Al Pacino, Jack Nicholson and a bunch of other huge celebs were all under one roof to honor the late Harry Dean Stanton.

The flock of stars hit up No Name in L.A. Monday night to pay tribute. Warren Beatty, Elliot Mintz, John Savage, Henry Buck and Anjelica Huston were all there too.

Check it out ... Mintz gave his take on what made Harry so great while Pacino and Anjelica shared some thoughts on the horrific Vegas tragedy.

TMZ broke the story ... Harry died peacefully last month at Cedars-Sinai Hospital in L.A. He was 91.