Yeah, the runtime selection could indeed leverage ifunc when available (the actual dispatch isn't so interesting, since a simple branch on CPUID is perfectly wo

Yeah, the runtime selection could indeed leverage ifunc when available (the actual dispatch isn't so interesting, since a simple branch on CPUID is perfectly workable in many cases: usually the dispatch is done when calling an expensive, long-running function, so a little bit of O(1) setup is in the noise). The really hard bit is getting dependencies compiled in multiple modes using different features, which will be especially important if/when Rust gets an ecosystem of libraries with SIMD utilities/functions. I hope we do get a wide variety of such things (rather than everyone just using the intrinsics directly, as in C/C++). BTW, the benchmarks are comparing to non-SIMD rust: the graphs are of how many times faster the SIMD Rust code is than scalar Rust code (i.e. if they were plotted, the scalar bars would all be at 1.0).