Move the -fms-compatibility using decl check after real access checking

Summary:
This avoids false positives from -Wmicrosoft when name lookup would
normally succeed in standard C++.  This triggered on a common CRTP
pattern in clang, where a derived class would have a private using decl
to pull in members of a dependent base:

class Verifier : InstVisitor<Verifier> {
private:
  using InstVisitor<Verifier>::visit;
  ...
  void anything() {
    visit(); // warned here
  }
};

Real access checks pass here because we're in the context of the
Verifier, but the -Wmicrosoft extension was just looking for the private
access specifier.

Reviewers: rsmith

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2679

llvm-svn: 201019

clang/lib/Sema/SemaAccess.cpp

@@ -1420,16 +1420,15 @@ static AccessResult CheckEffectiveAccess(Sema &S,
                                          AccessTarget &Entity) {
   assert(Entity.getAccess() != AS_public && "called for public access!");
 
-  if (S.getLangOpts().MSVCCompat &&
-      IsMicrosoftUsingDeclarationAccessBug(S, Loc, Entity))
-    return AR_accessible;
-
   switch (IsAccessible(S, EC, Entity)) {
   case AR_dependent:
     DelayDependentAccess(S, EC, Loc, Entity);
     return AR_dependent;
 
   case AR_inaccessible:
+    if (S.getLangOpts().MSVCCompat &&
+        IsMicrosoftUsingDeclarationAccessBug(S, Loc, Entity))
+      return AR_accessible;
     if (!Entity.isQuiet())
       DiagnoseBadAccess(S, Loc, EC, Entity);
     return AR_inaccessible;

clang/test/SemaCXX/MicrosoftCompatibility.cpp

@@ -111,6 +111,9 @@ public:
 class B : public A {
 private:   
   using A::f;
+  void g() {
+    f(); // no diagnostic
+  }
 };
 
 class C : public B {