DwarfDebug.cpp

  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));
  }

  // Emit common frame information.
  emitCommonDebugFrame();

  // Emit function debug frame information
  for (std::vector<FunctionDebugFrameInfo>::iterator I = DebugFrames.begin(),
         E = DebugFrames.end(); I != E; ++I)
    emitFunctionDebugFrame(*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 source line correspondence into a debug line section.
  emitDebugLines();

  // 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();
  
  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;
}

/// 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);
    Scope->addVariable(RegVar);
    if (AbsDbgVariable) {
      recordVariableFrameIndex(AbsDbgVariable, VP.first);
      VarToAbstractVarMap[RegVar] = AbsDbgVariable;
    }
  }
}

/// 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);

  SmallVector<const MachineInstr *, 8> DbgValues;
  // Collect variable information from DBG_VALUE machine instructions;
  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;
      if (!MInsn->isDebugValue())
        continue;

      // Ignore Undef values.
      if (MInsn->getOperand(0).isReg() && !MInsn->getOperand(0).getReg())
        continue;

      DbgValues.push_back(MInsn);
    }

  for(SmallVector<const MachineInstr *, 8>::iterator I = DbgValues.begin(),
        E = DbgValues.end(); I != E; ++I) {
    const MachineInstr *MInsn = *I;

    DIVariable DV(MInsn->getOperand(MInsn->getNumOperands() - 1).getMetadata());
    if (Processed.count(DV) != 0)
      continue;

    DbgScope *Scope = findDbgScope(MInsn);
    if (!Scope && DV.getTag() == dwarf::DW_TAG_arg_variable)
      Scope = CurrentFnDbgScope;
    // If variable scope is not found then skip this variable.
    if (!Scope)
      continue;

    Processed.insert(DV);
    DbgVariable *RegVar = new DbgVariable(DV);
    DbgVariableToDbgInstMap[RegVar] = MInsn;
    Scope->addVariable(RegVar);
    if (DV.getTag() != dwarf::DW_TAG_arg_variable)
      DbgValueStartMap[MInsn] = RegVar;
    if (DbgVariable *AbsVar = findAbstractVariable(DV, MInsn->getDebugLoc())) {
      DbgVariableToDbgInstMap[AbsVar] = MInsn;
      VarToAbstractVarMap[RegVar] = AbsVar;
    }
  }

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

}

/// beginScope - Process beginning of a scope.
void DwarfDebug::beginScope(const MachineInstr *MI) {
  // Check location.
  DebugLoc DL = MI->getDebugLoc();
  if (DL.isUnknown() && !UnknownLocations)
    return;
 
  DbgVariable *LocalVar = NULL;
  if (MI->isDebugValue()) {
    DenseMap<const MachineInstr *, DbgVariable *>::iterator DI
      = DbgValueStartMap.find(MI);
    if (DI != DbgValueStartMap.end())
      LocalVar = DI->second;
  }

  MCSymbol *Label = NULL;
  if (DL == PrevInstLoc)
    Label = PrevLabel;
  // Do not emit line number entry for arguments.
  else if (!MI->isDebugValue() || LocalVar) {
    const MDNode *Scope = 0;
    if (DL.isUnknown() == false) {
      Scope = DL.getScope(Asm->MF->getFunction()->getContext());
      // FIXME: Should only verify each scope once!
      if (!DIScope(Scope).Verify())
        return;
    } 
    // else ...
    // This instruction has no debug location. If the preceding instruction
    // did, emit debug location information to indicate that the debug
    // location is now unknown.
    
    Label = recordSourceLine(DL.getLine(), DL.getCol(), Scope);
    PrevInstLoc = DL;
    PrevLabel = Label;
  }

  // If this instruction begins a scope then note down corresponding label
  // even if previous label is reused.
  if (InsnsBeginScopeSet.count(MI) != 0)
    LabelsBeforeInsn[MI] = Label;
  
  // If this is a DBG_VALUE instruction then record label to identify variable.
  if (LocalVar)
    DbgVariableLabelsMap[LocalVar] = Label;
}

/// endScope - Process end of a scope.
void DwarfDebug::endScope(const MachineInstr *MI) {
  if (InsnsEndScopeSet.count(MI) != 0) {
    // Emit a label if this instruction ends a scope.
    MCSymbol *Label = MMI->getContext().CreateTempSymbol();
    Asm->OutStreamer.EmitLabel(Label);
    LabelsAfterInsn[MI] = Label;
  }
}

/// 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();
      if (SPName == Asm->MF->getFunction()->getName())
        CurrentFnDbgScope = WScope;
    }
    
    return WScope;
  }

  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;
  getOrCreateAbstractScope(Scope);

  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) {
  if (MInsn->isDebugValue())
    return false;
  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;
      }

      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!");      
      InsnsBeginScopeSet.insert(RI->first);
      InsnsEndScopeSet.insert(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;
  
  collectVariableInfo(MF);

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

/// 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.
    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("func_end",
                                                  Asm->getFunctionNumber()));
    
    // Get function line info.
    if (!Lines.empty()) {
      // Get section line info.
      unsigned ID = SectionMap.insert(Asm->getCurrentSection());
      if (SectionSourceLines.size() < ID) SectionSourceLines.resize(ID);
      std::vector<SrcLineInfo> &SectionLineInfos = SectionSourceLines[ID-1];
      // Append the function info to section info.
      SectionLineInfos.insert(SectionLineInfos.end(),
                              Lines.begin(), Lines.end());
    }
    
    // Construct abstract scopes.
    for (SmallVector<DbgScope *, 4>::iterator AI = AbstractScopesList.begin(),
           AE = AbstractScopesList.end(); AI != AE; ++AI)
      constructScopeDIE(*AI);
    
    DIE *CurFnDIE = constructScopeDIE(CurrentFnDbgScope);
    
    if (!DisableFramePointerElim(*MF))
      addUInt(CurFnDIE, dwarf::DW_AT_APPLE_omit_frame_ptr, 
              dwarf::DW_FORM_flag, 1);


    DebugFrames.push_back(FunctionDebugFrameInfo(Asm->getFunctionNumber(),
                                                 MMI->getFrameMoves()));
  }

  // Clear debug info
  CurrentFnDbgScope = NULL;
  DbgVariableToFrameIndexMap.clear();
  VarToAbstractVarMap.clear();
  DbgVariableToDbgInstMap.clear();
  DbgVariableLabelsMap.clear();
  DeleteContainerSeconds(DbgScopeMap);
  InsnsBeginScopeSet.clear();
  InsnsEndScopeSet.clear();
  DbgValueStartMap.clear();
  ConcreteScopes.clear();
  DeleteContainerSeconds(AbstractScopes);
  AbstractScopesList.clear();
  AbstractVariables.clear();
  LabelsBeforeInsn.clear();
  LabelsAfterInsn.clear();
  Lines.clear();
  PrevLabel = NULL;
}

/// recordVariableFrameIndex - Record a variable's index.
void DwarfDebug::recordVariableFrameIndex(const DbgVariable *V, int Index) {
  assert (V && "Invalid DbgVariable!");
  DbgVariableToFrameIndexMap[V] = Index;
}

/// findVariableFrameIndex - Return true if frame index for the variable
/// is found. Update FI to hold value of the index.
bool DwarfDebug::findVariableFrameIndex(const DbgVariable *V, int *FI) {
  assert (V && "Invalid DbgVariable!");
  DenseMap<const DbgVariable *, int>::iterator I =
    DbgVariableToFrameIndexMap.find(V);
  if (I == DbgVariableToFrameIndexMap.end())
    return false;
  *FI = I->second;
  return true;
}

/// findVariableLabel - Find MCSymbol for the variable.
const MCSymbol *DwarfDebug::findVariableLabel(const DbgVariable *V) {
  DenseMap<const DbgVariable *, const MCSymbol *>::iterator I
    = DbgVariableLabelsMap.find(V);
  if (I == DbgVariableLabelsMap.end())
    return NULL;
  else return I->second;
}

/// findDbgScope - Find DbgScope for the debug loc attached with an 
/// instruction.
DbgScope *DwarfDebug::findDbgScope(const MachineInstr *MInsn) {
  DbgScope *Scope = NULL;
  LLVMContext &Ctx = 
    MInsn->getParent()->getParent()->getFunction()->getContext();
  DebugLoc DL = MInsn->getDebugLoc();

  if (DL.isUnknown()) 
    return Scope;

  if (const MDNode *IA = DL.getInlinedAt(Ctx))
    Scope = ConcreteScopes.lookup(IA);
  if (Scope == 0)
    Scope = DbgScopeMap.lookup(DL.getScope(Ctx));
    
  return Scope;
}


/// recordSourceLine - Register a source line with debug info. Returns the
/// unique label that was emitted and which provides correspondence to
/// the source line list.
MCSymbol *DwarfDebug::recordSourceLine(unsigned Line, unsigned Col, const MDNode *S) {
  StringRef Dir;
  StringRef Fn;

  unsigned Src = 1;
  if (S) {
    DIDescriptor Scope(S);

    if (Scope.isCompileUnit()) {
      DICompileUnit CU(S);
      Dir = CU.getDirectory();
      Fn = CU.getFilename();
    } else if (Scope.isSubprogram()) {
      DISubprogram SP(S);
      Dir = SP.getDirectory();
      Fn = SP.getFilename();
    } else if (Scope.isLexicalBlock()) {
      DILexicalBlock DB(S);
      Dir = DB.getDirectory();
      Fn = DB.getFilename();
    } else
      assert(0 && "Unexpected scope info");

    Src = GetOrCreateSourceID(Dir, Fn);
  }

  MCSymbol *Label = MMI->getContext().CreateTempSymbol();
  Lines.push_back(SrcLineInfo(Line, Col, Src, Label));

  Asm->OutStreamer.EmitLabel(Label);
  return Label;
}

//===----------------------------------------------------------------------===//
// Emit Methods
//===----------------------------------------------------------------------===//

/// computeSizeAndOffset - Compute the size and offset of a DIE.
///
unsigned
DwarfDebug::computeSizeAndOffset(DIE *Die, unsigned Offset, bool Last) {
  // Get the children.
  const std::vector<DIE *> &Children = Die->getChildren();

  // If not last sibling and has children then add sibling offset attribute.
  if (!Last && !Children.empty())
    Die->addSiblingOffset(DIEValueAllocator);

  // Record the abbreviation.
  assignAbbrevNumber(Die->getAbbrev());

  // Get the abbreviation for this DIE.
  unsigned AbbrevNumber = Die->getAbbrevNumber();
  const DIEAbbrev *Abbrev = Abbreviations[AbbrevNumber - 1];

  // Set DIE offset
  Die->setOffset(Offset);

  // Start the size with the size of abbreviation code.
  Offset += MCAsmInfo::getULEB128Size(AbbrevNumber);

  const SmallVector<DIEValue*, 32> &Values = Die->getValues();
  const SmallVector<DIEAbbrevData, 8> &AbbrevData = Abbrev->getData();

  // Size the DIE attribute values.
  for (unsigned i = 0, N = Values.size(); i < N; ++i)
    // Size attribute value.
    Offset += Values[i]->SizeOf(Asm, AbbrevData[i].getForm());

  // Size the DIE children if any.
  if (!Children.empty()) {
    assert(Abbrev->getChildrenFlag() == dwarf::DW_CHILDREN_yes &&
           "Children flag not set");

    for (unsigned j = 0, M = Children.size(); j < M; ++j)
      Offset = computeSizeAndOffset(Children[j], Offset, (j + 1) == M);

    // End of children marker.
    Offset += sizeof(int8_t);
  }

  Die->setSize(Offset - Die->getOffset());
  return Offset;
}

/// computeSizeAndOffsets - Compute the size and offset of all the DIEs.
///
void DwarfDebug::computeSizeAndOffsets() {
  unsigned PrevOffset = 0;
  for (DenseMap<const MDNode *, CompileUnit *>::iterator I = CUMap.begin(),
         E = CUMap.end(); I != E; ++I) {
    // Compute size of compile unit header.
    static unsigned Offset = PrevOffset +
      sizeof(int32_t) + // Length of Compilation Unit Info
      sizeof(int16_t) + // DWARF version number
      sizeof(int32_t) + // Offset Into Abbrev. Section
      sizeof(int8_t);   // Pointer Size (in bytes)
    computeSizeAndOffset(I->second->getCUDie(), Offset, true);
    PrevOffset = Offset;
  }
}

/// EmitSectionSym - Switch to the specified MCSection and emit an assembler
/// temporary label to it if SymbolStem is specified.
static MCSymbol *EmitSectionSym(AsmPrinter *Asm, const MCSection *Section,
                                const char *SymbolStem = 0) {
  Asm->OutStreamer.SwitchSection(Section);
  if (!SymbolStem) return 0;
  
  MCSymbol *TmpSym = Asm->GetTempSymbol(SymbolStem);
  Asm->OutStreamer.EmitLabel(TmpSym);
  return TmpSym;
}

/// EmitSectionLabels - Emit initial Dwarf sections with a label at
/// the start of each one.
void DwarfDebug::EmitSectionLabels() {
  const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();

  // Dwarf sections base addresses.
  if (Asm->MAI->doesDwarfRequireFrameSection()) {
    DwarfFrameSectionSym =
      EmitSectionSym(Asm, TLOF.getDwarfFrameSection(), "section_debug_frame");
   }

  DwarfInfoSectionSym = 
    EmitSectionSym(Asm, TLOF.getDwarfInfoSection(), "section_info");
  DwarfAbbrevSectionSym = 
    EmitSectionSym(Asm, TLOF.getDwarfAbbrevSection(), "section_abbrev");
  EmitSectionSym(Asm, TLOF.getDwarfARangesSection());
  
  if (const MCSection *MacroInfo = TLOF.getDwarfMacroInfoSection())
    EmitSectionSym(Asm, MacroInfo);

  EmitSectionSym(Asm, TLOF.getDwarfLineSection());
  EmitSectionSym(Asm, TLOF.getDwarfLocSection());
  EmitSectionSym(Asm, TLOF.getDwarfPubNamesSection());
  EmitSectionSym(Asm, TLOF.getDwarfPubTypesSection());
  DwarfStrSectionSym = 
    EmitSectionSym(Asm, TLOF.getDwarfStrSection(), "section_str");
  DwarfDebugRangeSectionSym = EmitSectionSym(Asm, TLOF.getDwarfRangesSection(),
                                             "debug_range");

  TextSectionSym = EmitSectionSym(Asm, TLOF.getTextSection(), "text_begin");
  EmitSectionSym(Asm, TLOF.getDataSection());
}

/// emitDIE - Recusively Emits a debug information entry.
///
void DwarfDebug::emitDIE(DIE *Die) {
  // Get the abbreviation for this DIE.
  unsigned AbbrevNumber = Die->getAbbrevNumber();
  const DIEAbbrev *Abbrev = Abbreviations[AbbrevNumber - 1];

  // Emit the code (index) for the abbreviation.
  if (Asm->isVerbose())
    Asm->OutStreamer.AddComment("Abbrev [" + Twine(AbbrevNumber) + "] 0x" +
                                Twine::utohexstr(Die->getOffset()) + ":0x" +
                                Twine::utohexstr(Die->getSize()) + " " +
                                dwarf::TagString(Abbrev->getTag()));
  Asm->EmitULEB128(AbbrevNumber);

  const SmallVector<DIEValue*, 32> &Values = Die->getValues();
  const SmallVector<DIEAbbrevData, 8> &AbbrevData = Abbrev->getData();

  // Emit the DIE attribute values.
  for (unsigned i = 0, N = Values.size(); i < N; ++i) {
    unsigned Attr = AbbrevData[i].getAttribute();
    unsigned Form = AbbrevData[i].getForm();
    assert(Form && "Too many attributes for DIE (check abbreviation)");

    if (Asm->isVerbose())
      Asm->OutStreamer.AddComment(dwarf::AttributeString(Attr));
    
    switch (Attr) {
    case dwarf::DW_AT_sibling:
      Asm->EmitInt32(Die->getSiblingOffset());
      break;
    case dwarf::DW_AT_abstract_origin: {
      DIEEntry *E = cast<DIEEntry>(Values[i]);
      DIE *Origin = E->getEntry();
      unsigned Addr = Origin->getOffset();
      Asm->EmitInt32(Addr);
      break;
    }
    case dwarf::DW_AT_ranges: {
      // DW_AT_range Value encodes offset in debug_range section.
      DIEInteger *V = cast<DIEInteger>(Values[i]);
      Asm->EmitLabelOffsetDifference(DwarfDebugRangeSectionSym,
                                     V->getValue(),
                                     DwarfDebugRangeSectionSym,
                                     4);
      break;
    }
    default:
      // Emit an attribute using the defined form.
      Values[i]->EmitValue(Asm, Form);
      break;
    }
  }

  // Emit the DIE children if any.
  if (Abbrev->getChildrenFlag() == dwarf::DW_CHILDREN_yes) {
    const std::vector<DIE *> &Children = Die->getChildren();

    for (unsigned j = 0, M = Children.size(); j < M; ++j)
      emitDIE(Children[j]);

    if (Asm->isVerbose())
      Asm->OutStreamer.AddComment("End Of Children Mark");
    Asm->EmitInt8(0);
  }
}

/// emitDebugInfo - Emit the debug info section.
///
void DwarfDebug::emitDebugInfo() {
  // Start debug info section.
  Asm->OutStreamer.SwitchSection(
                            Asm->getObjFileLowering().getDwarfInfoSection());
  for (DenseMap<const MDNode *, CompileUnit *>::iterator I = CUMap.begin(),
         E = CUMap.end(); I != E; ++I) {
    CompileUnit *TheCU = I->second;
    DIE *Die = TheCU->getCUDie();
    
    // Emit the compile units header.
    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("info_begin",
                                                  TheCU->getID()));
    
    // Emit size of content not including length itself
    unsigned ContentSize = Die->getSize() +
      sizeof(int16_t) + // DWARF version number
      sizeof(int32_t) + // Offset Into Abbrev. Section
      sizeof(int8_t) +  // Pointer Size (in bytes)
      sizeof(int32_t);  // FIXME - extra pad for gdb bug.
    
    Asm->OutStreamer.AddComment("Length of Compilation Unit Info");
    Asm->EmitInt32(ContentSize);
    Asm->OutStreamer.AddComment("DWARF version number");
    Asm->EmitInt16(dwarf::DWARF_VERSION);
    Asm->OutStreamer.AddComment("Offset Into Abbrev. Section");
    Asm->EmitSectionOffset(Asm->GetTempSymbol("abbrev_begin"),
                           DwarfAbbrevSectionSym);
    Asm->OutStreamer.AddComment("Address Size (in bytes)");
    Asm->EmitInt8(Asm->getTargetData().getPointerSize());
    
    emitDIE(Die);
    // FIXME - extra padding for gdb bug.
    Asm->OutStreamer.AddComment("4 extra padding bytes for GDB");
    Asm->EmitInt8(0);
    Asm->EmitInt8(0);
    Asm->EmitInt8(0);
    Asm->EmitInt8(0);
    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("info_end", TheCU->getID()));
  }
}

/// emitAbbreviations - Emit the abbreviation section.
///
void DwarfDebug::emitAbbreviations() const {
  // Check to see if it is worth the effort.
  if (!Abbreviations.empty()) {
    // Start the debug abbrev section.
    Asm->OutStreamer.SwitchSection(
                            Asm->getObjFileLowering().getDwarfAbbrevSection());

    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("abbrev_begin"));

    // For each abbrevation.
    for (unsigned i = 0, N = Abbreviations.size(); i < N; ++i) {
      // Get abbreviation data
      const DIEAbbrev *Abbrev = Abbreviations[i];

      // Emit the abbrevations code (base 1 index.)
      Asm->EmitULEB128(Abbrev->getNumber(), "Abbreviation Code");

      // Emit the abbreviations data.
      Abbrev->Emit(Asm);
    }

    // Mark end of abbreviations.
    Asm->EmitULEB128(0, "EOM(3)");

    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("abbrev_end"));
  }
}

/// emitEndOfLineMatrix - Emit the last address of the section and the end of
/// the line matrix.
///
void DwarfDebug::emitEndOfLineMatrix(unsigned SectionEnd) {
  // Define last address of section.
  Asm->OutStreamer.AddComment("Extended Op");
  Asm->EmitInt8(0);
  
  Asm->OutStreamer.AddComment("Op size");
  Asm->EmitInt8(Asm->getTargetData().getPointerSize() + 1);
  Asm->OutStreamer.AddComment("DW_LNE_set_address");
  Asm->EmitInt8(dwarf::DW_LNE_set_address);

  Asm->OutStreamer.AddComment("Section end label");

  Asm->OutStreamer.EmitSymbolValue(Asm->GetTempSymbol("section_end",SectionEnd),
                                   Asm->getTargetData().getPointerSize(),
                                   0/*AddrSpace*/);

  // Mark end of matrix.
  Asm->OutStreamer.AddComment("DW_LNE_end_sequence");
  Asm->EmitInt8(0);
  Asm->EmitInt8(1);
  Asm->EmitInt8(1);
}

/// emitDebugLines - Emit source line information.
///
void DwarfDebug::emitDebugLines() {
  // If the target is using .loc/.file, the assembler will be emitting the
  // .debug_line table automatically.
  if (Asm->MAI->hasDotLocAndDotFile())
    return;

  // Minimum line delta, thus ranging from -10..(255-10).
  const int MinLineDelta = -(dwarf::DW_LNS_fixed_advance_pc + 1);
  // Maximum line delta, thus ranging from -10..(255-10).
  const int MaxLineDelta = 255 + MinLineDelta;

  // Start the dwarf line section.
  Asm->OutStreamer.SwitchSection(
                            Asm->getObjFileLowering().getDwarfLineSection());

  // Construct the section header.
  Asm->OutStreamer.AddComment("Length of Source Line Info");
  Asm->EmitLabelDifference(Asm->GetTempSymbol("line_end"),
                           Asm->GetTempSymbol("line_begin"), 4);
  Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("line_begin"));

  Asm->OutStreamer.AddComment("DWARF version number");
  Asm->EmitInt16(dwarf::DWARF_VERSION); 

  Asm->OutStreamer.AddComment("Prolog Length");
  Asm->EmitLabelDifference(Asm->GetTempSymbol("line_prolog_end"),
                           Asm->GetTempSymbol("line_prolog_begin"), 4);
  Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("line_prolog_begin"));

  Asm->OutStreamer.AddComment("Minimum Instruction Length");
  Asm->EmitInt8(1);
  Asm->OutStreamer.AddComment("Default is_stmt_start flag");
  Asm->EmitInt8(1);
  Asm->OutStreamer.AddComment("Line Base Value (Special Opcodes)");
  Asm->EmitInt8(MinLineDelta);
  Asm->OutStreamer.AddComment("Line Range Value (Special Opcodes)");
  Asm->EmitInt8(MaxLineDelta);
  Asm->OutStreamer.AddComment("Special Opcode Base");
  Asm->EmitInt8(-MinLineDelta);