Re: [PATCH] c++: fix ICE in convert_nontype_argument [PR116384]

[Jason Merrill <jason@redhat.com>]

On 8/16/24 4:07 PM, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK for trunk and 14.

> -- >8 --
> Here we ICE since r14-8291 in C++11/C++14 modes.  Fortunately
> this is an easy one.
> 
> The important bit of r14-8291 is this:
> 
> @@ -20056,9 +20071,12 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>          RETURN (retval);
>        }
>      if (IMPLICIT_CONV_EXPR_NONTYPE_ARG (t))
> -     /* We'll pass this to convert_nontype_argument again, we don't need
> -        to actually perform any conversion here.  */
> -     RETURN (expr);
> +     {
> +       tree r = convert_nontype_argument (type, expr, complain);
> +       if (r == NULL_TREE)
> +         r = error_mark_node;
> +       RETURN (r);
> +     }
> 
> which obviously means that instead of returning right away we go
> to convert_nontype_argument.  When type is error_mark_node and we're
> in C++17, in convert_nontype_argument we go down this path:
> 
>        else if (INTEGRAL_OR_ENUMERATION_TYPE_P (type)
>                 || cxx_dialect >= cxx17)
>          {
>            expr = build_converted_constant_expr (type, expr, complain);
>            if (expr == error_mark_node)
>              return (complain & tf_error) ? NULL_TREE : error_mark_node;
> 	  // ...
> 	}
> 
> but pre-C++17, we take a different route and end up crashing on
> gcc_unreachable.
> 
> It would of course also work to check for error_mark_node early in
> build_converted_constant_expr.
> 
> 	PR c++/116384
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (tsubst_expr) <case IMPLICIT_CONV_EXPR>: Bail if tsubst
> 	returns error_mark_node.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/vt-116384.C: New test.
> ---
>   gcc/cp/pt.cc                           |  2 ++
>   gcc/testsuite/g++.dg/cpp0x/vt-116384.C | 26 ++++++++++++++++++++++++++
>   2 files changed, 28 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/vt-116384.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 8725a5eeb3f..684ee0c8a60 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -20217,6 +20217,8 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>       case IMPLICIT_CONV_EXPR:
>         {
>   	tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
> +	if (type == error_mark_node)
> +	  RETURN (error_mark_node);
>   	tree expr = RECUR (TREE_OPERAND (t, 0));
>   	if (dependent_type_p (type) || type_dependent_expression_p (expr))
>   	  {
> diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-116384.C b/gcc/testsuite/g++.dg/cpp0x/vt-116384.C
> new file mode 100644
> index 00000000000..54d7f0774c5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/vt-116384.C
> @@ -0,0 +1,26 @@
> +// PR c++/116384
> +// { dg-do compile { target c++11 } }
> +
> +namespace a {
> +template <bool, typename> struct c;
> +template <typename> struct d;
> +}
> +namespace e {
> +namespace g {
> +template <typename> using h = void;
> +template <typename, template <typename> class, typename...> struct detector {};
> +template <template <typename> class i, typename... args>
> +struct detector<h<i<args...>>, i, args...>;
> +}
> +template <template <typename> class i, typename... args>
> +using j = g::detector<void, i, args...>;
> +template <bool b, typename k = void> using l = typename a::c<b, k>::m;
> +template <typename> struct conjunction;
> +namespace g {
> +template <typename k> using n = l<conjunction<a::d<k>>::p>;
> +}
> +template <typename k, g::n<k> = true> class o;
> +}
> +struct r;
> +template <typename k> using q = e::o<k>;
> +void s() { e::j<q, r> f; }
> 
> base-commit: c8981bde45d365330a5e7c2e33c8dbaf3495248a