Re: C++ PATCH for c++/85847, ICE with template_id_expr in new()

[Jason Merrill <jason at redhat dot com>]

On Wed, May 23, 2018 at 9:46 AM, Marek Polacek <polacek@redhat.com> wrote:
> The diagnostic code in build_new{,_1} was using maybe_constant_value to fold
> the array length, but that breaks while parsing a template, because we might
> then leak template codes to the constexpr machinery.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk/8?
>
> 2018-05-23  Marek Polacek  <polacek@redhat.com>
>
>         PR c++/85847
>         * init.c (build_new_1): Use fold_non_dependent_expr.
>         (build_new): Likewise.
>
>         * g++.dg/cpp0x/new3.C: New test.
>
> @@ -2860,7 +2860,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
>    /* Lots of logic below. depends on whether we have a constant number of
>       elements, so go ahead and fold it now.  */
>    if (outer_nelts)
> -    outer_nelts = maybe_constant_value (outer_nelts);
> +    outer_nelts = fold_non_dependent_expr (outer_nelts);

If outer_nelts is non-constant, this will mean that it ends up
instantiated but still non-constant, which can lead to problems when
the result is used in building up other expressions.

I think we want to put the result of folding in a separate variable
for use with things that want to know about a constant size, and keep
the original outer_nelts for use in building outer_nelts_check.

>        /* Try to determine the constant value only for the purposes
>          of the diagnostic below but continue to use the original
>          value and handle const folding later.  */
> -      const_tree cst_nelts = maybe_constant_value (nelts);
> +      const_tree cst_nelts = fold_non_dependent_expr (nelts);

...like we do here.

Jason