VDUP has a syntax that takes an R register and copies it into each lane of a D/Q register:
https://github.com/unknownbrackets/ppsspp/blob/f74b765ff3f94985941f361c434440acb2408d35/Common/ArmEmitter.cpp#L2139

Of course, it also can replicate a scalar:
https://github.com/unknownbrackets/ppsspp/blob/f74b765ff3f94985941f361c434440acb2408d35/Common/ArmEmitter.cpp#L2122

I suppose ARMXEmitter::WriteInstruction ought to have an assert that's it's an R reg, but I'm not sure of all the callers...

-[Unknown]