How could I get alias set information from data_reference_p

[Li Feng <nemokingdom at gmail dot com>]

Hi,

I'm now working on Graphite branch and need to know
the alias set information for each data_reference_p, which
would be an integer (or alias_set_type) stands for which
alias set it is in.

I tried to get the alias set information with get_alias_set (tree)
(I've no idea how this function works, just a experimental
trying), for my testcase, it returns 2 for all the
data_reference_p->ref, which I think is unreasonable.
So I think I may go wrong somewhere.

The question will be: how could I get it's relevant
alias set information from data_reference_p?

p.s. :
In Graphite, the data reference was built for each
gimple stmt with:
get_references_in_stmt (stmt, &references);
then for each ref in references, data reference is created with:
dr = create_data_ref (nest, *ref->pos, stmt, ref->is_read);

Thanks,
Li