I'm not for sure but a loop station? Or it could have been just a dual sweep solo? Boss has a loop station.
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overdub? Sounds like two guitarists doubling a part, or playing similar parts. oh and for examples how about any iron maiden song
That's two guitars playing in harmony, if the tone/sound's what you're referring to. One guy plays the notes, the other harmonizes.

As for the techniques used, it sounds like alt picking with some slides in there. I don't really think it's sweeping, unless it's horribly messy.
Quote by HorizonShadow
Just eat the headstock.

That'll make you look mad.