1 files changed, 15 insertions, 1 deletions
diff --git a/include/llvm/Support/Casting.h b/include/llvm/Support/Casting.h
index 3aab436..0c71882 100644
--- a/include/llvm/Support/Casting.h
+++ b/include/llvm/Support/Casting.h
@@ -15,6 +15,7 @@
 #ifndef LLVM_SUPPORT_CASTING_H
 #define LLVM_SUPPORT_CASTING_H
 
+#include "llvm/Support/type_traits.h"
 #include <cassert>
 
 namespace llvm {
@@ -44,13 +45,23 @@ template<typename From> struct simplify_type<const From> {
 // The core of the implementation of isa<X> is here; To and From should be
 // the names of classes.  This template can be specialized to customize the
 // implementation of isa<> without rewriting it from scratch.
-template <typename To, typename From>
+template <typename To, typename From, typename Enabler = void>
 struct isa_impl {
   static inline bool doit(const From &Val) {
     return To::classof(&Val);
   }
 };
 
+/// \brief Always allow upcasts, and perform no dynamic check for them.
+template <typename To, typename From>
+struct isa_impl<To, From,
+                typename llvm::enable_if_c<
+                  llvm::is_base_of<To, From>::value
+                >::type
+               > {
+  static inline bool doit(const From &) { return true; }
+};
+
 template <typename To, typename From> struct isa_impl_cl {
   static inline bool doit(const From &Val) {
     return isa_impl<To, From>::doit(Val);
@@ -65,18 +76,21 @@ template <typename To, typename From> struct isa_impl_cl<To, const From> {
 
 template <typename To, typename From> struct isa_impl_cl<To, From*> {
   static inline bool doit(const From *Val) {
+    assert(Val && "isa<> used on a null pointer");
     return isa_impl<To, From>::doit(*Val);
   }
 };
 
 template <typename To, typename From> struct isa_impl_cl<To, const From*> {
   static inline bool doit(const From *Val) {
+    assert(Val && "isa<> used on a null pointer");
     return isa_impl<To, From>::doit(*Val);
   }
 };
 
 template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
   static inline bool doit(const From *Val) {
+    assert(Val && "isa<> used on a null pointer");
     return isa_impl<To, From>::doit(*Val);
   }
 };