x86 backend update

[Stephen Weeks]

> Steve, did that self-compile ever finish?  

I killed it after 3 or so hours (on a 733MhZ machine).  When I killed it, it was
spinning using 200M of RAM, without much variance in memory usage, so it looked
like a loop to me.  I'll let one run overnight tonight.

> I thought I had recreated the
> problem: the native backend spit out 8 .s files then didn't add anything
> to the last one for a long time.  So, I added some Control.messageStr
> printing to try to pinpoint where it wasn't making progress, but that
> self-compile finished; 

You could save a version of mlton.sml (without the Control.messageStr's)
corresponding to the one that failed and compile it with a G0 MLton that has the 
messageStr's.

> The only issue with the asserts might be if some basic block was very,
> very large.  That's never occured before, except in the initGlobals block,
> but I special case that.  The other oddity is that it is occuring at
> something like the very last block of the program (because the last
> self-compile I did a couple of days ago needed 8 .s files).  Very strange.

It might be that I am running with this new contification stuff, which should
produce larger CPS functions, and therefore larger blocks.  But I wouldn't
imagine it would matter that much.