Shall we update the spec to add constraints on the axes and the input rank for the reduction operator?

[mei1127]

(This was raised by @a-sully in Chromium CL-5496412 review.)

For WebNN's reduction operator: Austion proposed to update the spec to add constraints on the axes and the input rank.

The Chromium code which validates reductions also fails if the input rank is zero values in axes are duplicated Shall we update the spec and add WPTs accordingly?

/cc @a-sully

[inexorabletash]

Makes sense to me - I put up a PR

[fdwr]

also fails if the input rank is zero

(repeating here too) Nop reductions are valid (where axes are empty), and scalars are just another instance of a nop:

x = tensorflow.constant([3,3,3], dtype=tensorflow.float32)
y = tensorflow.reduce_sum(x, axis=[])

# value: tf.Tensor([3. 3. 3.], shape=(3,), dtype=float32)
# shape: (3,)

x = tensorflow.constant([], dtype=tensorflow.float32)
y = tensorflow.reduce_sum(x, axis=[])

# value: tf.Tensor([], shape=(0,), dtype=float32)
# shape: (0,)

What's not valid is a scalar reduction with non-empty axes, because that would index axes beyond the rank, but the existing check that each axis < inputRank already validates that condition, and so checking input rank is redundant and unnecessarily exclusionary. So, we should remove that line in Chromium.

[inexorabletash]

Groovy. I have a Chromium CL (with WPT changes) up to remove the rank check crrev.com/c/5529350 but I'm a bit rusty so it may not land for a bit.

[fdwr]

chromium-wpt-export-bot pushed a commit to web-platform-tests/wpt

Oh interesting. So making the change in Chromium land actually pushes it back into web-platform-tests/wpt.

[inexorabletash]

Yeah, we have two-way sync set up with WPT. Mozilla and Apple have something similar. It's not perfect and requires some babysitting, but it's super great when it works.