What is the best way to implement multiple versions of the same function that uses a specific CPU instructions if available (tested at run time), or falls back to a slower implementation if not?
For example, x86 BMI2 provides a very useful PDEP instruction. How would I write a C code such that it tests BMI2 availability of the executing CPU on startup, and uses one of the two implementations -- one that uses _pdep_u64 call (available with -mbmi2), and another that does bit manipulation "by hand" using C code. Are there any built-in support for such cases? How would I make GCC compile for older arch while providing access to the newer intrinsic? I suspect execution is faster if the function is invoked via a global function pointer, rather than an if/else every time?