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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/109745] [13/14 Regression] Incorrect code generated with
 -O1 when having a constexpr object modifying a mutable member
Date: Thu, 11 May 2023 20:31:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109745

--- Comment #4 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:02777f20be4f40160f1b4ed34fa59ba75245b5b7

commit r14-742-g02777f20be4f40160f1b4ed34fa59ba75245b5b7
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 11 16:31:33 2023 -0400

    c++: 'mutable' subobject of constexpr variable [PR109745]

    r13-2701-g7107ea6fb933f1 made us correctly accept during constexpr
    evaluation 'mutable' member accesses of objects constructed during
    that evaluation, while continuing to reject such accesses for constexpr
    objects constructed outside of that evaluation, by considering the
    CONSTRUCTOR_MUTABLE_POISON flag during cxx_eval_component_reference.

    However, this flag is set only for the outermost CONSTRUCTOR of a
    constexpr variable initializer, so if we're accessing a 'mutable' member
    of a nested CONSTRUCTOR, the flag won't be set and we won't reject the
    access.  This can lead to us accepting invalid code, as in the first
    testcase, or even wrong code generation due to our speculative constexpr
    evaluation, as in the second and third testcase.

    This patch fixes this by setting CONSTRUCTOR_MUTABLE_POISON recursively
    rather than only on the outermost CONSTRUCTOR.

            PR c++/109745

    gcc/cp/ChangeLog:

            * typeck2.cc (poison_mutable_constructors): Define.
            (store_init_value): Use it instead of setting
            CONSTRUCTOR_MUTABLE_POISON directly.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-mutable4.C: New test.
            * g++.dg/cpp0x/constexpr-mutable5.C: New test.
            * g++.dg/cpp1y/constexpr-mutable2.C: New test.=