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

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[].

2023-01-19  Jakub Jelinek  <[email protected]>

	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.

Author: jakubjelinek

gcc/cp/call.cc

@@ -5187,7 +5187,7 @@ build_operator_new_call (tree fnname, vec<tree, va_gc> **args,
    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/cp-tree.h

@@ -6599,6 +6599,7 @@ inline tree build_new_op (const op_location_t &loc, enum tree_code code,
   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/tree.cc

@@ -3693,14 +3693,20 @@ build_min_non_dep_op_overload (enum tree_code op,
 {
   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
+      /* For ARRAY_REF, 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.  */
+      || op == ARRAY_REF)
     expected_nargs -= 1;
   if ((op == POSTINCREMENT_EXPR
        || op == POSTDECREMENT_EXPR)
@@ -3715,6 +3721,8 @@ build_min_non_dep_op_overload (enum tree_code op,
   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 +3754,8 @@ build_min_non_dep_op_overload (enum tree_code op,
   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 +3769,15 @@ build_min_non_dep_op_overload (tree non_dep, tree overload, tree object,
   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 +3788,8 @@ build_min_non_dep_op_overload (tree non_dep, tree overload, tree object,
   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

@@ -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

@@ -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 ();
+}