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

2 files changed, 17 insertions, 2 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index b5feadb96de..30c3b62c191 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/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;
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 86732484bcd..1cac948d032 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/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;
 }