Any usable SIMD implementation?

[Johan Engelen via Digitalmars-d]

On Thursday, 7 April 2016 at 11:25:47 UTC, Johannes Pfau wrote:
> Am Thu, 07 Apr 2016 10:52:42 +0000
> schrieb Kai Nacke <kai at redstar.de>:
>
>> glibc has a special mechanism for resolving the called 
>> function during loading. See the section on the GNU Indirect 
>> Function Mechanism here: 
>> https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/W51a7ffcf4dfd_4b40_9d82_446ebc23c550/page/Optimized%20Libraries
>> 
>> Would be awesome to have something similar in druntime/Phobos.
>> 
>> Regards,
>> Kai
>
> Available in GCC as the 'ifunc' attribute: 
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
>
> What do you mean by 'something similar in druntime/phobos'? A 
> platform independent (slightly slower) variant?:
>
> http://dpaste.dzfl.pl/0aa81325a26a

I thought that the ifunc mechanism means an indirect call (i.e. a 
function ptr is set at the start of the program) ? That would be 
the same as what you are doing without performance difference.

https://gcc.gnu.org/wiki/FunctionMultiVersioning
"To keep the cost of dispatching low, the IFUNC mechanism is used 
for dispatching. This makes the call to the dispatcher a one-time 
thing during startup and a call to a function version is a single 
jump ** indirect ** instruction." (emphasis mine)
I looked into this some time ago and did not see a reason to use 
the ifunc mechanism (which would not be available on Windows). I 
thought it should be implementable in a library, exactly as you 
did in your dpaste! :-)  (does `&foo` return `impl`?)