py: Specialise builtin funcs to use separate type for fixed arg count.

Builtin functions with a fixed number of arguments (0, 1, 2 or 3) are
quite common.  Before this patch the wrapper for such a function cost
3 machine words.  After this patch it only takes 2, which can reduce the
code size by quite a bit (and pays off even more, the more functions are
added).  It also makes function dispatch slightly more efficient in CPU
usage, and furthermore reduces stack usage for these cases.  On x86 and
Thumb archs the dispatch functions are now tail-call optimised by the
compiler.

The bare-arm port has its code size increase by 76 bytes, but stmhal drops
by 904 bytes.  Stack usage by these builtin functions is decreased by 48
bytes on Thumb2 archs.

1 files changed, 61 insertions, 25 deletions

diff --git a/py/objfun.c b/py/objfun.c
index 405f38127..6b8fe6d38 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -50,11 +50,66 @@
 /******************************************************************************/
 /* builtin functions                                                          */
 
-// mp_obj_fun_builtin_t defined in obj.h
+STATIC mp_obj_t fun_builtin_0_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    (void)args;
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin_0));
+    mp_obj_fun_builtin_fixed_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_arg_check_num(n_args, n_kw, 0, 0, false);
+    return self->fun._0();
+}
 
-STATIC mp_obj_t fun_builtin_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
-    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin));
-    mp_obj_fun_builtin_t *self = MP_OBJ_TO_PTR(self_in);
+const mp_obj_type_t mp_type_fun_builtin_0 = {
+    { &mp_type_type },
+    .name = MP_QSTR_function,
+    .call = fun_builtin_0_call,
+    .unary_op = mp_generic_unary_op,
+};
+
+STATIC mp_obj_t fun_builtin_1_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin_1));
+    mp_obj_fun_builtin_fixed_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_arg_check_num(n_args, n_kw, 1, 1, false);
+    return self->fun._1(args[0]);
+}
+
+const mp_obj_type_t mp_type_fun_builtin_1 = {
+    { &mp_type_type },
+    .name = MP_QSTR_function,
+    .call = fun_builtin_1_call,
+    .unary_op = mp_generic_unary_op,
+};
+
+STATIC mp_obj_t fun_builtin_2_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin_2));
+    mp_obj_fun_builtin_fixed_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_arg_check_num(n_args, n_kw, 2, 2, false);
+    return self->fun._2(args[0], args[1]);
+}
+
+const mp_obj_type_t mp_type_fun_builtin_2 = {
+    { &mp_type_type },
+    .name = MP_QSTR_function,
+    .call = fun_builtin_2_call,
+    .unary_op = mp_generic_unary_op,
+};
+
+STATIC mp_obj_t fun_builtin_3_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin_3));
+    mp_obj_fun_builtin_fixed_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_arg_check_num(n_args, n_kw, 3, 3, false);
+    return self->fun._3(args[0], args[1], args[2]);
+}
+
+const mp_obj_type_t mp_type_fun_builtin_3 = {
+    { &mp_type_type },
+    .name = MP_QSTR_function,
+    .call = fun_builtin_3_call,
+    .unary_op = mp_generic_unary_op,
+};
+
+STATIC mp_obj_t fun_builtin_var_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_fun_builtin_var));
+    mp_obj_fun_builtin_var_t *self = MP_OBJ_TO_PTR(self_in);
 
     // check number of arguments
     mp_arg_check_num(n_args, n_kw, self->n_args_min, self->n_args_max, self->is_kw);
@@ -68,25 +123,6 @@ STATIC mp_obj_t fun_builtin_call(mp_obj_t self_in, size_t n_args, size_t n_kw, c
 
         return self->fun.kw(n_args, args, &kw_args);
 
-    } else if (self->n_args_min <= 3 && self->n_args_min == self->n_args_max) {
-        // function requires a fixed number of arguments
-
-        // dispatch function call
-        switch (self->n_args_min) {
-            case 0:
-                return self->fun._0();
-
-            case 1:
-                return self->fun._1(args[0]);
-
-            case 2:
-                return self->fun._2(args[0], args[1]);
-
-            case 3:
-            default:
-                return self->fun._3(args[0], args[1], args[2]);
-        }
-
     } else {
         // function takes a variable number of arguments, but no keywords
 
@@ -94,10 +130,10 @@ STATIC mp_obj_t fun_builtin_call(mp_obj_t self_in, size_t n_args, size_t n_kw, c
     }
 }
 
-const mp_obj_type_t mp_type_fun_builtin = {
+const mp_obj_type_t mp_type_fun_builtin_var = {
     { &mp_type_type },
     .name = MP_QSTR_function,
-    .call = fun_builtin_call,
+    .call = fun_builtin_var_call,
     .unary_op = mp_generic_unary_op,
 };