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Add explanation for subgroup vs dynamically uniform. #2118
Add explanation for subgroup vs dynamically uniform. #2118
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While everything in this PR seems technically correct, it's concerning because this part suggests that you can't use a peeling loop to remove the need for the nonuniform decoration, which I think existing content relies on. Maybe we should change VUID 06274 to say
is not dynamically uniform or subgroup uniform
? In the long term I'd prefer to get rid of the nonuniform decoration entirely (I think there are other, implementation-dependent cases where nonuniform is misleading/wrong), but I think that's a harder change to get through.There was a problem hiding this comment.
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Is it realistic for an application to be able to know whether they're subgroup-uniform or not in this case? Doesn't that depend on the hardware/driver and how it might pack draws?
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Peeling loops to avoid nonuniformEXT are technically out of spec, since dynamically uniform is the requirement, not subgroup uniform. Not sure why it's specced like that, but it is what it is. Desktop content in the wild definitely relies on it because it works there.
I think a compiler could optimize away nonuniformEXT if the input is subgroup uniform and the hardware only cares about that kind of uniform for descriptor access.
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Are you sure about this? My read of the spec says the opposite: