Introduce a new OpaquePtr<N> struct type, which is a simple POD wrapper for a
pointer.  Its purpose in life is to be a glorified void*, but which does not
implicitly convert to void* or other OpaquePtr's with a different UID.

Introduce Action::DeclPtrTy which is a typedef for OpaquePtr<0>.  Change the 
entire parser/sema interface to use DeclPtrTy instead of DeclTy*.  This
makes the C++ compiler enforce that these aren't convertible to other opaque
types.

We should also convert ExprTy, StmtTy, TypeTy, AttrTy, BaseTy, etc,
but I don't plan to do that in the short term.

The one outstanding known problem with this patch is that we lose the 
bitmangling optimization where ActionResult<DeclPtrTy> doesn't know how to
bitmangle the success bit into the low bit of DeclPtrTy.  I will rectify
this with a subsequent patch.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67952 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/ParseAST.cpp b/lib/Sema/ParseAST.cpp
index fdc57b6..59a04da 100644
--- a/lib/Sema/ParseAST.cpp
+++ b/lib/Sema/ParseAST.cpp
@@ -44,14 +44,14 @@
   
   Consumer->Initialize(Ctx);
   
-  Parser::DeclTy *ADecl;
+  Parser::DeclPtrTy ADecl;
   
   while (!P.ParseTopLevelDecl(ADecl)) {  // Not end of file.
     // If we got a null return and something *was* parsed, ignore it.  This
     // is due to a top-level semicolon, an action override, or a parse error
     // skipping something.
     if (ADecl) {
-      Decl* D = static_cast<Decl*>(ADecl);      
+      Decl *D = ADecl.getAs<Decl>();      
       Consumer->HandleTopLevelDecl(D);
     }
   };