raw slot ref/set VOPs should be refactored

[Nathan Froyd]

Bug #629058 points out that we could do a better job of coalescing raw-slot slot calculations. This is hard, because each RAW-INSTANCE/* vop contains logic to:

- Pull the length out of the structure instance;
- Compute the offset of the raw slot;
- Access the member question.

An all-assembly CSE pass could do the necessary coalescing, but I hope you agree that'd be rather ugly.

The better solution is to refactor the raw-slot logic to DEFKNOWN functions suitable for doing the three steps above. So you'd end up with something like:

  (%RAW-INSTANCE-REF/WORD X (%RAW-SLOT-OFFSET (%INSTANCE-LENGTH X) **magic-index** 1#|nwords|#))

This is a tedious job, since it needs to be done across all backends, but it's quite straightforward and will make new ports somewhat easier. It also removes a good deal of OAOOM from */cell.lisp and might even give a nice place in *defstruct.lisp to document exactly how raw slots work.

Once the above is done, fixing Bug #629058 boils down to "just" implementing a basic-block value numbering pass or something similar on IR2.

[Douglas Katzman (dougk)]

this bug is obsolete, there are not calculations involved in accessing a raw slot.