Adding a MACHINE_ARCH note

[Dimitry Andric]

On Jul 10, 2013, at 03:08, Peter Wemm <peter at wemm.org> wrote:
> On Tue, Jul 9, 2013 at 5:56 PM, Adrian Chadd <adrian at freebsd.org> wrote:
>> ... boy I'd like to see this particular x86 hiccup fixed before this
>> stuff is mainstream.
> 
> I'm not entirely sure how much support there is behind "x32".  I don't
> know if its much more than an academic curiosity or if there's real
> demand for it.

It seems to be driven by Intel and Google.  The idea is that for some
applications (or maybe even most :), an ILP32 model will perform better.
Quoting from one of the presentations:

On Core i7 2600K 3.40GHz:
- Improved SPEC CPU 2K/2006 INT geomean by 7-10% over ia32 and 5-8% over
  Intel64.
- Improved SPEC CPU 2K/2006 FP geomean by 5-11% over ia32.
- Very little changes in SPEC CPU 2K/2006 FP geomean, comparing against
  Intel64.
- Comparing against ia32 PIC, x32 PIC:
  - Improved SPEC CPU 2K INT by another 10%.
  - Improved SPEC CPU 2K FP by another 3%.
  - Improved SPEC CPU 2006 INT by another 6%
  - Improved SPEC CPU 2006 FP by another 2%.

As to how often it is actually used in practice, I am not sure.


>  gcc-4.8 and clang have it, or have patches for it.

You also need a fairly recent binutils.  And kernel + libc support...
It is probably not a trivial task. :-)

-Dimitry