Function multiversioning question

[Martin Reinecke]

>> This creates a nasty asymmetry in the sense that gcc's own optimizations
>> will be able to use all target features (because the compiler knows that
>> it is OK to use specific features like AVX instructions) whereas the
>> user has no way to hand-optimize where this becomes necessary. At least
>> not using this nice mechanism.
> 
> They can, just not based on preprocessor macros.

I was thinking about decisions at compile time (along the lines of "ah,
I'm in the AVX-specific version of the function, therefore I will call
AVX intrinsics"), and I don't see a way to make them without access to
macros.
At runtime this is of course possible.

Cheers,
  Martin