Question about building an exportable snapshop

While working on the issue [1], I realize that if a subtransaction
hasn't done any catalog change then we don't add this in the commit
xid list even if we are building a full snapshot [2]. That means when
we will convert this to the MVCC snapshot we will add this to a
running xid list. If my understanding is correct then how visibility
will work? Because if I look at the code in XidInMVCCSnapshot(), then
if the suboverflowed is not set then first we are going to look into
the snapshot->subxip array and if we don't find it there then we look
into the snapshot->xip array, and now we will be finding even
committed subxips in the snapshot->xip array. Am I missing something?

[2]
/*
* Add subtransaction to base snapshot if catalog modifying, we don't
* distinguish to toplevel transactions there.
*/
if (ReorderBufferXidHasCatalogChanges(builder->reorder, subxid))
{
sub_needs_timetravel = true;
needs_snapshot = true;

[3]

[1] https://www.postgresql.org/message-id/CAFiTN-tqopqpfS6HHug2nnOGieJJ_nm-Nvy0WBZ%3DZpo-LqtSJA%40mail.gmail.com

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com