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Subject: [Bug c++/86355] [9/10/11 Regression] Internal compiler error with
 pack expansion and fold expression
Date: Fri, 09 Jul 2021 20:14:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D86355

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:542d90bfd802274f38637aaaffc2dd1de62c9ec6

commit r11-8714-g542d90bfd802274f38637aaaffc2dd1de62c9ec6
Author: Jason Merrill <jason@redhat.com>
Date:   Wed May 26 17:38:42 2021 -0400

    c++: argument pack with expansion [PR86355]

    This testcase revealed that we were using PACK_EXPANSION_EXTRA_ARGS a l=
ot
    more than necessary; use_pack_expansion_extra_args_p meant to use it in=
 the
    case of corresponding arguments in different argument packs differing in
    whether they are pack expansions, but it was mistakenly also returning =
true
    for the case of a single argument pack containing both expansion and
    non-expansion elements.

    Surprisingly, just disabling that didn't lead to any regressions in the
    testsuite; it seems other changes have prevented us getting to this poi=
nt
    for code that used to exercise it.  So this patch limits the check to
    arguments in the same position in the packs, and asserts that we never
    actually see a mismatch.

            PR c++/86355

    gcc/cp/ChangeLog:

            * pt.c (use_pack_expansion_extra_args_p): Don't compare
            args from the same argument pack.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/alias-decl-variadic2.C: New test.=