[Bug c++/93998] [10 Regression] ICE in adjust_temp_type, at cp/constexpr.c:1426

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93998

--- Comment #7 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:0e0ffbfc23ba98ac40cbc6330e2750a6448b79d9

commit r10-6998-g0e0ffbfc23ba98ac40cbc6330e2750a6448b79d9
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 3 19:49:12 2020 +0100

    c++: Fix non-constant TARGET_EXPR constexpr handing [PR93998]

    We ICE on the following testcase since I've added the SAVE_EXPR-like
    constexpr handling where the TARGET_EXPR initializer (and cleanup) is
    evaluated only once (because it might have side-effects like new or delete
    expressions in it).
    The problem is if the TARGET_EXPR (but I guess in theory SAVE_EXPR too)
    initializer is *non_constant_p.  We still remember the result, but already
    not that it is *non_constant_p.  Normally that wouldn't be a big problem,
    if something is *non_constant_p, we only or into it and so the whole
    expression will be non-constant too.  Except in the builtins handling,
    we try to evaluate the arguments with non_constant_p pointing into a dummy1
    bool which we ignore.  This is because some builtins might fold into a
    constant even if they don't have a constexpr argument.  Unfortunately if
    we evaluate the TARGET_EXPR first in the argument of such a builtin and
then
    once again, we don't set *non_constant_p.

    So, either we don't remember the TARGET_EXPR/SAVE_EXPR result if it wasn't
    constant, like the following patch does, or we could remember it, but in
    some way that would make it clear that it is non-constant (e.g. by
    pushing into the global->values SAVE_EXPR, SAVE_EXPR entry and perhaps
    for TARGET_EXPR don't remember it on TARGET_EXPR_SLOT, but the TARGET_EXPR
    itself and similarly push TARGET_EXPR, TARGET_EXPR and if we see those
    after the lookup, diagnose + set *non_constant_p.  Or we could perhaps
    during the builtin argument evaluation push expressions into a different
    save_expr vec and undo them afterwards.

    2020-03-03  Jakub Jelinek  <jakub@redhat.com>

        PR c++/93998
        * constexpr.c (cxx_eval_constant_expression)
        <case TARGET_EXPR, case SAVE_EXPR>: Don't record anything if
        *non_constant_p is true.

        * g++.dg/ext/pr93998.C: New test.