On November 21, 2014 8:45:09 PM CET, Diego Novillo <dnovi...@google.com> wrote:
>On Fri, Nov 21, 2014 at 1:48 PM, Andrew MacLeod <amacl...@redhat.com>
>wrote:
>
>> 1 - introduce a TYPE_REF tree node, which is effectively just a
>'typed' tree
>> node, and the TREE_TYPE() field of a TYPE_REF node would point to the
>type
>> node. Any routines which utilize a TYPE node in a tree list would
>have to
>> be modified to make use of this new TYPE_REF node to refer to the
>type.
>>
>> 2 - change the field (list->value in this case) to be a tagged union
>of {
>> tree tree_value, tree_type_ptr type_value } and use a bit in the base
>to
>> flag which kind of value it is. This would be compatible with GTY,
>and would
>> require changing routines and algorithms to check the bit and use the
>right
>> field.
>
>Seems to me that option 2 would also help against code that blindly
>looks at TREE_VALUE and assumes it to be a tree. Wouldn't that make
>initial implementation a bit more challenging?
>
>Option 1 does seem easier, but I kind of like the forcing of rvalues
>that option 2 provides.
>
>Also liking option 1. The final change to the final type should be
>simpler that way.
I don't like either :). It seems you are concerned about uses from trees. An
intermediate step here that would be useful is doing what David did for RTL
insns and now gimple - expose tree_type as static type but keep tree as its
base.
Thus make references to trees that are always types use tree_type * while
keeping those that can refer to types and sth else refer to tree.
That's something that would not be completely artificial at this point.
Richard.
>
>Diego.
