Re: [PATCH] c++, v2: Fix up mangling ICE with void{} [PR106863]

[Jason Merrill <jason@redhat.com>]

On 10/20/22 10:38, Jakub Jelinek wrote:
> On Thu, Oct 20, 2022 at 10:19:59AM -0400, Jason Merrill wrote:
>> I think in a template we want the same early-return behavior as in the
>> processing_template_decl block farther down in the function: specifically,
>> we want to return a CONSTRUCTOR (for which COMPOUND_LITERAL_P is true), so
>> it mangles as void{} rather than void().
> 
> So like this then?
> 
> 2022-10-20  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/106863
> 	* semantics.cc (finish_compound_literal): For void{}, if
> 	processing_template_decl return a COMPOUND_LITERAL_P
> 	CONSTRUCTOR rather than void_node.
> 
> 	* g++.dg/cpp0x/dr2351-2.C: New test.
> 
> --- gcc/cp/semantics.cc.jj	2022-10-19 01:14:58.343483355 +0200
> +++ gcc/cp/semantics.cc	2022-10-20 16:32:30.605571968 +0200
> @@ -3164,7 +3164,16 @@ finish_compound_literal (tree type, tree
>       {
>         /* DR2351 */
>         if (VOID_TYPE_P (type) && CONSTRUCTOR_NELTS (compound_literal) == 0)
> -	return void_node;
> +	{
> +	  if (!processing_template_decl)
> +	    return void_node;
> +	  TREE_TYPE (compound_literal) = type;
> +	  TREE_HAS_CONSTRUCTOR (compound_literal) = 1;
> +	  CONSTRUCTOR_IS_DEPENDENT (compound_literal) = 0;
> +	  if (fcl_context == fcl_c99)
> +	    CONSTRUCTOR_C99_COMPOUND_LITERAL (compound_literal) = 1;

I don't think it's possible to get here with the C compound literal 
syntax, so you can drop these two lines.  OK with that change.

> +	  return compound_literal;
> +	}
>         else if (VOID_TYPE_P (type)
>   	       && processing_template_decl
>   	       && maybe_zero_constructor_nelts (compound_literal))
> --- gcc/testsuite/g++.dg/cpp0x/dr2351-2.C.jj	2022-10-20 16:27:19.645821706 +0200
> +++ gcc/testsuite/g++.dg/cpp0x/dr2351-2.C	2022-10-20 16:27:19.645821706 +0200
> @@ -0,0 +1,16 @@
> +// DR2351
> +// { dg-do compile { target c++11 } }
> +
> +void bar (int);
> +
> +template <typename T>
> +auto foo (T t) -> decltype (bar (t), void{})
> +{
> +  return bar (t);
> +}
> +
> +int
> +main ()
> +{
> +  foo (0);
> +}
> 
> 
> 	Jakub
>