This isn't a silly question at all, and it's quite complicated. When compiling C/C++, with some compilers you are able to specify multiple architectures and pr

This isn't a silly question at all, and it's quite complicated. When compiling C/C++, with some compilers you are able to specify multiple architectures and provide a fat binary. It's been a few years now since I've worked on this sort of thing, but the Intel compiler for e.g. used to allow you to do something like this at the compilation stage -march=avx,avx2,avx512 And at runtime, your processor would use the most recent instruction set. In practice, you don't always want to do this, since you produce fat binaries - i.e. every function call that's got vector instructions will have multiple versions, and the file size goes up, library is slower to load, etc... I can't remember if there was an overhead too to each function call. So instead of doing this, what is also common is to compile N versions of the library (one per instruction set), and then load the appropriate version at runtime. This you can do with any compiler, and is indeed what Intel do themselves with the MKL library - if you look into the package for it, you can see that you end up with multiple shared libraries, each with a suffix saying which instruction set it supports (e.g. libmkl_avx.so, libmkl_avx2.so, libmkl_avx512.so). I'm not familiar with simdjson so not sure which approach it takes. Interestingly, if you use ARM processors, the SVE instruction set is designed so that you don't need to re-compile if a new processor family comes along with longer vector processing units.