Re: Unifying the x86 FPU register sets

[Jim Blandy <jimb at cygnus dot com>]

> Jim> Yes.  It's my understanding that we can accomplish this with the
> Jim> gdbarch mechanism.
> 
> I was checking the rs6000/powerpc target (the other target I'm most
> familiar with), and NUM_REGS and REGISTER_BYTES are both set to the
> largest number for any powerpc varient.  There is no REGISTER_NAMES
> array, being replaced by a REGISTER_NAME() function which returns ""
> for registers not present for the selected varient.  This seems a 
> easy enough thing to do now before adding HAVE_FPU_REGS, etc. to
> derived target's tm-* headers.

I'm concerned about changing NUM_REGS for x86 targets which are not
actively maintained, or whose maintainers aren't participating in this
discussion.  I would like to be able to promise, "If you haven't
changed your target's code, then all the changes visible to your
configuration should be backwards-compatible."

I don't see how to do that without parameterizing the register file.
Perhaps the two parameters I chose --- HAVE_I387_REGS and
HAVE_SSE_REGS --- are not the best; perhaps simply something like
EXPANDED_I386_REGISTER_FILE, enabling the full set, would be better.

If you can see another way to deal with this, I'm all ears.