[Bug c++/91966] [8/9 Regression] pack expansion for Cartesian product breaks if certain indirections are involved since r6-1487-g1a4cd2cd7e7266b0

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91966

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:70ae61692245b5002f32454c8447655ad65a8535

commit r9-8450-g70ae61692245b5002f32454c8447655ad65a8535
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Apr 2 23:40:46 2020 -0400

    c++: alias template and parameter packs (PR91966).

    In this testcase, when we do a pack expansion of count_better_mins<nums>,
    nums appears both in the definition of count_better_mins and as its
template
    argument.  The intent is that we get a expansion over pairs of elements of
    the pack, i.e. less<2,2>, less<2,7>, less<7,2>, ....  But if we substitute
    into the definition of count_better_mins when parsing the template, we end
    up with sum<less<nums,nums>...>, which never gives us less<2,7>.  We could
    deal with this by somehow marking up the use of 'nums' as an argument for
    'num', but it's simpler to mark the alias as complex, so we need to
    instantiate it later with all its arguments rather than replace it early
    with its expansion.

    gcc/cp/ChangeLog
    2020-04-03  Jason Merrill  <jason@redhat.com>

            PR c++/91966
            * pt.c (complex_pack_expansion_r): New.
            (complex_alias_template_p): Use it.