Add {ExternalSemaSource,SemaConsumer}::ForgetSema callback, and update PCHReader

to use it so it at least won't try to access Sema once it is gone.

llvm-svn: 90261

clang/include/clang/Frontend/PCHReader.h

@@ -625,6 +625,9 @@ public:
   /// tree.
   virtual void InitializeSema(Sema &S);
 
+  /// \brief Inform the semantic consumer that Sema is no longer available.
+  virtual void ForgetSema() { SemaObj = 0; }
+
   /// \brief Retrieve the IdentifierInfo for the named identifier.
   ///
   /// This routine builds a new IdentifierInfo for the given identifier. If any

clang/include/clang/Sema/ExternalSemaSource.h

@@ -34,6 +34,9 @@ public:
   /// tree.
   virtual void InitializeSema(Sema &S) {}
 
+  /// \brief Inform the semantic consumer that Sema is no longer available.
+  virtual void ForgetSema() {}
+
   /// \brief Load the contents of the global method pool for a given
   /// selector.
   ///

clang/include/clang/Sema/SemaConsumer.h

@@ -34,6 +34,9 @@ namespace clang {
     /// tree.
     virtual void InitializeSema(Sema &S) {}
 
+    /// \brief Inform the semantic consumer that Sema is no longer available.
+    virtual void ForgetSema() {}
+
     // isa/cast/dyn_cast support
     static bool classof(const ASTConsumer *Consumer) {
       return Consumer->SemaConsumer;

clang/lib/Sema/ParseAST.cpp

@@ -75,7 +75,7 @@ void clang::ParseAST(Preprocessor &PP, ASTConsumer *Consumer,
   while ((ADecl = P.RetrievePendingObjCImpDecl()))
     Consumer->HandleTopLevelDecl(ADecl.getAsVal<DeclGroupRef>());
 
-  // process any TopLevelDecls generated by #pragma weak
+  // Process any TopLevelDecls generated by #pragma weak.
   for (llvm::SmallVector<Decl*,2>::iterator
         I = S.WeakTopLevelDecls().begin(),
         E = S.WeakTopLevelDecls().end(); I != E; ++I)
@@ -83,6 +83,13 @@ void clang::ParseAST(Preprocessor &PP, ASTConsumer *Consumer,
 
   Consumer->HandleTranslationUnit(Ctx);
 
+  if (ExternalSemaSource *ESS =
+        dyn_cast_or_null<ExternalSemaSource>(Ctx.getExternalSource()))
+    ESS->ForgetSema();
+
+  if (SemaConsumer *SC = dyn_cast<SemaConsumer>(Consumer))
+    SC->ForgetSema();
+
   if (PrintStats) {
     fprintf(stderr, "\nSTATISTICS:\n");
     P.getActions().PrintStats();