When loading a precompiled preamble, use the file ID of the

precompiled preamble as the "main" source file's file ID within the
source manager. This makes compiling with a precompiled preamble
produce the same source locations as when compiling without the
precompiled preamble; prior to this change, we ended up with different
file IDs for source locations within the precompiled preamble
vs. those after the precompiled preamble, even for entities (e.g.,
preprocessing entities) in the same file.

llvm-svn: 120390

clang/include/clang/Basic/SourceManager.h

@@ -452,6 +452,13 @@ public:
     return MainFileID;
   }
 
+  /// \brief Set the file ID for the precompiled preamble, which is also the
+  /// main file.
+  void SetPreambleFileID(FileID Preamble) {
+    assert(MainFileID.isInvalid() && "MainFileID already set!");
+    MainFileID = Preamble;
+  }
+  
   //===--------------------------------------------------------------------===//
   // Methods to create new FileID's and instantiations.
   //===--------------------------------------------------------------------===//

clang/lib/Frontend/CompilerInstance.cpp

@@ -474,8 +474,11 @@ bool CompilerInstance::InitializeSourceManager(llvm::StringRef InputFile,
                                                FileManager &FileMgr,
                                                SourceManager &SourceMgr,
                                                const FrontendOptions &Opts) {
-  // Figure out where to get and map in the main file.
-  if (InputFile != "-") {
+  // Figure out where to get and map in the main file, unless it's already
+  // been created (e.g., by a precompiled preamble).
+  if (!SourceMgr.getMainFileID().isInvalid()) {
+    // Do nothing: the main file has already been set.
+  } else if (InputFile != "-") {
     const FileEntry *File = FileMgr.getFile(InputFile);
     if (!File) {
       Diags.Report(diag::err_fe_error_reading) << InputFile;

clang/lib/Serialization/ASTReader.cpp

@@ -2239,6 +2239,18 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
   if (DeserializationListener)
     DeserializationListener->ReaderInitialized(this);
 
+  // If this AST file is a precompiled preamble, then set the main file ID of 
+  // the source manager to the file source file from which the preamble was
+  // built. This is the only valid way to use a precompiled preamble.
+  if (Type == Preamble) {
+    SourceLocation Loc
+      = SourceMgr.getLocation(FileMgr.getFile(getOriginalSourceFile()), 1, 1);
+    if (Loc.isValid()) {
+      std::pair<FileID, unsigned> Decomposed = SourceMgr.getDecomposedLoc(Loc);
+      SourceMgr.SetPreambleFileID(Decomposed.first);
+    }
+  }
+  
   return Success;
 }