//===--- DebugInfo.cpp - Debug Information Helper Classes -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the helper classes used to build and interpret debug
// information in LLVM IR form.
//
//===----------------------------------------------------------------------===//

#include "llvm/IR/DebugInfo.h"
#include "LLVMContextImpl.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/GVMaterializer.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace llvm::dwarf;

//===----------------------------------------------------------------------===//
// DIDescriptor
//===----------------------------------------------------------------------===//

static Metadata *getField(const MDNode *DbgNode, unsigned Elt) {
  if (!DbgNode || Elt >= DbgNode->getNumOperands())
    return nullptr;
  return DbgNode->getOperand(Elt);
}

static MDNode *getNodeField(const MDNode *DbgNode, unsigned Elt) {
  return dyn_cast_or_null<MDNode>(getField(DbgNode, Elt));
}

DIDescriptor DIDescriptor::getDescriptorField(unsigned Elt) const {
  MDNode *Field = getNodeField(DbgNode, Elt);
  return DIDescriptor(Field);
}

/// \brief Return the size reported by the variable's type.
unsigned DIVariable::getSizeInBits(const DITypeIdentifierMap &Map) {
  DIType Ty = getType().resolve(Map);
  // Follow derived types until we reach a type that
  // reports back a size.
  while (isa<MDDerivedType>(Ty) && !Ty.getSizeInBits()) {
    DIDerivedType DT = cast<MDDerivedType>(Ty);
    Ty = DT.getTypeDerivedFrom().resolve(Map);
  }
  assert(Ty.getSizeInBits() && "type with size 0");
  return Ty.getSizeInBits();
}

//===----------------------------------------------------------------------===//
// Simple Descriptor Constructors and other Methods
//===----------------------------------------------------------------------===//

void DIDescriptor::replaceAllUsesWith(LLVMContext &, DIDescriptor D) {
  assert(DbgNode && "Trying to replace an unverified type!");
  assert(DbgNode->isTemporary() && "Expected temporary node");
  TempMDNode Temp(get());

  // Since we use a TrackingVH for the node, its easy for clients to manufacture
  // legitimate situations where they want to replaceAllUsesWith() on something
  // which, due to uniquing, has merged with the source. We shield clients from
  // this detail by allowing a value to be replaced with replaceAllUsesWith()
  // itself.
  if (Temp.get() == D.get()) {
    DbgNode = MDNode::replaceWithUniqued(std::move(Temp));
    return;
  }

  Temp->replaceAllUsesWith(D.get());
  DbgNode = D.get();
}

void DIDescriptor::replaceAllUsesWith(MDNode *D) {
  assert(DbgNode && "Trying to replace an unverified type!");
  assert(DbgNode != D && "This replacement should always happen");
  assert(DbgNode->isTemporary() && "Expected temporary node");
  TempMDNode Node(get());
  Node->replaceAllUsesWith(D);
}

#ifndef NDEBUG
/// \brief Check if a value can be a reference to a type.
static bool isTypeRef(const Metadata *MD) {
  if (!MD)
    return true;
  if (auto *S = dyn_cast<MDString>(MD))
    return !S->getString().empty();
  return isa<MDType>(MD);
}

/// \brief Check if a value can be a ScopeRef.
static bool isScopeRef(const Metadata *MD) {
  if (!MD)
    return true;
  if (auto *S = dyn_cast<MDString>(MD))
    return !S->getString().empty();
  return isa<MDScope>(MD);
}

/// \brief Check if a value can be a DescriptorRef.
static bool isDescriptorRef(const Metadata *MD) {
  if (!MD)
    return true;
  if (auto *S = dyn_cast<MDString>(MD))
    return !S->getString().empty();
  return isa<MDNode>(MD);
}
#endif

void DICompositeType::setArraysHelper(MDNode *Elements, MDNode *TParams) {
  TypedTrackingMDRef<MDCompositeTypeBase> N(get());
  if (Elements)
    N->replaceElements(cast<MDTuple>(Elements));
  if (TParams)
    N->replaceTemplateParams(cast<MDTuple>(TParams));
  DbgNode = N;
}

DIScopeRef DIScope::getRef() const { return MDScopeRef::get(get()); }

void DICompositeType::setContainingType(DICompositeType ContainingType) {
  TypedTrackingMDRef<MDCompositeTypeBase> N(get());
  N->replaceVTableHolder(MDTypeRef::get(ContainingType));
  DbgNode = N;
}

bool DIVariable::isInlinedFnArgument(const Function *CurFn) {
  assert(CurFn && "Invalid function");
  DISubprogram SP = dyn_cast<MDSubprogram>(getContext());
  if (!SP)
    return false;
  // This variable is not inlined function argument if its scope
  // does not describe current function.
  return !SP.describes(CurFn);
}

Function *DISubprogram::getFunction() const {
  if (auto *N = get())
    if (auto *C = dyn_cast_or_null<ConstantAsMetadata>(N->getFunction()))
      return dyn_cast<Function>(C->getValue());
  return nullptr;
}

bool DISubprogram::describes(const Function *F) {
  assert(F && "Invalid function");
  if (F == getFunction())
    return true;
  StringRef Name = getLinkageName();
  if (Name.empty())
    Name = getName();
  if (F->getName() == Name)
    return true;
  return false;
}

GlobalVariable *DIGlobalVariable::getGlobal() const {
  return dyn_cast_or_null<GlobalVariable>(getConstant());
}

DIScopeRef DIScope::getContext() const {
  if (DIType T = dyn_cast<MDType>(*this))
    return T.getContext();

  if (DISubprogram SP = dyn_cast<MDSubprogram>(*this))
    return DIScopeRef(SP.getContext());

  if (DILexicalBlock LB = dyn_cast<MDLexicalBlockBase>(*this))
    return DIScopeRef(LB.getContext());

  if (DINameSpace NS = dyn_cast<MDNamespace>(*this))
    return DIScopeRef(NS.getContext());

  assert((isa<MDFile>(*this) || isa<MDCompileUnit>(*this)) &&
         "Unhandled type of scope.");
  return DIScopeRef(nullptr);
}

StringRef DIScope::getName() const {
  if (DIType T = dyn_cast<MDType>(*this))
    return T.getName();
  if (DISubprogram SP = dyn_cast<MDSubprogram>(*this))
    return SP.getName();
  if (DINameSpace NS = dyn_cast<MDNamespace>(*this))
    return NS.getName();
  assert((isa<MDLexicalBlockBase>(*this) || isa<MDFile>(*this) ||
          isa<MDCompileUnit>(*this)) &&
         "Unhandled type of scope.");
  return StringRef();
}

StringRef DIScope::getFilename() const {
  if (auto *N = get())
    if (auto *F = N->getFile())
      return F->getFilename();
  return "";
}

StringRef DIScope::getDirectory() const {
  if (auto *N = get())
    if (auto *F = N->getFile())
      return F->getDirectory();
  return "";
}

void DICompileUnit::replaceSubprograms(DIArray Subprograms) {
  get()->replaceSubprograms(cast_or_null<MDTuple>(Subprograms.get()));
}

void DICompileUnit::replaceGlobalVariables(DIArray GlobalVariables) {
  get()->replaceGlobalVariables(cast_or_null<MDTuple>(GlobalVariables.get()));
}

DILocation DILocation::copyWithNewScope(LLVMContext &Ctx,
                                        DILexicalBlockFile NewScope) {
  assert(NewScope && "Expected valid scope");

  const auto *Old = cast<MDLocation>(DbgNode);
  return DILocation(MDLocation::get(Ctx, Old->getLine(), Old->getColumn(),
                                    NewScope, Old->getInlinedAt()));
}

unsigned DILocation::computeNewDiscriminator(LLVMContext &Ctx) {
  std::pair<const char *, unsigned> Key(getFilename().data(), getLineNumber());
  return ++Ctx.pImpl->DiscriminatorTable[Key];
}

DIVariable llvm::createInlinedVariable(MDNode *DV, MDNode *InlinedScope,
                                       LLVMContext &VMContext) {
  return cast<MDLocalVariable>(DV)
      ->withInline(cast_or_null<MDLocation>(InlinedScope));
}

DIVariable llvm::cleanseInlinedVariable(MDNode *DV, LLVMContext &VMContext) {
  return cast<MDLocalVariable>(DV)->withoutInline();
}

DISubprogram llvm::getDISubprogram(const MDNode *Scope) {
  if (auto *LocalScope = dyn_cast_or_null<MDLocalScope>(Scope))
    return LocalScope->getSubprogram();
  return nullptr;
}

DISubprogram llvm::getDISubprogram(const Function *F) {
  // We look for the first instr that has a debug annotation leading back to F.
  for (auto &BB : *F) {
    auto Inst = std::find_if(BB.begin(), BB.end(), [](const Instruction &Inst) {
      return Inst.getDebugLoc();
    });
    if (Inst == BB.end())
      continue;
    DebugLoc DLoc = Inst->getDebugLoc();
    const MDNode *Scope = DLoc.getInlinedAtScope();
    DISubprogram Subprogram = getDISubprogram(Scope);
    return Subprogram.describes(F) ? Subprogram : DISubprogram();
  }

  return DISubprogram();
}

DICompositeType llvm::getDICompositeType(DIType T) {
  if (auto *C = dyn_cast_or_null<MDCompositeTypeBase>(T))
    return C;

  if (auto *D = dyn_cast_or_null<MDDerivedTypeBase>(T)) {
    // This function is currently used by dragonegg and dragonegg does
    // not generate identifier for types, so using an empty map to resolve
    // DerivedFrom should be fine.
    DITypeIdentifierMap EmptyMap;
    return getDICompositeType(
        DIDerivedType(D).getTypeDerivedFrom().resolve(EmptyMap));
  }

  return nullptr;
}

DITypeIdentifierMap
llvm::generateDITypeIdentifierMap(const NamedMDNode *CU_Nodes) {
  DITypeIdentifierMap Map;
  for (unsigned CUi = 0, CUe = CU_Nodes->getNumOperands(); CUi != CUe; ++CUi) {
    DICompileUnit CU = cast<MDCompileUnit>(CU_Nodes->getOperand(CUi));
    DIArray Retain = CU.getRetainedTypes();
    for (unsigned Ti = 0, Te = Retain.getNumElements(); Ti != Te; ++Ti) {
      if (!isa<MDCompositeType>(Retain.getElement(Ti)))
        continue;
      DICompositeType Ty = cast<MDCompositeType>(Retain.getElement(Ti));
      if (MDString *TypeId = Ty.getIdentifier()) {
        // Definition has priority over declaration.
        // Try to insert (TypeId, Ty) to Map.
        std::pair<DITypeIdentifierMap::iterator, bool> P =
            Map.insert(std::make_pair(TypeId, Ty));
        // If TypeId already exists in Map and this is a definition, replace
        // whatever we had (declaration or definition) with the definition.
        if (!P.second && !Ty.isForwardDecl())
          P.first->second = Ty;
      }
    }
  }
  return Map;
}

//===----------------------------------------------------------------------===//
// DebugInfoFinder implementations.
//===----------------------------------------------------------------------===//

void DebugInfoFinder::reset() {
  CUs.clear();
  SPs.clear();
  GVs.clear();
  TYs.clear();
  Scopes.clear();
  NodesSeen.clear();
  TypeIdentifierMap.clear();
  TypeMapInitialized = false;
}

void DebugInfoFinder::InitializeTypeMap(const Module &M) {
  if (!TypeMapInitialized)
    if (NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu")) {
      TypeIdentifierMap = generateDITypeIdentifierMap(CU_Nodes);
      TypeMapInitialized = true;
    }
}

void DebugInfoFinder::processModule(const Module &M) {
  InitializeTypeMap(M);
  if (NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu")) {
    for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
      DICompileUnit CU = cast<MDCompileUnit>(CU_Nodes->getOperand(i));
      addCompileUnit(CU);
      DIArray GVs = CU.getGlobalVariables();
      for (unsigned i = 0, e = GVs.getNumElements(); i != e; ++i) {
        DIGlobalVariable DIG = cast<MDGlobalVariable>(GVs.getElement(i));
        if (addGlobalVariable(DIG)) {
          processScope(DIG.getContext());
          processType(DIG.getType().resolve(TypeIdentifierMap));
        }
      }
      DIArray SPs = CU.getSubprograms();
      for (unsigned i = 0, e = SPs.getNumElements(); i != e; ++i)
        processSubprogram(cast<MDSubprogram>(SPs.getElement(i)));
      DIArray EnumTypes = CU.getEnumTypes();
      for (unsigned i = 0, e = EnumTypes.getNumElements(); i != e; ++i)
        processType(cast<MDType>(EnumTypes.getElement(i)));
      DIArray RetainedTypes = CU.getRetainedTypes();
      for (unsigned i = 0, e = RetainedTypes.getNumElements(); i != e; ++i)
        processType(cast<MDType>(RetainedTypes.getElement(i)));
      DIArray Imports = CU.getImportedEntities();
      for (unsigned i = 0, e = Imports.getNumElements(); i != e; ++i) {
        DIImportedEntity Import = cast<MDImportedEntity>(Imports.getElement(i));
        DIDescriptor Entity = Import.getEntity().resolve(TypeIdentifierMap);
        if (auto *T = dyn_cast<MDType>(Entity))
          processType(T);
        else if (auto *SP = dyn_cast<MDSubprogram>(Entity))
          processSubprogram(SP);
        else if (auto *NS = dyn_cast<MDNamespace>(Entity))
          processScope(NS->getScope());
      }
    }
  }
}

void DebugInfoFinder::processLocation(const Module &M, DILocation Loc) {
  if (!Loc)
    return;
  InitializeTypeMap(M);
  processScope(Loc.getScope());
  processLocation(M, Loc.getOrigLocation());
}

void DebugInfoFinder::processType(DIType DT) {
  if (!addType(DT))
    return;
  processScope(DT.getContext().resolve(TypeIdentifierMap));
  if (DICompositeType DCT = dyn_cast<MDCompositeTypeBase>(DT)) {
    processType(DCT.getTypeDerivedFrom().resolve(TypeIdentifierMap));
    if (DISubroutineType ST = dyn_cast<MDSubroutineType>(DCT)) {
      DITypeArray DTA = ST.getTypeArray();
      for (unsigned i = 0, e = DTA.getNumElements(); i != e; ++i)
        processType(DTA.getElement(i).resolve(TypeIdentifierMap));
      return;
    }
    DIArray DA = DCT.getElements();
    for (unsigned i = 0, e = DA.getNumElements(); i != e; ++i) {
      DIDescriptor D = DA.getElement(i);
      if (DIType T = dyn_cast<MDType>(D))
        processType(T);
      else if (DISubprogram SP = dyn_cast<MDSubprogram>(D))
        processSubprogram(SP);
    }
  } else if (DIDerivedType DDT = dyn_cast<MDDerivedTypeBase>(DT)) {
    processType(DDT.getTypeDerivedFrom().resolve(TypeIdentifierMap));
  }
}

void DebugInfoFinder::processScope(DIScope Scope) {
  if (!Scope)
    return;
  if (DIType Ty = dyn_cast<MDType>(Scope)) {
    processType(Ty);
    return;
  }
  if (DICompileUnit CU = dyn_cast<MDCompileUnit>(Scope)) {
    addCompileUnit(CU);
    return;
  }
  if (DISubprogram SP = dyn_cast<MDSubprogram>(Scope)) {
    processSubprogram(SP);
    return;
  }
  if (!addScope(Scope))
    return;
  if (DILexicalBlock LB = dyn_cast<MDLexicalBlockBase>(Scope)) {
    processScope(LB.getContext());
  } else if (DINameSpace NS = dyn_cast<MDNamespace>(Scope)) {
    processScope(NS.getContext());
  }
}

void DebugInfoFinder::processSubprogram(DISubprogram SP) {
  if (!addSubprogram(SP))
    return;
  processScope(SP.getContext().resolve(TypeIdentifierMap));
  processType(SP.getType());
  DIArray TParams = SP.getTemplateParams();
  for (unsigned I = 0, E = TParams.getNumElements(); I != E; ++I) {
    DIDescriptor Element = TParams.getElement(I);
    if (DITemplateTypeParameter TType =
            dyn_cast<MDTemplateTypeParameter>(Element)) {
      processType(TType.getType().resolve(TypeIdentifierMap));
    } else if (DITemplateValueParameter TVal =
                   dyn_cast<MDTemplateValueParameter>(Element)) {
      processType(TVal.getType().resolve(TypeIdentifierMap));
    }
  }
}

void DebugInfoFinder::processDeclare(const Module &M,
                                     const DbgDeclareInst *DDI) {
  MDNode *N = dyn_cast<MDNode>(DDI->getVariable());
  if (!N)
    return;
  InitializeTypeMap(M);

  DIVariable DV = dyn_cast<MDLocalVariable>(N);
  if (!DV)
    return;

  if (!NodesSeen.insert(DV).second)
    return;
  processScope(DV.getContext());
  processType(DV.getType().resolve(TypeIdentifierMap));
}

void DebugInfoFinder::processValue(const Module &M, const DbgValueInst *DVI) {
  MDNode *N = dyn_cast<MDNode>(DVI->getVariable());
  if (!N)
    return;
  InitializeTypeMap(M);

  DIVariable DV = dyn_cast<MDLocalVariable>(N);
  if (!DV)
    return;

  if (!NodesSeen.insert(DV).second)
    return;
  processScope(DV.getContext());
  processType(DV.getType().resolve(TypeIdentifierMap));
}

bool DebugInfoFinder::addType(DIType DT) {
  if (!DT)
    return false;

  if (!NodesSeen.insert(DT).second)
    return false;

  TYs.push_back(DT);
  return true;
}

bool DebugInfoFinder::addCompileUnit(DICompileUnit CU) {
  if (!CU)
    return false;
  if (!NodesSeen.insert(CU).second)
    return false;

  CUs.push_back(CU);
  return true;
}

bool DebugInfoFinder::addGlobalVariable(DIGlobalVariable DIG) {
  if (!DIG)
    return false;

  if (!NodesSeen.insert(DIG).second)
    return false;

  GVs.push_back(DIG);
  return true;
}

bool DebugInfoFinder::addSubprogram(DISubprogram SP) {
  if (!SP)
    return false;

  if (!NodesSeen.insert(SP).second)
    return false;

  SPs.push_back(SP);
  return true;
}

bool DebugInfoFinder::addScope(DIScope Scope) {
  if (!Scope)
    return false;
  // FIXME: Ocaml binding generates a scope with no content, we treat it
  // as null for now.
  if (Scope->getNumOperands() == 0)
    return false;
  if (!NodesSeen.insert(Scope).second)
    return false;
  Scopes.push_back(Scope);
  return true;
}

//===----------------------------------------------------------------------===//
// DIDescriptor: dump routines for all descriptors.
//===----------------------------------------------------------------------===//

void DIDescriptor::dump() const {
  print(dbgs());
  dbgs() << '\n';
}

void DIDescriptor::print(raw_ostream &OS) const {
  if (!get())
    return;
  get()->print(OS);
}

static void printDebugLoc(DebugLoc DL, raw_ostream &CommentOS,
                          const LLVMContext &Ctx) {
  if (!DL)
    return;

  DIScope Scope = cast<MDScope>(DL.getScope());
  // Omit the directory, because it's likely to be long and uninteresting.
  CommentOS << Scope.getFilename();
  CommentOS << ':' << DL.getLine();
  if (DL.getCol() != 0)
    CommentOS << ':' << DL.getCol();

  DebugLoc InlinedAtDL = DL.getInlinedAt();
  if (!InlinedAtDL)
    return;

  CommentOS << " @[ ";
  printDebugLoc(InlinedAtDL, CommentOS, Ctx);
  CommentOS << " ]";
}

void DIVariable::printExtendedName(raw_ostream &OS) const {
  const LLVMContext &Ctx = DbgNode->getContext();
  StringRef Res = getName();
  if (!Res.empty())
    OS << Res << "," << getLineNumber();
  if (auto *InlinedAt = get()->getInlinedAt()) {
    if (DebugLoc InlinedAtDL = InlinedAt) {
      OS << " @[";
      printDebugLoc(InlinedAtDL, OS, Ctx);
      OS << "]";
    }
  }
}

template <> DIRef<DIDescriptor>::DIRef(const Metadata *V) : Val(V) {
  assert(isDescriptorRef(V) &&
         "DIDescriptorRef should be a MDString or MDNode");
}
template <> DIRef<DIScope>::DIRef(const Metadata *V) : Val(V) {
  assert(isScopeRef(V) && "DIScopeRef should be a MDString or MDNode");
}
template <> DIRef<DIType>::DIRef(const Metadata *V) : Val(V) {
  assert(isTypeRef(V) && "DITypeRef should be a MDString or MDNode");
}

template <>
DIDescriptorRef DIDescriptor::getFieldAs<DIDescriptorRef>(unsigned Elt) const {
  return DIDescriptorRef(cast_or_null<Metadata>(getField(DbgNode, Elt)));
}
template <>
DIScopeRef DIDescriptor::getFieldAs<DIScopeRef>(unsigned Elt) const {
  return DIScopeRef(cast_or_null<Metadata>(getField(DbgNode, Elt)));
}
template <> DITypeRef DIDescriptor::getFieldAs<DITypeRef>(unsigned Elt) const {
  return DITypeRef(cast_or_null<Metadata>(getField(DbgNode, Elt)));
}

template <>
DIDescriptor
DIRef<DIDescriptor>::resolve(const DITypeIdentifierMap &Map) const {
  return DIDescriptor(DebugNodeRef(Val).resolve(Map));
}
template <>
DIScope DIRef<DIScope>::resolve(const DITypeIdentifierMap &Map) const {
  return MDScopeRef(Val).resolve(Map);
}
template <>
DIType DIRef<DIType>::resolve(const DITypeIdentifierMap &Map) const {
  return MDTypeRef(Val).resolve(Map);
}

bool llvm::stripDebugInfo(Function &F) {
  bool Changed = false;
  for (BasicBlock &BB : F) {
    for (Instruction &I : BB) {
      if (I.getDebugLoc()) {
        Changed = true;
        I.setDebugLoc(DebugLoc());
      }
    }
  }
  return Changed;
}

bool llvm::StripDebugInfo(Module &M) {
  bool Changed = false;

  // Remove all of the calls to the debugger intrinsics, and remove them from
  // the module.
  if (Function *Declare = M.getFunction("llvm.dbg.declare")) {
    while (!Declare->use_empty()) {
      CallInst *CI = cast<CallInst>(Declare->user_back());
      CI->eraseFromParent();
    }
    Declare->eraseFromParent();
    Changed = true;
  }

  if (Function *DbgVal = M.getFunction("llvm.dbg.value")) {
    while (!DbgVal->use_empty()) {
      CallInst *CI = cast<CallInst>(DbgVal->user_back());
      CI->eraseFromParent();
    }
    DbgVal->eraseFromParent();
    Changed = true;
  }

  for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),
         NME = M.named_metadata_end(); NMI != NME;) {
    NamedMDNode *NMD = NMI;
    ++NMI;
    if (NMD->getName().startswith("llvm.dbg.")) {
      NMD->eraseFromParent();
      Changed = true;
    }
  }

  for (Function &F : M)
    Changed |= stripDebugInfo(F);

  if (GVMaterializer *Materializer = M.getMaterializer())
    Materializer->setStripDebugInfo();

  return Changed;
}

unsigned llvm::getDebugMetadataVersionFromModule(const Module &M) {
  if (auto *Val = mdconst::dyn_extract_or_null<ConstantInt>(
          M.getModuleFlag("Debug Info Version")))
    return Val->getZExtValue();
  return 0;
}

llvm::DenseMap<const llvm::Function *, llvm::DISubprogram>
llvm::makeSubprogramMap(const Module &M) {
  DenseMap<const Function *, DISubprogram> R;

  NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu");
  if (!CU_Nodes)
    return R;

  for (MDNode *N : CU_Nodes->operands()) {
    DICompileUnit CUNode = cast<MDCompileUnit>(N);
    DIArray SPs = CUNode.getSubprograms();
    for (unsigned i = 0, e = SPs.getNumElements(); i != e; ++i) {
      DISubprogram SP = cast<MDSubprogram>(SPs.getElement(i));
      if (Function *F = SP.getFunction())
        R.insert(std::make_pair(F, SP));
    }
  }
  return R;
}