Thanks for the interesting discussion.
In terms of the definition of the target, I see two categories of arguments presented here :
C1 : The executor, runtime, should belong to the target – even if means duplication.
C2 : The targets should be hierarchical and recursive
For C1, I would rather use this argument to make runtime and executor an attribute of the target rather than to support calling an Array of Targets, another target. I can see this being true in the following scenario (as pointed out by @tqchen), if its a scenario we want to target for.
The following scenario is motivated by the fact it is economical run a single model inference across multiple machines considering the data transfer costs of intermediary tensors of the model. Just want to make sure if this is something the community considers as a compilation scenario that TVM should aim for.
For C2,
The examples presented so far does not seem to go beyond mostly a flat Array of Targets. Maybe in the multiple machine scenario, an alternative could have been a Array of CompilationConfig (or whatever we decide to call it). However, This would not be viable if we have recursive targets (where the recursion depth > 1)
Do you guys see a likely scenario in which we will have a Composite Target that is composed of Composite Targets of Composite Targets ? (i.e. where we cant express the target we want to compile to as a Array of Targets coupled with a host target – I believe host target differs only in the multiple machine scenario),
If that is the case, how would TVM establish codegen path divergence (partitioning at different levels of IR) to such an hierarchical target ?