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Subject: [Bug c++/56104] [4.7/4.8 Regression] Wrong "dereferencing type-punned pointer" warning
Date: Fri, 25 Jan 2013 14:58:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56104

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-25 14:57:47 UTC ---
Guess the relevant change in the patch is:
--- trunk/gcc/cp/typeck.c    2011/07/19 13:28:15    176460
+++ trunk/gcc/cp/typeck.c    2011/07/19 14:01:59    176461
@@ -3078,8 +3078,7 @@
         return error_mark_node;
     }
       /* ...and then the delta in the PMF.  */
-      instance_ptr = build2 (POINTER_PLUS_EXPR, TREE_TYPE (instance_ptr),
-                 instance_ptr, fold_convert (sizetype, delta));
+      instance_ptr = fold_build_pointer_plus (instance_ptr, delta);

       /* Hand back the adjusted 'this' argument to our caller.  */
       *instance_ptrptr = instance_ptr;
where we didn't fold the POINTER_PLUS_EXPR in this case before (delta is 0
here), but now we do.
The above is followed by:
      /* Next extract the vtable pointer from the object.  */
      vtbl = build1 (NOP_EXPR, build_pointer_type (vtbl_ptr_type_node),
                     instance_ptr);
      vtbl = cp_build_indirect_ref (vtbl, RO_NULL, complain);
      if (vtbl == error_mark_node)
        return error_mark_node;
and during cp_build_indirect_ref this warns, instance_ptr here is ADDR_EXPR of
cc VAR_DECL, and as the class type of cc isn't virtual, it doesn't have a
vtable pointer at the beginning.