py/objtype: Optimise slot RAM usage for instance types.

In all cases other than where you have a native base with a protocol, it
now fits into 4 GC blocks (like it did before the slots representation).

Signed-off-by: Jim Mussared <[email protected]>

Author: jimmo

py/misc.h

@@ -72,6 +72,7 @@ typedef unsigned int uint;
 #define m_new_obj(type) (m_new(type, 1))
 #define m_new_obj_maybe(type) (m_new_maybe(type, 1))
 #define m_new_obj_var(obj_type, var_type, var_num) ((obj_type *)m_malloc(sizeof(obj_type) + sizeof(var_type) * (var_num)))
+#define m_new_obj_var0(obj_type, var_type, var_num) ((obj_type *)m_malloc0(sizeof(obj_type) + sizeof(var_type) * (var_num)))
 #define m_new_obj_var_maybe(obj_type, var_type, var_num) ((obj_type *)m_malloc_maybe(sizeof(obj_type) + sizeof(var_type) * (var_num)))
 #if MICROPY_ENABLE_FINALISER
 #define m_new_obj_with_finaliser(type) ((type *)(m_malloc_with_finaliser(sizeof(type))))

py/objnamedtuple.c

@@ -143,8 +143,7 @@ STATIC mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args,
 }
 
 mp_obj_namedtuple_type_t *mp_obj_new_namedtuple_base(size_t n_fields, mp_obj_t *fields) {
-    mp_obj_namedtuple_type_t *o = m_new_obj_var(mp_obj_namedtuple_type_t, qstr, n_fields);
-    memset(&o->base, 0, sizeof(o->base));
+    mp_obj_namedtuple_type_t *o = m_new_obj_var0(mp_obj_namedtuple_type_t, qstr, n_fields);
     o->n_fields = n_fields;
     for (size_t i = 0; i < n_fields; i++) {
         o->fields[i] = mp_obj_str_get_qstr(fields[i]);

py/objtype.c

@@ -1148,10 +1148,15 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
         #endif
     }
 
-    // Allocate a full-sized mp_obj_full_type_t instance (i.e. all slots / extended fields).
-    // Given that Python types use almost all the slots anyway, this doesn't cost anything
-    // extra.
-    mp_obj_type_t *o = (mp_obj_type_t *)m_new0(mp_obj_full_type_t, 1);
+    const void *base_protocol = NULL;
+    if (bases_len > 0) {
+        base_protocol = MP_OBJ_TYPE_GET_SLOT_OR_NULL(((mp_obj_type_t *)MP_OBJ_TO_PTR(bases_items[0])), protocol);
+    }
+
+    // Allocate a variable-sized mp_obj_type_t with as many slots as we need
+    // (currently 9, plus 1 for base, plus 1 for base-protocol).
+    // Note: 11 slots pushes it from 4 to 5 GC blocks.
+    mp_obj_type_t *o = m_new_obj_var0(mp_obj_type_t, void *, 9 + (bases_len ? 1 : 0) + (base_protocol ? 1 : 0));
     o->base.type = &mp_type_type;
     o->flags = base_flags;
     o->name = name;
@@ -1166,13 +1171,10 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
     // MP_OBJ_TYPE_SET_SLOT(o, iternext, not implemented)
     MP_OBJ_TYPE_SET_SLOT(o, buffer, instance_get_buffer, 7);
 
-    if (bases_len > 0) {
-        // Inherit protocol from a base class. This allows to define an
-        // abstract base class which would translate C-level protocol to
-        // Python method calls, and any subclass inheriting from it will
-        // support this feature.
-        MP_OBJ_TYPE_SET_SLOT(o, protocol, MP_OBJ_TYPE_GET_SLOT_OR_NULL(((mp_obj_type_t *)MP_OBJ_TO_PTR(bases_items[0])), protocol), 8);
+    mp_obj_dict_t *locals_ptr = MP_OBJ_TO_PTR(locals_dict);
+    MP_OBJ_TYPE_SET_SLOT(o, locals_dict, locals_ptr, 8);
 
+    if (bases_len > 0) {
         if (bases_len >= 2) {
             #if MICROPY_MULTIPLE_INHERITANCE
             MP_OBJ_TYPE_SET_SLOT(o, parent, MP_OBJ_TO_PTR(bases_tuple), 9);
@@ -1182,10 +1184,15 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
         } else {
             MP_OBJ_TYPE_SET_SLOT(o, parent, MP_OBJ_TO_PTR(bases_items[0]), 9);
         }
-    }
 
-    mp_obj_dict_t *locals_ptr = MP_OBJ_TO_PTR(locals_dict);
-    MP_OBJ_TYPE_SET_SLOT(o, locals_dict, locals_ptr, 10);
+        // Inherit protocol from a base class. This allows to define an
+        // abstract base class which would translate C-level protocol to
+        // Python method calls, and any subclass inheriting from it will
+        // support this feature.
+        if (base_protocol) {
+            MP_OBJ_TYPE_SET_SLOT(o, protocol, base_protocol, 10);
+        }
+    }
 
     #if ENABLE_SPECIAL_ACCESSORS
     // Check if the class has any special accessor methods