[Bug c++/108243] [10/11/12/13 Regression] Missed optimization for static const std::string_view(const char*)

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108243

--- Comment #12 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:cbaa1d9c218d9c0b5e34e510a462ff4e299a0f3f

commit r13-6421-gcbaa1d9c218d9c0b5e34e510a462ff4e299a0f3f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Mar 2 14:03:21 2023 -0500

    c++: constant non-copy-init is manifestly constant [PR108243]

    According to [basic.start.static]/2 and [expr.const]/2, a variable
    with static storage duration initialized with a constant initializer
    has constant initialization, and such an initializer is manifestly
    constant-evaluated.

    For copy initialization, we're already getting this right because in
    that case check_initializer would consistently call store_init_value,
    which for TREE_STATIC variables calls fold_non_dependent_init with
    m_c_e=true.

    But for direct (or default) initialization, check_initializer doesn't
    always call store_init_value.  We instead however always call
    maybe_constant_init from expand_default_init[1], albeit with m_c_e=false
    which means we don't get the "manifestly constant-evaluated" part right
    for non-copy-init.

    This patch fixes this by setting m_c_e=true in maybe_constant_init for
    static storage duration variables, mainly for benefit of the call
    to maybe_constant_init from expand_default_init.

    [1]: this maybe_constant_init call isn't reached in the copy-init
    case because there init is a CONSTRUCTOR rather than a TREE_LIST,
    and so we exit early from expand_default_init, returning an INIT_EXPR.
    This INIT_EXPR is ultimately what causes us to consistently hit the
    store_init_value code path from check_initializer in the copy-init case.

            PR c++/108243

    gcc/cp/ChangeLog:

            * constexpr.cc (maybe_constant_init_1): Override
            manifestly_const_eval to true if is_static.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/is-constant-evaluated14.C: New test.