Check in LLVM r95781.
diff --git a/lib/Frontend/PCHWriterDecl.cpp b/lib/Frontend/PCHWriterDecl.cpp
new file mode 100644
index 0000000..1901b2f
--- /dev/null
+++ b/lib/Frontend/PCHWriterDecl.cpp
@@ -0,0 +1,611 @@
+//===--- PCHWriterDecl.cpp - Declaration Serialization --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements serialization for Declarations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Frontend/PCHWriter.h"
+#include "clang/AST/DeclVisitor.h"
+#include "clang/AST/Expr.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Bitcode/BitstreamWriter.h"
+#include "llvm/Support/ErrorHandling.h"
+using namespace clang;
+
+//===----------------------------------------------------------------------===//
+// Declaration serialization
+//===----------------------------------------------------------------------===//
+
+namespace {
+  class PCHDeclWriter : public DeclVisitor<PCHDeclWriter, void> {
+
+    PCHWriter &Writer;
+    ASTContext &Context;
+    PCHWriter::RecordData &Record;
+
+  public:
+    pch::DeclCode Code;
+    unsigned AbbrevToUse;
+
+    PCHDeclWriter(PCHWriter &Writer, ASTContext &Context,
+                  PCHWriter::RecordData &Record)
+      : Writer(Writer), Context(Context), Record(Record) {
+    }
+
+    void VisitDecl(Decl *D);
+    void VisitTranslationUnitDecl(TranslationUnitDecl *D);
+    void VisitNamedDecl(NamedDecl *D);
+    void VisitTypeDecl(TypeDecl *D);
+    void VisitTypedefDecl(TypedefDecl *D);
+    void VisitTagDecl(TagDecl *D);
+    void VisitEnumDecl(EnumDecl *D);
+    void VisitRecordDecl(RecordDecl *D);
+    void VisitValueDecl(ValueDecl *D);
+    void VisitEnumConstantDecl(EnumConstantDecl *D);
+    void VisitDeclaratorDecl(DeclaratorDecl *D);
+    void VisitFunctionDecl(FunctionDecl *D);
+    void VisitFieldDecl(FieldDecl *D);
+    void VisitVarDecl(VarDecl *D);
+    void VisitImplicitParamDecl(ImplicitParamDecl *D);
+    void VisitParmVarDecl(ParmVarDecl *D);
+    void VisitFileScopeAsmDecl(FileScopeAsmDecl *D);
+    void VisitBlockDecl(BlockDecl *D);
+    void VisitDeclContext(DeclContext *DC, uint64_t LexicalOffset,
+                          uint64_t VisibleOffset);
+    void VisitObjCMethodDecl(ObjCMethodDecl *D);
+    void VisitObjCContainerDecl(ObjCContainerDecl *D);
+    void VisitObjCInterfaceDecl(ObjCInterfaceDecl *D);
+    void VisitObjCIvarDecl(ObjCIvarDecl *D);
+    void VisitObjCProtocolDecl(ObjCProtocolDecl *D);
+    void VisitObjCAtDefsFieldDecl(ObjCAtDefsFieldDecl *D);
+    void VisitObjCClassDecl(ObjCClassDecl *D);
+    void VisitObjCForwardProtocolDecl(ObjCForwardProtocolDecl *D);
+    void VisitObjCCategoryDecl(ObjCCategoryDecl *D);
+    void VisitObjCImplDecl(ObjCImplDecl *D);
+    void VisitObjCCategoryImplDecl(ObjCCategoryImplDecl *D);
+    void VisitObjCImplementationDecl(ObjCImplementationDecl *D);
+    void VisitObjCCompatibleAliasDecl(ObjCCompatibleAliasDecl *D);
+    void VisitObjCPropertyDecl(ObjCPropertyDecl *D);
+    void VisitObjCPropertyImplDecl(ObjCPropertyImplDecl *D);
+  };
+}
+
+void PCHDeclWriter::VisitDecl(Decl *D) {
+  Writer.AddDeclRef(cast_or_null<Decl>(D->getDeclContext()), Record);
+  Writer.AddDeclRef(cast_or_null<Decl>(D->getLexicalDeclContext()), Record);
+  Writer.AddSourceLocation(D->getLocation(), Record);
+  Record.push_back(D->isInvalidDecl());
+  Record.push_back(D->hasAttrs());
+  Record.push_back(D->isImplicit());
+  Record.push_back(D->isUsed());
+  Record.push_back(D->getAccess());
+  Record.push_back(D->getPCHLevel());
+}
+
+void PCHDeclWriter::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
+  VisitDecl(D);
+  Code = pch::DECL_TRANSLATION_UNIT;
+}
+
+void PCHDeclWriter::VisitNamedDecl(NamedDecl *D) {
+  VisitDecl(D);
+  Writer.AddDeclarationName(D->getDeclName(), Record);
+}
+
+void PCHDeclWriter::VisitTypeDecl(TypeDecl *D) {
+  VisitNamedDecl(D);
+  Writer.AddTypeRef(QualType(D->getTypeForDecl(), 0), Record);
+}
+
+void PCHDeclWriter::VisitTypedefDecl(TypedefDecl *D) {
+  VisitTypeDecl(D);
+  Writer.AddTypeSourceInfo(D->getTypeSourceInfo(), Record);
+  Code = pch::DECL_TYPEDEF;
+}
+
+void PCHDeclWriter::VisitTagDecl(TagDecl *D) {
+  VisitTypeDecl(D);
+  Writer.AddDeclRef(D->getPreviousDeclaration(), Record);
+  Record.push_back((unsigned)D->getTagKind()); // FIXME: stable encoding
+  Record.push_back(D->isDefinition());
+  Record.push_back(D->isDefinedInDeclarator());
+  Writer.AddDeclRef(D->getTypedefForAnonDecl(), Record);
+  Writer.AddSourceLocation(D->getRBraceLoc(), Record);
+  Writer.AddSourceLocation(D->getTagKeywordLoc(), Record);
+}
+
+void PCHDeclWriter::VisitEnumDecl(EnumDecl *D) {
+  VisitTagDecl(D);
+  Writer.AddTypeRef(D->getIntegerType(), Record);
+  Writer.AddTypeRef(D->getPromotionType(), Record);
+  // FIXME: C++ InstantiatedFrom
+  Code = pch::DECL_ENUM;
+}
+
+void PCHDeclWriter::VisitRecordDecl(RecordDecl *D) {
+  VisitTagDecl(D);
+  Record.push_back(D->hasFlexibleArrayMember());
+  Record.push_back(D->isAnonymousStructOrUnion());
+  Record.push_back(D->hasObjectMember());
+  Code = pch::DECL_RECORD;
+}
+
+void PCHDeclWriter::VisitValueDecl(ValueDecl *D) {
+  VisitNamedDecl(D);
+  Writer.AddTypeRef(D->getType(), Record);
+}
+
+void PCHDeclWriter::VisitEnumConstantDecl(EnumConstantDecl *D) {
+  VisitValueDecl(D);
+  Record.push_back(D->getInitExpr()? 1 : 0);
+  if (D->getInitExpr())
+    Writer.AddStmt(D->getInitExpr());
+  Writer.AddAPSInt(D->getInitVal(), Record);
+  Code = pch::DECL_ENUM_CONSTANT;
+}
+
+void PCHDeclWriter::VisitDeclaratorDecl(DeclaratorDecl *D) {
+  VisitValueDecl(D);
+  Writer.AddTypeSourceInfo(D->getTypeSourceInfo(), Record);
+}
+
+void PCHDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
+  VisitDeclaratorDecl(D);
+  Record.push_back(D->isThisDeclarationADefinition());
+  if (D->isThisDeclarationADefinition())
+    Writer.AddStmt(D->getBody());
+  Writer.AddDeclRef(D->getPreviousDeclaration(), Record);
+  Record.push_back(D->getStorageClass()); // FIXME: stable encoding
+  Record.push_back(D->isInlineSpecified());
+  Record.push_back(D->isVirtualAsWritten());
+  Record.push_back(D->isPure());
+  Record.push_back(D->hasInheritedPrototype());
+  Record.push_back(D->hasWrittenPrototype());
+  Record.push_back(D->isDeleted());
+  Record.push_back(D->isTrivial());
+  Record.push_back(D->isCopyAssignment());
+  Record.push_back(D->hasImplicitReturnZero());
+  Writer.AddSourceLocation(D->getLocEnd(), Record);
+  // FIXME: C++ TemplateOrInstantiation
+  Record.push_back(D->param_size());
+  for (FunctionDecl::param_iterator P = D->param_begin(), PEnd = D->param_end();
+       P != PEnd; ++P)
+    Writer.AddDeclRef(*P, Record);
+  Code = pch::DECL_FUNCTION;
+}
+
+void PCHDeclWriter::VisitObjCMethodDecl(ObjCMethodDecl *D) {
+  VisitNamedDecl(D);
+  // FIXME: convert to LazyStmtPtr?
+  // Unlike C/C++, method bodies will never be in header files.
+  Record.push_back(D->getBody() != 0);
+  if (D->getBody() != 0) {
+    Writer.AddStmt(D->getBody());
+    Writer.AddDeclRef(D->getSelfDecl(), Record);
+    Writer.AddDeclRef(D->getCmdDecl(), Record);
+  }
+  Record.push_back(D->isInstanceMethod());
+  Record.push_back(D->isVariadic());
+  Record.push_back(D->isSynthesized());
+  // FIXME: stable encoding for @required/@optional
+  Record.push_back(D->getImplementationControl());
+  // FIXME: stable encoding for in/out/inout/bycopy/byref/oneway
+  Record.push_back(D->getObjCDeclQualifier());
+  Writer.AddTypeRef(D->getResultType(), Record);
+  Writer.AddSourceLocation(D->getLocEnd(), Record);
+  Record.push_back(D->param_size());
+  for (ObjCMethodDecl::param_iterator P = D->param_begin(),
+                                   PEnd = D->param_end(); P != PEnd; ++P)
+    Writer.AddDeclRef(*P, Record);
+  Code = pch::DECL_OBJC_METHOD;
+}
+
+void PCHDeclWriter::VisitObjCContainerDecl(ObjCContainerDecl *D) {
+  VisitNamedDecl(D);
+  SourceRange R = D->getAtEndRange();
+  Writer.AddSourceLocation(R.getBegin(), Record);
+  Writer.AddSourceLocation(R.getEnd(), Record);
+  // Abstract class (no need to define a stable pch::DECL code).
+}
+
+void PCHDeclWriter::VisitObjCInterfaceDecl(ObjCInterfaceDecl *D) {
+  VisitObjCContainerDecl(D);
+  Writer.AddTypeRef(QualType(D->getTypeForDecl(), 0), Record);
+  Writer.AddDeclRef(D->getSuperClass(), Record);
+  Record.push_back(D->protocol_size());
+  for (ObjCInterfaceDecl::protocol_iterator P = D->protocol_begin(),
+         PEnd = D->protocol_end();
+       P != PEnd; ++P)
+    Writer.AddDeclRef(*P, Record);
+  for (ObjCInterfaceDecl::protocol_loc_iterator PL = D->protocol_loc_begin(),
+         PLEnd = D->protocol_loc_end();
+       PL != PLEnd; ++PL)
+    Writer.AddSourceLocation(*PL, Record);
+  Record.push_back(D->ivar_size());
+  for (ObjCInterfaceDecl::ivar_iterator I = D->ivar_begin(),
+                                     IEnd = D->ivar_end(); I != IEnd; ++I)
+    Writer.AddDeclRef(*I, Record);
+  Writer.AddDeclRef(D->getCategoryList(), Record);
+  Record.push_back(D->isForwardDecl());
+  Record.push_back(D->isImplicitInterfaceDecl());
+  Writer.AddSourceLocation(D->getClassLoc(), Record);
+  Writer.AddSourceLocation(D->getSuperClassLoc(), Record);
+  Writer.AddSourceLocation(D->getLocEnd(), Record);
+  Code = pch::DECL_OBJC_INTERFACE;
+}
+
+void PCHDeclWriter::VisitObjCIvarDecl(ObjCIvarDecl *D) {
+  VisitFieldDecl(D);
+  // FIXME: stable encoding for @public/@private/@protected/@package
+  Record.push_back(D->getAccessControl());
+  Code = pch::DECL_OBJC_IVAR;
+}
+
+void PCHDeclWriter::VisitObjCProtocolDecl(ObjCProtocolDecl *D) {
+  VisitObjCContainerDecl(D);
+  Record.push_back(D->isForwardDecl());
+  Writer.AddSourceLocation(D->getLocEnd(), Record);
+  Record.push_back(D->protocol_size());
+  for (ObjCProtocolDecl::protocol_iterator
+       I = D->protocol_begin(), IEnd = D->protocol_end(); I != IEnd; ++I)
+    Writer.AddDeclRef(*I, Record);
+  for (ObjCProtocolDecl::protocol_loc_iterator PL = D->protocol_loc_begin(),
+         PLEnd = D->protocol_loc_end();
+       PL != PLEnd; ++PL)
+    Writer.AddSourceLocation(*PL, Record);
+  Code = pch::DECL_OBJC_PROTOCOL;
+}
+
+void PCHDeclWriter::VisitObjCAtDefsFieldDecl(ObjCAtDefsFieldDecl *D) {
+  VisitFieldDecl(D);
+  Code = pch::DECL_OBJC_AT_DEFS_FIELD;
+}
+
+void PCHDeclWriter::VisitObjCClassDecl(ObjCClassDecl *D) {
+  VisitDecl(D);
+  Record.push_back(D->size());
+  for (ObjCClassDecl::iterator I = D->begin(), IEnd = D->end(); I != IEnd; ++I)
+    Writer.AddDeclRef(I->getInterface(), Record);
+  for (ObjCClassDecl::iterator I = D->begin(), IEnd = D->end(); I != IEnd; ++I)
+    Writer.AddSourceLocation(I->getLocation(), Record);
+  Code = pch::DECL_OBJC_CLASS;
+}
+
+void PCHDeclWriter::VisitObjCForwardProtocolDecl(ObjCForwardProtocolDecl *D) {
+  VisitDecl(D);
+  Record.push_back(D->protocol_size());
+  for (ObjCForwardProtocolDecl::protocol_iterator
+       I = D->protocol_begin(), IEnd = D->protocol_end(); I != IEnd; ++I)
+    Writer.AddDeclRef(*I, Record);
+  for (ObjCForwardProtocolDecl::protocol_loc_iterator 
+         PL = D->protocol_loc_begin(), PLEnd = D->protocol_loc_end();
+       PL != PLEnd; ++PL)
+    Writer.AddSourceLocation(*PL, Record);
+  Code = pch::DECL_OBJC_FORWARD_PROTOCOL;
+}
+
+void PCHDeclWriter::VisitObjCCategoryDecl(ObjCCategoryDecl *D) {
+  VisitObjCContainerDecl(D);
+  Writer.AddDeclRef(D->getClassInterface(), Record);
+  Record.push_back(D->protocol_size());
+  for (ObjCCategoryDecl::protocol_iterator
+       I = D->protocol_begin(), IEnd = D->protocol_end(); I != IEnd; ++I)
+    Writer.AddDeclRef(*I, Record);
+  for (ObjCCategoryDecl::protocol_loc_iterator 
+         PL = D->protocol_loc_begin(), PLEnd = D->protocol_loc_end();
+       PL != PLEnd; ++PL)
+    Writer.AddSourceLocation(*PL, Record);
+  Writer.AddDeclRef(D->getNextClassCategory(), Record);
+  Writer.AddSourceLocation(D->getAtLoc(), Record);
+  Writer.AddSourceLocation(D->getCategoryNameLoc(), Record);
+  Code = pch::DECL_OBJC_CATEGORY;
+}
+
+void PCHDeclWriter::VisitObjCCompatibleAliasDecl(ObjCCompatibleAliasDecl *D) {
+  VisitNamedDecl(D);
+  Writer.AddDeclRef(D->getClassInterface(), Record);
+  Code = pch::DECL_OBJC_COMPATIBLE_ALIAS;
+}
+
+void PCHDeclWriter::VisitObjCPropertyDecl(ObjCPropertyDecl *D) {
+  VisitNamedDecl(D);
+  Writer.AddSourceLocation(D->getAtLoc(), Record);
+  Writer.AddTypeRef(D->getType(), Record);
+  // FIXME: stable encoding
+  Record.push_back((unsigned)D->getPropertyAttributes());
+  // FIXME: stable encoding
+  Record.push_back((unsigned)D->getPropertyImplementation());
+  Writer.AddDeclarationName(D->getGetterName(), Record);
+  Writer.AddDeclarationName(D->getSetterName(), Record);
+  Writer.AddDeclRef(D->getGetterMethodDecl(), Record);
+  Writer.AddDeclRef(D->getSetterMethodDecl(), Record);
+  Writer.AddDeclRef(D->getPropertyIvarDecl(), Record);
+  Code = pch::DECL_OBJC_PROPERTY;
+}
+
+void PCHDeclWriter::VisitObjCImplDecl(ObjCImplDecl *D) {
+  VisitObjCContainerDecl(D);
+  Writer.AddDeclRef(D->getClassInterface(), Record);
+  // Abstract class (no need to define a stable pch::DECL code).
+}
+
+void PCHDeclWriter::VisitObjCCategoryImplDecl(ObjCCategoryImplDecl *D) {
+  VisitObjCImplDecl(D);
+  Writer.AddIdentifierRef(D->getIdentifier(), Record);
+  Code = pch::DECL_OBJC_CATEGORY_IMPL;
+}
+
+void PCHDeclWriter::VisitObjCImplementationDecl(ObjCImplementationDecl *D) {
+  VisitObjCImplDecl(D);
+  Writer.AddDeclRef(D->getSuperClass(), Record);
+  Code = pch::DECL_OBJC_IMPLEMENTATION;
+}
+
+void PCHDeclWriter::VisitObjCPropertyImplDecl(ObjCPropertyImplDecl *D) {
+  VisitDecl(D);
+  Writer.AddSourceLocation(D->getLocStart(), Record);
+  Writer.AddDeclRef(D->getPropertyDecl(), Record);
+  Writer.AddDeclRef(D->getPropertyIvarDecl(), Record);
+  Code = pch::DECL_OBJC_PROPERTY_IMPL;
+}
+
+void PCHDeclWriter::VisitFieldDecl(FieldDecl *D) {
+  VisitDeclaratorDecl(D);
+  Record.push_back(D->isMutable());
+  Record.push_back(D->getBitWidth()? 1 : 0);
+  if (D->getBitWidth())
+    Writer.AddStmt(D->getBitWidth());
+  Code = pch::DECL_FIELD;
+}
+
+void PCHDeclWriter::VisitVarDecl(VarDecl *D) {
+  VisitDeclaratorDecl(D);
+  Record.push_back(D->getStorageClass()); // FIXME: stable encoding
+  Record.push_back(D->isThreadSpecified());
+  Record.push_back(D->hasCXXDirectInitializer());
+  Record.push_back(D->isDeclaredInCondition());
+  Writer.AddDeclRef(D->getPreviousDeclaration(), Record);
+  Record.push_back(D->getInit()? 1 : 0);
+  if (D->getInit())
+    Writer.AddStmt(D->getInit());
+  Code = pch::DECL_VAR;
+}
+
+void PCHDeclWriter::VisitImplicitParamDecl(ImplicitParamDecl *D) {
+  VisitVarDecl(D);
+  Code = pch::DECL_IMPLICIT_PARAM;
+}
+
+void PCHDeclWriter::VisitParmVarDecl(ParmVarDecl *D) {
+  VisitVarDecl(D);
+  Record.push_back(D->getObjCDeclQualifier()); // FIXME: stable encoding
+  Code = pch::DECL_PARM_VAR;
+
+
+  // If the assumptions about the DECL_PARM_VAR abbrev are true, use it.  Here
+  // we dynamically check for the properties that we optimize for, but don't
+  // know are true of all PARM_VAR_DECLs.
+  if (!D->getTypeSourceInfo() &&
+      !D->hasAttrs() &&
+      !D->isImplicit() &&
+      !D->isUsed() &&
+      D->getAccess() == AS_none &&
+      D->getPCHLevel() == 0 &&
+      D->getStorageClass() == 0 &&
+      !D->hasCXXDirectInitializer() && // Can params have this ever?
+      D->getObjCDeclQualifier() == 0)
+    AbbrevToUse = Writer.getParmVarDeclAbbrev();
+
+  // Check things we know are true of *every* PARM_VAR_DECL, which is more than
+  // just us assuming it.
+  assert(!D->isInvalidDecl() && "Shouldn't emit invalid decls");
+  assert(!D->isThreadSpecified() && "PARM_VAR_DECL can't be __thread");
+  assert(D->getAccess() == AS_none && "PARM_VAR_DECL can't be public/private");
+  assert(!D->isDeclaredInCondition() && "PARM_VAR_DECL can't be in condition");
+  assert(D->getPreviousDeclaration() == 0 && "PARM_VAR_DECL can't be redecl");
+  assert(D->getInit() == 0 && "PARM_VAR_DECL never has init");
+}
+
+void PCHDeclWriter::VisitFileScopeAsmDecl(FileScopeAsmDecl *D) {
+  VisitDecl(D);
+  Writer.AddStmt(D->getAsmString());
+  Code = pch::DECL_FILE_SCOPE_ASM;
+}
+
+void PCHDeclWriter::VisitBlockDecl(BlockDecl *D) {
+  VisitDecl(D);
+  Writer.AddStmt(D->getBody());
+  Record.push_back(D->param_size());
+  for (FunctionDecl::param_iterator P = D->param_begin(), PEnd = D->param_end();
+       P != PEnd; ++P)
+    Writer.AddDeclRef(*P, Record);
+  Code = pch::DECL_BLOCK;
+}
+
+/// \brief Emit the DeclContext part of a declaration context decl.
+///
+/// \param LexicalOffset the offset at which the DECL_CONTEXT_LEXICAL
+/// block for this declaration context is stored. May be 0 to indicate
+/// that there are no declarations stored within this context.
+///
+/// \param VisibleOffset the offset at which the DECL_CONTEXT_VISIBLE
+/// block for this declaration context is stored. May be 0 to indicate
+/// that there are no declarations visible from this context. Note
+/// that this value will not be emitted for non-primary declaration
+/// contexts.
+void PCHDeclWriter::VisitDeclContext(DeclContext *DC, uint64_t LexicalOffset,
+                                     uint64_t VisibleOffset) {
+  Record.push_back(LexicalOffset);
+  Record.push_back(VisibleOffset);
+}
+
+
+//===----------------------------------------------------------------------===//
+// PCHWriter Implementation
+//===----------------------------------------------------------------------===//
+
+void PCHWriter::WriteDeclsBlockAbbrevs() {
+  using namespace llvm;
+  // Abbreviation for DECL_PARM_VAR.
+  BitCodeAbbrev *Abv = new BitCodeAbbrev();
+  Abv->Add(BitCodeAbbrevOp(pch::DECL_PARM_VAR));
+
+  // Decl
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Location
+  Abv->Add(BitCodeAbbrevOp(0));                       // isInvalidDecl (!?)
+  Abv->Add(BitCodeAbbrevOp(0));                       // HasAttrs
+  Abv->Add(BitCodeAbbrevOp(0));                       // isImplicit
+  Abv->Add(BitCodeAbbrevOp(0));                       // isUsed
+  Abv->Add(BitCodeAbbrevOp(AS_none));                 // C++ AccessSpecifier
+  Abv->Add(BitCodeAbbrevOp(0));                       // PCH level
+
+  // NamedDecl
+  Abv->Add(BitCodeAbbrevOp(0));                       // NameKind = Identifier
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Name
+  // ValueDecl
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Type
+  // DeclaratorDecl
+  Abv->Add(BitCodeAbbrevOp(pch::PREDEF_TYPE_NULL_ID)); // InfoType
+  // VarDecl
+  Abv->Add(BitCodeAbbrevOp(0));                       // StorageClass
+  Abv->Add(BitCodeAbbrevOp(0));                       // isThreadSpecified
+  Abv->Add(BitCodeAbbrevOp(0));                       // hasCXXDirectInitializer
+  Abv->Add(BitCodeAbbrevOp(0));                       // isDeclaredInCondition
+  Abv->Add(BitCodeAbbrevOp(0));                       // PrevDecl
+  Abv->Add(BitCodeAbbrevOp(0));                       // HasInit
+  // ParmVarDecl
+  Abv->Add(BitCodeAbbrevOp(0));                       // ObjCDeclQualifier
+
+  ParmVarDeclAbbrev = Stream.EmitAbbrev(Abv);
+}
+
+/// isRequiredDecl - Check if this is a "required" Decl, which must be seen by
+/// consumers of the AST.
+///
+/// Such decls will always be deserialized from the PCH file, so we would like
+/// this to be as restrictive as possible. Currently the predicate is driven by
+/// code generation requirements, if other clients have a different notion of
+/// what is "required" then we may have to consider an alternate scheme where
+/// clients can iterate over the top-level decls and get information on them,
+/// without necessary deserializing them. We could explicitly require such
+/// clients to use a separate API call to "realize" the decl. This should be
+/// relatively painless since they would presumably only do it for top-level
+/// decls.
+//
+// FIXME: This predicate is essentially IRgen's predicate to determine whether a
+// declaration can be deferred. Merge them somehow.
+static bool isRequiredDecl(const Decl *D, ASTContext &Context) {
+  // File scoped assembly must be seen.
+  if (isa<FileScopeAsmDecl>(D))
+    return true;
+
+  // Otherwise if this isn't a function or a file scoped variable it doesn't
+  // need to be seen.
+  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
+    if (!VD->isFileVarDecl())
+      return false;
+  } else if (!isa<FunctionDecl>(D))
+    return false;
+
+  // Aliases and used decls must be seen.
+  if (D->hasAttr<AliasAttr>() || D->hasAttr<UsedAttr>())
+    return true;
+
+  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    // Forward declarations don't need to be seen.
+    if (!FD->isThisDeclarationADefinition())
+      return false;
+
+    // Constructors and destructors must be seen.
+    if (FD->hasAttr<ConstructorAttr>() || FD->hasAttr<DestructorAttr>())
+      return true;
+
+    // Otherwise, this is required unless it is static.
+    //
+    // FIXME: Inlines.
+    return FD->getStorageClass() != FunctionDecl::Static;
+  } else {
+    const VarDecl *VD = cast<VarDecl>(D);
+
+    // In C++, this doesn't need to be seen if it is marked "extern".
+    if (Context.getLangOptions().CPlusPlus && !VD->getInit() &&
+        (VD->getStorageClass() == VarDecl::Extern ||
+         VD->isExternC()))
+      return false;
+
+    // In C, this doesn't need to be seen unless it is a definition.
+    if (!Context.getLangOptions().CPlusPlus && !VD->getInit())
+      return false;
+
+    // Otherwise, this is required unless it is static.
+    return VD->getStorageClass() != VarDecl::Static;
+  }
+}
+
+void PCHWriter::WriteDecl(ASTContext &Context, Decl *D) {
+  RecordData Record;
+  PCHDeclWriter W(*this, Context, Record);
+
+  // If this declaration is also a DeclContext, write blocks for the
+  // declarations that lexically stored inside its context and those
+  // declarations that are visible from its context. These blocks
+  // are written before the declaration itself so that we can put
+  // their offsets into the record for the declaration.
+  uint64_t LexicalOffset = 0;
+  uint64_t VisibleOffset = 0;
+  DeclContext *DC = dyn_cast<DeclContext>(D);
+  if (DC) {
+    LexicalOffset = WriteDeclContextLexicalBlock(Context, DC);
+    VisibleOffset = WriteDeclContextVisibleBlock(Context, DC);
+  }
+
+  // Determine the ID for this declaration
+  pch::DeclID &ID = DeclIDs[D];
+  if (ID == 0)
+    ID = DeclIDs.size();
+
+  unsigned Index = ID - 1;
+
+  // Record the offset for this declaration
+  if (DeclOffsets.size() == Index)
+    DeclOffsets.push_back(Stream.GetCurrentBitNo());
+  else if (DeclOffsets.size() < Index) {
+    DeclOffsets.resize(Index+1);
+    DeclOffsets[Index] = Stream.GetCurrentBitNo();
+  }
+
+  // Build and emit a record for this declaration
+  Record.clear();
+  W.Code = (pch::DeclCode)0;
+  W.AbbrevToUse = 0;
+  W.Visit(D);
+  if (DC) W.VisitDeclContext(DC, LexicalOffset, VisibleOffset);
+
+  if (!W.Code)
+    llvm::llvm_report_error(llvm::StringRef("unexpected declaration kind '") +
+                            D->getDeclKindName() + "'");
+  Stream.EmitRecord(W.Code, Record, W.AbbrevToUse);
+
+  // If the declaration had any attributes, write them now.
+  if (D->hasAttrs())
+    WriteAttributeRecord(D->getAttrs());
+
+  // Flush any expressions that were written as part of this declaration.
+  FlushStmts();
+
+  // Note "external" declarations so that we can add them to a record in the
+  // PCH file later.
+  //
+  // FIXME: This should be renamed, the predicate is much more complicated.
+  if (isRequiredDecl(D, Context))
+    ExternalDefinitions.push_back(Index + 1);
+}