Index: cfe/trunk/include/clang/AST/Expr.h
===================================================================
--- cfe/trunk/include/clang/AST/Expr.h
+++ cfe/trunk/include/clang/AST/Expr.h
@@ -23,6 +23,7 @@
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/CharInfo.h"
+#include "clang/Basic/LangOptions.h"
 #include "clang/Basic/TypeTraits.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -2575,6 +2576,14 @@
     HadMultipleCandidates = V;
   }
 
+  /// \brief Returns true if virtual dispatch is performed.
+  /// If the member access is fully qualified, (i.e. X::f()), virtual
+  /// dispatching is not performed. In -fapple-kext mode qualified
+  /// calls to virtual method will still go through the vtable.
+  bool performsVirtualDispatch(const LangOptions &LO) const {
+    return LO.AppleKext || !hasQualifier();
+  }
+
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == MemberExprClass;
   }
Index: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1100,6 +1100,9 @@
 def note_pure_virtual_function : Note<
   "unimplemented pure virtual method %0 in %1">;
 
+def note_pure_qualified_call_kext : Note<
+  "qualified call to %0::%1 is treated as a virtual call to %1 due to -fapple-kext">;
+
 def err_deleted_decl_not_first : Error<
   "deleted definition must be first declaration">;
 
@@ -1312,8 +1315,9 @@
   "%q0 is not a member of class %1">;
 
 def warn_call_to_pure_virtual_member_function_from_ctor_dtor : Warning<
-  "call to pure virtual member function %0; overrides of %0 in subclasses are "
-  "not available in the %select{constructor|destructor}1 of %2">;
+  "call to pure virtual member function %0 has undefined behavior; "
+  "overrides of %0 in subclasses are not available in the "
+  "%select{constructor|destructor}1 of %2">;
 
 def note_member_declared_at : Note<"member is declared here">;
 def note_ivar_decl : Note<"instance variable is declared here">;
Index: cfe/trunk/lib/Sema/SemaExpr.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaExpr.cpp
+++ cfe/trunk/lib/Sema/SemaExpr.cpp
@@ -13241,7 +13241,8 @@
   if (!MD)
     return;
   // Only attempt to devirtualize if this is truly a virtual call.
-  bool IsVirtualCall = MD->isVirtual() && !ME->hasQualifier();
+  bool IsVirtualCall = MD->isVirtual() &&
+                          ME->performsVirtualDispatch(SemaRef.getLangOpts());
   if (!IsVirtualCall)
     return;
   const Expr *Base = ME->getBase();
@@ -13275,7 +13276,7 @@
   //   expression, is odr-used, unless it is a pure virtual function and its
   //   name is not explicitly qualified.
   bool OdrUse = true;
-  if (!E->hasQualifier()) {
+  if (E->performsVirtualDispatch(getLangOpts())) {
     if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(E->getMemberDecl()))
       if (Method->isPure())
         OdrUse = false;
Index: cfe/trunk/lib/Sema/SemaOverload.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaOverload.cpp
+++ cfe/trunk/lib/Sema/SemaOverload.cpp
@@ -11772,13 +11772,19 @@
       TheCall->getMethodDecl()->isPure()) {
     const CXXMethodDecl *MD = TheCall->getMethodDecl();
 
-    if (isa<CXXThisExpr>(MemExpr->getBase()->IgnoreParenCasts())) {
-      Diag(MemExpr->getLocStart(), 
+    if (isa<CXXThisExpr>(MemExpr->getBase()->IgnoreParenCasts()) &&
+        MemExpr->performsVirtualDispatch(getLangOpts())) {
+      Diag(MemExpr->getLocStart(),
            diag::warn_call_to_pure_virtual_member_function_from_ctor_dtor)
         << MD->getDeclName() << isa<CXXDestructorDecl>(CurContext)
         << MD->getParent()->getDeclName();
 
       Diag(MD->getLocStart(), diag::note_previous_decl) << MD->getDeclName();
+      if (getLangOpts().AppleKext)
+        Diag(MemExpr->getLocStart(),
+             diag::note_pure_qualified_call_kext)
+             << MD->getParent()->getDeclName()
+             << MD->getDeclName();
     }
   }
   return MaybeBindToTemporary(TheCall);
Index: cfe/trunk/test/SemaCXX/warn-pure-virtual-call-from-ctor-dtor.cpp
===================================================================
--- cfe/trunk/test/SemaCXX/warn-pure-virtual-call-from-ctor-dtor.cpp
+++ cfe/trunk/test/SemaCXX/warn-pure-virtual-call-from-ctor-dtor.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 %s -fsyntax-only -verify
 struct A {
-  A() { f(); } // expected-warning {{call to pure virtual member function 'f'; overrides of 'f' in subclasses are not available in the constructor of 'A'}}
-  ~A() { f(); } // expected-warning {{call to pure virtual member function 'f'; overrides of 'f' in subclasses are not available in the destructor of 'A'}}
+  A() { f(); } // expected-warning {{call to pure virtual member function 'f' has undefined behavior; overrides of 'f' in subclasses are not available in the constructor of 'A'}}
+  ~A() { f(); } // expected-warning {{call to pure virtual member function 'f' has undefined behavior; overrides of 'f' in subclasses are not available in the destructor of 'A'}}
 
   virtual void f() = 0; // expected-note 2 {{'f' declared here}}
 };
@@ -12,3 +12,11 @@
   B() { a->f(); };
   ~B() { a->f(); };
 };
+
+// Don't warn if the call is fully qualified. (PR23215)
+struct C {
+    virtual void f() = 0;
+    C() {
+        C::f();
+    }
+};
Index: cfe/trunk/test/SemaCXX/warn-pure-virtual-kext.cpp
===================================================================
--- cfe/trunk/test/SemaCXX/warn-pure-virtual-kext.cpp
+++ cfe/trunk/test/SemaCXX/warn-pure-virtual-kext.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 %s -fapple-kext -fsyntax-only -verify
+
+struct A {
+    virtual void f() = 0; // expected-note {{'f' declared here}}
+    A() {
+        A::f(); // expected-warning {{call to pure virtual member function 'f' has undefined behavior; overrides of 'f' in subclasses are not available in the constructor of 'A'}} // expected-note {{qualified call to 'A'::'f' is treated as a virtual call to 'f' due to -fapple-kext}}
+    }
+};