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They are parallel, a data dependency cannot be pipelined as easily.

So no, they are not in-order.

Radeons do not have speculative execution but that doors not make them in-order.

Radeons compute units are in-order though, in the usual sense of the word, and I'd love to hear it if there really was an out-of-order GPU. It'd be rather surprising.

One thing that they do have to deal with data dependencies is that load (and texture fetch etc.) instructions don't block. Instead, there's a separate instruction for waiting on the result of a previous load.

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