(merge_attributes): Moved here from c-typeck.c.

From-SVN: r10955

gcc/tree.c

@@ -3114,6 +3114,44 @@ lookup_attribute (attr_name, list)
 
   return NULL_TREE;
 }
+
+/* Return an attribute list that is the union of a1 and a2.  */
+
+tree
+merge_attributes (a1, a2)
+     register tree a1, a2;
+{
+  tree attributes;
+
+  /* Either one unset?  Take the set one.  */
+
+  if (! (attributes = a1))
+    attributes = a2;
+
+  /* One that completely contains the other?  Take it.  */
+
+  else if (a2 && ! attribute_list_contained (a1, a2))
+    if (attribute_list_contained (a2, a1))
+      attributes = a2;
+    else
+      {
+	/* Pick the longest list, and hang on the other list.  */
+	/* ??? For the moment we punt on the issue of attrs with args.  */
+
+	if (list_length (a1) < list_length (a2))
+	  attributes = a2, a2 = a1;
+
+	for (; a2; a2 = TREE_CHAIN (a2))
+	  if (lookup_attribute (IDENTIFIER_POINTER (TREE_PURPOSE (a2)),
+				attributes) == NULL_TREE)
+	    {
+	      a1 = copy_node (a2);
+	      TREE_CHAIN (a1) = attributes;
+	      attributes = a1;
+	    }
+      }
+  return attributes;
+}
 
 /* Return a type like TYPE except that its TYPE_READONLY is CONSTP
    and its TYPE_VOLATILE is VOLATILEP.