[v2,03/27] qom: clean up/optimize object_dynamic_cast

The interface loop can be performed only on the parent object.  It
does not need to be done on each interface.  Similarly, we can
simplify the code by switching early from the implementation
object to the parent object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qom/object.c |   38 ++++++++++++++++++--------------------
 1 files changed, 18 insertions(+), 20 deletions(-)

On 02/04/2012 02:02 AM, Paolo Bonzini wrote:
> The interface loop can be performed only on the parent object.  It
> does not need to be done on each interface.  Similarly, we can
> simplify the code by switching early from the implementation
> object to the parent object.
>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
>   qom/object.c |   38 ++++++++++++++++++--------------------
>   1 files changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/qom/object.c b/qom/object.c
> index 4261944..4d21f0a 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -372,7 +372,6 @@ static bool object_is_type(Object *obj, const char *typename)
>   {
>       TypeImpl *target_type = type_get_by_name(typename);
>       TypeImpl *type = obj->class->type;
> -    GSList *i;
>
>       /* Check if typename is a direct ancestor of type */
>       while (type) {
> @@ -383,15 +382,6 @@ static bool object_is_type(Object *obj, const char *typename)
>           type = type_get_parent(type);
>       }
>
> -    /* Check if obj has an interface of typename */
> -    for (i = obj->interfaces; i; i = i->next) {
> -        Interface *iface = i->data;
> -
> -        if (object_is_type(OBJECT(iface), typename)) {
> -            return true;
> -        }
> -    }
> -
>       return false;
>   }

So this changes object_is_type() to only determine if the the object is a direct 
ancestor.  I think it's worth changing the name to something like 
object_is_ancestor_of() or something like that.

>
> @@ -404,6 +394,24 @@ Object *object_dynamic_cast(Object *obj, const char *typename)
>           return obj;
>       }
>
> +    /* Check if obj is an interface and its containing object is a direct
> +     * ancestor of typename.  In principle we could do this test at the very
> +     * beginning of object_dynamic_cast, avoiding a second call to
> +     * object_is_type.  However, casting between interfaces is relatively
> +     * rare, and object_is_type(obj, TYPE_INTERFACE) would fail almost always.
> +     *
> +     * Perhaps we could add a magic value to the object header for increased
> +     * (run-time) type safety and to speed up tests like this one.  If we ever
> +     * do that we can revisit the order here.
> +     */
> +    if (object_is_type(obj, TYPE_INTERFACE)) {
> +        assert(!obj->interfaces);
> +        obj = INTERFACE(obj)->obj;
> +        if (object_is_type(obj, typename)) {
> +            return obj;
> +        }
> +    }
> +
>       /* Check if obj has an interface of typename */
>       for (i = obj->interfaces; i; i = i->next) {
>           Interface *iface = i->data;
> @@ -413,16 +421,6 @@ Object *object_dynamic_cast(Object *obj, const char *typename)
>           }
>       }
>
> -    /* Check if obj is an interface and its containing object is a direct
> -     * ancestor of typename */
> -    if (object_is_type(obj, TYPE_INTERFACE)) {
> -        Interface *iface = INTERFACE(obj);
> -
> -        if (object_is_type(iface->obj, typename)) {
> -            return iface->obj;
> -        }
> -    }
> -
>       return NULL;
>   }

This looks pretty right to me.  We really need a unit test for this stuff.  I've 
got one in my tree, I'll dig it out so we can start more rigorously validating 
these different casting cases.

Regards,

Anthony Liguori

>