Re: [PATCH] c++: Fix ICE during explanation of failed __has_unique_object_representation [PR126867]

On 8/18/26 3:45 AM, Jakub Jelinek wrote:
> Hi!
> 
> The following testcase ICEs since r16-5520 added explain
> arguments to type_has_unique_obj_representations and
> record_has_unique_obj_representations.  Most of the location_t
> arguments in that change look correct, either DECL_SOURCE_LOCATION
> of some FIELD_DECL or in type_has_unique_obj_representations use
> loc, which is initialized to
>    location_t loc = input_location;
>    if (tree m = TYPE_MAIN_DECL (t))
>      loc = DECL_SOURCE_LOCATION (m);
> But in record_has_unique_obj_representations we don't have
> a variable like that and t at that point is the RECORD_TYPE
> or UNION_TYPE, so using DECL_SOURCE_LOCATION on it will surely ICE
> in a checking compiler.
> location_of call does the above dances, so it seems easiest to
> call it rather than duplicate it by hand.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/16.3?

OK.
> 2026-08-17  Jakub Jelinek  <[email protected]>
> 
> 	PR c++/126867
> 	* tree.cc (record_has_unique_obj_representations): Use
> 	location_of (const_cast <tree> (t)) rather than
> 	DECL_SOURCE_LOCATION (t).
> 
> 	* g++.dg/cpp1z/has-unique-obj-representations6.C: New test.
> 
> --- gcc/cp/tree.cc.jj	2026-07-24 18:38:54.337025261 +0200
> +++ gcc/cp/tree.cc	2026-08-17 12:32:40.551645418 +0200
> @@ -5274,7 +5274,7 @@ record_has_unique_obj_representations (c
>   	    inform (DECL_SOURCE_LOCATION (last_named_field),
>   		    "padding occurs after %qD", last_named_field);
>   	  else
> -	    inform (DECL_SOURCE_LOCATION (t),
> +	    inform (location_of (const_cast <tree> (t)),
>   		    "%qT has padding and no data fields", t);
>   	}
>         return false;
> --- gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C.jj	2026-08-17 12:37:22.573052447 +0200
> +++ gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C	2026-08-17 12:38:16.061371108 +0200
> @@ -0,0 +1,10 @@
> +// PR c++/126867
> +// { dg-do compile { target c++17 } }
> +
> +template <class T>
> +constexpr bool U = __has_unique_object_representations (T);
> +
> +struct S {};		// { dg-message "'S' does not have unique object representations, because" }
> +			// { dg-message "'S' has padding and no data fields" "" { target *-*-* } .-1 }
> +
> +static_assert (U <S>);	// { dg-error "static assertion failed" }
> 
> 	Jakub
>