Constants / Root variables as Ops?

[ricardoV94]

Most rewrites we have to do something like if x.inputs[0].owner is not None and isinstance(x.inputs[0].owner.op, log) , when we are looking for say a log operation. The first check is to rule out root variables / constants that have no owner and therefore no owner.op.

What if constants came out of a no-input Operation (parametrized by the constant value, so they can be distinguished merged), and root variables from a no-input Operation that can never be merged? Then we could always and safely do isinstance(x.inputs[0].owner.op, log) because all variables always have an owner and and Op (they may just not have any further inputs).

We did something similar recently for the Outputs of an OpFromGraph: #790

[ricardoV94]

Alternatively we can have a helper function output_of(variable, type) that takes care of the annoying if owner is not None part, but adds a callable overhead in our rewrites

[jessegrabowski]

I prefer the Root pseudo-Op option. It's elegant, and makes all the logic for rewrites consistent end-to-end. I agree the if owner is None checks everywhere are horrible.