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

[Toon Moene <toon at moene dot indiv dot nluug dot nl>]

Harvey J. Stein wrote:
> 
> Toon Moene <toon@moene.indiv.nluug.nl> writes:
> 
>  > I must say that I am *not* amused.  This discussion goes into a
>  > direction that will leave us with a compiler that, although
>  > numerical-politically correct, will be generating such slow code as
>  > to be totally unuseable.
> 
> Do you really think it'll make it that much slower?  If you're doing
> computations, how much time is spent dumping & restoring FP registers?
> Is dumping 10 bytes instead of 8 bytes (current practice) going to
> have a substantial impact in total run time?  You've mentioned in
> other posts a factor of 2, as if because it's 16 byte aligned it has
> to move 16 bytes of data.  But even if it's 16 byte aligned, it's
> still only 10 bytes of data, so why should it take 2x as long?

For a thoroughly 32-bit application like mine, 16-byte spills are four
times as large as necessary - and yes, having all this data move in and
out of registers does have a cost (think cache footprint).

-- 
Toon Moene (toon@moene.indiv.nluug.nl)
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