Make sure that we don't end up making an #undef'd macro visible after

the fact. Test cases will come when we're actually (de-)serializing
macro history.

llvm-svn: 164549

clang/include/clang/Lex/Preprocessor.h

@@ -278,7 +278,8 @@ class Preprocessor : public RefCountedBase<Preprocessor> {
   /// keep a mapping to the history of all macro definitions and #undefs in
   /// the reverse order (the latest one is in the head of the list).
   llvm::DenseMap<IdentifierInfo*, MacroInfo*> Macros;
-
+  friend class ASTReader;
+  
   /// \brief Macros that we want to warn because they are not used at the end
   /// of the translation unit; we store just their SourceLocations instead
   /// something like MacroInfo*. The benefit of this is that when we are

clang/lib/Serialization/ASTReader.cpp

@@ -2552,9 +2552,15 @@ void ASTReader::makeNamesVisible(const HiddenNames &Names) {
     else {
       IdentifierInfo *II = Names[I].get<IdentifierInfo *>();
       if (!II->hasMacroDefinition()) {
-        II->setHasMacroDefinition(true);
-        if (DeserializationListener)
-          DeserializationListener->MacroVisible(II);
+        // Make sure that this macro hasn't been #undef'd in the mean-time.
+        llvm::DenseMap<IdentifierInfo*, MacroInfo*>::iterator Known
+          = PP.Macros.find(II);
+        if (Known == PP.Macros.end() ||
+            Known->second->getUndefLoc().isInvalid()) {
+          II->setHasMacroDefinition(true);
+          if (DeserializationListener)
+            DeserializationListener->MacroVisible(II);
+        }
       }
     }
   }