIDescriptor GVContext = GV.getContext();
  TheCU->addToContextOwner(VariableDIE, GVContext);
  // Add location.
  if (isGlobalVariable) {
    DIEBlock *Block = new (DIEValueAllocator) DIEBlock();
    TheCU->addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_addr);
    TheCU->addLabel(Block, 0, dwarf::DW_FORM_udata,
             Asm->Mang->getSymbol(GV.getGlobal()));
    // Do not create specification DIE if context is either compile unit
    // or a subprogram.
    if (GV.isDefinition() && !GVContext.isCompileUnit() &&
        !GVContext.isFile() && !isSubprogramContext(GVContext)) {
      // Create specification DIE.
      DIE *VariableSpecDIE = new DIE(dwarf::DW_TAG_variable);
      TheCU->addDIEEntry(VariableSpecDIE, dwarf::DW_AT_specification,
                  dwarf::DW_FORM_ref4, VariableDIE);
      TheCU->addBlock(VariableSpecDIE, dwarf::DW_AT_location, 0, Block);
      TheCU->addUInt(VariableDIE, dwarf::DW_AT_declaration, dwarf::DW_FORM_flag, 1);
      TheCU->addDie(VariableSpecDIE);
    } else {
      TheCU->addBlock(VariableDIE, dwarf::DW_AT_location, 0, Block);
    } 
  } else if (ConstantInt *CI = 
             dyn_cast_or_null<ConstantInt>(GV.getConstant()))
    TheCU->addConstantValue(VariableDIE, CI, isUnsignedDIType(GTy));
  else if (const ConstantExpr *CE = getMergedGlobalExpr(N->getOperand(11))) {
    // GV is a merged global.
    DIEBlock *Block = new (DIEValueAllocator) DIEBlock();
    TheCU->addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_addr);
    TheCU->addLabel(Block, 0, dwarf::DW_FORM_udata,
                    Asm->Mang->getSymbol(cast<GlobalValue>(CE->getOperand(0))));
    ConstantInt *CII = cast<ConstantInt>(CE->getOperand(2));
    TheCU->addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_constu);
    TheCU->addUInt(Block, 0, dwarf::DW_FORM_udata, CII->getZExtValue());
    TheCU->addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_plus);
    TheCU->addBlock(VariableDIE, dwarf::DW_AT_location, 0, Block);
  }

  return;
}

/// construct SubprogramDIE - Construct subprogram DIE.
void DwarfDebug::constructSubprogramDIE(const MDNode *N) {
  DISubprogram SP(N);

  // Check for pre-existence.
  CompileUnit *TheCU = getCompileUnit(N);
  if (TheCU->getDIE(N))
    return;

  if (!SP.isDefinition())
    // This is a method declaration which will be handled while constructing
    // class type.
    return;

  DIE *SubprogramDie = createSubprogramDIE(SP);

  // Add to map.
  TheCU->insertDIE(N, SubprogramDie);

  // Add to context owner.
  TheCU->addToContextOwner(SubprogramDie, SP.getContext());

  // Expose as global.
  TheCU->addGlobal(SP.getName(), SubprogramDie);

  return;
}

/// beginModule - Emit all Dwarf sections that should come prior to the
/// content. Create global DIEs and emit initial debug info sections.
/// This is inovked by the target AsmPrinter.
void DwarfDebug::beginModule(Module *M) {
  if (DisableDebugInfoPrinting)
    return;

  // If module has named metadata anchors then use them, otherwise scan the module
  // using debug info finder to collect debug info.
  NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
  if (CU_Nodes) {

    NamedMDNode *GV_Nodes = M->getNamedMetadata("llvm.dbg.gv");
    NamedMDNode *SP_Nodes = M->getNamedMetadata("llvm.dbg.sp");
    if (!GV_Nodes && !SP_Nodes)
      // If there are not any global variables or any functions then
      // there is not any debug info in this module.
      return;

    for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i)
      constructCompileUnit(CU_Nodes->getOperand(i));

    if (GV_Nodes)
      for (unsigned i = 0, e = GV_Nodes->getNumOperands(); i != e; ++i)
        constructGlobalVariableDIE(GV_Nodes->getOperand(i));

    if (SP_Nodes)
      for (unsigned i = 0, e = SP_Nodes->getNumOperands(); i != e; ++i)
        constructSubprogramDIE(SP_Nodes->getOperand(i));
    
  } else {

    DebugInfoFinder DbgFinder;
    DbgFinder.processModule(*M);
    
    bool HasDebugInfo = false;
    // Scan all the compile-units to see if there are any marked as the main unit.
    // if not, we do not generate debug info.
    for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
           E = DbgFinder.compile_unit_end(); I != E; ++I) {
      if (DICompileUnit(*I).isMain()) {
        HasDebugInfo = true;
        break;
      }
    }
    if (!HasDebugInfo) return;
    
    // Create all the compile unit DIEs.
    for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
           E = DbgFinder.compile_unit_end(); I != E; ++I)
      constructCompileUnit(*I);
    
    // Create DIEs for each global variable.
    for (DebugInfoFinder::iterator I = DbgFinder.global_variable_begin(),
           E = DbgFinder.global_variable_end(); I != E; ++I)
      constructGlobalVariableDIE(*I);
    
    // Create DIEs for each subprogram.
    for (DebugInfoFinder::iterator I = DbgFinder.subprogram_begin(),
           E = DbgFinder.subprogram_end(); I != E; ++I)
      constructSubprogramDIE(*I);
  }
  
  // Tell MMI that we have debug info.
  MMI->setDebugInfoAvailability(true);
  
  // Emit initial sections.
  EmitSectionLabels();

  //getOrCreateTypeDIE
  if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.enum"))
    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
      DIType Ty(NMD->getOperand(i));
      getCompileUnit(Ty)->getOrCreateTypeDIE(Ty);
    }

  if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.ty"))
    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
      DIType Ty(NMD->getOperand(i));
      getCompileUnit(Ty)->getOrCreateTypeDIE(Ty);
    }

  // Prime section data.
  SectionMap.insert(Asm->getObjFileLowering().getTextSection());
}

/// endModule - Emit all Dwarf sections that should come after the content.
///
void DwarfDebug::endModule() {
  if (!FirstCU) return;
  const Module *M = MMI->getModule();
  DenseMap<const MDNode *, DbgScope *> DeadFnScopeMap;
  if (NamedMDNode *AllSPs = M->getNamedMetadata("llvm.dbg.sp")) {
    for (unsigned SI = 0, SE = AllSPs->getNumOperands(); SI != SE; ++SI) {
      if (ProcessedSPNodes.count(AllSPs->getOperand(SI)) != 0) continue;
      DISubprogram SP(AllSPs->getOperand(SI));
      if (!SP.Verify()) continue;

      // Collect info for variables that were optimized out.
      if (!SP.isDefinition()) continue;
      StringRef FName = SP.getLinkageName();
      if (FName.empty())
        FName = SP.getName();
      NamedMDNode *NMD = getFnSpecificMDNode(*(MMI->getModule()), FName);
      if (!NMD) continue;
      unsigned E = NMD->getNumOperands();
      if (!E) continue;
      DbgScope *Scope = new DbgScope(NULL, DIDescriptor(SP), NULL);
      DeadFnScopeMap[SP] = Scope;
      for (unsigned I = 0; I != E; ++I) {
        DIVariable DV(NMD->getOperand(I));
        if (!DV.Verify()) continue;
        Scope->addVariable(new DbgVariable(DV));
      }

      // Construct subprogram DIE and add variables DIEs.
      constructSubprogramDIE(SP);
      DIE *ScopeDIE = getCompileUnit(SP)->getDIE(SP);
      const SmallVector<DbgVariable *, 8> &Variables = Scope->getDbgVariables();
      for (unsigned i = 0, N = Variables.size(); i < N; ++i) {
        DIE *VariableDIE = constructVariableDIE(Variables[i], Scope);
        if (VariableDIE)
          ScopeDIE->addChild(VariableDIE);
      }
    }
  }

  // Attach DW_AT_inline attribute with inlined subprogram DIEs.
  for (SmallPtrSet<DIE *, 4>::iterator AI = InlinedSubprogramDIEs.begin(),
         AE = InlinedSubprogramDIEs.end(); AI != AE; ++AI) {
    DIE *ISP = *AI;
    FirstCU->addUInt(ISP, dwarf::DW_AT_inline, 0, dwarf::DW_INL_inlined);
  }

  for (DenseMap<DIE *, const MDNode *>::iterator CI = ContainingTypeMap.begin(),
         CE = ContainingTypeMap.end(); CI != CE; ++CI) {
    DIE *SPDie = CI->first;
    const MDNode *N = dyn_cast_or_null<MDNode>(CI->second);
    if (!N) continue;
    DIE *NDie = getCompileUnit(N)->getDIE(N);
    if (!NDie) continue;
    getCompileUnit(N)->addDIEEntry(SPDie, dwarf::DW_AT_containing_type, 
                                   dwarf::DW_FORM_ref4, NDie);
  }

  // Standard sections final addresses.
  Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getTextSection());
  Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("text_end"));
  Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getDataSection());
  Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("data_end"));

  // End text sections.
  for (unsigned i = 1, N = SectionMap.size(); i <= N; ++i) {
    Asm->OutStreamer.SwitchSection(SectionMap[i]);
    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("section_end", i));
  }

  // Compute DIE offsets and sizes.
  computeSizeAndOffsets();

  // Emit all the DIEs into a debug info section
  emitDebugInfo();

  // Corresponding abbreviations into a abbrev section.
  emitAbbreviations();

  // Emit info into a debug pubnames section.
  emitDebugPubNames();

  // Emit info into a debug pubtypes section.
  emitDebugPubTypes();

  // Emit info into a debug loc section.
  emitDebugLoc();

  // Emit info into a debug aranges section.
  EmitDebugARanges();

  // Emit info into a debug ranges section.
  emitDebugRanges();

  // Emit info into a debug macinfo section.
  emitDebugMacInfo();

  // Emit inline info.
  emitDebugInlineInfo();

  // Emit info into a debug str section.
  emitDebugStr();

  // clean up.
  DeleteContainerSeconds(DeadFnScopeMap);
  for (DenseMap<const MDNode *, CompileUnit *>::iterator I = CUMap.begin(),
         E = CUMap.end(); I != E; ++I)
    delete I->second;
  FirstCU = NULL;  // Reset for the next Module, if any.
}

/// findAbstractVariable - Find abstract variable, if any, associated with Var.
DbgVariable *DwarfDebug::findAbstractVariable(DIVariable &Var,
                                              DebugLoc ScopeLoc) {

  DbgVariable *AbsDbgVariable = AbstractVariables.lookup(Var);
  if (AbsDbgVariable)
    return AbsDbgVariable;

  LLVMContext &Ctx = Var->getContext();
  DbgScope *Scope = AbstractScopes.lookup(ScopeLoc.getScope(Ctx));
  if (!Scope)
    return NULL;

  AbsDbgVariable = new DbgVariable(Var);
  Scope->addVariable(AbsDbgVariable);
  AbstractVariables[Var] = AbsDbgVariable;
  return AbsDbgVariable;
}

/// addCurrentFnArgument - If Var is an current function argument that add
/// it in CurrentFnArguments list.
bool DwarfDebug::addCurrentFnArgument(const MachineFunction *MF,
                                      DbgVariable *Var, DbgScope *Scope) {
  if (Scope != CurrentFnDbgScope) 
    return false;
  DIVariable DV = Var->getVariable();
  if (DV.getTag() != dwarf::DW_TAG_arg_variable)
    return false;
  unsigned ArgNo = DV.getArgNumber();
  if (ArgNo == 0) 
    return false;

  size_t Size = CurrentFnArguments.size();
  if (Size == 0)
    CurrentFnArguments.resize(MF->getFunction()->arg_size());
  // llvm::Function argument size is not good indicator of how many
  // arguments does the function have at source level.
  if (ArgNo > Size)
    CurrentFnArguments.resize(ArgNo * 2);
  CurrentFnArguments[ArgNo - 1] = Var;
  return true;
}

/// collectVariableInfoFromMMITable - Collect variable information from
/// side table maintained by MMI.
void
DwarfDebug::collectVariableInfoFromMMITable(const MachineFunction * MF,
                                   SmallPtrSet<const MDNode *, 16> &Processed) {
  const LLVMContext &Ctx = Asm->MF->getFunction()->getContext();
  MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo();
  for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(),
         VE = VMap.end(); VI != VE; ++VI) {
    const MDNode *Var = VI->first;
    if (!Var) continue;
    Processed.insert(Var);
    DIVariable DV(Var);
    const std::pair<unsigned, DebugLoc> &VP = VI->second;

    DbgScope *Scope = 0;
    if (const MDNode *IA = VP.second.getInlinedAt(Ctx))
      Scope = ConcreteScopes.lookup(IA);
    if (Scope == 0)
      Scope = DbgScopeMap.lookup(VP.second.getScope(Ctx));

    // If variable scope is not found then skip this variable.
    if (Scope == 0)
      continue;

    DbgVariable *AbsDbgVariable = findAbstractVariable(DV, VP.second);
    DbgVariable *RegVar = new DbgVariable(DV);
    recordVariableFrameIndex(RegVar, VP.first);
    if (!addCurrentFnArgument(MF, RegVar, Scope))
      Scope->addVariable(RegVar);
    if (AbsDbgVariable) {
      recordVariableFrameIndex(AbsDbgVariable, VP.first);
      VarToAbstractVarMap[RegVar] = AbsDbgVariable;
    }
  }
}

/// isDbgValueInDefinedReg - Return true if debug value, encoded by
/// DBG_VALUE instruction, is in a defined reg.
static bool isDbgValueInDefinedReg(const MachineInstr *MI) {
  assert (MI->isDebugValue() && "Invalid DBG_VALUE machine instruction!");
  return MI->getNumOperands() == 3 &&
         MI->getOperand(0).isReg() && MI->getOperand(0).getReg() &&
         MI->getOperand(1).isImm() && MI->getOperand(1).getImm() == 0;
}

/// collectVariableInfo - Populate DbgScope entries with variables' info.
void
DwarfDebug::collectVariableInfo(const MachineFunction *MF,
                                SmallPtrSet<const MDNode *, 16> &Processed) {

  /// collection info from MMI table.
  collectVariableInfoFromMMITable(MF, Processed);

  for (SmallVectorImpl<const MDNode*>::const_iterator
         UVI = UserVariables.begin(), UVE = UserVariables.end(); UVI != UVE;
         ++UVI) {
    const MDNode *Var = *UVI;
    if (Processed.count(Var))
      continue;

    // History contains relevant DBG_VALUE instructions for Var and instructions
    // clobbering it.
    SmallVectorImpl<const MachineInstr*> &History = DbgValues[Var];
    if (History.empty())
      continue;
    const MachineInstr *MInsn = History.front();

    DIVariable DV(Var);
    DbgScope *Scope = NULL;
    if (DV.getTag() == dwarf::DW_TAG_arg_variable &&
        DISubprogram(DV.getContext()).describes(MF->getFunction()))
      Scope = CurrentFnDbgScope;
    else
      Scope = findDbgScope(MInsn);
    // If variable scope is not found then skip this variable.
    if (!Scope)
      continue;

    Processed.insert(DV);
    assert(MInsn->isDebugValue() && "History must begin with debug value");
    DbgVariable *RegVar = new DbgVariable(DV);
    if (!addCurrentFnArgument(MF, RegVar, Scope))
      Scope->addVariable(RegVar);
    if (DbgVariable *AbsVar = findAbstractVariable(DV, MInsn->getDebugLoc())) {
      DbgVariableToDbgInstMap[AbsVar] = MInsn;
      VarToAbstractVarMap[RegVar] = AbsVar;
    }

    // Simple ranges that are fully coalesced.
    if (History.size() <= 1 || (History.size() == 2 &&
                                MInsn->isIdenticalTo(History.back()))) {
      DbgVariableToDbgInstMap[RegVar] = MInsn;
      continue;
    }

    // handle multiple DBG_VALUE instructions describing one variable.
    RegVar->setDotDebugLocOffset(DotDebugLocEntries.size());

    for (SmallVectorImpl<const MachineInstr*>::const_iterator
           HI = History.begin(), HE = History.end(); HI != HE; ++HI) {
      const MachineInstr *Begin = *HI;
      assert(Begin->isDebugValue() && "Invalid History entry");
      MachineLocation MLoc;
      if (Begin->getNumOperands() == 3) {
        if (Begin->getOperand(0).isReg() && Begin->getOperand(1).isImm())
          MLoc.set(Begin->getOperand(0).getReg(), Begin->getOperand(1).getImm());
      } else
        MLoc = Asm->getDebugValueLocation(Begin);

      // FIXME: emitDebugLoc only understands registers.
      if (!MLoc.getReg())
        continue;

      // Compute the range for a register location.
      const MCSymbol *FLabel = getLabelBeforeInsn(Begin);
      const MCSymbol *SLabel = 0;

      if (HI + 1 == HE)
        // If Begin is the last instruction in History then its value is valid
        // until the end of the function.
        SLabel = FunctionEndSym;
      else {
        const MachineInstr *End = HI[1];
        if (End->isDebugValue())
          SLabel = getLabelBeforeInsn(End);
        else {
          // End is a normal instruction clobbering the range.
          SLabel = getLabelAfterInsn(End);
          assert(SLabel && "Forgot label after clobber instruction");
          ++HI;
        }
      }

      // The value is valid until the next DBG_VALUE or clobber.
      DotDebugLocEntries.push_back(DotDebugLocEntry(FLabel, SLabel, MLoc, Var));
    }
    DotDebugLocEntries.push_back(DotDebugLocEntry());
  }

  // Collect info for variables that were optimized out.
  const Function *F = MF->getFunction();
  if (NamedMDNode *NMD = getFnSpecificMDNode(*(F->getParent()), F->getName())) {
    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
      DIVariable DV(cast<MDNode>(NMD->getOperand(i)));
      if (!DV || !Processed.insert(DV))
        continue;
      DbgScope *Scope = DbgScopeMap.lookup(DV.getContext());
      if (Scope)
        Scope->addVariable(new DbgVariable(DV));
    }
  }
}

/// getLabelBeforeInsn - Return Label preceding the instruction.
const MCSymbol *DwarfDebug::getLabelBeforeInsn(const MachineInstr *MI) {
  MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
  assert(Label && "Didn't insert label before instruction");
  return Label;
}

/// getLabelAfterInsn - Return Label immediately following the instruction.
const MCSymbol *DwarfDebug::getLabelAfterInsn(const MachineInstr *MI) {
  return LabelsAfterInsn.lookup(MI);
}

/// beginInstruction - Process beginning of an instruction.
void DwarfDebug::beginInstruction(const MachineInstr *MI) {
  // Check if source location changes, but ignore DBG_VALUE locations.
  if (!MI->isDebugValue()) {
    DebugLoc DL = MI->getDebugLoc();
    if (DL != PrevInstLoc && (!DL.isUnknown() || UnknownLocations)) {
      PrevInstLoc = DL;
      if (!DL.isUnknown()) {
        const MDNode *Scope = DL.getScope(Asm->MF->getFunction()->getContext());
        recordSourceLine(DL.getLine(), DL.getCol(), Scope);
      } else
        recordSourceLine(0, 0, 0);
    }
  }

  // Insert labels where requested.
  DenseMap<const MachineInstr*, MCSymbol*>::iterator I =
    LabelsBeforeInsn.find(MI);

  // No label needed.
  if (I == LabelsBeforeInsn.end())
    return;

  // Label already assigned.
  if (I->second)
    return;

  if (!PrevLabel) {
    PrevLabel = MMI->getContext().CreateTempSymbol();
    Asm->OutStreamer.EmitLabel(PrevLabel);
  }
  I->second = PrevLabel;
}

/// endInstruction - Process end of an instruction.
void DwarfDebug::endInstruction(const MachineInstr *MI) {
  // Don't create a new label after DBG_VALUE instructions.
  // They don't generate code.
  if (!MI->isDebugValue())
    PrevLabel = 0;

  DenseMap<const MachineInstr*, MCSymbol*>::iterator I =
    LabelsAfterInsn.find(MI);

  // No label needed.
  if (I == LabelsAfterInsn.end())
    return;

  // Label already assigned.
  if (I->second)
    return;

  // We need a label after this instruction.
  if (!PrevLabel) {
    PrevLabel = MMI->getContext().CreateTempSymbol();
    Asm->OutStreamer.EmitLabel(PrevLabel);
  }
  I->second = PrevLabel;
}

/// getOrCreateDbgScope - Create DbgScope for the scope.
DbgScope *DwarfDebug::getOrCreateDbgScope(const MDNode *Scope,
                                          const MDNode *InlinedAt) {
  if (!InlinedAt) {
    DbgScope *WScope = DbgScopeMap.lookup(Scope);
    if (WScope)
      return WScope;
    WScope = new DbgScope(NULL, DIDescriptor(Scope), NULL);
    DbgScopeMap.insert(std::make_pair(Scope, WScope));
    if (DIDescriptor(Scope).isLexicalBlock()) {
      DbgScope *Parent =
        getOrCreateDbgScope(DILexicalBlock(Scope).getContext(), NULL);
      WScope->setParent(Parent);
      Parent->addScope(WScope);
    }

    if (!WScope->getParent()) {
      StringRef SPName = DISubprogram(Scope).getLinkageName();
      // We used to check only for a linkage name, but that fails
      // since we began omitting the linkage name for private
      // functions.  The new way is to check for the name in metadata,
      // but that's not supported in old .ll test cases.  Ergo, we
      // check both.
      if (SPName == Asm->MF->getFunction()->getName() ||
          DISubprogram(Scope).getFunction() == Asm->MF->getFunction())
        CurrentFnDbgScope = WScope;
    }

    return WScope;
  }

  getOrCreateAbstractScope(Scope);
  DbgScope *WScope = DbgScopeMap.lookup(InlinedAt);
  if (WScope)
    return WScope;

  WScope = new DbgScope(NULL, DIDescriptor(Scope), InlinedAt);
  DbgScopeMap.insert(std::make_pair(InlinedAt, WScope));
  DILocation DL(InlinedAt);
  DbgScope *Parent =
    getOrCreateDbgScope(DL.getScope(), DL.getOrigLocation());
  WScope->setParent(Parent);
  Parent->addScope(WScope);

  ConcreteScopes[InlinedAt] = WScope;

  return WScope;
}

/// hasValidLocation - Return true if debug location entry attached with
/// machine instruction encodes valid location info.
static bool hasValidLocation(LLVMContext &Ctx,
                             const MachineInstr *MInsn,
                             const MDNode *&Scope, const MDNode *&InlinedAt) {
  DebugLoc DL = MInsn->getDebugLoc();
  if (DL.isUnknown()) return false;

  const MDNode *S = DL.getScope(Ctx);

  // There is no need to create another DIE for compile unit. For all
  // other scopes, create one DbgScope now. This will be translated
  // into a scope DIE at the end.
  if (DIScope(S).isCompileUnit()) return false;

  Scope = S;
  InlinedAt = DL.getInlinedAt(Ctx);
  return true;
}

/// calculateDominanceGraph - Calculate dominance graph for DbgScope
/// hierarchy.
static void calculateDominanceGraph(DbgScope *Scope) {
  assert (Scope && "Unable to calculate scop edominance graph!");
  SmallVector<DbgScope *, 4> WorkStack;
  WorkStack.push_back(Scope);
  unsigned Counter = 0;
  while (!WorkStack.empty()) {
    DbgScope *WS = WorkStack.back();
    const SmallVector<DbgScope *, 4> &Children = WS->getScopes();
    bool visitedChildren = false;
    for (SmallVector<DbgScope *, 4>::const_iterator SI = Children.begin(),
           SE = Children.end(); SI != SE; ++SI) {
      DbgScope *ChildScope = *SI;
      if (!ChildScope->getDFSOut()) {
        WorkStack.push_back(ChildScope);
        visitedChildren = true;
        ChildScope->setDFSIn(++Counter);
        break;
      }
    }
    if (!visitedChildren) {
      WorkStack.pop_back();
      WS->setDFSOut(++Counter);
    }
  }
}

/// printDbgScopeInfo - Print DbgScope info for each machine instruction.
static
void printDbgScopeInfo(LLVMContext &Ctx, const MachineFunction *MF,
                       DenseMap<const MachineInstr *, DbgScope *> &MI2ScopeMap)
{
#ifndef NDEBUG
  unsigned PrevDFSIn = 0;
  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
       I != E; ++I) {
    for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
         II != IE; ++II) {
      const MachineInstr *MInsn = II;
      const MDNode *Scope = NULL;
      const MDNode *InlinedAt = NULL;

      // Check if instruction has valid location information.
      if (hasValidLocation(Ctx, MInsn, Scope, InlinedAt)) {
        dbgs() << " [ ";
        if (InlinedAt)
          dbgs() << "*";
        DenseMap<const MachineInstr *, DbgScope *>::iterator DI =
          MI2ScopeMap.find(MInsn);
        if (DI != MI2ScopeMap.end()) {
          DbgScope *S = DI->second;
          dbgs() << S->getDFSIn();
          PrevDFSIn = S->getDFSIn();
        } else
          dbgs() << PrevDFSIn;
      } else
        dbgs() << " [ x" << PrevDFSIn;
      dbgs() << " ]";
      MInsn->dump();
    }
    dbgs() << "\n";
  }
#endif
}
/// extractScopeInformation - Scan machine instructions in this function
/// and collect DbgScopes. Return true, if at least one scope was found.
bool DwarfDebug::extractScopeInformation() {
  // If scope information was extracted using .dbg intrinsics then there is not
  // any need to extract these information by scanning each instruction.
  if (!DbgScopeMap.empty())
    return false;

  // Scan each instruction and create scopes. First build working set of scopes.
  LLVMContext &Ctx = Asm->MF->getFunction()->getContext();
  SmallVector<DbgRange, 4> MIRanges;
  DenseMap<const MachineInstr *, DbgScope *> MI2ScopeMap;
  const MDNode *PrevScope = NULL;
  const MDNode *PrevInlinedAt = NULL;
  const MachineInstr *RangeBeginMI = NULL;
  const MachineInstr *PrevMI = NULL;
  for (MachineFunction::const_iterator I = Asm->MF->begin(), E = Asm->MF->end();
       I != E; ++I) {
    for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
         II != IE; ++II) {
      const MachineInstr *MInsn = II;
      const MDNode *Scope = NULL;
      const MDNode *InlinedAt = NULL;

      // Check if instruction has valid location information.
      if (!hasValidLocation(Ctx, MInsn, Scope, InlinedAt)) {
        PrevMI = MInsn;
        continue;
      }

      // If scope has not changed then skip this instruction.
      if (Scope == PrevScope && PrevInlinedAt == InlinedAt) {
        PrevMI = MInsn;
        continue;
      }

      // Ignore DBG_VALUE. It does not contribute any instruction in output.
      if (MInsn->isDebugValue())
        continue;

      if (RangeBeginMI) {
        // If we have alread seen a beginning of a instruction range and
        // current instruction scope does not match scope of first instruction
        // in this range then create a new instruction range.
        DbgRange R(RangeBeginMI, PrevMI);
        MI2ScopeMap[RangeBeginMI] = getOrCreateDbgScope(PrevScope,
                                                        PrevInlinedAt);
        MIRanges.push_back(R);
      }

      // This is a beginning of a new instruction range.
      RangeBeginMI = MInsn;

      // Reset previous markers.
      PrevMI = MInsn;
      PrevScope = Scope;
      PrevInlinedAt = InlinedAt;
    }
  }

  // Create last instruction range.
  if (RangeBeginMI && PrevMI && PrevScope) {
    DbgRange R(RangeBeginMI, PrevMI);
    MIRanges.push_back(R);
    MI2ScopeMap[RangeBeginMI] = getOrCreateDbgScope(PrevScope, PrevInlinedAt);
  }

  if (!CurrentFnDbgScope)
    return false;

  calculateDominanceGraph(CurrentFnDbgScope);
  if (PrintDbgScope)
    printDbgScopeInfo(Ctx, Asm->MF, MI2ScopeMap);

  // Find ranges of instructions covered by each DbgScope;
  DbgScope *PrevDbgScope = NULL;
  for (SmallVector<DbgRange, 4>::const_iterator RI = MIRanges.begin(),
         RE = MIRanges.end(); RI != RE; ++RI) {
    const DbgRange &R = *RI;
    DbgScope *S = MI2ScopeMap.lookup(R.first);
    assert (S && "Lost DbgScope for a machine instruction!");
    if (PrevDbgScope && !PrevDbgScope->dominates(S))
      PrevDbgScope->closeInsnRange(S);
    S->openInsnRange(R.first);
    S->extendInsnRange(R.second);
    PrevDbgScope = S;
  }

  if (PrevDbgScope)
    PrevDbgScope->closeInsnRange();

  identifyScopeMarkers();

  return !DbgScopeMap.empty();
}

/// identifyScopeMarkers() -
/// Each DbgScope has first instruction and last instruction to mark beginning
/// and end of a scope respectively. Create an inverse map that list scopes
/// starts (and ends) with an instruction. One instruction may start (or end)
/// multiple scopes. Ignore scopes that are not reachable.
void DwarfDebug::identifyScopeMarkers() {
  SmallVector<DbgScope *, 4> WorkList;
  WorkList.push_back(CurrentFnDbgScope);
  while (!WorkList.empty()) {
    DbgScope *S = WorkList.pop_back_val();

    const SmallVector<DbgScope *, 4> &Children = S->getScopes();
    if (!Children.empty())
      for (SmallVector<DbgScope *, 4>::const_iterator SI = Children.begin(),
             SE = Children.end(); SI != SE; ++SI)
        WorkList.push_back(*SI);

    if (S->isAbstractScope())
      continue;

    const SmallVector<DbgRange, 4> &Ranges = S->getRanges();
    if (Ranges.empty())
      continue;
    for (SmallVector<DbgRange, 4>::const_iterator RI = Ranges.begin(),
           RE = Ranges.end(); RI != RE; ++RI) {
      assert(RI->first && "DbgRange does not have first instruction!");
      assert(RI->second && "DbgRange does not have second instruction!");
      requestLabelBeforeInsn(RI->first);
      requestLabelAfterInsn(RI->second);
    }
  }
}

/// FindFirstDebugLoc - Find the first debug location in the function. This
/// is intended to be an approximation for the source position of the
/// beginning of the function.
static DebugLoc FindFirstDebugLoc(const MachineFunction *MF) {
  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
       I != E; ++I)
    for (MachineBasicBlock::const_iterator MBBI = I->begin(), MBBE = I->end();
         MBBI != MBBE; ++MBBI) {
      DebugLoc DL = MBBI->getDebugLoc();
      if (!DL.isUnknown())
        return DL;
    }
  return DebugLoc();
}

/// beginFunction - Gather pre-function debug information.  Assumes being
/// emitted immediately after the function entry point.
void DwarfDebug::beginFunction(const MachineFunction *MF) {
  if (!MMI->hasDebugInfo()) return;
  if (!extractScopeInformation()) return;

  FunctionBeginSym = Asm->GetTempSymbol("func_begin",
                                        Asm->getFunctionNumber());
  // Assumes in correct section after the entry point.
  Asm->OutStreamer.EmitLabel(FunctionBeginSym);

  // Emit label for the implicitly defined dbg.stoppoint at the start of the
  // function.
  DebugLoc FDL = FindFirstDebugLoc(MF);
  if (FDL.isUnknown()) return;

  const MDNode *Scope = FDL.getScope(MF->getFunction()->getContext());
  const MDNode *TheScope = 0;

  DISubprogram SP = getDISubprogram(Scope);
  unsigned Line, Col;
  if (SP.Verify()) {
    Line = SP.getLineNumber();
    Col = 0;
    TheScope = SP;
  } else {
    Line = FDL.getLine();
    Col = FDL.getCol();
    TheScope = Scope;
  }

  recordSourceLine(Line, Col, TheScope);

  assert(UserVariables.empty() && DbgValues.empty() && "Maps weren't cleaned");

  /// ProcessedArgs - Collection of arguments already processed.
  SmallPtrSet<const MDNode *, 8> ProcessedArgs;

  const TargetRegisterInfo *TRI = Asm->TM.getRegisterInfo();

  /// LiveUserVar - Map physreg numbers to the MDNode they contain.
  std::vector<const MDNode*> LiveUserVar(TRI->getNumRegs());

  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
       I != E; ++I) {
    bool AtBlockEntry = true;
    for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
         II != IE; ++II) {
      const MachineInstr *MI = II;

      if (MI->isDebugValue()) {
        assert (MI->getNumOperands() > 1 && "Invalid machine instruction!");

        // Keep track of user variables.
        const MDNode *Var =
          MI->getOperand(MI->getNumOperands() - 1).getMetadata();

        // Variable is in a register, we need to check for clobbers.
        if (isDbgValueInDefinedReg(MI))
          LiveUserVar[MI->getOperand(0).getReg()] = Var;

        // Check the history of this variable.
        SmallVectorImpl<const MachineInstr*> &History = DbgValues[Var];
        if (History.empty()) {
          UserVariables.push_back(Var);
          // The first mention of a function argument gets the FunctionBeginSym
          // label, so arguments are visible when breaking at function entry.
          DIVariable DV(Var);
          if (DV.Verify() && DV.getTag() == dwarf::DW_TAG_arg_variable &&
              DISubprogram(getDISubprogram(DV.getContext()))
                .describes(MF->getFunction()))
            LabelsBeforeInsn[MI] = FunctionBeginSym;
        } else {
          // We have seen this variable before. Try to coalesce DBG_VALUEs.
          const MachineInstr *Prev = History.back();
          if (Prev->isDebugValue()) {
            // Coalesce identical entries at the end of History.
            if (History.size() >= 2 &&
                Prev->isIdenticalTo(History[History.size() - 2]))
              History.pop_back();

            // Terminate old register assignments that don't reach MI;
            MachineFunction::const_iterator PrevMBB = Prev->getParent();
            if (PrevMBB != I && (!AtBlockEntry || llvm::next(PrevMBB) != I) &&
                isDbgValueInDefinedReg(Prev)) {
              // Previous register assignment needs to terminate at the end of
              // its basic block.
              MachineBasicBlock::const_iterator LastMI =
                PrevMBB->getLastNonDebugInstr();
              if (LastMI == PrevMBB->end())
                // Drop DBG_VALUE for empty range.
                History.pop_back();
              else {
                // Terminate after LastMI.
                History.push_back(LastMI);
              }
            }
          }
        }
        History.push_back(MI);
      } else {
        // Not a DBG_VALUE instruction.
        if (!MI->isLabel())
          AtBlockEntry = false;

        // Check if the instruction clobbers any registers with debug vars.
        for (MachineInstr::const_mop_iterator MOI = MI->operands_begin(),
               MOE = MI->operands_end(); MOI != MOE; ++MOI) {
          if (!MOI->isReg() || !MOI->isDef() || !MOI->getReg())
            continue;
          for (const unsigned *AI = TRI->getOverlaps(MOI->getReg());
               unsigned Reg = *AI; ++AI) {
            const MDNode *Var = LiveUserVar[Reg];
            if (!Var)
              continue;
            // Reg is now clobbered.
            LiveUserVar[Reg] = 0;

            // Was MD last defined by a DBG_VALUE referring to Reg?
            DbgValueHistoryMap::iterator HistI = DbgValues.find(Var);
            if (HistI == DbgValues.end())
              continue;
            SmallVectorImpl<const MachineInstr*> &History = HistI->second;
            if (History.empty())
              continue;
            const MachineInstr *Prev = History.back();
            // Sanity-check: Register assignments are terminated at the end of
            // their block.
            if (!Prev->isDebugValue() || Prev->getParent() != MI->getParent())
              continue;
            // Is the variable still in Reg?
            if (!isDbgValueInDefinedReg(Prev) ||
                Prev->getOperand(0).getReg() != Reg)
              continue;
            // Var is clobbered. Make sure the next instruction gets a label.
            History.push_back(MI);
          }
        }
      }
    }
  }

  for (DbgValueHistoryMap::iterator I = DbgValues.begin(), E = DbgValues.end();
       I != E; ++I) {
    SmallVectorImpl<const MachineInstr*> &History = I->second;
    if (History.empty())
      continue;

    // Make sure the final register assignments are terminated.
    const MachineInstr *Prev = History.back();
    if (Prev->isDebugValue() && isDbgValueInDefinedReg(Prev)) {
      const MachineBasicBlock *PrevMBB = Prev->getParent();
      MachineBasicBlock::const_iterator LastMI = PrevMBB->getLastNonDebugInstr();
      if (LastMI == PrevMBB->end())
        // Drop DBG_VALUE for empty range.
        History.pop_back();
      else {
        // Terminate after LastMI.
        History.push_back(LastMI);
      }
    }
    // Request labels for the full history.
    for (unsigned i = 0, e = History.size(); i != e; ++i) {
      const MachineInstr *MI = History[i];
      if (MI->isDebugValue())
        requestLabelBeforeInsn(MI);
      else
        requestLabelAfterInsn(MI);
    }
  }

  PrevInstLoc = DebugLoc();
  PrevLabel = FunctionBeginSym;
}

/// endFunction - Gather and emit post-function debug information.
///
void DwarfDebug::endFunction(const MachineFunction *MF) {
  if (!MMI->hasDebugInfo() || DbgScopeMap.empty()) return;

  if (CurrentFnDbgScope) {

    // Define end label for subprogram.