Hollywood can be a rough town, and most successful folks in the biz keep their friends close including this actor ... can you guess who this supportive star is?

We ran into this actor while he was leaving a gym in West Hollywood and asked him how he felt about his pal Taylor Swift branching out from music ... and it sounded like he was all for it!

He didn't stick around for too long, though ... but hey, sometimes you just gotta keep on truckin'!

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