SIMD back-end operations are needed, using the ReservationStation
infrastructure. it would be nice to still be able to do early-out.
will need unary selection and cancellation done, first.
with PartitionedSignal in place, the idea here is to have a Stage API
class which automatically understands and carries the Partition Context
throughout all pipelines.
the IO Data (as defined by regspecs) is then *automatically* allocated
PartitionedSignals rather than scalar Signals and thus the ALUs, comprising
as they do of Stage API pipelines, do not need massive intrusive conversion.
a wrapper around nmigen dsl.Module can then allocate PartitionedSignals.
however this should not be "all-in", it should be dynamic runtime configureable
as to whether the ALU should be instantiated as scalar or as SIMD.