On Thu, Jun 5, 2014 at 11:35 AM, FX <fxcoud...@gmail.com> wrote:
>> Please look at libgcc/config/i386/crtfastmath.c for how to set
>> MXCSR_FTZ from mxcsr. You already have all necessary bits in place,
>> the function is basically only:
>>
>> + if (has_sse())
>> + {
>> + unsigned int cw_sse;
>> +
>> + __asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (cw_sse));
>> + cw_sse |= MXCSR_DAZ;
>> + __asm__ __volatile__ ("%vldmxcsr\t%0" : : "m" (cw_sse));
>> + }
Oops, the above should read MXCSR_FTZ.
> Thanks for the suggestion!
>
>
>> Please note, that FTZ applies only to SSE math. x87 and (IIRC) soft-FP
>> don't handle this setting.
>
> Yeah, that’s also why I prefer for now to have it declared as unsupported:
> the Fortran standard doesn’t really allow for partial support such as this,
> so I’m still trying to figure out what The Right Thing To Do is.
Referring to some older mails [1], this looks like a performance-only
setting (sort of fast-math). So, we can perhaps just set this bit,
regardless of the details. Maybe soft-fp will grow support for FTZ
sometime, it looks like a useful addition from the performance POV.
[1] https://gcc.gnu.org/ml/fortran/2013-11/msg00133.html
Uros.
