c++: adjust accessor fixits for explicit object parm

In a couple of places in the xobj patch I noticed that is_this_parameter
probably wanted to change to is_object_parameter; this implements that and
does the additional adjustments needed to make the accessor fixits handle
xobj parms.

gcc/cp/ChangeLog:

	* semantics.cc (is_object_parameter): New.
	* cp-tree.h (is_object_parameter): Declare.
	* call.cc (maybe_warn_class_memaccess): Use it.
	* search.cc (field_access_p): Use it.
	(class_of_object_parm): New.
	(field_accessor_p): Adjust for explicit object parms.

gcc/testsuite/ChangeLog:

	* g++.dg/torture/accessor-fixits-9-xobj.C: New test.

4 files changed, 30 insertions, 7 deletions

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 7d3d676..191664e 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -10815,8 +10815,7 @@ maybe_warn_class_memaccess (location_t loc, tree fndecl,
      be more permissive.  */
   if (current_function_decl
       && DECL_OBJECT_MEMBER_FUNCTION_P (current_function_decl)
-      /* ??? is_object_parameter?  */
-      && is_this_parameter (tree_strip_nop_conversions (dest)))
+      && is_object_parameter (tree_strip_nop_conversions (dest)))
     {
       tree ctx = DECL_CONTEXT (current_function_decl);
       bool special = same_type_ignoring_top_level_qualifiers_p (ctx, desttype);
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index dbc7177..f3f265a 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7784,6 +7784,7 @@ extern void finish_handler_parms		(tree, tree);
 extern void finish_handler			(tree);
 extern void finish_cleanup			(tree, tree);
 extern bool is_this_parameter                   (tree);
+extern bool is_object_parameter                 (tree);
 
 enum {
   BCS_NORMAL = 0,
diff --git a/gcc/cp/search.cc b/gcc/cp/search.cc
index dc76714..2b4ed5d 100644
--- a/gcc/cp/search.cc
+++ b/gcc/cp/search.cc
@@ -1737,8 +1737,7 @@ field_access_p (tree component_ref, tree field_decl, tree field_type)
     return false;
 
   tree ptr = STRIP_NOPS (TREE_OPERAND (indirect_ref, 0));
-  /* ??? is_object_parameter?  */
-  if (!is_this_parameter (ptr))
+  if (!is_object_parameter (ptr))
     return false;
 
   /* Must access the correct field.  */
@@ -1818,6 +1817,17 @@ reference_accessor_p (tree init_expr, tree field_decl, tree field_type,
   return true;
 }
 
+/* Return the class of the `this' or explicit object parameter of FN.  */
+
+static tree
+class_of_object_parm (const_tree fn)
+{
+  tree fntype = TREE_TYPE (fn);
+  if (DECL_XOBJ_MEMBER_FUNCTION_P (fn))
+    return non_reference (TREE_VALUE (TYPE_ARG_TYPES (fntype)));
+  return class_of_this_parm (fntype);
+}
+
 /* Return true if FN is an accessor method for FIELD_DECL.
    i.e. a method of the form { return FIELD; }, with no
    conversions.
@@ -1835,15 +1845,14 @@ field_accessor_p (tree fn, tree field_decl, bool const_p)
   if (TREE_CODE (field_decl) != FIELD_DECL)
     return false;
 
-  tree fntype = TREE_TYPE (fn);
-  if (TREE_CODE (fntype) != METHOD_TYPE)
+  if (!DECL_OBJECT_MEMBER_FUNCTION_P (fn))
     return false;
 
   /* If the field is accessed via a const "this" argument, verify
      that the "this" parameter is const.  */
   if (const_p)
     {
-      tree this_class = class_of_this_parm (fntype);
+      tree this_class = class_of_object_parm (fn);
       if (!TYPE_READONLY (this_class))
 	return false;
     }
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 86e1adf..3299e27 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12832,6 +12832,20 @@ is_this_parameter (tree t)
   return true;
 }
 
+/* As above, or a C++23 explicit object parameter.  */
+
+bool
+is_object_parameter (tree t)
+{
+  if (is_this_parameter (t))
+    return true;
+  if (TREE_CODE (t) != PARM_DECL)
+    return false;
+  tree ctx = DECL_CONTEXT (t);
+  return (ctx && DECL_XOBJ_MEMBER_FUNCTION_P (ctx)
+	  && t == DECL_ARGUMENTS (ctx));
+}
+
 /* Insert the deduced return type for an auto function.  */
 
 void