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Subject: [Bug c++/91966] [8/9 Regression] pack expansion for Cartesian
 product  breaks if certain indirections are involved since
 r6-1487-g1a4cd2cd7e7266b0
Date: Fri, 03 Apr 2020 19:26:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D91966

--- 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 substit=
ute
    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 co=
uld
    deal with this by somehow marking up the use of 'nums' as an argument f=
or
    '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.=