Re: GCC/powerpc AltiVec expectations.

[Alex Rosenberg <alexr at spies dot com>]

Mac OS X requires VRSAVE support.

Mac OS classic also does.

Neither has any specific rules about register allocation.

Since I wrote the classic Mac OS AltiVec register save and restore routines
used in the Nanokernel context switcher, the Thread Manager, the Process
Manager, and setjmp/longjmp, I can answer this authoritatively: it tests
VRSAVE by moving it into the CR and then has a series of branches that test
each bit (and they all are predicted with 100% accuracy).

Alex

on 7/2/02 11:48 AM, Kumar Gala at kumar.gala@motorola.com wrote:

> I am not sure if this is true on Mac OS X, but the Mac OS classic ABI
> allocates registers in numeric order if I remember correctly.  Therefor
> its much easier to use VRSAVE to know from (0 to N) are used and (N+1 to
> 31) are not.  In a SVR4 ABI the allocation is not as straight forwarded
> and thus the OS has to look at each bit position of VRSAVE to determine
> what to save and restore.
> 
> - kumar
> 
> On Tuesday, July 2, 2002, at 12:46 PM, Alex Rosenberg wrote:
> 
>> on 7/2/02 10:32 AM, Aldy Hernandez at aldyh@redhat.com wrote:
>> 
>>> On Tue, Jul 02, 2002 at 09:52:46AM -0700, Alex Rosenberg wrote:
>>>> on 7/2/02 7:43 AM, Aldy Hernandez at aldyh@redhat.com wrote:
>>>> 
>>>>> vrsave generation is on by default in gcc, though since the minority
>>>>> OS need it, it should be switched to off.
>>>> 
>>>> "Minority?"
>>> 
>>> linux doesn't need it.
>>> 
>>> i believe macos x doesn't need it.
>> 
>> Mac OS X requires it.

+------------------------------------------------------------+
| Alexander M. Rosenberg           <mailto:alexr@_spies.com> |
| Nobody cares what I say. Remove the underscore to mail me. |