DwarfDebug.cpp

//===-- llvm/CodeGen/DwarfDebug.cpp - Dwarf Debug Framework ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing dwarf debug info into asm files.
//
//===----------------------------------------------------------------------===//

#include "DwarfDebug.h"
#include "llvm/Module.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/Support/Timer.h"
#include "llvm/System/Path.h"
#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetFrameInfo.h"
#include <ostream>
using namespace llvm;

static TimerGroup &getDwarfTimerGroup() {
  static TimerGroup DwarfTimerGroup("Dwarf Debugging");
  return DwarfTimerGroup;
}

//===----------------------------------------------------------------------===//

/// Configuration values for initial hash set sizes (log2).
///
static const unsigned InitDiesSetSize          = 9; // log2(512)
static const unsigned InitAbbreviationsSetSize = 9; // log2(512)
static const unsigned InitValuesSetSize        = 9; // log2(512)

namespace llvm {

//===----------------------------------------------------------------------===//
/// CompileUnit - This dwarf writer support class manages information associate
/// with a source file.
class VISIBILITY_HIDDEN CompileUnit {
  /// ID - File identifier for source.
  ///
  unsigned ID;

  /// Die - Compile unit debug information entry.
  ///
  DIE *Die;

  /// GVToDieMap - Tracks the mapping of unit level debug informaton
  /// variables to debug information entries.
  std::map<GlobalVariable *, DIE *> GVToDieMap;

  /// GVToDIEEntryMap - Tracks the mapping of unit level debug informaton
  /// descriptors to debug information entries using a DIEEntry proxy.
  std::map<GlobalVariable *, DIEEntry *> GVToDIEEntryMap;

  /// Globals - A map of globally visible named entities for this unit.
  ///
  StringMap<DIE*> Globals;

  /// DiesSet - Used to uniquely define dies within the compile unit.
  ///
  FoldingSet<DIE> DiesSet;
public:
  CompileUnit(unsigned I, DIE *D)
    : ID(I), Die(D), GVToDieMap(),
      GVToDIEEntryMap(), Globals(), DiesSet(InitDiesSetSize)
  {}

  ~CompileUnit() {
    delete Die;
  }

  // Accessors.
  unsigned getID()           const { return ID; }
  DIE* getDie()              const { return Die; }
  StringMap<DIE*> &getGlobals() { return Globals; }

  /// hasContent - Return true if this compile unit has something to write out.
  ///
  bool hasContent() const {
    return !Die->getChildren().empty();
  }

  /// AddGlobal - Add a new global entity to the compile unit.
  ///
  void AddGlobal(const std::string &Name, DIE *Die) {
    Globals[Name] = Die;
  }

  /// getDieMapSlotFor - Returns the debug information entry map slot for the
  /// specified debug variable.
  DIE *&getDieMapSlotFor(GlobalVariable *GV) {
    return GVToDieMap[GV];
  }

  /// getDIEEntrySlotFor - Returns the debug information entry proxy slot for the
  /// specified debug variable.
  DIEEntry *&getDIEEntrySlotFor(GlobalVariable *GV) {
    return GVToDIEEntryMap[GV];
  }

  /// AddDie - Adds or interns the DIE to the compile unit.
  ///
  DIE *AddDie(DIE &Buffer) {
    FoldingSetNodeID ID;
    Buffer.Profile(ID);
    void *Where;
    DIE *Die = DiesSet.FindNodeOrInsertPos(ID, Where);

    if (!Die) {
      Die = new DIE(Buffer);
      DiesSet.InsertNode(Die, Where);
      this->Die->AddChild(Die);
      Buffer.Detach();
    }

    return Die;
  }
};

//===----------------------------------------------------------------------===//
/// DbgVariable - This class is used to track local variable information.
///
class VISIBILITY_HIDDEN DbgVariable {
  DIVariable Var;                    // Variable Descriptor.
  unsigned FrameIndex;               // Variable frame index.
public:
  DbgVariable(DIVariable V, unsigned I) : Var(V), FrameIndex(I)  {}

  // Accessors.
  DIVariable getVariable()  const { return Var; }
  unsigned getFrameIndex() const { return FrameIndex; }
};

//===----------------------------------------------------------------------===//
/// DbgScope - This class is used to track scope information.
///
class DbgConcreteScope;
class VISIBILITY_HIDDEN DbgScope {
  DbgScope *Parent;                   // Parent to this scope.
  DIDescriptor Desc;                  // Debug info descriptor for scope.
                                      // Either subprogram or block.
  unsigned StartLabelID;              // Label ID of the beginning of scope.
  unsigned EndLabelID;                // Label ID of the end of scope.
  SmallVector<DbgScope *, 4> Scopes;  // Scopes defined in scope.
  SmallVector<DbgVariable *, 8> Variables;// Variables declared in scope.
  SmallVector<DbgConcreteScope *, 8> ConcreteInsts;// Concrete insts of funcs.
public:
  DbgScope(DbgScope *P, DIDescriptor D)
    : Parent(P), Desc(D), StartLabelID(0), EndLabelID(0) {}
  virtual ~DbgScope();

  // Accessors.
  DbgScope *getParent()          const { return Parent; }
  DIDescriptor getDesc()         const { return Desc; }
  unsigned getStartLabelID()     const { return StartLabelID; }
  unsigned getEndLabelID()       const { return EndLabelID; }
  SmallVector<DbgScope *, 4> &getScopes() { return Scopes; }
  SmallVector<DbgVariable *, 8> &getVariables() { return Variables; }
  SmallVector<DbgConcreteScope*,8> &getConcreteInsts() { return ConcreteInsts; }
  void setStartLabelID(unsigned S) { StartLabelID = S; }
  void setEndLabelID(unsigned E)   { EndLabelID = E; }

  /// AddScope - Add a scope to the scope.
  ///
  void AddScope(DbgScope *S) { Scopes.push_back(S); }

  /// AddVariable - Add a variable to the scope.
  ///
  void AddVariable(DbgVariable *V) { Variables.push_back(V); }

  /// AddConcreteInst - Add a concrete instance to the scope.
  ///
  void AddConcreteInst(DbgConcreteScope *C) { ConcreteInsts.push_back(C); }

#ifndef NDEBUG
  void dump() const;
#endif
};

#ifndef NDEBUG
void DbgScope::dump() const {
  static unsigned IndentLevel = 0;
  std::string Indent(IndentLevel, ' ');

  cerr << Indent; Desc.dump();
  cerr << " [" << StartLabelID << ", " << EndLabelID << "]\n";

  IndentLevel += 2;

  for (unsigned i = 0, e = Scopes.size(); i != e; ++i)
    if (Scopes[i] != this)
      Scopes[i]->dump();

  IndentLevel -= 2;
}
#endif

//===----------------------------------------------------------------------===//
/// DbgConcreteScope - This class is used to track a scope that holds concrete
/// instance information.
///
class VISIBILITY_HIDDEN DbgConcreteScope : public DbgScope {
  CompileUnit *Unit;
  DIE *Die;                           // Debug info for this concrete scope.
public:
  DbgConcreteScope(DIDescriptor D) : DbgScope(NULL, D) {}

  // Accessors.
  DIE *getDie() const { return Die; }
  void setDie(DIE *D) { Die = D; }
};

DbgScope::~DbgScope() {
  for (unsigned i = 0, N = Scopes.size(); i < N; ++i)
    delete Scopes[i];
  for (unsigned j = 0, M = Variables.size(); j < M; ++j)
    delete Variables[j];
  for (unsigned k = 0, O = ConcreteInsts.size(); k < O; ++k)
    delete ConcreteInsts[k];
}

} // end llvm namespace

DwarfDebug::DwarfDebug(raw_ostream &OS, AsmPrinter *A, const TargetAsmInfo *T)
  : Dwarf(OS, A, T, "dbg"), MainCU(0),
    AbbreviationsSet(InitAbbreviationsSetSize), Abbreviations(),
    ValuesSet(InitValuesSetSize), Values(), StringPool(), SectionMap(),
    SectionSourceLines(), didInitial(false), shouldEmit(false),
    FunctionDbgScope(0), DebugTimer(0) {
  if (TimePassesIsEnabled)
    DebugTimer = new Timer("Dwarf Debug Writer",
                           getDwarfTimerGroup());
}
DwarfDebug::~DwarfDebug() {
  for (unsigned j = 0, M = Values.size(); j < M; ++j)
    delete Values[j];

  for (DenseMap<const GlobalVariable *, DbgScope *>::iterator
         I = AbstractInstanceRootMap.begin(),
         E = AbstractInstanceRootMap.end(); I != E;++I)
    delete I->second;

  delete DebugTimer;
}

/// AssignAbbrevNumber - Define a unique number for the abbreviation.
///
void DwarfDebug::AssignAbbrevNumber(DIEAbbrev &Abbrev) {
  // Profile the node so that we can make it unique.
  FoldingSetNodeID ID;
  Abbrev.Profile(ID);

  // Check the set for priors.
  DIEAbbrev *InSet = AbbreviationsSet.GetOrInsertNode(&Abbrev);

  // If it's newly added.
  if (InSet == &Abbrev) {
    // Add to abbreviation list.
    Abbreviations.push_back(&Abbrev);

    // Assign the vector position + 1 as its number.
    Abbrev.setNumber(Abbreviations.size());
  } else {
    // Assign existing abbreviation number.
    Abbrev.setNumber(InSet->getNumber());
  }
}

/// NewDIEEntry - Creates a new DIEEntry to be a proxy for a debug information
/// entry.
DIEEntry *DwarfDebug::NewDIEEntry(DIE *Entry) {
  DIEEntry *Value;

  if (Entry) {
    FoldingSetNodeID ID;
    DIEEntry::Profile(ID, Entry);
    void *Where;
    Value = static_cast<DIEEntry *>(ValuesSet.FindNodeOrInsertPos(ID, Where));

    if (Value) return Value;

    Value = new DIEEntry(Entry);
    ValuesSet.InsertNode(Value, Where);
  } else {
    Value = new DIEEntry(Entry);
  }

  Values.push_back(Value);
  return Value;
}

/// SetDIEEntry - Set a DIEEntry once the debug information entry is defined.
///
void DwarfDebug::SetDIEEntry(DIEEntry *Value, DIE *Entry) {
  Value->setEntry(Entry);

  // Add to values set if not already there.  If it is, we merely have a
  // duplicate in the values list (no harm.)
  ValuesSet.GetOrInsertNode(Value);
}

/// AddUInt - Add an unsigned integer attribute data and value.
///
void DwarfDebug::AddUInt(DIE *Die, unsigned Attribute,
                         unsigned Form, uint64_t Integer) {
  if (!Form) Form = DIEInteger::BestForm(false, Integer);

  FoldingSetNodeID ID;
  DIEInteger::Profile(ID, Integer);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEInteger(Integer);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddSInt - Add an signed integer attribute data and value.
///
void DwarfDebug::AddSInt(DIE *Die, unsigned Attribute,
                         unsigned Form, int64_t Integer) {
  if (!Form) Form = DIEInteger::BestForm(true, Integer);

  FoldingSetNodeID ID;
  DIEInteger::Profile(ID, (uint64_t)Integer);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEInteger(Integer);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddString - Add a string attribute data and value.
///
void DwarfDebug::AddString(DIE *Die, unsigned Attribute, unsigned Form,
                           const std::string &String) {
  FoldingSetNodeID ID;
  DIEString::Profile(ID, String);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEString(String);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddLabel - Add a Dwarf label attribute data and value.
///
void DwarfDebug::AddLabel(DIE *Die, unsigned Attribute, unsigned Form,
                          const DWLabel &Label) {
  FoldingSetNodeID ID;
  DIEDwarfLabel::Profile(ID, Label);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEDwarfLabel(Label);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddObjectLabel - Add an non-Dwarf label attribute data and value.
///
void DwarfDebug::AddObjectLabel(DIE *Die, unsigned Attribute, unsigned Form,
                                const std::string &Label) {
  FoldingSetNodeID ID;
  DIEObjectLabel::Profile(ID, Label);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEObjectLabel(Label);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddSectionOffset - Add a section offset label attribute data and value.
///
void DwarfDebug::AddSectionOffset(DIE *Die, unsigned Attribute, unsigned Form,
                                  const DWLabel &Label, const DWLabel &Section,
                                  bool isEH, bool useSet) {
  FoldingSetNodeID ID;
  DIESectionOffset::Profile(ID, Label, Section);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIESectionOffset(Label, Section, isEH, useSet);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddDelta - Add a label delta attribute data and value.
///
void DwarfDebug::AddDelta(DIE *Die, unsigned Attribute, unsigned Form,
                          const DWLabel &Hi, const DWLabel &Lo) {
  FoldingSetNodeID ID;
  DIEDelta::Profile(ID, Hi, Lo);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = new DIEDelta(Hi, Lo);
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  }

  Die->AddValue(Attribute, Form, Value);
}

/// AddBlock - Add block data.
///
void DwarfDebug::AddBlock(DIE *Die, unsigned Attribute, unsigned Form,
                          DIEBlock *Block) {
  Block->ComputeSize(TD);
  FoldingSetNodeID ID;
  Block->Profile(ID);
  void *Where;
  DIEValue *Value = ValuesSet.FindNodeOrInsertPos(ID, Where);

  if (!Value) {
    Value = Block;
    ValuesSet.InsertNode(Value, Where);
    Values.push_back(Value);
  } else {
    // Already exists, reuse the previous one.
    delete Block;
    Block = cast<DIEBlock>(Value);
  }

  Die->AddValue(Attribute, Block->BestForm(), Value);
}

/// AddSourceLine - Add location information to specified debug information
/// entry.
void DwarfDebug::AddSourceLine(DIE *Die, const DIVariable *V) {
  // If there is no compile unit specified, don't add a line #.
  if (V->getCompileUnit().isNull())
    return;

  unsigned Line = V->getLineNumber();
  unsigned FileID = FindCompileUnit(V->getCompileUnit()).getID();
  assert(FileID && "Invalid file id");
  AddUInt(Die, dwarf::DW_AT_decl_file, 0, FileID);
  AddUInt(Die, dwarf::DW_AT_decl_line, 0, Line);
}

/// AddSourceLine - Add location information to specified debug information
/// entry.
void DwarfDebug::AddSourceLine(DIE *Die, const DIGlobal *G) {
  // If there is no compile unit specified, don't add a line #.
  if (G->getCompileUnit().isNull())
    return;

  unsigned Line = G->getLineNumber();
  unsigned FileID = FindCompileUnit(G->getCompileUnit()).getID();
  assert(FileID && "Invalid file id");
  AddUInt(Die, dwarf::DW_AT_decl_file, 0, FileID);
  AddUInt(Die, dwarf::DW_AT_decl_line, 0, Line);
}
void DwarfDebug::AddSourceLine(DIE *Die, const DIType *Ty) {
  // If there is no compile unit specified, don't add a line #.
  DICompileUnit CU = Ty->getCompileUnit();
  if (CU.isNull())
    return;

  unsigned Line = Ty->getLineNumber();
  unsigned FileID = FindCompileUnit(CU).getID();
  assert(FileID && "Invalid file id");
  AddUInt(Die, dwarf::DW_AT_decl_file, 0, FileID);
  AddUInt(Die, dwarf::DW_AT_decl_line, 0, Line);
}

/// AddAddress - Add an address attribute to a die based on the location
/// provided.
void DwarfDebug::AddAddress(DIE *Die, unsigned Attribute,
                            const MachineLocation &Location) {
  unsigned Reg = RI->getDwarfRegNum(Location.getReg(), false);
  DIEBlock *Block = new DIEBlock();

  if (Location.isReg()) {
    if (Reg < 32) {
      AddUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_reg0 + Reg);
    } else {
      AddUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_regx);
      AddUInt(Block, 0, dwarf::DW_FORM_udata, Reg);
    }
  } else {
    if (Reg < 32) {
      AddUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_breg0 + Reg);
    } else {
      AddUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_bregx);
      AddUInt(Block, 0, dwarf::DW_FORM_udata, Reg);
    }

    AddUInt(Block, 0, dwarf::DW_FORM_sdata, Location.getOffset());
  }

  AddBlock(Die, Attribute, 0, Block);
}

/// AddType - Add a new type attribute to the specified entity.
void DwarfDebug::AddType(CompileUnit *DW_Unit, DIE *Entity, DIType Ty) {
  if (Ty.isNull())
    return;

  // Check for pre-existence.
  DIEEntry *&Slot = DW_Unit->getDIEEntrySlotFor(Ty.getGV());

  // If it exists then use the existing value.
  if (Slot) {
    Entity->AddValue(dwarf::DW_AT_type, dwarf::DW_FORM_ref4, Slot);
    return;
  }

  // Set up proxy.
  Slot = NewDIEEntry();

  // Construct type.
  DIE Buffer(dwarf::DW_TAG_base_type);
  if (Ty.isBasicType(Ty.getTag()))
    ConstructTypeDIE(DW_Unit, Buffer, DIBasicType(Ty.getGV()));
  else if (Ty.isDerivedType(Ty.getTag()))
    ConstructTypeDIE(DW_Unit, Buffer, DIDerivedType(Ty.getGV()));
  else {
    assert(Ty.isCompositeType(Ty.getTag()) && "Unknown kind of DIType");
    ConstructTypeDIE(DW_Unit, Buffer, DICompositeType(Ty.getGV()));
  }

  // Add debug information entry to entity and appropriate context.
  DIE *Die = NULL;
  DIDescriptor Context = Ty.getContext();
  if (!Context.isNull())
    Die = DW_Unit->getDieMapSlotFor(Context.getGV());

  if (Die) {
    DIE *Child = new DIE(Buffer);
    Die->AddChild(Child);
    Buffer.Detach();
    SetDIEEntry(Slot, Child);
  } else {
    Die = DW_Unit->AddDie(Buffer);
    SetDIEEntry(Slot, Die);
  }

  Entity->AddValue(dwarf::DW_AT_type, dwarf::DW_FORM_ref4, Slot);
}

/// ConstructTypeDIE - Construct basic type die from DIBasicType.
void DwarfDebug::ConstructTypeDIE(CompileUnit *DW_Unit, DIE &Buffer,
                                  DIBasicType BTy) {
  // Get core information.
  std::string Name;
  BTy.getName(Name);
  Buffer.setTag(dwarf::DW_TAG_base_type);
  AddUInt(&Buffer, dwarf::DW_AT_encoding,  dwarf::DW_FORM_data1,
          BTy.getEncoding());

  // Add name if not anonymous or intermediate type.
  if (!Name.empty())
    AddString(&Buffer, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);
  uint64_t Size = BTy.getSizeInBits() >> 3;
  AddUInt(&Buffer, dwarf::DW_AT_byte_size, 0, Size);
}

/// ConstructTypeDIE - Construct derived type die from DIDerivedType.
void DwarfDebug::ConstructTypeDIE(CompileUnit *DW_Unit, DIE &Buffer,
                                  DIDerivedType DTy) {
  // Get core information.
  std::string Name;
  DTy.getName(Name);
  uint64_t Size = DTy.getSizeInBits() >> 3;
  unsigned Tag = DTy.getTag();

  // FIXME - Workaround for templates.
  if (Tag == dwarf::DW_TAG_inheritance) Tag = dwarf::DW_TAG_reference_type;

  Buffer.setTag(Tag);

  // Map to main type, void will not have a type.
  DIType FromTy = DTy.getTypeDerivedFrom();
  AddType(DW_Unit, &Buffer, FromTy);

  // Add name if not anonymous or intermediate type.
  if (!Name.empty())
    AddString(&Buffer, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);

  // Add size if non-zero (derived types might be zero-sized.)
  if (Size)
    AddUInt(&Buffer, dwarf::DW_AT_byte_size, 0, Size);

  // Add source line info if available and TyDesc is not a forward declaration.
  if (!DTy.isForwardDecl())
    AddSourceLine(&Buffer, &DTy);
}

/// ConstructTypeDIE - Construct type DIE from DICompositeType.
void DwarfDebug::ConstructTypeDIE(CompileUnit *DW_Unit, DIE &Buffer,
                                  DICompositeType CTy) {
  // Get core information.
  std::string Name;
  CTy.getName(Name);

  uint64_t Size = CTy.getSizeInBits() >> 3;
  unsigned Tag = CTy.getTag();
  Buffer.setTag(Tag);

  switch (Tag) {
  case dwarf::DW_TAG_vector_type:
  case dwarf::DW_TAG_array_type:
    ConstructArrayTypeDIE(DW_Unit, Buffer, &CTy);
    break;
  case dwarf::DW_TAG_enumeration_type: {
    DIArray Elements = CTy.getTypeArray();

    // Add enumerators to enumeration type.
    for (unsigned i = 0, N = Elements.getNumElements(); i < N; ++i) {
      DIE *ElemDie = NULL;
      DIEnumerator Enum(Elements.getElement(i).getGV());
      ElemDie = ConstructEnumTypeDIE(DW_Unit, &Enum);
      Buffer.AddChild(ElemDie);
    }
  }
    break;
  case dwarf::DW_TAG_subroutine_type: {
    // Add return type.
    DIArray Elements = CTy.getTypeArray();
    DIDescriptor RTy = Elements.getElement(0);
    AddType(DW_Unit, &Buffer, DIType(RTy.getGV()));

    // Add prototype flag.
    AddUInt(&Buffer, dwarf::DW_AT_prototyped, dwarf::DW_FORM_flag, 1);

    // Add arguments.
    for (unsigned i = 1, N = Elements.getNumElements(); i < N; ++i) {
      DIE *Arg = new DIE(dwarf::DW_TAG_formal_parameter);
      DIDescriptor Ty = Elements.getElement(i);
      AddType(DW_Unit, Arg, DIType(Ty.getGV()));
      Buffer.AddChild(Arg);
    }
  }
    break;
  case dwarf::DW_TAG_structure_type:
  case dwarf::DW_TAG_union_type:
  case dwarf::DW_TAG_class_type: {
    // Add elements to structure type.
    DIArray Elements = CTy.getTypeArray();

    // A forward struct declared type may not have elements available.
    if (Elements.isNull())
      break;

    // Add elements to structure type.
    for (unsigned i = 0, N = Elements.getNumElements(); i < N; ++i) {
      DIDescriptor Element = Elements.getElement(i);
      DIE *ElemDie = NULL;
      if (Element.getTag() == dwarf::DW_TAG_subprogram)
        ElemDie = CreateSubprogramDIE(DW_Unit,
                                      DISubprogram(Element.getGV()));
      else if (Element.getTag() == dwarf::DW_TAG_variable) // ??
        ElemDie = CreateGlobalVariableDIE(DW_Unit,
                                          DIGlobalVariable(Element.getGV()));
      else
        ElemDie = CreateMemberDIE(DW_Unit,
                                  DIDerivedType(Element.getGV()));
      Buffer.AddChild(ElemDie);
    }

    // FIXME: We'd like an API to register additional attributes for the
    // frontend to use while synthesizing, and then we'd use that api in clang
    // instead of this.
    if (Name == "__block_literal_generic")
      AddUInt(&Buffer, dwarf::DW_AT_APPLE_block, dwarf::DW_FORM_flag, 1);

    unsigned RLang = CTy.getRunTimeLang();
    if (RLang)
      AddUInt(&Buffer, dwarf::DW_AT_APPLE_runtime_class,
              dwarf::DW_FORM_data1, RLang);
    break;
  }
  default:
    break;
  }

  // Add name if not anonymous or intermediate type.
  if (!Name.empty())
    AddString(&Buffer, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);

  if (Tag == dwarf::DW_TAG_enumeration_type ||
      Tag == dwarf::DW_TAG_structure_type || Tag == dwarf::DW_TAG_union_type) {
    // Add size if non-zero (derived types might be zero-sized.)
    if (Size)
      AddUInt(&Buffer, dwarf::DW_AT_byte_size, 0, Size);
    else {
      // Add zero size if it is not a forward declaration.
      if (CTy.isForwardDecl())
        AddUInt(&Buffer, dwarf::DW_AT_declaration, dwarf::DW_FORM_flag, 1);
      else
        AddUInt(&Buffer, dwarf::DW_AT_byte_size, 0, 0);
    }

    // Add source line info if available.
    if (!CTy.isForwardDecl())
      AddSourceLine(&Buffer, &CTy);
  }
}

/// ConstructSubrangeDIE - Construct subrange DIE from DISubrange.
void DwarfDebug::ConstructSubrangeDIE(DIE &Buffer, DISubrange SR, DIE *IndexTy){
  int64_t L = SR.getLo();
  int64_t H = SR.getHi();
  DIE *DW_Subrange = new DIE(dwarf::DW_TAG_subrange_type);

  if (L != H) {
    AddDIEEntry(DW_Subrange, dwarf::DW_AT_type, dwarf::DW_FORM_ref4, IndexTy);
    if (L)
      AddSInt(DW_Subrange, dwarf::DW_AT_lower_bound, 0, L);
    AddSInt(DW_Subrange, dwarf::DW_AT_upper_bound, 0, H);
  }

  Buffer.AddChild(DW_Subrange);
}

/// ConstructArrayTypeDIE - Construct array type DIE from DICompositeType.
void DwarfDebug::ConstructArrayTypeDIE(CompileUnit *DW_Unit, DIE &Buffer,
                                       DICompositeType *CTy) {
  Buffer.setTag(dwarf::DW_TAG_array_type);
  if (CTy->getTag() == dwarf::DW_TAG_vector_type)
    AddUInt(&Buffer, dwarf::DW_AT_GNU_vector, dwarf::DW_FORM_flag, 1);

  // Emit derived type.
  AddType(DW_Unit, &Buffer, CTy->getTypeDerivedFrom());
  DIArray Elements = CTy->getTypeArray();

  // Construct an anonymous type for index type.
  DIE IdxBuffer(dwarf::DW_TAG_base_type);
  AddUInt(&IdxBuffer, dwarf::DW_AT_byte_size, 0, sizeof(int32_t));
  AddUInt(&IdxBuffer, dwarf::DW_AT_encoding, dwarf::DW_FORM_data1,
          dwarf::DW_ATE_signed);
  DIE *IndexTy = DW_Unit->AddDie(IdxBuffer);

  // Add subranges to array type.
  for (unsigned i = 0, N = Elements.getNumElements(); i < N; ++i) {
    DIDescriptor Element = Elements.getElement(i);
    if (Element.getTag() == dwarf::DW_TAG_subrange_type)
      ConstructSubrangeDIE(Buffer, DISubrange(Element.getGV()), IndexTy);
  }
}

/// ConstructEnumTypeDIE - Construct enum type DIE from DIEnumerator.
DIE *DwarfDebug::ConstructEnumTypeDIE(CompileUnit *DW_Unit, DIEnumerator *ETy) {
  DIE *Enumerator = new DIE(dwarf::DW_TAG_enumerator);
  std::string Name;
  ETy->getName(Name);
  AddString(Enumerator, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);
  int64_t Value = ETy->getEnumValue();
  AddSInt(Enumerator, dwarf::DW_AT_const_value, dwarf::DW_FORM_sdata, Value);
  return Enumerator;
}

/// CreateGlobalVariableDIE - Create new DIE using GV.
DIE *DwarfDebug::CreateGlobalVariableDIE(CompileUnit *DW_Unit,
                                         const DIGlobalVariable &GV) {
  DIE *GVDie = new DIE(dwarf::DW_TAG_variable);
  std::string Name;
  GV.getDisplayName(Name);
  AddString(GVDie, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);
  std::string LinkageName;
  GV.getLinkageName(LinkageName);
  if (!LinkageName.empty())
    AddString(GVDie, dwarf::DW_AT_MIPS_linkage_name, dwarf::DW_FORM_string,
              LinkageName);
  AddType(DW_Unit, GVDie, GV.getType());
  if (!GV.isLocalToUnit())
    AddUInt(GVDie, dwarf::DW_AT_external, dwarf::DW_FORM_flag, 1);
  AddSourceLine(GVDie, &GV);
  return GVDie;
}

/// CreateMemberDIE - Create new member DIE.
DIE *DwarfDebug::CreateMemberDIE(CompileUnit *DW_Unit, const DIDerivedType &DT){
  DIE *MemberDie = new DIE(DT.getTag());
  std::string Name;
  DT.getName(Name);
  if (!Name.empty())
    AddString(MemberDie, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);

  AddType(DW_Unit, MemberDie, DT.getTypeDerivedFrom());

  AddSourceLine(MemberDie, &DT);

  uint64_t Size = DT.getSizeInBits();
  uint64_t FieldSize = DT.getOriginalTypeSize();

  if (Size != FieldSize) {
    // Handle bitfield.
    AddUInt(MemberDie, dwarf::DW_AT_byte_size, 0, DT.getOriginalTypeSize()>>3);
    AddUInt(MemberDie, dwarf::DW_AT_bit_size, 0, DT.getSizeInBits());

    uint64_t Offset = DT.getOffsetInBits();
    uint64_t FieldOffset = Offset;
    uint64_t AlignMask = ~(DT.getAlignInBits() - 1);
    uint64_t HiMark = (Offset + FieldSize) & AlignMask;
    FieldOffset = (HiMark - FieldSize);
    Offset -= FieldOffset;

    // Maybe we need to work from the other end.
    if (TD->isLittleEndian()) Offset = FieldSize - (Offset + Size);
    AddUInt(MemberDie, dwarf::DW_AT_bit_offset, 0, Offset);
  }

  DIEBlock *Block = new DIEBlock();
  AddUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_plus_uconst);
  AddUInt(Block, 0, dwarf::DW_FORM_udata, DT.getOffsetInBits() >> 3);
  AddBlock(MemberDie, dwarf::DW_AT_data_member_location, 0, Block);

  if (DT.isProtected())
    AddUInt(MemberDie, dwarf::DW_AT_accessibility, 0,
            dwarf::DW_ACCESS_protected);
  else if (DT.isPrivate())
    AddUInt(MemberDie, dwarf::DW_AT_accessibility, 0,
            dwarf::DW_ACCESS_private);

  return MemberDie;
}

/// CreateSubprogramDIE - Create new DIE using SP.
DIE *DwarfDebug::CreateSubprogramDIE(CompileUnit *DW_Unit,
                                     const DISubprogram &SP,
                                     bool IsConstructor,
                                     bool IsInlined) {
  DIE *SPDie = new DIE(dwarf::DW_TAG_subprogram);

  std::string Name;
  SP.getName(Name);
  AddString(SPDie, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);

  std::string LinkageName;
  SP.getLinkageName(LinkageName);

  if (!LinkageName.empty())
    AddString(SPDie, dwarf::DW_AT_MIPS_linkage_name, dwarf::DW_FORM_string,
              LinkageName);

  AddSourceLine(SPDie, &SP);

  DICompositeType SPTy = SP.getType();
  DIArray Args = SPTy.getTypeArray();

  // Add prototyped tag, if C or ObjC.
  unsigned Lang = SP.getCompileUnit().getLanguage();
  if (Lang == dwarf::DW_LANG_C99 || Lang == dwarf::DW_LANG_C89 ||
      Lang == dwarf::DW_LANG_ObjC)
    AddUInt(SPDie, dwarf::DW_AT_prototyped, dwarf::DW_FORM_flag, 1);

  // Add Return Type.
  unsigned SPTag = SPTy.getTag();
  if (!IsConstructor) {
    if (Args.isNull() || SPTag != dwarf::DW_TAG_subroutine_type)
      AddType(DW_Unit, SPDie, SPTy);
    else
      AddType(DW_Unit, SPDie, DIType(Args.getElement(0).getGV()));
  }

  if (!SP.isDefinition()) {
    AddUInt(SPDie, dwarf::DW_AT_declaration, dwarf::DW_FORM_flag, 1);

    // Add arguments. Do not add arguments for subprogram definition. They will
    // be handled through RecordVariable.
    if (SPTag == dwarf::DW_TAG_subroutine_type)
      for (unsigned i = 1, N =  Args.getNumElements(); i < N; ++i) {
        DIE *Arg = new DIE(dwarf::DW_TAG_formal_parameter);
        AddType(DW_Unit, Arg, DIType(Args.getElement(i).getGV()));
        AddUInt(Arg, dwarf::DW_AT_artificial, dwarf::DW_FORM_flag, 1); // ??
        SPDie->AddChild(Arg);
      }
  }

  if (!SP.isLocalToUnit() && !IsInlined)
    AddUInt(SPDie, dwarf::DW_AT_external, dwarf::DW_FORM_flag, 1);

  // DW_TAG_inlined_subroutine may refer to this DIE.
  DIE *&Slot = DW_Unit->getDieMapSlotFor(SP.getGV());
  Slot = SPDie;
  return SPDie;
}

/// FindCompileUnit - Get the compile unit for the given descriptor.
///
CompileUnit &DwarfDebug::FindCompileUnit(DICompileUnit Unit) const {
  DenseMap<Value *, CompileUnit *>::const_iterator I =
    CompileUnitMap.find(Unit.getGV());
  assert(I != CompileUnitMap.end() && "Missing compile unit.");
  return *I->second;
}

/// NewDbgScopeVariable - Create a new scope variable.
///
DIE *DwarfDebug::NewDbgScopeVariable(DbgVariable *DV, CompileUnit *Unit) {
  // Get the descriptor.
  const DIVariable &VD = DV->getVariable();

  // Translate tag to proper Dwarf tag.  The result variable is dropped for
  // now.
  unsigned Tag;
  switch (VD.getTag()) {
  case dwarf::DW_TAG_return_variable:
    return NULL;
  case dwarf::DW_TAG_arg_variable:
    Tag = dwarf::DW_TAG_formal_parameter;
    break;
  case dwarf::DW_TAG_auto_variable:    // fall thru
  default:
    Tag = dwarf::DW_TAG_variable;
    break;
  }

  // Define variable debug information entry.
  DIE *VariableDie = new DIE(Tag);
  std::string Name;
  VD.getName(Name);
  AddString(VariableDie, dwarf::DW_AT_name, dwarf::DW_FORM_string, Name);

  // Add source line info if available.
  AddSourceLine(VariableDie, &VD);

  // Add variable type.
  AddType(Unit, VariableDie, VD.getType());

  // Add variable address.
  MachineLocation Location;
  Location.set(RI->getFrameRegister(*MF),
               RI->getFrameIndexOffset(*MF, DV->getFrameIndex()));
  AddAddress(VariableDie, dwarf::DW_AT_location, Location);

  return VariableDie;
}

/// getOrCreateScope - Returns the scope associated with the given descriptor.
///
DbgScope *DwarfDebug::getOrCreateScope(GlobalVariable *V) {
  DbgScope *&Slot = DbgScopeMap[V];
  if (Slot) return Slot;

  DbgScope *Parent = NULL;
  DIBlock Block(V);

  // Don't create a new scope if we already created one for an inlined function.
  DenseMap<const GlobalVariable *, DbgScope *>::iterator
    II = AbstractInstanceRootMap.find(V);
  if (II != AbstractInstanceRootMap.end())
    return LexicalScopeStack.back();

  if (!Block.isNull()) {
    DIDescriptor ParentDesc = Block.getContext();
    Parent =
      ParentDesc.isNull() ?  NULL : getOrCreateScope(ParentDesc.getGV());
  }

  Slot = new DbgScope(Parent, DIDescriptor(V));

  if (Parent)
    Parent->AddScope(Slot);
  else
    // First function is top level function.
    FunctionDbgScope = Slot;

  return Slot;
}

/// ConstructDbgScope - Construct the components of a scope.
///