c++: Implement C++23 P2589R1 - - static operator[]

  Hi!

As stage1 is very close, here is a patch that implements the static
operator[] paper.
One thing that doesn't work properly is the same problem as I've filed
yesterday for static operator() - PR107624 - that side-effects of
the postfix-expression on which the call or subscript operator are
applied are thrown away, I assume we have to add them into COMPOUND_EXPR
somewhere after we find out that the we've chosen a static member function
operator.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
provided the paper gets voted into C++23?

2022-11-11  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-cppbuiltin.cc (c_cpp_builtins): Bump C++23
	__cpp_multidimensional_subscript macro value to 202211L.
gcc/cp/
	* decl.cc (grok_op_properties): Implement C++23 P2589R1
	- static operator[].  Handle operator[] similarly to operator()
	- allow static member functions, but pedwarn on it for C++20 and
	older.  Unlike operator(), perform rest of checks on it though for
	C++20.
	* call.cc (add_operator_candidates): For operator[] with class
	typed first parameter, pass that parameter as first_arg and
	an adjusted arglist without that parameter.
gcc/testsuite/
	* g++.dg/cpp23/subscript9.C: New test.
	* g++.dg/cpp23/feat-cxx2b.C: Expect a newer
	__cpp_multidimensional_subscript value.
	* g++.old-deja/g++.bugs/900210_10.C: Don't expect an error
	for C++23 or later.
	

	Jakub
  

On 11/10/22 21:40, Jakub Jelinek wrote:
> Hi!
> 
> As stage1 is very close, here is a patch that implements the static
> operator[] paper.
> One thing that doesn't work properly is the same problem as I've filed
> yesterday for static operator() - PR107624 - that side-effects of
> the postfix-expression on which the call or subscript operator are
> applied are thrown away, I assume we have to add them into COMPOUND_EXPR
> somewhere after we find out that the we've chosen a static member function
> operator.

Indeed.  The code in build_new_method_call for this case has the comment

               /* In an expression of the form `a->f()' where `f' turns 

                  out to be a static member function, `a' is 

                  none-the-less evaluated.  */

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
> provided the paper gets voted into C++23?

OK.

> 2022-11-11  Jakub Jelinek  <jakub@redhat.com>
> 
> gcc/c-family/
> 	* c-cppbuiltin.cc (c_cpp_builtins): Bump C++23
> 	__cpp_multidimensional_subscript macro value to 202211L.
> gcc/cp/
> 	* decl.cc (grok_op_properties): Implement C++23 P2589R1
> 	- static operator[].  Handle operator[] similarly to operator()
> 	- allow static member functions, but pedwarn on it for C++20 and
> 	older.  Unlike operator(), perform rest of checks on it though for
> 	C++20.
> 	* call.cc (add_operator_candidates): For operator[] with class
> 	typed first parameter, pass that parameter as first_arg and
> 	an adjusted arglist without that parameter.
> gcc/testsuite/
> 	* g++.dg/cpp23/subscript9.C: New test.
> 	* g++.dg/cpp23/feat-cxx2b.C: Expect a newer
> 	__cpp_multidimensional_subscript value.
> 	* g++.old-deja/g++.bugs/900210_10.C: Don't expect an error
> 	for C++23 or later.
> 	
> --- gcc/c-family/c-cppbuiltin.cc.jj	2022-10-14 09:35:56.182990495 +0200
> +++ gcc/c-family/c-cppbuiltin.cc	2022-11-10 22:29:12.539832741 +0100
> @@ -1075,7 +1075,7 @@ c_cpp_builtins (cpp_reader *pfile)
>   	  cpp_define (pfile, "__cpp_size_t_suffix=202011L");
>   	  cpp_define (pfile, "__cpp_if_consteval=202106L");
>   	  cpp_define (pfile, "__cpp_constexpr=202110L");
> -	  cpp_define (pfile, "__cpp_multidimensional_subscript=202110L");
> +	  cpp_define (pfile, "__cpp_multidimensional_subscript=202211L");
>   	  cpp_define (pfile, "__cpp_named_character_escapes=202207L");
>   	  cpp_define (pfile, "__cpp_static_call_operator=202207L");
>   	  cpp_define (pfile, "__cpp_implicit_move=202207L");
> --- gcc/cp/decl.cc.jj	2022-11-08 09:54:37.313400209 +0100
> +++ gcc/cp/decl.cc	2022-11-10 21:26:06.891359343 +0100
> @@ -15377,7 +15377,15 @@ grok_op_properties (tree decl, bool comp
>        an enumeration, or a reference to an enumeration.  13.4.0.6 */
>     if (! methodp || DECL_STATIC_FUNCTION_P (decl))
>       {
> -      if (operator_code == CALL_EXPR)
> +      if (operator_code == TYPE_EXPR
> +	  || operator_code == COMPONENT_REF
> +	  || operator_code == NOP_EXPR)
> +	{
> +	  error_at (loc, "%qD must be a non-static member function", decl);
> +	  return false;
> +	}
> +
> +      if (operator_code == CALL_EXPR || operator_code == ARRAY_REF)
>   	{
>   	  if (! DECL_STATIC_FUNCTION_P (decl))
>   	    {
> @@ -15386,52 +15394,41 @@ grok_op_properties (tree decl, bool comp
>   	    }
>   	  if (cxx_dialect < cxx23
>   	      /* For lambdas we diagnose static lambda specifier elsewhere.  */
> -	      && ! LAMBDA_FUNCTION_P (decl)
> +	      && (operator_code == ARRAY_REF || ! LAMBDA_FUNCTION_P (decl))
>   	      /* For instantiations, we have diagnosed this already.  */
>   	      && ! DECL_USE_TEMPLATE (decl))
>   	    pedwarn (loc, OPT_Wc__23_extensions, "%qD may be a static member "
> -	      "function only with %<-std=c++23%> or %<-std=gnu++23%>", decl);
> -	  /* There are no further restrictions on the arguments to an
> -	     overloaded "operator ()".  */
> -	  return true;
> -	}
> -      if (operator_code == TYPE_EXPR
> -	  || operator_code == COMPONENT_REF
> -	  || operator_code == ARRAY_REF
> -	  || operator_code == NOP_EXPR)
> -	{
> -	  error_at (loc, "%qD must be a non-static member function", decl);
> -	  return false;
> +		     "function only with %<-std=c++23%> or %<-std=gnu++23%>",
> +		     decl);
>   	}
> -
> -      if (DECL_STATIC_FUNCTION_P (decl))
> +      else if (DECL_STATIC_FUNCTION_P (decl))
>   	{
>   	  error_at (loc, "%qD must be either a non-static member "
>   		    "function or a non-member function", decl);
>   	  return false;
>   	}
> -
> -      for (tree arg = argtypes; ; arg = TREE_CHAIN (arg))
> -	{
> -	  if (!arg || arg == void_list_node)
> -	    {
> -	      if (complain)
> -		error_at(loc, "%qD must have an argument of class or "
> -			 "enumerated type", decl);
> -	      return false;
> -	    }
> +      else
> +	for (tree arg = argtypes; ; arg = TREE_CHAIN (arg))
> +	  {
> +	    if (!arg || arg == void_list_node)
> +	      {
> +		if (complain)
> +		  error_at (loc, "%qD must have an argument of class or "
> +			    "enumerated type", decl);
> +		return false;
> +	      }
>         
> -	  tree type = non_reference (TREE_VALUE (arg));
> -	  if (type == error_mark_node)
> -	    return false;
> -	
> -	  /* MAYBE_CLASS_TYPE_P, rather than CLASS_TYPE_P, is used
> -	     because these checks are performed even on template
> -	     functions.  */
> -	  if (MAYBE_CLASS_TYPE_P (type)
> -	      || TREE_CODE (type) == ENUMERAL_TYPE)
> -	    break;
> -	}
> +	    tree type = non_reference (TREE_VALUE (arg));
> +	    if (type == error_mark_node)
> +	      return false;
> +
> +	    /* MAYBE_CLASS_TYPE_P, rather than CLASS_TYPE_P, is used
> +	       because these checks are performed even on template
> +	       functions.  */
> +	    if (MAYBE_CLASS_TYPE_P (type)
> +		|| TREE_CODE (type) == ENUMERAL_TYPE)
> +	      break;
> +	  }
>       }
>   
>     if (operator_code == CALL_EXPR)
> --- gcc/cp/call.cc.jj	2022-11-08 09:54:37.283400616 +0100
> +++ gcc/cp/call.cc	2022-11-10 22:26:38.096936491 +0100
> @@ -6589,12 +6589,36 @@ add_operator_candidates (z_candidate **c
>         if (fns == error_mark_node)
>   	return error_mark_node;
>         if (fns)
> -	add_candidates (BASELINK_FUNCTIONS (fns),
> -			NULL_TREE, arglist, NULL_TREE,
> -			NULL_TREE, false,
> -			BASELINK_BINFO (fns),
> -			BASELINK_ACCESS_BINFO (fns),
> -			flags, candidates, complain);
> +	{
> +	  if (code == ARRAY_REF)
> +	    {
> +	      vec<tree,va_gc> *restlist = make_tree_vector ();
> +	      for (unsigned i = 1; i < nargs; ++i)
> +		vec_safe_push (restlist, (*arglist)[i]);
> +	      z_candidate *save_cand = *candidates;
> +	      add_candidates (BASELINK_FUNCTIONS (fns),
> +			      (*arglist)[0], restlist, NULL_TREE,
> +			      NULL_TREE, false,
> +			      BASELINK_BINFO (fns),
> +			      BASELINK_ACCESS_BINFO (fns),
> +			      flags, candidates, complain);
> +	      /* Release the vec if we didn't add a candidate that uses it.  */
> +	      for (z_candidate *c = *candidates; c != save_cand; c = c->next)
> +		if (c->args == restlist)
> +		  {
> +		    restlist = NULL;
> +		    break;
> +		  }
> +	      release_tree_vector (restlist);
> +	    }
> +	  else
> +	    add_candidates (BASELINK_FUNCTIONS (fns),
> +			    NULL_TREE, arglist, NULL_TREE,
> +			    NULL_TREE, false,
> +			    BASELINK_BINFO (fns),
> +			    BASELINK_ACCESS_BINFO (fns),
> +			    flags, candidates, complain);
> +	}
>       }
>     /* Per [over.match.oper]3.2, if no operand has a class type, then
>        only non-member functions that have type T1 or reference to
> --- gcc/testsuite/g++.dg/cpp23/subscript9.C.jj	2022-11-10 21:06:58.155974655 +0100
> +++ gcc/testsuite/g++.dg/cpp23/subscript9.C	2022-11-11 08:26:26.502445107 +0100
> @@ -0,0 +1,29 @@
> +// P2589R1
> +// { dg-do run { target c++23 } }
> +
> +extern "C" void abort ();
> +
> +struct S
> +{
> +  S () {};
> +  static int &operator[] () { return a[0]; }
> +  static int &operator[] (int x) { return a[x]; }
> +  static int &operator[] (int x, long y) { return a[x + y * 8]; }
> +  static int a[64];
> +};
> +int S::a[64];
> +
> +int
> +main ()
> +{
> +  S s;
> +  for (int i = 0; i < 64; i++)
> +    s.a[i] = 64 - i;
> +  if (s[] != 64 || s[3] != 61 || s[4, 5] != 20)
> +    abort ();
> +  s[]++;
> +  s[42]++;
> +  ++s[3, 2];
> +  if (s.a[0] != 65 || s.a[42] != 23 || s.a[19] != 46)
> +    abort ();
> +}
> --- gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C.jj	2022-10-06 08:56:28.785125656 +0200
> +++ gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C	2022-11-10 22:31:49.187698955 +0100
> @@ -556,8 +556,8 @@
>   
>   #ifndef __cpp_multidimensional_subscript
>   #  error "__cpp_multidimensional_subscript"
> -#elif __cpp_multidimensional_subscript != 202110
> -#  error "__cpp_multidimensional_subscript != 202110"
> +#elif __cpp_multidimensional_subscript != 202211
> +#  error "__cpp_multidimensional_subscript != 202211"
>   #endif
>   
>   #ifndef __cpp_named_character_escapes
> --- gcc/testsuite/g++.old-deja/g++.bugs/900210_10.C.jj	2020-01-14 20:02:47.021606269 +0100
> +++ gcc/testsuite/g++.old-deja/g++.bugs/900210_10.C	2022-11-11 01:41:13.840971578 +0100
> @@ -9,7 +9,7 @@
>   // keywords: operator[], static function members
>   
>   struct struct0 {
> -  static int operator[] ();		/* { dg-error "" } */
> +  static int operator[] ();		/* { dg-error "" "" { target c++20_down } } */
>   };
>   
>   int main () { return 0; }
> 
> 	Jakub
>