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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/108975] [11 Regression] ICE on constexpr variable used as
 nontype template since r9-5473-ge32fc4499f863f
Date: Wed, 20 Dec 2023 01:55:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108975

--- Comment #22 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:035fa0105e8d12ca6750545369dd901cb0a2aff0

commit r12-10063-g035fa0105e8d12ca6750545369dd901cb0a2aff0
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Apr 25 15:59:22 2023 -0400

    c++: value dependence of by-ref lambda capture [PR108975]

    We are still ICEing on the generic lambda version of the testcase from
    this PR, even after r13-6743-g6f90de97634d6f, due to the by-ref capture
    of the constant local variable 'dim' being considered value-dependent
    when regenerating the lambda (at which point processing_template_decl is
    set since the lambda is generic), which prevents us from constant foldi=
ng
    its uses.  Later during prune_lambda_captures we end up not thoroughly
    walking the body of the lambda and overlook the (non-folded) uses of
    'dim' within the array bound and using-decls.

    We could fix this by making prune_lambda_captures walk the body of the
    lambda more thoroughly so that it finds these uses of 'dim', but ideally
    we should be able to constant fold all uses of 'dim' ahead of time and
    prune the implicit capture after all.

    To that end this patch makes value_dependent_expression_p return false
    for such by-ref captures of constant local variables, allowing their
    uses to get constant folded ahead of time.  It seems we just need to
    disable the predicate's conservative early exit for reference variables
    (added by r5-5022-g51d72abe5ea04e) when DECL_HAS_VALUE_EXPR_P.  This
    effectively makes us treat by-value and by-ref captures more consistent=
ly
    when it comes to value dependence.

            PR c++/108975

    gcc/cp/ChangeLog:

            * pt.cc (value_dependent_expression_p) <case VAR_DECL>:
            Suppress conservative early exit for reference variables
            when DECL_HAS_VALUE_EXPR_P.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/lambda/lambda-const11a.C: New test.

    (cherry picked from commit 3d674e29d7f89bf93fcfcc963ff0248c6347586d)=