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.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "dwarfdebug"
#include "DwarfDebug.h"
#include "DIE.h"
#include "DwarfAccelTable.h"
#include "DwarfCompileUnit.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/Triple.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/Constants.h"
#include "llvm/DIBuilder.h"
#include "llvm/DataLayout.h"
#include "llvm/DebugInfo.h"
#include "llvm/Instructions.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetFrameLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;

static cl::opt<bool> DisableDebugInfoPrinting("disable-debug-info-print",
                                              cl::Hidden,
     cl::desc("Disable debug info printing"));

static cl::opt<bool> UnknownLocations("use-unknown-locations", cl::Hidden,
     cl::desc("Make an absence of debug location information explicit."),
     cl::init(false));

namespace {
  enum DefaultOnOff {
    Default, Enable, Disable
  };
}

static cl::opt<DefaultOnOff> DwarfAccelTables("dwarf-accel-tables", cl::Hidden,
     cl::desc("Output prototype dwarf accelerator tables."),
     cl::values(
                clEnumVal(Default, "Default for platform"),
                clEnumVal(Enable, "Enabled"),
                clEnumVal(Disable, "Disabled"),
                clEnumValEnd),
     cl::init(Default));

static cl::opt<DefaultOnOff> DarwinGDBCompat("darwin-gdb-compat", cl::Hidden,
     cl::desc("Compatibility with Darwin gdb."),
     cl::values(
                clEnumVal(Default, "Default for platform"),
                clEnumVal(Enable, "Enabled"),
                clEnumVal(Disable, "Disabled"),
                clEnumValEnd),
     cl::init(Default));

static cl::opt<DefaultOnOff> DwarfFission("dwarf-fission", cl::Hidden,
     cl::desc("Output prototype dwarf fission."),
     cl::values(
                clEnumVal(Default, "Default for platform"),
                clEnumVal(Enable, "Enabled"),
                clEnumVal(Disable, "Disabled"),
                clEnumValEnd),
     cl::init(Default));

namespace {
  const char *DWARFGroupName = "DWARF Emission";
  const char *DbgTimerName = "DWARF Debug Writer";
} // end anonymous namespace

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

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

namespace llvm {

DIType DbgVariable::getType() const {
  DIType Ty = Var.getType();
  // FIXME: isBlockByrefVariable should be reformulated in terms of complex
  // addresses instead.
  if (Var.isBlockByrefVariable()) {
    /* Byref variables, in Blocks, are declared by the programmer as
       "SomeType VarName;", but the compiler creates a
       __Block_byref_x_VarName struct, and gives the variable VarName
       either the struct, or a pointer to the struct, as its type.  This
       is necessary for various behind-the-scenes things the compiler
       needs to do with by-reference variables in blocks.

       However, as far as the original *programmer* is concerned, the
       variable should still have type 'SomeType', as originally declared.

       The following function dives into the __Block_byref_x_VarName
       struct to find the original type of the variable.  This will be
       passed back to the code generating the type for the Debug
       Information Entry for the variable 'VarName'.  'VarName' will then
       have the original type 'SomeType' in its debug information.

       The original type 'SomeType' will be the type of the field named
       'VarName' inside the __Block_byref_x_VarName struct.

       NOTE: In order for this to not completely fail on the debugger
       side, the Debug Information Entry for the variable VarName needs to
       have a DW_AT_location that tells the debugger how to unwind through
       the pointers and __Block_byref_x_VarName struct to find the actual
       value of the variable.  The function addBlockByrefType does this.  */
    DIType subType = Ty;
    unsigned tag = Ty.getTag();

    if (tag == dwarf::DW_TAG_pointer_type) {
      DIDerivedType DTy = DIDerivedType(Ty);
      subType = DTy.getTypeDerivedFrom();
    }

    DICompositeType blockStruct = DICompositeType(subType);
    DIArray Elements = blockStruct.getTypeArray();

    for (unsigned i = 0, N = Elements.getNumElements(); i < N; ++i) {
      DIDescriptor Element = Elements.getElement(i);
      DIDerivedType DT = DIDerivedType(Element);
      if (getName() == DT.getName())
        return (DT.getTypeDerivedFrom());
    }
  }
  return Ty;
}

} // end llvm namespace

DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
  : Asm(A), MMI(Asm->MMI), FirstCU(0), FissionCU(0),
    AbbreviationsSet(InitAbbreviationsSetSize),
    SourceIdMap(DIEValueAllocator), StringPool(DIEValueAllocator),
    PrevLabel(NULL) {
  NextStringPoolNumber = 0;

  DwarfInfoSectionSym = DwarfAbbrevSectionSym = 0;
  DwarfStrSectionSym = TextSectionSym = 0;
  DwarfDebugRangeSectionSym = DwarfDebugLocSectionSym = 0;
  FunctionBeginSym = FunctionEndSym = 0;

  // Turn on accelerator tables and older gdb compatibility
  // for Darwin.
  bool IsDarwin = Triple(M->getTargetTriple()).isOSDarwin();
  if (DarwinGDBCompat == Default) {
    if (IsDarwin)
      IsDarwinGDBCompat = true;
    else
      IsDarwinGDBCompat = false;
  } else
    IsDarwinGDBCompat = DarwinGDBCompat == Enable ? true : false;

  if (DwarfAccelTables == Default) {
    if (IsDarwin)
      HasDwarfAccelTables = true;
    else
      HasDwarfAccelTables = false;
  } else
    HasDwarfAccelTables = DwarfAccelTables == Enable ? true : false;

  if (DwarfFission == Default)
    HasDwarfFission = false;
  else
    HasDwarfFission = DwarfFission == Enable ? true : false;

  {
    NamedRegionTimer T(DbgTimerName, DWARFGroupName, TimePassesIsEnabled);
    beginModule();
  }
}
DwarfDebug::~DwarfDebug() {
}

// 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;
}

MCSymbol *DwarfDebug::getStringPool() {
  return Asm->GetTempSymbol("section_str");
}

MCSymbol *DwarfDebug::getStringPoolEntry(StringRef Str) {
  std::pair<MCSymbol*, unsigned> &Entry = StringPool[Str];
  if (Entry.first) return Entry.first;

  Entry.second = NextStringPoolNumber++;
  return Entry.first = Asm->GetTempSymbol("string", Entry.second);
}

// 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());
  }
}

// If special LLVM prefix that is used to inform the asm
// printer to not emit usual symbol prefix before the symbol name is used then
// return linkage name after skipping this special LLVM prefix.
static StringRef getRealLinkageName(StringRef LinkageName) {
  char One = '\1';
  if (LinkageName.startswith(StringRef(&One, 1)))
    return LinkageName.substr(1);
  return LinkageName;
}

static bool isObjCClass(StringRef Name) {
  return Name.startswith("+") || Name.startswith("-");
}

static bool hasObjCCategory(StringRef Name) {
  if (!isObjCClass(Name)) return false;

  size_t pos = Name.find(')');
  if (pos != std::string::npos) {
    if (Name[pos+1] != ' ') return false;
    return true;
  }
  return false;
}

static void getObjCClassCategory(StringRef In, StringRef &Class,
                                 StringRef &Category) {
  if (!hasObjCCategory(In)) {
    Class = In.slice(In.find('[') + 1, In.find(' '));
    Category = "";
    return;
  }

  Class = In.slice(In.find('[') + 1, In.find('('));
  Category = In.slice(In.find('[') + 1, In.find(' '));
  return;
}

static StringRef getObjCMethodName(StringRef In) {
  return In.slice(In.find(' ') + 1, In.find(']'));
}

// Add the various names to the Dwarf accelerator table names.
static void addSubprogramNames(CompileUnit *TheCU, DISubprogram SP,
                               DIE* Die) {
  if (!SP.isDefinition()) return;

  TheCU->addAccelName(SP.getName(), Die);

  // If the linkage name is different than the name, go ahead and output
  // that as well into the name table.
  if (SP.getLinkageName() != "" && SP.getName() != SP.getLinkageName())
    TheCU->addAccelName(SP.getLinkageName(), Die);

  // If this is an Objective-C selector name add it to the ObjC accelerator
  // too.
  if (isObjCClass(SP.getName())) {
    StringRef Class, Category;
    getObjCClassCategory(SP.getName(), Class, Category);
    TheCU->addAccelObjC(Class, Die);
    if (Category != "")
      TheCU->addAccelObjC(Category, Die);
    // Also add the base method name to the name table.
    TheCU->addAccelName(getObjCMethodName(SP.getName()), Die);
  }
}

// Find DIE for the given subprogram and attach appropriate DW_AT_low_pc
// and DW_AT_high_pc attributes. If there are global variables in this
// scope then create and insert DIEs for these variables.
DIE *DwarfDebug::updateSubprogramScopeDIE(CompileUnit *SPCU,
                                          const MDNode *SPNode) {
  DIE *SPDie = SPCU->getDIE(SPNode);

  assert(SPDie && "Unable to find subprogram DIE!");
  DISubprogram SP(SPNode);

  // If we're updating an abstract DIE, then we will be adding the children and
  // object pointer later on. But what we don't want to do is process the
  // concrete DIE twice.
  if (DIE *AbsSPDIE = AbstractSPDies.lookup(SPNode)) {
    // Pick up abstract subprogram DIE.
    SPDie = new DIE(dwarf::DW_TAG_subprogram);
    SPCU->addDIEEntry(SPDie, dwarf::DW_AT_abstract_origin,
                      dwarf::DW_FORM_ref4, AbsSPDIE);
    SPCU->addDie(SPDie);
  } else {
    DISubprogram SPDecl = SP.getFunctionDeclaration();
    if (!SPDecl.isSubprogram()) {
      // There is not any need to generate specification DIE for a function
      // defined at compile unit level. If a function is defined inside another
      // function then gdb prefers the definition at top level and but does not
      // expect specification DIE in parent function. So avoid creating
      // specification DIE for a function defined inside a function.
      if (SP.isDefinition() && !SP.getContext().isCompileUnit() &&
          !SP.getContext().isFile() &&
          !isSubprogramContext(SP.getContext())) {
        SPCU->addFlag(SPDie, dwarf::DW_AT_declaration);

        // Add arguments.
        DICompositeType SPTy = SP.getType();
        DIArray Args = SPTy.getTypeArray();
        unsigned SPTag = SPTy.getTag();
        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);
            DIType ATy = DIType(Args.getElement(i));
            SPCU->addType(Arg, ATy);
            if (ATy.isArtificial())
              SPCU->addFlag(Arg, dwarf::DW_AT_artificial);
            if (ATy.isObjectPointer())
              SPCU->addDIEEntry(SPDie, dwarf::DW_AT_object_pointer,
                                dwarf::DW_FORM_ref4, Arg);
            SPDie->addChild(Arg);
          }
        DIE *SPDeclDie = SPDie;
        SPDie = new DIE(dwarf::DW_TAG_subprogram);
        SPCU->addDIEEntry(SPDie, dwarf::DW_AT_specification,
                          dwarf::DW_FORM_ref4, SPDeclDie);
        SPCU->addDie(SPDie);
      }
    }
  }

  SPCU->addLabel(SPDie, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr,
                 Asm->GetTempSymbol("func_begin", Asm->getFunctionNumber()));
  SPCU->addLabel(SPDie, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr,
                 Asm->GetTempSymbol("func_end", Asm->getFunctionNumber()));
  const TargetRegisterInfo *RI = Asm->TM.getRegisterInfo();
  MachineLocation Location(RI->getFrameRegister(*Asm->MF));
  SPCU->addAddress(SPDie, dwarf::DW_AT_frame_base, Location);

  // Add name to the name table, we do this here because we're guaranteed
  // to have concrete versions of our DW_TAG_subprogram nodes.
  addSubprogramNames(SPCU, SP, SPDie);

  return SPDie;
}

// Construct new DW_TAG_lexical_block for this scope and attach
// DW_AT_low_pc/DW_AT_high_pc labels.
DIE *DwarfDebug::constructLexicalScopeDIE(CompileUnit *TheCU,
                                          LexicalScope *Scope) {
  DIE *ScopeDIE = new DIE(dwarf::DW_TAG_lexical_block);
  if (Scope->isAbstractScope())
    return ScopeDIE;

  const SmallVector<InsnRange, 4> &Ranges = Scope->getRanges();
  if (Ranges.empty())
    return 0;

  SmallVector<InsnRange, 4>::const_iterator RI = Ranges.begin();
  if (Ranges.size() > 1) {
    // .debug_range section has not been laid out yet. Emit offset in
    // .debug_range as a uint, size 4, for now. emitDIE will handle
    // DW_AT_ranges appropriately.
    TheCU->addUInt(ScopeDIE, dwarf::DW_AT_ranges, dwarf::DW_FORM_data4,
                   DebugRangeSymbols.size()
                   * Asm->getDataLayout().getPointerSize());
    for (SmallVector<InsnRange, 4>::const_iterator RI = Ranges.begin(),
         RE = Ranges.end(); RI != RE; ++RI) {
      DebugRangeSymbols.push_back(getLabelBeforeInsn(RI->first));
      DebugRangeSymbols.push_back(getLabelAfterInsn(RI->second));
    }
    DebugRangeSymbols.push_back(NULL);
    DebugRangeSymbols.push_back(NULL);
    return ScopeDIE;
  }

  const MCSymbol *Start = getLabelBeforeInsn(RI->first);
  const MCSymbol *End = getLabelAfterInsn(RI->second);

  if (End == 0) return 0;

  assert(Start->isDefined() && "Invalid starting label for an inlined scope!");
  assert(End->isDefined() && "Invalid end label for an inlined scope!");

  TheCU->addLabel(ScopeDIE, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr, Start);
  TheCU->addLabel(ScopeDIE, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr, End);

  return ScopeDIE;
}

// This scope represents inlined body of a function. Construct DIE to
// represent this concrete inlined copy of the function.
DIE *DwarfDebug::constructInlinedScopeDIE(CompileUnit *TheCU,
                                          LexicalScope *Scope) {
  const SmallVector<InsnRange, 4> &Ranges = Scope->getRanges();
  assert(Ranges.empty() == false &&
         "LexicalScope does not have instruction markers!");

  if (!Scope->getScopeNode())
    return NULL;
  DIScope DS(Scope->getScopeNode());
  DISubprogram InlinedSP = getDISubprogram(DS);
  DIE *OriginDIE = TheCU->getDIE(InlinedSP);
  if (!OriginDIE) {
    DEBUG(dbgs() << "Unable to find original DIE for an inlined subprogram.");
    return NULL;
  }

  SmallVector<InsnRange, 4>::const_iterator RI = Ranges.begin();
  const MCSymbol *StartLabel = getLabelBeforeInsn(RI->first);
  const MCSymbol *EndLabel = getLabelAfterInsn(RI->second);

  if (StartLabel == 0 || EndLabel == 0) {
    llvm_unreachable("Unexpected Start and End labels for an inlined scope!");
  }
  assert(StartLabel->isDefined() &&
         "Invalid starting label for an inlined scope!");
  assert(EndLabel->isDefined() &&
         "Invalid end label for an inlined scope!");

  DIE *ScopeDIE = new DIE(dwarf::DW_TAG_inlined_subroutine);
  TheCU->addDIEEntry(ScopeDIE, dwarf::DW_AT_abstract_origin,
                     dwarf::DW_FORM_ref4, OriginDIE);

  if (Ranges.size() > 1) {
    // .debug_range section has not been laid out yet. Emit offset in
    // .debug_range as a uint, size 4, for now. emitDIE will handle
    // DW_AT_ranges appropriately.
    TheCU->addUInt(ScopeDIE, dwarf::DW_AT_ranges, dwarf::DW_FORM_data4,
                   DebugRangeSymbols.size()
                   * Asm->getDataLayout().getPointerSize());
    for (SmallVector<InsnRange, 4>::const_iterator RI = Ranges.begin(),
         RE = Ranges.end(); RI != RE; ++RI) {
      DebugRangeSymbols.push_back(getLabelBeforeInsn(RI->first));
      DebugRangeSymbols.push_back(getLabelAfterInsn(RI->second));
    }
    DebugRangeSymbols.push_back(NULL);
    DebugRangeSymbols.push_back(NULL);
  } else {
    TheCU->addLabel(ScopeDIE, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr,
                    StartLabel);
    TheCU->addLabel(ScopeDIE, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr,
                    EndLabel);
  }

  InlinedSubprogramDIEs.insert(OriginDIE);

  // Track the start label for this inlined function.
  //.debug_inlined section specification does not clearly state how
  // to emit inlined scope that is split into multiple instruction ranges.
  // For now, use first instruction range and emit low_pc/high_pc pair and
  // corresponding .debug_inlined section entry for this pair.
  DenseMap<const MDNode *, SmallVector<InlineInfoLabels, 4> >::iterator
    I = InlineInfo.find(InlinedSP);

  if (I == InlineInfo.end()) {
    InlineInfo[InlinedSP].push_back(std::make_pair(StartLabel, ScopeDIE));
    InlinedSPNodes.push_back(InlinedSP);
  } else
    I->second.push_back(std::make_pair(StartLabel, ScopeDIE));

  DILocation DL(Scope->getInlinedAt());
  TheCU->addUInt(ScopeDIE, dwarf::DW_AT_call_file, 0,
                 getOrCreateSourceID(DL.getFilename(), DL.getDirectory()));
  TheCU->addUInt(ScopeDIE, dwarf::DW_AT_call_line, 0, DL.getLineNumber());

  // Add name to the name table, we do this here because we're guaranteed
  // to have concrete versions of our DW_TAG_inlined_subprogram nodes.
  addSubprogramNames(TheCU, InlinedSP, ScopeDIE);

  return ScopeDIE;
}

// Construct a DIE for this scope.
DIE *DwarfDebug::constructScopeDIE(CompileUnit *TheCU, LexicalScope *Scope) {
  if (!Scope || !Scope->getScopeNode())
    return NULL;

  SmallVector<DIE *, 8> Children;
  DIE *ObjectPointer = NULL;

  // Collect arguments for current function.
  if (LScopes.isCurrentFunctionScope(Scope))
    for (unsigned i = 0, N = CurrentFnArguments.size(); i < N; ++i)
      if (DbgVariable *ArgDV = CurrentFnArguments[i])
        if (DIE *Arg =
            TheCU->constructVariableDIE(ArgDV, Scope->isAbstractScope())) {
          Children.push_back(Arg);
          if (ArgDV->isObjectPointer()) ObjectPointer = Arg;
        }

  // Collect lexical scope children first.
  const SmallVector<DbgVariable *, 8> &Variables = ScopeVariables.lookup(Scope);
  for (unsigned i = 0, N = Variables.size(); i < N; ++i)
    if (DIE *Variable =
        TheCU->constructVariableDIE(Variables[i], Scope->isAbstractScope())) {
      Children.push_back(Variable);
      if (Variables[i]->isObjectPointer()) ObjectPointer = Variable;
    }
  const SmallVector<LexicalScope *, 4> &Scopes = Scope->getChildren();
  for (unsigned j = 0, M = Scopes.size(); j < M; ++j)
    if (DIE *Nested = constructScopeDIE(TheCU, Scopes[j]))
      Children.push_back(Nested);
  DIScope DS(Scope->getScopeNode());
  DIE *ScopeDIE = NULL;
  if (Scope->getInlinedAt())
    ScopeDIE = constructInlinedScopeDIE(TheCU, Scope);
  else if (DS.isSubprogram()) {
    ProcessedSPNodes.insert(DS);
    if (Scope->isAbstractScope()) {
      ScopeDIE = TheCU->getDIE(DS);
      // Note down abstract DIE.
      if (ScopeDIE)
        AbstractSPDies.insert(std::make_pair(DS, ScopeDIE));
    }
    else
      ScopeDIE = updateSubprogramScopeDIE(TheCU, DS);
  }
  else {
    // There is no need to emit empty lexical block DIE.
    if (Children.empty())
      return NULL;
    ScopeDIE = constructLexicalScopeDIE(TheCU, Scope);
  }

  if (!ScopeDIE) return NULL;

  // Add children
  for (SmallVector<DIE *, 8>::iterator I = Children.begin(),
         E = Children.end(); I != E; ++I)
    ScopeDIE->addChild(*I);

  if (DS.isSubprogram() && ObjectPointer != NULL)
    TheCU->addDIEEntry(ScopeDIE, dwarf::DW_AT_object_pointer,
                       dwarf::DW_FORM_ref4, ObjectPointer);

  if (DS.isSubprogram())
    TheCU->addPubTypes(DISubprogram(DS));

  return ScopeDIE;
}

// Look up the source id with the given directory and source file names.
// If none currently exists, create a new id and insert it in the
// SourceIds map. This can update DirectoryNames and SourceFileNames maps
// as well.
unsigned DwarfDebug::getOrCreateSourceID(StringRef FileName,
                                         StringRef DirName) {
  // If FE did not provide a file name, then assume stdin.
  if (FileName.empty())
    return getOrCreateSourceID("<stdin>", StringRef());

  // TODO: this might not belong here. See if we can factor this better.
  if (DirName == CompilationDir)
    DirName = "";

  unsigned SrcId = SourceIdMap.size()+1;

  // We look up the file/dir pair by concatenating them with a zero byte.
  SmallString<128> NamePair;
  NamePair += DirName;
  NamePair += '\0'; // Zero bytes are not allowed in paths.
  NamePair += FileName;

  StringMapEntry<unsigned> &Ent = SourceIdMap.GetOrCreateValue(NamePair, SrcId);
  if (Ent.getValue() != SrcId)
    return Ent.getValue();

  // Print out a .file directive to specify files for .loc directives.
  Asm->OutStreamer.EmitDwarfFileDirective(SrcId, DirName, FileName);

  return SrcId;
}

// Create new CompileUnit for the given metadata node with tag DW_TAG_compile_unit.
CompileUnit *DwarfDebug::constructCompileUnit(const MDNode *N) {
  DICompileUnit DIUnit(N);
  StringRef FN = DIUnit.getFilename();
  CompilationDir = DIUnit.getDirectory();
  unsigned ID = getOrCreateSourceID(FN, CompilationDir);

  DIE *Die = new DIE(dwarf::DW_TAG_compile_unit);
  CompileUnit *NewCU = new CompileUnit(ID, DIUnit.getLanguage(), Die,
                                       Asm, this);
  NewCU->addString(Die, dwarf::DW_AT_producer, DIUnit.getProducer());
  NewCU->addUInt(Die, dwarf::DW_AT_language, dwarf::DW_FORM_data2,
                 DIUnit.getLanguage());
  NewCU->addString(Die, dwarf::DW_AT_name, FN);
  // 2.17.1 requires that we use DW_AT_low_pc for a single entry point
  // into an entity.
  NewCU->addUInt(Die, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr, 0);
  // DW_AT_stmt_list is a offset of line number information for this
  // compile unit in debug_line section.
  if (Asm->MAI->doesDwarfUseRelocationsAcrossSections())
    NewCU->addLabel(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
                    Asm->GetTempSymbol("section_line"));
  else
    NewCU->addUInt(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4, 0);

  if (!CompilationDir.empty())
    NewCU->addString(Die, dwarf::DW_AT_comp_dir, CompilationDir);
  if (DIUnit.isOptimized())
    NewCU->addFlag(Die, dwarf::DW_AT_APPLE_optimized);

  StringRef Flags = DIUnit.getFlags();
  if (!Flags.empty())
    NewCU->addString(Die, dwarf::DW_AT_APPLE_flags, Flags);

  if (unsigned RVer = DIUnit.getRunTimeVersion())
    NewCU->addUInt(Die, dwarf::DW_AT_APPLE_major_runtime_vers,
            dwarf::DW_FORM_data1, RVer);

  if (!FirstCU)
    FirstCU = NewCU;
  if (useDwarfFission() && !FissionCU)
    FissionCU = constructFissionCU(N);

  CUMap.insert(std::make_pair(N, NewCU));
  return NewCU;
}

// Construct subprogram DIE.
void DwarfDebug::constructSubprogramDIE(CompileUnit *TheCU,
                                        const MDNode *N) {
  CompileUnit *&CURef = SPMap[N];
  if (CURef)
    return;
  CURef = TheCU;

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

  DIE *SubprogramDie = TheCU->getOrCreateSubprogramDIE(SP);

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

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

  return;
}

// Collect debug info from named mdnodes such as llvm.dbg.enum and llvm.dbg.ty.
void DwarfDebug::collectInfoFromNamedMDNodes(const Module *M) {
  if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.sp"))
    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
      const MDNode *N = NMD->getOperand(i);
      if (CompileUnit *CU = CUMap.lookup(DISubprogram(N).getCompileUnit()))
        constructSubprogramDIE(CU, N);
    }

  if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.gv"))
    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
      const MDNode *N = NMD->getOperand(i);
      if (CompileUnit *CU = CUMap.lookup(DIGlobalVariable(N).getCompileUnit()))
        CU->createGlobalVariableDIE(N);
    }

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

// Collect debug info using DebugInfoFinder.
// FIXME - Remove this when dragonegg switches to DIBuilder.
bool DwarfDebug::collectLegacyDebugInfo(const Module *M) {
  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 false;

  // 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) {
    const MDNode *N = *I;
    if (CompileUnit *CU = CUMap.lookup(DIGlobalVariable(N).getCompileUnit()))
      CU->createGlobalVariableDIE(N);
  }

  // Create DIEs for each subprogram.
  for (DebugInfoFinder::iterator I = DbgFinder.subprogram_begin(),
         E = DbgFinder.subprogram_end(); I != E; ++I) {
    const MDNode *N = *I;
    if (CompileUnit *CU = CUMap.lookup(DISubprogram(N).getCompileUnit()))
      constructSubprogramDIE(CU, N);
  }

  return HasDebugInfo;
}

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

  const Module *M = MMI->getModule();

  // 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) {
    for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
      DICompileUnit CUNode(CU_Nodes->getOperand(i));
      CompileUnit *CU = constructCompileUnit(CUNode);
      DIArray GVs = CUNode.getGlobalVariables();
      for (unsigned i = 0, e = GVs.getNumElements(); i != e; ++i)
        CU->createGlobalVariableDIE(GVs.getElement(i));
      DIArray SPs = CUNode.getSubprograms();
      for (unsigned i = 0, e = SPs.getNumElements(); i != e; ++i)
        constructSubprogramDIE(CU, SPs.getElement(i));
      DIArray EnumTypes = CUNode.getEnumTypes();
      for (unsigned i = 0, e = EnumTypes.getNumElements(); i != e; ++i)
        CU->getOrCreateTypeDIE(EnumTypes.getElement(i));
      DIArray RetainedTypes = CUNode.getRetainedTypes();
      for (unsigned i = 0, e = RetainedTypes.getNumElements(); i != e; ++i)
        CU->getOrCreateTypeDIE(RetainedTypes.getElement(i));
    }
  } else if (!collectLegacyDebugInfo(M))
    return;

  collectInfoFromNamedMDNodes(M);

  // Tell MMI that we have debug info.
  MMI->setDebugInfoAvailability(true);

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

// Attach DW_AT_inline attribute with inlined subprogram DIEs.
void DwarfDebug::computeInlinedDIEs() {
  // 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<const MDNode *, DIE *>::iterator AI = AbstractSPDies.begin(),
         AE = AbstractSPDies.end(); AI != AE; ++AI) {
    DIE *ISP = AI->second;
    if (InlinedSubprogramDIEs.count(ISP))
      continue;
    FirstCU->addUInt(ISP, dwarf::DW_AT_inline, 0, dwarf::DW_INL_inlined);
  }
}

// Collect info for variables that were optimized out.
void DwarfDebug::collectDeadVariables() {
  const Module *M = MMI->getModule();
  DenseMap<const MDNode *, LexicalScope *> DeadFnScopeMap;

  if (NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu")) {
    for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
      DICompileUnit TheCU(CU_Nodes->getOperand(i));
      DIArray Subprograms = TheCU.getSubprograms();
      for (unsigned i = 0, e = Subprograms.getNumElements(); i != e; ++i) {
        DISubprogram SP(Subprograms.getElement(i));
        if (ProcessedSPNodes.count(SP) != 0) continue;
        if (!SP.Verify()) continue;
        if (!SP.isDefinition()) continue;
        DIArray Variables = SP.getVariables();
        if (Variables.getNumElements() == 0) continue;

        LexicalScope *Scope =
          new LexicalScope(NULL, DIDescriptor(SP), NULL, false);
        DeadFnScopeMap[SP] = Scope;

        // Construct subprogram DIE and add variables DIEs.
        CompileUnit *SPCU = CUMap.lookup(TheCU);
        assert(SPCU && "Unable to find Compile Unit!");
        constructSubprogramDIE(SPCU, SP);
        DIE *ScopeDIE = SPCU->getDIE(SP);
        for (unsigned vi = 0, ve = Variables.getNumElements(); vi != ve; ++vi) {
          DIVariable DV(Variables.getElement(vi));
          if (!DV.Verify()) continue;
          DbgVariable *NewVar = new DbgVariable(DV, NULL);
          if (DIE *VariableDIE =
              SPCU->constructVariableDIE(NewVar, Scope->isAbstractScope()))
            ScopeDIE->addChild(VariableDIE);
        }
      }
    }
  }
  DeleteContainerSeconds(DeadFnScopeMap);
}

void DwarfDebug::finalizeModuleInfo() {
  // Collect info for variables that were optimized out.
  collectDeadVariables();

  // Attach DW_AT_inline attribute with inlined subprogram DIEs.
  computeInlinedDIEs();

  // Emit DW_AT_containing_type attribute to connect types with their
  // vtable holding type.
  for (DenseMap<const MDNode *, CompileUnit *>::iterator CUI = CUMap.begin(),
         CUE = CUMap.end(); CUI != CUE; ++CUI) {
    CompileUnit *TheCU = CUI->second;
    TheCU->constructContainingTypeDIEs();
  }

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

void DwarfDebug::endSections() {
  // 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 = 0, E = SectionMap.size(); I != E; ++I) {
    Asm->OutStreamer.SwitchSection(SectionMap[I]);
    Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("section_end", I+1));
  }
}

// Emit all Dwarf sections that should come after the content.
void DwarfDebug::endModule() {

  if (!FirstCU) return;

  // End any existing sections.
  // TODO: Does this need to happen?
  endSections();

  // Finalize the debug info for the module.
  finalizeModuleInfo();

  // Emit initial sections.
  emitSectionLabels();

  if (!useDwarfFission()) {
    // Emit all the DIEs into a debug info section.
    emitDebugInfo();

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

    // 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.
    // TODO: When we don't need the option anymore we
    // can remove all of the code that this section
    // depends upon.
    if (useDarwinGDBCompat())
      emitDebugInlineInfo();
  } else {
    // TODO: Fill this in for Fission sections and separate
    // out information into new sections.

    // Emit the debug info section and compile units.
    emitDebugInfo();
    emitDebugInfoDWO();

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

    // 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.
    // TODO: When we don't need the option anymore we
    // can remove all of the code that this section
    // depends upon.
    if (useDarwinGDBCompat())
      emitDebugInlineInfo();
  }

  // Emit info into the dwarf accelerator table sections.
  if (useDwarfAccelTables()) {
    emitAccelNames();
    emitAccelObjC();
    emitAccelNamespaces();
    emitAccelTypes();
  }

  // Emit info into a debug pubtypes section.
  // TODO: When we don't need the option anymore we can
  // remove all of the code that adds to the table.
  if (useDarwinGDBCompat())
    emitDebugPubTypes();

  // Finally emit string information into a string table.
  emitDebugStr();

  // clean up.
  SPMap.clear();
  for (DenseMap<const MDNode *, CompileUnit *>::iterator I = CUMap.begin(),
         E = CUMap.end(); I != E; ++I)
    delete I->second;
  // Reset these for the next Module if we have one.
  FirstCU = NULL;
  FissionCU = NULL;
}

// Find abstract variable, if any, associated with Var.
DbgVariable *DwarfDebug::findAbstractVariable(DIVariable &DV,
                                              DebugLoc ScopeLoc) {
  LLVMContext &Ctx = DV->getContext();
  // More then one inlined variable corresponds to one abstract variable.
  DIVariable Var = cleanseInlinedVariable(DV, Ctx);
  DbgVariable *AbsDbgVariable = AbstractVariables.lookup(Var);
  if (AbsDbgVariable)
    return AbsDbgVariable;

  LexicalScope *Scope = LScopes.findAbstractScope(ScopeLoc.getScope(Ctx));
  if (!Scope)
    return NULL;