IA32: printing FP register variables

[Jim Blandy]

> I have a similar problem as you have, Jim.  I'm working on the CodeWarrior
> x86/Linux port, and I have no way to represent that a value has been
> allocated to a MMX register.  While CW will also allocate local variables to
> floating point stack locations, we don't emit any useful debugging info for
> those variables.

I don't have an MMX manual handy, but it seems like a much easier case
than the FPU, since the registers don't shift around every time you do
an operation.

> As long as the relative position of items on the stack didn't change
> (this var is always 2 from the top), this should be OK.

Well, the reason this problem seems hard to me is exactly because the
position of items relative to the top of the stack *will* change,
whenever you execute instructions like FILD, FDIVP, etc.  If they were
a constant distance, then we could simply assign register numbers to
ST(0) -- ST(7) in the usual way, and everything would work.