https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105321
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
As you mention, this slightly modified test compiles fine:
bool handle_error();
constexpr int echo(int value, bool yes = false) noexcept
{
return (!yes || handle_error()), value;
}
static_assert(echo(10) == 10, "");
In the original test 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/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.
In the working test, we evaluate "!yes" in cxx_eval_unary_expression which
evaluates its operand with
3217 tree arg = cxx_eval_constant_expression (ctx, orig_arg, /*lval*/false,
3218 non_constant_p, overflow_p);
where lval is false, so the PARM_DECL is evaluated into a constant.
