[PATCH] get rid of some TYPE_ARG_TYPES usage by introducing nth_arg_type

[Nathan Froyd <froydnj at codesourcery dot com>]

Various places in the compiler grab TYPE_ARG_TYPES and grovel through it
when what they're really trying to do is index into the list of argument
types.  The patch below introduces nth_arg_type for such situatiosn and
changes a hodgepodge of places to use it.  You could, of course, use
function_args_iterator, but I think this approach is somewhat clearer.

Tested on x86_64-unknown-linux-gnu.  OK to commit?

-Nathan

gcc/
	* tree.h (nth_arg_type): Declare.
	* tree.c (nth_arg_type): Define.
	* dbxout.c (dbxout_type_method_1): Call it.
	* dwarf2out.c (decl_class_context): Likewise.
	* tree-ssa-math-opts.c (execute_optimize_bswap): Likewise.

gcc/cp/
	* cp-tree.h (DECL_CONST_MEMFUNC_P): Call nth_arg_type.
	(DECL_VOLATILE_MEMFUNC_P, type_of_this_parm): Likewise.

gcc/fortran/
	* trans-decl.c (create_main_function): Call nth_arg_type.

gcc/objc/
	* objc-next-runtime-abi-01.c (next_sjlj_build_enter_and_setjmp):
	Call nth_arg_type.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index ada01fb..53848c3 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -2256,15 +2256,13 @@ struct GTY((variable_size)) lang_decl {
    has `this' as const X *const.  */
 #define DECL_CONST_MEMFUNC_P(NODE)					 \
   (DECL_NONSTATIC_MEMBER_FUNCTION_P (NODE)				 \
-   && CP_TYPE_CONST_P (TREE_TYPE (TREE_VALUE				 \
-				  (TYPE_ARG_TYPES (TREE_TYPE (NODE))))))
+   && CP_TYPE_CONST_P (TREE_TYPE (nth_arg_type (TREE_TYPE (NODE), 0))))
 
 /* Nonzero for FUNCTION_DECL means that this member function
    has `this' as volatile X *const.  */
 #define DECL_VOLATILE_MEMFUNC_P(NODE)					 \
   (DECL_NONSTATIC_MEMBER_FUNCTION_P (NODE)				 \
-   && CP_TYPE_VOLATILE_P (TREE_TYPE (TREE_VALUE				 \
-				  (TYPE_ARG_TYPES (TREE_TYPE (NODE))))))
+   && CP_TYPE_VOLATILE_P (TREE_TYPE (nth_arg_type (TREE_TYPE (NODE), 0))))
 
 /* Nonzero for a DECL means that this member is a non-static member.  */
 #define DECL_NONSTATIC_MEMBER_P(NODE)		\
@@ -4660,10 +4658,8 @@ struct GTY(()) tinst_level {
 static inline tree
 type_of_this_parm (const_tree fntype)
 {
-  function_args_iterator iter;
   gcc_assert (TREE_CODE (fntype) == METHOD_TYPE);
-  function_args_iter_init (&iter, fntype);
-  return function_args_iter_cond (&iter);
+  return nth_arg_type (fntype, 0);
 }
 
 /* Return the class of the `this' parameter of FNTYPE.  */
diff --git a/gcc/dbxout.c b/gcc/dbxout.c
index 3190803..f5e985e 100644
--- a/gcc/dbxout.c
+++ b/gcc/dbxout.c
@@ -1585,7 +1585,7 @@ dbxout_type_method_1 (tree decl)
     c2 = '?';
   else /* it's a METHOD_TYPE.  */
     {
-      tree firstarg = TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (decl)));
+      tree firstarg = nth_arg_type (TREE_TYPE (decl), 0);
       /* A for normal functions.
 	 B for `const' member functions.
 	 C for `volatile' member functions.
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index b85a55e..d95c3f4 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -7484,7 +7484,7 @@ decl_class_context (tree decl)
     context = DECL_CONTEXT (decl);
   else
     context = TYPE_MAIN_VARIANT
-      (TREE_TYPE (TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (decl)))));
+      (TREE_TYPE (nth_arg_type (TREE_TYPE (decl), 0)));
 
   if (context && !TYPE_P (context))
     context = NULL_TREE;
diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
index d771484..19d3e03 100644
--- a/gcc/fortran/trans-decl.c
+++ b/gcc/fortran/trans-decl.c
@@ -4518,7 +4518,7 @@ create_main_function (tree fndecl)
 {
   tree old_context;
   tree ftn_main;
-  tree tmp, decl, result_decl, argc, argv, typelist, arglist;
+  tree tmp, decl, result_decl, argc, argv, fntype, arglist;
   stmtblock_t body;
 
   old_context = current_function_decl;
@@ -4559,21 +4559,20 @@ create_main_function (tree fndecl)
   /* Get the arguments.  */
 
   arglist = NULL_TREE;
-  typelist = TYPE_ARG_TYPES (TREE_TYPE (ftn_main));
+  fntype = TREE_TYPE (ftn_main);
 
-  tmp = TREE_VALUE (typelist);
+  tmp = nth_arg_type (fntype, 0);
   argc = build_decl (input_location, PARM_DECL, get_identifier ("argc"), tmp);
   DECL_CONTEXT (argc) = ftn_main;
-  DECL_ARG_TYPE (argc) = TREE_VALUE (typelist);
+  DECL_ARG_TYPE (argc) = tmp;
   TREE_READONLY (argc) = 1;
   gfc_finish_decl (argc);
   arglist = chainon (arglist, argc);
 
-  typelist = TREE_CHAIN (typelist);
-  tmp = TREE_VALUE (typelist);
+  tmp = nth_arg_type (fntype, 1);
   argv = build_decl (input_location, PARM_DECL, get_identifier ("argv"), tmp);
   DECL_CONTEXT (argv) = ftn_main;
-  DECL_ARG_TYPE (argv) = TREE_VALUE (typelist);
+  DECL_ARG_TYPE (argv) = tmp;
   TREE_READONLY (argv) = 1;
   DECL_BY_REFERENCE (argv) = 1;
   gfc_finish_decl (argv);
diff --git a/gcc/objc/objc-next-runtime-abi-01.c b/gcc/objc/objc-next-runtime-abi-01.c
index d5b795f..37b2b10 100644
--- a/gcc/objc/objc-next-runtime-abi-01.c
+++ b/gcc/objc/objc-next-runtime-abi-01.c
@@ -2584,7 +2584,7 @@ next_sjlj_build_enter_and_setjmp (struct objc_try_context **ctcp)
 #ifdef OBJCPLUS
   /* Convert _setjmp argument to type that is expected.  */
   if (prototype_p (TREE_TYPE (objc_setjmp_decl)))
-    t = convert (TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (objc_setjmp_decl))), t);
+    t = convert (nth_arg_type (TREE_TYPE (objc_setjmp_decl), 0), t);
   else
     t = convert (ptr_type_node, t);
 #else
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index b9f631e..5e6feb1 100644
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -1181,13 +1181,13 @@ execute_optimize_bswap (void)
   if (bswap32_p)
     {
       tree fndecl = built_in_decls[BUILT_IN_BSWAP32];
-      bswap32_type = TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (fndecl)));
+      bswap32_type = nth_arg_type (TREE_TYPE (fndecl), 0);
     }
 
   if (bswap64_p)
     {
       tree fndecl = built_in_decls[BUILT_IN_BSWAP64];
-      bswap64_type = TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (fndecl)));
+      bswap64_type = nth_arg_type (TREE_TYPE (fndecl), 0);
     }
 
   memset (&bswap_stats, 0, sizeof (bswap_stats));
diff --git a/gcc/tree.c b/gcc/tree.c
index 3357d84..2925e13 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -10704,6 +10704,29 @@ prototype_p (tree fntype)
   return (t != NULL_TREE);
 }
 
+/* Return the Nth argument type from FNTYPE.  */
+
+tree
+nth_arg_type (const_tree fntype, int n)
+{
+  function_args_iterator iter;
+  tree t;
+  int i;
+
+  gcc_assert (fntype != NULL_TREE);
+  gcc_assert (n >= 0);
+
+  i = 0;
+  FOREACH_FUNCTION_ARGS (fntype, t, iter)
+    {
+      if (n == i)
+	return t;
+      i++;
+    }
+
+  gcc_unreachable ();
+}
+
 /* If BLOCK is inlined from an __attribute__((__artificial__))
    routine, return pointer to location from where it has been
    called.  */
diff --git a/gcc/tree.h b/gcc/tree.h
index 805fe06..9788071 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5074,6 +5074,7 @@ extern tree create_artificial_label (location_t);
 extern const char *get_name (tree);
 extern bool stdarg_p (const_tree);
 extern bool prototype_p (tree);
+extern tree nth_arg_type (const_tree, int);
 extern bool is_typedef_decl (tree x);
 extern bool typedef_variant_p (tree);
 extern bool auto_var_in_fn_p (const_tree, const_tree);