lib/Sema/SemaTemplateInstantiateDecl.cpp

//===--- SemaTemplateInstantiateDecl.cpp - C++ Template Decl Instantiation ===/
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//===----------------------------------------------------------------------===/
//
//  This file implements C++ template instantiation for declarations.
//
//===----------------------------------------------------------------------===/
#include "Sema.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/AST/Expr.h"
#include "clang/Basic/PrettyStackTrace.h"
#include "clang/Lex/Preprocessor.h"
#include "llvm/Support/Compiler.h"

using namespace clang;

namespace {
  class VISIBILITY_HIDDEN TemplateDeclInstantiator
    : public DeclVisitor<TemplateDeclInstantiator, Decl *> {
    Sema &SemaRef;
    DeclContext *Owner;
    const MultiLevelTemplateArgumentList &TemplateArgs;

    void InstantiateAttrs(Decl *Tmpl, Decl *New);
      
  public:
    typedef Sema::OwningExprResult OwningExprResult;

    TemplateDeclInstantiator(Sema &SemaRef, DeclContext *Owner,
                             const MultiLevelTemplateArgumentList &TemplateArgs)
      : SemaRef(SemaRef), Owner(Owner), TemplateArgs(TemplateArgs) { }

    // FIXME: Once we get closer to completion, replace these manually-written
    // declarations with automatically-generated ones from
    // clang/AST/DeclNodes.def.
    Decl *VisitTranslationUnitDecl(TranslationUnitDecl *D);
    Decl *VisitNamespaceDecl(NamespaceDecl *D);
    Decl *VisitTypedefDecl(TypedefDecl *D);
    Decl *VisitVarDecl(VarDecl *D);
    Decl *VisitFieldDecl(FieldDecl *D);
    Decl *VisitStaticAssertDecl(StaticAssertDecl *D);
    Decl *VisitEnumDecl(EnumDecl *D);
    Decl *VisitEnumConstantDecl(EnumConstantDecl *D);
    Decl *VisitFriendDecl(FriendDecl *D);
    Decl *VisitFunctionDecl(FunctionDecl *D,
                            TemplateParameterList *TemplateParams = 0);
    Decl *VisitCXXRecordDecl(CXXRecordDecl *D);
    Decl *VisitCXXMethodDecl(CXXMethodDecl *D,
                             TemplateParameterList *TemplateParams = 0);
    Decl *VisitCXXConstructorDecl(CXXConstructorDecl *D);
    Decl *VisitCXXDestructorDecl(CXXDestructorDecl *D);
    Decl *VisitCXXConversionDecl(CXXConversionDecl *D);
    ParmVarDecl *VisitParmVarDecl(ParmVarDecl *D);
    Decl *VisitClassTemplateDecl(ClassTemplateDecl *D);
    Decl *VisitClassTemplatePartialSpecializationDecl(
                                    ClassTemplatePartialSpecializationDecl *D);
    Decl *VisitFunctionTemplateDecl(FunctionTemplateDecl *D);
    Decl *VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D);
    Decl *VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
    Decl *VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
    Decl *VisitUnresolvedUsingDecl(UnresolvedUsingDecl *D);

    // Base case. FIXME: Remove once we can instantiate everything.
    Decl *VisitDecl(Decl *) {
      assert(false && "Template instantiation of unknown declaration kind!");
      return 0;
    }

    const LangOptions &getLangOptions() {
      return SemaRef.getLangOptions();
    }

    // Helper functions for instantiating methods.
    QualType SubstFunctionType(FunctionDecl *D,
                             llvm::SmallVectorImpl<ParmVarDecl *> &Params);
    bool InitFunctionInstantiation(FunctionDecl *New, FunctionDecl *Tmpl);
    bool InitMethodInstantiation(CXXMethodDecl *New, CXXMethodDecl *Tmpl);

    TemplateParameterList *
      SubstTemplateParams(TemplateParameterList *List);
      
    bool InstantiateClassTemplatePartialSpecialization(
                                              ClassTemplateDecl *ClassTemplate,
                           ClassTemplatePartialSpecializationDecl *PartialSpec);
  };
}

// FIXME: Is this too simple?
void TemplateDeclInstantiator::InstantiateAttrs(Decl *Tmpl, Decl *New) {
  for (const Attr *TmplAttr = Tmpl->getAttrs(); TmplAttr; 
       TmplAttr = TmplAttr->getNext()) {
    
    // FIXME: Is cloning correct for all attributes?
    Attr *NewAttr = TmplAttr->clone(SemaRef.Context);
    
    New->addAttr(NewAttr);
  }
}

Decl *
TemplateDeclInstantiator::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
  assert(false && "Translation units cannot be instantiated");
  return D;
}

Decl *
TemplateDeclInstantiator::VisitNamespaceDecl(NamespaceDecl *D) {
  assert(false && "Namespaces cannot be instantiated");
  return D;
}

Decl *TemplateDeclInstantiator::VisitTypedefDecl(TypedefDecl *D) {
  bool Invalid = false;
  DeclaratorInfo *DI = D->getTypeDeclaratorInfo();
  if (DI->getType()->isDependentType()) {
    DI = SemaRef.SubstType(DI, TemplateArgs,
                           D->getLocation(), D->getDeclName());
    if (!DI) {
      Invalid = true;
      DI = SemaRef.Context.getTrivialDeclaratorInfo(SemaRef.Context.IntTy);
    }
  }

  // Create the new typedef
  TypedefDecl *Typedef
    = TypedefDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                          D->getIdentifier(), DI);
  if (Invalid)
    Typedef->setInvalidDecl();

  Owner->addDecl(Typedef);

  return Typedef;
}

Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
  // Do substitution on the type of the declaration
  DeclaratorInfo *DI = SemaRef.SubstType(D->getDeclaratorInfo(),
                                         TemplateArgs,
                                         D->getTypeSpecStartLoc(),
                                         D->getDeclName());
  if (!DI)
    return 0;

  // Build the instantiated declaration
  VarDecl *Var = VarDecl::Create(SemaRef.Context, Owner,
                                 D->getLocation(), D->getIdentifier(),
                                 DI->getType(), DI,
                                 D->getStorageClass());
  Var->setThreadSpecified(D->isThreadSpecified());
  Var->setCXXDirectInitializer(D->hasCXXDirectInitializer());
  Var->setDeclaredInCondition(D->isDeclaredInCondition());

  // If we are instantiating a static data member defined
  // out-of-line, the instantiation will have the same lexical
  // context (which will be a namespace scope) as the template.
  if (D->isOutOfLine())
    Var->setLexicalDeclContext(D->getLexicalDeclContext());

  // FIXME: In theory, we could have a previous declaration for variables that
  // are not static data members.
  bool Redeclaration = false;
  SemaRef.CheckVariableDeclaration(Var, 0, Redeclaration);

  if (D->isOutOfLine()) {
    D->getLexicalDeclContext()->addDecl(Var);
    Owner->makeDeclVisibleInContext(Var);
  } else {
    Owner->addDecl(Var);
  }

  // Link instantiations of static data members back to the template from
  // which they were instantiated.
  if (Var->isStaticDataMember())
    SemaRef.Context.setInstantiatedFromStaticDataMember(Var, D, 
                                                     TSK_ImplicitInstantiation);
  
  if (D->getInit()) {
    OwningExprResult Init
      = SemaRef.SubstExpr(D->getInit(), TemplateArgs);
    if (Init.isInvalid())
      Var->setInvalidDecl();
    else if (!D->getType()->isDependentType() &&
             !D->getInit()->isTypeDependent() &&
             !D->getInit()->isValueDependent()) {
      // If neither the declaration's type nor its initializer are dependent,
      // we don't want to redo all the checking, especially since the
      // initializer might have been wrapped by a CXXConstructExpr since we did
      // it the first time.
      Var->setInit(SemaRef.Context, Init.takeAs<Expr>());
    }
    else if (ParenListExpr *PLE = dyn_cast<ParenListExpr>((Expr *)Init.get())) {
      // FIXME: We're faking all of the comma locations, which is suboptimal.
      // Do we even need these comma locations?
      llvm::SmallVector<SourceLocation, 4> FakeCommaLocs;
      if (PLE->getNumExprs() > 0) {
        FakeCommaLocs.reserve(PLE->getNumExprs() - 1);
        for (unsigned I = 0, N = PLE->getNumExprs() - 1; I != N; ++I) {
          Expr *E = PLE->getExpr(I)->Retain();
          FakeCommaLocs.push_back(
                                SemaRef.PP.getLocForEndOfToken(E->getLocEnd()));
        }
        PLE->getExpr(PLE->getNumExprs() - 1)->Retain();
      }

      // Add the direct initializer to the declaration.
      SemaRef.AddCXXDirectInitializerToDecl(Sema::DeclPtrTy::make(Var),
                                            PLE->getLParenLoc(),
                                            Sema::MultiExprArg(SemaRef,
                                                       (void**)PLE->getExprs(),
                                                           PLE->getNumExprs()),
                                            FakeCommaLocs.data(),
                                            PLE->getRParenLoc());

      // When Init is destroyed, it will destroy the instantiated ParenListExpr;
      // we've explicitly retained all of its subexpressions already.
    } else
      SemaRef.AddInitializerToDecl(Sema::DeclPtrTy::make(Var), move(Init),
                                   D->hasCXXDirectInitializer());
  } else if (!Var->isStaticDataMember() || Var->isOutOfLine())
    SemaRef.ActOnUninitializedDecl(Sema::DeclPtrTy::make(Var), false);

  return Var;
}

Decl *TemplateDeclInstantiator::VisitFieldDecl(FieldDecl *D) {
  bool Invalid = false;
  DeclaratorInfo *DI = D->getDeclaratorInfo();
  if (DI->getType()->isDependentType())  {
    DI = SemaRef.SubstType(DI, TemplateArgs,
                           D->getLocation(), D->getDeclName());
    if (!DI) {
      DI = D->getDeclaratorInfo();
      Invalid = true;
    } else if (DI->getType()->isFunctionType()) {
      // C++ [temp.arg.type]p3:
      //   If a declaration acquires a function type through a type
      //   dependent on a template-parameter and this causes a
      //   declaration that does not use the syntactic form of a
      //   function declarator to have function type, the program is
      //   ill-formed.
      SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
        << DI->getType();
      Invalid = true;
    }
  }

  Expr *BitWidth = D->getBitWidth();
  if (Invalid)
    BitWidth = 0;
  else if (BitWidth) {
    // The bit-width expression is not potentially evaluated.
    EnterExpressionEvaluationContext Unevaluated(SemaRef, Action::Unevaluated);

    OwningExprResult InstantiatedBitWidth
      = SemaRef.SubstExpr(BitWidth, TemplateArgs);
    if (InstantiatedBitWidth.isInvalid()) {
      Invalid = true;
      BitWidth = 0;
    } else
      BitWidth = InstantiatedBitWidth.takeAs<Expr>();
  }

  FieldDecl *Field = SemaRef.CheckFieldDecl(D->getDeclName(),
                                            DI->getType(), DI,
                                            cast<RecordDecl>(Owner),
                                            D->getLocation(),
                                            D->isMutable(),
                                            BitWidth,
                                            D->getTypeSpecStartLoc(),
                                            D->getAccess(),
                                            0);
  if (!Field) {
    cast<Decl>(Owner)->setInvalidDecl();
    return 0;
  }

  InstantiateAttrs(D, Field);
  
  if (Invalid)
    Field->setInvalidDecl();

  if (!Field->getDeclName()) {
    // Keep track of where this decl came from.
    SemaRef.Context.setInstantiatedFromUnnamedFieldDecl(Field, D);
  }

  Field->setImplicit(D->isImplicit());
  Owner->addDecl(Field);

  return Field;
}

Decl *TemplateDeclInstantiator::VisitFriendDecl(FriendDecl *D) {
  FriendDecl::FriendUnion FU;

  // Handle friend type expressions by simply substituting template
  // parameters into the pattern type.
  if (Type *Ty = D->getFriendType()) {
    QualType T = SemaRef.SubstType(QualType(Ty,0), TemplateArgs,
                                   D->getLocation(), DeclarationName());
    if (T.isNull()) return 0;

    assert(getLangOptions().CPlusPlus0x || T->isRecordType());
    FU = T.getTypePtr();

  // Handle everything else by appropriate substitution.
  } else {
    NamedDecl *ND = D->getFriendDecl();
    assert(ND && "friend decl must be a decl or a type!");

    // FIXME: We have a problem here, because the nested call to Visit(ND)
    // will inject the thing that the friend references into the current
    // owner, which is wrong.
    Decl *NewND = Visit(ND);
    if (!NewND) return 0;

    FU = cast<NamedDecl>(NewND);
  }

  FriendDecl *FD =
    FriendDecl::Create(SemaRef.Context, Owner, D->getLocation(), FU,
                       D->getFriendLoc());
  FD->setAccess(AS_public);
  Owner->addDecl(FD);
  return FD;
}

Decl *TemplateDeclInstantiator::VisitStaticAssertDecl(StaticAssertDecl *D) {
  Expr *AssertExpr = D->getAssertExpr();

  // The expression in a static assertion is not potentially evaluated.
  EnterExpressionEvaluationContext Unevaluated(SemaRef, Action::Unevaluated);

  OwningExprResult InstantiatedAssertExpr
    = SemaRef.SubstExpr(AssertExpr, TemplateArgs);
  if (InstantiatedAssertExpr.isInvalid())
    return 0;

  OwningExprResult Message(SemaRef, D->getMessage());
  D->getMessage()->Retain();
  Decl *StaticAssert
    = SemaRef.ActOnStaticAssertDeclaration(D->getLocation(),
                                           move(InstantiatedAssertExpr),
                                           move(Message)).getAs<Decl>();
  return StaticAssert;
}

Decl *TemplateDeclInstantiator::VisitEnumDecl(EnumDecl *D) {
  EnumDecl *Enum = EnumDecl::Create(SemaRef.Context, Owner,
                                    D->getLocation(), D->getIdentifier(),
                                    D->getTagKeywordLoc(),
                                    /*PrevDecl=*/0);
  Enum->setInstantiationOfMemberEnum(D);
  Enum->setAccess(D->getAccess());
  Owner->addDecl(Enum);
  Enum->startDefinition();

  llvm::SmallVector<Sema::DeclPtrTy, 4> Enumerators;

  EnumConstantDecl *LastEnumConst = 0;
  for (EnumDecl::enumerator_iterator EC = D->enumerator_begin(),
         ECEnd = D->enumerator_end();
       EC != ECEnd; ++EC) {
    // The specified value for the enumerator.
    OwningExprResult Value = SemaRef.Owned((Expr *)0);
    if (Expr *UninstValue = EC->getInitExpr()) {
      // The enumerator's value expression is not potentially evaluated.
      EnterExpressionEvaluationContext Unevaluated(SemaRef,
                                                   Action::Unevaluated);

      Value = SemaRef.SubstExpr(UninstValue, TemplateArgs);
    }

    // Drop the initial value and continue.
    bool isInvalid = false;
    if (Value.isInvalid()) {
      Value = SemaRef.Owned((Expr *)0);
      isInvalid = true;
    }

    EnumConstantDecl *EnumConst
      = SemaRef.CheckEnumConstant(Enum, LastEnumConst,
                                  EC->getLocation(), EC->getIdentifier(),
                                  move(Value));

    if (isInvalid) {
      if (EnumConst)
        EnumConst->setInvalidDecl();
      Enum->setInvalidDecl();
    }

    if (EnumConst) {
      Enum->addDecl(EnumConst);
      Enumerators.push_back(Sema::DeclPtrTy::make(EnumConst));
      LastEnumConst = EnumConst;
    }
  }

  // FIXME: Fixup LBraceLoc and RBraceLoc
  // FIXME: Empty Scope and AttributeList (required to handle attribute packed).
  SemaRef.ActOnEnumBody(Enum->getLocation(), SourceLocation(), SourceLocation(),
                        Sema::DeclPtrTy::make(Enum),
                        &Enumerators[0], Enumerators.size(),
                        0, 0);

  return Enum;
}

Decl *TemplateDeclInstantiator::VisitEnumConstantDecl(EnumConstantDecl *D) {
  assert(false && "EnumConstantDecls can only occur within EnumDecls.");
  return 0;
}

namespace {
  class SortDeclByLocation {
    SourceManager &SourceMgr;
    
  public:
    explicit SortDeclByLocation(SourceManager &SourceMgr) 
      : SourceMgr(SourceMgr) { }
    
    bool operator()(const Decl *X, const Decl *Y) const {
      return SourceMgr.isBeforeInTranslationUnit(X->getLocation(),
                                                 Y->getLocation());
    }
  };
}

Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
  // Create a local instantiation scope for this class template, which
  // will contain the instantiations of the template parameters.
  Sema::LocalInstantiationScope Scope(SemaRef);
  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return NULL;

  CXXRecordDecl *Pattern = D->getTemplatedDecl();
  CXXRecordDecl *RecordInst
    = CXXRecordDecl::Create(SemaRef.Context, Pattern->getTagKind(), Owner,
                            Pattern->getLocation(), Pattern->getIdentifier(),
                            Pattern->getTagKeywordLoc(), /*PrevDecl=*/ NULL,
                            /*DelayTypeCreation=*/true);

  ClassTemplateDecl *Inst
    = ClassTemplateDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                D->getIdentifier(), InstParams, RecordInst, 0);
  RecordInst->setDescribedClassTemplate(Inst);
  if (D->getFriendObjectKind())
    Inst->setObjectOfFriendDecl(true);
  else
    Inst->setAccess(D->getAccess());
  Inst->setInstantiatedFromMemberTemplate(D);
  
  // Trigger creation of the type for the instantiation.
  SemaRef.Context.getTypeDeclType(RecordInst);
  
  // Finish handling of friends.
  if (Inst->getFriendObjectKind()) {
    return Inst;
  }
  
  Owner->addDecl(Inst);
  
  // First, we sort the partial specializations by location, so 
  // that we instantiate them in the order they were declared.
  llvm::SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
  for (llvm::FoldingSet<ClassTemplatePartialSpecializationDecl>::iterator
         P = D->getPartialSpecializations().begin(), 
         PEnd = D->getPartialSpecializations().end();
       P != PEnd; ++P)
    PartialSpecs.push_back(&*P);
  std::sort(PartialSpecs.begin(), PartialSpecs.end(),
            SortDeclByLocation(SemaRef.SourceMgr));
  
  // Instantiate all of the partial specializations of this member class 
  // template.
  for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
    InstantiateClassTemplatePartialSpecialization(Inst, PartialSpecs[I]);
  
  return Inst;
}

Decl *
TemplateDeclInstantiator::VisitClassTemplatePartialSpecializationDecl(
                                   ClassTemplatePartialSpecializationDecl *D) {
  ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();
  
  // Lookup the already-instantiated declaration in the instantiation
  // of the class template and return that.
  DeclContext::lookup_result Found
    = Owner->lookup(ClassTemplate->getDeclName());
  if (Found.first == Found.second)
    return 0;
  
  ClassTemplateDecl *InstClassTemplate
    = dyn_cast<ClassTemplateDecl>(*Found.first);
  if (!InstClassTemplate)
    return 0;
  
  Decl *DCanon = D->getCanonicalDecl();
  for (llvm::FoldingSet<ClassTemplatePartialSpecializationDecl>::iterator
            P = InstClassTemplate->getPartialSpecializations().begin(),
         PEnd = InstClassTemplate->getPartialSpecializations().end();
       P != PEnd; ++P) {
    if (P->getInstantiatedFromMember()->getCanonicalDecl() == DCanon)
      return &*P;
  }
  
  return 0;
}

Decl *
TemplateDeclInstantiator::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
  // Create a local instantiation scope for this function template, which
  // will contain the instantiations of the template parameters and then get
  // merged with the local instantiation scope for the function template 
  // itself.
  Sema::LocalInstantiationScope Scope(SemaRef);
  
  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return NULL;
  
  FunctionDecl *Instantiated = 0;
  if (CXXMethodDecl *DMethod = dyn_cast<CXXMethodDecl>(D->getTemplatedDecl()))
    Instantiated = cast_or_null<FunctionDecl>(VisitCXXMethodDecl(DMethod, 
                                                                 InstParams));
  else
    Instantiated = cast_or_null<FunctionDecl>(VisitFunctionDecl(
                                                          D->getTemplatedDecl(), 
                                                                InstParams));
  
  if (!Instantiated)
    return 0;

  // Link the instantiated function template declaration to the function
  // template from which it was instantiated.
  FunctionTemplateDecl *InstTemplate 
    = Instantiated->getDescribedFunctionTemplate();
  InstTemplate->setAccess(D->getAccess());
  assert(InstTemplate && 
         "VisitFunctionDecl/CXXMethodDecl didn't create a template!");
  if (!InstTemplate->getInstantiatedFromMemberTemplate())
    InstTemplate->setInstantiatedFromMemberTemplate(D);
  
  // Add non-friends into the owner.
  if (!InstTemplate->getFriendObjectKind())
    Owner->addDecl(InstTemplate);
  return InstTemplate;
}

Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
  CXXRecordDecl *PrevDecl = 0;
  if (D->isInjectedClassName())
    PrevDecl = cast<CXXRecordDecl>(Owner);

  CXXRecordDecl *Record
    = CXXRecordDecl::Create(SemaRef.Context, D->getTagKind(), Owner,
                            D->getLocation(), D->getIdentifier(),
                            D->getTagKeywordLoc(), PrevDecl);
  Record->setImplicit(D->isImplicit());
  // FIXME: Check against AS_none is an ugly hack to work around the issue that
  // the tag decls introduced by friend class declarations don't have an access
  // specifier. Remove once this area of the code gets sorted out.
  if (D->getAccess() != AS_none)
    Record->setAccess(D->getAccess());
  if (!D->isInjectedClassName())
    Record->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);

  // If the original function was part of a friend declaration,
  // inherit its namespace state.
  if (Decl::FriendObjectKind FOK = D->getFriendObjectKind())
    Record->setObjectOfFriendDecl(FOK == Decl::FOK_Declared);

  Record->setAnonymousStructOrUnion(D->isAnonymousStructOrUnion());

  Owner->addDecl(Record);
  return Record;
}

/// Normal class members are of more specific types and therefore
/// don't make it here.  This function serves two purposes:
///   1) instantiating function templates
///   2) substituting friend declarations
/// FIXME: preserve function definitions in case #2
  Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
                                       TemplateParameterList *TemplateParams) {
  // Check whether there is already a function template specialization for
  // this declaration.
  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
  void *InsertPos = 0;
  if (FunctionTemplate && !TemplateParams) {
    llvm::FoldingSetNodeID ID;
    FunctionTemplateSpecializationInfo::Profile(ID,
                             TemplateArgs.getInnermost().getFlatArgumentList(),
                                       TemplateArgs.getInnermost().flat_size(),
                                                SemaRef.Context);

    FunctionTemplateSpecializationInfo *Info
      = FunctionTemplate->getSpecializations().FindNodeOrInsertPos(ID,
                                                                   InsertPos);

    // If we already have a function template specialization, return it.
    if (Info)
      return Info->Function;
  }

  Sema::LocalInstantiationScope Scope(SemaRef, TemplateParams != 0);

  llvm::SmallVector<ParmVarDecl *, 4> Params;
  QualType T = SubstFunctionType(D, Params);
  if (T.isNull())
    return 0;

  // Build the instantiated method declaration.
  DeclContext *DC = SemaRef.FindInstantiatedContext(D->getDeclContext(),
                                                    TemplateArgs);
  FunctionDecl *Function =
      FunctionDecl::Create(SemaRef.Context, DC, D->getLocation(),
                           D->getDeclName(), T, D->getDeclaratorInfo(),
                           D->getStorageClass(),
                           D->isInlineSpecified(), D->hasWrittenPrototype());
  Function->setLexicalDeclContext(Owner);

  // Attach the parameters
  for (unsigned P = 0; P < Params.size(); ++P)
    Params[P]->setOwningFunction(Function);
  Function->setParams(SemaRef.Context, Params.data(), Params.size());

  if (TemplateParams) {
    // Our resulting instantiation is actually a function template, since we
    // are substituting only the outer template parameters. For example, given
    //
    //   template<typename T>
    //   struct X {
    //     template<typename U> friend void f(T, U);
    //   };
    //
    //   X<int> x;
    //
    // We are instantiating the friend function template "f" within X<int>, 
    // which means substituting int for T, but leaving "f" as a friend function
    // template.
    // Build the function template itself.
    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, Owner,
                                                    Function->getLocation(),
                                                    Function->getDeclName(),
                                                    TemplateParams, Function);
    Function->setDescribedFunctionTemplate(FunctionTemplate);
    FunctionTemplate->setLexicalDeclContext(D->getLexicalDeclContext());
  } else if (FunctionTemplate) {
    // Record this function template specialization.
    Function->setFunctionTemplateSpecialization(SemaRef.Context,
                                                FunctionTemplate,
                                                &TemplateArgs.getInnermost(),
                                                InsertPos);
  }
    
  if (InitFunctionInstantiation(Function, D))
    Function->setInvalidDecl();

  bool Redeclaration = false;
  bool OverloadableAttrRequired = false;
    
  NamedDecl *PrevDecl = 0;
  if (TemplateParams || !FunctionTemplate) {
    // Look only into the namespace where the friend would be declared to 
    // find a previous declaration. This is the innermost enclosing namespace, 
    // as described in ActOnFriendFunctionDecl.
    Sema::LookupResult R(SemaRef, Function->getDeclName(), SourceLocation(),
                         Sema::LookupOrdinaryName,
                         Sema::LookupResult::ForRedeclaration);
    SemaRef.LookupQualifiedName(R, DC);
    
    PrevDecl = R.getAsSingleDecl(SemaRef.Context);

    // In C++, the previous declaration we find might be a tag type
    // (class or enum). In this case, the new declaration will hide the
    // tag type. Note that this does does not apply if we're declaring a
    // typedef (C++ [dcl.typedef]p4).
    if (PrevDecl && PrevDecl->getIdentifierNamespace() == Decl::IDNS_Tag)
      PrevDecl = 0;
  }
  
  SemaRef.CheckFunctionDeclaration(Function, PrevDecl, false, Redeclaration,
                                   /*FIXME:*/OverloadableAttrRequired);

  // If the original function was part of a friend declaration,
  // inherit its namespace state and add it to the owner.
  NamedDecl *FromFriendD 
      = TemplateParams? cast<NamedDecl>(D->getDescribedFunctionTemplate()) : D;
  if (FromFriendD->getFriendObjectKind()) {
    NamedDecl *ToFriendD = 0;
    if (TemplateParams) {
      ToFriendD = cast<NamedDecl>(FunctionTemplate);
      PrevDecl = FunctionTemplate->getPreviousDeclaration();
    } else {
      ToFriendD = Function;
      PrevDecl = Function->getPreviousDeclaration();
    }
    ToFriendD->setObjectOfFriendDecl(PrevDecl != NULL);
    if (!Owner->isDependentContext() && !PrevDecl)
      DC->makeDeclVisibleInContext(ToFriendD, /* Recoverable = */ false);

    if (!TemplateParams)
      Function->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
  }

  return Function;
}

Decl *
TemplateDeclInstantiator::VisitCXXMethodDecl(CXXMethodDecl *D,
                                      TemplateParameterList *TemplateParams) {
  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
  void *InsertPos = 0;
  if (FunctionTemplate && !TemplateParams) {
    // We are creating a function template specialization from a function
    // template. Check whether there is already a function template
    // specialization for this particular set of template arguments.
    llvm::FoldingSetNodeID ID;
    FunctionTemplateSpecializationInfo::Profile(ID,
                            TemplateArgs.getInnermost().getFlatArgumentList(),
                                      TemplateArgs.getInnermost().flat_size(),
                                                SemaRef.Context);

    FunctionTemplateSpecializationInfo *Info
      = FunctionTemplate->getSpecializations().FindNodeOrInsertPos(ID,
                                                                   InsertPos);

    // If we already have a function template specialization, return it.
    if (Info)
      return Info->Function;
  }

  Sema::LocalInstantiationScope Scope(SemaRef, TemplateParams != 0);

  llvm::SmallVector<ParmVarDecl *, 4> Params;
  QualType T = SubstFunctionType(D, Params);
  if (T.isNull())
    return 0;

  // Build the instantiated method declaration.
  CXXRecordDecl *Record = cast<CXXRecordDecl>(Owner);
  CXXMethodDecl *Method = 0;

  DeclarationName Name = D->getDeclName();
  if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
    QualType ClassTy = SemaRef.Context.getTypeDeclType(Record);
    Name = SemaRef.Context.DeclarationNames.getCXXConstructorName(
                                    SemaRef.Context.getCanonicalType(ClassTy));
    Method = CXXConstructorDecl::Create(SemaRef.Context, Record,
                                        Constructor->getLocation(),
                                        Name, T,
                                        Constructor->getDeclaratorInfo(),
                                        Constructor->isExplicit(),
                                        Constructor->isInlineSpecified(), false);
  } else if (CXXDestructorDecl *Destructor = dyn_cast<CXXDestructorDecl>(D)) {
    QualType ClassTy = SemaRef.Context.getTypeDeclType(Record);
    Name = SemaRef.Context.DeclarationNames.getCXXDestructorName(
                                   SemaRef.Context.getCanonicalType(ClassTy));
    Method = CXXDestructorDecl::Create(SemaRef.Context, Record,
                                       Destructor->getLocation(), Name,
                                       T, Destructor->isInlineSpecified(), false);
  } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
    CanQualType ConvTy
      = SemaRef.Context.getCanonicalType(
                                      T->getAs<FunctionType>()->getResultType());
    Name = SemaRef.Context.DeclarationNames.getCXXConversionFunctionName(
                                                                      ConvTy);
    Method = CXXConversionDecl::Create(SemaRef.Context, Record,
                                       Conversion->getLocation(), Name,
                                       T, Conversion->getDeclaratorInfo(),
                                       Conversion->isInlineSpecified(),
                                       Conversion->isExplicit());
  } else {
    Method = CXXMethodDecl::Create(SemaRef.Context, Record, D->getLocation(),
                                   D->getDeclName(), T, D->getDeclaratorInfo(),
                                   D->isStatic(), D->isInlineSpecified());
  }

  if (TemplateParams) {
    // Our resulting instantiation is actually a function template, since we
    // are substituting only the outer template parameters. For example, given
    //
    //   template<typename T>
    //   struct X {
    //     template<typename U> void f(T, U);
    //   };
    //
    //   X<int> x;
    //
    // We are instantiating the member template "f" within X<int>, which means
    // substituting int for T, but leaving "f" as a member function template.
    // Build the function template itself.
    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, Record,
                                                    Method->getLocation(),
                                                    Method->getDeclName(),
                                                    TemplateParams, Method);
    if (D->isOutOfLine())
      FunctionTemplate->setLexicalDeclContext(D->getLexicalDeclContext());
    Method->setDescribedFunctionTemplate(FunctionTemplate);
  } else if (FunctionTemplate) {
    // Record this function template specialization.
    Method->setFunctionTemplateSpecialization(SemaRef.Context,
                                              FunctionTemplate,
                                              &TemplateArgs.getInnermost(),
                                              InsertPos);
  } else {
    // Record that this is an instantiation of a member function.
    Method->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
  }
  
  // If we are instantiating a member function defined
  // out-of-line, the instantiation will have the same lexical
  // context (which will be a namespace scope) as the template.
  if (D->isOutOfLine())
    Method->setLexicalDeclContext(D->getLexicalDeclContext());

  // Attach the parameters
  for (unsigned P = 0; P < Params.size(); ++P)
    Params[P]->setOwningFunction(Method);
  Method->setParams(SemaRef.Context, Params.data(), Params.size());

  if (InitMethodInstantiation(Method, D))
    Method->setInvalidDecl();

  NamedDecl *PrevDecl = 0;

  if (!FunctionTemplate || TemplateParams) {
    Sema::LookupResult R(SemaRef, Name, SourceLocation(),
                         Sema::LookupOrdinaryName,
                         Sema::LookupResult::ForRedeclaration);
    SemaRef.LookupQualifiedName(R, Owner);
    PrevDecl = R.getAsSingleDecl(SemaRef.Context);

    // In C++, the previous declaration we find might be a tag type
    // (class or enum). In this case, the new declaration will hide the
    // tag type. Note that this does does not apply if we're declaring a
    // typedef (C++ [dcl.typedef]p4).
    if (PrevDecl && PrevDecl->getIdentifierNamespace() == Decl::IDNS_Tag)
      PrevDecl = 0;
  }

  bool Redeclaration = false;
  bool OverloadableAttrRequired = false;
  SemaRef.CheckFunctionDeclaration(Method, PrevDecl, false, Redeclaration,
                                   /*FIXME:*/OverloadableAttrRequired);

  if (!FunctionTemplate && (!Method->isInvalidDecl() || !PrevDecl) &&
      !Method->getFriendObjectKind())
    Owner->addDecl(Method);

  return Method;
}

Decl *TemplateDeclInstantiator::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

Decl *TemplateDeclInstantiator::VisitCXXDestructorDecl(CXXDestructorDecl *D) {
  return VisitCXXMethodDecl(D);
}

Decl *TemplateDeclInstantiator::VisitCXXConversionDecl(CXXConversionDecl *D) {
  return VisitCXXMethodDecl(D);
}

ParmVarDecl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
  QualType T;
  DeclaratorInfo *DI = D->getDeclaratorInfo();
  if (DI) {
    DI = SemaRef.SubstType(DI, TemplateArgs, D->getLocation(),
                           D->getDeclName());
    if (DI) T = DI->getType();
  } else {
    T = SemaRef.SubstType(D->getType(), TemplateArgs, D->getLocation(),
                          D->getDeclName());
    DI = 0;
  }

  if (T.isNull())
    return 0;

  T = SemaRef.adjustParameterType(T);

  // Allocate the parameter
  ParmVarDecl *Param
    = ParmVarDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                          D->getIdentifier(), T, DI, D->getStorageClass(), 0);

  // Mark the default argument as being uninstantiated.
  if (D->hasUninstantiatedDefaultArg())
    Param->setUninstantiatedDefaultArg(D->getUninstantiatedDefaultArg());
  else if (Expr *Arg = D->getDefaultArg())
    Param->setUninstantiatedDefaultArg(Arg);
  
  // Note: we don't try to instantiate function parameters until after
  // we've instantiated the function's type. Therefore, we don't have
  // to check for 'void' parameter types here.
  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
  return Param;
}

Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
                                                    TemplateTypeParmDecl *D) {
  // TODO: don't always clone when decls are refcounted.
  const Type* T = D->getTypeForDecl();
  assert(T->isTemplateTypeParmType());
  const TemplateTypeParmType *TTPT = T->getAs<TemplateTypeParmType>();

  TemplateTypeParmDecl *Inst =
    TemplateTypeParmDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                 TTPT->getDepth() - 1, TTPT->getIndex(),
                                 TTPT->getName(),
                                 D->wasDeclaredWithTypename(),
                                 D->isParameterPack());

  if (D->hasDefaultArgument())
    Inst->setDefaultArgument(D->getDefaultArgumentInfo(), false);  

  // Introduce this template parameter's instantiation into the instantiation 
  // scope.
  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Inst);
  
  return Inst;
}

Decl *TemplateDeclInstantiator::VisitNonTypeTemplateParmDecl(
                                                 NonTypeTemplateParmDecl *D) {
  // Substitute into the type of the non-type template parameter.
  QualType T;
  DeclaratorInfo *DI = D->getDeclaratorInfo();
  if (DI) {
    DI = SemaRef.SubstType(DI, TemplateArgs, D->getLocation(),
                           D->getDeclName());
    if (DI) T = DI->getType();
  } else {
    T = SemaRef.SubstType(D->getType(), TemplateArgs, D->getLocation(),
                          D->getDeclName());
    DI = 0;
  }
  if (T.isNull())
    return 0;
  
  // Check that this type is acceptable for a non-type template parameter.
  bool Invalid = false;
  T = SemaRef.CheckNonTypeTemplateParameterType(T, D->getLocation());
  if (T.isNull()) {
    T = SemaRef.Context.IntTy;
    Invalid = true;
  }
  
  NonTypeTemplateParmDecl *Param
    = NonTypeTemplateParmDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                      D->getDepth() - 1, D->getPosition(),
                                      D->getIdentifier(), T, DI);
  if (Invalid)
    Param->setInvalidDecl();
  
  Param->setDefaultArgument(D->getDefaultArgument());
  
  // Introduce this template parameter's instantiation into the instantiation 
  // scope.
  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
  return Param;
}

Decl *
TemplateDeclInstantiator::VisitTemplateTemplateParmDecl(
                                                  TemplateTemplateParmDecl *D) {
  // Instantiate the template parameter list of the template template parameter.
  TemplateParameterList *TempParams = D->getTemplateParameters();
  TemplateParameterList *InstParams;
  {
    // Perform the actual substitution of template parameters within a new,
    // local instantiation scope.
    Sema::LocalInstantiationScope Scope(SemaRef);
    InstParams = SubstTemplateParams(TempParams);
    if (!InstParams)
      return NULL;
  }  
  
  // Build the template template parameter.
  TemplateTemplateParmDecl *Param
    = TemplateTemplateParmDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                       D->getDepth() - 1, D->getPosition(),
                                       D->getIdentifier(), InstParams);
  Param->setDefaultArgument(D->getDefaultArgument());
  
  // Introduce this template parameter's instantiation into the instantiation 
  // scope.
  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
  
  return Param;
}

Decl *
TemplateDeclInstantiator::VisitUnresolvedUsingDecl(UnresolvedUsingDecl *D) {
  NestedNameSpecifier *NNS =
    SemaRef.SubstNestedNameSpecifier(D->getTargetNestedNameSpecifier(),
                                     D->getTargetNestedNameRange(),
                                     TemplateArgs);
  if (!NNS)
    return 0;

  CXXScopeSpec SS;
  SS.setRange(D->getTargetNestedNameRange());
  SS.setScopeRep(NNS);

  NamedDecl *UD =
    SemaRef.BuildUsingDeclaration(/*Scope*/ 0, D->getAccess(),
                                  D->getLocation(), SS, D->getTargetNameLocation(),
                                  D->getDeclName(), 0, D->isTypeName());
  if (UD)
    SemaRef.Context.setInstantiatedFromUnresolvedUsingDecl(cast<UsingDecl>(UD),
                                                           D);
  return UD;
}

Decl *Sema::SubstDecl(Decl *D, DeclContext *Owner,
                      const MultiLevelTemplateArgumentList &TemplateArgs) {
  TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
  return Instantiator.Visit(D);
}

/// \brief Instantiates a nested template parameter list in the current
/// instantiation context.
///
/// \param L The parameter list to instantiate
///
/// \returns NULL if there was an error
TemplateParameterList *
TemplateDeclInstantiator::SubstTemplateParams(TemplateParameterList *L) {
  // Get errors for all the parameters before bailing out.
  bool Invalid = false;

  unsigned N = L->size();
  typedef llvm::SmallVector<NamedDecl *, 8> ParamVector;
  ParamVector Params;
  Params.reserve(N);
  for (TemplateParameterList::iterator PI = L->begin(), PE = L->end();
       PI != PE; ++PI) {
    NamedDecl *D = cast_or_null<NamedDecl>(Visit(*PI));
    Params.push_back(D);
    Invalid = Invalid || !D || D->isInvalidDecl();
  }

  // Clean up if we had an error.
  if (Invalid) {
    for (ParamVector::iterator PI = Params.begin(), PE = Params.end();
         PI != PE; ++PI)
      if (*PI)
        (*PI)->Destroy(SemaRef.Context);
    return NULL;
  }

  TemplateParameterList *InstL
    = TemplateParameterList::Create(SemaRef.Context, L->getTemplateLoc(),
                                    L->getLAngleLoc(), &Params.front(), N,
                                    L->getRAngleLoc());
  return InstL;
}

/// \brief Instantiate the declaration of a class template partial 
/// specialization.
///
/// \param ClassTemplate the (instantiated) class template that is partially
// specialized by the instantiation of \p PartialSpec.
///
/// \param PartialSpec the (uninstantiated) class template partial 
/// specialization that we are instantiating.
///
/// \returns true if there was an error, false otherwise.
bool 
TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(
                                            ClassTemplateDecl *ClassTemplate,
                          ClassTemplatePartialSpecializationDecl *PartialSpec) {
  // Create a local instantiation scope for this class template partial
  // specialization, which will contain the instantiations of the template
  // parameters.
  Sema::LocalInstantiationScope Scope(SemaRef);
  
  // Substitute into the template parameters of the class template partial
  // specialization.
  TemplateParameterList *TempParams = PartialSpec->getTemplateParameters();
  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
  if (!InstParams)
    return true;
  
  // Substitute into the template arguments of the class template partial
  // specialization.
  const TemplateArgumentLoc *PartialSpecTemplateArgs
    = PartialSpec->getTemplateArgsAsWritten();
  unsigned N = PartialSpec->getNumTemplateArgsAsWritten();

  llvm::SmallVector<TemplateArgumentLoc, 4> InstTemplateArgs(N);
  for (unsigned I = 0; I != N; ++I) {
    if (SemaRef.Subst(PartialSpecTemplateArgs[I], InstTemplateArgs[I],
                      TemplateArgs))
      return true;
  }
  

  // Check that the template argument list is well-formed for this
  // class template.
  TemplateArgumentListBuilder Converted(ClassTemplate->getTemplateParameters(), 
                                        InstTemplateArgs.size());
  if (SemaRef.CheckTemplateArgumentList(ClassTemplate, 
                                        PartialSpec->getLocation(),
                                        /*FIXME:*/PartialSpec->getLocation(),
                                        InstTemplateArgs.data(), 
                                        InstTemplateArgs.size(),
                                        /*FIXME:*/PartialSpec->getLocation(), 
                                        false,
                                        Converted))
    return true;

  // Figure out where to insert this class template partial specialization
  // in the member template's set of class template partial specializations.
  llvm::FoldingSetNodeID ID;
  ClassTemplatePartialSpecializationDecl::Profile(ID,
                                                  Converted.getFlatArguments(),
                                                  Converted.flatSize(),
                                                  SemaRef.Context);
  void *InsertPos = 0;
  ClassTemplateSpecializationDecl *PrevDecl
    = ClassTemplate->getPartialSpecializations().FindNodeOrInsertPos(ID,
                                                                     InsertPos);
  
  // Build the canonical type that describes the converted template
  // arguments of the class template partial specialization.
  QualType CanonType 
    = SemaRef.Context.getTemplateSpecializationType(TemplateName(ClassTemplate),
                                                  Converted.getFlatArguments(),
                                                    Converted.flatSize());

  // Build the fully-sugared type for this class template
  // specialization as the user wrote in the specialization
  // itself. This means that we'll pretty-print the type retrieved
  // from the specialization's declaration the way that the user
  // actually wrote the specialization, rather than formatting the
  // name based on the "canonical" representation used to store the
  // template arguments in the specialization.
  QualType WrittenTy
    = SemaRef.Context.getTemplateSpecializationType(TemplateName(ClassTemplate),
                                                    InstTemplateArgs.data(),
                                                    InstTemplateArgs.size(),
                                                    CanonType);
  
  if (PrevDecl) {
    // We've already seen a partial specialization with the same template
    // parameters and template arguments. This can happen, for example, when
    // substituting the outer template arguments ends up causing two
    // class template partial specializations of a member class template
    // to have identical forms, e.g.,
    //
    //   template<typename T, typename U>
    //   struct Outer {
    //     template<typename X, typename Y> struct Inner;
    //     template<typename Y> struct Inner<T, Y>;
    //     template<typename Y> struct Inner<U, Y>;
    //   };
    //
    //   Outer<int, int> outer; // error: the partial specializations of Inner
    //                          // have the same signature.
    SemaRef.Diag(PartialSpec->getLocation(), diag::err_partial_spec_redeclared)
      << WrittenTy;
    SemaRef.Diag(PrevDecl->getLocation(), diag::note_prev_partial_spec_here)
      << SemaRef.Context.getTypeDeclType(PrevDecl);
    return true;
  }
  
  
  // Create the class template partial specialization declaration.
  ClassTemplatePartialSpecializationDecl *InstPartialSpec
    = ClassTemplatePartialSpecializationDecl::Create(SemaRef.Context, Owner, 
                                                     PartialSpec->getLocation(), 
                                                     InstParams,
                                                     ClassTemplate, 
                                                     Converted,
                                                     InstTemplateArgs.data(),
                                                     InstTemplateArgs.size(),
                                                     0);
  InstPartialSpec->setInstantiatedFromMember(PartialSpec);
  InstPartialSpec->setTypeAsWritten(WrittenTy);
  
  // Add this partial specialization to the set of class template partial
  // specializations.
  ClassTemplate->getPartialSpecializations().InsertNode(InstPartialSpec,
                                                        InsertPos);
  return false;
}

/// \brief Does substitution on the type of the given function, including
/// all of the function parameters.
///
/// \param D The function whose type will be the basis of the substitution
///
/// \param Params the instantiated parameter declarations

/// \returns the instantiated function's type if successful, a NULL
/// type if there was an error.
QualType
TemplateDeclInstantiator::SubstFunctionType(FunctionDecl *D,
                              llvm::SmallVectorImpl<ParmVarDecl *> &Params) {
  bool InvalidDecl = false;

  // Substitute all of the function's formal parameter types.
  TemplateDeclInstantiator ParamInstantiator(SemaRef, 0, TemplateArgs);
  llvm::SmallVector<QualType, 4> ParamTys;
  for (FunctionDecl::param_iterator P = D->param_begin(),
                                 PEnd = D->param_end();
       P != PEnd; ++P) {
    if (ParmVarDecl *PInst = ParamInstantiator.VisitParmVarDecl(*P)) {
      if (PInst->getType()->isVoidType()) {
        SemaRef.Diag(PInst->getLocation(), diag::err_param_with_void_type);
        PInst->setInvalidDecl();
      } else if (SemaRef.RequireNonAbstractType(PInst->getLocation(),
                                                PInst->getType(),
                                                diag::err_abstract_type_in_decl,
                                                Sema::AbstractParamType))
        PInst->setInvalidDecl();

      Params.push_back(PInst);
      ParamTys.push_back(PInst->getType());

      if (PInst->isInvalidDecl())
        InvalidDecl = true;
    } else
      InvalidDecl = true;
  }

  // FIXME: Deallocate dead declarations.
  if (InvalidDecl)
    return QualType();

  const FunctionProtoType *Proto = D->getType()->getAs<FunctionProtoType>();
  assert(Proto && "Missing prototype?");
  QualType ResultType
    = SemaRef.SubstType(Proto->getResultType(), TemplateArgs,
                        D->getLocation(), D->getDeclName());
  if (ResultType.isNull())
    return QualType();

  return SemaRef.BuildFunctionType(ResultType, ParamTys.data(), ParamTys.size(),
                                   Proto->isVariadic(), Proto->getTypeQuals(),
                                   D->getLocation(), D->getDeclName());
}

/// \brief Initializes the common fields of an instantiation function
/// declaration (New) from the corresponding fields of its template (Tmpl).
///
/// \returns true if there was an error
bool
TemplateDeclInstantiator::InitFunctionInstantiation(FunctionDecl *New,
                                                    FunctionDecl *Tmpl) {
  if (Tmpl->isDeleted())
    New->setDeleted();

  // If we are performing substituting explicitly-specified template arguments
  // or deduced template arguments into a function template and we reach this
  // point, we are now past the point where SFINAE applies and have committed
  // to keeping the new function template specialization. We therefore
  // convert the active template instantiation for the function template
  // into a template instantiation for this specific function template
  // specialization, which is not a SFINAE context, so that we diagnose any
  // further errors in the declaration itself.
  typedef Sema::ActiveTemplateInstantiation ActiveInstType;
  ActiveInstType &ActiveInst = SemaRef.ActiveTemplateInstantiations.back();
  if (ActiveInst.Kind == ActiveInstType::ExplicitTemplateArgumentSubstitution ||
      ActiveInst.Kind == ActiveInstType::DeducedTemplateArgumentSubstitution) {
    if (FunctionTemplateDecl *FunTmpl
          = dyn_cast<FunctionTemplateDecl>((Decl *)ActiveInst.Entity)) {
      assert(FunTmpl->getTemplatedDecl() == Tmpl &&
             "Deduction from the wrong function template?");
      (void) FunTmpl;
      ActiveInst.Kind = ActiveInstType::TemplateInstantiation;
      ActiveInst.Entity = reinterpret_cast<uintptr_t>(New);
      --SemaRef.NonInstantiationEntries;
    }
  }

  return false;
}

/// \brief Initializes common fields of an instantiated method
/// declaration (New) from the corresponding fields of its template
/// (Tmpl).
///
/// \returns true if there was an error
bool
TemplateDeclInstantiator::InitMethodInstantiation(CXXMethodDecl *New,
                                                  CXXMethodDecl *Tmpl) {
  if (InitFunctionInstantiation(New, Tmpl))
    return true;

  CXXRecordDecl *Record = cast<CXXRecordDecl>(Owner);
  New->setAccess(Tmpl->getAccess());
  if (Tmpl->isVirtualAsWritten()) {
    New->setVirtualAsWritten(true);
    Record->setAggregate(false);
    Record->setPOD(false);
    Record->setEmpty(false);
    Record->setPolymorphic(true);
  }
  if (Tmpl->isPure()) {
    New->setPure();
    Record->setAbstract(true);
  }

  // FIXME: attributes
  // FIXME: New needs a pointer to Tmpl
  return false;
}

/// \brief Instantiate the definition of the given function from its
/// template.
///
/// \param PointOfInstantiation the point at which the instantiation was
/// required. Note that this is not precisely a "point of instantiation"
/// for the function, but it's close.
///
/// \param Function the already-instantiated declaration of a
/// function template specialization or member function of a class template
/// specialization.
///
/// \param Recursive if true, recursively instantiates any functions that
/// are required by this instantiation.
///
/// \param DefinitionRequired if true, then we are performing an explicit
/// instantiation where the body of the function is required. Complain if
/// there is no such body.
void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                         FunctionDecl *Function,
                                         bool Recursive,
                                         bool DefinitionRequired) {
  if (Function->isInvalidDecl())
    return;

  assert(!Function->getBody() && "Already instantiated!");

  // Never instantiate an explicit specialization.
  if (Function->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
    return;
  
  // Find the function body that we'll be substituting.
  const FunctionDecl *PatternDecl = Function->getTemplateInstantiationPattern();
  Stmt *Pattern = 0;
  if (PatternDecl)
    Pattern = PatternDecl->getBody(PatternDecl);

  if (!Pattern) {
    if (DefinitionRequired) {
      if (Function->getPrimaryTemplate())
        Diag(PointOfInstantiation, 
             diag::err_explicit_instantiation_undefined_func_template)
          << Function->getPrimaryTemplate();
      else
        Diag(PointOfInstantiation, 
             diag::err_explicit_instantiation_undefined_member)
          << 1 << Function->getDeclName() << Function->getDeclContext();
      
      if (PatternDecl)
        Diag(PatternDecl->getLocation(), 
             diag::note_explicit_instantiation_here);
    }
      
    return;
  }

  // C++0x [temp.explicit]p9:
  //   Except for inline functions, other explicit instantiation declarations
  //   have the effect of suppressing the implicit instantiation of the entity
  //   to which they refer.
  if (Function->getTemplateSpecializationKind()
        == TSK_ExplicitInstantiationDeclaration &&
      !PatternDecl->isInlined())
    return;

  InstantiatingTemplate Inst(*this, PointOfInstantiation, Function);
  if (Inst)
    return;

  // If we're performing recursive template instantiation, create our own
  // queue of pending implicit instantiations that we will instantiate later,
  // while we're still within our own instantiation context.
  std::deque<PendingImplicitInstantiation> SavedPendingImplicitInstantiations;
  if (Recursive)
    PendingImplicitInstantiations.swap(SavedPendingImplicitInstantiations);

  ActOnStartOfFunctionDef(0, DeclPtrTy::make(Function));

  // Introduce a new scope where local variable instantiations will be
  // recorded.
  LocalInstantiationScope Scope(*this);

  // Introduce the instantiated function parameters into the local
  // instantiation scope.
  for (unsigned I = 0, N = PatternDecl->getNumParams(); I != N; ++I)
    Scope.InstantiatedLocal(PatternDecl->getParamDecl(I),
                            Function->getParamDecl(I));

  // Enter the scope of this instantiation. We don't use
  // PushDeclContext because we don't have a scope.
  DeclContext *PreviousContext = CurContext;
  CurContext = Function;

  MultiLevelTemplateArgumentList TemplateArgs =
    getTemplateInstantiationArgs(Function);

  // If this is a constructor, instantiate the member initializers.
  if (const CXXConstructorDecl *Ctor =
        dyn_cast<CXXConstructorDecl>(PatternDecl)) {
    InstantiateMemInitializers(cast<CXXConstructorDecl>(Function), Ctor,
                               TemplateArgs);
  }

  // Instantiate the function body.
  OwningStmtResult Body = SubstStmt(Pattern, TemplateArgs);

  if (Body.isInvalid())
    Function->setInvalidDecl();
  
  ActOnFinishFunctionBody(DeclPtrTy::make(Function), move(Body),
                          /*IsInstantiation=*/true);

  CurContext = PreviousContext;

  DeclGroupRef DG(Function);
  Consumer.HandleTopLevelDecl(DG);

  if (Recursive) {
    // Instantiate any pending implicit instantiations found during the
    // instantiation of this template.
    PerformPendingImplicitInstantiations();

    // Restore the set of pending implicit instantiations.
    PendingImplicitInstantiations.swap(SavedPendingImplicitInstantiations);
  }
}

/// \brief Instantiate the definition of the given variable from its
/// template.
///
/// \param PointOfInstantiation the point at which the instantiation was
/// required. Note that this is not precisely a "point of instantiation"
/// for the function, but it's close.
///
/// \param Var the already-instantiated declaration of a static member
/// variable of a class template specialization.
///
/// \param Recursive if true, recursively instantiates any functions that
/// are required by this instantiation.
///
/// \param DefinitionRequired if true, then we are performing an explicit
/// instantiation where an out-of-line definition of the member variable
/// is required. Complain if there is no such definition.
void Sema::InstantiateStaticDataMemberDefinition(
                                          SourceLocation PointOfInstantiation,
                                                 VarDecl *Var,
                                                 bool Recursive,
                                                 bool DefinitionRequired) {
  if (Var->isInvalidDecl())
    return;

  // Find the out-of-line definition of this static data member.
  VarDecl *Def = Var->getInstantiatedFromStaticDataMember();
  assert(Def && "This data member was not instantiated from a template?");
  assert(Def->isStaticDataMember() && "Not a static data member?");  
  Def = Def->getOutOfLineDefinition();

  if (!Def) {
    // We did not find an out-of-line definition of this static data member,
    // so we won't perform any instantiation. Rather, we rely on the user to
    // instantiate this definition (or provide a specialization for it) in
    // another translation unit.
    if (DefinitionRequired) {
      Def = Var->getInstantiatedFromStaticDataMember();
      Diag(PointOfInstantiation, 
           diag::err_explicit_instantiation_undefined_member)
        << 2 << Var->getDeclName() << Var->getDeclContext();
      Diag(Def->getLocation(), diag::note_explicit_instantiation_here);
    }    
    
    return;
  }

  // Never instantiate an explicit specialization.
  if (Var->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
    return;
  
  // C++0x [temp.explicit]p9:
  //   Except for inline functions, other explicit instantiation declarations
  //   have the effect of suppressing the implicit instantiation of the entity
  //   to which they refer.
  if (Var->getTemplateSpecializationKind() 
        == TSK_ExplicitInstantiationDeclaration)
    return;

  InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
  if (Inst)
    return;

  // If we're performing recursive template instantiation, create our own
  // queue of pending implicit instantiations that we will instantiate later,
  // while we're still within our own instantiation context.
  std::deque<PendingImplicitInstantiation> SavedPendingImplicitInstantiations;
  if (Recursive)
    PendingImplicitInstantiations.swap(SavedPendingImplicitInstantiations);

  // Enter the scope of this instantiation. We don't use
  // PushDeclContext because we don't have a scope.
  DeclContext *PreviousContext = CurContext;
  CurContext = Var->getDeclContext();

  VarDecl *OldVar = Var;
  Var = cast_or_null<VarDecl>(SubstDecl(Def, Var->getDeclContext(),
                                          getTemplateInstantiationArgs(Var)));
  CurContext = PreviousContext;

  if (Var) {
    Var->setPreviousDeclaration(OldVar);
    MemberSpecializationInfo *MSInfo = OldVar->getMemberSpecializationInfo();
    assert(MSInfo && "Missing member specialization information?");
    Var->setTemplateSpecializationKind(MSInfo->getTemplateSpecializationKind(),
                                       MSInfo->getPointOfInstantiation());
    DeclGroupRef DG(Var);
    Consumer.HandleTopLevelDecl(DG);
  }

  if (Recursive) {
    // Instantiate any pending implicit instantiations found during the
    // instantiation of this template.
    PerformPendingImplicitInstantiations();

    // Restore the set of pending implicit instantiations.
    PendingImplicitInstantiations.swap(SavedPendingImplicitInstantiations);
  }
}

void
Sema::InstantiateMemInitializers(CXXConstructorDecl *New,
                                 const CXXConstructorDecl *Tmpl,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {

  llvm::SmallVector<MemInitTy*, 4> NewInits;

  // Instantiate all the initializers.
  for (CXXConstructorDecl::init_const_iterator Inits = Tmpl->init_begin(),
                                            InitsEnd = Tmpl->init_end();
       Inits != InitsEnd; ++Inits) {
    CXXBaseOrMemberInitializer *Init = *Inits;

    ASTOwningVector<&ActionBase::DeleteExpr> NewArgs(*this);

    // Instantiate all the arguments.
    for (ExprIterator Args = Init->arg_begin(), ArgsEnd = Init->arg_end();
         Args != ArgsEnd; ++Args) {
      OwningExprResult NewArg = SubstExpr(*Args, TemplateArgs);

      if (NewArg.isInvalid())
        New->setInvalidDecl();
      else
        NewArgs.push_back(NewArg.takeAs<Expr>());
    }

    MemInitResult NewInit;

    if (Init->isBaseInitializer()) {
      QualType BaseType(Init->getBaseClass(), 0);
      BaseType = SubstType(BaseType, TemplateArgs, Init->getSourceLocation(),
                           New->getDeclName());

      NewInit = BuildBaseInitializer(BaseType,
                                     (Expr **)NewArgs.data(),
                                     NewArgs.size(),
                                     Init->getSourceLocation(),
                                     Init->getRParenLoc(),
                                     New->getParent());
    } else if (Init->isMemberInitializer()) {
      FieldDecl *Member;

      // Is this an anonymous union?
      if (FieldDecl *UnionInit = Init->getAnonUnionMember())
        Member = cast<FieldDecl>(FindInstantiatedDecl(UnionInit, TemplateArgs));
      else
        Member = cast<FieldDecl>(FindInstantiatedDecl(Init->getMember(),
                                                      TemplateArgs));

      NewInit = BuildMemberInitializer(Member, (Expr **)NewArgs.data(),
                                       NewArgs.size(),
                                       Init->getSourceLocation(),
                                       Init->getRParenLoc());
    }

    if (NewInit.isInvalid())
      New->setInvalidDecl();
    else {
      // FIXME: It would be nice if ASTOwningVector had a release function.
      NewArgs.take();

      NewInits.push_back((MemInitTy *)NewInit.get());
    }
  }

  // Assign all the initializers to the new constructor.
  ActOnMemInitializers(DeclPtrTy::make(New),
                       /*FIXME: ColonLoc */
                       SourceLocation(),
                       NewInits.data(), NewInits.size());
}

// TODO: this could be templated if the various decl types used the
// same method name.
static bool isInstantiationOf(ClassTemplateDecl *Pattern,
                              ClassTemplateDecl *Instance) {
  Pattern = Pattern->getCanonicalDecl();

  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromMemberTemplate();
  } while (Instance);

  return false;
}

static bool isInstantiationOf(FunctionTemplateDecl *Pattern,
                              FunctionTemplateDecl *Instance) {
  Pattern = Pattern->getCanonicalDecl();
  
  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromMemberTemplate();
  } while (Instance);
  
  return false;
}

static bool 
isInstantiationOf(ClassTemplatePartialSpecializationDecl *Pattern,
                  ClassTemplatePartialSpecializationDecl *Instance) {
  Pattern 
    = cast<ClassTemplatePartialSpecializationDecl>(Pattern->getCanonicalDecl());
  do {
    Instance = cast<ClassTemplatePartialSpecializationDecl>(
                                                Instance->getCanonicalDecl());
    if (Pattern == Instance)
      return true;
    Instance = Instance->getInstantiatedFromMember();
  } while (Instance);
  
  return false;
}

static bool isInstantiationOf(CXXRecordDecl *Pattern,
                              CXXRecordDecl *Instance) {
  Pattern = Pattern->getCanonicalDecl();

  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromMemberClass();
  } while (Instance);

  return false;
}

static bool isInstantiationOf(FunctionDecl *Pattern,
                              FunctionDecl *Instance) {
  Pattern = Pattern->getCanonicalDecl();

  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromMemberFunction();
  } while (Instance);

  return false;
}

static bool isInstantiationOf(EnumDecl *Pattern,
                              EnumDecl *Instance) {
  Pattern = Pattern->getCanonicalDecl();

  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromMemberEnum();
  } while (Instance);

  return false;
}

static bool isInstantiationOf(UnresolvedUsingDecl *Pattern,
                              UsingDecl *Instance,
                              ASTContext &C) {
  return C.getInstantiatedFromUnresolvedUsingDecl(Instance) == Pattern;
}

static bool isInstantiationOfStaticDataMember(VarDecl *Pattern,
                                              VarDecl *Instance) {
  assert(Instance->isStaticDataMember());

  Pattern = Pattern->getCanonicalDecl();

  do {
    Instance = Instance->getCanonicalDecl();
    if (Pattern == Instance) return true;
    Instance = Instance->getInstantiatedFromStaticDataMember();
  } while (Instance);

  return false;
}

static bool isInstantiationOf(ASTContext &Ctx, NamedDecl *D, Decl *Other) {
  if (D->getKind() != Other->getKind()) {
    if (UnresolvedUsingDecl *UUD = dyn_cast<UnresolvedUsingDecl>(D)) {
      if (UsingDecl *UD = dyn_cast<UsingDecl>(Other)) {
        return isInstantiationOf(UUD, UD, Ctx);
      }
    }

    return false;
  }

  if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(Other))
    return isInstantiationOf(cast<CXXRecordDecl>(D), Record);

  if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Other))
    return isInstantiationOf(cast<FunctionDecl>(D), Function);

  if (EnumDecl *Enum = dyn_cast<EnumDecl>(Other))
    return isInstantiationOf(cast<EnumDecl>(D), Enum);

  if (VarDecl *Var = dyn_cast<VarDecl>(Other))
    if (Var->isStaticDataMember())
      return isInstantiationOfStaticDataMember(cast<VarDecl>(D), Var);

  if (ClassTemplateDecl *Temp = dyn_cast<ClassTemplateDecl>(Other))
    return isInstantiationOf(cast<ClassTemplateDecl>(D), Temp);

  if (FunctionTemplateDecl *Temp = dyn_cast<FunctionTemplateDecl>(Other))
    return isInstantiationOf(cast<FunctionTemplateDecl>(D), Temp);

  if (ClassTemplatePartialSpecializationDecl *PartialSpec
        = dyn_cast<ClassTemplatePartialSpecializationDecl>(Other))
    return isInstantiationOf(cast<ClassTemplatePartialSpecializationDecl>(D),
                             PartialSpec);

  if (FieldDecl *Field = dyn_cast<FieldDecl>(Other)) {
    if (!Field->getDeclName()) {
      // This is an unnamed field.
      return Ctx.getInstantiatedFromUnnamedFieldDecl(Field) ==
        cast<FieldDecl>(D);
    }
  }

  return D->getDeclName() && isa<NamedDecl>(Other) &&
    D->getDeclName() == cast<NamedDecl>(Other)->getDeclName();
}

template<typename ForwardIterator>
static NamedDecl *findInstantiationOf(ASTContext &Ctx,
                                      NamedDecl *D,
                                      ForwardIterator first,
                                      ForwardIterator last) {
  for (; first != last; ++first)
    if (isInstantiationOf(Ctx, D, *first))
      return cast<NamedDecl>(*first);

  return 0;
}

/// \brief Finds the instantiation of the given declaration context
/// within the current instantiation.
///
/// \returns NULL if there was an error
DeclContext *Sema::FindInstantiatedContext(DeclContext* DC,
                          const MultiLevelTemplateArgumentList &TemplateArgs) {
  if (NamedDecl *D = dyn_cast<NamedDecl>(DC)) {
    Decl* ID = FindInstantiatedDecl(D, TemplateArgs);
    return cast_or_null<DeclContext>(ID);
  } else return DC;
}

/// \brief Find the instantiation of the given declaration within the
/// current instantiation.
///
/// This routine is intended to be used when \p D is a declaration
/// referenced from within a template, that needs to mapped into the
/// corresponding declaration within an instantiation. For example,
/// given:
///
/// \code
/// template<typename T>
/// struct X {
///   enum Kind {
///     KnownValue = sizeof(T)
///   };
///
///   bool getKind() const { return KnownValue; }
/// };
///
/// template struct X<int>;
/// \endcode
///
/// In the instantiation of X<int>::getKind(), we need to map the
/// EnumConstantDecl for KnownValue (which refers to
/// X<T>::<Kind>::KnownValue) to its instantiation
/// (X<int>::<Kind>::KnownValue). InstantiateCurrentDeclRef() performs
/// this mapping from within the instantiation of X<int>.
NamedDecl *Sema::FindInstantiatedDecl(NamedDecl *D,
                          const MultiLevelTemplateArgumentList &TemplateArgs) {
  if (OverloadedFunctionDecl *Ovl = dyn_cast<OverloadedFunctionDecl>(D)) {
    // Transform all of the elements of the overloaded function set.
    OverloadedFunctionDecl *Result
      = OverloadedFunctionDecl::Create(Context, CurContext, Ovl->getDeclName());

    for (OverloadedFunctionDecl::function_iterator F = Ovl->function_begin(),
                                                FEnd = Ovl->function_end();
         F != FEnd; ++F) {
      Result->addOverload(
        AnyFunctionDecl::getFromNamedDecl(FindInstantiatedDecl(*F,
                                                               TemplateArgs)));
    }

    return Result;
  }

  DeclContext *ParentDC = D->getDeclContext();
  if (isa<ParmVarDecl>(D) || isa<NonTypeTemplateParmDecl>(D) ||
      isa<TemplateTypeParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
      ParentDC->isFunctionOrMethod()) {
    // D is a local of some kind. Look into the map of local
    // declarations to their instantiations.
    return cast<NamedDecl>(CurrentInstantiationScope->getInstantiationOf(D));
  }

  if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
    if (!Record->isDependentContext())
      return D;
    
    // If the RecordDecl is actually the injected-class-name or a "templated"
    // declaration for a class template or class template partial 
    // specialization, substitute into the injected-class-name of the
    // class template or partial specialization to find the new DeclContext.
    QualType T;
    ClassTemplateDecl *ClassTemplate = Record->getDescribedClassTemplate();
    
    if (ClassTemplate) {
      T = ClassTemplate->getInjectedClassNameType(Context);
    } else if (ClassTemplatePartialSpecializationDecl *PartialSpec
                 = dyn_cast<ClassTemplatePartialSpecializationDecl>(Record)) {
      T = Context.getTypeDeclType(Record);
      ClassTemplate = PartialSpec->getSpecializedTemplate();
    }
    
    if (!T.isNull()) {
      // Substitute into the injected-class-name to get the type corresponding
      // to the instantiation we want. This substitution should never fail,
      // since we know we can instantiate the injected-class-name or we wouldn't
      // have gotten to the injected-class-name!
      // FIXME: Can we use the CurrentInstantiationScope to avoid this extra
      // instantiation in the common case?
      T = SubstType(T, TemplateArgs, SourceLocation(), DeclarationName());
      assert(!T.isNull() && "Instantiation of injected-class-name cannot fail.");
    
      if (!T->isDependentType()) {
        assert(T->isRecordType() && "Instantiation must produce a record type");
        return T->getAs<RecordType>()->getDecl();
      }
    
      // We are performing "partial" template instantiation to create the 
      // member declarations for the members of a class template 
      // specialization. Therefore, D is actually referring to something in 
      // the current instantiation. Look through the current context,
      // which contains actual instantiations, to find the instantiation of 
      // the "current instantiation" that D refers to.
      for (DeclContext *DC = CurContext; !DC->isFileContext();
           DC = DC->getParent()) {
        if (ClassTemplateSpecializationDecl *Spec
              = dyn_cast<ClassTemplateSpecializationDecl>(DC))
          if (isInstantiationOf(ClassTemplate, 
                                Spec->getSpecializedTemplate()))
            return Spec;
      }

      assert(false &&
             "Unable to find declaration for the current instantiation");
      return Record;
    }
    
    // Fall through to deal with other dependent record types (e.g.,
    // anonymous unions in class templates).
  }

  if (!ParentDC->isDependentContext())
    return D;
  
  ParentDC = FindInstantiatedContext(ParentDC, TemplateArgs);
  if (!ParentDC)
    return 0;

  if (ParentDC != D->getDeclContext()) {
    // We performed some kind of instantiation in the parent context,
    // so now we need to look into the instantiated parent context to
    // find the instantiation of the declaration D.
    NamedDecl *Result = 0;
    if (D->getDeclName()) {
      DeclContext::lookup_result Found = ParentDC->lookup(D->getDeclName());
      Result = findInstantiationOf(Context, D, Found.first, Found.second);
    } else {
      // Since we don't have a name for the entity we're looking for,
      // our only option is to walk through all of the declarations to
      // find that name. This will occur in a few cases:
      //
      //   - anonymous struct/union within a template
      //   - unnamed class/struct/union/enum within a template
      //
      // FIXME: Find a better way to find these instantiations!
      Result = findInstantiationOf(Context, D,
                                   ParentDC->decls_begin(),
                                   ParentDC->decls_end());
    }

    assert(Result && "Unable to find instantiation of declaration!");
    D = Result;
  }

  return D;
}

/// \brief Performs template instantiation for all implicit template
/// instantiations we have seen until this point.
void Sema::PerformPendingImplicitInstantiations() {
  while (!PendingImplicitInstantiations.empty()) {
    PendingImplicitInstantiation Inst = PendingImplicitInstantiations.front();
    PendingImplicitInstantiations.pop_front();

    // Instantiate function definitions
    if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Inst.first)) {
      PrettyStackTraceActionsDecl CrashInfo(DeclPtrTy::make(Function),
                                            Function->getLocation(), *this,
                                            Context.getSourceManager(),
                                           "instantiating function definition");

      if (!Function->getBody())
        InstantiateFunctionDefinition(/*FIXME:*/Inst.second, Function, true);
      continue;
    }

    // Instantiate static data member definitions.
    VarDecl *Var = cast<VarDecl>(Inst.first);
    assert(Var->isStaticDataMember() && "Not a static data member?");

    PrettyStackTraceActionsDecl CrashInfo(DeclPtrTy::make(Var),
                                          Var->getLocation(), *this,
                                          Context.getSourceManager(),
                                          "instantiating static data member "
                                          "definition");

    InstantiateStaticDataMemberDefinition(/*FIXME:*/Inst.second, Var, true);
  }
}