Revert "[NFC] [Serialization] Avoid using DeclID directly as much as possible"

This reverts commit 42070a5c092ed420bf92ebf38229c594885e94c7.

I forgot to touch lldb.

17 files changed, 282 insertions, 299 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 475b47a..a7386f755 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -1083,8 +1083,7 @@ void ASTContext::addModuleInitializer(Module *M, Decl *D) {
   Inits->Initializers.push_back(D);
 }
 
-void ASTContext::addLazyModuleInitializers(Module *M,
-                                           ArrayRef<GlobalDeclID> IDs) {
+void ASTContext::addLazyModuleInitializers(Module *M, ArrayRef<DeclID> IDs) {
   auto *&Inits = ModuleInitializers[M];
   if (!Inits)
     Inits = new (*this) PerModuleInitializers;
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index e7e95c1..f452902 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2151,7 +2151,7 @@ VarDecl *VarDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation StartL,
   return new (C, DC) VarDecl(Var, C, DC, StartL, IdL, Id, T, TInfo, S);
 }
 
-VarDecl *VarDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+VarDecl *VarDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       VarDecl(Var, C, nullptr, SourceLocation(), SourceLocation(), nullptr,
               QualType(), nullptr, SC_None);
@@ -2929,7 +2929,7 @@ QualType ParmVarDecl::getOriginalType() const {
   return T;
 }
 
-ParmVarDecl *ParmVarDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ParmVarDecl *ParmVarDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       ParmVarDecl(ParmVar, C, nullptr, SourceLocation(), SourceLocation(),
                   nullptr, QualType(), nullptr, SC_None, nullptr);
@@ -4553,7 +4553,7 @@ FieldDecl *FieldDecl::Create(const ASTContext &C, DeclContext *DC,
                                BW, Mutable, InitStyle);
 }
 
-FieldDecl *FieldDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+FieldDecl *FieldDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) FieldDecl(Field, nullptr, SourceLocation(),
                                SourceLocation(), nullptr, QualType(), nullptr,
                                nullptr, false, ICIS_NoInit);
@@ -4863,7 +4863,7 @@ EnumDecl *EnumDecl::Create(ASTContext &C, DeclContext *DC,
   return Enum;
 }
 
-EnumDecl *EnumDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+EnumDecl *EnumDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   EnumDecl *Enum =
       new (C, ID) EnumDecl(C, nullptr, SourceLocation(), SourceLocation(),
                            nullptr, nullptr, false, false, false);
@@ -5025,8 +5025,7 @@ RecordDecl *RecordDecl::Create(const ASTContext &C, TagKind TK, DeclContext *DC,
   return R;
 }
 
-RecordDecl *RecordDecl::CreateDeserialized(const ASTContext &C,
-                                           GlobalDeclID ID) {
+RecordDecl *RecordDecl::CreateDeserialized(const ASTContext &C, DeclID ID) {
   RecordDecl *R = new (C, ID)
       RecordDecl(Record, TagTypeKind::Struct, C, nullptr, SourceLocation(),
                  SourceLocation(), nullptr, nullptr);
@@ -5298,7 +5297,7 @@ PragmaCommentDecl *PragmaCommentDecl::Create(const ASTContext &C,
 }
 
 PragmaCommentDecl *PragmaCommentDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID,
+                                                         DeclID ID,
                                                          unsigned ArgSize) {
   return new (C, ID, additionalSizeToAlloc<char>(ArgSize + 1))
       PragmaCommentDecl(nullptr, SourceLocation(), PCK_Unknown);
@@ -5323,7 +5322,7 @@ PragmaDetectMismatchDecl::Create(const ASTContext &C, TranslationUnitDecl *DC,
 }
 
 PragmaDetectMismatchDecl *
-PragmaDetectMismatchDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+PragmaDetectMismatchDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                              unsigned NameValueSize) {
   return new (C, ID, additionalSizeToAlloc<char>(NameValueSize + 1))
       PragmaDetectMismatchDecl(nullptr, SourceLocation(), 0);
@@ -5350,7 +5349,7 @@ LabelDecl *LabelDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) LabelDecl(DC, IdentL, II, nullptr, GnuLabelL);
 }
 
-LabelDecl *LabelDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+LabelDecl *LabelDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) LabelDecl(nullptr, SourceLocation(), nullptr, nullptr,
                                SourceLocation());
 }
@@ -5391,7 +5390,7 @@ ImplicitParamDecl *ImplicitParamDecl::Create(ASTContext &C, QualType Type,
 }
 
 ImplicitParamDecl *ImplicitParamDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID) ImplicitParamDecl(C, QualType(), ImplicitParamKind::Other);
 }
 
@@ -5409,7 +5408,7 @@ FunctionDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
   return New;
 }
 
-FunctionDecl *FunctionDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+FunctionDecl *FunctionDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) FunctionDecl(
       Function, C, nullptr, SourceLocation(), DeclarationNameInfo(), QualType(),
       nullptr, SC_None, false, false, ConstexprSpecKind::Unspecified, nullptr);
@@ -5419,7 +5418,7 @@ BlockDecl *BlockDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L) {
   return new (C, DC) BlockDecl(DC, L);
 }
 
-BlockDecl *BlockDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+BlockDecl *BlockDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) BlockDecl(nullptr, SourceLocation());
 }
 
@@ -5433,7 +5432,7 @@ CapturedDecl *CapturedDecl::Create(ASTContext &C, DeclContext *DC,
       CapturedDecl(DC, NumParams);
 }
 
-CapturedDecl *CapturedDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+CapturedDecl *CapturedDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                                unsigned NumParams) {
   return new (C, ID, additionalSizeToAlloc<ImplicitParamDecl *>(NumParams))
       CapturedDecl(nullptr, NumParams);
@@ -5460,7 +5459,7 @@ EnumConstantDecl *EnumConstantDecl::Create(ASTContext &C, EnumDecl *CD,
 }
 
 EnumConstantDecl *EnumConstantDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID) EnumConstantDecl(C, nullptr, SourceLocation(), nullptr,
                                       QualType(), nullptr, llvm::APSInt());
 }
@@ -5487,7 +5486,7 @@ IndirectFieldDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
 }
 
 IndirectFieldDecl *IndirectFieldDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID)
       IndirectFieldDecl(C, nullptr, SourceLocation(), DeclarationName(),
                         QualType(), std::nullopt);
@@ -5548,7 +5547,7 @@ bool TypedefNameDecl::isTransparentTagSlow() const {
   return isTransparent;
 }
 
-TypedefDecl *TypedefDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+TypedefDecl *TypedefDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) TypedefDecl(C, nullptr, SourceLocation(), SourceLocation(),
                                  nullptr, nullptr);
 }
@@ -5561,8 +5560,7 @@ TypeAliasDecl *TypeAliasDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) TypeAliasDecl(C, DC, StartLoc, IdLoc, Id, TInfo);
 }
 
-TypeAliasDecl *TypeAliasDecl::CreateDeserialized(ASTContext &C,
-                                                 GlobalDeclID ID) {
+TypeAliasDecl *TypeAliasDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) TypeAliasDecl(C, nullptr, SourceLocation(),
                                    SourceLocation(), nullptr, nullptr);
 }
@@ -5593,7 +5591,7 @@ FileScopeAsmDecl *FileScopeAsmDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 FileScopeAsmDecl *FileScopeAsmDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID) FileScopeAsmDecl(nullptr, nullptr, SourceLocation(),
                                       SourceLocation());
 }
@@ -5611,7 +5609,7 @@ TopLevelStmtDecl *TopLevelStmtDecl::Create(ASTContext &C, Stmt *Statement) {
 }
 
 TopLevelStmtDecl *TopLevelStmtDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID)
       TopLevelStmtDecl(/*DC=*/nullptr, SourceLocation(), /*S=*/nullptr);
 }
@@ -5632,7 +5630,7 @@ EmptyDecl *EmptyDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L) {
   return new (C, DC) EmptyDecl(DC, L);
 }
 
-EmptyDecl *EmptyDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+EmptyDecl *EmptyDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) EmptyDecl(nullptr, SourceLocation());
 }
 
@@ -5665,8 +5663,7 @@ HLSLBufferDecl *HLSLBufferDecl::Create(ASTContext &C,
   return Result;
 }
 
-HLSLBufferDecl *HLSLBufferDecl::CreateDeserialized(ASTContext &C,
-                                                   GlobalDeclID ID) {
+HLSLBufferDecl *HLSLBufferDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) HLSLBufferDecl(nullptr, false, SourceLocation(), nullptr,
                                     SourceLocation(), SourceLocation());
 }
@@ -5722,7 +5719,7 @@ ImportDecl *ImportDecl::CreateImplicit(ASTContext &C, DeclContext *DC,
   return Import;
 }
 
-ImportDecl *ImportDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+ImportDecl *ImportDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                            unsigned NumLocations) {
   return new (C, ID, additionalSizeToAlloc<SourceLocation>(NumLocations))
       ImportDecl(EmptyShell());
@@ -5755,6 +5752,6 @@ ExportDecl *ExportDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) ExportDecl(DC, ExportLoc);
 }
 
-ExportDecl *ExportDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ExportDecl *ExportDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ExportDecl(nullptr, SourceLocation());
 }
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index c33babf..a2d88cf 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -70,8 +70,8 @@ void Decl::updateOutOfDate(IdentifierInfo &II) const {
 #define ABSTRACT_DECL(DECL)
 #include "clang/AST/DeclNodes.inc"
 
-void *Decl::operator new(std::size_t Size, const ASTContext &Context,
-                         GlobalDeclID ID, std::size_t Extra) {
+void *Decl::operator new(std::size_t Size, const ASTContext &Context, DeclID ID,
+                         std::size_t Extra) {
   // Allocate an extra 8 bytes worth of storage, which ensures that the
   // resulting pointer will still be 8-byte aligned.
   static_assert(sizeof(unsigned) * 2 >= alignof(Decl),
@@ -85,7 +85,7 @@ void *Decl::operator new(std::size_t Size, const ASTContext &Context,
   PrefixPtr[0] = 0;
 
   // Store the global declaration ID in the second 4 bytes.
-  PrefixPtr[1] = ID.get();
+  PrefixPtr[1] = ID;
 
   return Result;
 }
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 75c4412..c525c33 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -57,8 +57,7 @@ using namespace clang;
 
 void AccessSpecDecl::anchor() {}
 
-AccessSpecDecl *AccessSpecDecl::CreateDeserialized(ASTContext &C,
-                                                   GlobalDeclID ID) {
+AccessSpecDecl *AccessSpecDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) AccessSpecDecl(EmptyShell());
 }
 
@@ -69,7 +68,7 @@ void LazyASTUnresolvedSet::getFromExternalSource(ASTContext &C) const {
 
   for (ASTUnresolvedSet::iterator I = Impl.begin(); I != Impl.end(); ++I)
     I.setDecl(cast<NamedDecl>(Source->GetExternalDecl(
-        GlobalDeclID(reinterpret_cast<uintptr_t>(I.getDecl()) >> 2))));
+        reinterpret_cast<uintptr_t>(I.getDecl()) >> 2)));
   Impl.Decls.setLazy(false);
 }
 
@@ -162,7 +161,7 @@ CXXRecordDecl::CreateLambda(const ASTContext &C, DeclContext *DC,
 }
 
 CXXRecordDecl *CXXRecordDecl::CreateDeserialized(const ASTContext &C,
-                                                 GlobalDeclID ID) {
+                                                 DeclID ID) {
   auto *R = new (C, ID)
       CXXRecordDecl(CXXRecord, TagTypeKind::Struct, C, nullptr,
                     SourceLocation(), SourceLocation(), nullptr, nullptr);
@@ -2163,8 +2162,8 @@ CXXDeductionGuideDecl *CXXDeductionGuideDecl::Create(
                                            TInfo, EndLocation, Ctor, Kind);
 }
 
-CXXDeductionGuideDecl *
-CXXDeductionGuideDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+CXXDeductionGuideDecl *CXXDeductionGuideDecl::CreateDeserialized(ASTContext &C,
+                                                                 DeclID ID) {
   return new (C, ID) CXXDeductionGuideDecl(
       C, nullptr, SourceLocation(), ExplicitSpecifier(), DeclarationNameInfo(),
       QualType(), nullptr, SourceLocation(), nullptr,
@@ -2176,8 +2175,8 @@ RequiresExprBodyDecl *RequiresExprBodyDecl::Create(
   return new (C, DC) RequiresExprBodyDecl(C, DC, StartLoc);
 }
 
-RequiresExprBodyDecl *
-RequiresExprBodyDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+RequiresExprBodyDecl *RequiresExprBodyDecl::CreateDeserialized(ASTContext &C,
+                                                               DeclID ID) {
   return new (C, ID) RequiresExprBodyDecl(C, nullptr, SourceLocation());
 }
 
@@ -2282,8 +2281,7 @@ CXXMethodDecl::Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
       isInline, ConstexprKind, EndLocation, TrailingRequiresClause);
 }
 
-CXXMethodDecl *CXXMethodDecl::CreateDeserialized(ASTContext &C,
-                                                 GlobalDeclID ID) {
+CXXMethodDecl *CXXMethodDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) CXXMethodDecl(
       CXXMethod, C, nullptr, SourceLocation(), DeclarationNameInfo(),
       QualType(), nullptr, SC_None, false, false,
@@ -2701,7 +2699,7 @@ CXXConstructorDecl::CXXConstructorDecl(
 void CXXConstructorDecl::anchor() {}
 
 CXXConstructorDecl *CXXConstructorDecl::CreateDeserialized(ASTContext &C,
-                                                           GlobalDeclID ID,
+                                                           DeclID ID,
                                                            uint64_t AllocKind) {
   bool hasTrailingExplicit = static_cast<bool>(AllocKind & TAKHasTailExplicit);
   bool isInheritingConstructor =
@@ -2848,7 +2846,7 @@ bool CXXConstructorDecl::isSpecializationCopyingObject() const {
 void CXXDestructorDecl::anchor() {}
 
 CXXDestructorDecl *CXXDestructorDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID) CXXDestructorDecl(
       C, nullptr, SourceLocation(), DeclarationNameInfo(), QualType(), nullptr,
       false, false, false, ConstexprSpecKind::Unspecified, nullptr);
@@ -2880,7 +2878,7 @@ void CXXDestructorDecl::setOperatorDelete(FunctionDecl *OD, Expr *ThisArg) {
 void CXXConversionDecl::anchor() {}
 
 CXXConversionDecl *CXXConversionDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID) CXXConversionDecl(
       C, nullptr, SourceLocation(), DeclarationNameInfo(), QualType(), nullptr,
       false, false, ExplicitSpecifier(), ConstexprSpecKind::Unspecified,
@@ -2925,8 +2923,7 @@ LinkageSpecDecl *LinkageSpecDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) LinkageSpecDecl(DC, ExternLoc, LangLoc, Lang, HasBraces);
 }
 
-LinkageSpecDecl *LinkageSpecDecl::CreateDeserialized(ASTContext &C,
-                                                     GlobalDeclID ID) {
+LinkageSpecDecl *LinkageSpecDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       LinkageSpecDecl(nullptr, SourceLocation(), SourceLocation(),
                       LinkageSpecLanguageIDs::C, false);
@@ -2948,7 +2945,7 @@ UsingDirectiveDecl *UsingDirectiveDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 UsingDirectiveDecl *UsingDirectiveDecl::CreateDeserialized(ASTContext &C,
-                                                           GlobalDeclID ID) {
+                                                           DeclID ID) {
   return new (C, ID) UsingDirectiveDecl(nullptr, SourceLocation(),
                                         SourceLocation(),
                                         NestedNameSpecifierLoc(),
@@ -2987,8 +2984,7 @@ NamespaceDecl *NamespaceDecl::Create(ASTContext &C, DeclContext *DC,
       NamespaceDecl(C, DC, Inline, StartLoc, IdLoc, Id, PrevDecl, Nested);
 }
 
-NamespaceDecl *NamespaceDecl::CreateDeserialized(ASTContext &C,
-                                                 GlobalDeclID ID) {
+NamespaceDecl *NamespaceDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) NamespaceDecl(C, nullptr, false, SourceLocation(),
                                    SourceLocation(), nullptr, nullptr, false);
 }
@@ -3050,7 +3046,7 @@ NamespaceAliasDecl *NamespaceAliasDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 NamespaceAliasDecl *NamespaceAliasDecl::CreateDeserialized(ASTContext &C,
-                                                           GlobalDeclID ID) {
+                                                           DeclID ID) {
   return new (C, ID) NamespaceAliasDecl(C, nullptr, SourceLocation(),
                                         SourceLocation(), nullptr,
                                         NestedNameSpecifierLoc(),
@@ -3105,8 +3101,7 @@ UsingShadowDecl::UsingShadowDecl(Kind K, ASTContext &C, EmptyShell Empty)
     : NamedDecl(K, nullptr, SourceLocation(), DeclarationName()),
       redeclarable_base(C) {}
 
-UsingShadowDecl *UsingShadowDecl::CreateDeserialized(ASTContext &C,
-                                                     GlobalDeclID ID) {
+UsingShadowDecl *UsingShadowDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) UsingShadowDecl(UsingShadow, C, EmptyShell());
 }
 
@@ -3129,7 +3124,7 @@ ConstructorUsingShadowDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 ConstructorUsingShadowDecl *
-ConstructorUsingShadowDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ConstructorUsingShadowDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ConstructorUsingShadowDecl(C, EmptyShell());
 }
 
@@ -3177,7 +3172,7 @@ UsingDecl *UsingDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation UL,
   return new (C, DC) UsingDecl(DC, UL, QualifierLoc, NameInfo, HasTypename);
 }
 
-UsingDecl *UsingDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+UsingDecl *UsingDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) UsingDecl(nullptr, SourceLocation(),
                                NestedNameSpecifierLoc(), DeclarationNameInfo(),
                                false);
@@ -3201,8 +3196,7 @@ UsingEnumDecl *UsingEnumDecl::Create(ASTContext &C, DeclContext *DC,
       UsingEnumDecl(DC, EnumType->getType()->getAsTagDecl()->getDeclName(), UL, EL, NL, EnumType);
 }
 
-UsingEnumDecl *UsingEnumDecl::CreateDeserialized(ASTContext &C,
-                                                 GlobalDeclID ID) {
+UsingEnumDecl *UsingEnumDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       UsingEnumDecl(nullptr, DeclarationName(), SourceLocation(),
                     SourceLocation(), SourceLocation(), nullptr);
@@ -3221,7 +3215,7 @@ UsingPackDecl *UsingPackDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC, Extra) UsingPackDecl(DC, InstantiatedFrom, UsingDecls);
 }
 
-UsingPackDecl *UsingPackDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+UsingPackDecl *UsingPackDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                                  unsigned NumExpansions) {
   size_t Extra = additionalSizeToAlloc<NamedDecl *>(NumExpansions);
   auto *Result =
@@ -3247,7 +3241,7 @@ UnresolvedUsingValueDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 UnresolvedUsingValueDecl *
-UnresolvedUsingValueDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+UnresolvedUsingValueDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) UnresolvedUsingValueDecl(nullptr, QualType(),
                                               SourceLocation(),
                                               NestedNameSpecifierLoc(),
@@ -3277,8 +3271,7 @@ UnresolvedUsingTypenameDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 UnresolvedUsingTypenameDecl *
-UnresolvedUsingTypenameDecl::CreateDeserialized(ASTContext &C,
-                                                GlobalDeclID ID) {
+UnresolvedUsingTypenameDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) UnresolvedUsingTypenameDecl(
       nullptr, SourceLocation(), SourceLocation(), NestedNameSpecifierLoc(),
       SourceLocation(), nullptr, SourceLocation());
@@ -3291,8 +3284,7 @@ UnresolvedUsingIfExistsDecl::Create(ASTContext &Ctx, DeclContext *DC,
 }
 
 UnresolvedUsingIfExistsDecl *
-UnresolvedUsingIfExistsDecl::CreateDeserialized(ASTContext &Ctx,
-                                                GlobalDeclID ID) {
+UnresolvedUsingIfExistsDecl::CreateDeserialized(ASTContext &Ctx, DeclID ID) {
   return new (Ctx, ID)
       UnresolvedUsingIfExistsDecl(nullptr, SourceLocation(), DeclarationName());
 }
@@ -3316,7 +3308,7 @@ StaticAssertDecl *StaticAssertDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 StaticAssertDecl *StaticAssertDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID) StaticAssertDecl(nullptr, SourceLocation(), nullptr,
                                       nullptr, SourceLocation(), false);
 }
@@ -3338,7 +3330,7 @@ BindingDecl *BindingDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) BindingDecl(DC, IdLoc, Id);
 }
 
-BindingDecl *BindingDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+BindingDecl *BindingDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) BindingDecl(nullptr, SourceLocation(), nullptr);
 }
 
@@ -3369,7 +3361,7 @@ DecompositionDecl *DecompositionDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 DecompositionDecl *DecompositionDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID,
+                                                         DeclID ID,
                                                          unsigned NumBindings) {
   size_t Extra = additionalSizeToAlloc<BindingDecl *>(NumBindings);
   auto *Result = new (C, ID, Extra)
@@ -3407,8 +3399,7 @@ MSPropertyDecl *MSPropertyDecl::Create(ASTContext &C, DeclContext *DC,
   return new (C, DC) MSPropertyDecl(DC, L, N, T, TInfo, StartL, Getter, Setter);
 }
 
-MSPropertyDecl *MSPropertyDecl::CreateDeserialized(ASTContext &C,
-                                                   GlobalDeclID ID) {
+MSPropertyDecl *MSPropertyDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) MSPropertyDecl(nullptr, SourceLocation(),
                                     DeclarationName(), QualType(), nullptr,
                                     SourceLocation(), nullptr, nullptr);
@@ -3425,7 +3416,7 @@ MSGuidDecl *MSGuidDecl::Create(const ASTContext &C, QualType T, Parts P) {
   return new (C, DC) MSGuidDecl(DC, T, P);
 }
 
-MSGuidDecl *MSGuidDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+MSGuidDecl *MSGuidDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) MSGuidDecl(nullptr, QualType(), Parts());
 }
 
@@ -3535,7 +3526,7 @@ UnnamedGlobalConstantDecl::Create(const ASTContext &C, QualType T,
 }
 
 UnnamedGlobalConstantDecl *
-UnnamedGlobalConstantDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+UnnamedGlobalConstantDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       UnnamedGlobalConstantDecl(C, nullptr, QualType(), APValue());
 }
diff --git a/clang/lib/AST/DeclFriend.cpp b/clang/lib/AST/DeclFriend.cpp
index 04b9b93..f6d11e5 100644
--- a/clang/lib/AST/DeclFriend.cpp
+++ b/clang/lib/AST/DeclFriend.cpp
@@ -62,7 +62,7 @@ FriendDecl *FriendDecl::Create(ASTContext &C, DeclContext *DC,
   return FD;
 }
 
-FriendDecl *FriendDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+FriendDecl *FriendDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                            unsigned FriendTypeNumTPLists) {
   std::size_t Extra =
       additionalSizeToAlloc<TemplateParameterList *>(FriendTypeNumTPLists);
diff --git a/clang/lib/AST/DeclObjC.cpp b/clang/lib/AST/DeclObjC.cpp
index 83062b0..f98ec67 100644
--- a/clang/lib/AST/DeclObjC.cpp
+++ b/clang/lib/AST/DeclObjC.cpp
@@ -862,8 +862,7 @@ ObjCMethodDecl *ObjCMethodDecl::Create(
       isImplicitlyDeclared, isDefined, impControl, HasRelatedResultType);
 }
 
-ObjCMethodDecl *ObjCMethodDecl::CreateDeserialized(ASTContext &C,
-                                                   GlobalDeclID ID) {
+ObjCMethodDecl *ObjCMethodDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ObjCMethodDecl(SourceLocation(), SourceLocation(),
                                     Selector(), QualType(), nullptr, nullptr);
 }
@@ -1487,7 +1486,7 @@ ObjCTypeParamDecl *ObjCTypeParamDecl::Create(ASTContext &ctx, DeclContext *dc,
 }
 
 ObjCTypeParamDecl *ObjCTypeParamDecl::CreateDeserialized(ASTContext &ctx,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (ctx, ID) ObjCTypeParamDecl(ctx, nullptr,
                                          ObjCTypeParamVariance::Invariant,
                                          SourceLocation(), 0, SourceLocation(),
@@ -1552,7 +1551,7 @@ ObjCInterfaceDecl *ObjCInterfaceDecl::Create(
 }
 
 ObjCInterfaceDecl *ObjCInterfaceDecl::CreateDeserialized(const ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   auto *Result = new (C, ID)
       ObjCInterfaceDecl(C, nullptr, SourceLocation(), nullptr, nullptr,
                         SourceLocation(), nullptr, false);
@@ -1866,7 +1865,7 @@ ObjCIvarDecl *ObjCIvarDecl::Create(ASTContext &C, ObjCContainerDecl *DC,
                                   synthesized);
 }
 
-ObjCIvarDecl *ObjCIvarDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ObjCIvarDecl *ObjCIvarDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ObjCIvarDecl(nullptr, SourceLocation(), SourceLocation(),
                                   nullptr, QualType(), nullptr,
                                   ObjCIvarDecl::None, nullptr, false);
@@ -1915,7 +1914,7 @@ ObjCAtDefsFieldDecl
 }
 
 ObjCAtDefsFieldDecl *ObjCAtDefsFieldDecl::CreateDeserialized(ASTContext &C,
-                                                             GlobalDeclID ID) {
+                                                             DeclID ID) {
   return new (C, ID) ObjCAtDefsFieldDecl(nullptr, SourceLocation(),
                                          SourceLocation(), nullptr, QualType(),
                                          nullptr);
@@ -1950,7 +1949,7 @@ ObjCProtocolDecl *ObjCProtocolDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 ObjCProtocolDecl *ObjCProtocolDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   ObjCProtocolDecl *Result =
       new (C, ID) ObjCProtocolDecl(C, nullptr, nullptr, SourceLocation(),
                                    SourceLocation(), nullptr);
@@ -2149,7 +2148,7 @@ ObjCCategoryDecl *ObjCCategoryDecl::Create(
 }
 
 ObjCCategoryDecl *ObjCCategoryDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID) ObjCCategoryDecl(nullptr, SourceLocation(),
                                       SourceLocation(), SourceLocation(),
                                       nullptr, nullptr, nullptr);
@@ -2189,8 +2188,8 @@ ObjCCategoryImplDecl *ObjCCategoryImplDecl::Create(
                                           atStartLoc, CategoryNameLoc);
 }
 
-ObjCCategoryImplDecl *
-ObjCCategoryImplDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ObjCCategoryImplDecl *ObjCCategoryImplDecl::CreateDeserialized(ASTContext &C,
+                                                               DeclID ID) {
   return new (C, ID) ObjCCategoryImplDecl(nullptr, nullptr, nullptr,
                                           SourceLocation(), SourceLocation(),
                                           SourceLocation());
@@ -2297,7 +2296,7 @@ ObjCImplementationDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 ObjCImplementationDecl *
-ObjCImplementationDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ObjCImplementationDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ObjCImplementationDecl(nullptr, nullptr, nullptr,
                                             SourceLocation(), SourceLocation());
 }
@@ -2340,7 +2339,7 @@ ObjCCompatibleAliasDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 ObjCCompatibleAliasDecl *
-ObjCCompatibleAliasDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ObjCCompatibleAliasDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) ObjCCompatibleAliasDecl(nullptr, SourceLocation(),
                                              nullptr, nullptr);
 }
@@ -2361,7 +2360,7 @@ ObjCPropertyDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
 }
 
 ObjCPropertyDecl *ObjCPropertyDecl::CreateDeserialized(ASTContext &C,
-                                                       GlobalDeclID ID) {
+                                                       DeclID ID) {
   return new (C, ID) ObjCPropertyDecl(nullptr, SourceLocation(), nullptr,
                                       SourceLocation(), SourceLocation(),
                                       QualType(), nullptr, None);
@@ -2393,8 +2392,8 @@ ObjCPropertyImplDecl *ObjCPropertyImplDecl::Create(ASTContext &C,
                                           ivarLoc);
 }
 
-ObjCPropertyImplDecl *
-ObjCPropertyImplDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ObjCPropertyImplDecl *ObjCPropertyImplDecl::CreateDeserialized(ASTContext &C,
+                                                               DeclID ID) {
   return new (C, ID) ObjCPropertyImplDecl(nullptr, SourceLocation(),
                                           SourceLocation(), nullptr, Dynamic,
                                           nullptr, SourceLocation());
diff --git a/clang/lib/AST/DeclOpenMP.cpp b/clang/lib/AST/DeclOpenMP.cpp
index 81ca48e..9f1d2bd 100644
--- a/clang/lib/AST/DeclOpenMP.cpp
+++ b/clang/lib/AST/DeclOpenMP.cpp
@@ -35,9 +35,8 @@ OMPThreadPrivateDecl *OMPThreadPrivateDecl::Create(ASTContext &C,
   return D;
 }
 
-OMPThreadPrivateDecl *OMPThreadPrivateDecl::CreateDeserialized(ASTContext &C,
-                                                               GlobalDeclID ID,
-                                                               unsigned N) {
+OMPThreadPrivateDecl *
+OMPThreadPrivateDecl::CreateDeserialized(ASTContext &C, DeclID ID, unsigned N) {
   return OMPDeclarativeDirective::createEmptyDirective<OMPThreadPrivateDecl>(
       C, ID, 0, N);
 }
@@ -63,8 +62,7 @@ OMPAllocateDecl *OMPAllocateDecl::Create(ASTContext &C, DeclContext *DC,
   return D;
 }
 
-OMPAllocateDecl *OMPAllocateDecl::CreateDeserialized(ASTContext &C,
-                                                     GlobalDeclID ID,
+OMPAllocateDecl *OMPAllocateDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                                      unsigned NVars,
                                                      unsigned NClauses) {
   return OMPDeclarativeDirective::createEmptyDirective<OMPAllocateDecl>(
@@ -90,8 +88,7 @@ OMPRequiresDecl *OMPRequiresDecl::Create(ASTContext &C, DeclContext *DC,
                                                                    L);
 }
 
-OMPRequiresDecl *OMPRequiresDecl::CreateDeserialized(ASTContext &C,
-                                                     GlobalDeclID ID,
+OMPRequiresDecl *OMPRequiresDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                                      unsigned N) {
   return OMPDeclarativeDirective::createEmptyDirective<OMPRequiresDecl>(
       C, ID, N, 0, SourceLocation());
@@ -119,7 +116,7 @@ OMPDeclareReductionDecl *OMPDeclareReductionDecl::Create(
 }
 
 OMPDeclareReductionDecl *
-OMPDeclareReductionDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+OMPDeclareReductionDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) OMPDeclareReductionDecl(
       OMPDeclareReduction, /*DC=*/nullptr, SourceLocation(), DeclarationName(),
       QualType(), /*PrevDeclInScope=*/nullptr);
@@ -149,9 +146,8 @@ OMPDeclareMapperDecl *OMPDeclareMapperDecl::Create(
       C, DC, Clauses, 1, L, Name, T, VarName, PrevDeclInScope);
 }
 
-OMPDeclareMapperDecl *OMPDeclareMapperDecl::CreateDeserialized(ASTContext &C,
-                                                               GlobalDeclID ID,
-                                                               unsigned N) {
+OMPDeclareMapperDecl *
+OMPDeclareMapperDecl::CreateDeserialized(ASTContext &C, DeclID ID, unsigned N) {
   return OMPDeclarativeDirective::createEmptyDirective<OMPDeclareMapperDecl>(
       C, ID, N, 1, SourceLocation(), DeclarationName(), QualType(),
       DeclarationName(), /*PrevDeclInScope=*/nullptr);
@@ -181,7 +177,7 @@ OMPCapturedExprDecl *OMPCapturedExprDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 OMPCapturedExprDecl *OMPCapturedExprDecl::CreateDeserialized(ASTContext &C,
-                                                             GlobalDeclID ID) {
+                                                             DeclID ID) {
   return new (C, ID) OMPCapturedExprDecl(C, nullptr, nullptr, QualType(),
                                          /*TInfo=*/nullptr, SourceLocation());
 }
diff --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
index d27a30e..ca998b5 100644
--- a/clang/lib/AST/DeclTemplate.cpp
+++ b/clang/lib/AST/DeclTemplate.cpp
@@ -337,10 +337,9 @@ void RedeclarableTemplateDecl::loadLazySpecializationsImpl() const {
   CommonBase *CommonBasePtr = getMostRecentDecl()->getCommonPtr();
   if (CommonBasePtr->LazySpecializations) {
     ASTContext &Context = getASTContext();
-    GlobalDeclID *Specs = CommonBasePtr->LazySpecializations;
+    DeclID *Specs = CommonBasePtr->LazySpecializations;
     CommonBasePtr->LazySpecializations = nullptr;
-    unsigned SpecSize = (*Specs++).get();
-    for (unsigned I = 0; I != SpecSize; ++I)
+    for (uint32_t I = 0, N = *Specs++; I != N; ++I)
       (void)Context.getExternalSource()->GetExternalDecl(Specs[I]);
   }
 }
@@ -418,8 +417,8 @@ FunctionTemplateDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
   return TD;
 }
 
-FunctionTemplateDecl *
-FunctionTemplateDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+FunctionTemplateDecl *FunctionTemplateDecl::CreateDeserialized(ASTContext &C,
+                                                               DeclID ID) {
   return new (C, ID) FunctionTemplateDecl(C, nullptr, SourceLocation(),
                                           DeclarationName(), nullptr, nullptr);
 }
@@ -504,7 +503,7 @@ ClassTemplateDecl *ClassTemplateDecl::Create(ASTContext &C, DeclContext *DC,
 }
 
 ClassTemplateDecl *ClassTemplateDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID) ClassTemplateDecl(C, nullptr, SourceLocation(),
                                        DeclarationName(), nullptr, nullptr);
 }
@@ -653,14 +652,14 @@ TemplateTypeParmDecl *TemplateTypeParmDecl::Create(
 }
 
 TemplateTypeParmDecl *
-TemplateTypeParmDecl::CreateDeserialized(const ASTContext &C, GlobalDeclID ID) {
+TemplateTypeParmDecl::CreateDeserialized(const ASTContext &C, DeclID ID) {
   return new (C, ID)
       TemplateTypeParmDecl(nullptr, SourceLocation(), SourceLocation(), nullptr,
                            false, false, std::nullopt);
 }
 
 TemplateTypeParmDecl *
-TemplateTypeParmDecl::CreateDeserialized(const ASTContext &C, GlobalDeclID ID,
+TemplateTypeParmDecl::CreateDeserialized(const ASTContext &C, DeclID ID,
                                          bool HasTypeConstraint) {
   return new (C, ID,
               additionalSizeToAlloc<TypeConstraint>(HasTypeConstraint ? 1 : 0))
@@ -760,7 +759,7 @@ NonTypeTemplateParmDecl *NonTypeTemplateParmDecl::Create(
 }
 
 NonTypeTemplateParmDecl *
-NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                             bool HasTypeConstraint) {
   return new (C, ID, additionalSizeToAlloc<std::pair<QualType,
                                                      TypeSourceInfo *>,
@@ -771,7 +770,7 @@ NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
 }
 
 NonTypeTemplateParmDecl *
-NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                             unsigned NumExpandedTypes,
                                             bool HasTypeConstraint) {
   auto *NTTP =
@@ -837,13 +836,13 @@ TemplateTemplateParmDecl::Create(const ASTContext &C, DeclContext *DC,
 }
 
 TemplateTemplateParmDecl *
-TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) TemplateTemplateParmDecl(nullptr, SourceLocation(), 0, 0,
                                               false, nullptr, false, nullptr);
 }
 
 TemplateTemplateParmDecl *
-TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID,
+TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, DeclID ID,
                                              unsigned NumExpansions) {
   auto *TTP =
       new (C, ID, additionalSizeToAlloc<TemplateParameterList *>(NumExpansions))
@@ -949,8 +948,7 @@ ClassTemplateSpecializationDecl::Create(ASTContext &Context, TagKind TK,
 }
 
 ClassTemplateSpecializationDecl *
-ClassTemplateSpecializationDecl::CreateDeserialized(ASTContext &C,
-                                                    GlobalDeclID ID) {
+ClassTemplateSpecializationDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   auto *Result =
     new (C, ID) ClassTemplateSpecializationDecl(C, ClassTemplateSpecialization);
   Result->setMayHaveOutOfDateDef(false);
@@ -1036,7 +1034,7 @@ ConceptDecl *ConceptDecl::Create(ASTContext &C, DeclContext *DC,
   return TD;
 }
 
-ConceptDecl *ConceptDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+ConceptDecl *ConceptDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   ConceptDecl *Result = new (C, ID) ConceptDecl(nullptr, SourceLocation(),
                                                 DeclarationName(),
                                                 nullptr, nullptr);
@@ -1070,7 +1068,7 @@ ImplicitConceptSpecializationDecl *ImplicitConceptSpecializationDecl::Create(
 
 ImplicitConceptSpecializationDecl *
 ImplicitConceptSpecializationDecl::CreateDeserialized(
-    const ASTContext &C, GlobalDeclID ID, unsigned NumTemplateArgs) {
+    const ASTContext &C, DeclID ID, unsigned NumTemplateArgs) {
   return new (C, ID, additionalSizeToAlloc<TemplateArgument>(NumTemplateArgs))
       ImplicitConceptSpecializationDecl(EmptyShell{}, NumTemplateArgs);
 }
@@ -1133,7 +1131,7 @@ Create(ASTContext &Context, TagKind TK,DeclContext *DC,
 
 ClassTemplatePartialSpecializationDecl *
 ClassTemplatePartialSpecializationDecl::CreateDeserialized(ASTContext &C,
-                                                           GlobalDeclID ID) {
+                                                           DeclID ID) {
   auto *Result = new (C, ID) ClassTemplatePartialSpecializationDecl(C);
   Result->setMayHaveOutOfDateDef(false);
   return Result;
@@ -1160,7 +1158,7 @@ FriendTemplateDecl::Create(ASTContext &Context, DeclContext *DC,
 }
 
 FriendTemplateDecl *FriendTemplateDecl::CreateDeserialized(ASTContext &C,
-                                                           GlobalDeclID ID) {
+                                                           DeclID ID) {
   return new (C, ID) FriendTemplateDecl(EmptyShell());
 }
 
@@ -1179,8 +1177,8 @@ TypeAliasTemplateDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
   return TD;
 }
 
-TypeAliasTemplateDecl *
-TypeAliasTemplateDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+TypeAliasTemplateDecl *TypeAliasTemplateDecl::CreateDeserialized(ASTContext &C,
+                                                                 DeclID ID) {
   return new (C, ID) TypeAliasTemplateDecl(C, nullptr, SourceLocation(),
                                            DeclarationName(), nullptr, nullptr);
 }
@@ -1217,8 +1215,7 @@ VarTemplateDecl *VarTemplateDecl::Create(ASTContext &C, DeclContext *DC,
   return TD;
 }
 
-VarTemplateDecl *VarTemplateDecl::CreateDeserialized(ASTContext &C,
-                                                     GlobalDeclID ID) {
+VarTemplateDecl *VarTemplateDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID) VarTemplateDecl(C, nullptr, SourceLocation(),
                                      DeclarationName(), nullptr, nullptr);
 }
@@ -1340,8 +1337,7 @@ VarTemplateSpecializationDecl *VarTemplateSpecializationDecl::Create(
 }
 
 VarTemplateSpecializationDecl *
-VarTemplateSpecializationDecl::CreateDeserialized(ASTContext &C,
-                                                  GlobalDeclID ID) {
+VarTemplateSpecializationDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   return new (C, ID)
       VarTemplateSpecializationDecl(VarTemplateSpecialization, C);
 }
@@ -1433,7 +1429,7 @@ VarTemplatePartialSpecializationDecl::Create(
 
 VarTemplatePartialSpecializationDecl *
 VarTemplatePartialSpecializationDecl::CreateDeserialized(ASTContext &C,
-                                                         GlobalDeclID ID) {
+                                                         DeclID ID) {
   return new (C, ID) VarTemplatePartialSpecializationDecl(C);
 }
 
@@ -1547,7 +1543,7 @@ TemplateParamObjectDecl *TemplateParamObjectDecl::Create(const ASTContext &C,
 }
 
 TemplateParamObjectDecl *
-TemplateParamObjectDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+TemplateParamObjectDecl::CreateDeserialized(ASTContext &C, DeclID ID) {
   auto *TPOD = new (C, ID) TemplateParamObjectDecl(nullptr, QualType(), APValue());
   C.addDestruction(&TPOD->Value);
   return TPOD;
diff --git a/clang/lib/AST/ExternalASTSource.cpp b/clang/lib/AST/ExternalASTSource.cpp
index e96a474..26ded22 100644
--- a/clang/lib/AST/ExternalASTSource.cpp
+++ b/clang/lib/AST/ExternalASTSource.cpp
@@ -68,7 +68,7 @@ bool ExternalASTSource::layoutRecordType(
   return false;
 }
 
-Decl *ExternalASTSource::GetExternalDecl(GlobalDeclID ID) { return nullptr; }
+Decl *ExternalASTSource::GetExternalDecl(DeclID ID) { return nullptr; }
 
 Selector ExternalASTSource::GetExternalSelector(uint32_t ID) {
   return Selector();
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 2f75313e..361331d 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -1067,7 +1067,7 @@ public:
 
   std::vector<Decl *> takeTopLevelDecls() { return std::move(TopLevelDecls); }
 
-  std::vector<LocalDeclID> takeTopLevelDeclIDs() {
+  std::vector<DeclID> takeTopLevelDeclIDs() {
     return std::move(TopLevelDeclIDs);
   }
 
@@ -1101,7 +1101,7 @@ public:
 private:
   unsigned Hash = 0;
   std::vector<Decl *> TopLevelDecls;
-  std::vector<LocalDeclID> TopLevelDeclIDs;
+  std::vector<DeclID> TopLevelDeclIDs;
   llvm::SmallVector<ASTUnit::StandaloneDiagnostic, 4> PreambleDiags;
 };
 
@@ -1471,9 +1471,7 @@ void ASTUnit::RealizeTopLevelDeclsFromPreamble() {
   for (const auto TopLevelDecl : TopLevelDeclsInPreamble) {
     // Resolve the declaration ID to an actual declaration, possibly
     // deserializing the declaration in the process.
-    //
-    // FIMXE: We shouldn't convert a LocalDeclID to GlobalDeclID directly.
-    if (Decl *D = Source.GetExternalDecl(GlobalDeclID(TopLevelDecl.get())))
+    if (Decl *D = Source.GetExternalDecl(TopLevelDecl))
       Resolved.push_back(D);
   }
   TopLevelDeclsInPreamble.clear();
diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index a2af738..91ce16e 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -80,7 +80,7 @@ public:
     if (Previous)
       Previous->TypeRead(Idx, T);
   }
-  void DeclRead(GlobalDeclID ID, const Decl *D) override {
+  void DeclRead(DeclID ID, const Decl *D) override {
     if (Previous)
       Previous->DeclRead(ID, D);
   }
@@ -102,7 +102,7 @@ public:
                                    bool DeletePrevious)
       : DelegatingDeserializationListener(Previous, DeletePrevious) {}
 
-  void DeclRead(GlobalDeclID ID, const Decl *D) override {
+  void DeclRead(DeclID ID, const Decl *D) override {
     llvm::outs() << "PCH DECL: " << D->getDeclKindName();
     if (const NamedDecl *ND = dyn_cast<NamedDecl>(D)) {
       llvm::outs() << " - ";
@@ -128,7 +128,7 @@ public:
       : DelegatingDeserializationListener(Previous, DeletePrevious), Ctx(Ctx),
         NamesToCheck(NamesToCheck) {}
 
-  void DeclRead(GlobalDeclID ID, const Decl *D) override {
+  void DeclRead(DeclID ID, const Decl *D) override {
     if (const NamedDecl *ND = dyn_cast<NamedDecl>(D))
       if (NamesToCheck.find(ND->getNameAsString()) != NamesToCheck.end()) {
         unsigned DiagID
diff --git a/clang/lib/Frontend/MultiplexConsumer.cpp b/clang/lib/Frontend/MultiplexConsumer.cpp
index c74bfd8..9e885c8 100644
--- a/clang/lib/Frontend/MultiplexConsumer.cpp
+++ b/clang/lib/Frontend/MultiplexConsumer.cpp
@@ -52,8 +52,7 @@ void MultiplexASTDeserializationListener::TypeRead(
     Listeners[i]->TypeRead(Idx, T);
 }
 
-void MultiplexASTDeserializationListener::DeclRead(GlobalDeclID ID,
-                                                   const Decl *D) {
+void MultiplexASTDeserializationListener::DeclRead(DeclID ID, const Decl *D) {
   for (size_t i = 0, e = Listeners.size(); i != e; ++i)
     Listeners[i]->DeclRead(ID, D);
 }
diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index 79e656e..e48c724 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -46,7 +46,7 @@ void MultiplexExternalSemaSource::AddSource(ExternalSemaSource *Source) {
 // ExternalASTSource.
 //===----------------------------------------------------------------------===//
 
-Decl *MultiplexExternalSemaSource::GetExternalDecl(GlobalDeclID ID) {
+Decl *MultiplexExternalSemaSource::GetExternalDecl(DeclID ID) {
   for(size_t i = 0; i < Sources.size(); ++i)
     if (Decl *Result = Sources[i]->GetExternalDecl(ID))
       return Result;
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index c99d6ed..df9984d 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5101,9 +5101,8 @@ void ASTReader::InitializeContext() {
 
   // If there's a listener, notify them that we "read" the translation unit.
   if (DeserializationListener)
-    DeserializationListener->DeclRead(
-        GlobalDeclID(PREDEF_DECL_TRANSLATION_UNIT_ID),
-        Context.getTranslationUnitDecl());
+    DeserializationListener->DeclRead(PREDEF_DECL_TRANSLATION_UNIT_ID,
+                                      Context.getTranslationUnitDecl());
 
   // FIXME: Find a better way to deal with collisions between these
   // built-in types. Right now, we just ignore the problem.
@@ -6011,9 +6010,9 @@ llvm::Error ASTReader::ReadSubmoduleBlock(ModuleFile &F,
     case SUBMODULE_INITIALIZERS: {
       if (!ContextObj)
         break;
-      SmallVector<GlobalDeclID, 16> Inits;
+      SmallVector<DeclID, 16> Inits;
       for (auto &ID : Record)
-        Inits.push_back(getGlobalDeclID(F, LocalDeclID(ID)));
+        Inits.push_back(getGlobalDeclID(F, LocalDeclID(ID)).get());
       ContextObj->addLazyModuleInitializers(CurrentModule, Inits);
       break;
     }
@@ -7518,7 +7517,9 @@ ASTRecordReader::readASTTemplateArgumentListInfo() {
   return ASTTemplateArgumentListInfo::Create(getContext(), Result);
 }
 
-Decl *ASTReader::GetExternalDecl(GlobalDeclID ID) { return GetDecl(ID); }
+Decl *ASTReader::GetExternalDecl(DeclID ID) {
+  return GetDecl(GlobalDeclID(ID));
+}
 
 void ASTReader::CompleteRedeclChain(const Decl *D) {
   if (NumCurrentElementsDeserializing) {
@@ -7766,7 +7767,7 @@ static Decl *getPredefinedDecl(ASTContext &Context, PredefinedDeclIDs ID) {
 Decl *ASTReader::GetExistingDecl(GlobalDeclID ID) {
   assert(ContextObj && "reading decl with no AST context");
   if (ID.get() < NUM_PREDEF_DECL_IDS) {
-    Decl *D = getPredefinedDecl(*ContextObj, (PredefinedDeclIDs)ID);
+    Decl *D = getPredefinedDecl(*ContextObj, (PredefinedDeclIDs)ID.get());
     if (D) {
       // Track that we have merged the declaration with ID \p ID into the
       // pre-existing predefined declaration \p D.
@@ -7803,17 +7804,17 @@ Decl *ASTReader::GetDecl(GlobalDeclID ID) {
   if (!DeclsLoaded[Index]) {
     ReadDeclRecord(ID);
     if (DeserializationListener)
-      DeserializationListener->DeclRead(ID, DeclsLoaded[Index]);
+      DeserializationListener->DeclRead(ID.get(), DeclsLoaded[Index]);
   }
 
   return DeclsLoaded[Index];
 }
 
-LocalDeclID ASTReader::mapGlobalIDToModuleFileGlobalID(ModuleFile &M,
-                                                       GlobalDeclID GlobalID) {
+DeclID ASTReader::mapGlobalIDToModuleFileGlobalID(ModuleFile &M,
+                                                  GlobalDeclID GlobalID) {
   DeclID ID = GlobalID.get();
   if (ID < NUM_PREDEF_DECL_IDS)
-    return LocalDeclID(ID);
+    return ID;
 
   GlobalDeclMapType::const_iterator I = GlobalDeclMap.find(GlobalID);
   assert(I != GlobalDeclMap.end() && "Corrupted global declaration map");
@@ -7822,9 +7823,9 @@ LocalDeclID ASTReader::mapGlobalIDToModuleFileGlobalID(ModuleFile &M,
   llvm::DenseMap<ModuleFile *, DeclID>::iterator Pos =
       M.GlobalToLocalDeclIDs.find(Owner);
   if (Pos == M.GlobalToLocalDeclIDs.end())
-    return LocalDeclID();
+    return 0;
 
-  return LocalDeclID(ID - Owner->BaseDeclID + Pos->second);
+  return ID - Owner->BaseDeclID + Pos->second;
 }
 
 GlobalDeclID ASTReader::ReadDeclID(ModuleFile &F, const RecordData &Record,
@@ -7991,7 +7992,6 @@ ASTReader::FindExternalVisibleDeclsByName(const DeclContext *DC,
   // Load the list of declarations.
   SmallVector<NamedDecl *, 64> Decls;
   llvm::SmallPtrSet<NamedDecl *, 8> Found;
-
   for (GlobalDeclID ID : It->second.Table.find(Name)) {
     NamedDecl *ND = cast<NamedDecl>(GetDecl(ID));
     if (ND->getDeclName() == Name && Found.insert(ND).second)
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 744f11d..9707eed 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -273,15 +273,17 @@ namespace clang {
       auto *&LazySpecializations = D->getCommonPtr()->LazySpecializations;
 
       if (auto &Old = LazySpecializations) {
-        IDs.insert(IDs.end(), Old + 1, Old + 1 + Old[0].get());
+        IDs.insert(IDs.end(), GlobalDeclIDIterator(Old + 1),
+                   GlobalDeclIDIterator(Old + 1 + Old[0]));
         llvm::sort(IDs);
         IDs.erase(std::unique(IDs.begin(), IDs.end()), IDs.end());
       }
 
-      auto *Result = new (C) GlobalDeclID[1 + IDs.size()];
-      *Result = GlobalDeclID(IDs.size());
+      auto *Result = new (C) DeclID[1 + IDs.size()];
+      *Result = IDs.size();
 
-      std::copy(IDs.begin(), IDs.end(), Result + 1);
+      std::copy(DeclIDIterator(IDs.begin()), DeclIDIterator(IDs.end()),
+                Result + 1);
 
       LazySpecializations = Result;
     }
@@ -556,7 +558,7 @@ void ASTDeclReader::Visit(Decl *D) {
 
     // If this is a tag declaration with a typedef name for linkage, it's safe
     // to load that typedef now.
-    if (NamedDeclForTagDecl.isValid())
+    if (NamedDeclForTagDecl != GlobalDeclID())
       cast<TagDecl>(D)->TypedefNameDeclOrQualifier =
           cast<TypedefNameDecl>(Reader.GetDecl(NamedDeclForTagDecl));
   } else if (auto *ID = dyn_cast<ObjCInterfaceDecl>(D)) {
@@ -601,7 +603,7 @@ void ASTDeclReader::VisitDecl(Decl *D) {
     GlobalDeclID SemaDCIDForTemplateParmDecl = readDeclID();
     GlobalDeclID LexicalDCIDForTemplateParmDecl =
         HasStandaloneLexicalDC ? readDeclID() : GlobalDeclID();
-    if (LexicalDCIDForTemplateParmDecl.isInvalid())
+    if (LexicalDCIDForTemplateParmDecl == GlobalDeclID())
       LexicalDCIDForTemplateParmDecl = SemaDCIDForTemplateParmDecl;
     Reader.addPendingDeclContextInfo(D,
                                      SemaDCIDForTemplateParmDecl,
@@ -1858,7 +1860,7 @@ void ASTDeclReader::VisitNamespaceDecl(NamespaceDecl *D) {
 
   mergeRedeclarable(D, Redecl);
 
-  if (AnonNamespace.isValid()) {
+  if (AnonNamespace != GlobalDeclID()) {
     // Each module has its own anonymous namespace, which is disjoint from
     // any other module's anonymous namespaces, so don't attach the anonymous
     // namespace at all.
@@ -2790,9 +2792,9 @@ ASTDeclReader::VisitRedeclarable(Redeclarable<T> *D) {
 
   uint64_t RedeclOffset = 0;
 
-  // invalid FirstDeclID  indicates that this declaration was the only
-  // declaration of its entity, and is used for space optimization.
-  if (FirstDeclID.isInvalid()) {
+  // 0 indicates that this declaration was the only declaration of its entity,
+  // and is used for space optimization.
+  if (FirstDeclID == GlobalDeclID()) {
     FirstDeclID = ThisDeclID;
     IsKeyDecl = true;
     IsFirstLocalDecl = true;
@@ -3827,232 +3829,240 @@ Decl *ASTReader::ReadDeclRecord(GlobalDeclID ID) {
         Twine("ASTReader::readDeclRecord failed reading decl code: ") +
         toString(MaybeDeclCode.takeError()));
 
+  DeclID RawGlobalID = ID.get();
   switch ((DeclCode)MaybeDeclCode.get()) {
   case DECL_CONTEXT_LEXICAL:
   case DECL_CONTEXT_VISIBLE:
     llvm_unreachable("Record cannot be de-serialized with readDeclRecord");
   case DECL_TYPEDEF:
-    D = TypedefDecl::CreateDeserialized(Context, ID);
+    D = TypedefDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_TYPEALIAS:
-    D = TypeAliasDecl::CreateDeserialized(Context, ID);
+    D = TypeAliasDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_ENUM:
-    D = EnumDecl::CreateDeserialized(Context, ID);
+    D = EnumDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_RECORD:
-    D = RecordDecl::CreateDeserialized(Context, ID);
+    D = RecordDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_ENUM_CONSTANT:
-    D = EnumConstantDecl::CreateDeserialized(Context, ID);
+    D = EnumConstantDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_FUNCTION:
-    D = FunctionDecl::CreateDeserialized(Context, ID);
+    D = FunctionDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_LINKAGE_SPEC:
-    D = LinkageSpecDecl::CreateDeserialized(Context, ID);
+    D = LinkageSpecDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_EXPORT:
-    D = ExportDecl::CreateDeserialized(Context, ID);
+    D = ExportDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_LABEL:
-    D = LabelDecl::CreateDeserialized(Context, ID);
+    D = LabelDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_NAMESPACE:
-    D = NamespaceDecl::CreateDeserialized(Context, ID);
+    D = NamespaceDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_NAMESPACE_ALIAS:
-    D = NamespaceAliasDecl::CreateDeserialized(Context, ID);
+    D = NamespaceAliasDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_USING:
-    D = UsingDecl::CreateDeserialized(Context, ID);
+    D = UsingDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_USING_PACK:
-    D = UsingPackDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = UsingPackDecl::CreateDeserialized(Context, RawGlobalID,
+                                          Record.readInt());
     break;
   case DECL_USING_SHADOW:
-    D = UsingShadowDecl::CreateDeserialized(Context, ID);
+    D = UsingShadowDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_USING_ENUM:
-    D = UsingEnumDecl::CreateDeserialized(Context, ID);
+    D = UsingEnumDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CONSTRUCTOR_USING_SHADOW:
-    D = ConstructorUsingShadowDecl::CreateDeserialized(Context, ID);
+    D = ConstructorUsingShadowDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_USING_DIRECTIVE:
-    D = UsingDirectiveDecl::CreateDeserialized(Context, ID);
+    D = UsingDirectiveDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_UNRESOLVED_USING_VALUE:
-    D = UnresolvedUsingValueDecl::CreateDeserialized(Context, ID);
+    D = UnresolvedUsingValueDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_UNRESOLVED_USING_TYPENAME:
-    D = UnresolvedUsingTypenameDecl::CreateDeserialized(Context, ID);
+    D = UnresolvedUsingTypenameDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_UNRESOLVED_USING_IF_EXISTS:
-    D = UnresolvedUsingIfExistsDecl::CreateDeserialized(Context, ID);
+    D = UnresolvedUsingIfExistsDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CXX_RECORD:
-    D = CXXRecordDecl::CreateDeserialized(Context, ID);
+    D = CXXRecordDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CXX_DEDUCTION_GUIDE:
-    D = CXXDeductionGuideDecl::CreateDeserialized(Context, ID);
+    D = CXXDeductionGuideDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CXX_METHOD:
-    D = CXXMethodDecl::CreateDeserialized(Context, ID);
+    D = CXXMethodDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CXX_CONSTRUCTOR:
-    D = CXXConstructorDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = CXXConstructorDecl::CreateDeserialized(Context, RawGlobalID,
+                                               Record.readInt());
     break;
   case DECL_CXX_DESTRUCTOR:
-    D = CXXDestructorDecl::CreateDeserialized(Context, ID);
+    D = CXXDestructorDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CXX_CONVERSION:
-    D = CXXConversionDecl::CreateDeserialized(Context, ID);
+    D = CXXConversionDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_ACCESS_SPEC:
-    D = AccessSpecDecl::CreateDeserialized(Context, ID);
+    D = AccessSpecDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_FRIEND:
-    D = FriendDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = FriendDecl::CreateDeserialized(Context, RawGlobalID, Record.readInt());
     break;
   case DECL_FRIEND_TEMPLATE:
-    D = FriendTemplateDecl::CreateDeserialized(Context, ID);
+    D = FriendTemplateDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CLASS_TEMPLATE:
-    D = ClassTemplateDecl::CreateDeserialized(Context, ID);
+    D = ClassTemplateDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CLASS_TEMPLATE_SPECIALIZATION:
-    D = ClassTemplateSpecializationDecl::CreateDeserialized(Context, ID);
+    D = ClassTemplateSpecializationDecl::CreateDeserialized(Context,
+                                                            RawGlobalID);
     break;
   case DECL_CLASS_TEMPLATE_PARTIAL_SPECIALIZATION:
-    D = ClassTemplatePartialSpecializationDecl::CreateDeserialized(Context, ID);
+    D = ClassTemplatePartialSpecializationDecl::CreateDeserialized(Context,
+                                                                   RawGlobalID);
     break;
   case DECL_VAR_TEMPLATE:
-    D = VarTemplateDecl::CreateDeserialized(Context, ID);
+    D = VarTemplateDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_VAR_TEMPLATE_SPECIALIZATION:
-    D = VarTemplateSpecializationDecl::CreateDeserialized(Context, ID);
+    D = VarTemplateSpecializationDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_VAR_TEMPLATE_PARTIAL_SPECIALIZATION:
-    D = VarTemplatePartialSpecializationDecl::CreateDeserialized(Context, ID);
+    D = VarTemplatePartialSpecializationDecl::CreateDeserialized(Context,
+                                                                 RawGlobalID);
     break;
   case DECL_FUNCTION_TEMPLATE:
-    D = FunctionTemplateDecl::CreateDeserialized(Context, ID);
+    D = FunctionTemplateDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_TEMPLATE_TYPE_PARM: {
     bool HasTypeConstraint = Record.readInt();
-    D = TemplateTypeParmDecl::CreateDeserialized(Context, ID,
+    D = TemplateTypeParmDecl::CreateDeserialized(Context, RawGlobalID,
                                                  HasTypeConstraint);
     break;
   }
   case DECL_NON_TYPE_TEMPLATE_PARM: {
     bool HasTypeConstraint = Record.readInt();
-    D = NonTypeTemplateParmDecl::CreateDeserialized(Context, ID,
+    D = NonTypeTemplateParmDecl::CreateDeserialized(Context, RawGlobalID,
                                                     HasTypeConstraint);
     break;
   }
   case DECL_EXPANDED_NON_TYPE_TEMPLATE_PARM_PACK: {
     bool HasTypeConstraint = Record.readInt();
     D = NonTypeTemplateParmDecl::CreateDeserialized(
-        Context, ID, Record.readInt(), HasTypeConstraint);
+        Context, RawGlobalID, Record.readInt(), HasTypeConstraint);
     break;
   }
   case DECL_TEMPLATE_TEMPLATE_PARM:
-    D = TemplateTemplateParmDecl::CreateDeserialized(Context, ID);
+    D = TemplateTemplateParmDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_EXPANDED_TEMPLATE_TEMPLATE_PARM_PACK:
-    D = TemplateTemplateParmDecl::CreateDeserialized(Context, ID,
+    D = TemplateTemplateParmDecl::CreateDeserialized(Context, RawGlobalID,
                                                      Record.readInt());
     break;
   case DECL_TYPE_ALIAS_TEMPLATE:
-    D = TypeAliasTemplateDecl::CreateDeserialized(Context, ID);
+    D = TypeAliasTemplateDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CONCEPT:
-    D = ConceptDecl::CreateDeserialized(Context, ID);
+    D = ConceptDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_REQUIRES_EXPR_BODY:
-    D = RequiresExprBodyDecl::CreateDeserialized(Context, ID);
+    D = RequiresExprBodyDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_STATIC_ASSERT:
-    D = StaticAssertDecl::CreateDeserialized(Context, ID);
+    D = StaticAssertDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_METHOD:
-    D = ObjCMethodDecl::CreateDeserialized(Context, ID);
+    D = ObjCMethodDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_INTERFACE:
-    D = ObjCInterfaceDecl::CreateDeserialized(Context, ID);
+    D = ObjCInterfaceDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_IVAR:
-    D = ObjCIvarDecl::CreateDeserialized(Context, ID);
+    D = ObjCIvarDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_PROTOCOL:
-    D = ObjCProtocolDecl::CreateDeserialized(Context, ID);
+    D = ObjCProtocolDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_AT_DEFS_FIELD:
-    D = ObjCAtDefsFieldDecl::CreateDeserialized(Context, ID);
+    D = ObjCAtDefsFieldDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_CATEGORY:
-    D = ObjCCategoryDecl::CreateDeserialized(Context, ID);
+    D = ObjCCategoryDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_CATEGORY_IMPL:
-    D = ObjCCategoryImplDecl::CreateDeserialized(Context, ID);
+    D = ObjCCategoryImplDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_IMPLEMENTATION:
-    D = ObjCImplementationDecl::CreateDeserialized(Context, ID);
+    D = ObjCImplementationDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_COMPATIBLE_ALIAS:
-    D = ObjCCompatibleAliasDecl::CreateDeserialized(Context, ID);
+    D = ObjCCompatibleAliasDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_PROPERTY:
-    D = ObjCPropertyDecl::CreateDeserialized(Context, ID);
+    D = ObjCPropertyDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_PROPERTY_IMPL:
-    D = ObjCPropertyImplDecl::CreateDeserialized(Context, ID);
+    D = ObjCPropertyImplDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_FIELD:
-    D = FieldDecl::CreateDeserialized(Context, ID);
+    D = FieldDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_INDIRECTFIELD:
-    D = IndirectFieldDecl::CreateDeserialized(Context, ID);
+    D = IndirectFieldDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_VAR:
-    D = VarDecl::CreateDeserialized(Context, ID);
+    D = VarDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_IMPLICIT_PARAM:
-    D = ImplicitParamDecl::CreateDeserialized(Context, ID);
+    D = ImplicitParamDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_PARM_VAR:
-    D = ParmVarDecl::CreateDeserialized(Context, ID);
+    D = ParmVarDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_DECOMPOSITION:
-    D = DecompositionDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = DecompositionDecl::CreateDeserialized(Context, RawGlobalID,
+                                              Record.readInt());
     break;
   case DECL_BINDING:
-    D = BindingDecl::CreateDeserialized(Context, ID);
+    D = BindingDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_FILE_SCOPE_ASM:
-    D = FileScopeAsmDecl::CreateDeserialized(Context, ID);
+    D = FileScopeAsmDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_TOP_LEVEL_STMT_DECL:
-    D = TopLevelStmtDecl::CreateDeserialized(Context, ID);
+    D = TopLevelStmtDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_BLOCK:
-    D = BlockDecl::CreateDeserialized(Context, ID);
+    D = BlockDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_MS_PROPERTY:
-    D = MSPropertyDecl::CreateDeserialized(Context, ID);
+    D = MSPropertyDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_MS_GUID:
-    D = MSGuidDecl::CreateDeserialized(Context, ID);
+    D = MSGuidDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_UNNAMED_GLOBAL_CONSTANT:
-    D = UnnamedGlobalConstantDecl::CreateDeserialized(Context, ID);
+    D = UnnamedGlobalConstantDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_TEMPLATE_PARAM_OBJECT:
-    D = TemplateParamObjectDecl::CreateDeserialized(Context, ID);
+    D = TemplateParamObjectDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_CAPTURED:
-    D = CapturedDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = CapturedDecl::CreateDeserialized(Context, RawGlobalID,
+                                         Record.readInt());
     break;
   case DECL_CXX_BASE_SPECIFIERS:
     Error("attempt to read a C++ base-specifier record as a declaration");
@@ -4063,62 +4073,66 @@ Decl *ASTReader::ReadDeclRecord(GlobalDeclID ID) {
   case DECL_IMPORT:
     // Note: last entry of the ImportDecl record is the number of stored source
     // locations.
-    D = ImportDecl::CreateDeserialized(Context, ID, Record.back());
+    D = ImportDecl::CreateDeserialized(Context, RawGlobalID, Record.back());
     break;
   case DECL_OMP_THREADPRIVATE: {
     Record.skipInts(1);
     unsigned NumChildren = Record.readInt();
     Record.skipInts(1);
-    D = OMPThreadPrivateDecl::CreateDeserialized(Context, ID, NumChildren);
+    D = OMPThreadPrivateDecl::CreateDeserialized(Context, RawGlobalID,
+                                                 NumChildren);
     break;
   }
   case DECL_OMP_ALLOCATE: {
     unsigned NumClauses = Record.readInt();
     unsigned NumVars = Record.readInt();
     Record.skipInts(1);
-    D = OMPAllocateDecl::CreateDeserialized(Context, ID, NumVars, NumClauses);
+    D = OMPAllocateDecl::CreateDeserialized(Context, RawGlobalID, NumVars,
+                                            NumClauses);
     break;
   }
   case DECL_OMP_REQUIRES: {
     unsigned NumClauses = Record.readInt();
     Record.skipInts(2);
-    D = OMPRequiresDecl::CreateDeserialized(Context, ID, NumClauses);
+    D = OMPRequiresDecl::CreateDeserialized(Context, RawGlobalID, NumClauses);
     break;
   }
   case DECL_OMP_DECLARE_REDUCTION:
-    D = OMPDeclareReductionDecl::CreateDeserialized(Context, ID);
+    D = OMPDeclareReductionDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OMP_DECLARE_MAPPER: {
     unsigned NumClauses = Record.readInt();
     Record.skipInts(2);
-    D = OMPDeclareMapperDecl::CreateDeserialized(Context, ID, NumClauses);
+    D = OMPDeclareMapperDecl::CreateDeserialized(Context, RawGlobalID,
+                                                 NumClauses);
     break;
   }
   case DECL_OMP_CAPTUREDEXPR:
-    D = OMPCapturedExprDecl::CreateDeserialized(Context, ID);
+    D = OMPCapturedExprDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_PRAGMA_COMMENT:
-    D = PragmaCommentDecl::CreateDeserialized(Context, ID, Record.readInt());
+    D = PragmaCommentDecl::CreateDeserialized(Context, RawGlobalID,
+                                              Record.readInt());
     break;
   case DECL_PRAGMA_DETECT_MISMATCH:
-    D = PragmaDetectMismatchDecl::CreateDeserialized(Context, ID,
+    D = PragmaDetectMismatchDecl::CreateDeserialized(Context, RawGlobalID,
                                                      Record.readInt());
     break;
   case DECL_EMPTY:
-    D = EmptyDecl::CreateDeserialized(Context, ID);
+    D = EmptyDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_LIFETIME_EXTENDED_TEMPORARY:
-    D = LifetimeExtendedTemporaryDecl::CreateDeserialized(Context, ID);
+    D = LifetimeExtendedTemporaryDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_OBJC_TYPE_PARAM:
-    D = ObjCTypeParamDecl::CreateDeserialized(Context, ID);
+    D = ObjCTypeParamDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_HLSL_BUFFER:
-    D = HLSLBufferDecl::CreateDeserialized(Context, ID);
+    D = HLSLBufferDecl::CreateDeserialized(Context, RawGlobalID);
     break;
   case DECL_IMPLICIT_CONCEPT_SPECIALIZATION:
-    D = ImplicitConceptSpecializationDecl::CreateDeserialized(Context, ID,
-                                                              Record.readInt());
+    D = ImplicitConceptSpecializationDecl::CreateDeserialized(
+        Context, RawGlobalID, Record.readInt());
     break;
   }
 
@@ -4410,9 +4424,8 @@ namespace {
       // Map global ID of the definition down to the local ID used in this
       // module file. If there is no such mapping, we'll find nothing here
       // (or in any module it imports).
-      LocalDeclID LocalID =
-          Reader.mapGlobalIDToModuleFileGlobalID(M, InterfaceID);
-      if (LocalID.isInvalid())
+      DeclID LocalID = Reader.mapGlobalIDToModuleFileGlobalID(M, InterfaceID);
+      if (!LocalID)
         return true;
 
       // Perform a binary search to find the local redeclarations for this
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 0408eeb..842ea58 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -3043,7 +3043,7 @@ void ASTWriter::WriteSubmodules(Module *WritingModule) {
     RecordData Inits;
     for (Decl *D : Context->getModuleInitializers(Mod))
       if (wasDeclEmitted(D))
-        AddDeclRef(D, Inits);
+        Inits.push_back(GetDeclRef(D));
     if (!Inits.empty())
       Stream.EmitRecord(SUBMODULE_INITIALIZERS, Inits);
 
@@ -3226,7 +3226,7 @@ uint64_t ASTWriter::WriteDeclContextLexicalBlock(ASTContext &Context,
       continue;
 
     KindDeclPairs.push_back(D->getKind());
-    KindDeclPairs.push_back(GetDeclRef(D).get());
+    KindDeclPairs.push_back(GetDeclRef(D));
   }
 
   ++NumLexicalDeclContexts;
@@ -3261,7 +3261,7 @@ void ASTWriter::WriteTypeDeclOffsets() {
   unsigned DeclOffsetAbbrev = Stream.EmitAbbrev(std::move(Abbrev));
   {
     RecordData::value_type Record[] = {DECL_OFFSET, DeclOffsets.size(),
-                                       FirstDeclID.get() - NUM_PREDEF_DECL_IDS};
+                                       FirstDeclID - NUM_PREDEF_DECL_IDS};
     Stream.EmitRecordWithBlob(DeclOffsetAbbrev, Record, bytes(DeclOffsets));
   }
 }
@@ -3282,7 +3282,7 @@ void ASTWriter::WriteFileDeclIDsMap() {
     Info.FirstDeclIndex = FileGroupedDeclIDs.size();
     llvm::stable_sort(Info.DeclIDs);
     for (auto &LocDeclEntry : Info.DeclIDs)
-      FileGroupedDeclIDs.push_back(LocDeclEntry.second.get());
+      FileGroupedDeclIDs.push_back(LocDeclEntry.second);
   }
 
   auto Abbrev = std::make_shared<BitCodeAbbrev>();
@@ -3420,11 +3420,11 @@ public:
     for (const ObjCMethodList *Method = &Methods.Instance; Method;
          Method = Method->getNext())
       if (ShouldWriteMethodListNode(Method))
-        LE.write<DeclID>((DeclID)Writer.getDeclID(Method->getMethod()));
+        LE.write<DeclID>(Writer.getDeclID(Method->getMethod()));
     for (const ObjCMethodList *Method = &Methods.Factory; Method;
          Method = Method->getNext())
       if (ShouldWriteMethodListNode(Method))
-        LE.write<DeclID>((DeclID)Writer.getDeclID(Method->getMethod()));
+        LE.write<DeclID>(Writer.getDeclID(Method->getMethod()));
 
     assert(Out.tell() - Start == DataLen && "Data length is wrong");
   }
@@ -3743,8 +3743,8 @@ public:
       // Only emit declarations that aren't from a chained PCH, though.
       SmallVector<NamedDecl *, 16> Decls(IdResolver.decls(II));
       for (NamedDecl *D : llvm::reverse(Decls))
-        LE.write<DeclID>((DeclID)Writer.getDeclID(
-            getDeclForLocalLookup(PP.getLangOpts(), D)));
+        LE.write<DeclID>(
+            Writer.getDeclID(getDeclForLocalLookup(PP.getLangOpts(), D)));
     }
   }
 };
@@ -3860,7 +3860,7 @@ namespace {
 // Trait used for the on-disk hash table used in the method pool.
 class ASTDeclContextNameLookupTrait {
   ASTWriter &Writer;
-  llvm::SmallVector<LocalDeclID, 64> DeclIDs;
+  llvm::SmallVector<DeclID, 64> DeclIDs;
 
 public:
   using key_type = DeclarationNameKey;
@@ -3893,10 +3893,8 @@ public:
 
   data_type ImportData(const reader::ASTDeclContextNameLookupTrait::data_type &FromReader) {
     unsigned Start = DeclIDs.size();
-    DeclIDs.insert(
-        DeclIDs.end(),
-        DeclIDIterator<GlobalDeclID, LocalDeclID>(FromReader.begin()),
-        DeclIDIterator<GlobalDeclID, LocalDeclID>(FromReader.end()));
+    DeclIDs.insert(DeclIDs.end(), DeclIDIterator(FromReader.begin()),
+                   DeclIDIterator(FromReader.end()));
     return std::make_pair(Start, DeclIDs.size());
   }
 
@@ -3985,7 +3983,7 @@ public:
     endian::Writer LE(Out, llvm::endianness::little);
     uint64_t Start = Out.tell(); (void)Start;
     for (unsigned I = Lookup.first, N = Lookup.second; I != N; ++I)
-      LE.write<DeclID>((DeclID)DeclIDs[I]);
+      LE.write<DeclID>(DeclIDs[I]);
     assert(Out.tell() - Start == DataLen && "Data length is wrong");
   }
 };
@@ -4319,8 +4317,7 @@ void ASTWriter::WriteDeclContextVisibleUpdate(const DeclContext *DC) {
     DC = cast<DeclContext>(Chain->getKeyDeclaration(cast<Decl>(DC)));
 
   // Write the lookup table
-  RecordData::value_type Record[] = {UPDATE_VISIBLE,
-                                     getDeclID(cast<Decl>(DC)).get()};
+  RecordData::value_type Record[] = {UPDATE_VISIBLE, getDeclID(cast<Decl>(DC))};
   Stream.EmitRecordWithBlob(UpdateVisibleAbbrev, Record, LookupTable);
 }
 
@@ -4374,7 +4371,7 @@ void ASTWriter::WriteObjCCategories() {
            Cat = Class->known_categories_begin(),
            CatEnd = Class->known_categories_end();
          Cat != CatEnd; ++Cat, ++Size) {
-      assert(getDeclID(*Cat).isValid() && "Bogus category");
+      assert(getDeclID(*Cat) != 0 && "Bogus category");
       AddDeclRef(*Cat, Categories);
     }
 
@@ -5092,7 +5089,7 @@ void ASTWriter::WriteSpecialDeclRecords(Sema &SemaRef) {
       if (!D || !wasDeclEmitted(D))
         SemaDeclRefs.push_back(0);
       else
-        AddDeclRef(D, SemaDeclRefs);
+        SemaDeclRefs.push_back(getDeclID(D));
     };
 
     AddEmittedDeclRefOrZero(SemaRef.getStdNamespace());
@@ -5103,10 +5100,10 @@ void ASTWriter::WriteSpecialDeclRecords(Sema &SemaRef) {
     Stream.EmitRecord(SEMA_DECL_REFS, SemaDeclRefs);
 
   // Write the record containing decls to be checked for deferred diags.
-  RecordData DeclsToCheckForDeferredDiags;
+  SmallVector<DeclID, 64> DeclsToCheckForDeferredDiags;
   for (auto *D : SemaRef.DeclsToCheckForDeferredDiags)
     if (wasDeclEmitted(D))
-      AddDeclRef(D, DeclsToCheckForDeferredDiags);
+      DeclsToCheckForDeferredDiags.push_back(getDeclID(D));
   if (!DeclsToCheckForDeferredDiags.empty())
     Stream.EmitRecord(DECLS_TO_CHECK_FOR_DEFERRED_DIAGS,
         DeclsToCheckForDeferredDiags);
@@ -5476,7 +5473,7 @@ void ASTWriter::WriteDeclAndTypes(ASTContext &Context) {
     if (VisibleOffset)
       VisibleOffset -= DeclTypesBlockStartOffset;
 
-    AddDeclRef(NS, DelayedNamespaceRecord);
+    DelayedNamespaceRecord.push_back(getDeclID(NS));
     DelayedNamespaceRecord.push_back(LexicalOffset);
     DelayedNamespaceRecord.push_back(VisibleOffset);
   }
@@ -5510,7 +5507,7 @@ void ASTWriter::WriteDeclAndTypes(ASTContext &Context) {
       continue;
 
     NewGlobalKindDeclPairs.push_back(D->getKind());
-    NewGlobalKindDeclPairs.push_back(GetDeclRef(D).get());
+    NewGlobalKindDeclPairs.push_back(GetDeclRef(D));
   }
 
   auto Abv = std::make_shared<llvm::BitCodeAbbrev>();
@@ -5571,7 +5568,7 @@ void ASTWriter::WriteDeclUpdatesBlocks(RecordDataImpl &OffsetsRecord) {
       case UPD_CXX_ADDED_TEMPLATE_SPECIALIZATION:
       case UPD_CXX_ADDED_ANONYMOUS_NAMESPACE:
         assert(Update.getDecl() && "no decl to add?");
-        Record.AddDeclRef(Update.getDecl());
+        Record.push_back(GetDeclRef(Update.getDecl()));
         break;
 
       case UPD_CXX_ADDED_FUNCTION_DEFINITION:
@@ -5712,7 +5709,7 @@ void ASTWriter::WriteDeclUpdatesBlocks(RecordDataImpl &OffsetsRecord) {
       }
     }
 
-    AddDeclRef(D, OffsetsRecord);
+    OffsetsRecord.push_back(GetDeclRef(D));
     OffsetsRecord.push_back(Record.Emit(DECL_UPDATES));
   }
 }
@@ -5977,18 +5974,18 @@ void ASTWriter::AddEmittedDeclRef(const Decl *D, RecordDataImpl &Record) {
   if (!wasDeclEmitted(D))
     return;
 
-  Record.push_back(GetDeclRef(D).get());
+  Record.push_back(GetDeclRef(D));
 }
 
 void ASTWriter::AddDeclRef(const Decl *D, RecordDataImpl &Record) {
-  Record.push_back(GetDeclRef(D).get());
+  Record.push_back(GetDeclRef(D));
 }
 
-LocalDeclID ASTWriter::GetDeclRef(const Decl *D) {
+DeclID ASTWriter::GetDeclRef(const Decl *D) {
   assert(WritingAST && "Cannot request a declaration ID before AST writing");
 
   if (!D) {
-    return LocalDeclID();
+    return 0;
   }
 
   // If the DeclUpdate from the GMF gets touched, emit it.
@@ -6002,14 +5999,14 @@ LocalDeclID ASTWriter::GetDeclRef(const Decl *D) {
   // If D comes from an AST file, its declaration ID is already known and
   // fixed.
   if (D->isFromASTFile())
-    return LocalDeclID(D->getGlobalID());
+    return D->getGlobalID();
 
   assert(!(reinterpret_cast<uintptr_t>(D) & 0x01) && "Invalid decl pointer");
-  LocalDeclID &ID = DeclIDs[D];
-  if (ID.isInvalid()) {
+  DeclID &ID = DeclIDs[D];
+  if (ID == 0) {
     if (DoneWritingDeclsAndTypes) {
       assert(0 && "New decl seen after serializing all the decls to emit!");
-      return LocalDeclID();
+      return 0;
     }
 
     // We haven't seen this declaration before. Give it a new ID and
@@ -6021,14 +6018,14 @@ LocalDeclID ASTWriter::GetDeclRef(const Decl *D) {
   return ID;
 }
 
-LocalDeclID ASTWriter::getDeclID(const Decl *D) {
+DeclID ASTWriter::getDeclID(const Decl *D) {
   if (!D)
-    return LocalDeclID();
+    return 0;
 
   // If D comes from an AST file, its declaration ID is already known and
   // fixed.
   if (D->isFromASTFile())
-    return LocalDeclID(D->getGlobalID());
+    return D->getGlobalID();
 
   assert(DeclIDs.contains(D) && "Declaration not emitted!");
   return DeclIDs[D];
@@ -6049,8 +6046,8 @@ bool ASTWriter::wasDeclEmitted(const Decl *D) const {
   return Emitted;
 }
 
-void ASTWriter::associateDeclWithFile(const Decl *D, LocalDeclID ID) {
-  assert(ID.isValid());
+void ASTWriter::associateDeclWithFile(const Decl *D, DeclID ID) {
+  assert(ID);
   assert(D);
 
   SourceLocation Loc = D->getLocation();
@@ -6082,7 +6079,7 @@ void ASTWriter::associateDeclWithFile(const Decl *D, LocalDeclID ID) {
   if (!Info)
     Info = std::make_unique<DeclIDInFileInfo>();
 
-  std::pair<unsigned, LocalDeclID> LocDecl(Offset, ID);
+  std::pair<unsigned, DeclID> LocDecl(Offset, ID);
   LocDeclIDsTy &Decls = Info->DeclIDs;
   Decls.push_back(LocDecl);
 }
@@ -6352,7 +6349,7 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
       Writer->Context->getLangOpts().ModulesDebugInfo && !D->isDependentType();
   Record->push_back(ModulesDebugInfo);
   if (ModulesDebugInfo)
-    Writer->AddDeclRef(D, Writer->ModularCodegenDecls);
+    Writer->ModularCodegenDecls.push_back(Writer->GetDeclRef(D));
 
   // IsLambda bit is already saved.
 
@@ -6456,7 +6453,7 @@ void ASTWriter::ReaderInitialized(ASTReader *Reader) {
 
   // Note, this will get called multiple times, once one the reader starts up
   // and again each time it's done reading a PCH or module.
-  FirstDeclID = LocalDeclID(NUM_PREDEF_DECL_IDS + Chain->getTotalNumDecls());
+  FirstDeclID = NUM_PREDEF_DECL_IDS + Chain->getTotalNumDecls();
   FirstTypeID = NUM_PREDEF_TYPE_IDS + Chain->getTotalNumTypes();
   FirstIdentID = NUM_PREDEF_IDENT_IDS + Chain->getTotalNumIdentifiers();
   FirstMacroID = NUM_PREDEF_MACRO_IDS + Chain->getTotalNumMacros();
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 0edc4fed..fe86719 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -223,9 +223,9 @@ namespace clang {
         assert(!Common->LazySpecializations);
       }
 
-      ArrayRef<GlobalDeclID> LazySpecializations;
+      ArrayRef<DeclID> LazySpecializations;
       if (auto *LS = Common->LazySpecializations)
-        LazySpecializations = llvm::ArrayRef(LS + 1, LS[0].get());
+        LazySpecializations = llvm::ArrayRef(LS + 1, LS[0]);
 
       // Add a slot to the record for the number of specializations.
       unsigned I = Record.size();
@@ -243,9 +243,7 @@ namespace clang {
         assert(D->isCanonicalDecl() && "non-canonical decl in set");
         AddFirstDeclFromEachModule(D, /*IncludeLocal*/true);
       }
-      Record.append(
-          DeclIDIterator<GlobalDeclID, DeclID>(LazySpecializations.begin()),
-          DeclIDIterator<GlobalDeclID, DeclID>(LazySpecializations.end()));
+      Record.append(LazySpecializations.begin(), LazySpecializations.end());
 
       // Update the size entry we added earlier.
       Record[I] = Record.size() - I - 1;
@@ -1168,7 +1166,7 @@ void ASTDeclWriter::VisitVarDecl(VarDecl *D) {
   Record.push_back(VarDeclBits);
 
   if (ModulesCodegen)
-    Writer.AddDeclRef(D, Writer.ModularCodegenDecls);
+    Writer.ModularCodegenDecls.push_back(Writer.GetDeclRef(D));
 
   if (D->hasAttr<BlocksAttr>()) {
     BlockVarCopyInit Init = Writer.Context->getBlockVarCopyInit(D);
@@ -2788,10 +2786,10 @@ void ASTWriter::WriteDecl(ASTContext &Context, Decl *D) {
                                       "serializing");
 
   // Determine the ID for this declaration.
-  LocalDeclID ID;
+  DeclID ID;
   assert(!D->isFromASTFile() && "should not be emitting imported decl");
-  LocalDeclID &IDR = DeclIDs[D];
-  if (IDR.isInvalid())
+  DeclID &IDR = DeclIDs[D];
+  if (IDR == 0)
     IDR = NextDeclID++;
 
   ID = IDR;
@@ -2809,7 +2807,7 @@ void ASTWriter::WriteDecl(ASTContext &Context, Decl *D) {
 
   // Record the offset for this declaration
   SourceLocation Loc = D->getLocation();
-  unsigned Index = ID.get() - FirstDeclID.get();
+  unsigned Index = ID - FirstDeclID;
   if (DeclOffsets.size() == Index)
     DeclOffsets.emplace_back(getAdjustedLocation(Loc), Offset,
                              DeclTypesBlockStartOffset);
@@ -2829,7 +2827,7 @@ void ASTWriter::WriteDecl(ASTContext &Context, Decl *D) {
   // Note declarations that should be deserialized eagerly so that we can add
   // them to a record in the AST file later.
   if (isRequiredDecl(D, Context, WritingModule))
-    AddDeclRef(D, EagerlyDeserializedDecls);
+    EagerlyDeserializedDecls.push_back(ID);
 }
 
 void ASTRecordWriter::AddFunctionDefinition(const FunctionDecl *FD) {
@@ -2865,7 +2863,7 @@ void ASTRecordWriter::AddFunctionDefinition(const FunctionDecl *FD) {
   }
   Record->push_back(ModulesCodegen);
   if (ModulesCodegen)
-    Writer->AddDeclRef(FD, Writer->ModularCodegenDecls);
+    Writer->ModularCodegenDecls.push_back(Writer->GetDeclRef(FD));
   if (auto *CD = dyn_cast<CXXConstructorDecl>(FD)) {
     Record->push_back(CD->getNumCtorInitializers());
     if (CD->getNumCtorInitializers())