c++: Fix up handling of non-dependent subscript with static operator[] [PR108437]

  Hi!

As the following testcases shows, when adding static operator[]
support I've missed that the 2 build_min_non_dep_op_overload functions
need to be adjusted.  The first one we only use for the single index
case, but as cp_tree_code_length (ARRAY_REF) is 2, we were running
into an assertion there which compared nargs and expected_nargs.
For ARRAY_REF, the operator[] is either a non-static member or newly
static member, never out of class and for the static member case
if user uses single index the operator[] needs to have a single
argument as well, but the function is called with 2 - the object
it is invoked on and the index.  We need to evaluate side-effects
of the object and use just a single argument in the call - the index.
The other build_min_non_dep_op_overload overload has been added
solely for ARRAY_REF - CALL_EXPR is the other operator that accepts
variable number of operands but that one goes through different
routines.  There we asserted it is a METHOD_TYPE, so again
we shouldn't assert that but handle the case when it is not one
by making sure object's side-effects are evaluated if needed and
passing all the index arguments to the static operator[].

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

2023-01-19  Jakub Jelinek  <jakub@redhat.com>

	PR c++/108437
	* cp-tree.h (keep_unused_object_arg): Declare.
	* call.cc (keep_unused_object_arg): No longer static.
	* tree.cc (build_min_non_dep_op_overload): Handle ARRAY_REF
	with overload being static member function.

	* g++.dg/cpp23/subscript12.C: New test.
	* g++.dg/cpp23/subscript13.C: New test.


	Jakub
  

On 1/19/23 03:52, Jakub Jelinek wrote:
> Hi!
> 
> As the following testcases shows, when adding static operator[]
> support I've missed that the 2 build_min_non_dep_op_overload functions
> need to be adjusted.  The first one we only use for the single index
> case, but as cp_tree_code_length (ARRAY_REF) is 2, we were running
> into an assertion there which compared nargs and expected_nargs.

> For ARRAY_REF, the operator[] is either a non-static member or newly
> static member, never out of class and for the static member case
> if user uses single index the operator[] needs to have a single
> argument as well, but the function is called with 2 - the object
> it is invoked on and the index.

This should be in a comment for the new special handling of ARRAY_REF.

OK with that change.

> We need to evaluate side-effects
> of the object and use just a single argument in the call - the index.
> The other build_min_non_dep_op_overload overload has been added
> solely for ARRAY_REF - CALL_EXPR is the other operator that accepts
> variable number of operands but that one goes through different
> routines.  There we asserted it is a METHOD_TYPE, so again
> we shouldn't assert that but handle the case when it is not one
> by making sure object's side-effects are evaluated if needed and
> passing all the index arguments to the static operator[].
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> 2023-01-19  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/108437
> 	* cp-tree.h (keep_unused_object_arg): Declare.
> 	* call.cc (keep_unused_object_arg): No longer static.
> 	* tree.cc (build_min_non_dep_op_overload): Handle ARRAY_REF
> 	with overload being static member function.
> 
> 	* g++.dg/cpp23/subscript12.C: New test.
> 	* g++.dg/cpp23/subscript13.C: New test.
> 
> --- gcc/cp/cp-tree.h.jj	2023-01-16 11:52:16.067734300 +0100
> +++ gcc/cp/cp-tree.h	2023-01-18 16:47:55.258697839 +0100
> @@ -6599,6 +6599,7 @@ inline tree build_new_op (const op_locat
>     return build_new_op (loc, code, flags, arg1, arg2, NULL_TREE, NULL_TREE,
>   		       NULL, complain);
>   }
> +extern tree keep_unused_object_arg		(tree, tree, tree);
>   extern tree build_op_call			(tree, vec<tree, va_gc> **,
>   						 tsubst_flags_t);
>   extern tree build_op_subscript			(const op_location_t &, tree,
> --- gcc/cp/call.cc.jj	2023-01-16 11:52:16.059734418 +0100
> +++ gcc/cp/call.cc	2023-01-18 16:48:02.966586328 +0100
> @@ -5187,7 +5187,7 @@ build_operator_new_call (tree fnname, ve
>      or static operator(), in which cases the source expression
>      would be `obj[...]' or `obj(...)'.  */
>   
> -static tree
> +tree
>   keep_unused_object_arg (tree result, tree obj, tree fn)
>   {
>     if (result == NULL_TREE
> --- gcc/cp/tree.cc.jj	2023-01-16 11:52:16.093733917 +0100
> +++ gcc/cp/tree.cc	2023-01-18 17:01:08.937242864 +0100
> @@ -3693,14 +3693,14 @@ build_min_non_dep_op_overload (enum tree
>   {
>     va_list p;
>     int nargs, expected_nargs;
> -  tree fn, call;
> +  tree fn, call, obj = NULL_TREE;
>   
>     non_dep = extract_call_expr (non_dep);
>   
>     nargs = call_expr_nargs (non_dep);
>   
>     expected_nargs = cp_tree_code_length (op);
> -  if (TREE_CODE (TREE_TYPE (overload)) == METHOD_TYPE)
> +  if (TREE_CODE (TREE_TYPE (overload)) == METHOD_TYPE || op == ARRAY_REF)
>       expected_nargs -= 1;
>     if ((op == POSTINCREMENT_EXPR
>          || op == POSTDECREMENT_EXPR)
> @@ -3715,6 +3715,8 @@ build_min_non_dep_op_overload (enum tree
>     if (TREE_CODE (TREE_TYPE (overload)) == FUNCTION_TYPE)
>       {
>         fn = overload;
> +      if (op == ARRAY_REF)
> +	obj = va_arg (p, tree);
>         for (int i = 0; i < nargs; i++)
>   	{
>   	  tree arg = va_arg (p, tree);
> @@ -3746,6 +3748,8 @@ build_min_non_dep_op_overload (enum tree
>     CALL_EXPR_ORDERED_ARGS (call_expr) = CALL_EXPR_ORDERED_ARGS (non_dep);
>     CALL_EXPR_REVERSE_ARGS (call_expr) = CALL_EXPR_REVERSE_ARGS (non_dep);
>   
> +  if (obj)
> +    return keep_unused_object_arg (call, obj, overload);
>     return call;
>   }
>   
> @@ -3759,11 +3763,15 @@ build_min_non_dep_op_overload (tree non_
>     non_dep = extract_call_expr (non_dep);
>   
>     unsigned int nargs = call_expr_nargs (non_dep);
> -  gcc_assert (TREE_CODE (TREE_TYPE (overload)) == METHOD_TYPE);
> -  tree binfo = TYPE_BINFO (TREE_TYPE (object));
> -  tree method = build_baselink (binfo, binfo, overload, NULL_TREE);
> -  tree fn = build_min (COMPONENT_REF, TREE_TYPE (overload),
> -		       object, method, NULL_TREE);
> +  tree fn = overload;
> +  if (TREE_CODE (TREE_TYPE (overload)) == METHOD_TYPE)
> +    {
> +      tree binfo = TYPE_BINFO (TREE_TYPE (object));
> +      tree method = build_baselink (binfo, binfo, overload, NULL_TREE);
> +      fn = build_min (COMPONENT_REF, TREE_TYPE (overload),
> +		      object, method, NULL_TREE);
> +      object = NULL_TREE;
> +    }
>     gcc_assert (vec_safe_length (args) == nargs);
>   
>     tree call = build_min_non_dep_call_vec (non_dep, fn, args);
> @@ -3774,6 +3782,8 @@ build_min_non_dep_op_overload (tree non_
>     CALL_EXPR_ORDERED_ARGS (call_expr) = CALL_EXPR_ORDERED_ARGS (non_dep);
>     CALL_EXPR_REVERSE_ARGS (call_expr) = CALL_EXPR_REVERSE_ARGS (non_dep);
>   
> +  if (object)
> +    return keep_unused_object_arg (call, object, overload);
>     return call;
>   }
>   
> --- gcc/testsuite/g++.dg/cpp23/subscript12.C.jj	2023-01-18 17:15:04.963153521 +0100
> +++ gcc/testsuite/g++.dg/cpp23/subscript12.C	2023-01-18 17:14:40.816503156 +0100
> @@ -0,0 +1,34 @@
> +// PR c++/108437
> +// { dg-do run { target c++23 } }
> +
> +struct S { static int &operator[] (int x) { static int a[2]; return a[x]; } };
> +struct U { static int &operator[] (int x, int y, int z) { static int a[2]; return a[x + y + z]; } };
> +struct V { static int &operator[] () { static int a; return a; } };
> +
> +template <class T, class W, class X> void
> +foo ()
> +{
> +  S s;
> +  s[0]++;
> +  T t;
> +  t[0]++;
> +  U u;
> +  u[0, 0, 0]++;
> +  V v;
> +  v[]++;
> +  W w;
> +  w[0, 0, 0]++;
> +  X x;
> +  x[]++;
> +}
> +
> +int
> +main ()
> +{
> +  S::operator[] (0) = 1;
> +  U::operator[] (0, 0, 0) = 2;
> +  V::operator[] () = 3;
> +  foo <S, U, V> ();
> +  if (S::operator[] (0) != 3 || U::operator[] (0, 0, 0) != 4 || V::operator[] () != 5)
> +    __builtin_abort ();
> +}
> --- gcc/testsuite/g++.dg/cpp23/subscript13.C.jj	2023-01-18 17:15:08.110107955 +0100
> +++ gcc/testsuite/g++.dg/cpp23/subscript13.C	2023-01-18 17:14:55.833285718 +0100
> @@ -0,0 +1,43 @@
> +// PR c++/108437
> +// { dg-do run { target c++23 } }
> +
> +struct S { static int &operator[] (int x) { static int a[2]; return a[x]; } };
> +struct U { static int &operator[] (int x, int y, int z) { static int a[2]; return a[x + y + z]; } };
> +struct V { static int &operator[] () { static int a; return a; } };
> +int cnt;
> +
> +template <typename T>
> +T &
> +bar (T &x)
> +{
> +  ++cnt;
> +  return x;
> +}
> +
> +template <class T, class W, class X> void
> +foo ()
> +{
> +  S s;
> +  bar (s)[0]++;
> +  T t;
> +  bar (t)[0]++;
> +  U u;
> +  bar (u)[0, 0, 0]++;
> +  V v;
> +  bar (v)[]++;
> +  W w;
> +  bar (w)[0, 0, 0]++;
> +  X x;
> +  bar (x)[]++;
> +}
> +
> +int
> +main ()
> +{
> +  S::operator[] (0) = 1;
> +  U::operator[] (0, 0, 0) = 2;
> +  V::operator[] () = 3;
> +  foo <S, U, V> ();
> +  if (S::operator[] (0) != 3 || U::operator[] (0, 0, 0) != 4 || V::operator[] () != 5 || cnt != 6)
> +    __builtin_abort ();
> +}
> 
> 	Jakub
>