[WIP] UxT-Reducer streaming terminals

[devreal]

Implement UxT reduction streaming terminals. The types of edge inputs and the types of the op arguments (if different) are passed as tuples instead of variadic template arguments. This allows us to convert between U and T and to use different U and T for the reducer signature.

This is WIP and so far only contains a draft of the interface in the PaRSEC backend, no UxT reducer tests yet.

Signed-off-by: Joseph Schuchart schuchart@icl.utk.edu

[devreal]

A note from the discussion today: we will lose some static type-checking ability with this approach since reducers effectively become converters between the type of the terminal (T) and the type of the op() argument (U). We will have to throw an exception if that conversion is not possible and no reducer is set.

[devreal]

@evaleev I adapted the madness backend to the new tuple-based TT type list. Please take a look at it if you get a chance.

@pnookala Could you take a look at how the MRA benchmark could work with the new interface? It would be a good test case to try out before merging :) In short, you can use different types in the input edge and the op argument and provide a reducer that "converts" between the two.

[devreal]

Pushed some fixes. I still cannot compile spmm with the madness backend and I have a hard time figuring out where the template void-voodoo goes haywire...

[therault]

This approach is problematic, because it removes the compile-time checking capabilities of reducers.

It is replaced with PR #229