common tree nodes question

[Aldy Hernandez]

>>         new_type = type_for_mode (new_mode, TREE_UNSIGNED (type));
> [...]
>> !       t = TYPE_MAIN_VARIANT (new_type);
> [...]
>> !       TYPE_DEBUG_REPRESENTATION_TYPE (t) = rt;
>
> You can't modify T.  You need to create a new type which is a
> variant of new_type to hold your TYPE_DEBUG_REPRESENTATION_TYPE.

been there done that.  i tried making a copy of the node with
copy_node and then doing magic on that.  didn't work because then
the FE gets all confused because of type inequality.

suggestions?