[C++ PATCH] Don't ignore side-effects on decltype(nullptr) typed args passed to ... (PR c++/92992)

[Marek Polacek]

On Thu, Dec 19, 2019 at 12:40:12AM +0100, Jakub Jelinek wrote:
> Hi!
> 
> While looking at PR92666, I've spotted a wrong-code issue where we ignore
> any side-effects on arguments passed to ellipsis if they have
> decltype(nullptr) type.
> 
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk and release branches?

Looks fine to me, and reminds me of c++/90473.

> 2019-12-19  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/92992
> 	* call.c (convert_arg_to_ellipsis): For decltype(nullptr) arguments
> 	that have side-effects use cp_build_compound_expr.
> 
> 	* g++.dg/cpp0x/nullptr45.C: New test.
> 
> --- gcc/cp/call.c.jj	2019-12-17 10:19:51.013282361 +0100
> +++ gcc/cp/call.c	2019-12-18 18:23:01.441357443 +0100
> @@ -7822,7 +7822,12 @@ convert_arg_to_ellipsis (tree arg, tsubs
>        arg = convert_to_real_nofold (double_type_node, arg);
>      }
>    else if (NULLPTR_TYPE_P (arg_type))
> -    arg = null_pointer_node;
> +    {
> +      if (TREE_SIDE_EFFECTS (arg))
> +	arg = cp_build_compound_expr (arg, null_pointer_node, complain);
> +      else
> +	arg = null_pointer_node;
> +    }

FWIW, I was wondering if this should be nullptr_node instead but
http://eel.is/c++draft/expr.call#12.sentence-5 says "An argument that has
type cv std::nullptr_­t is converted to type void*."  Perhaps there should
be a comment to that effect...

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Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA