[Bug c/35579] [4.1/4.2/4.3/4.4 Regression] casts to void do not silence -Wunused warnings for the case of __attribute__(( warn_unused_result ))

[bonzini at gnu dot org]

------- Comment #7 from bonzini at gnu dot org  2008-10-17 11:12 -------
Totally untested patch.

Index: c-common.c
===================================================================
--- c-common.c  (revisione 134435)
+++ c-common.c  (copia locale)
@@ -6762,7 +6762,8 @@ c_warn_unused_result (tree *top_p)
          ftype = TREE_TYPE (ftype);
        }

-      if (lookup_attribute ("warn_unused_result", TYPE_ATTRIBUTES (ftype)))
+      if (lookup_attribute ("warn_unused_result", TYPE_ATTRIBUTES (ftype))
+         && !TREE_NO_WARNING (t))
        {
          if (fdecl)
            warning (0, "%Hignoring return value of %qD, "
Index: c-convert.c
===================================================================
--- c-convert.c (revisione 134435)
+++ c-convert.c (copia locale)
@@ -96,7 +96,11 @@ convert (tree type, tree expr)
       return error_mark_node;
     }
   if (code == VOID_TYPE)
-    return fold_convert (type, e);
+    {
+      if (TREE_CODE (e) == CALL_EXPR)
+       TREE_NO_WARNING (e) == 1;
+      return fold_convert (type, e);
+    }
   if (code == INTEGER_TYPE || code == ENUMERAL_TYPE)
     return fold (convert_to_integer (type, e));
   if (code == BOOLEAN_TYPE)
Index: cp/cvt.c
===================================================================
--- cp/cvt.c    (revisione 134435)
+++ cp/cvt.c    (copia locale)
@@ -825,6 +825,7 @@ convert_to_void (tree expr, const char *
       break;

     case CALL_EXPR:   /* We have a special meaning for volatile void fn().  */
+      TREE_NO_WARNING (expr) = 1;
       break;

     case INDIRECT_REF:


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35579