Teach ASTReader how to read only the Preprocessor state from an AST file, not the ASTContext state.

We use this when running a preprocessor-only action on an AST file in order to
avoid paying the runtime cost of loading the extra information.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306760 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 17 insertions, 5 deletions

diff --git a/include/clang/Frontend/ASTUnit.h b/include/clang/Frontend/ASTUnit.h
index 2950c31c2d..1ac4f07a35 100644
--- a/include/clang/Frontend/ASTUnit.h
+++ b/include/clang/Frontend/ASTUnit.h
@@ -628,6 +628,15 @@ public:
          IntrusiveRefCntPtr<DiagnosticsEngine> Diags, bool CaptureDiagnostics,
          bool UserFilesAreVolatile);
 
+  enum WhatToLoad {
+    /// Load options and the preprocessor state.
+    LoadPreprocessorOnly,
+    /// Load the AST, but do not restore Sema state.
+    LoadASTOnly,
+    /// Load everything, including Sema.
+    LoadEverything
+  };
+
   /// \brief Create a ASTUnit from an AST file.
   ///
   /// \param Filename - The AST file to load.
@@ -640,7 +649,7 @@ public:
   /// \returns - The initialized ASTUnit or null if the AST failed to load.
   static std::unique_ptr<ASTUnit> LoadFromASTFile(
       const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
-      IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
+      WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
       const FileSystemOptions &FileSystemOpts, bool UseDebugInfo = false,
       bool OnlyLocalDecls = false, ArrayRef<RemappedFile> RemappedFiles = None,
       bool CaptureDiagnostics = false, bool AllowPCHWithCompilerErrors = false,
diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index 9b94aadd76..eafa051758 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -400,7 +400,7 @@ private:
   Preprocessor &PP;
 
   /// \brief The AST context into which we'll read the AST files.
-  ASTContext &Context;
+  ASTContext *ContextObj = nullptr;
 
   /// \brief The AST consumer.
   ASTConsumer *Consumer = nullptr;
@@ -1387,7 +1387,7 @@ public:
   /// precompiled header will be loaded.
   ///
   /// \param Context the AST context that this precompiled header will be
-  /// loaded into.
+  /// loaded into, if any.
   ///
   /// \param PCHContainerRdr the PCHContainerOperations to use for loading and
   /// creating modules.
@@ -1419,7 +1419,7 @@ public:
   ///
   /// \param ReadTimer If non-null, a timer used to track the time spent
   /// deserializing.
-  ASTReader(Preprocessor &PP, ASTContext &Context,
+  ASTReader(Preprocessor &PP, ASTContext *Context,
             const PCHContainerReader &PCHContainerRdr,
             ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
             StringRef isysroot = "", bool DisableValidation = false,
@@ -2208,7 +2208,10 @@ public:
   void completeVisibleDeclsMap(const DeclContext *DC) override;
 
   /// \brief Retrieve the AST context that this AST reader supplements.
-  ASTContext &getContext() { return Context; }
+  ASTContext &getContext() {
+    assert(ContextObj && "requested AST context when not loading AST");
+    return *ContextObj;
+  }
 
   // \brief Contains the IDs for declarations that were requested before we have
   // access to a Sema object.