Re: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86

[Richard Henderson <rth@cygnus.com>]

On Sat, Dec 19, 1998 at 12:58:10AM -0500, N8TM@aol.com wrote:
> How much extra time?

One extra cycle on read; since we're committed to read-modify-write
anyway, probably one to three extra cycles on write depending on
if we actually straddle a 16-byte boundary.

> Is it feasible to make the XFmode spills use aligned addresses,
> and would alignment be as much of an improvement as in DFmode?

If we were to spill in XFmode, then yes, alignment would be just 
as important as in DFmode.

> The only quantification I've seen is my test of one application
> indicating that changing spills from SFmode to XFmode appears to
> make that application run 25% longer on a PPro.

I have not tried quantifing the change.  I would want to examine
things more closely, however, because 25% seems low to me.

And before I even did that, someone would have to do a much better
job convincing me that it was even a good idea.  Cause from where
I'm sitting now, I agree with Toon that the idea is losing all the
way around. 


r~