py/obj: Introduce mp_obj_malloc_with_finaliser to allocate and set type.

Following 709e8328d9.

Using this helps to reduce code size.  And it ensure that the type is
always set as soon as the object is allocated, which is important for the
GC to function correctly.

Signed-off-by: Damien George <damien@micropython.org>

py/obj.c

@@ -44,6 +44,15 @@ MP_NOINLINE void *mp_obj_malloc_helper(size_t num_bytes, const mp_obj_type_t *ty
     return base;
 }
 
+#if MICROPY_ENABLE_FINALISER
+// Allocates an object and also sets type, for mp_obj_malloc{,_var}_with_finaliser macros.
+MP_NOINLINE void *mp_obj_malloc_with_finaliser_helper(size_t num_bytes, const mp_obj_type_t *type) {
+    mp_obj_base_t *base = (mp_obj_base_t *)m_malloc_with_finaliser(num_bytes);
+    base->type = type;
+    return base;
+}
+#endif
+
 const mp_obj_type_t *MICROPY_WRAP_MP_OBJ_GET_TYPE(mp_obj_get_type)(mp_const_obj_t o_in) {
     #if MICROPY_OBJ_IMMEDIATE_OBJS && MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_A
 

py/obj.h

@@ -916,6 +916,16 @@ extern const struct _mp_obj_exception_t mp_const_GeneratorExit_obj;
 #define mp_obj_malloc_var(struct_type, var_field, var_type, var_num, obj_type) ((struct_type *)mp_obj_malloc_helper(offsetof(struct_type, var_field) + sizeof(var_type) * (var_num), obj_type))
 void *mp_obj_malloc_helper(size_t num_bytes, const mp_obj_type_t *type);
 
+// Object allocation macros for allocating objects that have a finaliser.
+#if MICROPY_ENABLE_FINALISER
+#define mp_obj_malloc_with_finaliser(struct_type, obj_type) ((struct_type *)mp_obj_malloc_with_finaliser_helper(sizeof(struct_type), obj_type))
+#define mp_obj_malloc_var_with_finaliser(struct_type, var_type, var_num, obj_type) ((struct_type *)mp_obj_malloc_with_finaliser_helper(sizeof(struct_type) + sizeof(var_type) * (var_num), obj_type))
+void *mp_obj_malloc_with_finaliser_helper(size_t num_bytes, const mp_obj_type_t *type);
+#else
+#define mp_obj_malloc_with_finaliser(struct_type, obj_type) mp_obj_malloc(struct_type, obj_type)
+#define mp_obj_malloc_var_with_finaliser(struct_type, var_type, var_num, obj_type) mp_obj_malloc_var(struct_type, var_type, var_num, obj_type)
+#endif
+
 // These macros are derived from more primitive ones and are used to
 // check for more specific object types.
 // Note: these are kept as macros because inline functions sometimes use much