Miley Cyrus -- My Little Dog IS DEAD

Miley Cyrus is having a really ruff day ... because her super cute pooch Lila has officially checked in to the big dog park in the sky.

Miley took to Twitter moments ago to break the tragic news to her fans, tweeting ... "My heart has never been so broken. Lila my sweet baby girl has passed away."

She added, "Can't think of one good reason to get out of bed today."

It's unclear how Lila kicked the can, but she was only two years old.