[c++] introduce {class,type}_of_this functions

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index f5bd521..7ad9279 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -1146,8 +1146,8 @@  standard_conversion (tree to, tree from, tree expr, bool c_cast_p,
     {
       tree fromfn = TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (from));
       tree tofn = TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (to));
-      tree fbase = TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (fromfn)));
-      tree tbase = TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (tofn)));
+      tree fbase = class_of_this (fromfn);
+      tree tbase = class_of_this (tofn);
 
       if (!DERIVED_FROM_P (fbase, tbase)
 	  || !same_type_p (TREE_TYPE (fromfn), TREE_TYPE (tofn))
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 9d13393..d410e02 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4616,6 +4616,24 @@  struct GTY(()) tinst_level {
   bool in_system_header_p;
 };
 
+/* Return the type of the `this' parameter of FNTYPE.  */
+
+static inline tree
+type_of_this (const_tree fntype)
+{
+  function_args_iterator iter;
+  function_args_iter_init (&iter, fntype);
+  return function_args_iter_cond (&iter);
+}
+
+/* Return the class of the `this' parameter of FNTYPE.  */
+
+static inline tree
+class_of_this (const_tree fntype)
+{
+  return TREE_TYPE (type_of_this (fntype));
+}
+
 /* A parameter list indicating for a function with no parameters,
    e.g  "int f(void)".  */
 extern cp_parameter_declarator *no_parameters;
diff --git a/gcc/cp/cxx-pretty-print.c b/gcc/cp/cxx-pretty-print.c
index bd0381b..eeb6d07 100644
--- a/gcc/cp/cxx-pretty-print.c
+++ b/gcc/cp/cxx-pretty-print.c
@@ -1363,7 +1363,7 @@  pp_cxx_ptr_operator (cxx_pretty_printer *pp, tree t)
 static inline tree
 pp_cxx_implicit_parameter_type (tree mf)
 {
-  return TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (mf))));
+  return class_of_this (TREE_TYPE (mf));
 }
 
 /*
@@ -1652,8 +1652,7 @@  pp_cxx_direct_abstract_declarator (cxx_pretty_printer *pp, tree t)
       if (TREE_CODE (t) == METHOD_TYPE)
 	{
 	  pp_base (pp)->padding = pp_before;
-	  pp_cxx_cv_qualifier_seq
-	    (pp, TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (t))));
+	  pp_cxx_cv_qualifier_seq (pp, class_of_this (t));
 	}
       pp_cxx_exception_specification (pp, t);
       break;
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 3622c2c..962dd22 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6924,7 +6924,7 @@  build_this_parm (tree type, cp_cv_quals quals)
   tree parm;
   cp_cv_quals this_quals;
 
-  this_type = TREE_VALUE (TYPE_ARG_TYPES (type));
+  this_type = type_of_this (type);
   /* The `this' parameter is implicitly `const'; it cannot be
      assigned to.  */
   this_quals = (quals & TYPE_QUAL_RESTRICT) | TYPE_QUAL_CONST;
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index ef8de31..02d9fd9 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -161,8 +161,7 @@  change_return_type (tree new_ret, tree fntype)
     }
   else
     newtype = build_method_type_directly
-      (TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (fntype))),
-       new_ret, TREE_CHAIN (args));
+      (class_of_this (fntype), new_ret, TREE_CHAIN (args));
   if (raises)
     newtype = build_exception_variant (newtype, raises);
   if (attrs)
@@ -1249,8 +1248,7 @@  cp_reconstruct_complex_type (tree type, tree bottom)
 	 so we must compensate by getting rid of it.  */
       outer
 	= build_method_type_directly
-	    (TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (type))),
-	     inner,
+	    (class_of_this (type), inner,
 	     TREE_CHAIN (TYPE_ARG_TYPES (type)));
     }
   else if (TREE_CODE (type) == OFFSET_TYPE)
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index fce7403..b364824 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -794,8 +794,7 @@  dump_type_suffix (tree t, int flags)
 	dump_parameters (arg, flags & ~TFF_FUNCTION_DEFAULT_ARGUMENTS);
 
 	if (TREE_CODE (t) == METHOD_TYPE)
-	  pp_cxx_cv_qualifier_seq
-	    (cxx_pp, TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (t))));
+	  pp_cxx_cv_qualifier_seq (cxx_pp, class_of_this (t));
 	else
 	  pp_cxx_cv_qualifier_seq (cxx_pp, t);
 	dump_exception_spec (TYPE_RAISES_EXCEPTIONS (t), flags);
@@ -1360,8 +1359,7 @@  dump_function_decl (tree t, int flags)
       if (TREE_CODE (fntype) == METHOD_TYPE)
 	{
 	  pp_base (cxx_pp)->padding = pp_before;
-	  pp_cxx_cv_qualifier_seq
-	    (cxx_pp, TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (fntype))));
+	  pp_cxx_cv_qualifier_seq (cxx_pp, class_of_this (fntype));
 	}
 
       if (flags & TFF_EXCEPTION_SPECIFICATION)
diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 3dbc3b7..98bc900 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2247,7 +2247,7 @@  write_function_type (const tree type)
     {
       /* The first parameter must be a POINTER_TYPE pointing to the
 	 `this' parameter.  */
-      tree this_type = TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (type)));
+      tree this_type = class_of_this (type);
       write_CV_qualifiers_for_type (this_type);
     }
 
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index d109e1b..46679cd 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -15600,8 +15600,8 @@  unify (tree tparms, tree targs, tree parm, tree arg, int strict)
 	if (TREE_CODE (parm) == METHOD_TYPE
 	    && (!check_cv_quals_for_unify
 		(UNIFY_ALLOW_NONE,
-		 TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (arg))),
-		 TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (parm))))))
+		 class_of_this (arg),
+		 class_of_this (parm))))
 	  return 1;
 
 	if (unify (tparms, targs, TREE_TYPE (parm),
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index afe0dbc..aa0de85 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -834,7 +834,7 @@  merge_types (tree t1, tree t2)
       {
 	/* Get this value the long way, since TYPE_METHOD_BASETYPE
 	   is just the main variant of this.  */
-	tree basetype = TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (t2)));
+	tree basetype = class_of_this (t2);
 	tree raises = merge_exception_specifiers (TYPE_RAISES_EXCEPTIONS (t1),
 						  TYPE_RAISES_EXCEPTIONS (t2));
 	tree t3;
@@ -8034,7 +8034,7 @@  type_memfn_quals (const_tree type)
   if (TREE_CODE (type) == FUNCTION_TYPE)
     return TYPE_QUALS (type);
   else if (TREE_CODE (type) == METHOD_TYPE)
-    return cp_type_quals (TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (type))));
+    return cp_type_quals (class_of_this (type));
   else
     gcc_unreachable ();
 }