re PR c++/19542 (attribute(sentinel) has problems with C++ __null)

        PR c++/19542
        * c-common.c (c_common_nodes_and_builtins): Create global null_node.
        (warn_strict_null_sentinel): Define.
        (check_function_sentinel): Check for null_node as valid sentinel too.
        * c-common.h (c_tree_index): Added CTI_NULL.
        (null_node) Define global_tree[CTI_NULL].
        (warn_strict_null_sentinel): Declare.
        * c-opts.c: (c_common_handle_option): Handle -Wstrict-null-sentinel.
        * c.opt: (Wstrict-null-sentinel): New C++ option.
        * doc/invoke.texi (C++ Options): Document -Wstrict-null-sentinel.

        * cp-tree.h (cp_tree_index): Remove CPTI_NULL, to be defined in C
        common frontend.
        (null_node): Remove.
        * lex.c (cxx_init): Move null_node initialisation to C common frontend.

        * g++.dg/warn/sentinel.C: New testcase for __null sentinels added.

From-SVN: r99091

1 files changed, 20 insertions, 2 deletions

diff --git a/gcc/c-common.c b/gcc/c-common.c
index 8aa0aea..22aa82e 100644
--- a/gcc/c-common.c
+++ b/gcc/c-common.c
@@ -284,6 +284,12 @@ int warn_unknown_pragmas; /* Tri state variable.  */
 
 int warn_format;
 
+/* Warn about using __null (as NULL in C++) as sentinel.  For code compiled
+   with GCC this doesn't matter as __null is guaranteed to have the right
+   size.  */
+
+int warn_strict_null_sentinel;
+
 /* Zero means that faster, ...NonNil variants of objc_msgSend...
    calls will be used in ObjC; passing nil receivers to such calls
    will most likely result in crashes.  */
@@ -3279,6 +3285,11 @@ c_common_nodes_and_builtins (void)
     mudflap_init ();
 
   main_identifier_node = get_identifier ("main");
+
+  /* Create the built-in __null node.  It is important that this is
+     not shared.  */
+  null_node = make_node (INTEGER_CST);
+  TREE_TYPE (null_node) = c_common_type_for_size (POINTER_SIZE, 0);
 }
 
 /* Look up the function in built_in_decls that corresponds to DECL
@@ -5134,8 +5145,15 @@ check_function_sentinel (tree attrs, tree params)
 	    }
 
 	  /* Validate the sentinel.  */
-	  if (!POINTER_TYPE_P (TREE_TYPE (TREE_VALUE (sentinel)))
-	      || !integer_zerop (TREE_VALUE (sentinel)))
+	  if ((!POINTER_TYPE_P (TREE_TYPE (TREE_VALUE (sentinel)))
+	       || !integer_zerop (TREE_VALUE (sentinel)))
+	      /* Although __null (in C++) is only an integer we allow it
+		 nevertheless, as we are guaranteed that it's exactly
+		 as wide as a pointer, and we don't want to force
+		 users to cast the NULL they have written there.
+		 We warn with -Wstrict-null-sentinel, though.  */
+              && (warn_strict_null_sentinel
+		  || null_node != TREE_VALUE (sentinel)))
 	    warning (0, "missing sentinel in function call");
 	}
     }