On Wed, Mar 14, 2018 at 11:59 AM, Marek Polacek <pola...@redhat.com> wrote:
> cxx_constant_value doesn't understand template codes, and neither it
> understands OVERLOADs, so if we pass an OVERLOAD to it, we crash. Here
> instantiate_non_dependent_expr got an OVERLOAD, but since it calls
> is_nondependent_constant_expression which checks type_unknown_p, it left the
> expression as it was. We can't use is_nondependent_constant_expression in
> finish_if_stmt_cond because i_n_c_e checks is_constant_expression and that is
> not suitable here; we'd miss diagnostics. So I did the following; I think we
> should reject the testcase with an error.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-03-14 Marek Polacek <pola...@redhat.com>
>
> PR c++/84854
> * semantics.c (finish_if_stmt_cond): Give error if the condition
> is an overloaded function with no contextual type information.
>
> * g++.dg/cpp1z/constexpr-if15.C: New test.
>
> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> index fdf37bea770..a056e9445e9 100644
> --- gcc/cp/semantics.c
> +++ gcc/cp/semantics.c
> @@ -735,8 +735,16 @@ finish_if_stmt_cond (tree cond, tree if_stmt)
> && require_constant_expression (cond)
> && !value_dependent_expression_p (cond))
> {
> - cond = instantiate_non_dependent_expr (cond);
> - cond = cxx_constant_value (cond, NULL_TREE);
> + if (type_unknown_p (cond))
> + {
> + cxx_incomplete_type_error (cond, TREE_TYPE (cond));
> + cond = error_mark_node;
I think I'd prefer to skip this block when type_unknown_p, and leave
error handling up to the code shared with regular if.
Jason
