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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/100295] Internal compiler error from generic lambda
 capturing parameter pack and expanding it in if constexpr
Date: Thu, 15 Dec 2022 21:03:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100295

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:18499b9f848707aee42d810e99ac0a4c9788433c

commit r13-4730-g18499b9f848707aee42d810e99ac0a4c9788433c
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Dec 15 16:02:05 2022 -0500

    c++: extract_local_specs and unevaluated contexts [PR100295]

    Here during partial instantiation of the constexpr if, extra_local_specs
    walks the statement looking for local specializations within to capture.
    However, we're thwarted by the fact that 'ts' first appears inside an
    unevaluated context, and so the calls to process_outer_var_ref for its
    local specializations are a no-op.  And since we walk each tree exactly
    once, we end up not capturing the local specializations despite 'ts'
    later occurring in an evaluated context.

    This patch fixes this by making extract_local_specs walk evaluated
    contexts first before walking unevaluated contexts.  We could probably
    get away with not walking unevaluated contexts at all, but this approach
    seems more clearly safe.

            PR c++/100295
            PR c++/107579

    gcc/cp/ChangeLog:

            * pt.cc (el_data::skip_unevaluated_operands): New data member.
            (extract_locals_r): If skip_unevaluated_operands is true,
            don't walk into unevaluated contexts.
            (extract_local_specs): Walk the pattern twice, first with
            skip_unevaluated_operands true followed by it set to false.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/constexpr-if-lambda5.C: New test.=