For an actor, getting cut from a film can be as demoralizing as it gets.

You struggle to memorize your lines, toil long hours filming your scenes — and for zero reward. (In the world outside of Hollywood, we call that an “internship.”)

And then when the film is released, you’re not in it.

Whitey Bulger in “Black Mass.”Photo:

Modal Trigger Johnny Depp stars as mobster

It happens more often than we might think, as story lines get rejiggered and overlong films get trimmed all the time.

The latest casualty is actress Sienna Miller. She was meant to appear in Friday’s “Black Mass,” the accent-heavy drama starring Johnny Depp as Boston crime boss Whitey Bulger.

Miller played Bulger’s longtime girlfriend Catherine Greig, but all of her scenes were left on the cutting-room floor after director Scott Cooper (“Crazy Heart”) decided the movie should focus more on the gangster’s younger years.

“It came down to narrative choices,” Cooper told the Boston Globe.

Miller is in good company. Here are four more cases of stars who got brutally snipped out of the picture.

Shailene Woodley in “The Amazing Spider-Man 2,” 2014

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Shailene WoodleyPhoto: AP

The “Divergent” actress was tapped to play Mary Jane Watson in the superhero sequel, presumably setting up a love triangle with Gwen Stacy (Emma Stone) and Peter Parker (Andrew Garfield).

Unfortunately — or fortunately, considering how terrible this film turned out to be — Woodley was cut after the producers felt the movie was already overstuffed.

She was meant to return in “Spider-Man 3” — a sequel that will now never arrive since Sony cut a deal with Marvel Studios to reboot the franchise.

Harrison Ford in “E.T. the Extra-Terrestrial,” 1982

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Harrison FordPhoto: Getty Images)

Even Ford’s close connections to the film — his buddy Steven Spielberg directed and his second wife Melissa Mathison wrote it — couldn’t save the “Star Wars” actor’s cameo.

He was cast in “E.T.” as a high-school principal who lectures Elliott (Henry Thomas) after the boy releases live frogs destined for a biology class. The bit was cut for time.

In the deleted scene, available online, Ford is hard to recognize (except for his voice), as he’s shot completely from behind. Spielberg made the decision to film most of the adults from the waist down or from the back to convey authority.

Kevin Costner in “The Big Chill,” 1983

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Kevin CostnerPhoto: Getty Images

Costner has the dubious distinction of being on the unkind end of one of the most infamous excises in film history.

The then-unknown actor was presumably headed for a star-making turn in this popular baby-boomer drama about a group of friends who gather for the funeral of a pal who committed suicide.

Costner played that dead friend, and although the actor shot several flashback scenes showing him alive and well, the only bit that ended up in the finished film was a brief shot of his corpse.

On the plus side, director Lawrence Kasdan felt so guilty about the chop, he rewarded Costner with a role in 1985’s acclaimed Western “Silverado.”

An endless parade of actors in “The Thin Red Line,” 1998

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Mickey RourkePhoto: Getty Images

Director Terrence Malick — whom actor Christopher Plummer once called “mad as a hatter” — has developed a rep for slicing folks from his films (including “The Thin Red Line”), as he “finds” the movie during the editing process.

Jessica Chastain, Michael Sheen, Rachel Weisz and Amanda Peet were all booted from Malick’s 2012 movie “To the Wonder.” (But Ben Affleck was left in? Go figure.)

But that’s nothing compared to Malick’s 1998 war picture, “The Thin Red Line.”

Mickey Rourke, Lukas Haas, Bill Pullman and Billy Bob Thornton (performing a voice-over) filmed footage that was never used, while Gary Oldman, Viggo Mortensen and Martin Sheen were all set for roles that were killed.

A bitter Rourke blamed his bad-boy rep.

“There were political reasons why I was out of the movie,” he said in 2005. “That really upset me.”

Here’s hoping the craft-service table was top-notch, at least.

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