[fpc-devel] The new XMM intrinsics

J. Gareth Moreton gareth at moreton-family.com
Sat Jan 18 20:44:04 CET 2020

Seems fair.

The main thing that I'm wary of is memory alignment.  SSE works best 
with structures that are aligned to a 16-byte boundary - attempting to 
call MOVAPS with a structure that isn't aligned will trigger an access 
violation, while MOVUPS is considerably slower on older processors.  
This is why I suggested something like the following some time ago, 
instead of depending on slightly messy pre-processor directives:

*type *TVector4 = *record*
   X, Y, Z, W: Single
*end **align *16;

Gareth aka. Kit

On 18/01/2020 19:39, Sven Barth via fpc-devel wrote:
> Am 18.01.2020 um 18:52 schrieb J. Gareth Moreton:
>> I think more than anything I would like to see a degree of "ease of 
>> use" for the SIMD intrinsics, since modifying __m128 data in C/C++ is 
>> not that straightforward.  Just as a straightforward example, what 
>> might be the best way to ensure these following record types are 
>> compatible with the __m128 data types?
>> *type *TVector4 = *record*
>>   X, Y, Z, W: Single;
>> *end*; // compatible with __m128f
>> *type *TComplex = *record*
>>   Re, Im: Double;
>> *end*; // compatible with __m128d
>> Programmers on their own projects, whether it be a game or a 
>> mathematical program, would much rather work with those constructs if 
>> it can be helped... or at least I would.
> The compiler currently considers corresponding arrays as compatible, 
> like "array[0..3] of Single" or "array[0..1] of Double". In theory 
> nothing would stop us from implementing similar compatibility with the 
> records you mentioned.
> Though to be really useable it would need to be flexible enough to 
> handle for the following for example as well:
> === code begin ===
> type
>   TVector3 = record
>     X, Y, Z: Single;
>   end;
>   TVector4 = record
>     P: TVector3;
>     W: Single;
>   end;
> === code end ===
> Regards,
> Sven
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