Any usable SIMD implementation?

[xenon325 via Digitalmars-d]

On Thursday, 7 April 2016 at 00:42:30 UTC, Walter Bright wrote:
> [...] especially if one is writing applications that 
> dynamically adjusts based on the CPU the user is running on. 
> The main trouble comes about when different modules are 
> compiled with different settings. What happens with template 
> code generation, when the templates are pulled from different 
> modules? What happens when COMDAT functions are generated? (The 
> linker picks one arbitrarily and discards the others.) Which 
> settings wind up in the executable will be not easily 
> predictable.
>
> I suspect that using a pragma would be a much better approach:
>
>    pragma(SIMD, AFX)
>    {
> 	... code ...
>    }
>
> Doing it on the command line is certainly the traditional way, 
> but it strikes me as being bug-prone and as unhygienic and 
> obsolete as the C preprocessor is (for similar reasons).

Have you seen how GCC's function multiversioning [1] ?

This whole thread is far too low-level for me and I'm not sure if 
GCC's dispatcher overhead is OK, but the syntax looks really nice 
and it seems to address all of your concerns.

	__attribute__ ((target ("default")))
	int foo ()
	{
	  // The default version of foo.
	  return 0;
	}

	__attribute__ ((target ("sse4.2")))
	int foo ()
	{
	  // foo version for SSE4.2
	  return 1;
	}

	__attribute__ ((target ("arch=atom")))
	int foo ()
	{
	  // foo version for the Intel ATOM processor
	  return 2;
	}


[1] https://gcc.gnu.org/wiki/FunctionMultiVersioning

-Alexander