[OM Cooker] One users reasons for using i586 on 64 bit hardware.
Tomasz Gajc
tpgxyz at gmail.com
Mon Dec 26 10:10:49 EST 2016
What are real performance gain?
Doubt that it will be significant.
26.12.2016 2:59 PM "Colin Close" <itchka at compuserve.com> napisał(a):
> The X32_ABI looks interesting and I think that is what D21 was referring
> to at the end of his post.
> It does look like this would offer improved performance for 32bit apps
> running on 64bit boxes.
> What is more the SSE instructions become available.
> I wonder what is involved in creating such a release?
> Best,
> Colin
>
> On Monday, 26 December 2016 07:53:05 GMT Paulo César Pereira de Andrade
> wrote:
> > 2016-12-25 16:33 GMT-05:00 His Shadow <shadowpilot34 at gmail.com>:
> > > I thought that only addresses doubled, not the instruction opcodes.
> >
> > This is mostly right. Instructions that use 64 bit operands, or
> > registers with absolute value larger than 7 also need a prefix
> > https://en.wikipedia.org/wiki/VEX_prefix#REX
> >
> > Running in 32 bit mode also uses only 8 from the 16 registers.
> >
> > It is possible to have a 32 bit distro enabled, just that some
> > directories will conflict, e.g. there is no /bin32 or /bin64.
> >
> > About the upper 32 bits, some instructions do not touch the upper
> > 32 bit, some zero fill and other sign fill the result, and most have
> > some encoding to tell if using 32 or 64 input operands.
> >
> > Some distros have a x32 version:
> > https://en.wikipedia.org/wiki/X32_ABI
> > that uses 32 bit pointers.
> >
> > Thanks,
> > Paulo
> >
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