Start factoring the on-disk records for an AST file into a control

block, which stores information about how the AST file to generated,
from the AST block, which stores the actual serialized AST. The
information in the control block should be enough to determine whether
the AST file is up-to-date and compatible with the current translation
unit, and reading it should not cause any side effects that aren't
easy to undo. That way, we can back out from an attempt to read an
incompatible or out-of-date AST file.

Note that there is still more factoring to do. In particular,
information about the source files used to generate the AST file
(along with their time stamps, sizes, etc.) still resides in the
source manager block. 

llvm-svn: 166166

1 files changed, 27 insertions, 23 deletions

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index c37f881d982..b6f302605b1 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -978,11 +978,12 @@ adjustFilenameForRelocatablePCH(const char *Filename, StringRef isysroot) {
   return Filename + Pos;
 }
 
-/// \brief Write the AST metadata (e.g., i686-apple-darwin9).
-void ASTWriter::WriteMetadata(ASTContext &Context, StringRef isysroot,
-                              const std::string &OutputFile) {
+/// \brief Write the control block.
+void ASTWriter::WriteControlBlock(ASTContext &Context, StringRef isysroot,
+                                  const std::string &OutputFile) {
   using namespace llvm;
-
+  Stream.EnterSubblock(CONTROL_BLOCK_ID, 4);
+  
   // Metadata
   const TargetInfo &Target = Context.getTargetInfo();
   const TargetOptions &TargetOpts = Target.getTargetOpts();
@@ -1008,6 +1009,7 @@ void ASTWriter::WriteMetadata(ASTContext &Context, StringRef isysroot,
   }
   Stream.EmitRecord(METADATA, Record);
 
+  // Imports
   if (Chain) {
     serialization::ModuleManager &Mgr = Chain->getModuleManager();
     llvm::SmallVector<char, 128> ModulePaths;
@@ -1029,6 +1031,22 @@ void ASTWriter::WriteMetadata(ASTContext &Context, StringRef isysroot,
     Stream.EmitRecord(IMPORTS, Record);
   }
 
+  // Language options.
+  Record.clear();
+  const LangOptions &LangOpts = Context.getLangOpts();
+#define LANGOPT(Name, Bits, Default, Description) \
+  Record.push_back(LangOpts.Name);
+#define ENUM_LANGOPT(Name, Type, Bits, Default, Description) \
+  Record.push_back(static_cast<unsigned>(LangOpts.get##Name()));
+#include "clang/Basic/LangOptions.def"  
+
+  Record.push_back((unsigned) LangOpts.ObjCRuntime.getKind());
+  AddVersionTuple(LangOpts.ObjCRuntime.getVersion(), Record);
+  
+  Record.push_back(LangOpts.CurrentModule.size());
+  Record.append(LangOpts.CurrentModule.begin(), LangOpts.CurrentModule.end());
+  Stream.EmitRecord(LANGUAGE_OPTIONS, Record);
+
   // Original file name and file ID
   SourceManager &SM = Context.getSourceManager();
   if (const FileEntry *MainFile = SM.getFileEntryForID(SM.getMainFileID())) {
@@ -1079,23 +1097,8 @@ void ASTWriter::WriteMetadata(ASTContext &Context, StringRef isysroot,
   Record.push_back(VERSION_CONTROL_BRANCH_REVISION);
   Stream.EmitRecordWithBlob(RepoAbbrevCode, Record,
                             getClangFullRepositoryVersion());
-}
 
-/// \brief Write the LangOptions structure.
-void ASTWriter::WriteLanguageOptions(const LangOptions &LangOpts) {
-  RecordData Record;
-#define LANGOPT(Name, Bits, Default, Description) \
-  Record.push_back(LangOpts.Name);
-#define ENUM_LANGOPT(Name, Type, Bits, Default, Description) \
-  Record.push_back(static_cast<unsigned>(LangOpts.get##Name()));
-#include "clang/Basic/LangOptions.def"  
-
-  Record.push_back((unsigned) LangOpts.ObjCRuntime.getKind());
-  AddVersionTuple(LangOpts.ObjCRuntime.getVersion(), Record);
-  
-  Record.push_back(LangOpts.CurrentModule.size());
-  Record.append(LangOpts.CurrentModule.begin(), LangOpts.CurrentModule.end());
-  Stream.EmitRecord(LANGUAGE_OPTIONS, Record);
+  Stream.ExitBlock();
 }
 
 //===----------------------------------------------------------------------===//
@@ -3433,12 +3436,13 @@ void ASTWriter::WriteASTCore(Sema &SemaRef, MemorizeStatCalls *StatCalls,
     if (!I->second)
       AddDeclRef(I->first, KnownNamespaces);
   }
-  
+
+  // Write the control block
+  WriteControlBlock(Context, isysroot, OutputFile);
+
   // Write the remaining AST contents.
   RecordData Record;
   Stream.EnterSubblock(AST_BLOCK_ID, 5);
-  WriteLanguageOptions(Context.getLangOpts());
-  WriteMetadata(Context, isysroot, OutputFile);
   if (StatCalls && isysroot.empty())
     WriteStatCache(*StatCalls);