Avoid passing objects with __declspec(align) members by value (PR24113) - clang-tools-extra part

[hans]

Summary

This is the clang-tools-extra part of http://reviews.llvm.org/D11167

[hans]

I won't pursue this after r242157.

clang-modernize/UseNullptr/NullptrActions.cpp

bool expandsFrom(SourceLocation TestLoc, SourceLocation TestMacroLoc) {
     llvm_unreachable("expandsFrom");
   }
 
   /// \brief Given a starting point \c Start in the AST, find an ancestor that
   /// doesn't expand from the macro called at file location \c MacroLoc.
   ///
   /// \pre MacroLoc.isFileID()
   /// \returns true if such an ancestor was found, false otherwise.
-  bool findContainingAncestor(ast_type_traits::DynTypedNode Start,
+  bool findContainingAncestor(const ast_type_traits::DynTypedNode &Start,
                               SourceLocation MacroLoc,
                               ast_type_traits::DynTypedNode &Result) {
     // Below we're only following the first parent back up the AST. This should
     // be fine since for the statements we care about there should only be one
     // parent as far up as we care. If this assumption doesn't hold, need to
     // revisit what to do here.
 
     assert(MacroLoc.isFileID());
 
+    ast_type_traits::DynTypedNode Node = Start;
+
     do {
-      const auto &Parents = Context.getParents(Start);
+      const auto &Parents = Context.getParents(Node);
       if (Parents.empty())
         return false;
       assert(Parents.size() == 1 &&
              "Found an ancestor with more than one parent!");
 
       const ast_type_traits::DynTypedNode &Parent = Parents[0];
 
       SourceLocation Loc;
       if (const Decl *D = Parent.get<Decl>())
         Loc = D->getLocStart();
       else if (const Stmt *S = Parent.get<Stmt>())
         Loc = S->getLocStart();
       else
         llvm_unreachable("Expected to find Decl or Stmt containing ancestor");
 
       if (!expandsFrom(Loc, MacroLoc)) {
         Result = Parent;
         return true;
       }
-      Start = Parent;
+      Node = Parent;
     } while (1);
 
     llvm_unreachable("findContainingAncestor");
   }
 
 private:
   SourceManager &SM;
   ASTContext &Context;