[Bug c++/99456] [11 regression] ABI breakage with some static initialization

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99456

--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:82bb66730bc42b8694fdebef607ea6e49e8496bf

commit r11-7740-g82bb66730bc42b8694fdebef607ea6e49e8496bf
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 19 18:36:56 2021 +0100

    c++: Only reject reinterpret casts from pointers to integers for
manifestly_const_eval evaluation [PR99456]

    My PR82304/PR95307 fix moved reinterpret cast from pointer to integer
    diagnostics from cxx_eval_outermost_constant_expr where it caught
    invalid code only at the outermost level down into
    cxx_eval_constant_expression.
    Unfortunately, it regressed following testcase, we emit worse code
    including dynamic initialization of some vars.
    While the initializers are not constant expressions due to the
    reinterpret_cast in there, there is no reason not to fold them as an
    optimization.

    I've tried to make this dependent on !ctx->quiet, but that regressed
    two further tests, and on ctx->strict, which regressed other tests,
    so this patch bases that on manifestly_const_eval.

    The new testcase is now optimized as much as it used to be in GCC 10
    and the only regression it causes is an extra -Wnarrowing warning
    on vla22.C test on invalid code (which the patch adjusts).

    2021-03-19  Jakub Jelinek  <jakub@redhat.com>

            PR c++/99456
            * constexpr.c (cxx_eval_constant_expression): For CONVERT_EXPR from
            INDIRECT_TYPE_P to ARITHMETIC_TYPE_P, when
!ctx->manifestly_const_eval
            don't diagnose it, set *non_constant_p nor return t.

            * g++.dg/opt/pr99456.C: New test.
            * g++.dg/ext/vla22.C: Expect a -Wnarrowing warning for c++11 and
            later.