c++: Fix up ICE in build_min_non_dep_op_overload [PR109319]

  Hi!

The following testcase ICEs, because grok_array_decl during
processing_template_decl handling of a non-dependent subscript
emits a -Wcomma-subscript pedwarn, we decide to pass to the
single index argument the index expressions as if it was wrapped
with () around it, but then when preparing it for later instantiation
we don't actually take that into account and ICE on a mismatch of
number of index arguments (the overload expects a single index,
testcase has two index expressions in this case).
For non-dependent subscript which are builtin subscripts we also
emit the same pedwarn and don't ICE, but emit the same pedwarn
again whenever we instantiate it, which is also IMHO undesirable,
it is enough to warn once during parsing the template.

The following patch fixes it by turning even the original index expressions
(those which didn't go through make_args_non_dependent) into a single
index using comma expression(s).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2023-03-30  Jakub Jelinek  <jakub@redhat.com>

	PR c++/109319
	* decl2.cc (grok_array_decl): After emitting a pedwarn for
	-Wcomma-subscript, if processing_template_decl set orig_index_exp
	to compound expr from orig_index_exp_list.

	* g++.dg/cpp23/subscript14.C: New test.


	Jakub
  

On 3/30/23 03:47, Jakub Jelinek wrote:
> Hi!
> 
> The following testcase ICEs, because grok_array_decl during
> processing_template_decl handling of a non-dependent subscript
> emits a -Wcomma-subscript pedwarn, we decide to pass to the
> single index argument the index expressions as if it was wrapped
> with () around it, but then when preparing it for later instantiation
> we don't actually take that into account and ICE on a mismatch of
> number of index arguments (the overload expects a single index,
> testcase has two index expressions in this case).
> For non-dependent subscript which are builtin subscripts we also
> emit the same pedwarn and don't ICE, but emit the same pedwarn
> again whenever we instantiate it, which is also IMHO undesirable,
> it is enough to warn once during parsing the template.
> 
> The following patch fixes it by turning even the original index expressions
> (those which didn't go through make_args_non_dependent) into a single
> index using comma expression(s).
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

> 2023-03-30  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/109319
> 	* decl2.cc (grok_array_decl): After emitting a pedwarn for
> 	-Wcomma-subscript, if processing_template_decl set orig_index_exp
> 	to compound expr from orig_index_exp_list.
> 
> 	* g++.dg/cpp23/subscript14.C: New test.
> 
> --- gcc/cp/decl2.cc.jj	2023-03-20 20:29:34.000000000 +0100
> +++ gcc/cp/decl2.cc	2023-03-29 15:17:14.952173134 +0200
> @@ -474,11 +474,23 @@ grok_array_decl (location_t loc, tree ar
>   					     &overload, complain);
>   		}
>   	      else
> -		/* If it would be valid albeit deprecated expression in C++20,
> -		   just pedwarn on it and treat it as if wrapped in ().  */
> -		pedwarn (loc, OPT_Wcomma_subscript,
> -			 "top-level comma expression in array subscript "
> -			 "changed meaning in C++23");
> +		{
> +		  /* If it would be valid albeit deprecated expression in
> +		     C++20, just pedwarn on it and treat it as if wrapped
> +		     in ().  */
> +		  pedwarn (loc, OPT_Wcomma_subscript,
> +			   "top-level comma expression in array subscript "
> +			   "changed meaning in C++23");
> +		  if (processing_template_decl)
> +		    {
> +		      orig_index_exp
> +			= build_x_compound_expr_from_vec (orig_index_exp_list,
> +							  NULL, complain);
> +		      if (orig_index_exp == error_mark_node)
> +			expr = error_mark_node;
> +		      release_tree_vector (orig_index_exp_list);
> +		    }
> +		}
>   	    }
>   	}
>       }
> @@ -519,6 +531,15 @@ grok_array_decl (location_t loc, tree ar
>   	      return error_mark_node;
>   	    }
>   	  index_exp = idx;
> +	  if (processing_template_decl)
> +	    {
> +	      orig_index_exp
> +		= build_x_compound_expr_from_vec (orig_index_exp_list,
> +						  NULL, complain);
> +	      release_tree_vector (orig_index_exp_list);
> +	      if (orig_index_exp == error_mark_node)
> +		return error_mark_node;
> +	    }
>   	}
>   
>         if (TREE_CODE (TREE_TYPE (index_exp)) == ARRAY_TYPE)
> --- gcc/testsuite/g++.dg/cpp23/subscript14.C.jj	2023-03-29 15:29:46.037076158 +0200
> +++ gcc/testsuite/g++.dg/cpp23/subscript14.C	2023-03-29 15:34:18.645051075 +0200
> @@ -0,0 +1,42 @@
> +// PR c++/109319
> +// { dg-do compile { target c++11 } }
> +// { dg-options "" }
> +
> +struct A { static int &operator[] (int x) { static int a[2]; return a[x]; } };	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
> +struct B { int &operator[] (int x) { static int b[2]; return b[x]; } };
> +int c[2];
> +
> +template <typename T, typename U, typename V>
> +int
> +foo ()
> +{
> +  A a;
> +  ++a[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  B b;			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++b[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++c[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  T d;			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++d[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  U e;			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++e[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  extern V f[2];	// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++f[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  return 0;		// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +}
> +
> +int f[2];
> +
> +int
> +main ()
> +{
> +  A a;
> +  ++a[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  B b;			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++b[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +			// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  ++c[0, 1];		// { dg-warning "top-level comma expression in array subscript changed meaning" "" { target c++23 } }
> +  foo <A, B, int> ();	// { dg-warning "top-level comma expression in array subscript is deprecated" "" { target c++20_only } .-1 }
> +  if (a.operator[] (1) != 3 || b.operator[] (1) != 3 || c[1] != 2 || f[1] != 1)
> +    __builtin_abort ();
> +}
> 
> 	Jakub
>