Introduce safe_as_a

gcc/
2014-08-18  David Malcolm  <dmalcolm@redhat.com>

	* is-a.h (template<T, U> safe_as_a <U *p>) New function.

From-SVN: r214117

gcc/ChangeLog

+2014-08-18  David Malcolm  <dmalcolm@redhat.com>
+
+	* is-a.h (template<T, U> safe_as_a <U *p>) New function.
+
 2014-08-18  Jan Hubicka  <hubicka@ucw.cz>
 
 	* ipa-visibility.c (update_visibility_by_resolution_info): Do no turn UNDEF

gcc/is-a.h

@@ -46,6 +46,14 @@ TYPE as_a <TYPE> (pointer)
 
       do_something_with (as_a <cgraph_node *> *ptr);
 
+TYPE safe_as_a <TYPE> (pointer)
+
+    Like as_a <TYPE> (pointer), but where pointer could be NULL.  This
+    adds a check against NULL where the regular is_a_helper hook for TYPE
+    assumes non-NULL.
+
+      do_something_with (safe_as_a <cgraph_node *> *ptr);
+
 TYPE dyn_cast <TYPE> (pointer)
 
     Converts pointer to TYPE if and only if "is_a <TYPE> pointer".  Otherwise,
@@ -185,6 +193,22 @@ as_a (U *p)
   return is_a_helper <T>::cast (p);
 }
 
+/* Similar to as_a<>, but where the pointer can be NULL, even if
+   is_a_helper<T> doesn't check for NULL.  */
+
+template <typename T, typename U>
+inline T
+safe_as_a (U *p)
+{
+  if (p)
+    {
+      gcc_checking_assert (is_a <T> (p));
+      return is_a_helper <T>::cast (p);
+    }
+  else
+    return NULL;
+}
+
 /* A generic checked conversion from a base type U to a derived type T.  See
    the discussion above for when to use this function.  */