py: Revert mp_load_attr() to its previous state (not supporting default val).

Based on the discussion in #433. mp_load_attr() is critical-path function,
so any extra check will slowdown any script. As supporting default val
required only for getattr() builtin, move correspending implementation
there (still as a separate function due to concerns of maintainability
of such almost-duplicated code instances).

py/builtin.c

@@ -400,6 +400,22 @@ STATIC mp_obj_t mp_builtin_id(mp_obj_t o_in) {
 
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_id_obj, mp_builtin_id);
 
+// See mp_load_attr() if making any changes
+STATIC inline mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t defval) {
+    mp_obj_t dest[2];
+    // use load_method, raising or not raising exception
+    ((defval == MP_OBJ_NULL) ? mp_load_method : mp_load_method_maybe)(base, attr, dest);
+    if (dest[0] == MP_OBJ_NULL) {
+        return defval;
+    } else if (dest[1] == MP_OBJ_NULL) {
+        // load_method returned just a normal attribute
+        return dest[0];
+    } else {
+        // load_method returned a method, so build a bound method object
+        return mp_obj_new_bound_meth(dest[0], dest[1]);
+    }
+}
+
 STATIC mp_obj_t mp_builtin_getattr(uint n_args, const mp_obj_t *args) {
     assert(MP_OBJ_IS_QSTR(args[1]));
     mp_obj_t defval = MP_OBJ_NULL;

py/runtime.c

@@ -672,14 +672,12 @@ too_long:
     nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "too many values to unpack (expected %d)", num));
 }
 
-mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t defval) {
+mp_obj_t mp_load_attr(mp_obj_t base, qstr attr) {
     DEBUG_OP_printf("load attr %p.%s\n", base, qstr_str(attr));
+    // use load_method
     mp_obj_t dest[2];
-    // use load_method, raising or not raising exception
-    ((defval == MP_OBJ_NULL) ? mp_load_method : mp_load_method_maybe)(base, attr, dest);
-    if (dest[0] == MP_OBJ_NULL) {
-        return defval;
-    } else if (dest[1] == MP_OBJ_NULL) {
+    mp_load_method(base, attr, dest);
+    if (dest[1] == MP_OBJ_NULL) {
         // load_method returned just a normal attribute
         return dest[0];
     } else {
@@ -688,10 +686,6 @@ mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t defval) {
     }
 }
 
-mp_obj_t mp_load_attr(mp_obj_t base, qstr attr) {
-    return mp_load_attr_default(base, attr, MP_OBJ_NULL);
-}
-
 // no attribute found, returns:     dest[0] == MP_OBJ_NULL, dest[1] == MP_OBJ_NULL
 // normal attribute found, returns: dest[0] == <attribute>, dest[1] == MP_OBJ_NULL
 // method attribute found, returns: dest[0] == <method>,    dest[1] == <self>

py/runtime.h

@@ -45,7 +45,6 @@ mp_obj_t mp_call_method_n_kw_var(bool have_self, uint n_args_n_kw, const mp_obj_
 void mp_unpack_sequence(mp_obj_t seq, uint num, mp_obj_t *items);
 mp_obj_t mp_store_map(mp_obj_t map, mp_obj_t key, mp_obj_t value);
 mp_obj_t mp_load_attr(mp_obj_t base, qstr attr);
-mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t defval);
 void mp_load_method(mp_obj_t base, qstr attr, mp_obj_t *dest);
 void mp_load_method_maybe(mp_obj_t base, qstr attr, mp_obj_t *dest);
 void mp_store_attr(mp_obj_t base, qstr attr, mp_obj_t val);