[Bug c++/71879] Error in unevaluated context breaks SFINAE

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71879

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>:

https://gcc.gnu.org/g:f645da0e4ab9438dfd0c047c710c7ec6a7d6d8f3

commit r11-6842-gf645da0e4ab9438dfd0c047c710c7ec6a7d6d8f3
Author: Patrick Palka <ppa...@redhat.com>
Date:   Thu Jan 21 14:04:55 2021 -0500

    c++: Fix excessive instantiation inside decltype [PR71879]

    Here after resolving the address of a template-id inside decltype, we
    end up instantiating the chosen specialization (from the call to
    mark_used in resolve_nondeduced_context), even though only its type is
    needed.

    This patch sets cp_unevaluated_operand throughout finish_decltype_type,
    so that in particular it's set during the call to
    resolve_nondeduced_context within.

    gcc/cp/ChangeLog:

            PR c++/71879
            * semantics.c (finish_decltype_type): Set up a cp_unevaluated
            sentinel at the start of the function.  Remove a now-redundant
            manual adjustment of cp_unevaluated_operand.

    gcc/testsuite/ChangeLog:

            PR c++/71879
            * g++.dg/cpp0x/decltype-71879.C: New test.