[Bug c++/105321] [9/10/11/12 Regression] "non-constant condition" issued for function containing a short-circuited unevaluated non-constant expression

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105321

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:93b65ed9706e2ceb4be7b28c9ff9be759e68a614

commit r12-8216-g93b65ed9706e2ceb4be7b28c9ff9be759e68a614
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Apr 20 16:02:52 2022 -0400

    c++: wrong error with constexpr COMPOUND_EXPR [PR105321]

    Here we issue a bogus error for the first assert in the test.  Therein
    we have

    <retval> = (void) (VIEW_CONVERT_EXPR<bool>(yes) || handle_error ());,
VIEW_CONVERT_EXPR<int>(value);

    which has a COMPOUND_EXPR, so we get to cxx_eval_constant_expression
    <case COMPOUND_EXPR>.  The problem here is that we call

    7044             /* Check that the LHS is constant and then discard it.  */
    7045             cxx_eval_constant_expression (ctx, op0,
    7046                                           true, non_constant_p,
overflow_p,
    7047                                           jump_target);

    where lval is always true, so the PARM_DECL 'yes' is not evaluated into
    its value.

    Fixed by always passing false for 'lval' in cxx_eval_logical_expression;
    there's no case where we actually expect an lvalue from a TRUTH_*.

            PR c++/105321

    gcc/cp/ChangeLog:

            * constexpr.cc (cxx_eval_logical_expression): Always pass false for
lval
            to cxx_eval_constant_expression.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-105321.C: New test.