[LLVMdev] Removing SimpleRewriter (formerly SimpleSpiller)

[Lang Hames]

> One thing I would recommend is that the code that does IR
> changes be separated from the code (if any) that does dataflow
> information updates.  The entanglement of these two functions
> is part of the reason that the coalescing code is so complicated.
> Separating the actions allows the code to be reused by other
> passes (different register allocators, for example).

The new framework will definitely be doing both IR modifications and
liveness info updates. Keeping these concerns separate is a good idea,
and I'll do my best, however the primary goal at the moment is
incremental improvement of the current scheme.

- Lang.